thodg/libgit2

diff --git a/src/cli/cmd.h b/src/cli/cmd.h
index cc1743e..664b502 100644
--- a/src/cli/cmd.h
+++ b/src/cli/cmd.h
@@ -26,6 +26,7 @@ extern const cli_cmd_spec *cli_cmd_spec_byname(const char *name);
 
 /* Commands */
 extern int cmd_cat_file(int argc, char **argv);
+extern int cmd_hash_object(int argc, char **argv);
 extern int cmd_help(int argc, char **argv);
 
 #endif /* CLI_cmd_h__ */
diff --git a/src/cli/cmd_hash_object.c b/src/cli/cmd_hash_object.c
new file mode 100644
index 0000000..5cfe914
--- /dev/null
+++ b/src/cli/cmd_hash_object.c
@@ -0,0 +1,135 @@
+/*
+ * Copyright (C) the libgit2 contributors. All rights reserved.
+ *
+ * This file is part of libgit2, distributed under the GNU GPL v2 with
+ * a Linking Exception. For full terms see the included COPYING file.
+ */
+
+#include <git2.h>
+#include "cli.h"
+#include "cmd.h"
+
+#include "futils.h"
+
+#define COMMAND_NAME "hash-object"
+
+static int show_help;
+static char *type_name;
+static int write_object, read_stdin, literally;
+static char **filenames;
+
+static const cli_opt_spec opts[] = {
+	{ CLI_OPT_TYPE_SWITCH,   "help",      0, &show_help,    1,
+	  CLI_OPT_USAGE_HIDDEN | CLI_OPT_USAGE_STOP_PARSING, NULL,
+	  "display help about the " COMMAND_NAME " command" },
+
+	{ CLI_OPT_TYPE_VALUE,     NULL,      't', &type_name,    0,
+	  CLI_OPT_USAGE_DEFAULT, "type",     "the type of object to hash (default: \"blob\")" },
+	{ CLI_OPT_TYPE_SWITCH,    NULL,      'w', &write_object, 1,
+	  CLI_OPT_USAGE_DEFAULT,  NULL,      "write the object to the object database" },
+	{ CLI_OPT_TYPE_SWITCH,   "literally", 0, &literally,    1,
+	  CLI_OPT_USAGE_DEFAULT,  NULL,      "do not validate the object contents" },
+	{ CLI_OPT_TYPE_SWITCH,   "stdin",     0, &read_stdin,   1,
+	  CLI_OPT_USAGE_REQUIRED, NULL,      "read content from stdin" },
+	{ CLI_OPT_TYPE_ARGS,     "file",      0, &filenames,    0,
+	  CLI_OPT_USAGE_CHOICE,  "file",     "the file (or files) to read and hash" },
+	{ 0 },
+};
+
+static void print_help(void)
+{
+	cli_opt_usage_fprint(stdout, PROGRAM_NAME, COMMAND_NAME, opts);
+	printf("\n");
+
+	printf("Compute the object ID for a given file and optionally write that file\nto the object database.\n");
+	printf("\n");
+
+	printf("Options:\n");
+
+	cli_opt_help_fprint(stdout, opts);
+}
+
+static int hash_buf(git_odb *odb, git_str *buf, git_object_t type)
+{
+	git_oid oid;
+
+	if (!literally) {
+		int valid = 0;
+
+		if (git_object_rawcontent_is_valid(&valid, buf->ptr, buf->size, type) < 0 || !valid)
+			return cli_error_git();
+	}
+
+	if (write_object) {
+		if (git_odb_write(&oid, odb, buf->ptr, buf->size, type) < 0)
+			return cli_error_git();
+	} else {
+		if (git_odb_hash(&oid, buf->ptr, buf->size, type) < 0)
+			return cli_error_git();
+	}
+
+	if (printf("%s\n", git_oid_tostr_s(&oid)) < 0)
+		return cli_error_os();
+
+	return 0;
+}
+
+int cmd_hash_object(int argc, char **argv)
+{
+	git_repository *repo = NULL;
+	git_odb *odb = NULL;
+	git_str buf = GIT_STR_INIT;
+	cli_opt invalid_opt;
+	git_object_t type = GIT_OBJECT_BLOB;
+	char **filename;
+	int ret = 0;
+
+	if (cli_opt_parse(&invalid_opt, opts, argv + 1, argc - 1, CLI_OPT_PARSE_GNU))
+		return cli_opt_usage_error(COMMAND_NAME, opts, &invalid_opt);
+
+	if (show_help) {
+		print_help();
+		return 0;
+	}
+
+	if (type_name && (type = git_object_string2type(type_name)) == GIT_OBJECT_INVALID)
+		return cli_error_usage("invalid object type '%s'", type_name);
+
+	if (write_object &&
+	    (git_repository_open_ext(&repo, ".", GIT_REPOSITORY_OPEN_FROM_ENV, NULL) < 0 ||
+	     git_repository_odb(&odb, repo) < 0)) {
+		ret = cli_error_git();
+		goto done;
+	}
+
+	/*
+	 * TODO: we're reading blobs, we shouldn't pull them all into main
+	 * memory, we should just stream them into the odb instead.
+	 * (Or create a `git_odb_writefile` API.)
+	 */
+	if (read_stdin) {
+		if (git_futils_readbuffer_fd_full(&buf, fileno(stdin)) < 0) {
+			ret = cli_error_git();
+			goto done;
+		}
+
+		if ((ret = hash_buf(odb, &buf, type)) != 0)
+			goto done;
+	} else {
+		for (filename = filenames; *filename; filename++) {
+			if (git_futils_readbuffer(&buf, *filename) < 0) {
+				ret = cli_error_git();
+				goto done;
+			}
+
+			if ((ret = hash_buf(odb, &buf, type)) != 0)
+				goto done;
+		}
+	}
+
+done:
+	git_str_dispose(&buf);
+	git_odb_free(odb);
+	git_repository_free(repo);
+	return ret;
+}
diff --git a/src/cli/main.c b/src/cli/main.c
index 4b42236..08abb32 100644
--- a/src/cli/main.c
+++ b/src/cli/main.c
@@ -28,8 +28,9 @@ const cli_opt_spec cli_common_opts[] = {
 };
 
 const cli_cmd_spec cli_cmds[] = {
-	{ "cat-file", cmd_cat_file, "Display an object in the repository" },
-	{ "help",     cmd_help,     "Display help information" },
+	{ "cat-file",    cmd_cat_file,    "Display an object in the repository" },
+	{ "hash-object", cmd_hash_object, "Hash a raw object and product its object ID" },
+	{ "help",        cmd_help,        "Display help information" },
 	{ NULL }
 };