Add fuzzing by way of ClusterFuzzLite

.clusterfuzzlite/Dockerfile

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+FROM gcr.io/oss-fuzz-base/base-builder
+RUN apt-get update && apt-get install -y make autoconf automake libtool
+
+COPY . $SRC/frozen
+COPY .clusterfuzzlite/build.sh $SRC/build.sh
+WORKDIR $SRC/frozen

.clusterfuzzlite/README.md

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+# ClusterFuzzLite set up
+
+This folder contains a fuzzing set for [ClusterFuzzLite](https://google.github.io/clusterfuzzlite).
+
+## Reproduce locally
+
+To reproduce this set up the way ClusterFuzzLite does it (by way of [OSS-Fuzz](https://github.com/google/oss)) you can do:
+
+```sh
+git clone https://github.com/google/oss-fuzz
+git https://github.com/cesanta/frozen
+cd frozen
+
+# Build the fuzzers in .clusterfuzzlite
+python3 ../oss-fuzz/infra/helper.py build_fuzzers --external $PWD
+
+# Run the fuzzer for 180 seconds
+python3 ../oss-fuzz/infra/helper.py run_fuzzer --external $PWD json_walk_fuzzer -- -max_total_time=180
+```

.clusterfuzzlite/build.sh

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+#!/bin/bash -eu
+# Supply build instructions
+# Use the following environment variables to build the code
+# $CXX:               c++ compiler
+# $CC:                c compiler
+# CFLAGS:             compiler flags for C files
+# CXXFLAGS:           compiler flags for CPP files
+# LIB_FUZZING_ENGINE: linker flag for fuzzing harnesses
+$CC $CFLAGS -c frozen.c -o frozen.o
+
+# Copy all fuzzer executables to $OUT/
+$CC $CFLAGS $LIB_FUZZING_ENGINE \
+  $SRC/frozen/.clusterfuzzlite/json_walk_fuzzer.c \
+  -o $OUT/json_walk_fuzzer \
+  frozen.o \
+  -I$PWD

.clusterfuzzlite/json_walk_fuzzer.c

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+#include <stdint.h>
+#include <frozen.h>
+
+int 
+LLVMFuzzerTestOneInput(const uint8_t *data, size_t size)
+{
+    json_walk((const char*)data, size, NULL, NULL);
+    return 0;
+}

.clusterfuzzlite/project.yaml

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+language: c

.github/workflows/cflite_pr.yml

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+name: ClusterFuzzLite PR fuzzing
+on:
+  workflow_dispatch:
+  pull_request:
+    branches: [ master ]
+permissions: read-all
+jobs:
+  PR:
+    runs-on: ubuntu-latest
+    strategy:
+      fail-fast: false
+      matrix:
+        sanitizer: [address]
+    steps:
+    - name: Build Fuzzers (${{ matrix.sanitizer }})
+      id: build
+      uses: google/clusterfuzzlite/actions/build_fuzzers@v1
+      with:
+        sanitizer: ${{ matrix.sanitizer }}
+        language: c
+        bad-build-check: false
+    - name: Run Fuzzers (${{ matrix.sanitizer }})
+      id: run
+      uses: google/clusterfuzzlite/actions/run_fuzzers@v1
+      with:
+        github-token: ${{ secrets.GITHUB_TOKEN }}
+        fuzz-seconds: 100
+        mode: 'code-change'
+        report-unreproducible-crashes: false
+        sanitizer: ${{ matrix.sanitizer }}