tests: Add fuzzing harness for functions/classes in span.h

src/test/fuzz/span.cpp

@@ -0,0 +1,39 @@
+// Copyright (c) 2020 The Bitcoin Core developers
+// Distributed under the MIT software license, see the accompanying
+// file COPYING or http://www.opensource.org/licenses/mit-license.php.
+
+#include <span.h>
+#include <test/fuzz/FuzzedDataProvider.h>
+#include <test/fuzz/fuzz.h>
+#include <test/fuzz/util.h>
+
+#include <cassert>
+#include <cstddef>
+#include <cstdint>
+#include <string>
+#include <vector>
+
+void test_one_input(const std::vector<uint8_t>& buffer)
+{
+    FuzzedDataProvider fuzzed_data_provider(buffer.data(), buffer.size());
+
+    std::string str = fuzzed_data_provider.ConsumeBytesAsString(32);
+    const Span<const char> span = MakeSpan(str);
+    (void)span.data();
+    (void)span.begin();
+    (void)span.end();
+    if (span.size() > 0) {
+        const std::ptrdiff_t idx = fuzzed_data_provider.ConsumeIntegralInRange<std::ptrdiff_t>(0U, span.size() - 1U);
+        (void)span.first(idx);
+        (void)span.last(idx);
+        (void)span.subspan(idx);
+        (void)span.subspan(idx, span.size() - idx);
+        (void)span[idx];
+    }
+
+    std::string another_str = fuzzed_data_provider.ConsumeBytesAsString(32);
+    const Span<const char> another_span = MakeSpan(another_str);
+    assert((span <= another_span) != (span > another_span));
+    assert((span == another_span) != (span != another_span));
+    assert((span >= another_span) != (span < another_span));
+}