Merge bitcoin/bitcoin#22029: [fuzz] Improve transport deserialization fuzz test coverage

e33714557747dd479f123425aa2dd08d272ef377 [fuzz] Occasional valid magic bytes for transport serialization test (Dhruv Mehta)
35571d8d9ec112bd7b6741d10052dded08410c77 [fuzz] Occasional valid checksum for transport serialization fuzz test (Dhruv Mehta)
654472a461bc9d1603c46dcb7a5b2dc87a44045a [fuzz] Add serialization to deserialization test (Dhruv Mehta)

Pull request description:

  This PR has 3 commits that increase the fuzz test coverage:

  Before commit 1:
  ```
  #306853 REDUCE cov: 798 ft: 5820 corp: 150/375Kb lim: 68333 exec/s: 1382 rss: 461Mb L: 254/63171 MS: 1 EraseBytes-
  #1453105 REDUCE cov: 798 ft: 5820 corp: 150/369Kb lim: 79613 exec/s: 1467 rss: 461Mb L: 6027/60873 MS: 1 EraseBytes-
  ```

  After commit 1 (adds serialization to de-serialization test):
  ```
  #303389 NEW cov: 1202 ft: 8382 corp: 157/382Kb lim: 68189 exec/s: 1451 rss: 447Mb L: 1386/65459 MS: 1 CopyPart-
  #1428759 REDUCE cov: 1202 ft: 8512 corp: 169/389Kb lim: 78749 exec/s: 1528 rss: 463Mb L: 1627/60488 MS: 1 EraseBytes-
  ```

  After commit 2 (provides an occasional checksum assist to the fuzzer inputs):
  ```
  #304820 NEW cov: 1440 ft: 4452 corp: 92/12551b lim: 2237 exec/s: 3386 rss: 486Mb L: 47/1111 MS: 1 ChangeByte-
  #1416181 REDUCE cov: 1442 ft: 5681 corp: 125/59Kb lim: 4096 exec/s: 3522 rss: 535Mb L: 2164/4049 MS: 1 EraseBytes-
  ```

  After commit 3 (provides an occasional magic bytes assist to the fuzzer inputs):
  ```
  #302684 NEW cov: 1454 ft: 3936 corp: 84/7056b lim: 2424 exec/s: 4146 rss: 477Mb L: 65/1108 MS: 3 CopyPart-CrossOver-CMP- DE: "\x0e\x00\x00\x00"-
  #1383925 REDUCE cov: 1454 ft: 4828 corp: 102/14573b lim: 4096 exec/s: 3954 rss: 534Mb L: 116/4050 MS: 2 EraseBytes-ChangeByte-
  ```

  If reviewers only accept the first commit, the seeds are not invalidated and new seeds are at: https://github.com/bitcoin-core/qa-assets/pull/61. In this case, we can also revert the test name change.

  If reviewers accept all three commits, the existing seeds are invalidated.

ACKs for top commit:
  practicalswift:
    Tested ACK e33714557747dd479f123425aa2dd08d272ef377

Tree-SHA512: d37f06eea0249322b00a99c4827359eb53aeb711751e5571f4681eeca06dc257e0c4cd4887150fc37cc2f689e26986112d768066ad274361615ba9b6a522c61a

2 files changed, 85 insertions, 43 deletions

diff --git a/src/test/fuzz/p2p_transport_deserializer.cpp b/src/test/fuzz/p2p_transport_deserializer.cpp
deleted file mode 100644
index 3a1fdaad8f..0000000000
--- a/src/test/fuzz/p2p_transport_deserializer.cpp
+++ /dev/null
@@ -1,43 +0,0 @@
-// Copyright (c) 2019-2020 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 <chainparams.h>
-#include <net.h>
-#include <protocol.h>
-#include <test/fuzz/fuzz.h>
-
-#include <cassert>
-#include <cstdint>
-#include <limits>
-#include <optional>
-#include <vector>
-
-void initialize_p2p_transport_deserializer()
-{
-    SelectParams(CBaseChainParams::REGTEST);
-}
-
-FUZZ_TARGET_INIT(p2p_transport_deserializer, initialize_p2p_transport_deserializer)
-{
-    // Construct deserializer, with a dummy NodeId
-    V1TransportDeserializer deserializer{Params(), (NodeId)0, SER_NETWORK, INIT_PROTO_VERSION};
-    Span<const uint8_t> msg_bytes{buffer};
-    while (msg_bytes.size() > 0) {
-        const int handled = deserializer.Read(msg_bytes);
-        if (handled < 0) {
-            break;
-        }
-        if (deserializer.Complete()) {
-            const std::chrono::microseconds m_time{std::numeric_limits<int64_t>::max()};
-            uint32_t out_err_raw_size{0};
-            std::optional<CNetMessage> result{deserializer.GetMessage(m_time, out_err_raw_size)};
-            if (result) {
-                assert(result->m_command.size() <= CMessageHeader::COMMAND_SIZE);
-                assert(result->m_raw_message_size <= buffer.size());
-                assert(result->m_raw_message_size == CMessageHeader::HEADER_SIZE + result->m_message_size);
-                assert(result->m_time == m_time);
-            }
-        }
-    }
-}
diff --git a/src/test/fuzz/p2p_transport_serialization.cpp b/src/test/fuzz/p2p_transport_serialization.cpp
new file mode 100644
index 0000000000..edee5aeef7
--- /dev/null
+++ b/src/test/fuzz/p2p_transport_serialization.cpp
@@ -0,0 +1,85 @@
+// Copyright (c) 2019-2020 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 <chainparams.h>
+#include <hash.h>
+#include <net.h>
+#include <netmessagemaker.h>
+#include <protocol.h>
+#include <test/fuzz/FuzzedDataProvider.h>
+#include <test/fuzz/fuzz.h>
+
+#include <cassert>
+#include <cstdint>
+#include <limits>
+#include <optional>
+#include <vector>
+
+void initialize_p2p_transport_serialization()
+{
+    SelectParams(CBaseChainParams::REGTEST);
+}
+
+FUZZ_TARGET_INIT(p2p_transport_serialization, initialize_p2p_transport_serialization)
+{
+    // Construct deserializer, with a dummy NodeId
+    V1TransportDeserializer deserializer{Params(), (NodeId)0, SER_NETWORK, INIT_PROTO_VERSION};
+    V1TransportSerializer serializer{};
+    FuzzedDataProvider fuzzed_data_provider{buffer.data(), buffer.size()};
+
+    auto checksum_assist = fuzzed_data_provider.ConsumeBool();
+    auto magic_bytes_assist = fuzzed_data_provider.ConsumeBool();
+    std::vector<uint8_t> mutable_msg_bytes;
+
+    auto header_bytes_remaining = CMessageHeader::HEADER_SIZE;
+    if (magic_bytes_assist) {
+        auto msg_start = Params().MessageStart();
+        for (size_t i = 0; i < CMessageHeader::MESSAGE_SIZE_SIZE; ++i) {
+            mutable_msg_bytes.push_back(msg_start[i]);
+        }
+        header_bytes_remaining -= CMessageHeader::MESSAGE_SIZE_SIZE;
+    }
+
+    if (checksum_assist) {
+        header_bytes_remaining -= CMessageHeader::CHECKSUM_SIZE;
+    }
+
+    auto header_random_bytes = fuzzed_data_provider.ConsumeBytes<uint8_t>(header_bytes_remaining);
+    mutable_msg_bytes.insert(mutable_msg_bytes.end(), header_random_bytes.begin(), header_random_bytes.end());
+    auto payload_bytes = fuzzed_data_provider.ConsumeRemainingBytes<uint8_t>();
+
+    if (checksum_assist && mutable_msg_bytes.size() == CMessageHeader::CHECKSUM_OFFSET) {
+        CHash256 hasher;
+        unsigned char hsh[32];
+        hasher.Write(payload_bytes);
+        hasher.Finalize(hsh);
+        for (size_t i = 0; i < CMessageHeader::CHECKSUM_SIZE; ++i) {
+           mutable_msg_bytes.push_back(hsh[i]);
+        }
+    }
+
+    mutable_msg_bytes.insert(mutable_msg_bytes.end(), payload_bytes.begin(), payload_bytes.end());
+    Span<const uint8_t> msg_bytes{mutable_msg_bytes};
+    while (msg_bytes.size() > 0) {
+        const int handled = deserializer.Read(msg_bytes);
+        if (handled < 0) {
+            break;
+        }
+        if (deserializer.Complete()) {
+            const std::chrono::microseconds m_time{std::numeric_limits<int64_t>::max()};
+            uint32_t out_err_raw_size{0};
+            std::optional<CNetMessage> result{deserializer.GetMessage(m_time, out_err_raw_size)};
+            if (result) {
+                assert(result->m_command.size() <= CMessageHeader::COMMAND_SIZE);
+                assert(result->m_raw_message_size <= mutable_msg_bytes.size());
+                assert(result->m_raw_message_size == CMessageHeader::HEADER_SIZE + result->m_message_size);
+                assert(result->m_time == m_time);
+
+                std::vector<unsigned char> header;
+                auto msg = CNetMsgMaker{result->m_recv.GetVersion()}.Make(result->m_command, MakeUCharSpan(result->m_recv));
+                serializer.prepareForTransport(msg, header);
+            }
+        }
+    }
+}