Merge bitcoin/bitcoin#28060: util: Teach AutoFile how to XOR

fa633aa streams: Teach AutoFile how to XOR (MarcoFalke)
000019e Add AutoFile::detail_fread member function (MarcoFalke)
fa7724b refactor: Modernize AutoFile (MarcoFalke)
fa8d227 doc: Remove comments that just repeat what the code does (MarcoFalke)
fafe2ca refactor: Remove redundant file check from AutoFile shift operators (MarcoFalke)
9999a49 Extract util::Xor, Add key_offset option, Add bench (MarcoFalke)

Pull request description:

  This allows `AutoFile` to roll an XOR pattern while reading or writing to the underlying file.

  This is needed for bitcoin/bitcoin#28052, but can also be used in any other place.

  Also, there are tests, so I've split this up from the larger pull to make review easier, hopefully.

ACKs for top commit:
  Crypt-iQ:
    crACK fa633aa
  willcl-ark:
    Lightly tested ACK fa633aa
  jamesob:
    reACK fa633aa ([`jamesob/ackr/28060.4.MarcoFalke.util_add_xorfile`](https://github.com/jamesob/bitcoin/tree/ackr/28060.4.MarcoFalke.util_add_xorfile))

Tree-SHA512: 6d66cad0a089a096d3f95e4f2b28bce80b349d4b76f53d09dc9a0bea4fc1b7c0652724469c37971ba27728c7d46398a4c1d289c252af4c0f83bb2fcbc6f8e90b

Author: fanquake

src/Makefile.am

@@ -717,6 +717,7 @@ libbitcoin_util_a_SOURCES = \
   logging.cpp \
   random.cpp \
   randomenv.cpp \
+  streams.cpp \
   support/cleanse.cpp \
   sync.cpp \
   util/asmap.cpp \
@@ -959,6 +960,7 @@ libbitcoinkernel_la_SOURCES = \
   script/sigcache.cpp \
   script/standard.cpp \
   signet.cpp \
+  streams.cpp \
   support/cleanse.cpp \
   support/lockedpool.cpp \
   sync.cpp \

src/Makefile.bench.include

@@ -52,7 +52,8 @@ bench_bench_bitcoin_SOURCES = \
   bench/streams_findbyte.cpp \
   bench/strencodings.cpp \
   bench/util_time.cpp \
-  bench/verify_script.cpp
+  bench/verify_script.cpp \
+  bench/xor.cpp
 
 nodist_bench_bench_bitcoin_SOURCES = $(GENERATED_BENCH_FILES)
 

src/bench/bench.h

@@ -14,7 +14,7 @@
 #include <string>
 #include <vector>
 
-#include <bench/nanobench.h>
+#include <bench/nanobench.h> // IWYU pragma: export
 
 /*
  * Usage:

src/bench/xor.cpp

@@ -0,0 +1,24 @@
+// Copyright (c) The Bitcoin Core developers
+// Distributed under the MIT software license, see the accompanying
+// file COPYING or https://opensource.org/license/mit/.
+
+#include <bench/bench.h>
+
+#include <random.h>
+#include <streams.h>
+
+#include <cstddef>
+#include <vector>
+
+static void Xor(benchmark::Bench& bench)
+{
+    FastRandomContext frc{/*fDeterministic=*/true};
+    auto data{frc.randbytes<std::byte>(1024)};
+    auto key{frc.randbytes<std::byte>(31)};
+
+    bench.batch(data.size()).unit("byte").run([&] {
+        util::Xor(data, key);
+    });
+}
+
+BENCHMARK(Xor, benchmark::PriorityLevel::HIGH);

src/hash.h

@@ -160,7 +160,6 @@ class CHashWriter : public HashWriter
 
     template<typename T>
     CHashWriter& operator<<(const T& obj) {
-        // Serialize to this stream
         ::Serialize(*this, obj);
         return (*this);
     }
@@ -228,7 +227,6 @@ class CHashVerifier : public CHashWriter
     template<typename T>
     CHashVerifier<Source>& operator>>(T&& obj)
     {
-        // Unserialize from this stream
         ::Unserialize(*this, obj);
         return (*this);
     }

src/streams.cpp

@@ -0,0 +1,66 @@
+// Copyright (c) 2009-present The Bitcoin Core developers
+// Distributed under the MIT software license, see the accompanying
+// file COPYING or https://opensource.org/license/mit/.
+
+#include <span.h>
+#include <streams.h>
+
+#include <array>
+
+std::size_t AutoFile::detail_fread(Span<std::byte> dst)
+{
+    if (!m_file) throw std::ios_base::failure("AutoFile::read: file handle is nullptr");
+    if (m_xor.empty()) {
+        return std::fread(dst.data(), 1, dst.size(), m_file);
+    } else {
+        const auto init_pos{std::ftell(m_file)};
+        if (init_pos < 0) throw std::ios_base::failure("AutoFile::read: ftell failed");
+        std::size_t ret{std::fread(dst.data(), 1, dst.size(), m_file)};
+        util::Xor(dst.subspan(0, ret), m_xor, init_pos);
+        return ret;
+    }
+}
+
+void AutoFile::read(Span<std::byte> dst)
+{
+    if (detail_fread(dst) != dst.size()) {
+        throw std::ios_base::failure(feof() ? "AutoFile::read: end of file" : "AutoFile::read: fread failed");
+    }
+}
+
+void AutoFile::ignore(size_t nSize)
+{
+    if (!m_file) throw std::ios_base::failure("AutoFile::ignore: file handle is nullptr");
+    unsigned char data[4096];
+    while (nSize > 0) {
+        size_t nNow = std::min<size_t>(nSize, sizeof(data));
+        if (std::fread(data, 1, nNow, m_file) != nNow) {
+            throw std::ios_base::failure(feof() ? "AutoFile::ignore: end of file" : "AutoFile::ignore: fread failed");
+        }
+        nSize -= nNow;
+    }
+}
+
+void AutoFile::write(Span<const std::byte> src)
+{
+    if (!m_file) throw std::ios_base::failure("AutoFile::write: file handle is nullptr");
+    if (m_xor.empty()) {
+        if (std::fwrite(src.data(), 1, src.size(), m_file) != src.size()) {
+            throw std::ios_base::failure("AutoFile::write: write failed");
+        }
+    } else {
+        auto current_pos{std::ftell(m_file)};
+        if (current_pos < 0) throw std::ios_base::failure("AutoFile::write: ftell failed");
+        std::array<std::byte, 4096> buf;
+        while (src.size() > 0) {
+            auto buf_now{Span{buf}.first(std::min<size_t>(src.size(), buf.size()))};
+            std::copy(src.begin(), src.begin() + buf_now.size(), buf_now.begin());
+            util::Xor(buf_now, m_xor, current_pos);
+            if (std::fwrite(buf_now.data(), 1, buf_now.size(), m_file) != buf_now.size()) {
+                throw std::ios_base::failure{"XorFile::write: failed"};
+            }
+            src = src.subspan(buf_now.size());
+            current_pos += buf_now.size();
+        }
+    }
+}