review: Make thread-safe by removing static allocation

* Also removed potention buffer overflow

src/link.c

@@ -77,12 +77,15 @@ static CURL *Link_to_curl(Link *link)
     if (ret) {
         lprintf(error, "%s", curl_easy_strerror(ret));
     }
+
     char *escaped_spaces = escape_char(link->f_url, ESCAPED_CHAR_SPACE);
     ret = curl_easy_setopt(curl, CURLOPT_URL,
                             escaped_spaces ? escaped_spaces : link->f_url);
     if (ret) {
         lprintf(error, "%s", curl_easy_strerror(ret));
     }
+    free(escaped_spaces);
+
     ret = curl_easy_setopt(curl, CURLOPT_TCP_KEEPALIVE, 1);
     if (ret) {
         lprintf(error, "%s", curl_easy_strerror(ret));

src/util.c

@@ -51,7 +51,6 @@ char *path_append(const char *path, const char *filename)
 
 char *escape_char(const char *url, const ESCAPE_CHAR c)
 {
-    static char escaped[MAX_PATH_LEN];
     char escape_me;
 
     /* A space, for example, becomes thrice bigger as '%20' after escaping */
@@ -73,29 +72,34 @@ char *escape_char(const char *url, const ESCAPE_CHAR c)
     int len = strnlen(url, MAX_PATH_LEN);
 
     /* Best case scenario of only one character to escape */
-    if (strnlen(url,MAX_PATH_LEN) + 3 > MAX_PATH_LEN) {
+    if (len + 3 > MAX_PATH_LEN) {
         lprintf(fatal, "URL too long: %s\n", url);
     }
 
-    memset(escaped, 0, MAX_PATH_LEN);
+    char *escaped = CALLOC(MAX_PATH_LEN, sizeof(char));
 
-    int j = 0;
+    int j = 0, k = 0;
     for (int i = 0; i < len; i++) {
+        /* Precaution against writing beyond the buffer, since we do not count
+         * all spaces beforehand to know the exact amount of memory to calloc
+         * for the escaped URL.
+         */
+        if (k > MAX_PATH_LEN) {
+            lprintf(fatal, "URL too long: %s\n", url);
+        }
         if (url[i] == escape_me) {
             switch (c) {
                 case ESCAPED_CHAR_SPACE:
                     strncpy(escaped + j, "%20", how_bigger);
                     break;
             }
-
-            j += how_bigger;
+            k = j + how_bigger;
+            j = k;
 
         } else {
             escaped[j++] = url[i];
         }
     }
-
-    escaped[j] = '\0';
     return escaped;
 }
 

src/util.h

@@ -30,7 +30,7 @@ char *path_append(const char *path, const char *filename);
  * the string with the escaped character. We don't use curl_easy_escape() on
  * the entire URL because it would break the URL. For example, 'http://a c'
  * becomes 'http:%2F%2Fa%20c', escaping more characters than we want.
- * \note DO NOT free the char * after use. It is statically allocated.
+ * \note You need to free the char * after use.
  */
 char *escape_char(const char *s, ESCAPE_CHAR c);