object-file.c: use "enum" return type for unpack_loose_header()

In a preceding commit we changed and documented unpack_loose_header()
from its previous behavior of returning any negative value or zero, to
only -1 or 0.

Let's add an "enum unpack_loose_header_result" type and use it for
these return values, and have the compiler assert that we're
exhaustively covering all of them.

Signed-off-by: Ævar Arnfjörð Bjarmason <avarab@gmail.com>
Signed-off-by: Junio C Hamano <gitster@pobox.com>

cache.h

@@ -1307,7 +1307,10 @@ int git_open_cloexec(const char *name, int flags);
  * unpack_loose_header() initializes the data stream needed to unpack
  * a loose object header.
  *
- * Returns 0 on success. Returns negative values on error.
+ * Returns:
+ *
+ * - ULHR_OK on success
+ * - ULHR_BAD on error
  *
  * It will only parse up to MAX_HEADER_LEN bytes unless an optional
  * "hdrbuf" argument is non-NULL. This is intended for use with
@@ -1315,9 +1318,17 @@ int git_open_cloexec(const char *name, int flags);
  * reporting. The full header will be extracted to "hdrbuf" for use
  * with parse_loose_header().
  */
-int unpack_loose_header(git_zstream *stream, unsigned char *map,
-			unsigned long mapsize, void *buffer,
-			unsigned long bufsiz, struct strbuf *hdrbuf);
+enum unpack_loose_header_result {
+	ULHR_OK,
+	ULHR_BAD,
+};
+enum unpack_loose_header_result unpack_loose_header(git_zstream *stream,
+						    unsigned char *map,
+						    unsigned long mapsize,
+						    void *buffer,
+						    unsigned long bufsiz,
+						    struct strbuf *hdrbuf);
+
 struct object_info;
 int parse_loose_header(const char *hdr, struct object_info *oi,
 		       unsigned int flags);

object-file.c

@@ -1210,10 +1210,12 @@ void *map_loose_object(struct repository *r,
 	return map_loose_object_1(r, NULL, oid, size);
 }
 
-int unpack_loose_header(git_zstream *stream,
-			unsigned char *map, unsigned long mapsize,
-			void *buffer, unsigned long bufsiz,
-			struct strbuf *header)
+enum unpack_loose_header_result unpack_loose_header(git_zstream *stream,
+						    unsigned char *map,
+						    unsigned long mapsize,
+						    void *buffer,
+						    unsigned long bufsiz,
+						    struct strbuf *header)
 {
 	int status;
 
@@ -1229,13 +1231,13 @@ int unpack_loose_header(git_zstream *stream,
 	status = git_inflate(stream, 0);
 	obj_read_lock();
 	if (status < Z_OK)
-		return -1;
+		return ULHR_BAD;
 
 	/*
 	 * Check if entire header is unpacked in the first iteration.
 	 */
 	if (memchr(buffer, '\0', stream->next_out - (unsigned char *)buffer))
-		return 0;
+		return ULHR_OK;
 
 	/*
 	 * We have a header longer than MAX_HEADER_LEN. The "header"
@@ -1243,7 +1245,7 @@ int unpack_loose_header(git_zstream *stream,
 	 * --allow-unknown-type".
 	 */
 	if (!header)
-		return -1;
+		return ULHR_BAD;
 
 	/*
 	 * buffer[0..bufsiz] was not large enough.  Copy the partial
@@ -1264,7 +1266,7 @@ int unpack_loose_header(git_zstream *stream,
 		stream->next_out = buffer;
 		stream->avail_out = bufsiz;
 	} while (status != Z_STREAM_END);
-	return -1;
+	return ULHR_BAD;
 }
 
 static void *unpack_loose_rest(git_zstream *stream,
@@ -1429,13 +1431,19 @@ static int loose_object_info(struct repository *r,
 	if (oi->disk_sizep)
 		*oi->disk_sizep = mapsize;
 
-	if (unpack_loose_header(&stream, map, mapsize, hdr, sizeof(hdr),
-				allow_unknown ? &hdrbuf : NULL) < 0)
+	switch (unpack_loose_header(&stream, map, mapsize, hdr, sizeof(hdr),
+				    allow_unknown ? &hdrbuf : NULL)) {
+	case ULHR_OK:
+		break;
+	case ULHR_BAD:
 		status = error(_("unable to unpack %s header"),
 			       oid_to_hex(oid));
-	if (status < 0)
-		; /* Do nothing */
-	else if (hdrbuf.len) {
+		break;
+	}
+
+	if (status < 0) {
+		/* Do nothing */
+	} else if (hdrbuf.len) {
 		if ((status = parse_loose_header(hdrbuf.buf, oi, flags)) < 0)
 			status = error(_("unable to parse %s header with --allow-unknown-type"),
 				       oid_to_hex(oid));

streaming.c

@@ -229,17 +229,16 @@ static int open_istream_loose(struct git_istream *st, struct repository *r,
 	st->u.loose.mapped = map_loose_object(r, oid, &st->u.loose.mapsize);
 	if (!st->u.loose.mapped)
 		return -1;
-	if ((unpack_loose_header(&st->z,
-				 st->u.loose.mapped,
-				 st->u.loose.mapsize,
-				 st->u.loose.hdr,
-				 sizeof(st->u.loose.hdr),
-				 NULL) < 0) ||
-	    (parse_loose_header(st->u.loose.hdr, &oi, 0) < 0)) {
-		git_inflate_end(&st->z);
-		munmap(st->u.loose.mapped, st->u.loose.mapsize);
-		return -1;
+	switch (unpack_loose_header(&st->z, st->u.loose.mapped,
+				    st->u.loose.mapsize, st->u.loose.hdr,
+				    sizeof(st->u.loose.hdr), NULL)) {
+	case ULHR_OK:
+		break;
+	case ULHR_BAD:
+		goto error;
 	}
+	if (parse_loose_header(st->u.loose.hdr, &oi, 0) < 0)
+		goto error;
 
 	st->u.loose.hdr_used = strlen(st->u.loose.hdr) + 1;
 	st->u.loose.hdr_avail = st->z.total_out;
@@ -248,6 +247,10 @@ static int open_istream_loose(struct git_istream *st, struct repository *r,
 	st->read = read_istream_loose;
 
 	return 0;
+error:
+	git_inflate_end(&st->z);
+	munmap(st->u.loose.mapped, st->u.loose.mapsize);
+	return -1;
 }