2 files changed, 83 insertions, 0 deletions
diff --git a/fuzzer/fuzz.py b/fuzzer/fuzz.py
new file mode 100644
index 0000000..a97b2f7
--- /dev/null
+++ b/fuzzer/fuzz.py
@@ -0,0 +1,79 @@
+import atheris
+
+with atheris.instrument_imports():
+    from math import isnan
+    import sys
+    import warnings
+
+    import tomli_w
+
+    import tomli
+
+# Disable any caching used so that the same lines of code run
+# on a given input consistently.
+tomli._re.cached_tz = tomli._re.cached_tz.__wrapped__
+
+# Suppress all warnings.
+warnings.simplefilter("ignore")
+
+
+def test_one_input(input_bytes: bytes) -> None:
+    # We need a Unicode string, not bytes
+    fdp = atheris.FuzzedDataProvider(input_bytes)
+    data = fdp.ConsumeUnicode(sys.maxsize)
+
+    try:
+        toml_obj = tomli.loads(data)
+    except (tomli.TOMLDecodeError, RecursionError):
+        return
+    except BaseException:
+        print_err(data)
+        raise
+
+    try:
+        recovered_data = tomli_w.dumps(toml_obj)
+    except RecursionError:
+        return
+    except BaseException:
+        print_err(data)
+        raise
+
+    roundtripped_obj = tomli.loads(recovered_data)
+    normalize_toml_obj(roundtripped_obj)
+    normalize_toml_obj(toml_obj)
+    if roundtripped_obj != toml_obj:
+        sys.stderr.write(
+            f"Original dict:\n{toml_obj}\nRoundtripped dict:\n{roundtripped_obj}\n"
+        )
+        sys.stderr.flush()
+        print_err(data)
+        raise Exception("Dicts not equal after roundtrip")
+
+
+def print_err(data):
+    codepoints = [hex(ord(x)) for x in data]
+    sys.stderr.write(f"Input was {type(data)}:\n{data}\nCodepoints:\n{codepoints}\n")
+    sys.stderr.flush()
+
+
+def normalize_toml_obj(toml_obj: dict) -> None:
+    """Make NaNs equal when compared (without using recursion)."""
+    to_process = [toml_obj]
+    while to_process:
+        cont = to_process.pop()
+        for k, v in cont.items() if isinstance(cont, dict) else enumerate(cont):
+            if isinstance(v, float) and isnan(v):
+                cont[k] = "nan"
+            elif isinstance(v, (dict, list)):
+                to_process.append(v)
+
+
+def main():
+    # For possible options, see https://llvm.org/docs/LibFuzzer.html#options
+    fuzzer_options = sys.argv
+    atheris.Setup(fuzzer_options, test_one_input)
+    atheris.Fuzz()
+
+
+if __name__ == "__main__":
+    main()
diff --git a/fuzzer/requirements.txt b/fuzzer/requirements.txt
new file mode 100644
index 0000000..b4d78cc
--- /dev/null
+++ b/fuzzer/requirements.txt
@@ -0,0 +1,4 @@
+# sudo apt-get install clang
+wheel
+atheris==2.0.3
+tomli_w>=0.2.2