add missing misc/concat_strings.h

misc/concat_strings.h

@@ -0,0 +1,77 @@
+/**
+ * @file concat_strings.h
+ * @author Ambroz Bizjak <ambrop7@gmail.com>
+ * 
+ * @section LICENSE
+ * 
+ * This file is part of BadVPN.
+ * 
+ * BadVPN is free software: you can redistribute it and/or modify
+ * it under the terms of the GNU General Public License version 2
+ * as published by the Free Software Foundation.
+ * 
+ * BadVPN 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 General Public License for more details.
+ * 
+ * You should have received a copy of the GNU General Public License along
+ * with this program; if not, write to the Free Software Foundation, Inc.,
+ * 51 Franklin Street, Fifth Floor, Boston, MA 02110-1301 USA.
+ * 
+ * @section DESCRIPTION
+ * 
+ * Function for concatenating strings.
+ */
+
+#ifndef BADVPN_MISC_CONCAT_STRINGS_H
+#define BADVPN_MISC_CONCAT_STRINGS_H
+
+#include <string.h>
+#include <stdlib.h>
+#include <stdarg.h>
+
+#include <misc/debug.h>
+
+static char * concat_strings (int num, ...)
+{
+    ASSERT(num >= 0)
+    
+    // calculate sum of lengths
+    size_t sum = 0;
+    va_list ap;
+    va_start(ap, num);
+    for (int i = 0; i < num; i++) {
+        const char *str = va_arg(ap, const char *);
+        size_t str_len = strlen(str);
+        if (str_len > SIZE_MAX - 1 - sum) {
+            return NULL;
+        }
+        sum += str_len;
+    }
+    va_end(ap);
+    
+    // allocate memory
+    char *res_str = malloc(sum + 1);
+    if (!res_str) {
+        return NULL;
+    }
+    
+    // copy strings
+    sum = 0;
+    va_start(ap, num);
+    for (int i = 0; i < num; i++) {
+        const char *str = va_arg(ap, const char *);
+        size_t str_len = strlen(str);
+        memcpy(res_str + sum, str, str_len);
+        sum += str_len;
+    }
+    va_end(ap);
+    
+    // terminate
+    res_str[sum] = '\0';
+    
+    return res_str;
+}
+
+#endif