improve alloc_vprintf

The previous implementation was unnecessarily complex. Get rid of the loops,
let vsnprintf() tell us directly how much storage we need and allocate that. A
second pass writes the actual string. Also add a va_end() that was missing.
This should be much faster for large strings and less wasteful for small ones.

A quirk that has been retained is that some callers patch in a newline at the
end of the returned string and depend on alloc_vprintf to allocate at least
one byte extra.

Signed-off-by: Andreas Fritiofson <andreas.fritiofson@gmail.com>
Signed-off-by: Zachary T Welch <zw@superlucidity.net>

diff --git a/src/helper/log.c b/src/helper/log.c
index caaed42322d2f75733f70823a9f0778659e7d20e..2dcf7bb63ce820b78ef81ba9535174fb19111051 100644 (file)
--- a/src/helper/log.c
+++ b/src/helper/log.c
@@ -395,37 +395,26 @@ int log_remove_callback(log_callback_fn fn, void *priv)
 /* return allocated string w/printf() result */
 char *alloc_vprintf(const char *fmt, va_list ap)
 {
-       /* no buffer at the beginning, force realloc to do the job */
-       char *string = NULL;
-
-       /* start with buffer size suitable for typical messages */
-       int size = 128;
-
-       for (;;)
-       {
-               char *t = string;
-               va_list ap_copy;
-               int ret;
-               string = realloc(string, size);
-               if (string == NULL)
-               {
-                       if (t != NULL)
-                               free(t);
-                       return NULL;
-               }
+       va_list ap_copy;
+       int len;
+       char *string;
 
-               va_copy(ap_copy, ap);
+       /* determine the length of the buffer needed */
+       va_copy(ap_copy, ap);
+       len = vsnprintf(NULL, 0, fmt, ap_copy);
+       va_end(ap_copy);
 
-               ret = vsnprintf(string, size, fmt, ap_copy);
-               /* NB! The result of the vsnprintf() might be an *EMPTY* string! */
-               if ((ret >= 0) && ((ret + 1) < size))
-                       break;
+       /* allocate and make room for terminating zero. */
+       /* FIXME: The old version always allocated at least one byte extra and
+        * other code depend on that. They should be probably be fixed, but for
+        * now reserve the extra byte. */
+       string = malloc(len + 2);
+       if (string == NULL)
+               return NULL;
 
-               /* there was just enough or not enough space, allocate more in the next round */
-               size *= 2; /* double the buffer size */
-       }
+       /* do the real work */
+       vsnprintf(string, len + 1, fmt, ap);
 
-       /* the returned buffer is by principle guaranteed to be at least one character longer */
        return string;
 }