lib/sprintf.[ch]: Add [v]snprintf_()

These functions are like [v]snprintf(3), but return -1 on truncation, which makes it easier to test. snprintf(3) is iseful in two cases: - We don't care if the output is truncated. snprintf(3) is fine for those, and the return value can be ignored. - Truncation is bad. In that case, it's as bad as a hard error (-1) from snprintf, so merging both problems into the same error code makes it easier to handle errors. Return the length if no truncation so that we can use it if necessary. Signed-off-by: Alejandro Colomar <[email protected]>
shadow-maint · Sep 6, 2023 · 233370e · 233370e
1 parent 1814877
commit 233370e
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Showing 2 changed files with 41 additions and 10 deletions.
diff --git a/lib/sprintf.c b/lib/sprintf.c
@@ -18,6 +18,11 @@ extern inline int xasprintf(char **restrict s, const char *restrict fmt, ...);
 extern inline int xvasprintf(char **restrict s, const char *restrict fmt,
     va_list ap);
 
+extern inline int snprintf_(char *restrict s, int size,
+    const char *restrict fmt, ...);
+extern inline int vsnprintf_(char *restrict s, int size,
+    const char *restrict fmt, va_list ap);
+
 extern inline int xsnprintf(char *restrict s, int size,
     const char *restrict fmt, ...);
 extern inline int xvsnprintf(char *restrict s, int size,

diff --git a/lib/sprintf.h b/lib/sprintf.h
@@ -19,14 +19,7 @@
 
 
 #define SNPRINTF(s, fmt, ...)                                                 \
-({                                                                            \
-	size_t  sz_, len_;                                                    \
-                                                                              \
-	sz_ = SIZEOF_ARRAY(s);                                                \
-	len_ = snprintf(s, sz_, fmt __VA_OPT__(,) __VA_ARGS__);               \
-                                                                              \
-	(len_ >= sz_) ? -1 : len_;                                            \
-})
+	snprintf_(s, SIZEOF_ARRAY(s), fmt __VA_OPT__(,) __VA_ARGS__)
 
 #define XSNPRINTF(s, fmt, ...)                                                 \
 	xsnprintf(s, SIZEOF_ARRAY(s), fmt __VA_OPT__(,) __VA_ARGS__)
@@ -37,6 +30,12 @@ inline int xasprintf(char **restrict s, const char *restrict fmt, ...);
 format_attr(printf, 2, 0)
 inline int xvasprintf(char **restrict s, const char *restrict fmt, va_list ap);
 
+format_attr(printf, 3, 4)
+inline int snprintf_(char *restrict s, int size, const char *restrict fmt, ...);
+format_attr(printf, 3, 0)
+inline int vsnprintf_(char *restrict s, int size, const char *restrict fmt,
+    va_list ap);
+
 format_attr(printf, 3, 4)
 inline int xsnprintf(char *restrict s, int size, const char *restrict fmt, ...);
 format_attr(printf, 3, 0)
@@ -73,6 +72,33 @@ xvasprintf(char **restrict s, const char *restrict fmt, va_list ap)
 }
 
 
+inline int
+snprintf_(char *restrict s, int size, const char *restrict fmt, ...)
+{
+	int      len;
+	va_list  ap;
+
+	va_start(ap, fmt);
+	len = vsnprintf_(s, size, fmt, ap);
+	va_end(ap);
+
+	return len;
+}
+
+
+inline int
+vsnprintf_(char *restrict s, int size, const char *restrict fmt, va_list ap)
+{
+	int  len;
+
+	len = vsnprintf(s, size, fmt, ap);
+	if (len >= size)
+		len = -1;
+
+	return len;
+}
+
+
 inline int
 xsnprintf(char *restrict s, int size, const char *restrict fmt, ...)
 {
@@ -92,8 +118,8 @@ xvsnprintf(char *restrict s, int size, const char *restrict fmt, va_list ap)
 {
 	int  len;
 
-	len = vsnprintf(s, size, fmt, ap);
-	if (len == -1 || len >= size) {
+	len = vsnprintf_(s, size, fmt, ap);
+	if (len == -1) {
 		perror("snprintf");
 		exit(EXIT_FAILURE);
 	}