Updated the libfuzzer to target marshalling.

test/fuzzers/fuzz_dostring.c

@@ -2,15 +2,39 @@
 #include <string.h>
 #include <janet.h>
 
+
+char *cmd_start = "(def v (unmarshal (slurp ((dyn :";
+char *cmd_end = ") 1)) load-image-dict));
+
 int LLVMFuzzerTestOneInput(const uint8_t *data, size_t size) {
-    char *new_str = (char *)malloc(size + 1);
+    char *new_str = (char *)malloc(size + strlen(cmd_start) + strlen(cmd_end) + 1);
     if (new_str == NULL) {
         return 0;
     }
-    memcpy(new_str, data, size);
-    new_str[size] = '\0';
+    // Copy start of command into the string we will execute
+    memcpy(new_str, cmd_start, strlen(cmd_start));
 
-    /* janet logic */
+    // Copy fuzz-data into the exec string
+    char *datap = new_str + strlen(cmd_start);
+    memcpy(datap, data, size);
+
+    // Copy the end of the command into the exec string
+    end_data = datap + size;
+    memcpy(end_data, cmd_end, strlen(cmd_end));
+
+    char *null_terminator = end_data + strlen(cmd_end) + 1;
+    *null_terminator = '\0';
+
+    // Remove any parentheses from the fuzz data
+    for (int i = 0; i < size; i++)
+    {
+        if (datap[i] == '(')
+            datap[i] = (char)(datap[i] + 1);
+        if (datap[i] == ')')
+            datap[i] = (char)(datap[i] + 1);
+    }
+
+    // janet logic
     janet_init();
     JanetTable *env = janet_core_env(NULL);
     janet_dostring(env, new_str, "main", NULL);