pkt-line: introduce packet_read_with_status

The current pkt-line API encodes the status of a pkt-line read in the
length of the read content.  An error is indicated with '-1', a flush
with '0' (which can be confusing since a return value of '0' can also
indicate an empty pkt-line), and a positive integer for the length of
the read content otherwise.  This doesn't leave much room for allowing
the addition of additional special packets in the future.

To solve this introduce 'packet_read_with_status()' which reads a packet
and returns the status of the read encoded as an 'enum packet_status'
type.  This allows for easily identifying between special and normal
packets as well as errors.  It also enables easily adding a new special
packet in the future.

Signed-off-by: Brandon Williams <bmwill@google.com>
Signed-off-by: Junio C Hamano <gitster@pobox.com>

pkt-line.c

@@ -280,28 +280,39 @@ static int packet_length(const char *linelen)
 	return (val < 0) ? val : (val << 8) | hex2chr(linelen + 2);
 }
 
-int packet_read(int fd, char **src_buf, size_t *src_len,
-		char *buffer, unsigned size, int options)
+enum packet_read_status packet_read_with_status(int fd, char **src_buffer,
+						size_t *src_len, char *buffer,
+						unsigned size, int *pktlen,
+						int options)
 {
-	int len, ret;
+	int len;
 	char linelen[4];
 
-	ret = get_packet_data(fd, src_buf, src_len, linelen, 4, options);
-	if (ret < 0)
-		return ret;
+	if (get_packet_data(fd, src_buffer, src_len, linelen, 4, options) < 0) {
+		*pktlen = -1;
+		return PACKET_READ_EOF;
+	}
+
 	len = packet_length(linelen);
-	if (len < 0)
+
+	if (len < 0) {
 		die("protocol error: bad line length character: %.4s", linelen);
-	if (!len) {
+	} else if (!len) {
 		packet_trace("0000", 4, 0);
-		return 0;
+		*pktlen = 0;
+		return PACKET_READ_FLUSH;
+	} else if (len < 4) {
+		die("protocol error: bad line length %d", len);
 	}
+
 	len -= 4;
-	if (len >= size)
+	if ((unsigned)len >= size)
 		die("protocol error: bad line length %d", len);
-	ret = get_packet_data(fd, src_buf, src_len, buffer, len, options);
-	if (ret < 0)
-		return ret;
+
+	if (get_packet_data(fd, src_buffer, src_len, buffer, len, options) < 0) {
+		*pktlen = -1;
+		return PACKET_READ_EOF;
+	}
 
 	if ((options & PACKET_READ_CHOMP_NEWLINE) &&
 	    len && buffer[len-1] == '\n')
@@ -309,7 +320,19 @@ int packet_read(int fd, char **src_buf, size_t *src_len,
 
 	buffer[len] = 0;
 	packet_trace(buffer, len, 0);
-	return len;
+	*pktlen = len;
+	return PACKET_READ_NORMAL;
+}
+
+int packet_read(int fd, char **src_buffer, size_t *src_len,
+		char *buffer, unsigned size, int options)
+{
+	int pktlen = -1;
+
+	packet_read_with_status(fd, src_buffer, src_len, buffer, size,
+				&pktlen, options);
+
+	return pktlen;
 }
 
 static char *packet_read_line_generic(int fd,

pkt-line.h

@@ -65,6 +65,22 @@ int write_packetized_from_buf(const char *src_in, size_t len, int fd_out);
 int packet_read(int fd, char **src_buffer, size_t *src_len, char
 		*buffer, unsigned size, int options);
 
+/*
+ * Read a packetized line into a buffer like the 'packet_read()' function but
+ * returns an 'enum packet_read_status' which indicates the status of the read.
+ * The number of bytes read will be assigined to *pktlen if the status of the
+ * read was 'PACKET_READ_NORMAL'.
+ */
+enum packet_read_status {
+	PACKET_READ_EOF,
+	PACKET_READ_NORMAL,
+	PACKET_READ_FLUSH,
+};
+enum packet_read_status packet_read_with_status(int fd, char **src_buffer,
+						size_t *src_len, char *buffer,
+						unsigned size, int *pktlen,
+						int options);
+
 /*
  * Convenience wrapper for packet_read that is not gentle, and sets the
  * CHOMP_NEWLINE option. The return value is NULL for a flush packet,