1 files changed, 75 insertions, 0 deletions
diff --git a/libntp/xsbprintf.c b/libntp/xsbprintf.c
new file mode 100644
index 0000000000000..4586758bc88aa
--- /dev/null
+++ b/libntp/xsbprintf.c
@@ -0,0 +1,75 @@
+/*
+ * xsbprintf.c - string buffer formatting helpers
+ *
+ * Written by Juergen Perlinger (perlinger@ntp.org) for the NTP project.
+ * The contents of 'html/copyright.html' apply.
+ */
+
+#include <config.h>
+#include <sys/types.h>
+
+#include "ntp_stdlib.h"
+
+/* eXtended Varlist String Buffer printf
+ *
+ * Formats via 'vsnprintf' into a string buffer, with some semantic
+ * specialties:
+ *
+ * - The start of the buffer pointer is updated according to the number
+ *   of characters written.
+ * - If the buffer is insufficient to format the number of charactes,
+ *   the partial result will be be discarded, and zero is returned to
+ *   indicate nothing was written to the buffer.
+ * - On successful formatting, the return code is the return value of
+ *   the inner call to 'vsnprintf()'.
+ * - If there is any error, the state of the buffer will not be
+ *   changed. (Bytes in the buffer might be smashed, but the buffer
+ *   position does not change, and the NUL marker stays in place at the
+ *   current buffer position.)
+ * - If '(*ppbuf - pend) <= 0' (or ppbuf is NULL), fail with EINVAL.
+ */
+int
+xvsbprintf(
+	char       **ppbuf,	/* pointer to buffer pointer (I/O) */
+	char * const pend,	/* buffer end (I)		   */
+	char const  *pfmt,	/* printf-like format string       */
+	va_list      va		/* formatting args for above       */
+	)
+{
+	char *pbuf = (ppbuf) ? *ppbuf : NULL;
+	int   rc   = -1;
+	if (pbuf && (pend - pbuf > 0)) {
+		size_t blen = (size_t)(pend - pbuf);
+		rc = vsnprintf(pbuf, blen, pfmt, va);
+		if (rc > 0) {
+		    if ((size_t)rc >= blen)
+			rc = 0;
+		    pbuf += rc;
+		}
+		*pbuf = '\0'; /* fear of bad vsnprintf */
+		*ppbuf = pbuf;
+	} else {
+		errno = EINVAL;
+	}
+	return rc;
+}
+
+/* variadic wrapper around the buffer string formatter */
+int
+xsbprintf(
+	char       **ppbuf,	/* pointer to buffer pointer (I/O) */
+	char * const pend,	/* buffer end (I)		   */
+	char const  *pfmt,	/* printf-like format string       */
+	...			/* formatting args for above       */
+	)
+{
+	va_list va;
+	int     rc;
+	
+	va_start(va, pfmt);
+	rc = xvsbprintf(ppbuf, pend, pfmt, va);
+	va_end(va);
+	return rc;
+}
+
+/* that's all folks! */