Refactor the pack header reading function out of receive-pack.c

Signed-off-by: Junio C Hamano <junkio@cox.net>

pack.h

@@ -44,4 +44,9 @@ struct pack_header {
 #define PACK_IDX_SIGNATURE 0xff744f63	/* "\377tOc" */
 
 extern int verify_pack(struct packed_git *, int);
+
+#define PH_ERROR_EOF		(-1)
+#define PH_ERROR_PACK_SIGNATURE	(-2)
+#define PH_ERROR_PROTOCOL	(-3)
+extern int read_pack_header(int fd, struct pack_header *);
 #endif

receive-pack.c

@@ -250,20 +250,22 @@ static void read_head_info(void)
 
 static const char *parse_pack_header(struct pack_header *hdr)
 {
-	char *c = (char*)hdr;
-	ssize_t remaining = sizeof(struct pack_header);
-	do {
-		ssize_t r = xread(0, c, remaining);
-		if (r <= 0)
-			return "eof before pack header was fully read";
-		remaining -= r;
-		c += r;
-	} while (remaining > 0);
-	if (hdr->hdr_signature != htonl(PACK_SIGNATURE))
+	switch (read_pack_header(0, hdr)) {
+	case PH_ERROR_EOF:
+		return "eof before pack header was fully read";
+
+	case PH_ERROR_PACK_SIGNATURE:
 		return "protocol error (pack signature mismatch detected)";
-	if (!pack_version_ok(hdr->hdr_version))
+
+	case PH_ERROR_PROTOCOL:
 		return "protocol error (pack version unsupported)";
-	return NULL;
+
+	default:
+		return "unknown error in parse_pack_header";
+
+	case 0:
+		return NULL;
+	}
 }
 
 static const char *pack_lockfile;

sha1_file.c

@@ -2048,3 +2048,24 @@ int index_path(unsigned char *sha1, const char *path, struct stat *st, int write
 	}
 	return 0;
 }
+
+int read_pack_header(int fd, struct pack_header *header)
+{
+	char *c = (char*)header;
+	ssize_t remaining = sizeof(struct pack_header);
+	do {
+		ssize_t r = xread(fd, c, remaining);
+		if (r <= 0)
+			/* "eof before pack header was fully read" */
+			return PH_ERROR_EOF;
+		remaining -= r;
+		c += r;
+	} while (remaining > 0);
+	if (header->hdr_signature != htonl(PACK_SIGNATURE))
+		/* "protocol error (pack signature mismatch detected)" */
+		return PH_ERROR_PACK_SIGNATURE;
+	if (!pack_version_ok(header->hdr_version))
+		/* "protocol error (pack version unsupported)" */
+		return PH_ERROR_PROTOCOL;
+	return 0;
+}