Merge #18029: tests: Add fuzzing harness for AS-mapping (asmap)

4d2aceaad8 tests: Add fuzzer asmap to FUZZERS_MISSING_CORPORA (temporarily) (practicalswift)
8d07706985 tests: Add fuzzing harness for AS-mapping (asmap) (practicalswift)

Pull request description:

  Add fuzzing harness for AS-mapping (`asmap`).

  To test this PR:

  ```
  $ make distclean
  $ ./autogen.sh
  $ CC=clang CXX=clang++ ./configure --enable-fuzz \
        --with-sanitizers=address,fuzzer,undefined
  $ make
  $ src/test/fuzz/asmap
  …
  ```

ACKs for top commit:
  MarcoFalke:
    ACK 4d2aceaad8
  jonatack:
    ACK 4d2aceaad8

Tree-SHA512: bc4c63b48cd98c0cec9d10ecb43775b1bf1215241ff821fc7a866c7e2738605641fb88d044eabf2f48a8c16f2ced9ffce5165c9e6a83c73ece004350da7153e7

src/test/fuzz/asmap.cpp

@@ -0,0 +1,28 @@
+// 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 <netaddress.h>
+#include <test/fuzz/FuzzedDataProvider.h>
+#include <test/fuzz/fuzz.h>
+
+#include <cstdint>
+#include <vector>
+
+void test_one_input(const std::vector<uint8_t>& buffer)
+{
+    FuzzedDataProvider fuzzed_data_provider(buffer.data(), buffer.size());
+    const Network network = fuzzed_data_provider.PickValueInArray({NET_IPV4, NET_IPV6});
+    if (fuzzed_data_provider.remaining_bytes() < 16) {
+        return;
+    }
+    CNetAddr net_addr;
+    net_addr.SetRaw(network, fuzzed_data_provider.ConsumeBytes<uint8_t>(16).data());
+    std::vector<bool> asmap;
+    for (const char cur_byte : fuzzed_data_provider.ConsumeRemainingBytes<char>()) {
+        for (int bit = 0; bit < 8; ++bit) {
+            asmap.push_back((cur_byte >> bit) & 1);
+        }
+    }
+    (void)net_addr.GetMappedAS(asmap);
+}