diff contrib/fuzz/fuzzutil.cc @ 38173:fa0ddd5e8fff

fuzz: extract some common utilities and use modern C++ idioms

Alex Gaynor suggested we should probably copy the left and right sides
of diffs to new blocks so we can detect over-reads in the diffing
code, and I agree. Once I got into that, I realized we should do
things with C++17 idioms rather than keep using malloc() and
free(). This change is the result. I tried to split it more than this
and failed.

Everything still compiles and works in the oss-fuzz container, so I
think we can count on C++17 being available!

Differential Revision: https://phab.mercurial-scm.org/D3675

--- /dev/null	Thu Jan 01 00:00:00 1970 +0000
+++ b/contrib/fuzz/fuzzutil.cc	Sat Apr 28 22:18:50 2018 -0400
@@ -0,0 +1,26 @@
+#include "fuzzutil.h"
+
+#include <utility>
+
+std::optional<two_inputs> SplitInputs(const uint8_t *Data, size_t Size)
+{
+	if (!Size) {
+		return std::nullopt;
+	}
+	// figure out a random point in [0, Size] to split our input.
+	size_t left_size = (Data[0] / 255.0) * (Size - 1);
+
+	// Copy inputs to new allocations so if bdiff over-reads
+	// AddressSanitizer can detect it.
+	std::unique_ptr<char[]> left(new char[left_size]);
+	memcpy(left.get(), Data + 1, left_size);
+	// right starts at the next byte after left ends
+	size_t right_size = Size - (left_size + 1);
+	std::unique_ptr<char[]> right(new char[right_size]);
+	memcpy(right.get(), Data + 1 + left_size, right_size);
+	LOG(2) << "inputs are  " << left_size << " and " << right_size
+	       << " bytes" << std::endl;
+	two_inputs result = {std::move(right), right_size, std::move(left),
+	                     left_size};
+	return result;
+}