Improve fuzz testing to find string scan bug

corpus/example.bin

@@ -0,0 +1 @@
+"<22> <20>                                                           "

src/fuzz.cpp

@@ -42,6 +42,25 @@ std::pair<std::string, WeaselJsonStatus> runBatch(std::string copy) {
   return {state.result, s};
 }
 
+std::pair<std::string, WeaselJsonStatus> runPrefix(std::string copy,
+                                                   int prefix) {
+  SerializeState state;
+  auto c = serializeCallbacks();
+  std::unique_ptr<WeaselJsonParser, decltype(&WeaselJsonParser_destroy)> parser{
+      WeaselJsonParser_create(1024, &c, &state), WeaselJsonParser_destroy};
+  auto s = WeaselJsonParser_parse(parser.get(), copy.data(), prefix);
+  if (s != WeaselJson_AGAIN) {
+    return {state.result, s};
+  }
+  s = WeaselJsonParser_parse(parser.get(), copy.data() + prefix,
+                             copy.size() - prefix);
+  if (s != WeaselJson_AGAIN) {
+    return {state.result, s};
+  }
+  s = WeaselJsonParser_parse(parser.get(), nullptr, 0);
+  return {state.result, s};
+}
+
 void testStreaming(std::string const &json) {
   auto batch = runBatch(json);
   if (batch.second == WeaselJson_AGAIN) {
@@ -57,15 +76,36 @@ void testStreaming(std::string const &json) {
       bool batchOk = batch.second == WeaselJson_OK;
       if (streamingOk == batchOk && !batchOk) {
         // It's ok if the processed data doesn't match if parsing failed
-        continue;
+      } else {
+        printf("streaming: %s, %s\n",
+               streaming.second == WeaselJson_OK ? "accept" : "reject",
+               streaming.first.c_str());
+        printf("batch: %s, %s\n",
+               batch.second == WeaselJson_OK ? "accept" : "reject",
+               batch.first.c_str());
+        abort();
+      }
+    }
+    if (int(json.size()) > stride) {
+      auto prefix = runPrefix(json, stride);
+      if (prefix != batch) {
+        if (prefix.second == WeaselJson_AGAIN) {
+          abort();
+        }
+        bool prefixOk = prefix.second == WeaselJson_OK;
+        bool batchOk = batch.second == WeaselJson_OK;
+        if (prefixOk == batchOk && !batchOk) {
+          // It's ok if the processed data doesn't match if parsing failed
+        } else {
+          printf("prefix: %s, %s\n",
+                 prefix.second == WeaselJson_OK ? "accept" : "reject",
+                 prefix.first.c_str());
+          printf("batch: %s, %s\n",
+                 batch.second == WeaselJson_OK ? "accept" : "reject",
+                 batch.first.c_str());
+          abort();
+        }
       }
-      printf("streaming: %s, %s\n",
-             streaming.second == WeaselJson_OK ? "accept" : "reject",
-             streaming.first.c_str());
-      printf("batch: %s, %s\n",
-             batch.second == WeaselJson_OK ? "accept" : "reject",
-             batch.first.c_str());
-      abort();
     }
   }
 }