Merge bitcoin/bitcoin#26909: net: prevent peers.dat corruptions by only serializing once

5eabb61 addrdb: Only call Serialize() once (Martin Zumsande)
da6c7ae hash: add HashedSourceWriter (Martin Zumsande)

Pull request description:

  There have been various reports of corruption of `peers.dat` recently, see #26599.
  As explained in [this post](bitcoin/bitcoin#26599 (comment)) in more detail, the underlying issue is likely that we currently serialize `AddrMan` twice - once for the file stream, once for the hasher that helps create the checksum - and if `AddrMan` changes in between these two calls, the checksum doesn't match the data and the resulting `peers.dat` is corrupted.

  This PR attempts to fix this by introducing and using `HashedSourceWriter` - a class that keeps a running hash while serializing data, similar to the existing `CHashVerifier` which does the analogous thing while unserializing data. Something like this was suggested before, see bitcoin/bitcoin#10248 (comment).

  Fixes #26599 (not by changing the behavior in case of a crash, but by hopefully fixing the underlying cause of these corruptions).

ACKs for top commit:
  sipa:
    utACK 5eabb61
  naumenkogs:
    utACK 5eabb61

Tree-SHA512: f19ad37c37088d3a9825c60de2efe85cc2b7a21b79b9156024d33439e021443ef977a5f8424a7981bcc13d73d11e30eaa82de60e14d88b3568a67b03e02b153b

Author: MarcoFalke

src/addrdb.cpp

@@ -34,10 +34,9 @@ bool SerializeDB(Stream& stream, const Data& data)
 {
     // Write and commit header, data
     try {
-        CHashWriter hasher(stream.GetType(), stream.GetVersion());
-        stream << Params().MessageStart() << data;
-        hasher << Params().MessageStart() << data;
-        stream << hasher.GetHash();
+        HashedSourceWriter hashwriter{stream};
+        hashwriter << Params().MessageStart() << data;
+        stream << hashwriter.GetHash();
     } catch (const std::exception& e) {
         return error("%s: Serialize or I/O error - %s", __func__, e.what());
     }

src/addrman.cpp

@@ -1178,8 +1178,7 @@ void AddrMan::Unserialize(Stream& s_)
 }
 
 // explicit instantiation
-template void AddrMan::Serialize(CHashWriter& s) const;
-template void AddrMan::Serialize(CAutoFile& s) const;
+template void AddrMan::Serialize(HashedSourceWriter<CAutoFile>& s) const;
 template void AddrMan::Serialize(CDataStream& s) const;
 template void AddrMan::Unserialize(CAutoFile& s);
 template void AddrMan::Unserialize(CHashVerifier<CAutoFile>& s);

src/hash.h

@@ -6,6 +6,7 @@
 #ifndef BITCOIN_HASH_H
 #define BITCOIN_HASH_H
 
+#include <attributes.h>
 #include <crypto/common.h>
 #include <crypto/ripemd160.h>
 #include <crypto/sha256.h>
@@ -199,6 +200,30 @@ class CHashVerifier : public CHashWriter
     }
 };
 
+/** Writes data to an underlying source stream, while hashing the written data. */
+template <typename Source>
+class HashedSourceWriter : public CHashWriter
+{
+private:
+    Source& m_source;
+
+public:
+    explicit HashedSourceWriter(Source& source LIFETIMEBOUND) : CHashWriter{source.GetType(), source.GetVersion()}, m_source{source} {}
+
+    void write(Span<const std::byte> src)
+    {
+        m_source.write(src);
+        CHashWriter::write(src);
+    }
+
+    template <typename T>
+    HashedSourceWriter& operator<<(const T& obj)
+    {
+        ::Serialize(*this, obj);
+        return *this;
+    }
+};
+
 /** Compute the 256-bit hash of an object's serialization. */
 template<typename T>
 uint256 SerializeHash(const T& obj, int nType=SER_GETHASH, int nVersion=PROTOCOL_VERSION)

src/test/streams_tests.cpp

@@ -500,4 +500,18 @@ BOOST_AUTO_TEST_CASE(streams_buffered_file_rand)
     fs::remove(streams_test_filename);
 }
 
+BOOST_AUTO_TEST_CASE(streams_hashed)
+{
+    CDataStream stream(SER_NETWORK, INIT_PROTO_VERSION);
+    HashedSourceWriter hash_writer{stream};
+    const std::string data{"bitcoin"};
+    hash_writer << data;
+
+    CHashVerifier hash_verifier{&stream};
+    std::string result;
+    hash_verifier >> result;
+    BOOST_CHECK_EQUAL(data, result);
+    BOOST_CHECK_EQUAL(hash_writer.GetHash(), hash_verifier.GetHash());
+}
+
 BOOST_AUTO_TEST_SUITE_END()