Re: [PATCH 2/6] t/lib-git-daemon: record daemon log

> When we start git-daemon for our tests, we send its stderr
> log stream to a named pipe. We synchronously read the first
> line to make sure that the daemon started, and then dump the
> rest to descriptor 4. This is handy for debugging test
> output with "--verbose", but the tests themselves can't
> access the log data.
> 
> Let's dump the log into a file, as well, so that future
> tests can check the log. There are two subtleties worth
> calling out here:
> 
>   - we replace "cat" with a subshell loop around "read" to
>     ensure that there's no buffering (so that tests can be
>     sure that after a request has been served, the matching
>     log entries will have made it to the file)

> 
>   - we open the logfile for append, rather than just output.
>     That makes it OK for tests to truncate the logfile
>     without restarting the daemon (the OS will atomically
>     seek to the end of the file when outputting each line).
>     That allows tests to look at the log without worrying
>     about pollution from earlier tests.
> 
> Signed-off-by: Jeff King <peff@peff.net>
> ---
>  t/lib-git-daemon.sh | 12 ++++++++++--
>  1 file changed, 10 insertions(+), 2 deletions(-)
> 
> diff --git a/t/lib-git-daemon.sh b/t/lib-git-daemon.sh
> index 987d40680b..19f3ffdbb1 100644
> --- a/t/lib-git-daemon.sh
> +++ b/t/lib-git-daemon.sh
> @@ -53,11 +53,19 @@ start_git_daemon() {
>  		"$@" "$GIT_DAEMON_DOCUMENT_ROOT_PATH" \
>  		>&3 2>git_daemon_output &
>  	GIT_DAEMON_PID=$!
> +	>daemon.log
>  	{
>  		read line <&7
> +		echo "$line"
>  		echo >&4 "$line"
> -		cat <&7 >&4 &
> -	} 7<git_daemon_output &&
> +		(
> +			while read line <&7
> +			do
> +				echo "$line"
> +				echo >&4 "$line"
> +			done
> +		) &
> +	} 7<git_daemon_output >>"$TRASH_DIRECTORY/daemon.log" &&
>  
>  	# Check expected output
>  	if test x"$(expr "$line" : "\[[0-9]*\] \(.*\)")" != x"Ready to rumble"
>