Add Diff Fuzz Target

Adds a new `fuzz_diff.py` fuzz target that covers `Diff` class
initialization using fuzzed data.

fuzzing/fuzz-targets/fuzz_diff.py

@@ -0,0 +1,54 @@
+import sys
+import os
+import tempfile
+from binascii import Error as BinasciiError
+
+import atheris
+
+if getattr(sys, "frozen", False) and hasattr(sys, "_MEIPASS"):
+    path_to_bundled_git_binary = os.path.abspath(os.path.join(os.path.dirname(__file__), "git"))
+    os.environ["GIT_PYTHON_GIT_EXECUTABLE"] = path_to_bundled_git_binary
+
+with atheris.instrument_imports():
+    from git import Repo, Diff
+
+
+def TestOneInput(data):
+    fdp = atheris.FuzzedDataProvider(data)
+
+    with tempfile.TemporaryDirectory() as temp_dir:
+        repo = Repo.init(path=temp_dir)
+        try:
+            Diff(
+                repo,
+                a_rawpath=fdp.ConsumeBytes(fdp.ConsumeIntInRange(0, fdp.remaining_bytes())),
+                b_rawpath=fdp.ConsumeBytes(fdp.ConsumeIntInRange(0, fdp.remaining_bytes())),
+                a_blob_id=fdp.ConsumeBytes(20),
+                b_blob_id=fdp.ConsumeBytes(20),
+                a_mode=fdp.ConsumeBytes(fdp.ConsumeIntInRange(0, fdp.remaining_bytes())),
+                b_mode=fdp.ConsumeBytes(fdp.ConsumeIntInRange(0, fdp.remaining_bytes())),
+                new_file=fdp.ConsumeBool(),
+                deleted_file=fdp.ConsumeBool(),
+                copied_file=fdp.ConsumeBool(),
+                raw_rename_from=fdp.ConsumeBytes(fdp.ConsumeIntInRange(0, fdp.remaining_bytes())),
+                raw_rename_to=fdp.ConsumeBytes(fdp.ConsumeIntInRange(0, fdp.remaining_bytes())),
+                diff=fdp.ConsumeBytes(fdp.ConsumeIntInRange(0, fdp.remaining_bytes())),
+                change_type=fdp.PickValueInList(["A", "D", "C", "M", "R", "T", "U"]),
+                score=fdp.ConsumeIntInRange(0, fdp.remaining_bytes()),
+            )
+        except BinasciiError:
+            return -1
+        except AssertionError as e:
+            if "Require 20 byte binary sha, got" in str(e):
+                return -1
+            else:
+                raise e
+
+
+def main():
+    atheris.Setup(sys.argv, TestOneInput)
+    atheris.Fuzz()
+
+
+if __name__ == "__main__":
+    main()