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, 58 insertions, 0 deletions

diff --git a/pkt-line.h b/pkt-line.h
index 099b26b95f..11b04f026f 100644
--- a/pkt-line.h
+++ b/pkt-line.h
@@ -112,6 +112,64 @@ char *packet_read_line_buf(char **src_buf, size_t *src_len, int *size);
  */
 ssize_t read_packetized_to_strbuf(int fd_in, struct strbuf *sb_out);
 
+struct packet_reader {
+	/* source file descriptor */
+	int fd;
+
+	/* source buffer and its size */
+	char *src_buffer;
+	size_t src_len;
+
+	/* buffer that pkt-lines are read into and its size */
+	char *buffer;
+	unsigned buffer_size;
+
+	/* options to be used during reads */
+	int options;
+
+	/* status of the last read */
+	enum packet_read_status status;
+
+	/* length of data read during the last read */
+	int pktlen;
+
+	/* the last line read */
+	const char *line;
+
+	/* indicates if a line has been peeked */
+	int line_peeked;
+};
+
+/*
+ * Initialize a 'struct packet_reader' object which is an
+ * abstraction around the 'packet_read_with_status()' function.
+ */
+extern void packet_reader_init(struct packet_reader *reader, int fd,
+			       char *src_buffer, size_t src_len,
+			       int options);
+
+/*
+ * Perform a packet read and return the status of the read.
+ * The values of 'pktlen' and 'line' are updated based on the status of the
+ * read as follows:
+ *
+ * PACKET_READ_ERROR: 'pktlen' is set to '-1' and 'line' is set to NULL
+ * PACKET_READ_NORMAL: 'pktlen' is set to the number of bytes read
+ *		       'line' is set to point at the read line
+ * PACKET_READ_FLUSH: 'pktlen' is set to '0' and 'line' is set to NULL
+ */
+extern enum packet_read_status packet_reader_read(struct packet_reader *reader);
+
+/*
+ * Peek the next packet line without consuming it and return the status.
+ * The next call to 'packet_reader_read()' will perform a read of the same line
+ * that was peeked, consuming the line.
+ *
+ * Peeking multiple times without calling 'packet_reader_read()' will return
+ * the same result.
+ */
+extern enum packet_read_status packet_reader_peek(struct packet_reader *reader);
+
 #define DEFAULT_PACKET_MAX 1000
 #define LARGE_PACKET_MAX 65520
 #define LARGE_PACKET_DATA_MAX (LARGE_PACKET_MAX - 4)