common: Add utils.[ch] with a string_concat() function

Instead of doing malloc() and repeated strcat(), which is an O(n^2) way to concatenate multiple strings,
we define a single O(total_len) function that uses stpcpy().  This will also make the rest of the code
more legible and safer.

1 files changed, 85 insertions, 0 deletions

diff --git a/common/utils.c b/common/utils.c
new file mode 100644
index 0000000..b2b3768
--- /dev/null
+++ b/common/utils.c
@@ -0,0 +1,85 @@
+/*
+ * utils.c
+ * Miscellaneous utilities for string manipulation
+ *
+ * Copyright (c) 2013 Federico Mena Quintero
+ *
+ * This library is free software; you can redistribute it and/or
+ * modify it under the terms of the GNU Lesser General Public
+ * License as published by the Free Software Foundation; either
+ * version 2.1 of the License, or (at your option) any later version.
+ *
+ * This library is distributed in the hope that it will be useful,
+ * but WITHOUT ANY WARRANTY; without even the implied warranty of
+ * MERCHANTABILITY or FITNESS FOR A PARTICULAR PURPOSE.  See the GNU
+ * Lesser General Public License for more details.
+ *
+ * You should have received a copy of the GNU Lesser General Public
+ * License along with this library; if not, write to the Free Software
+ * Foundation, Inc., 51 Franklin Street, Fifth Floor, Boston, MA  02110-1301  USA
+ */
+
+#ifdef HAVE_CONFIG_H
+#include <config.h>
+#endif
+
+#include <stdarg.h>
+#include <stdlib.h>
+#include <string.h>
+
+#include "utils.h"
+
+/**
+ * Concatenate strings into a newly allocated string
+ *
+ * @note: Specify NULL for the last string in the varargs list
+ *
+ * @str: The first string in the list
+ * @...: Subsequent strings.  Use NULL for the last item.
+ *
+ * @return a newly allocated string, or NULL if @str is NULL.  This will also
+ * return NULL and set errno to ENOMEM if memory is exhausted.
+ */
+char *string_concat(const char *str, ...)
+{
+	size_t len;
+	va_list args;
+	char *s;
+	char *result;
+	char *dest;
+
+	if (!str)
+		return NULL;
+
+	/* Compute final length */
+
+	len = strlen(str) + 1; /* plus 1 for the null terminator */
+
+	va_start(args, str);
+	s = va_arg(args, char *);
+	while (s) {
+		len += strlen(s);
+		s = va_arg(args, char*);
+	}
+	va_end(args);
+
+	/* Concat each string */
+
+	result = malloc(len);
+	if (!result)
+		return NULL; /* errno remains set */
+
+	dest = result;
+
+	dest = stpcpy(dest, str);
+
+	va_start(args, str);
+	s = va_arg(args, char *);
+	while (s) {
+		dest = stpcpy(dest, s);
+		s = va_arg(args, char *);
+	}
+	va_end(args);
+
+	return result;
+}