pkt-line: add packet_read_line_gently()

Add packet_read_line_gently() to enable reading a line without dying on
EOF.

Signed-off-by: Ben Peart <benpeart@microsoft.com>
Signed-off-by: Junio C Hamano <gitster@pobox.com>

pkt-line.h

@@ -73,6 +73,17 @@ int packet_read(int fd, char **src_buffer, size_t *src_len, char
  */
 char *packet_read_line(int fd, int *size);
 
+/*
+ * Convenience wrapper for packet_read that sets the PACKET_READ_GENTLE_ON_EOF
+ * and CHOMP_NEWLINE options. The return value specifies the number of bytes
+ * read into the buffer or -1 on truncated input. If the *dst_line parameter
+ * is not NULL it will return NULL for a flush packet or when the number of
+ * bytes copied is zero and otherwise points to a static buffer (that may be
+ * overwritten by subsequent calls). If the size parameter is not NULL, the
+ * length of the packet is written to it.
+ */
+int packet_read_line_gently(int fd, int *size, char **dst_line);
+
 /*
  * Same as packet_read_line, but read from a buf rather than a descriptor;
  * see packet_read for details on how src_* is used.