Add a routine to determine a git_oid given an git_obj

Signed-off-by: Ramsay Jones <ramsay@ramsay1.demon.co.uk>
Signed-off-by: Shawn O. Pearce <spearce@spearce.org>

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

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);