modified strndupcat, added more comments

src/cache.c

@@ -19,8 +19,17 @@
  *
  * More information regarding block size can be found at:
  * https://wiki.vuze.com/w/Torrent_Piece_Size
+ *
+ * Note that at the current configuration, a 16GiB file uses 128MiB of memory to
+ * store the bitmap, but hey, I have 16GiB on my computer!
  */
 #define DATA_BLK_SZ         131072
+
+/**
+ * \brief the maximum length of a path
+ * \details This corresponds the maximum path length under Ext4. If you need
+ * longer path, then fuck you.
+ */
 #define MAX_PATH_LEN        4096
 
 /**
@@ -399,9 +408,3 @@ long Data_write(const Cache *cf, long offset, long len,
     }
     return byte_written;
 }
-
-
-
-
-
-

src/util.c

@@ -6,9 +6,18 @@
 
 char *strndupcat(const char *a, const char *b, int n)
 {
-    int na = strnlen(a, n/2);
-    int nb = strnlen(b, n/2);
+    int na = strnlen(a, n);
+    int nb = strnlen(b, n);
     int nc = na + nb + 1;
+    if (nc > n) {
+        fprintf(stderr,
+            "strndupcat(): resulting string length exceeds maximum limit!\n");
+        /*
+         * It is better to crash the program here, then corrupting the cache
+         * folder
+         */
+        exit(EXIT_FAILURE);
+    }
     char *c = calloc(nc, sizeof(char));
     if (!c) {
         fprintf(stderr, "strndupcat(): calloc failure!\n");
@@ -16,5 +25,6 @@ char *strndupcat(const char *a, const char *b, int n)
     }
     strncpy(c, a, na);
     strncat(c, b, nb);
+    c[nc-1] = '\0';
     return c;
 }

src/util.h

@@ -10,8 +10,6 @@
  * \brief strndup with concatenation
  * \details This function concatenate string a and string b together, and put
  * the result in a new string.
- * \note The maximum length of string a and string b is half the length of the
- * maximum length of the output string.
  * \param[in] a the first string
  * \param[in] b the second string
  * \param[n] c the maximum length of the output string