thodg/libgit2

diff --git a/src/git/odb.h b/src/git/odb.h
index e8b1744..0a7ee40 100644
--- a/src/git/odb.h
+++ b/src/git/odb.h
@@ -138,6 +138,20 @@ GIT_EXTERN(git_otype) git_obj_string_to_type(const char *str);
  */
 GIT_EXTERN(int) git_obj__loose_object_type(git_otype type);
 
+/**
+ * Determine the object-ID (sha1 hash) of the given git_obj.
+ *
+ * The input obj must be a valid loose object type and the data
+ * pointer must not be NULL, unless the len field is also zero.
+ *
+ * @param id the resulting object-ID.
+ * @param obj the object whose hash is to be determined.
+ * @return
+ * - GIT_SUCCESS if the object-ID was correctly determined.
+ * - GIT_ERROR if the given object is malformed.
+ */
+GIT_EXTERN(int) git_obj_hash(git_oid *id, git_obj *obj);
+
 /** @} */
 GIT_END_DECL
 #endif
diff --git a/src/odb.c b/src/odb.c
index a732c71..32a550a 100644
--- a/src/odb.c
+++ b/src/odb.c
@@ -27,6 +27,8 @@
 #include "git/zlib.h"
 #include "common.h"
 #include "fileops.h"
+#include "hash.h"
+#include <stdio.h>
 
 struct git_odb {
 	/** Path to the "objects" directory. */
@@ -83,6 +85,46 @@ int git_obj__loose_object_type(git_otype type)
 	return obj_type_table[type].loose;
 }
 
+static int format_object_header(char *hdr, size_t n, git_obj *obj)
+{
+	const char *type_str = git_obj_type_to_string(obj->type);
+	int len = snprintf(hdr, n, "%s %u", type_str, obj->len);
+
+	assert(len > 0);  /* otherwise snprintf() is broken */
+	assert(len < n);  /* otherwise the caller is broken! */
+
+	if (len < 0 || len >= n)
+		return GIT_ERROR;
+	return len+1;
+}
+
+int git_obj_hash(git_oid *id, git_obj *obj)
+{
+	git_buf_vec vec[2];
+	char hdr[64];
+	int  hdrlen;
+
+	assert(id && obj);
+
+	if (!git_obj__loose_object_type(obj->type))
+		return GIT_ERROR;
+
+	if (!obj->data && obj->len != 0)
+		return GIT_ERROR;
+
+	if ((hdrlen = format_object_header(hdr, sizeof(hdr), obj)) < 0)
+		return GIT_ERROR;
+
+	vec[0].data = hdr;
+	vec[0].len  = hdrlen;
+	vec[1].data = obj->data;
+	vec[1].len  = obj->len;
+
+	git_hash_vec(id, vec, 2);
+
+	return GIT_SUCCESS;
+}
+
 static int object_file_name(char *name, size_t n, char *dir, const git_oid *id)
 {
 	size_t len = strlen(dir);
diff --git a/tests/t0000-obj-hash.c b/tests/t0000-obj-hash.c
new file mode 100644
index 0000000..83131fe
--- /dev/null
+++ b/tests/t0000-obj-hash.c
@@ -0,0 +1,423 @@
+
+#include "test_lib.h"
+#include <git/odb.h>
+
+static char *commit_id = "3d7f8a6af076c8c3f20071a8935cdbe8228594d1";
+
+static unsigned char commit_data[] = {
+    0x74, 0x72, 0x65, 0x65, 0x20, 0x64, 0x66, 0x66,
+    0x32, 0x64, 0x61, 0x39, 0x30, 0x62, 0x32, 0x35,
+    0x34, 0x65, 0x31, 0x62, 0x65, 0x62, 0x38, 0x38,
+    0x39, 0x64, 0x31, 0x66, 0x31, 0x66, 0x31, 0x32,
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+    0x67, 0x6e, 0x65, 0x64, 0x2d, 0x6f, 0x66, 0x2d,
+    0x62, 0x79, 0x3a, 0x20, 0x41, 0x20, 0x55, 0x20,
+    0x54, 0x68, 0x6f, 0x72, 0x20, 0x3c, 0x61, 0x75,
+    0x74, 0x68, 0x6f, 0x72, 0x40, 0x65, 0x78, 0x61,
+    0x6d, 0x70, 0x6c, 0x65, 0x2e, 0x63, 0x6f, 0x6d,
+    0x3e, 0x0a,
+};
+
+static git_obj commit_obj = {
+	commit_data,
+	sizeof(commit_data),
+	GIT_OBJ_COMMIT
+};
+
+static char *tree_id = "dff2da90b254e1beb889d1f1f1288be1803782df";
+
+static unsigned char tree_data[] = {
+    0x31, 0x30, 0x30, 0x36, 0x34, 0x34, 0x20, 0x6f,
+    0x6e, 0x65, 0x00, 0x8b, 0x13, 0x78, 0x91, 0x79,
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+    0xd8, 0xc2, 0xe4, 0x8c, 0x53, 0x91,
+};
+
+static git_obj tree_obj = {
+	tree_data,
+	sizeof(tree_data),
+	GIT_OBJ_TREE
+};
+
+static char *tag_id = "09d373e1dfdc16b129ceec6dd649739911541e05";
+
+static unsigned char tag_data[] = {
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+    0x2e, 0x30, 0x2e, 0x31, 0x0a,
+};
+
+static git_obj tag_obj = {
+	tag_data,
+	sizeof(tag_data),
+	GIT_OBJ_TAG
+};
+
+static char *zero_id = "e69de29bb2d1d6434b8b29ae775ad8c2e48c5391";
+
+static unsigned char zero_data[] = {
+    0x00  /* dummy data */
+};
+
+static git_obj zero_obj = {
+	zero_data,
+	0,
+	GIT_OBJ_BLOB
+};
+
+static char *one_id = "8b137891791fe96927ad78e64b0aad7bded08bdc";
+
+static unsigned char one_data[] = {
+    0x0a,
+};
+
+static git_obj one_obj = {
+	one_data,
+	sizeof(one_data),
+	GIT_OBJ_BLOB
+};
+
+static char *two_id = "78981922613b2afb6025042ff6bd878ac1994e85";
+
+static unsigned char two_data[] = {
+    0x61, 0x0a,
+};
+
+static git_obj two_obj = {
+	two_data,
+	sizeof(two_data),
+	GIT_OBJ_BLOB
+};
+
+static char *some_id = "fd8430bc864cfcd5f10e5590f8a447e01b942bfe";
+
+static unsigned char some_data[] = {
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+    0x74, 0x68, 0x65, 0x20, 0x66, 0x69, 0x6c, 0x65,
+    0x20, 0x43, 0x4f, 0x50, 0x59, 0x49, 0x4e, 0x47,
+    0x2e, 0x20, 0x20, 0x49, 0x66, 0x20, 0x6e, 0x6f,
+    0x74, 0x2c, 0x20, 0x77, 0x72, 0x69, 0x74, 0x65,
+    0x20, 0x74, 0x6f, 0x0a, 0x20, 0x2a, 0x20, 0x74,
+    0x68, 0x65, 0x20, 0x46, 0x72, 0x65, 0x65, 0x20,
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+    0x46, 0x72, 0x61, 0x6e, 0x6b, 0x6c, 0x69, 0x6e,
+    0x20, 0x53, 0x74, 0x72, 0x65, 0x65, 0x74, 0x2c,
+    0x20, 0x46, 0x69, 0x66, 0x74, 0x68, 0x20, 0x46,
+    0x6c, 0x6f, 0x6f, 0x72, 0x2c, 0x0a, 0x20, 0x2a,
+    0x20, 0x42, 0x6f, 0x73, 0x74, 0x6f, 0x6e, 0x2c,
+    0x20, 0x4d, 0x41, 0x20, 0x30, 0x32, 0x31, 0x31,
+    0x30, 0x2d, 0x31, 0x33, 0x30, 0x31, 0x2c, 0x20,
+    0x55, 0x53, 0x41, 0x2e, 0x0a, 0x20, 0x2a, 0x2f,
+    0x0a,
+};
+
+static git_obj some_obj = {
+	some_data,
+	sizeof(some_data),
+	GIT_OBJ_BLOB
+};
+
+static git_obj junk_obj = {
+	NULL,
+	0,
+	GIT_OBJ_BAD
+};
+
+
+BEGIN_TEST(hash_junk)
+    git_oid id, id_zero;
+
+    must_pass(git_oid_mkstr(&id_zero, zero_id));
+
+    /* invalid types: */
+    junk_obj.data = some_data;
+    must_fail(git_obj_hash(&id, &junk_obj));
+
+    junk_obj.type = GIT_OBJ__EXT1;
+    must_fail(git_obj_hash(&id, &junk_obj));
+
+    junk_obj.type = GIT_OBJ__EXT2;
+    must_fail(git_obj_hash(&id, &junk_obj));
+
+    junk_obj.type = GIT_OBJ_OFS_DELTA;
+    must_fail(git_obj_hash(&id, &junk_obj));
+
+    junk_obj.type = GIT_OBJ_REF_DELTA;
+    must_fail(git_obj_hash(&id, &junk_obj));
+
+    /* data can be NULL only if len is zero: */
+    junk_obj.type = GIT_OBJ_BLOB;
+    junk_obj.data = NULL;
+    must_pass(git_obj_hash(&id, &junk_obj));
+    must_be_true(git_oid_cmp(&id, &id_zero) == 0);
+
+    junk_obj.len = 1;
+    must_fail(git_obj_hash(&id, &junk_obj));
+END_TEST
+
+BEGIN_TEST(hash_commit)
+    git_oid id1, id2;
+
+    must_pass(git_oid_mkstr(&id1, commit_id));
+
+    must_pass(git_obj_hash(&id2, &commit_obj));
+
+    must_be_true(git_oid_cmp(&id1, &id2) == 0);
+END_TEST
+
+BEGIN_TEST(hash_tree)
+    git_oid id1, id2;
+
+    must_pass(git_oid_mkstr(&id1, tree_id));
+
+    must_pass(git_obj_hash(&id2, &tree_obj));
+
+    must_be_true(git_oid_cmp(&id1, &id2) == 0);
+END_TEST
+
+BEGIN_TEST(hash_tag)
+    git_oid id1, id2;
+
+    must_pass(git_oid_mkstr(&id1, tag_id));
+
+    must_pass(git_obj_hash(&id2, &tag_obj));
+
+    must_be_true(git_oid_cmp(&id1, &id2) == 0);
+END_TEST
+
+BEGIN_TEST(hash_zero)
+    git_oid id1, id2;
+
+    must_pass(git_oid_mkstr(&id1, zero_id));
+
+    must_pass(git_obj_hash(&id2, &zero_obj));
+
+    must_be_true(git_oid_cmp(&id1, &id2) == 0);
+END_TEST
+
+BEGIN_TEST(hash_one)
+    git_oid id1, id2;
+
+    must_pass(git_oid_mkstr(&id1, one_id));
+
+    must_pass(git_obj_hash(&id2, &one_obj));
+
+    must_be_true(git_oid_cmp(&id1, &id2) == 0);
+END_TEST
+
+BEGIN_TEST(hash_two)
+    git_oid id1, id2;
+
+    must_pass(git_oid_mkstr(&id1, two_id));
+
+    must_pass(git_obj_hash(&id2, &two_obj));
+
+    must_be_true(git_oid_cmp(&id1, &id2) == 0);
+END_TEST
+
+BEGIN_TEST(hash_some)
+    git_oid id1, id2;
+
+    must_pass(git_oid_mkstr(&id1, some_id));
+
+    must_pass(git_obj_hash(&id2, &some_obj));
+
+    must_be_true(git_oid_cmp(&id1, &id2) == 0);
+END_TEST
+
+