transport-helper: be quiet on read errors from helpers

Prior to commit 81d340d, we did not print any error message
if a remote transport helper died unexpectedly. If a helper
did not print any error message (e.g., because it crashed),
the user could be left confused. That commit tried to
rectify the situation by printing a note that the helper
exited unexpectedly.

However, this makes a much more common case worse: when a
helper does die with a useful message, we print the extra
"Reading from 'git-remote-foo failed" message. This can also
end up confusing users, as they may not even know what
remote helpers are (e.g., the fact that http support comes
through git-remote-https is purely an implementation detail
that most users do not know or care about).

Since we do not have a good way of knowing whether the
helper printed a useful error, and since the common failure
mode is for it to do so, let's default to remaining quiet.
Debuggers can dig further by setting GIT_TRANSPORT_HELPER_DEBUG.

Signed-off-by: Jeff King <peff@peff.net>
Signed-off-by: Junio C Hamano <gitster@pobox.com>

Author: peff

t/t5801-remote-helpers.sh

@@ -210,9 +210,7 @@ test_expect_success 'proper failure checks for pushing' '
 	(GIT_REMOTE_TESTGIT_FAILURE=1 &&
 	export GIT_REMOTE_TESTGIT_FAILURE &&
 	cd local &&
-	test_must_fail git push --all 2> error &&
-	cat error &&
-	grep -q "Reading from helper .git-remote-testgit. failed" error
+	test_must_fail git push --all
 	)
 '
 

transport-helper.c

@@ -56,7 +56,7 @@ static int recvline_fh(FILE *helper, struct strbuf *buffer, const char *name)
 	if (strbuf_getline(buffer, helper, '\n') == EOF) {
 		if (debug)
 			fprintf(stderr, "Debug: Remote helper quit.\n");
-		die("Reading from helper 'git-remote-%s' failed", name);
+		exit(128);
 	}
 
 	if (debug)