added _hex2bin()

libpcp/util.c

@@ -83,3 +83,39 @@ char *_bin2hex(byte *bin, size_t len) {
   out[len*2] = '\0';
   return out;
 }
+
+/* via stackoverflow. yes, lazy */
+size_t _hex2bin(const char *hex_str, unsigned char *byte_array, size_t byte_array_max) {
+    size_t hex_str_len = strlen(hex_str);
+    size_t i = 0, j = 0;
+
+    // The output array size is half the hex_str length (rounded up)
+    size_t byte_array_size = (hex_str_len+1)/2;
+
+    if (byte_array_size > byte_array_max)
+    {
+        // Too big for the output array
+        return -1;
+    }
+
+    if (hex_str_len % 2 == 1)
+    {
+        // hex_str is an odd length, so assume an implicit "0" prefix
+        if (sscanf(&(hex_str[0]), "%1hhx", &(byte_array[0])) != 1)
+        {
+            return -1;
+        }
+
+        i = j = 1;
+    }
+
+    for (; i < hex_str_len; i+=2, j++)
+    {
+        if (sscanf(&(hex_str[i]), "%2hhx", &(byte_array[j])) != 1)
+        {
+            return -1;
+        }
+    }
+
+    return byte_array_size;
+}