pkt-line: allow peeking a packet line without consuming it

Sometimes it is advantageous to be able to peek the next packet line
without consuming it (e.g. to be able to determine the protocol version
a server is speaking).  In order to do that introduce 'struct
packet_reader' which is an abstraction around the normal packet reading
logic.  This enables a caller to be able to peek a single line at a time
using 'packet_reader_peek()' and having a caller consume a line by
calling 'packet_reader_read()'.

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

1 files changed, 50 insertions, 0 deletions

diff --git a/pkt-line.c b/pkt-line.c
index db2fb29ac3..1881dc8813 100644
--- a/pkt-line.c
+++ b/pkt-line.c
@@ -400,3 +400,53 @@ ssize_t read_packetized_to_strbuf(int fd_in, struct strbuf *sb_out)
 	}
 	return sb_out->len - orig_len;
 }
+
+/* Packet Reader Functions */
+void packet_reader_init(struct packet_reader *reader, int fd,
+			char *src_buffer, size_t src_len,
+			int options)
+{
+	memset(reader, 0, sizeof(*reader));
+
+	reader->fd = fd;
+	reader->src_buffer = src_buffer;
+	reader->src_len = src_len;
+	reader->buffer = packet_buffer;
+	reader->buffer_size = sizeof(packet_buffer);
+	reader->options = options;
+}
+
+enum packet_read_status packet_reader_read(struct packet_reader *reader)
+{
+	if (reader->line_peeked) {
+		reader->line_peeked = 0;
+		return reader->status;
+	}
+
+	reader->status = packet_read_with_status(reader->fd,
+						 &reader->src_buffer,
+						 &reader->src_len,
+						 reader->buffer,
+						 reader->buffer_size,
+						 &reader->pktlen,
+						 reader->options);
+
+	if (reader->status == PACKET_READ_NORMAL)
+		reader->line = reader->buffer;
+	else
+		reader->line = NULL;
+
+	return reader->status;
+}
+
+enum packet_read_status packet_reader_peek(struct packet_reader *reader)
+{
+	/* Only allow peeking a single line */
+	if (reader->line_peeked)
+		return reader->status;
+
+	/* Peek a line by reading it and setting peeked flag */
+	packet_reader_read(reader);
+	reader->line_peeked = 1;
+	return reader->status;
+}