--- /dev/null	Thu Jan 01 00:00:00 1970 +0000
+++ b/contrib/fuzz/xdiff.cc	Sat Mar 03 18:58:13 2018 -0500
@@ -0,0 +1,67 @@
+/*
+ * xdiff.cc - fuzzer harness for thirdparty/xdiff
+ *
+ * Copyright 2018, Google Inc.
+ *
+ * This software may be used and distributed according to the terms of
+ * the GNU General Public License, incorporated herein by reference.
+ */
+#include "thirdparty/xdiff/xdiff.h"
+#include <inttypes.h>
+#include <stdlib.h>
+
+extern "C" {
+
+int hunk_consumer(long a1, long a2, long b1, long b2, void *priv)
+{
+	// TODO: probably also test returning -1 from this when things break?
+	return 0;
+}
+
+int LLVMFuzzerTestOneInput(const uint8_t *Data, size_t Size)
+{
+	if (!Size) {
+		return 0;
+	}
+	// figure out a random point in [0, Size] to split our input.
+	size_t split = Data[0] / 255.0 * Size;
+
+	mmfile_t a, b;
+
+	// `a` input to diff is data[1:split]
+	a.ptr = (char *)Data + 1;
+	// which has len split-1
+	a.size = split - 1;
+	// `b` starts at the next byte after `a` ends
+	b.ptr = a.ptr + a.size;
+	b.size = Size - split;
+	xpparam_t xpp = {
+	    XDF_INDENT_HEURISTIC, /* flags */
+	    NULL,                 /* anchors */
+	    0,                    /* anchors_nr */
+	};
+	xdemitconf_t xecfg = {
+	    0,                  /* ctxlen */
+	    0,                  /* interhunkctxlen */
+	    XDL_EMIT_BDIFFHUNK, /* flags */
+	    NULL,               /* find_func */
+	    NULL,               /* find_func_priv */
+	    hunk_consumer,      /* hunk_consume_func */
+	};
+	xdemitcb_t ecb = {
+	    NULL, /* priv */
+	    NULL, /* outf */
+	};
+	xdl_diff(&a, &b, &xpp, &xecfg, &ecb);
+	return 0; // Non-zero return values are reserved for future use.
+}
+
+#ifdef HG_FUZZER_INCLUDE_MAIN
+int main(int argc, char **argv)
+{
+	const char data[] = "asdf";
+	return LLVMFuzzerTestOneInput((const uint8_t *)data, 4);
+}
+#endif
+
+} // extern "C"