Subject: Re: [PATCH v4] Refactor recv_sideband()

From: Junio C Hamano <[email-masked]>
Date: Tue, 28 Jun 2016 09:57:30 -0700

Lukas Fleischer <[email-masked]> writes:

> Before this patch, we used character buffer manipulations to split
> messages from the sideband at line breaks and insert "remote: " at the
> beginning of each line, using the packet size to determine the end of a
> message. However, since it is safe to assume that diagnostic messages
> from the sideband never contain NUL characters, we can also
> NUL-terminate the buffer, use strpbrk() for splitting lines and use
> format strings to insert the prefix.
>
> A strbuf is used for accumulating the output which is then printed using
> a single fprintf() call with a single conversion specifier per line,
> such that the atomicity of the output is preserved. See 9ac13ec (atomic
> write for sideband remote messages, 2006-10-11) for details.
>
> Helped-by: Jeff King <[email-masked]>
> Helped-by: Junio C Hamano <[email-masked]>
> Helped-by: Nicolas Pitre <[email-masked]>
> Signed-off-by: Lukas Fleischer <[email-masked]>
> ---
> Changes since v3:
> * The new code always frees the strbuf used for the output.
> * Switched back to fprintf() to support ANSI codes under Windows.
> * Added a comment on the tradeoff between atomicity and Windows support.

With input from Dscho that recent Git-for-Windows does the right
thing without limiting us to use only a subset of stdio, perhaps we
would want to squash something like this in.

diff --git a/sideband.c b/sideband.c
index 226a8c2..72e2c5c 100644
--- a/sideband.c
+++ b/sideband.c
@@ -58,13 +58,12 @@ int recv_sideband(const char *me, int in_stream, int out)
 			 * Append a suffix to each nonempty line to clear the
 			 * end of the screen line.
 			 *
-			 * The output is accumulated in a buffer and each line
-			 * is printed to stderr using fprintf() with a single
-			 * conversion specifier. This is a "best effort"
-			 * approach to supporting both inter-process atomicity
-			 * (single conversion specifiers are likely to end up
-			 * in single atomic write() system calls) and the ANSI
-			 * control code emulation under Windows.
+			 * The output is accumulated in a buffer and
+			 * each line is printed to stderr using
+			 * fwrite(3).  This is a "best effort"
+			 * approach to suppor inter-process atomicity
+			 * (single fwrite(3) call is likely to end up
+			 * in single atomic write() system calls).
 			 */
 			while ((brk = strpbrk(b, "\n\r"))) {
 				int linelen = brk - b;
@@ -75,8 +74,7 @@ int recv_sideband(const char *me, int in_stream, int out)
 				} else {
 					strbuf_addf(&outbuf, "%c", *brk);
 				}
-				fprintf(stderr, "%.*s", (int)outbuf.len,
-					outbuf.buf);
+				fwrite(output.buf, 1, output.len, stderr);
 				strbuf_reset(&outbuf);
 				strbuf_addf(&outbuf, "%s", PREFIX);
 
@@ -98,7 +96,7 @@ int recv_sideband(const char *me, int in_stream, int out)
 	}
 
 	if (outbuf.len > 0)
-		fprintf(stderr, "%.*s", (int)outbuf.len, outbuf.buf);
+		fwrite(output.buf, 1, output.len, stderr);
 	strbuf_release(&outbuf);
 	return retval;
 }