[WIP 02/15] pkt-line: introduce struct packet_reader

[Brandon Williams <bmwill@google.com>]

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>
---
 pkt-line.c | 61 +++++++++++++++++++++++++++++++++++++++++++++++++++++++++++++
 pkt-line.h | 20 ++++++++++++++++++++
 2 files changed, 81 insertions(+)

diff --git a/pkt-line.c b/pkt-line.c
index ac619f05b..518109bbe 100644
--- a/pkt-line.c
+++ b/pkt-line.c
@@ -406,3 +406,64 @@ 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)
+{
+	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 = PACKET_READ_CHOMP_NEWLINE | PACKET_READ_GENTLE_ON_EOF;
+
+	reader->line = NULL;
+	reader->line_peeked = 0;
+	reader->pktlen = 0;
+	reader->status = PACKET_READ_ERROR;
+}
+
+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);
+
+	switch (reader->status) {
+	case PACKET_READ_ERROR:
+		reader->pktlen = -1;
+		reader->line = NULL;
+		break;
+	case PACKET_READ_NORMAL:
+		reader->line = reader->buffer;
+		break;
+	case PACKET_READ_FLUSH:
+		reader->pktlen = 0;
+		reader->line = NULL;
+		break;
+	}
+
+	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;
+}
diff --git a/pkt-line.h b/pkt-line.h
index f1545929b..2b5c7cf11 100644
--- a/pkt-line.h
+++ b/pkt-line.h
@@ -104,6 +104,26 @@ 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 {
+	int fd;
+	char *src_buffer;
+	size_t src_len;
+
+	char *buffer;
+	unsigned buffer_size;
+	int options;
+
+	enum packet_read_status status;
+	int pktlen;
+	const char *line;
+	int line_peeked;
+};
+
+extern void packet_reader_init(struct packet_reader *reader, int fd,
+			       char *src_buffer, size_t src_len);
+extern enum packet_read_status packet_reader_read(struct packet_reader *reader);
+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)
-- 
2.15.1.424.g9478a66081-goog