Re: [msysGit] [PATCH v3 02/14] mingw: implement syslog

[Erik Faye-Lund <kusmabite@gmail.com>]

On Sun, Oct 10, 2010 at 11:28 PM, Eric Sunshine <ericsunshine@gmail.com> wrote:
> On 10/10/2010 4:37 PM, Erik Faye-Lund wrote:
>>
>> On Sun, Oct 10, 2010 at 9:50 PM, Eric Sunshine<ericsunshine@gmail.com>
>>  wrote:
>>>
>>> On 10/10/2010 9:20 AM, Erik Faye-Lund wrote:
>>>>
>>>> From: Mike Pape<dotzenlabs@gmail.com>
>>>>
>>>> Syslog does not usually exist on Windows, so we implement our own
>>>> using Window's ReportEvent mechanism.
>>>>
>>>> Signed-off-by: Mike Pape<dotzenlabs@gmail.com>
>>>> Signed-off-by: Erik Faye-Lund<kusmabite@gmail.com>
>>>> ---
>>>> +void syslog(int priority, const char *fmt, const char *arg)
>>>> +{
>>>> +       WORD logtype;
>>>> +
>>>> +       if (!ms_eventlog)
>>>> +               return;
>>>> +
>>>> +       if (strcmp(fmt, "%s")) {
>>>> +               warning("format string of syslog() not implemented");
>>>> +               return;
>>>> +       }
>>>
>>> It is not exactly clear what the intention is here. Is this trying to say
>>> that no formatting directives are allowed in 'fmt' or what? The simple
>>> case
>>> it is actually checking (where 'fmt' is solely '%s') could easily be
>>> handled
>>> manually, as could more complex formats.
>>>
>>
>> This is the result of the feed-back in v1, where we tried to implement
>> all format strings.
>
> In retrospect, when thinking more carefully about the conditional
> expression, I suppose the code is self-documenting, though perhaps a comment
> in code or in commit message would help.
>
>> But that turned out to be very complex (due to the
>> lack of a portable va_copy()) and since we control all call-sites for
>> syslog and already only use "%s" as the format, it should be OK.
>
> Do you mean vsnprintf() rather than va_copy()?
>

OK, I had to read some old discussions to figure out what the issue was :)

The problem was lack of portable va_copy, because I tried to add a
non-variadic version of strbuf_addf(), namely strbuf_vaddf() to do the
work.

I guess it could be implemented pretty easily with vsnprintf(),
though. I was afraid of doing that originally because I know there's
portability issues with the return value of snprintf. Luckily it seems
that we have a fix for that in compat/sprintf.c, and we rely on the
return value being correct in strbuf_addf() so it would probably be
safe.

Something like this (on top)

---8<---
diff --git a/compat/mingw.c b/compat/mingw.c
index bbe45d0..e3f3f92 100644
--- a/compat/mingw.c
+++ b/compat/mingw.c
@@ -1435,17 +1435,24 @@ void openlog(const char *ident, int logopt,
int facility)
 		warning("RegisterEventSource() failed: %lu", GetLastError());
 }

-void syslog(int priority, const char *fmt, const char *arg)
+void syslog(int priority, const char *fmt, ...)
 {
 	WORD logtype;
+	char *str;
+	int str_len;
+	va_list ap;

 	if (!ms_eventlog)
 		return;

-	if (strcmp(fmt, "%s")) {
-		warning("format string of syslog() not implemented");
-		return;
-	}
+	va_start(ap, fmt);
+	str_len = vsnprintf(NULL, 0, fmt, ap);
+	va_end(ap);
+
+	str = malloc(str_len + 1);
+	va_start(ap, fmt);
+	vsnprintf(str, str_len, fmt, ap);
+	va_end(ap);

 	switch (priority) {
 	case LOG_EMERG:
@@ -1478,8 +1485,9 @@ void syslog(int priority, const char *fmt, const
char *arg)
 	    NULL,
 	    1,
 	    0,
-	    (const char **)&arg,
+	    (const char **)&str,
 	    NULL);
+	free(str);
 }

 #undef signal
diff --git a/compat/mingw.h b/compat/mingw.h
index aed49d8..45a63a0 100644
--- a/compat/mingw.h
+++ b/compat/mingw.h
@@ -186,7 +186,7 @@ int setitimer(int type, struct itimerval *in,
struct itimerval *out);
 int sigaction(int sig, struct sigaction *in, struct sigaction *out);
 int link(const char *oldpath, const char *newpath);
 void openlog(const char *ident, int logopt, int facility);
-void syslog(int priority, const char *fmt, const char *arg);
+void syslog(int priority, const char *fmt, ...);

 /*
  * replacements of existing functions
---8<---

>> Are you suggesting that we report an error when we can't report the
>> string correctly? We could do that, but I'm not sure how the end-user
>> would benefit from that. ReportEvent is used to report errors (unless
>> the --verbose flag has been specified), and reporting that we can't
>> present an error message strike me as a bit confusing... Even the
>> corrupted error message is probably better :P
>
> I am not suggesting reporting an error. As a first-time reader of the code,
> I was trying to understand the presence of the comment which did not really
> seem to relate to the code. Perhaps adding a "FIXME" to the comment saying
> that the condition should perhaps be handled in the future would help to
> explain the comments presence.
>

A FIXME would certainly a good idea, if I don't just end up supporting
varargs here.

> (On the other hand, for the '%s' check above, the code does report a warning
> and then exits, so it is not inconceivable that a '%n' could also emit a
> warning.)
>

I guess I could add something like this:

if (strstr(arg, "%1"))
	warning("arg contains %1, message might be corrupted");

I don't want to return in that case, because I think some output is
better than no output, and it seems to work on Vista. In fact, working
on Vista is kind of demotivating me to add such a warning in the first
place...