From 31a0a5486f2348823e211621be1fa33ff5fdabb1 Mon Sep 17 00:00:00 2001
From: robertl <robertl>
Date: Thu, 5 Oct 2006 04:07:34 +0000
Subject: [PATCH] Make xasprintf work sensibly in light of both (sigh) C99 and
 SUSv1 definitions of snprintf.  Probably needs more abstraction work, but
 this is more correct in more cases.

---
 util.c | 80 ++++++++++++++++++++++++++++++++++++++++++++++++----------
 1 file changed, 67 insertions(+), 13 deletions(-)

diff --git a/util.c b/util.c
index d2e48bd4a..7dfcb446d 100644
--- a/util.c
+++ b/util.c
@@ -293,21 +293,75 @@ xfputs(const char *errtxt, const char *s, FILE *stream)
 int
 xasprintf(char **strp, const char *fmt, ...)
 {
+	/* From http://perfec.to/vsnprintf/pasprintf.c */
+/* size of first buffer malloc; start small to exercise grow routines */
+#define	FIRSTSIZE	64
 	va_list args;
-	int res;
-	
-	va_start(args, fmt);
-	res = vsnprintf((char *)NULL, 0, fmt, args);
-	*strp = xmalloc(res + 1);
-	va_end(args);
-	
-	va_start(args, fmt);
-	res = vsnprintf(*strp, res + 1, fmt, args);
-	va_end(args);
+	char *buf;
+	size_t bufsize;
+	char *newbuf;
+	size_t nextsize;
+	int outsize;
+
+	bufsize = 0;
+	for (;;) {
+		if (bufsize == 0) {
+			if ((buf = xmalloc(FIRSTSIZE)) == NULL) {
+				*strp = NULL;
+				return -1;
+			}
+			bufsize = 1;
+		} else if ((newbuf = xrealloc(buf, nextsize)) != NULL) {
+			buf = newbuf;
+			bufsize = nextsize;
+		} else {
+			xfree(buf);
+			*strp = NULL;
+			return -1;
+		}
 
-	is_fatal(res < 0, "(internal): vsnprintf returned %d!", res);
-	
-	return res;
+		va_start(args, fmt);
+		outsize = vsnprintf(buf, bufsize, fmt, args);
+		va_end(args);
+
+		if (outsize == -1) {
+			/* Clear indication that output was truncated, but no
+			 * clear indication of how big buffer needs to be, so
+			 * simply double existing buffer size for next time.
+			 */
+			nextsize = bufsize * 2;
+
+		} else if (outsize == bufsize) {
+			/* Output was truncated (since at least the \0 could
+			 * not fit), but no indication of how big the buffer
+			 * needs to be, so just double existing buffer size
+			 * for next time.
+			 */
+			nextsize = bufsize * 2;
+
+		} else if (outsize > bufsize) {
+			/* Output was truncated, but we were told exactly how
+			 * big the buffer needs to be next time. Add two chars
+			 * to the returned size. One for the \0, and one to
+			 * prevent ambiguity in the next case below.
+			 */
+			nextsize = outsize + 2;
+
+		} else if (outsize == bufsize - 1) {
+			/* This is ambiguous. May mean that the output string
+			 * exactly fits, but on some systems the output string
+			 * may have been trucated. We can't tell.
+			 * Just double the buffer size for next time.
+			 */
+			nextsize = bufsize * 2;
+
+		} else {
+			/* Output was not truncated */
+			break;
+		}
+	}
+	*strp = buf;
+	return 0;
 }
 
 /* 
-- 
2.30.2