1 files changed, 51 insertions, 1 deletions
diff --git a/object-file-convert.c b/object-file-convert.c
index 70b80fb61e..089b68442d 100644
--- a/object-file-convert.c
+++ b/object-file-convert.c
@@ -7,6 +7,8 @@
 #include "hash.h"
 #include "object.h"
 #include "loose.h"
+#include "commit.h"
+#include "gpg-interface.h"
 #include "object-file-convert.h"
 
 int repo_oid_to_algop(struct repository *repo, const struct object_id *src,
@@ -83,6 +85,52 @@ static int convert_tree_object(struct strbuf *out,
 	return 0;
 }
 
+static int convert_tag_object(struct strbuf *out,
+			      const struct git_hash_algo *from,
+			      const struct git_hash_algo *to,
+			      const char *buffer, size_t size)
+{
+	struct strbuf payload = STRBUF_INIT, temp = STRBUF_INIT, oursig = STRBUF_INIT, othersig = STRBUF_INIT;
+	size_t payload_size;
+	struct object_id oid, mapped_oid;
+	const char *p;
+
+	/* Add some slop for longer signature header in the new algorithm. */
+	strbuf_grow(out, size + 7);
+
+	/* Is there a signature for our algorithm? */
+	payload_size = parse_signed_buffer(buffer, size);
+	strbuf_add(&payload, buffer, payload_size);
+	if (payload_size != size) {
+		/* Yes, there is. */
+		strbuf_add(&oursig, buffer + payload_size, size - payload_size);
+	}
+	/* Now, is there a signature for the other algorithm? */
+	if (parse_buffer_signed_by_header(payload.buf, payload.len, &temp, &othersig, to)) {
+		/* Yes, there is. */
+		strbuf_swap(&payload, &temp);
+		strbuf_release(&temp);
+	}
+
+	/*
+	 * Our payload is now in payload and we may have up to two signatrures
+	 * in oursig and othersig.
+	 */
+	if (strncmp(payload.buf, "object ", 7) || payload.buf[from->hexsz + 7] != '\n')
+		return error("bogus tag object");
+	if (parse_oid_hex_algop(payload.buf + 7, &oid, &p, from) < 0)
+		return error("bad tag object ID");
+	if (repo_oid_to_algop(the_repository, &oid, to, &mapped_oid))
+		return error("unable to map tree %s in tag object",
+			     oid_to_hex(&oid));
+	strbuf_addf(out, "object %s", oid_to_hex(&mapped_oid));
+	strbuf_add(out, p, payload.len - (p - payload.buf));
+	strbuf_addbuf(out, &othersig);
+	if (oursig.len)
+		add_header_signature(out, &oursig, from);
+	return 0;
+}
+
 int convert_object_file(struct strbuf *outbuf,
 			const struct git_hash_algo *from,
 			const struct git_hash_algo *to,
@@ -100,8 +148,10 @@ int convert_object_file(struct strbuf *outbuf,
 	case OBJ_TREE:
 		ret = convert_tree_object(outbuf, from, to, buf, len);
 		break;
-	case OBJ_COMMIT:
 	case OBJ_TAG:
+		ret = convert_tag_object(outbuf, from, to, buf, len);
+		break;
+	case OBJ_COMMIT:
 	default:
 		/* Not implemented yet, so fail. */
 		ret = -1;