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

As other x...() wrappers around functions that allocate, these wrappers
are like [v]asprintf(3), but exit on failure.

Reviewed-by: Iker Pedrosa <ipedrosa@redhat.com>
Signed-off-by: Alejandro Colomar <alx@kernel.org>

lib/Makefile.am

@@ -133,6 +133,8 @@ libshadow_la_SOURCES = \
 	shell.c \
 	sizeof.h \
 	spawn.c \
+	sprintf.c \
+	sprintf.h \
 	sssd.c \
 	sssd.h \
 	stpecpy.c \

lib/sprintf.c

@@ -0,0 +1,19 @@
+/*
+ * SPDX-FileCopyrightText: 2023, Alejandro Colomar <alx@kernel.org>
+ * SPDX-License-Identifier: BSD-3-Clause
+ */
+
+#include <config.h>
+
+#ident "$Id$"
+
+#include "sprintf.h"
+
+#include <stdarg.h>
+#include <stddef.h>
+#include <stdio.h>
+
+
+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);

lib/sprintf.h

@@ -0,0 +1,55 @@
+/*
+ * SPDX-FileCopyrightText: 2023, Alejandro Colomar <alx@kernel.org>
+ * SPDX-License-Identifier: BSD-3-Clause
+ */
+
+
+#ifndef SHADOW_INCLUDE_LIB_SPRINTF_H_
+#define SHADOW_INCLUDE_LIB_SPRINTF_H_
+
+
+#include <config.h>
+
+#include <stdarg.h>
+#include <stddef.h>
+#include <stdio.h>
+
+#include "defines.h"
+
+
+format_attr(printf, 2, 3)
+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);
+
+
+inline int
+xasprintf(char **restrict s, const char *restrict fmt, ...)
+{
+	int      len;
+	va_list  ap;
+
+	va_start(ap, fmt);
+	len = xvasprintf(s, fmt, ap);
+	va_end(ap);
+
+	return len;
+}
+
+
+inline int
+xvasprintf(char **restrict s, const char *restrict fmt, va_list ap)
+{
+	int  len;
+
+	len = vasprintf(s, fmt, ap);
+	if (len == -1) {
+		perror("asprintf");
+		exit(EXIT_FAILURE);
+	}
+
+	return len;
+}
+
+
+#endif  // include guard