kc3-lang/smtp

diff --git a/Makefile b/Makefile
index 128e23b..4edc26d 100644
--- a/Makefile
+++ b/Makefile
@@ -17,8 +17,6 @@
 BDIR = build
 INSTALL_PREFIX = /usr/local
 
-SILENT = @
-
 CWARN += -Waggregate-return
 CWARN += -Wall
 CWARN += -Wbad-function-cast
@@ -42,6 +40,7 @@ CWARN += -Wmissing-declarations
 CWARN += -Wmissing-include-dirs
 CWARN += -Wmissing-prototypes
 CWARN += -Wnested-externs
+CWARN += -Wnull-dereference
 CWARN += -Wold-style-definition
 CWARN += -Wpacked
 CWARN += -Wpedantic
@@ -50,6 +49,7 @@ CWARN += -Wredundant-decls
 CWARN += -Wshadow
 CWARN += -Wstack-protector
 CWARN += -Wstrict-aliasing
+CWARN += -Wstrict-overflow=5
 CWARN += -Wstrict-prototypes
 CWARN += -Wswitch-default
 CWARN += -Wswitch-enum
@@ -61,17 +61,24 @@ CWARN += -Wvla
 CWARN += -Wwrite-strings
 
 CWARN.gcc += -Wno-aggressive-loop-optimizations
+CWARN.gcc += -Wduplicated-branches
+CWARN.gcc += -Wduplicated-cond
 CWARN.gcc += -Wjump-misses-init
 CWARN.gcc += -Wlogical-op
 CWARN.gcc += -Wnormalized=nfkc
+CWARN.gcc += -Wrestrict
 CWARN.gcc += -Wstack-usage=5000
+CWARN.gcc += -Wshift-overflow=2
 CWARN.gcc += -Wsync-nand
+CWARN.gcc += -Wstringop-overflow=4
 CWARN.gcc += -Wtrampolines
-CWARN.gcc += -Wunsafe-loop-optimizations
+##CWARN.gcc += -Wunsafe-loop-optimizations
 CWARN.gcc += -Wunsuffixed-float-constants
 CWARN.gcc += -Wvector-operation-performance
 
+CWARN.clang += -Weverything
 CWARN.clang += -Wno-format-nonliteral
+CWARN.clang += -fcomment-block-commands=retval
 
 CFLAGS += $(CWARN)
 CFLAGS += -fstack-protector-all
@@ -85,6 +92,7 @@ CFLAGS.debug   += -g3
 CFLAGS.debug   += -DSMTP_TEST
 CFLAGS.debug   += -Wno-missing-prototypes
 CFLAGS.debug   += -fprofile-arcs -ftest-coverage
+CFLAGS.debug += -ftrapv
 
 CFLAGS.clang   += -fsanitize=undefined
 
@@ -101,6 +109,8 @@ CFLAGS.gcc.debug     += $(CFLAGS.debug) $(CWARN.gcc)
 CFLAGS.gcc.release   += $(CFLAGS.release) $(CWARN.gcc)
 CFLAGS.clang.debug   += $(CFLAGS.debug) $(CFLAGS.clang) $(CWARN.clang)
 
+CDEF_POSIX = -D_POSIX_C_SOURCE=200112
+
 SCAN_BUILD = $(SILENT) scan-build -maxloop 100          \
                                   -o $(BDIR)/scan-build \
                                   --status-bugs         \
@@ -242,13 +252,13 @@ $(BDIR)/release/test_cpp_wrapper.o: test/test_cpp_wrapper.cpp | $(BDIR)/release
 	$(COMPILE.cpp.release) -Isrc
 
 $(BDIR)/debug/smtp.o: src/smtp.c | $(BDIR)/debug
-	$(COMPILE.c.debug)
+	$(COMPILE.c.debug) $(CDEF_POSIX)
 
 $(BDIR)/release/smtp_nossl.o: src/smtp.c | $(BDIR)/release
-	$(COMPILE.c.release) -USMTP_OPENSSL
+	$(COMPILE.c.release) $(CDEF_POSIX) -USMTP_OPENSSL
 
 $(BDIR)/release/smtp.o: src/smtp.c | $(BDIR)/release
-	$(COMPILE.c.release)
+	$(COMPILE.c.release) $(CDEF_POSIX)
 
 $(BDIR)/debug/test: $(BDIR)/debug/seams.o \
                     $(BDIR)/debug/smtp.o  \
@@ -256,10 +266,10 @@ $(BDIR)/debug/test: $(BDIR)/debug/seams.o \
 	$(LINK.c.debug) -lssl -lcrypto -lgcov
 
 $(BDIR)/debug/test.o: test/test.c | $(BDIR)/debug
-	$(COMPILE.c.debug) -Isrc/
+	$(COMPILE.c.debug) $(CDEF_POSIX) -Isrc/
 
 $(BDIR)/debug/seams.o: test/seams.c | $(BDIR)/debug
-	$(COMPILE.c.debug)
+	$(COMPILE.c.debug) $(CDEF_POSIX)
 
 $(BDIR)/debug/clang_test: $(BDIR)/debug/clang_seams.o \
                           $(BDIR)/debug/clang_smtp.o  \
@@ -267,13 +277,13 @@ $(BDIR)/debug/clang_test: $(BDIR)/debug/clang_seams.o \
 	$(LINK.c.clang) -lssl -lcrypto -lgcov -lubsan
 
 $(BDIR)/debug/clang_seams.o: test/seams.c | $(BDIR)/debug
-	$(COMPILE.c.clang)
+	$(COMPILE.c.clang) $(CDEF_POSIX)
 
 $(BDIR)/debug/clang_smtp.o: src/smtp.c | $(BDIR)/debug
-	$(COMPILE.c.clang)
+	$(COMPILE.c.clang) $(CDEF_POSIX)
 
 $(BDIR)/debug/clang_test.o: test/test.c | $(BDIR)/debug
-	$(COMPILE.c.clang) -Isrc/
+	$(COMPILE.c.clang) $(CDEF_POSIX) -Isrc/
 
 $(BDIR)/release/test_nossl: $(BDIR)/release/smtp_nossl.o \
                             $(BDIR)/release/test_nossl.o
diff --git a/src/smtp.c b/src/smtp.c
index 61b9b9b..51b5b21 100644
--- a/src/smtp.c
+++ b/src/smtp.c
@@ -30,11 +30,6 @@
 # include <winsock2.h>
 # include <ws2tcpip.h>
 #else /* POSIX */
-/**
- * Need to define this on some POSIX systems in order to get access to the
- * getaddrinfo and localtime_r functions.
- */
-# define _POSIX_C_SOURCE 200112L
 # include <netinet/in.h>
 # include <sys/select.h>
 # include <sys/socket.h>
@@ -104,11 +99,6 @@
  */
 struct smtp_address{
   /**
-   * Specify from, to, cc, bcc.
-   */
-  enum smtp_address_type type;
-
-  /**
    * Email address without any special formatting.
    *
    * For example: mail@example.com
@@ -119,6 +109,16 @@ struct smtp_address{
    * Description of the email address.
    */
   char *name;
+
+  /**
+   * Specify from, to, cc, bcc.
+   */
+  enum smtp_address_type type;
+
+  /**
+   * Padding structure to align.
+   */
+  char pad[4];
 };
 
 /**
@@ -201,18 +201,18 @@ struct smtp{
   size_t num_attachment;
 
   /**
-   * Status code indicating success/failure.
+   * Timeout in seconds to wait before returning with an error.
    *
-   * This code gets returned by most of the header functions.
+   * This applies to both writing to and reading from a network socket.
    */
-  enum smtp_status_code status_code;
+  long timeout_sec;
 
   /**
-   * Timeout in seconds to wait before returning with an error.
+   * Status code indicating success/failure.
    *
-   * This applies to both writing to and reading from a network socket.
+   * This code gets returned by most of the header functions.
    */
-  long timeout_sec;
+  enum smtp_status_code status_code;
 
   /**
    * Indicates if this context has an active TLS connection.
@@ -351,11 +351,11 @@ smtp_si_mul_size_t(const size_t a,
  * Wait until more data has been made available on the socket read end.
  *
  * @param[in] smtp SMTP client context.
- * @retval  0 If data available to read on the socket.
- * @retval -1 If the connection times out before any data appears on the
- *            socket.
+ * @retval SMTP_STATUS_OK   If data available to read on the socket.
+ * @retval SMTP_STATUS_RECV If the connection times out before any data
+ *                          appears on the socket.
  */
-static int
+static enum smtp_status_code
 smtp_str_getdelimfd_read_timeout(struct smtp *const smtp){
   fd_set readfds;
   struct timeval timeout;
@@ -369,7 +369,7 @@ smtp_str_getdelimfd_read_timeout(struct smtp *const smtp){
   if(sel_rc < 1){
     return smtp_status_code_set(smtp, SMTP_STATUS_RECV);
   }
-  return smtp->status_code;
+  return SMTP_STATUS_OK;
 }
 
 /**
@@ -402,7 +402,11 @@ smtp_str_getdelimfd_read(struct str_getdelimfd *const gdfd,
   if(smtp->tls_on){
 #ifdef SMTP_OPENSSL
     do{
-      bytes_read = SSL_read(smtp->tls, buf, count);
+      /*
+       * Count will never have a value greater than SMTP_GETDELIM_READ_SZ,
+       * so we can safely convert this to an int.
+       */
+      bytes_read = SSL_read(smtp->tls, buf, (int)count);
     } while(bytes_read <= 0 && BIO_should_retry(smtp->tls_bio));
 #endif /* SMTP_OPENSSL */
   }
@@ -504,7 +508,7 @@ smtp_str_getdelimfd_free(struct str_getdelimfd *const gdfd){
  * error code.
  *
  * @param[in] gdfd See @ref str_getdelimfd.
- * @return @ref str_getdelim_retcode.
+ * @return See @ref str_getdelim_retcode.
  */
 static enum str_getdelim_retcode
 smtp_str_getdelimfd_throw_error(struct str_getdelimfd *const gdfd){
@@ -520,7 +524,7 @@ smtp_str_getdelimfd_throw_error(struct str_getdelimfd *const gdfd){
  * to the caller for handling.
  *
  * @param[in] gdfd See @ref str_getdelimfd.
- * @return @ref str_getdelim_retcode.
+ * @return See @ref str_getdelim_retcode.
  */
 SMTP_LINKAGE enum str_getdelim_retcode
 smtp_str_getdelimfd(struct str_getdelimfd *const gdfd){
@@ -579,7 +583,9 @@ smtp_str_getdelimfd(struct str_getdelimfd *const gdfd){
                                           read_buf_ptr,
                                           SMTP_GETDELIM_READ_SZ);
     if(bytes_read < 0 ||
-       smtp_si_add_size_t(gdfd->_buf_len, bytes_read, &gdfd->_buf_len)){
+       smtp_si_add_size_t(gdfd->_buf_len,
+                          (size_t)bytes_read,
+                          &gdfd->_buf_len)){
       return smtp_str_getdelimfd_throw_error(gdfd);
     }
   }
@@ -770,7 +776,7 @@ smtp_str_replace(const char *const search,
  * table. Since 2^6 = 64, this array has 64 entries which maps directly from
  * the 6 bit value into the corresponding array value.
  */
-static unsigned char g_base64_encode_table[] = {
+static char g_base64_encode_table[] = {
   'A','B','C','D','E','F','G','H','I','J',
   'K','L','M','N','O','P','Q','R','S','T',
   'U','V','W','X','Y','Z',
@@ -919,12 +925,12 @@ g_base64_decode_table[] = {
  * @param[in]  buf    Buffer containing bytes to decode.
  * @param[out] decode Buffer for storing base64 decoded bytes.
  * @retval >0 Length of the decoded block.
- * @retval -1 If the block contains invalid base64 data.
+ * @retval  0 If the block contains invalid base64 data.
  */
-static int
+static size_t
 smtp_base64_decode_block(const unsigned char *const buf,
                          unsigned char *const decode){
-  int decode_block_len;
+  size_t decode_block_len;
   size_t i;
   signed char decode_table[4];
   unsigned char outb[3];
@@ -937,7 +943,7 @@ smtp_base64_decode_block(const unsigned char *const buf,
     }
     decode_table[i] = g_base64_decode_table[buf[i]];
     if(decode_table[i] < 0){
-      return -1;
+      return 0;
     }
   }
 
@@ -981,35 +987,36 @@ smtp_base64_decode_block(const unsigned char *const buf,
  * @retval >=0 Length of the data stored in the decode parameter.
  * @retval -1  Memory allocation failure or invalid base64 byte sequences.
  */
-SMTP_LINKAGE long
+SMTP_LINKAGE size_t
 smtp_base64_decode(const char *const buf,
                    unsigned char **decode){
   size_t buf_len;
   size_t buf_len_inc;
   size_t buf_i;
   unsigned char *b64_decode;
-  long decode_len;
-  int decode_block_len;
+  size_t decode_len;
+  size_t decode_block_len;
 
   *decode = NULL;
 
   buf_len = strlen(buf);
   if(buf_len % 4 != 0){
-    return -1;
+    return SIZE_MAX;
   }
 
   if(smtp_si_add_size_t(buf_len, 1, &buf_len_inc) ||
      (b64_decode = calloc(1, buf_len_inc)) == NULL){
-    return -1;
+    return SIZE_MAX;
   }
 
   decode_len = 0;
   for(buf_i = 0; buf_i < buf_len; buf_i += 4){
-    if((decode_block_len = smtp_base64_decode_block(
-                             (const unsigned char*)&buf[buf_i],
-                             &b64_decode[decode_len])) < 0){
+    decode_block_len = smtp_base64_decode_block(
+                         (const unsigned char*)&buf[buf_i],
+                         &b64_decode[decode_len]);
+    if(decode_block_len == 0){
       free(b64_decode);
-      return -1;
+      return SIZE_MAX;
     }
     decode_len += decode_block_len;
   }
@@ -1046,13 +1053,15 @@ smtp_bin2hex(const unsigned char *const s,
     return NULL;
   }
 
-  for(i = 0, j = 0; i < slen; i++, j += 2){
+  j = 0;
+  for(i = 0; i < slen; i++){
     hex = s[i];
     rc = sprintf(&snew[j], "%02x", hex);
     if(rc < 0 || (size_t)rc >= 3){
       free(snew);
       return NULL;
     }
+    j += 2;
   }
   snew[j] = '\0';
 
@@ -1072,22 +1081,25 @@ smtp_bin2hex(const unsigned char *const s,
  * @retval >0 Number of bytes for the current UTF-8 character sequence.
  * @retval -1 Invalid byte sequence.
  */
-SMTP_LINKAGE int
-smtp_utf8_charlen(unsigned char c){
-  if((c & 0x80) == 0){         /* 0XXXXXXX */
+SMTP_LINKAGE size_t
+smtp_utf8_charlen(char c){
+  unsigned char uc;
+
+  uc = (unsigned char)c;
+  if((uc & 0x80) == 0){         /* 0XXXXXXX */
     return 1;
   }
-  else if((c & 0xE0) == 0xC0){ /* 110XXXXX */
+  else if((uc & 0xE0) == 0xC0){ /* 110XXXXX */
     return 2;
   }
-  else if((c & 0xF0) == 0xE0){ /* 1110XXXX */
+  else if((uc & 0xF0) == 0xE0){ /* 1110XXXX */
     return 3;
   }
-  else if((c & 0xF8) == 0xF0){ /* 11110XXX */
+  else if((uc & 0xF8) == 0xF0){ /* 11110XXX */
     return 4;
   }
   else{                        /* invalid  */
-    return -1;
+    return 0;
   }
 }
 
@@ -1103,8 +1115,8 @@ smtp_utf8_charlen(unsigned char c){
  */
 SMTP_LINKAGE int
 smtp_str_has_nonascii_utf8(const char *const s){
-  int i;
-  int charlen;
+  size_t i;
+  size_t charlen;
 
   for(i = 0; s[i]; i++){
     charlen = smtp_utf8_charlen(s[i]);
@@ -1129,22 +1141,22 @@ smtp_str_has_nonascii_utf8(const char *const s){
  * @retval maxlen    If length of s has more bytes than maxlen.
  * @retval -1        If @p s contains an invalid UTF-8 byte sequence.
  */
-SMTP_LINKAGE long
+SMTP_LINKAGE size_t
 smtp_strnlen_utf8(const char *s,
                   size_t maxlen){
   size_t i;
-  int utf8_i;
-  int utf8_len;
+  size_t utf8_i;
+  size_t utf8_len;
 
   for(i = 0; *s && i < maxlen; i += utf8_len){
     utf8_len = smtp_utf8_charlen(*s);
-    if(utf8_len < 0){
-      return -1;
+    if(utf8_len == 0){
+      return SIZE_MAX;
     }
 
     for(utf8_i = 0; utf8_i < utf8_len; utf8_i++){
       if(!*s){
-        return -1;
+        return SIZE_MAX;
       }
       s += 1;
     }
@@ -1316,7 +1328,7 @@ smtp_chunk_split(const char *const s,
   size_t chunk_i;
   size_t snew_i;
   size_t body_i;
-  long body_copy_len;
+  size_t body_copy_len;
 
   if(chunklen < 1){
     errno = EINVAL;
@@ -1346,9 +1358,8 @@ smtp_chunk_split(const char *const s,
   snew_i = 0;
   for(chunk_i = 0; chunk_i < bodylen / chunklen + 1; chunk_i++){
     body_copy_len = smtp_strnlen_utf8(&s[body_i], chunklen);
-    if(body_copy_len < 0){
+    if(body_copy_len == SIZE_MAX){
       free(snew);
-      errno = EINVAL;
       return NULL;
     }
     memcpy(&snew[snew_i], &s[body_i], body_copy_len);
@@ -1465,6 +1476,7 @@ smtp_parse_cmd_line(char *const line,
   char *ep;
   char code_str[4];
   size_t line_len;
+  unsigned long int ulcode;
 
   line_len = strlen(line);
   if(line_len < 5){
@@ -1478,10 +1490,14 @@ smtp_parse_cmd_line(char *const line,
 
   memcpy(code_str, line, 3);
   code_str[3] = '\0';
-  cmd->code = strtoul(code_str, &ep, 10);
-  if(*ep != '\0'){
+  ulcode = strtoul(code_str, &ep, 10);
+  if(*ep != '\0' || ulcode > SMTP_BEGIN_MAIL){
     cmd->code = SMTP_INTERNAL_ERROR;
   }
+  else{
+    cmd->code = (enum smtp_result_code)ulcode;
+  }
+
   cmd->more = line[3] == '-' ? 1 : 0;
   return cmd->code;
 }
@@ -1524,7 +1540,7 @@ smtp_puts_dbg(struct smtp *const smtp,
  * Read a server response line.
  *
  * @param[in] smtp SMTP client context.
- * @return @ref str_getdelim_retcode.
+ * @return See @ref str_getdelim_retcode.
  */
 static enum str_getdelim_retcode
 smtp_getline(struct smtp *const smtp){
@@ -1554,7 +1570,7 @@ smtp_getline(struct smtp *const smtp){
  * then return the status code from the last response line.
  *
  * @param[in] smtp SMTP client context.
- * @return @ref smtp_result_code.
+ * @return See @ref smtp_result_code.
  */
 static int
 smtp_read_and_parse_code(struct smtp *const smtp){
@@ -1583,15 +1599,16 @@ smtp_read_and_parse_code(struct smtp *const smtp){
  * @param[in] smtp SMTP client context.
  * @param[in] buf Data to send to the SMTP server.
  * @param[in] len Number of bytes in buf.
- * @return @ref smtp_status_code.
+ * @return See @ref smtp_status_code.
  */
 SMTP_LINKAGE enum smtp_status_code
 smtp_write(struct smtp *const smtp,
            const char *const buf,
            size_t len){
   size_t bytes_to_send;
-  int bytes_sent;
+  long bytes_sent;
   const char *buf_offset;
+  int ssl_bytes_to_send;
 
   smtp_puts_dbg(smtp, "Client", buf);
 
@@ -1604,13 +1621,16 @@ smtp_write(struct smtp *const smtp,
 
     if(smtp->tls_on){
 #ifdef SMTP_OPENSSL
-      bytes_sent = SSL_write(smtp->tls, buf_offset, bytes_to_send);
+      /* bytes_to_send <= INT_MAX */
+      ssl_bytes_to_send = (int)bytes_to_send;
+      bytes_sent = SSL_write(smtp->tls, buf_offset, ssl_bytes_to_send);
       if(bytes_sent <= 0){
         return smtp_status_code_set(smtp, SMTP_STATUS_SEND);
       }
 #else /* !(SMTP_OPENSSL) */
       /* unreachable */
       bytes_sent = 0;
+      (void)ssl_bytes_to_send;
 #endif /* SMTP_OPENSSL */
     }
     else{
@@ -1619,7 +1639,7 @@ smtp_write(struct smtp *const smtp,
         return smtp_status_code_set(smtp, SMTP_STATUS_SEND);
       }
     }
-    bytes_to_send -= bytes_sent;
+    bytes_to_send -= (size_t)bytes_sent;
     buf_offset += bytes_sent;
   }
 
@@ -1650,7 +1670,7 @@ smtp_puts(struct smtp *const smtp,
 static enum smtp_status_code
 smtp_puts_terminate(struct smtp *const smtp,
                     const char *const s){
-  int rc;
+  enum smtp_status_code rc;
   char *line;
   char *concat;
   size_t slen;
@@ -1846,15 +1866,13 @@ smtp_tls_init(struct smtp *const smtp,
  * later on when we try to use that extension.
  *
  * @param[in] smtp SMTP client context.
- * @return @ref smtp_status_code.
+ * @return See @ref smtp_status_code.
  */
-static int
+static enum smtp_status_code
 smtp_ehlo(struct smtp *const smtp){
-  if(smtp_puts(smtp, "EHLO smtp\r\n") != SMTP_STATUS_OK){
-    return smtp->status_code;
+  if(smtp_puts(smtp, "EHLO smtp\r\n") == SMTP_STATUS_OK){
+    smtp_read_and_parse_code(smtp);
   }
-
-  smtp_read_and_parse_code(smtp);
   return smtp->status_code;
 }
 
@@ -1865,7 +1883,7 @@ smtp_ehlo(struct smtp *const smtp){
  *      or as shown in the format string: "\0%s\0%s", email, password.
  *   2. Base64 encode the text from (1).
  *   3. Send the constructed auth text from (2) to the server:
- *      "AUTH PLAIN <b64>\r\n".
+ *      "AUTH PLAIN <b64><CR><NL>".
  *
  * @param[in] smtp SMTP client context.
  * @param[in] user SMTP account user name.
@@ -1936,9 +1954,9 @@ smtp_auth_plain(struct smtp *const smtp,
  *
  *   1. Base64 encode the user name.
  *   2. Send string from (1) as part of the login:
- *      "AUTH LOGIN <b64_username>\r\n".
+ *      "AUTH LOGIN <b64_username><CR><NL>".
  *   3. Base64 encode the password and send that by itself on a separate
- *      line: "<b64_password>\r\n".
+ *      line: "<b64_password><CR><NL>".
  *
  * @param[in] smtp SMTP client context.
  * @param[in] user SMTP account user name.
@@ -1957,7 +1975,7 @@ smtp_auth_login(struct smtp *const smtp,
   char *concat;
 
   /* (1) */
-  if((b64_user = smtp_base64_encode(user, -1)) == NULL){
+  if((b64_user = smtp_base64_encode(user, SIZE_MAX)) == NULL){
     return -1;
   }
 
@@ -1984,7 +2002,7 @@ smtp_auth_login(struct smtp *const smtp,
   }
 
   /* (3) */
-  if((b64_pass = smtp_base64_encode(pass, -1)) == NULL){
+  if((b64_pass = smtp_base64_encode(pass, SIZE_MAX)) == NULL){
     return -1;
   }
   smtp_puts_terminate(smtp, b64_pass);
@@ -2003,7 +2021,7 @@ smtp_auth_login(struct smtp *const smtp,
 /**
  * Authenticate using the CRAM-MD5 method.
  *
- *   1. Send "AUTH CRAM-MD5\r\n" to the server.
+ *   1. Send "AUTH CRAM-MD5<CR><NL>" to the server.
  *   2. Decode the base64 challenge response from the server.
  *   3. Do an MD5 HMAC on (2) using the account password as the key.
  *   4. Convert the binary data in (3) to lowercase hex characters.
@@ -2023,7 +2041,7 @@ smtp_auth_cram_md5(struct smtp *const smtp,
                    const char *const pass){
   struct smtp_command cmd;
   unsigned char *challenge_decoded;
-  long challenge_decoded_len;
+  size_t challenge_decoded_len;
   const char *key;
   int key_len;
   unsigned char hmac[EVP_MAX_MD_SIZE];
@@ -2049,18 +2067,22 @@ smtp_auth_cram_md5(struct smtp *const smtp,
   }
 
   /* (2) */
-  challenge_decoded_len = smtp_base64_decode(cmd.text, &challenge_decoded);
-  if(challenge_decoded_len < 0){
+  challenge_decoded_len = smtp_base64_decode(cmd.text,
+                                             &challenge_decoded);
+  if(challenge_decoded_len == SIZE_MAX){
     return -1;
   }
 
   /* (3) */
   key = pass;
-  key_len = strlen(pass);
+  key_len = (int)strlen(pass);/*********************cast*/
   hmac_ret = HMAC(EVP_md5(),
-                  key, key_len,
-                  challenge_decoded, challenge_decoded_len,
-                  hmac, &hmac_len);
+                  key,
+                  key_len,
+                  challenge_decoded,
+                  challenge_decoded_len,
+                  hmac,
+                  &hmac_len);
   free(challenge_decoded);
   if(hmac_ret == NULL){
     return -1;
@@ -2135,9 +2157,9 @@ smtp_set_read_timeout(struct smtp *const smtp,
  * @param[in] smtp                SMTP client context.
  * @param[in] server              Server name or IP address.
  * @param[in] connection_security See @ref smtp_connection_security.
- * @return @ref smtp_status_code.
+ * @return See @ref smtp_status_code.
  */
-static int
+static enum smtp_status_code
 smtp_initiate_handshake(struct smtp *const smtp,
                         const char *const server,
                         enum smtp_connection_security connection_security){
@@ -2220,6 +2242,7 @@ smtp_date_rfc_2822(char *const date){
   struct tm tm_local;
   struct tm tm_utc;
   long offset_utc;
+  double diff_local_utc;
   int rc;
 
   const char weekday_abbreviation[7][4] = {
@@ -2277,7 +2300,8 @@ smtp_date_rfc_2822(char *const date){
    * For example, PST time zone will have an offset of -800 which will get
    * formatted as -0800 in the sprintf call below.
    */
-  offset_utc = difftime(t_local, t_utc);
+  diff_local_utc = difftime(t_local, t_utc);
+  offset_utc = (long)diff_local_utc;
   offset_utc = offset_utc / 60 / 60 * 100;
 
   rc = sprintf(date,
@@ -2322,9 +2346,12 @@ smtp_date_rfc_2822(char *const date){
 static void
 smtp_gen_mime_boundary(char *const boundary){
   size_t i;
+  unsigned int seed;
+
+  seed = (unsigned int)time(NULL);
+  srand(seed);
 
   strcpy(boundary, "mime");
-  srand(time(NULL));
   for(i = 4; i < SMTP_MIME_BOUNDARY_LEN - 1; i++){
     /* Modulo bias okay since we only need to prevent accidental collision. */
     boundary[i] = rand() % 26 + 'A';
@@ -2338,9 +2365,9 @@ smtp_gen_mime_boundary(char *const boundary){
  * @param[in] smtp     SMTP client context.
  * @param[in] boundary MIME boundary text.
  * @param[in] body     Email body text.
- * @return @ref smtp_status_code.
+ * @return See @ref smtp_status_code.
  */
-static int
+static enum smtp_status_code
 smtp_print_mime_header_and_body(struct smtp *const smtp,
                                 const char *const boundary,
                                 const char *const body){
@@ -2402,10 +2429,10 @@ smtp_print_mime_header_and_body(struct smtp *const smtp,
  *
  * @param[in] smtp       SMTP client context.
  * @param[in] boundary   MIME boundary text.
- * @param[in] attachment @ref smtp_attachment.
- * @return @ref smtp_status_code.
+ * @param[in] attachment See @ref smtp_attachment.
+ * @return See @ref smtp_status_code.
  */
-static int
+static enum smtp_status_code
 smtp_print_mime_attachment(struct smtp *const smtp,
                            const char *const boundary,
                            const struct smtp_attachment *const attachment){
@@ -2462,7 +2489,7 @@ smtp_print_mime_attachment(struct smtp *const smtp,
  * @param[in] boundary MIME boundary text.
  * @return See @ref smtp_status_code and @ref smtp_puts.
  */
-static int
+static enum smtp_status_code
 smtp_print_mime_end(struct smtp *const smtp,
                     const char *const boundary){
   char *concat;
@@ -2481,9 +2508,9 @@ smtp_print_mime_end(struct smtp *const smtp,
  *
  * @param[in] smtp SMTP client context.
  * @param[in] body Null-terminated string to send in the email body.
- * @return @ref smtp_status_code.
+ * @return See @ref smtp_status_code.
  */
-static int
+static enum smtp_status_code
 smtp_print_mime_email(struct smtp *const smtp,
                       const char *const body){
   char boundary[SMTP_MIME_BOUNDARY_LEN];
@@ -2517,9 +2544,9 @@ smtp_print_mime_email(struct smtp *const smtp,
  *
  * @param[in] smtp   SMTP client context.
  * @param[in] header See @ref smtp_header.
- * @return @ref smtp_status_code.
+ * @return See @ref smtp_status_code.
  */
-static int
+static enum smtp_status_code
 smtp_print_header(struct smtp *const smtp,
                   const struct smtp_header *const header){
   size_t key_len;
@@ -2562,14 +2589,14 @@ smtp_print_header(struct smtp *const smtp,
  *
  * The following example shows what the final header might look like when
  * the client sends an email to two CC addresses:
- * Cc: mail1@example.com, mail2@example.com
+ * Cc: mail1\@example.com, mail2\@example.com
  *
  * @param[in] smtp         SMTP client context.
- * @param[in] address_type @ref smtp_address_type.
+ * @param[in] address_type See @ref smtp_address_type.
  * @param[in] key          Header key value, for example, To From Cc.
- * @return @ref smtp_status_code.
+ * @return See @ref smtp_status_code.
  */
-static int
+static enum smtp_status_code
 smtp_append_address_to_header(struct smtp *const smtp,
                               enum smtp_address_type address_type,
                               const char *const key){
@@ -2624,7 +2651,7 @@ smtp_append_address_to_header(struct smtp *const smtp,
       concat = smtp_stpcpy(concat, address->email);
       concat = smtp_stpcpy(concat, ">");
       num_address_in_header += 1;
-      concat_len = concat - header_value;
+      concat_len = (size_t)(concat - header_value);
     }
   }
 
@@ -2639,15 +2666,15 @@ smtp_append_address_to_header(struct smtp *const smtp,
  * Send envelope MAIL FROM or RCPT TO header address.
  *
  * Examples:
- * MAIL FROM:<mail@example.com>
- * RCPT TO:<mail@example.com>
+ * MAIL FROM:<mail\@example.com>
+ * RCPT TO:<mail\@example.com>
  *
  * @param[in] smtp    SMTP client context.
  * @param[in] header  Either "MAIL FROM" or "RCPT TO".
- * @param[in] address @ref smtp_address -> email field.
- * @return @ref smtp_status_code.
+ * @param[in] address See @ref smtp_address -> email field.
+ * @return See @ref smtp_status_code.
  */
-static int
+static enum smtp_status_code
 smtp_mail_envelope_header(struct smtp *const smtp,
                           const char *const header,
                           const struct smtp_address *const address){
@@ -2760,7 +2787,7 @@ smtp_header_exists(const struct smtp *const smtp,
  */
 SMTP_LINKAGE int
 smtp_header_key_validate(const char *const key){
-  unsigned c;
+  unsigned char uc;
   size_t i;
   size_t keylen;
 
@@ -2770,8 +2797,8 @@ smtp_header_key_validate(const char *const key){
   }
 
   for(i = 0; i < keylen; i++){
-    c = key[i];
-    if(c <= ' ' || c > 126 || c == ':'){
+    uc = (unsigned char)key[i];
+    if(uc <= ' ' || uc > 126 || uc == ':'){
       return -1;
     }
   }
@@ -2791,13 +2818,13 @@ smtp_header_key_validate(const char *const key){
 SMTP_LINKAGE int
 smtp_header_value_validate(const char *const value){
   size_t i;
-  unsigned char c;
+  unsigned char uc;
 
   for(i = 0; value[i]; i++){
-    c = value[i];
-    if((c < ' ' || c > 126) &&
-        c != '\t' &&
-        c < 0x80){ /* Allow UTF-8 byte sequence. */
+    uc = (unsigned char)value[i];
+    if((uc < ' ' || uc > 126) &&
+        uc != '\t' &&
+        uc < 0x80){ /* Allow UTF-8 byte sequence. */
       return -1;
     }
   }
@@ -2817,12 +2844,12 @@ smtp_header_value_validate(const char *const value){
 SMTP_LINKAGE int
 smtp_address_validate_email(const char *const email){
   size_t i;
-  unsigned char c;
+  unsigned char uc;
 
   for(i = 0; email[i]; i++){
-    c = email[i];
-    if(c <= ' ' || c == 127 ||
-       c == '<' || c == '>'){
+    uc = (unsigned char)email[i];
+    if(uc <= ' ' || uc == 127 ||
+       uc == '<' || uc == '>'){
       return -1;
     }
   }
@@ -2842,11 +2869,11 @@ smtp_address_validate_email(const char *const email){
 SMTP_LINKAGE int
 smtp_address_validate_name(const char *const name){
   size_t i;
-  unsigned char c;
+  unsigned char uc;
 
   for(i = 0; name[i]; i++){
-    c = name[i];
-    if(c < ' ' || c == 127 || c == '\"'){
+    uc = (unsigned char)name[i];
+    if(uc < ' ' || uc == 127 || uc == '\"'){
       return -1;
     }
   }
@@ -2866,12 +2893,12 @@ smtp_address_validate_name(const char *const name){
 SMTP_LINKAGE int
 smtp_attachment_validate_name(const char *const name){
   size_t i;
-  unsigned c;
+  unsigned char uc;
 
   for(i = 0; name[i]; i++){
-    c = name[i];
-    if(c < ' ' || c == 127 ||
-       c == '\'' || c == '\"'){
+    uc = (unsigned char)name[i];
+    if(uc < ' ' || uc == 127 ||
+       uc == '\'' || uc == '\"'){
       return -1;
     }
   }
@@ -2890,18 +2917,20 @@ smtp_attachment_validate_name(const char *const name){
  * error codes when calling the other header functions because the
  * caller will always get a valid SMTP structure returned.
  */
-static struct smtp smtp_error = {
+static struct smtp
+g_smtp_error = {
   SMTP_FLAG_INVALID_MEMORY, /* flags                        */
   0,                        /* sock                         */
   {                         /* gdfd                         */
     NULL,                   /* _buf                         */
     0,                      /* _bufsz                       */
     0,                      /* _buf_len                     */
-    0,                      /* delim                        */
     NULL,                   /* line                         */
     0,                      /* line_len                     */
     NULL,                   /* getdelimfd_read              */
-    NULL                    /* user_data                    */
+    NULL,                   /* user_data                    */
+    0,                      /* delim                        */
+    {0}                     /* pad                          */
   },                        /* gdfd                         */
   NULL,                     /* header_list                  */
   0,                        /* num_headers                  */
@@ -2909,8 +2938,8 @@ static struct smtp smtp_error = {
   0,                        /* num_address                  */
   NULL,                     /* attachment_list              */
   0,                        /* num_attachment               */
-  SMTP_STATUS_NOMEM,        /* smtp_status_code status_code */
   0,                        /* timeout_sec                  */
+  SMTP_STATUS_NOMEM,        /* smtp_status_code status_code */
   0,                        /* tls_on                       */
   NULL                      /* cafile                       */
 #ifdef SMTP_OPENSSL
@@ -2950,7 +2979,7 @@ static struct smtp smtp_error = {
  *                                 allocation fails. When finished, the caller
  *                                 must free this context using
  *                                 @ref smtp_close.
- * @return @ref smtp_status_code.
+ * @return See @ref smtp_status_code.
  */
 enum smtp_status_code
 smtp_open(const char *const server,
@@ -2962,7 +2991,7 @@ smtp_open(const char *const server,
   struct smtp *snew;
 
   if((snew = calloc(1, sizeof(**smtp))) == NULL){
-    *smtp = &smtp_error;
+    *smtp = &g_smtp_error;
     return smtp_status_code_get(*smtp);
   }
   *smtp = snew;
@@ -2999,7 +3028,7 @@ smtp_open(const char *const server,
  * @param[in] auth_method See @ref smtp_authentication_method.
  * @param[in] user        Server authentication user name.
  * @param[in] pass        Server authentication user password.
- * @return @ref smtp_status_code.
+ * @return See @ref smtp_status_code.
  */
 enum smtp_status_code
 smtp_auth(struct smtp *const smtp,
@@ -3012,25 +3041,22 @@ smtp_auth(struct smtp *const smtp,
     return smtp->status_code;
   }
 
-  switch(auth_method){
-    case SMTP_AUTH_PLAIN:
-      auth_rc = smtp_auth_plain(smtp, user, pass);
-      break;
-    case SMTP_AUTH_LOGIN:
-      auth_rc = smtp_auth_login(smtp, user, pass);
-      break;
-
+  if(auth_method == SMTP_AUTH_PLAIN){
+    auth_rc = smtp_auth_plain(smtp, user, pass);
+  }
+  else if(auth_method == SMTP_AUTH_LOGIN){
+    auth_rc = smtp_auth_login(smtp, user, pass);
+  }
 #ifdef SMTP_OPENSSL
-    case SMTP_AUTH_CRAM_MD5:
-      auth_rc = smtp_auth_cram_md5(smtp, user, pass);
-      break;
+  else if(auth_method == SMTP_AUTH_CRAM_MD5){
+    auth_rc = smtp_auth_cram_md5(smtp, user, pass);
+  }
 #endif /* SMTP_OPENSSL */
-
-    case SMTP_AUTH_NONE:
-      auth_rc = 0;
-      break;
-    default:
-      return smtp_status_code_set(smtp, SMTP_STATUS_PARAM);
+  else if(auth_method == SMTP_AUTH_NONE){
+    auth_rc = 0;
+  }
+  else{
+    return smtp_status_code_set(smtp, SMTP_STATUS_PARAM);
   }
 
   if(auth_rc < 0){
@@ -3049,7 +3075,7 @@ smtp_auth(struct smtp *const smtp,
  *
  * @param[in] smtp SMTP client context.
  * @param[in] body Null-terminated string to send in the email body.
- * @return @ref smtp_status_code.
+ * @return See @ref smtp_status_code.
  */
 enum smtp_status_code
 smtp_mail(struct smtp *const smtp,
@@ -3162,7 +3188,7 @@ smtp_mail(struct smtp *const smtp,
  * SMTP context.
  *
  * @param[in] smtp SMTP client context.
- * @return @ref smtp_status_code.
+ * @return See @ref smtp_status_code.
  */
 enum smtp_status_code
 smtp_close(struct smtp *smtp){
@@ -3217,7 +3243,7 @@ smtp_close(struct smtp *smtp){
  * Get the current status/error code described in @ref smtp_status_code.
  *
  * @param[in] smtp SMTP client context.
- * @return @ref smtp_status_code.
+ * @return See @ref smtp_status_code.
  */
 enum smtp_status_code
 smtp_status_code_get(const struct smtp *const smtp){
@@ -3235,7 +3261,7 @@ smtp_status_code_get(const struct smtp *const smtp){
  *
  * @param[in] smtp        SMTP client context.
  * @param[in] status_code See @ref smtp_status_code.
- * @return @ref smtp_status_code.
+ * @return See @ref smtp_status_code.
  */
 enum smtp_status_code
 smtp_status_code_set(struct smtp *const smtp,
@@ -3303,7 +3329,7 @@ smtp_status_code_errstr(enum smtp_status_code status_code){
  * @param[in] value Value for new header. It must consist only of printable
  *                  US-ASCII, space, or horizontal tab. If set to NULL,
  *                  this will prevent the header from printing out.
- * @return @ref smtp_status_code.
+ * @return See @ref smtp_status_code.
  */
 enum smtp_status_code
 smtp_header_add(struct smtp *const smtp,
@@ -3387,7 +3413,7 @@ void smtp_header_clear_all(struct smtp *const smtp){
  *                  printable characters, excluding the quote characters. If
  *                  set to NULL or empty string, no name will get associated
  *                  with this email.
- * @return @ref smtp_status_code.
+ * @return See @ref smtp_status_code.
  */
 enum smtp_status_code
 smtp_address_add(struct smtp *const smtp,
@@ -3465,7 +3491,7 @@ void smtp_address_clear_all(struct smtp *const smtp){
  * @param[in] smtp SMTP client context.
  * @param[in] name Filename of the attachment shown to recipients.
  * @param[in] path Path of file location to read from.
- * @return @ref smtp_status_code.
+ * @return See @ref smtp_status_code.
  */
 enum smtp_status_code
 smtp_attachment_add_path(struct smtp *const smtp,
@@ -3498,7 +3524,7 @@ smtp_attachment_add_path(struct smtp *const smtp,
  * @param[in] smtp SMTP client context.
  * @param[in] name Filename of the attachment shown to recipients.
  * @param[in] fp   File pointer already opened by the caller.
- * @return @ref smtp_status_code.
+ * @return See @ref smtp_status_code.
  */
 enum smtp_status_code
 smtp_attachment_add_fp(struct smtp *const smtp,
@@ -3537,13 +3563,13 @@ smtp_attachment_add_fp(struct smtp *const smtp,
  * @param[in] data   Raw attachment data stored in memory.
  * @param[in] datasz Number of bytes in @p data, or -1 if data
  *                   null-terminated.
- * @return @ref smtp_status_code.
+ * @return See @ref smtp_status_code.
  */
 enum smtp_status_code
 smtp_attachment_add_mem(struct smtp *const smtp,
                         const char *const name,
                         const void *const data,
-                        long datasz){
+                        size_t datasz){
   size_t num_attachment_inc;
   struct smtp_attachment *new_attachment_list;
   struct smtp_attachment *new_attachment;
@@ -3557,7 +3583,7 @@ smtp_attachment_add_mem(struct smtp *const smtp,
     return smtp_status_code_set(smtp, SMTP_STATUS_PARAM);
   }
 
-  if(datasz < 0){
+  if(datasz == SIZE_MAX){
     datasz = strlen(data);
   }
 
diff --git a/src/smtp.h b/src/smtp.h
index e9d3cf1..51e6bd9 100644
--- a/src/smtp.h
+++ b/src/smtp.h
@@ -141,9 +141,9 @@ enum smtp_connection_security{
   /**
    * Use TLS when initially connecting to server.
    *
-   * @deprecated SMTP clients should not use this connection type unless
-   *             connecting to a legacy SMTP server which requires it.
-   *             Instead, use @ref SMTP_SECURITY_STARTTLS if possible.
+   * SMTP clients should not use this connection type unless
+   * connecting to a legacy SMTP server which requires it.
+   * Instead, use @ref SMTP_SECURITY_STARTTLS if possible.
    */
   SMTP_SECURITY_TLS,
 #endif /* SMTP_OPENSSL */
@@ -271,7 +271,7 @@ enum smtp_status_code
 smtp_attachment_add_mem(struct smtp *const smtp,
                         const char *const name,
                         const void *const data,
-                        long datasz);
+                        size_t datasz);
 
 void smtp_attachment_clear_all(struct smtp *const smtp);
 
@@ -391,11 +391,6 @@ struct str_getdelimfd{
   size_t _buf_len;
 
   /**
-   * Character delimiter used for determining line separation.
-   */
-  int delim;
-
-  /**
    * Current line containing the text up to the delimiter.
    */
   char *line;
@@ -422,6 +417,16 @@ struct str_getdelimfd{
    * User data which gets sent to the read handler function.
    */
   void *user_data;
+
+  /**
+   * Character delimiter used for determining line separation.
+   */
+  int delim;
+
+  /**
+   * Padding structure to align.
+   */
+  char pad[4];
 };
 
 #endif /* SMTP_INTERNAL_DEFINE */
diff --git a/test/seams.c b/test/seams.c
index 508836b..eeeb15a 100644
--- a/test/seams.c
+++ b/test/seams.c
@@ -10,13 +10,6 @@
  *
  * This software has been placed into the public domain using CC0.
  */
-
-/**
- * Need to define this on some POSIX systems in order to get access to the
- * getaddrinfo and localtime_r functions.
- */
-#define _POSIX_C_SOURCE 200112L
-
 #include <assert.h>
 #include <errno.h>
 #include <stdarg.h>
@@ -357,7 +350,7 @@ smtp_test_seam_connect(int socket,
 unsigned long
 smtp_test_seam_err_peek_error(void){
   if(smtp_test_seam_dec_err_ctr(&g_smtp_test_err_err_peek_error_ctr)){
-    return -1;
+    return 1;
   }
   return ERR_peek_error();
 }
@@ -429,7 +422,7 @@ smtp_test_seam_hmac(const EVP_MD *evp_md,
                     const void *key,
                     int key_len,
                     const unsigned char *d,
-                    int n,
+                    size_t n,
                     unsigned char *md,
                     unsigned int *md_len){
   if(smtp_test_seam_dec_err_ctr(&g_smtp_test_err_hmac_ctr)){
@@ -529,9 +522,9 @@ smtp_test_seam_recv(int socket,
     }
     if(*g_smtp_test_err_recv_bytes){
       bytes_inject_len = strlen(g_smtp_test_err_recv_bytes);
-      assert(bytes_inject_len < length);
+      assert(bytes_inject_len < length && bytes_inject_len < LONG_MAX);
       memcpy(buffer, g_smtp_test_err_recv_bytes, bytes_inject_len);
-      return bytes_inject_len;
+      return (long)bytes_inject_len;
     }
     errno = EBADF;
     return -1;
@@ -578,7 +571,7 @@ smtp_test_seam_select(int nfds,
  * @retval >=0 Number of bytes sent.
  * @retval  -1 Failed to send bytes over the network.
  */
-long
+ssize_t
 smtp_test_seam_send(int socket,
                     const void *buffer,
                     size_t length,
@@ -738,9 +731,9 @@ smtp_test_seam_ssl_read(SSL *ssl,
   if(smtp_test_seam_dec_err_ctr(&g_smtp_test_err_ssl_read_ctr)){
     if(*g_smtp_test_err_recv_bytes){
       bytes_inject_len = strlen(g_smtp_test_err_recv_bytes);
-      assert(bytes_inject_len < (size_t)num);
+      assert(bytes_inject_len < (size_t)num && bytes_inject_len < INT_MAX);
       memcpy(buf, g_smtp_test_err_recv_bytes, bytes_inject_len);
-      return bytes_inject_len;
+      return (int)bytes_inject_len;
     }
     return -1;
   }
diff --git a/test/test.c b/test/test.c
index 1b3d7cd..f0bd51f 100644
--- a/test/test.c
+++ b/test/test.c
@@ -12,12 +12,6 @@
  *
  * This software has been placed into the public domain using CC0.
  */
-
-/**
- * This POSIX declaration required for the setenv() function.
- */
-#define _POSIX_C_SOURCE 200112L
-
 #include <assert.h>
 #include <errno.h>
 #include <fcntl.h>
@@ -94,7 +88,9 @@
  * These default flags will get used for most test connections with the
  * SMTP server.
  */
-#define SMTP_TEST_DEFAULT_FLAGS               (SMTP_DEBUG | SMTP_NO_CERT_VERIFY)
+#define SMTP_TEST_DEFAULT_FLAGS               (enum smtp_flag)(  \
+                                              SMTP_DEBUG |       \
+                                              SMTP_NO_CERT_VERIFY)
 
 /**
  * Use the default certificate path for OpenSSL.
@@ -307,18 +303,18 @@ smtp_str_list_free(struct smtp_str_list *const list){
  *                       containing the rest of the string. A value of 0 has
  *                       the same meaning as 1. A negative value will cut off
  *                       the last @p limit strings from the result.
- * @param[out] slist
+ * @param[out] slist     See @ref smtp_str_list.
  * @retval  0 Successfully split the string and stored the results into
  *            @p slist.
  * @retval -1 Memory allocation failure.
  */
 static int
 smtp_str_split(const char *const s,
-               long slen,
+               size_t slen,
                const char *const delimiter,
                int limit,
                struct smtp_str_list *slist){
-  int i;
+  size_t i;
   size_t i1;
   size_t i2;
   size_t delimiter_len;
@@ -327,15 +323,16 @@ smtp_str_split(const char *const s,
   memset(slist, 0, sizeof(*slist));
   delimiter_len = strlen(delimiter);
 
-  if(slen < 0){
+  if(slen == SIZE_MAX){
     slen = strlen(s);
   }
 
   split_idx = 0;
 
-  for(i1 = 0, i2 = 0; i2 < (size_t)slen; i2++){
+  i1 = 0;
+  for(i2 = 0; i2 < slen; i2++){
     if(limit > 0 && limit - 1 <= split_idx){
-      if(smtp_str_list_append(slist, &s[i1], -1) < 0){
+      if(smtp_str_list_append(slist, &s[i1], SIZE_MAX) < 0){
         smtp_str_list_free(slist);
         return -1;
       }
@@ -364,7 +361,7 @@ smtp_str_split(const char *const s,
   }
 
   if(limit < 0){
-    for(i = 0; i < abs(limit); i++){
+    for(i = 0; i < (size_t)abs(limit); i++){
       free(slist->slist[slist->n - i - 1]);
     }
     slist->n -= i;
@@ -385,12 +382,12 @@ smtp_str_split(const char *const s,
 static size_t
 smtp_ffile_put_contents(FILE *stream,
                         const void *const data,
-                        long datasz){
-  long bytes_written;
+                        size_t datasz){
+  size_t bytes_written;
 
   bytes_written = 0;
 
-  if(datasz < 0){
+  if(datasz == SIZE_MAX){
     bytes_written = strlen(data);
     if(fputs(data, stream) == EOF){
       bytes_written = 0;
@@ -423,7 +420,7 @@ smtp_ffile_put_contents(FILE *stream,
 static size_t
 smtp_file_put_contents(const char *const filename,
                        const void *const data,
-                       long datasz,
+                       size_t datasz,
                        int flags){
   FILE *fp;
   size_t bytes_written;
@@ -508,8 +505,8 @@ smtp_unit_test_all_si(void){
   smtp_unit_test_si_size_t(smtp_si_add_size_t, 0, 1, &result, 1, 0);
   smtp_unit_test_si_size_t(smtp_si_add_size_t, 1, 0, &result, 1, 0);
   smtp_unit_test_si_size_t(smtp_si_add_size_t, 1, 1, &result, 2, 0);
-  smtp_unit_test_si_size_t(smtp_si_add_size_t, 1, 1, NULL, -1, 0);
-  smtp_unit_test_si_size_t(smtp_si_add_size_t, SIZE_MAX, 1, NULL, -1, 1);
+  smtp_unit_test_si_size_t(smtp_si_add_size_t, 1, 1, NULL, SIZE_MAX, 0);
+  smtp_unit_test_si_size_t(smtp_si_add_size_t, SIZE_MAX, 1, NULL, SIZE_MAX, 1);
   smtp_unit_test_si_size_t(smtp_si_add_size_t, SIZE_MAX, 0, &result, SIZE_MAX, 0);
   smtp_unit_test_si_size_t(smtp_si_add_size_t, SIZE_MAX, 1, &result, 0, 1);
   smtp_unit_test_si_size_t(smtp_si_add_size_t, SIZE_MAX - 1, 2, &result, 0, 1);
@@ -527,16 +524,16 @@ smtp_unit_test_all_si(void){
   smtp_unit_test_si_size_t(smtp_si_sub_size_t, 1, 0, &result, 1, 0);
   smtp_unit_test_si_size_t(smtp_si_sub_size_t, 1, 1, &result, 0, 0);
   smtp_unit_test_si_size_t(smtp_si_sub_size_t, 2, 3, &result, SIZE_MAX, 1);
-  smtp_unit_test_si_size_t(smtp_si_sub_size_t, 2, 1, NULL, -1, 0);
-  smtp_unit_test_si_size_t(smtp_si_sub_size_t, 1, 2, NULL, -1, 1);
+  smtp_unit_test_si_size_t(smtp_si_sub_size_t, 2, 1, NULL, SIZE_MAX, 0);
+  smtp_unit_test_si_size_t(smtp_si_sub_size_t, 1, 2, NULL, SIZE_MAX, 1);
 
   /* multiply */
   smtp_unit_test_si_size_t(smtp_si_mul_size_t, 0, 0, &result, 0, 0);
   smtp_unit_test_si_size_t(smtp_si_mul_size_t, 0, 1, &result, 0, 0);
   smtp_unit_test_si_size_t(smtp_si_mul_size_t, 1, 0, &result, 0, 0);
   smtp_unit_test_si_size_t(smtp_si_mul_size_t, 1, 1, &result, 1, 0);
-  smtp_unit_test_si_size_t(smtp_si_mul_size_t, 1, 1, NULL, -1, 0);
-  smtp_unit_test_si_size_t(smtp_si_mul_size_t, SIZE_MAX, 2, NULL, -1, 1);
+  smtp_unit_test_si_size_t(smtp_si_mul_size_t, 1, 1, NULL, SIZE_MAX, 0);
+  smtp_unit_test_si_size_t(smtp_si_mul_size_t, SIZE_MAX, 2, NULL, SIZE_MAX, 1);
   smtp_unit_test_si_size_t(smtp_si_mul_size_t, 100, 12, &result, 1200, 0);
   smtp_unit_test_si_size_t(smtp_si_mul_size_t, SIZE_MAX, 1, &result, SIZE_MAX, 0);
   smtp_unit_test_si_size_t(smtp_si_mul_size_t,
@@ -557,9 +554,9 @@ smtp_unit_test_all_si(void){
 static void
 smtp_unit_test_base64_decode(const char *const buf,
                              const char *const expect_str,
-                             long expect_str_len){
+                             size_t expect_str_len){
   unsigned char *decode;
-  long str_len;
+  size_t str_len;
 
   str_len = smtp_base64_decode(buf, &decode);
   if(expect_str){
@@ -590,17 +587,17 @@ smtp_unit_test_all_base64_decode(void){
                                26);
 
   /* invalid inputs */
-  smtp_unit_test_base64_decode("AB"     , NULL, -1);
-  smtp_unit_test_base64_decode("^^^^"   , NULL, -1);
-  smtp_unit_test_base64_decode("^^^\xFF", NULL, -1);
+  smtp_unit_test_base64_decode("AB"     , NULL, SIZE_MAX);
+  smtp_unit_test_base64_decode("^^^^"   , NULL, SIZE_MAX);
+  smtp_unit_test_base64_decode("^^^\xFF", NULL, SIZE_MAX);
 
   /* Wrap when calculating the buffer length. */
   g_smtp_test_err_si_add_size_t_ctr = 0;
-  smtp_unit_test_base64_decode("YQ=="    , NULL, -1);
+  smtp_unit_test_base64_decode("YQ=="    , NULL, SIZE_MAX);
   g_smtp_test_err_si_add_size_t_ctr = -1;
 
   g_smtp_test_err_calloc_ctr = 0;
-  smtp_unit_test_base64_decode("", NULL, -1);
+  smtp_unit_test_base64_decode("", NULL, SIZE_MAX);
   g_smtp_test_err_calloc_ctr = -1;
 }
 
@@ -632,15 +629,15 @@ smtp_unit_test_base64_encode(const char *const buf,
  */
 static void
 smtp_unit_test_all_base64_encode(void){
-  smtp_unit_test_base64_encode(""     , -1, "");
-  smtp_unit_test_base64_encode("a"    , -1, "YQ==");
-  smtp_unit_test_base64_encode("aa"   , -1, "YWE=");
-  smtp_unit_test_base64_encode("aaa"  , -1, "YWFh");
-  smtp_unit_test_base64_encode("aaaa" , -1, "YWFhYQ==");
-  smtp_unit_test_base64_encode("aaaaa", -1, "YWFhYWE=");
-  smtp_unit_test_base64_encode("12345", -1, "MTIzNDU=");
+  smtp_unit_test_base64_encode(""     , SIZE_MAX, "");
+  smtp_unit_test_base64_encode("a"    , SIZE_MAX, "YQ==");
+  smtp_unit_test_base64_encode("aa"   , SIZE_MAX, "YWE=");
+  smtp_unit_test_base64_encode("aaa"  , SIZE_MAX, "YWFh");
+  smtp_unit_test_base64_encode("aaaa" , SIZE_MAX, "YWFhYQ==");
+  smtp_unit_test_base64_encode("aaaaa", SIZE_MAX, "YWFhYWE=");
+  smtp_unit_test_base64_encode("12345", SIZE_MAX, "MTIzNDU=");
   smtp_unit_test_base64_encode(STR_ALPHABET_LOWERCASE,
-                               -1,
+                               SIZE_MAX,
                                "YWJjZGVmZ2hpamtsbW5vcHFyc3R1dnd4eXo=");
 
   /* binary data */
@@ -650,13 +647,13 @@ smtp_unit_test_all_base64_encode(void){
   /* Value would wrap */
   g_smtp_test_strlen_custom_ret = 1;
   g_smtp_test_strlen_ret_value = SIZE_MAX - 1;
-  smtp_unit_test_base64_encode("a", -1, NULL);
+  smtp_unit_test_base64_encode("a", SIZE_MAX, NULL);
   g_smtp_test_strlen_custom_ret = 0;
   g_smtp_test_strlen_ret_value = 0;
 
   /* calloc */
   g_smtp_test_err_calloc_ctr = 0;
-  smtp_unit_test_base64_encode("", -1, NULL);
+  smtp_unit_test_base64_encode("", SIZE_MAX, NULL);
   g_smtp_test_err_calloc_ctr = -1;
 }
 
@@ -891,7 +888,7 @@ smtp_unit_test_str_replace(const char *const search,
  */
 static void
 smtp_unit_test_all_str_replace(void){
-  size_t i;
+  int i;
 
   smtp_unit_test_str_replace("", "", "", "");
   smtp_unit_test_str_replace("a", "b", "", "");
@@ -1021,8 +1018,8 @@ smtp_unit_test_all_strnlen_utf8(void){
   smtp_unit_test_strnlen_utf8("𠜎", 3, 4);
 
   /* Invalid UTF-8 sequences. */
-  smtp_unit_test_strnlen_utf8("\xBF", 3, -1);
-  smtp_unit_test_strnlen_utf8("\xC0", 3, -1);
+  smtp_unit_test_strnlen_utf8("\xBF", 3, SIZE_MAX);
+  smtp_unit_test_strnlen_utf8("\xC0", 3, SIZE_MAX);
 }
 
 /**
@@ -1182,7 +1179,7 @@ smtp_unit_test_fold_whitespace(const char *const s,
  */
 static void
 smtp_unit_test_all_fold_whitespace(void){
-  size_t i;
+  int i;
 
   smtp_unit_test_fold_whitespace("Subject: Email Test",
                                  5,
@@ -1276,7 +1273,7 @@ smtp_unit_test_chunk_split(const char *const s,
  */
 static void
 smtp_unit_test_all_chunk_split(void){
-  size_t i;
+  int i;
 
   smtp_unit_test_chunk_split("", 0, "", NULL);
   smtp_unit_test_chunk_split("a", 0, "a", NULL);
@@ -1379,7 +1376,7 @@ smtp_unit_test_all_file_get_contents(void){
   smtp_unit_test_file_get_contents(test_str, strlen(test_str), test_str);
 
   test_str = "test";
-  smtp_unit_test_file_get_contents(test_str, -1, test_str);
+  smtp_unit_test_file_get_contents(test_str, SIZE_MAX, test_str);
 
   test_str = STR_ALPHABET_LOWERCASE;
   smtp_unit_test_file_get_contents(test_str, strlen(test_str), test_str);
@@ -1464,11 +1461,7 @@ smtp_unit_test_all_parse_cmd_line(void){
                                 0,
                                 "text");
   smtp_unit_test_parse_cmd_line("-22 text",
-                                -22,
-                                0,
-                                "text");
-  smtp_unit_test_parse_cmd_line("-22 text",
-                                -22,
+                                SMTP_INTERNAL_ERROR,
                                 0,
                                 "text");
   smtp_unit_test_parse_cmd_line("220 ready",
@@ -1632,9 +1625,9 @@ smtp_unit_test_all_smtp_status_code_errstr(void){
                                          "Success");
   smtp_unit_test_smtp_status_code_errstr(SMTP_STATUS_NOMEM,
                                          "Memory allocation failed");
-  smtp_unit_test_smtp_status_code_errstr(-1,
+  smtp_unit_test_smtp_status_code_errstr((enum smtp_status_code)-1,
                                          "Unknown error");
-  smtp_unit_test_smtp_status_code_errstr(99,
+  smtp_unit_test_smtp_status_code_errstr((enum smtp_status_code)99,
                                          "Unknown error");
 }
 
@@ -1676,7 +1669,7 @@ smtp_unit_test_getdelimfd_fp(struct str_getdelimfd *const gdfd,
   if(g_smtp_test_getdelimfd_fp_fail){
     return -1;
   }
-  return bytes_read;
+  return (long)bytes_read;
 }
 
 /**
@@ -1757,7 +1750,7 @@ smtp_unit_test_str_getdelimfd(const char *const input_string,
 /**
  * Test harness for @ref smtp_str_getdelimfd_set_line_and_buf.
  *
- * @param[in] gdfd          @ref str_getdelimfd.
+ * @param[in] gdfd          See @ref str_getdelimfd.
  * @param[in] copy_len      Number of bytes to copy to the internal line buffer.
  * @param[in] expect_result Expected result code (0 or -1) from
  *                          @ref smtp_str_getdelimfd_set_line_and_buf.
@@ -1780,7 +1773,7 @@ smtp_unit_test_all_str_getdelimfd(void){
   const char *s;
   struct str_getdelimfd gdfd;
   char test_str[] = "test";
-  size_t i;
+  int i;
 
   s = "";
   smtp_unit_test_str_getdelimfd(s,
@@ -2169,7 +2162,7 @@ smtp_test_config_load_from_file(const char *const config_path,
  */
 static void
 test_smtp_open_default(struct smtp_test_config *const config){
-  int rc;
+  enum smtp_status_code rc;
 
   rc = smtp_open(config->server,
                  config->port,
@@ -2200,7 +2193,7 @@ test_smtp_open_default(struct smtp_test_config *const config){
   rc = smtp_attachment_add_mem(config->smtp,
                                "test.txt",
                                "test attachment",
-                               -1);
+                               SIZE_MAX);
   assert(rc == SMTP_STATUS_OK);
 }
 
@@ -2211,7 +2204,7 @@ test_smtp_open_default(struct smtp_test_config *const config){
  */
 static void
 smtp_func_test_all_status_code_get(struct smtp_test_config *const config){
-  int rc;
+  enum smtp_status_code rc;
 
   rc = smtp_open(config->server,
                  config->port,
@@ -2257,7 +2250,7 @@ smtp_func_test_send_email(struct smtp_test_config *const config,
                           const char *const cafile,
                           const char *const subject,
                           const char *const body){
-  int rc;
+  enum smtp_status_code rc;
 
   rc = smtp_open(config->server,
                  port,
@@ -2417,8 +2410,8 @@ static void
 smtp_func_test_attachment_path(struct smtp_test_config *const config,
                                const char *const name,
                                const char *const path,
-                               int expect_rc){
-  int rc;
+                               enum smtp_status_code expect_rc){
+  enum smtp_status_code rc;
 
   strcpy(config->subject, "SMTP Test: Attachment (file path)");
   strcpy(config->body, "This email should contain a pdf attachment");
@@ -2475,9 +2468,10 @@ static void
 smtp_func_test_attachment_fp(struct smtp_test_config *const config,
                              const char *const name,
                              const char *const path,
-                             int expect_rc){
-  int rc;
+                             enum smtp_status_code expect_rc){
+  enum smtp_status_code rc;
   FILE *fp;
+  int fp_rc;
 
   strcpy(config->subject, "SMTP Test: Attachment (fp)");
   strcpy(config->body, "This email should contain a pdf attachment");
@@ -2517,8 +2511,8 @@ smtp_func_test_attachment_fp(struct smtp_test_config *const config,
   rc = smtp_close(config->smtp);
   assert(rc == expect_rc);
 
-  rc = fclose(fp);
-  assert(rc == 0);
+  fp_rc = fclose(fp);
+  assert(fp_rc == 0);
 }
 
 /**
@@ -2533,7 +2527,7 @@ smtp_func_test_attachment_mem(struct smtp_test_config *const config,
   size_t i;
   char attachment_name[SMTP_MAX_ATTACHMENT_NAME_LEN];
   char attachment_data[100];
-  int rc;
+  enum smtp_status_code rc;
 
   sprintf(config->subject,
           "SMTP Test: Attachments (%u)",
@@ -2576,7 +2570,7 @@ smtp_func_test_attachment_mem(struct smtp_test_config *const config,
     rc = smtp_attachment_add_mem(config->smtp,
                                  attachment_name,
                                  attachment_data,
-                                 -1);
+                                 SIZE_MAX);
     assert(rc == SMTP_STATUS_OK);
   }
 
@@ -2597,7 +2591,7 @@ smtp_func_test_attachment_mem(struct smtp_test_config *const config,
  */
 static void
 smtp_func_test_attachment_long_text(struct smtp_test_config *const config){
-  int rc;
+  enum smtp_status_code rc;
   char *long_text;
 
   /* Send Large attachment attachment with repeated text. */
@@ -2632,7 +2626,7 @@ smtp_func_test_attachment_long_text(struct smtp_test_config *const config){
   rc = smtp_attachment_add_mem(config->smtp,
                                "alphabet-repeat.txt",
                                long_text,
-                               -1);
+                               SIZE_MAX);
   assert(rc == SMTP_STATUS_OK);
   free(long_text);
 
@@ -2717,7 +2711,7 @@ smtp_func_test_all_attachments(struct smtp_test_config *const config){
  */
 static void
 smtp_func_test_all_address(struct smtp_test_config *const config){
-  int rc;
+  enum smtp_status_code rc;
 
   rc = smtp_open(config->server,
                  config->port,
@@ -2884,7 +2878,7 @@ smtp_func_test_all_address(struct smtp_test_config *const config){
  */
 static void
 smtp_func_test_all_names(struct smtp_test_config *const config){
-  int rc;
+  enum smtp_status_code rc;
   char *long_name;
 
   rc = smtp_open(config->server,
@@ -3035,7 +3029,7 @@ smtp_func_test_all_names(struct smtp_test_config *const config){
  */
 static void
 smtp_func_test_header_custom_date(struct smtp_test_config *const config){
-  int rc;
+  enum smtp_status_code rc;
 
   rc = smtp_open(config->server,
                  config->port,
@@ -3086,7 +3080,7 @@ smtp_func_test_header_custom_date(struct smtp_test_config *const config){
  */
 static void
 smtp_func_test_header_null_no_date(struct smtp_test_config *const config){
-  int rc;
+  enum smtp_status_code rc;
 
   rc = smtp_open(config->server,
                  config->port,
@@ -3135,7 +3129,7 @@ smtp_func_test_header_null_no_date(struct smtp_test_config *const config){
  */
 static void
 smtp_func_test_header_long(struct smtp_test_config *const config){
-  int rc;
+  enum smtp_status_code rc;
   char *long_text;
 
   rc = smtp_open(config->server,
@@ -3202,7 +3196,7 @@ smtp_func_test_all_headers(struct smtp_test_config *const config){
  */
 static void
 smtp_func_test_all_body(struct smtp_test_config *const config){
-  int rc;
+  enum smtp_status_code rc;
   char *long_body;
 
   rc = smtp_open(config->server,
@@ -3249,7 +3243,7 @@ smtp_func_test_all_body(struct smtp_test_config *const config){
  */
 static void
 smtp_func_test_all_write(struct smtp_test_config *const config){
-  int rc;
+  enum smtp_status_code rc;
 
   g_smtp_test_send_one_byte = 1;
   rc = smtp_open(config->server,
@@ -3271,7 +3265,7 @@ smtp_func_test_all_write(struct smtp_test_config *const config){
  */
 static void
 smtp_func_test_all_nodebug(struct smtp_test_config *const config){
-  int rc;
+  enum smtp_status_code rc;
 
   rc = smtp_open(config->server,
                  config->port,
@@ -3316,7 +3310,7 @@ smtp_func_test_all_nodebug(struct smtp_test_config *const config){
  */
 static void
 test_failure_misc(struct smtp_test_config *const config){
-  int rc;
+  enum smtp_status_code rc;
 
   /* Send buffer to large in @ref smtp_write. */
   rc = smtp_open(config->server,
@@ -3352,7 +3346,7 @@ test_failure_misc(struct smtp_test_config *const config){
  */
 static void
 test_failure_open(struct smtp_test_config *const config){
-  int rc;
+  enum smtp_status_code rc;
 
   /* Initial memory allocation failure for the SMTP client context. */
   g_smtp_test_err_calloc_ctr = 0;
@@ -3672,7 +3666,7 @@ test_failure_open(struct smtp_test_config *const config){
  */
 static void
 test_failure_address_add(struct smtp_test_config *const config){
-  int rc;
+  enum smtp_status_code rc;
 
   rc = smtp_open(config->server,
                  config->port,
@@ -3758,8 +3752,9 @@ test_failure_address_add(struct smtp_test_config *const config){
  */
 static void
 test_failure_attachment_add(struct smtp_test_config *const config){
-  int rc;
+  enum smtp_status_code rc;
   FILE *fp;
+  int fp_rc;
 
   rc = smtp_open(config->server,
                  config->port,
@@ -3772,7 +3767,10 @@ test_failure_attachment_add(struct smtp_test_config *const config){
 
   /* Invalid SMTP status code. */
   smtp_status_code_set(config->smtp, SMTP_STATUS_PARAM);
-  rc = smtp_attachment_add_mem(config->smtp, "valid", "test", -1);
+  rc = smtp_attachment_add_mem(config->smtp,
+                               "valid",
+                               "test",
+                               SIZE_MAX);
   assert(rc == SMTP_STATUS_PARAM);
 
 
@@ -3781,27 +3779,36 @@ test_failure_attachment_add(struct smtp_test_config *const config){
   rc = smtp_attachment_add_mem(config->smtp,
                                "\"invalid\"",
                                "test",
-                               -1);
+                               SIZE_MAX);
   assert(rc == SMTP_STATUS_PARAM);
 
   /* Wrap when increasing the attachment list size. */
   smtp_status_code_set(config->smtp, SMTP_STATUS_OK);
   g_smtp_test_err_si_add_size_t_ctr = 0;
-  rc = smtp_attachment_add_mem(config->smtp, "valid", "test", -1);
+  rc = smtp_attachment_add_mem(config->smtp,
+                               "valid",
+                               "test",
+                               SIZE_MAX);
   assert(rc == SMTP_STATUS_NOMEM);
   g_smtp_test_err_si_add_size_t_ctr = -1;
 
   /* Memory allocation failure while increasing the attachment list size. */
   smtp_status_code_set(config->smtp, SMTP_STATUS_OK);
   g_smtp_test_err_realloc_ctr = 0;
-  rc = smtp_attachment_add_mem(config->smtp, "valid", "test", -1);
+  rc = smtp_attachment_add_mem(config->smtp,
+                               "valid",
+                               "test",
+                               SIZE_MAX);
   assert(rc == SMTP_STATUS_NOMEM);
   g_smtp_test_err_realloc_ctr = -1;
 
   /* Memory allocation failure while using smtp_strdup on file name. */
   smtp_status_code_set(config->smtp, SMTP_STATUS_OK);
   g_smtp_test_err_malloc_ctr = 0;
-  rc = smtp_attachment_add_mem(config->smtp, "valid", "test", -1);
+  rc = smtp_attachment_add_mem(config->smtp,
+                               "valid",
+                               "test",
+                               SIZE_MAX);
   assert(rc == SMTP_STATUS_NOMEM);
   g_smtp_test_err_malloc_ctr = -1;
 
@@ -3809,14 +3816,20 @@ test_failure_attachment_add(struct smtp_test_config *const config){
   /* Memory allocation failure while using smtp_base64_encode. */
   smtp_status_code_set(config->smtp, SMTP_STATUS_OK);
   g_smtp_test_err_calloc_ctr = 0;
-  rc = smtp_attachment_add_mem(config->smtp, "valid", "test", -1);
+  rc = smtp_attachment_add_mem(config->smtp,
+                               "valid",
+                               "test",
+                               SIZE_MAX);
   assert(rc == SMTP_STATUS_NOMEM);
   g_smtp_test_err_calloc_ctr = -1;
 
   /* Memory allocation failure when splitting base64 lines into chunks. */
   smtp_status_code_set(config->smtp, SMTP_STATUS_OK);
   g_smtp_test_err_calloc_ctr = 1;
-  rc = smtp_attachment_add_mem(config->smtp, "valid", "test", -1);
+  rc = smtp_attachment_add_mem(config->smtp,
+                               "valid",
+                               "test",
+                               SIZE_MAX);
   assert(rc == SMTP_STATUS_NOMEM);
   g_smtp_test_err_calloc_ctr = -1;
 
@@ -3840,8 +3853,8 @@ test_failure_attachment_add(struct smtp_test_config *const config){
   rc = smtp_attachment_add_fp(config->smtp, "test", fp);
   g_smtp_test_err_ferror_ctr = -1;
   assert(rc == SMTP_STATUS_FILE);
-  rc = fclose(fp);
-  assert(rc == 0);
+  fp_rc = fclose(fp);
+  assert(fp_rc == 0);
 
   /* @ref smtp_file_get_contents memory allocation failure. */
   smtp_status_code_set(config->smtp, SMTP_STATUS_OK);
@@ -3867,7 +3880,7 @@ test_failure_attachment_add(struct smtp_test_config *const config){
  */
 static void
 test_failure_header_add(struct smtp_test_config *const config){
-  int rc;
+  enum smtp_status_code rc;
 
   rc = smtp_open(config->server,
                  config->port,
@@ -3941,7 +3954,7 @@ test_failure_header_add(struct smtp_test_config *const config){
  */
 static void
 test_failure_status_code_set(struct smtp_test_config *const config){
-  int rc;
+  enum smtp_status_code rc;
 
   rc = smtp_open(config->server,
                  config->port,
@@ -3951,7 +3964,7 @@ test_failure_status_code_set(struct smtp_test_config *const config){
                  &config->smtp);
   assert(rc == SMTP_STATUS_OK);
 
-  rc = smtp_status_code_set(config->smtp, -1);
+  rc = smtp_status_code_set(config->smtp, (enum smtp_status_code)-1);
   assert(rc == SMTP_STATUS_PARAM);
 
   rc = smtp_status_code_set(config->smtp, SMTP_STATUS__LAST);
@@ -3971,7 +3984,7 @@ test_failure_status_code_set(struct smtp_test_config *const config){
  */
 static void
 test_failure_mail(struct smtp_test_config *const config){
-  int rc;
+  enum smtp_status_code rc;
 
   /* Invalid SMTP client context. */
   test_smtp_open_default(config);
@@ -4284,7 +4297,7 @@ test_failure_mail(struct smtp_test_config *const config){
  */
 static void
 test_failure_close(struct smtp_test_config *const config){
-  int rc;
+  enum smtp_status_code rc;
 
   /* Failed to send the QUIT command. */
   rc = smtp_open(config->server,
@@ -4340,7 +4353,7 @@ test_failure_close(struct smtp_test_config *const config){
  */
 static void
 test_failure_auth(struct smtp_test_config *const config){
-  int rc;
+  enum smtp_status_code rc;
 
   smtp_test_sleep(15);
 
@@ -4359,7 +4372,7 @@ test_failure_auth(struct smtp_test_config *const config){
   /* Invalid authentication method. */
   test_smtp_open_default(config);
   rc = smtp_auth(config->smtp,
-                 -1,
+                 (enum smtp_authentication_method)-1,
                  config->user,
                  config->pass);
   assert(rc == SMTP_STATUS_PARAM);
@@ -4790,7 +4803,7 @@ test_failure_auth(struct smtp_test_config *const config){
  */
 static void
 test_failure_timeout(struct smtp_test_config *const config){
-  int rc;
+  enum smtp_status_code rc;
 
   rc = smtp_open(config->server,
                  config->port,
@@ -4878,7 +4891,7 @@ static void
 smtp_func_test_gmail_attachment(struct smtp_test_config *const config){
   const char *const name = "test.pdf";
   const char *const path = "test/test.pdf";
-  int rc;
+  enum smtp_status_code rc;
 
   strcpy(config->subject, "SMTP Test: GMail Attachment (file path)");
   strcpy(config->body, "This email should contain a pdf attachment");
diff --git a/test/test.h b/test/test.h
index 35b48c5..4d68af7 100644
--- a/test/test.h
+++ b/test/test.h
@@ -62,7 +62,7 @@ smtp_si_mul_size_t(const size_t a,
                    const size_t b,
                    size_t *const result);
 
-long
+size_t
 smtp_base64_decode(const char *const buf,
                    unsigned char **decode);
 
@@ -106,13 +106,13 @@ smtp_str_replace(const char *const search,
             const char *const replace,
             const char *const s);
 
-int
-smtp_utf8_charlen(unsigned char c);
+size_t
+smtp_utf8_charlen(char c);
 
 int
 smtp_str_has_nonascii_utf8(const char *const s);
 
-long
+size_t
 smtp_strnlen_utf8(const char *s,
                   size_t maxlen);
 
@@ -200,7 +200,7 @@ smtp_test_seam_hmac(const EVP_MD *evp_md,
                     const void *key,
                     int key_len,
                     const unsigned char *d,
-                    int n,
+                    size_t n,
                     unsigned char *md,
                     unsigned int *md_len);
 
@@ -232,7 +232,7 @@ smtp_test_seam_select(int nfds,
                       fd_set *errorfds,
                       struct timeval *timeout);
 
-long
+ssize_t
 smtp_test_seam_send(int socket,
                     const void *buffer,
                     size_t length,
@@ -290,14 +290,14 @@ smtp_test_seam_time(time_t *tloc);
  *
  * See @ref test_seams_countdown_global for more details.
  */
-int g_smtp_test_err_bio_new_socket_ctr;
+extern int g_smtp_test_err_bio_new_socket_ctr;
 
 /**
  * Counter for @ref smtp_test_seam_bio_should_retry.
  *
  * See @ref test_seams_countdown_global for more details.
  */
-int g_smtp_test_err_bio_should_retry_ctr;
+extern int g_smtp_test_err_bio_should_retry_ctr;
 
 /**
  * Value to force the BIO_should_retry() function to return.
@@ -306,98 +306,98 @@ int g_smtp_test_err_bio_should_retry_ctr;
  * @ref g_smtp_test_err_bio_should_retry_ctr
  * has a value of 0 and this does not have a value of -1.
  */
-int g_smtp_test_err_bio_should_retry_rc;
+extern int g_smtp_test_err_bio_should_retry_rc;
 
 /**
  * Counter for @ref smtp_test_seam_calloc.
  *
  * See @ref test_seams_countdown_global for more details.
  */
-int g_smtp_test_err_calloc_ctr;
+extern int g_smtp_test_err_calloc_ctr;
 
 /**
  * Counter for @ref smtp_test_seam_close.
  *
  * See @ref test_seams_countdown_global for more details.
  */
-int g_smtp_test_err_close_ctr;
+extern int g_smtp_test_err_close_ctr;
 
 /**
  * Counter for @ref smtp_test_seam_connect.
  *
  * See @ref test_seams_countdown_global for more details.
  */
-int g_smtp_test_err_connect_ctr;
+extern int g_smtp_test_err_connect_ctr;
 
 /**
  * Counter for @ref smtp_test_seam_err_peek_error.
  *
  * See @ref test_seams_countdown_global for more details.
  */
-int g_smtp_test_err_err_peek_error_ctr;
+extern int g_smtp_test_err_err_peek_error_ctr;
 
 /**
  * Counter for @ref smtp_test_seam_fclose.
  *
  * See @ref test_seams_countdown_global for more details.
  */
-int g_smtp_test_err_fclose_ctr;
+extern int g_smtp_test_err_fclose_ctr;
 
 /**
  * Counter for @ref smtp_test_seam_ferror.
  *
  * See @ref test_seams_countdown_global for more details.
  */
-int g_smtp_test_err_ferror_ctr;
+extern int g_smtp_test_err_ferror_ctr;
 
 /**
  * Counter for @ref smtp_test_seam_gmtime_r.
  *
  * See @ref test_seams_countdown_global for more details.
  */
-int g_smtp_test_err_gmtime_r_ctr;
+extern int g_smtp_test_err_gmtime_r_ctr;
 
 /**
  * Counter for @ref smtp_test_seam_hmac.
  *
  * See @ref test_seams_countdown_global for more details.
  */
-int g_smtp_test_err_hmac_ctr;
+extern int g_smtp_test_err_hmac_ctr;
 
 /**
  * Counter for @ref smtp_test_seam_localtime_r.
  *
  * See @ref test_seams_countdown_global for more details.
  */
-int g_smtp_test_err_localtime_r_ctr;
+extern int g_smtp_test_err_localtime_r_ctr;
 
 /**
  * Counter for @ref smtp_test_seam_malloc.
  *
  * See @ref test_seams_countdown_global for more details.
  */
-int g_smtp_test_err_malloc_ctr;
+extern int g_smtp_test_err_malloc_ctr;
 
 /**
  * Counter for @ref smtp_test_seam_mktime.
  *
  * See @ref test_seams_countdown_global for more details.
  */
-int g_smtp_test_err_mktime_ctr;
+extern int g_smtp_test_err_mktime_ctr;
 
 /**
  * Counter for @ref smtp_test_seam_realloc.
  *
  * See @ref test_seams_countdown_global for more details.
  */
-int g_smtp_test_err_realloc_ctr;
+extern int g_smtp_test_err_realloc_ctr;
 
 /**
  * Counter for @ref smtp_test_seam_recv.
  *
  * See @ref test_seams_countdown_global for more details.
  */
-int g_smtp_test_err_recv_ctr;
+extern int g_smtp_test_err_recv_ctr;
 
 /**
  * Value to force the recv() function to return.
@@ -406,7 +406,7 @@ int g_smtp_test_err_recv_ctr;
  * @ref g_smtp_test_err_recv_ctr
  * has a value of 0 and this does not have a value of -1.
  */
-int g_smtp_test_err_recv_rc;
+extern int g_smtp_test_err_recv_rc;
 
 /**
  * Set the received bytes in recv() and SSL_read() to this value if it
@@ -417,117 +417,117 @@ int g_smtp_test_err_recv_rc;
  *
  * See @ref test_seams_countdown_global for more details.
  */
-char g_smtp_test_err_recv_bytes[90];
+extern char g_smtp_test_err_recv_bytes[90];
 
 /**
  * Counter for @ref smtp_test_seam_select.
  *
  * See @ref test_seams_countdown_global for more details.
  */
-int g_smtp_test_err_select_ctr;
+extern int g_smtp_test_err_select_ctr;
 
 /**
  * Counter for @ref smtp_test_seam_send.
  *
  * See @ref test_seams_countdown_global for more details.
  */
-int g_smtp_test_err_send_ctr;
+extern int g_smtp_test_err_send_ctr;
 
 /**
  * Indicate if we should only send one byte at a time.
  */
-int g_smtp_test_send_one_byte;
+extern int g_smtp_test_send_one_byte;
 
 /**
  * Counter for @ref smtp_si_add_size_t.
  *
  * See @ref test_seams_countdown_global for more details.
  */
-int g_smtp_test_err_si_add_size_t_ctr;
+extern int g_smtp_test_err_si_add_size_t_ctr;
 
 /**
  * Counter for @ref smtp_si_sub_size_t.
  *
  * See @ref test_seams_countdown_global for more details.
  */
-int g_smtp_test_err_si_sub_size_t_ctr;
+extern int g_smtp_test_err_si_sub_size_t_ctr;
 
 /**
  * Counter for @ref smtp_si_mul_size_t.
  *
  * See @ref test_seams_countdown_global for more details.
  */
-int g_smtp_test_err_si_mul_size_t_ctr;
+extern int g_smtp_test_err_si_mul_size_t_ctr;
 
 /**
  * Counter for @ref smtp_test_seam_socket.
  *
  * See @ref test_seams_countdown_global for more details.
  */
-int g_smtp_test_err_socket_ctr;
+extern int g_smtp_test_err_socket_ctr;
 
 /**
  * Counter for @ref smtp_test_seam_ssl_connect.
  *
  * See @ref test_seams_countdown_global for more details.
  */
-int g_smtp_test_err_ssl_connect_ctr;
+extern int g_smtp_test_err_ssl_connect_ctr;
 
 /**
  * Counter for @ref smtp_test_seam_ssl_ctx_new.
  *
  * See @ref test_seams_countdown_global for more details.
  */
-int g_smtp_test_err_ssl_ctx_new_ctr;
+extern int g_smtp_test_err_ssl_ctx_new_ctr;
 
 /**
  * Counter for @ref smtp_test_seam_ssl_do_handshake.
  *
  * See @ref test_seams_countdown_global for more details.
  */
-int g_smtp_test_err_ssl_do_handshake_ctr;
+extern int g_smtp_test_err_ssl_do_handshake_ctr;
 
 /**
  * Counter for @ref smtp_test_seam_ssl_get_peer_certificate.
  *
  * See @ref test_seams_countdown_global for more details.
  */
-int g_smtp_test_err_ssl_get_peer_certificate_ctr;
+extern int g_smtp_test_err_ssl_get_peer_certificate_ctr;
 
 /**
  * Counter for @ref smtp_test_seam_x509_check_host.
  *
  * See @ref test_seams_countdown_global for more details.
  */
-int g_smtp_test_err_x509_check_host_ctr;
+extern int g_smtp_test_err_x509_check_host_ctr;
 
 /**
  * Counter for @ref smtp_test_seam_ssl_new.
  *
  * See @ref test_seams_countdown_global for more details.
  */
-int g_smtp_test_err_ssl_new_ctr;
+extern int g_smtp_test_err_ssl_new_ctr;
 
 /**
  * Counter for @ref smtp_test_seam_ssl_read.
  *
  * See @ref test_seams_countdown_global for more details.
  */
-int g_smtp_test_err_ssl_read_ctr;
+extern int g_smtp_test_err_ssl_read_ctr;
 
 /**
  * Counter for @ref smtp_test_seam_ssl_write.
  *
  * See @ref test_seams_countdown_global for more details.
  */
-int g_smtp_test_err_ssl_write_ctr;
+extern int g_smtp_test_err_ssl_write_ctr;
 
 /**
  * Counter for @ref smtp_test_seam_sprintf.
  *
  * See @ref test_seams_countdown_global for more details.
  */
-int g_smtp_test_err_sprintf_ctr;
+extern int g_smtp_test_err_sprintf_ctr;
 
 /**
  * Value to force the sprintf() function to return.
@@ -535,7 +535,7 @@ int g_smtp_test_err_sprintf_ctr;
  * This value will only get returned if @ref g_smtp_test_err_sprintf_ctr has
  * a value of 0.
  */
-int g_smtp_test_err_sprintf_rc;
+extern int g_smtp_test_err_sprintf_rc;
 
 /**
  * Indicates if the strlen() function should return a test value.
@@ -545,7 +545,7 @@ int g_smtp_test_err_sprintf_rc;
  *   - !0 - The strlen() function will return the value specified in
  *          @ref g_smtp_test_strlen_ret_value.
  */
-int g_smtp_test_strlen_custom_ret;
+extern int g_smtp_test_strlen_custom_ret;
 
 /**
  * Value to force the strlen() function to return.
@@ -553,7 +553,7 @@ int g_smtp_test_strlen_custom_ret;
  * This value will only get returned if @ref g_smtp_test_strlen_custom_ret
  * has been set.
  */
-size_t g_smtp_test_strlen_ret_value;
+extern size_t g_smtp_test_strlen_ret_value;
 
 /**
  * Indicates if the time() function should return a custom value.
@@ -563,7 +563,7 @@ size_t g_smtp_test_strlen_ret_value;
  *   - !0 - The time() function will return the value specified in
  *          @ref g_smtp_test_time_ret_value.
  */
-int g_smtp_test_time_custom_ret;
+extern int g_smtp_test_time_custom_ret;
 
 /**
  * Value to force the time() function to return.
@@ -571,7 +571,7 @@ int g_smtp_test_time_custom_ret;
  * This value will only get returned if @ref g_smtp_test_time_custom_ret has
  * a positive value.
  */
-time_t g_smtp_test_time_ret_value;
+extern time_t g_smtp_test_time_ret_value;
 
 #endif /* SMTP_TEST_H */