THRIFT-5855: cpp fuzzers
Add fuzzers for cpp support, to improve the reliability/robustness of the implementation
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+# C++ Fuzzing README
+
+To build the fuzz targets, run `make check` in this directory. The build system uses LLVM's libFuzzer for fuzzing the C++ Thrift implementation.
+
+These are standard libFuzzer targets, so you can run them using the standard libFuzzer interface. After building, you can run a fuzzer using:
+```bash
+./<fuzzer_name>
+```
+
+We currently have six fuzz targets:
+
+* FuzzParseBinary -- fuzzes the deserialization of the Binary protocol
+* FuzzParseCompact -- fuzzes the deserialization of the Compact protocol
+* FuzzParseJson -- fuzzes the deserialization of the JSON protocol
+* FuzzRoundtripBinary -- fuzzes the roundtrip of the Binary protocol (i.e. serializes then deserializes and compares the result)
+* FuzzRoundtripCompact -- fuzzes the roundtrip of the Compact protocol
+* FuzzRoundtripJson -- fuzzes the roundtrip of the JSON protocol
+
+The fuzzers use libFuzzer's built-in mutation engine to generate test cases. Each fuzzer implements the standard `LLVMFuzzerTestOneInput` interface and uses common testing code from `FuzzCommon.tcc`.
+
+For more information about libFuzzer and its options, see the [libFuzzer documentation](https://llvm.org/docs/LibFuzzer.html).
+
+You can also use the corpus generator from the Rust implementation to generate initial corpus files that can be used with these C++ fuzzers, since the wire formats are identical between implementations.
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