util: explicitly close all AutoFiles that have been written

There is no way to report a close error from `AutoFile` destructor.
Such an error could be serious if the file has been written to because
it may mean the file is now corrupted (same as if write fails).

So, change all users of `AutoFile` that use it to write data to
explicitly close the file and handle a possible error.

src/addrdb.cpp

@@ -24,6 +24,7 @@
 #include <univalue.h>
 #include <util/fs.h>
 #include <util/fs_helpers.h>
+#include <util/syserror.h>
 #include <util/translation.h>
 
 namespace {
@@ -61,7 +62,6 @@ bool SerializeFileDB(const std::string& prefix, const fs::path& path, const Data
     FILE *file = fsbridge::fopen(pathTmp, "wb");
     AutoFile fileout{file};
     if (fileout.IsNull()) {
-        fileout.fclose();
         remove(pathTmp);
         LogError("%s: Failed to open file %s\n", __func__, fs::PathToString(pathTmp));
         return false;
@@ -69,17 +69,22 @@ bool SerializeFileDB(const std::string& prefix, const fs::path& path, const Data
 
     // Serialize
     if (!SerializeDB(fileout, data)) {
-        fileout.fclose();
+        (void)fileout.fclose();
         remove(pathTmp);
         return false;
     }
     if (!fileout.Commit()) {
-        fileout.fclose();
+        (void)fileout.fclose();
         remove(pathTmp);
         LogError("%s: Failed to flush file %s\n", __func__, fs::PathToString(pathTmp));
         return false;
     }
-    fileout.fclose();
+    if (fileout.fclose() != 0) {
+        const int errno_save{errno};
+        remove(pathTmp);
+        LogError("Failed to close file %s: %s", fs::PathToString(pathTmp), SysErrorString(errno_save));
+        return false;
+    }
 
     // replace existing file, if any, with new file
     if (!RenameOver(pathTmp, path)) {

src/bench/streams_findbyte.cpp

@@ -28,7 +28,7 @@ static void FindByte(benchmark::Bench& bench)
     });
 
     // Cleanup
-    file.fclose();
+    assert(file.fclose() == 0);
     fs::remove("streams_tmp");
 }
 

src/index/blockfilterindex.cpp

@@ -151,7 +151,7 @@ bool BlockFilterIndex::CustomCommit(CDBBatch& batch)
         LogError("%s: Failed to open filter file %d\n", __func__, pos.nFile);
         return false;
     }
-    if (!file.Commit()) {
+    if (!file.Commit() || file.fclose() != 0) {
         LogError("%s: Failed to commit filter file %d\n", __func__, pos.nFile);
         return false;
     }
@@ -205,7 +205,7 @@ size_t BlockFilterIndex::WriteFilterToDisk(FlatFilePos& pos, const BlockFilter&
             LogPrintf("%s: Failed to truncate filter file %d\n", __func__, pos.nFile);
             return 0;
         }
-        if (!last_file.Commit()) {
+        if (!last_file.Commit() || last_file.fclose() != 0) {
             LogPrintf("%s: Failed to commit filter file %d\n", __func__, pos.nFile);
             return 0;
         }
@@ -229,6 +229,12 @@ size_t BlockFilterIndex::WriteFilterToDisk(FlatFilePos& pos, const BlockFilter&
     }
 
     fileout << filter.GetBlockHash() << filter.GetEncodedFilter();
+
+    if (fileout.fclose() != 0) {
+        LogPrintf("Failed to close filter file %d: %s", pos.nFile, SysErrorString(errno));
+        return 0;
+    }
+
     return data_size;
 }
 

src/net.cpp

@@ -4012,6 +4012,11 @@ static void CaptureMessageToFile(const CAddress& addr,
     uint32_t size = data.size();
     ser_writedata32(f, size);
     f << data;
+
+    if (f.fclose() != 0) {
+        throw std::ios_base::failure(
+            strprintf("Error closing %s after write, file contents are likely incomplete", fs::PathToString(path)));
+    }
 }
 
 std::function<void(const CAddress& addr,

src/node/blockstorage.cpp

@@ -947,6 +947,7 @@ bool BlockManager::WriteBlockUndo(const CBlockUndo& blockundo, BlockValidationSt
                 LogError("OpenUndoFile failed for %s while writing block undo", pos.ToString());
                 return FatalError(m_opts.notifications, state, _("Failed to write undo data."));
             }
+            {
                 BufferedWriter fileout{file};
 
                 // Write index header
@@ -959,8 +960,17 @@ bool BlockManager::WriteBlockUndo(const CBlockUndo& blockundo, BlockValidationSt
                     // Write undo data & checksum
                     fileout << blockundo << hasher.GetHash();
                 }
+            }
 
-            fileout.flush(); // Make sure `AutoFile`/`BufferedWriter` go out of scope before we call `FlushUndoFile`
+            if (file.fclose() != 0) {
+                LogPrintLevel(BCLog::BLOCKSTORAGE,
+                              BCLog::Level::Error,
+                              "Failed to close block undo file %s: %s",
+                              pos.ToString(),
+                              SysErrorString(errno));
+                return FatalError(m_opts.notifications, state, _("Failed to close block undo file."));
+            }
+            // Make sure that the file is closed before we call `FlushUndoFile`.
         }
 
         // rev files are written in block height order, whereas blk files are written as blocks come in (often out of order)
@@ -1093,6 +1103,7 @@ FlatFilePos BlockManager::WriteBlock(const CBlock& block, int nHeight)
         m_opts.notifications.fatalError(_("Failed to write block."));
         return FlatFilePos();
     }
+    {
         BufferedWriter fileout{file};
 
         // Write index header
@@ -1100,6 +1111,18 @@ FlatFilePos BlockManager::WriteBlock(const CBlock& block, int nHeight)
         pos.nPos += STORAGE_HEADER_BYTES;
         // Write block
         fileout << TX_WITH_WITNESS(block);
+    }
+
+    if (file.fclose() != 0) {
+        LogPrintLevel(BCLog::BLOCKSTORAGE,
+                      BCLog::Level::Error,
+                      "Failed to close block file %s: %s",
+                      pos.ToString(),
+                      SysErrorString(errno));
+        m_opts.notifications.fatalError(_("Failed to close file when writing block."));
+        return FlatFilePos();
+    }
+
     return pos;
 }
 
@@ -1142,6 +1165,11 @@ static auto InitBlocksdirXorKey(const BlockManager::Options& opts)
 #endif
         )};
         xor_key_file << xor_key;
+        if (xor_key_file.fclose() != 0) {
+            throw std::runtime_error{strprintf("Error closing XOR key file %s: %s\n",
+                                               fs::PathToString(xor_key_path),
+                                               SysErrorString(errno))};
+        }
     }
     // If the user disabled the key, it must be zero.
     if (!opts.use_xor && xor_key != decltype(xor_key){}) {

src/node/mempool_persist.cpp

@@ -17,6 +17,7 @@
 #include <util/fs.h>
 #include <util/fs_helpers.h>
 #include <util/signalinterrupt.h>
+#include <util/syserror.h>
 #include <util/time.h>
 #include <validation.h>
 
@@ -168,7 +169,8 @@ bool DumpMempool(const CTxMemPool& pool, const fs::path& dump_path, FopenFn mock
 
     auto mid = SteadyClock::now();
 
-    AutoFile file{mockable_fopen_function(dump_path + ".new", "wb")};
+    const fs::path file_fspath{dump_path + ".new"};
+    AutoFile file{mockable_fopen_function(file_fspath, "wb")};
     if (file.IsNull()) {
         return false;
     }
@@ -201,7 +203,10 @@ bool DumpMempool(const CTxMemPool& pool, const fs::path& dump_path, FopenFn mock
 
         if (!skip_file_commit && !file.Commit())
             throw std::runtime_error("Commit failed");
-        file.fclose();
+        if (file.fclose() != 0) {
+            throw std::runtime_error(
+                strprintf("Error closing %s: %s", fs::PathToString(file_fspath), SysErrorString(errno)));
+        }
         if (!RenameOver(dump_path + ".new", dump_path)) {
             throw std::runtime_error("Rename failed");
         }
@@ -213,6 +218,7 @@ bool DumpMempool(const CTxMemPool& pool, const fs::path& dump_path, FopenFn mock
                   fs::file_size(dump_path));
     } catch (const std::exception& e) {
         LogInfo("Failed to dump mempool: %s. Continuing anyway.\n", e.what());
+        (void)file.fclose();
         return false;
     }
     return true;

src/policy/fees.cpp

@@ -953,8 +953,8 @@ void CBlockPolicyEstimator::Flush() {
 void CBlockPolicyEstimator::FlushFeeEstimates()
 {
     AutoFile est_file{fsbridge::fopen(m_estimation_filepath, "wb")};
-    if (est_file.IsNull() || !Write(est_file)) {
-        LogPrintf("Failed to write fee estimates to %s. Continue anyway.\n", fs::PathToString(m_estimation_filepath));
+    if (est_file.IsNull() || !Write(est_file) || est_file.fclose() != 0) {
+        LogWarning("Failed to write fee estimates to %s. Continuing anyway.", fs::PathToString(m_estimation_filepath));
     } else {
         LogPrintf("Flushed fee estimates to %s.\n", fs::PathToString(m_estimation_filepath.filename()));
     }

src/rpc/blockchain.cpp

@@ -47,6 +47,7 @@
 #include <util/check.h>
 #include <util/fs.h>
 #include <util/strencodings.h>
+#include <util/syserror.h>
 #include <util/translation.h>
 #include <validation.h>
 #include <validationinterface.h>
@@ -3217,7 +3218,10 @@ UniValue WriteUTXOSnapshot(
 
     CHECK_NONFATAL(written_coins_count == maybe_stats->coins_count);
 
-    afile.fclose();
+    if (afile.fclose() != 0) {
+        throw std::ios_base::failure(
+            strprintf("Error closing %s: %s", fs::PathToString(temppath), SysErrorString(errno)));
+    }
 
     UniValue result(UniValue::VOBJ);
     result.pushKV("coins_written", written_coins_count);

src/streams.cpp

@@ -95,6 +95,7 @@ void AutoFile::write(std::span<const std::byte> src)
             src = src.subspan(buf_now.size());
         }
     }
+    m_was_written = true;
 }
 
 void AutoFile::write_buffer(std::span<std::byte> src)

src/streams.h

@@ -6,10 +6,13 @@
 #ifndef BITCOIN_STREAMS_H
 #define BITCOIN_STREAMS_H
 
+#include <logging.h>
 #include <serialize.h>
 #include <span.h>
 #include <support/allocators/zeroafterfree.h>
+#include <util/check.h>
 #include <util/overflow.h>
+#include <util/syserror.h>
 
 #include <algorithm>
 #include <assert.h>
@@ -386,7 +389,13 @@ public:
  *
  * Will automatically close the file when it goes out of scope if not null.
  * If you're returning the file pointer, return file.release().
- * If you need to close the file early, use file.fclose() instead of fclose(file).
+ * If you need to close the file early, use autofile.fclose() instead of fclose(underlying_FILE).
+ *
+ * @note If the file has been written to, then the caller must close it
+ * explicitly with the `fclose()` method, check if it returns an error and treat
+ * such an error as if the `write()` method failed. The OS's `fclose(3)` may
+ * fail to flush to disk data that has been previously written, rendering the
+ * file corrupt.
  */
 class AutoFile
 {
@@ -394,11 +403,26 @@ protected:
     std::FILE* m_file;
     std::vector<std::byte> m_xor;
     std::optional<int64_t> m_position;
+    bool m_was_written{false};
 
 public:
     explicit AutoFile(std::FILE* file, std::vector<std::byte> data_xor={});
 
-    ~AutoFile() { fclose(); }
+    ~AutoFile()
+    {
+        if (m_was_written) {
+            // Callers that wrote to the file must have closed it explicitly
+            // with the fclose() method and checked that the close succeeded.
+            // This is because here from the destructor we have no way to signal
+            // error due to close which, after write, could mean the file is
+            // corrupted and must be handled properly at the call site.
+            Assume(IsNull());
+        }
+
+        if (fclose() != 0) {
+            LogPrintLevel(BCLog::ALL, BCLog::Level::Error, "Failed to close file: %s", SysErrorString(errno));
+        }
+    }
 
     // Disallow copies
     AutoFile(const AutoFile&) = delete;
@@ -406,7 +430,7 @@ public:
 
     bool feof() const { return std::feof(m_file); }
 
-    int fclose()
+    [[nodiscard]] int fclose()
     {
         if (auto rel{release()}) return std::fclose(rel);
         return 0;

src/test/flatfile_tests.cpp

@@ -46,6 +46,7 @@ BOOST_AUTO_TEST_CASE(flatfile_open)
     {
         AutoFile file{seq.Open(FlatFilePos(0, pos1))};
         file << LIMITED_STRING(line1, 256);
+        BOOST_REQUIRE_EQUAL(file.fclose(), 0);
     }
 
     // Attempt to append to file opened in read-only mode.
@@ -58,6 +59,7 @@ BOOST_AUTO_TEST_CASE(flatfile_open)
     {
         AutoFile file{seq.Open(FlatFilePos(0, pos2))};
         file << LIMITED_STRING(line2, 256);
+        BOOST_REQUIRE_EQUAL(file.fclose(), 0);
     }
 
     // Read text from file in read-only mode.
@@ -79,6 +81,7 @@ BOOST_AUTO_TEST_CASE(flatfile_open)
 
         file >> LIMITED_STRING(text, 256);
         BOOST_CHECK_EQUAL(text, line2);
+        BOOST_REQUIRE_EQUAL(file.fclose(), 0);
     }
 
     // Ensure another file in the sequence has no data.
@@ -86,6 +89,7 @@ BOOST_AUTO_TEST_CASE(flatfile_open)
         std::string text;
         AutoFile file{seq.Open(FlatFilePos(1, pos2))};
         BOOST_CHECK_THROW(file >> LIMITED_STRING(text, 256), std::ios_base::failure);
+        BOOST_REQUIRE_EQUAL(file.fclose(), 0);
     }
 }
 

src/test/fuzz/autofile.cpp

@@ -47,7 +47,7 @@ FUZZ_TARGET(autofile)
                 }
             },
             [&] {
-                auto_file.fclose();
+                (void)auto_file.fclose();
             },
             [&] {
                 ReadFromStream(fuzzed_data_provider, auto_file);
@@ -62,5 +62,10 @@ FUZZ_TARGET(autofile)
         if (f != nullptr) {
             fclose(f);
         }
+    } else {
+        // FuzzedFileProvider::close() is expected to fail sometimes. Don't let
+        // the destructor of AutoFile be upset by a failing fclose(). Close it
+        // explicitly (and ignore any errors) so that the destructor is a noop.
+        (void)auto_file.fclose();
     }
 }

src/test/fuzz/policy_estimator.cpp

@@ -104,5 +104,6 @@ FUZZ_TARGET(policy_estimator, .init = initialize_policy_estimator)
         AutoFile fuzzed_auto_file{fuzzed_file_provider.open()};
         block_policy_estimator.Write(fuzzed_auto_file);
         block_policy_estimator.Read(fuzzed_auto_file);
+        (void)fuzzed_auto_file.fclose();
     }
 }

src/test/fuzz/policy_estimator_io.cpp

@@ -32,4 +32,5 @@ FUZZ_TARGET(policy_estimator_io, .init = initialize_policy_estimator_io)
     if (block_policy_estimator.Read(fuzzed_auto_file)) {
         block_policy_estimator.Write(fuzzed_auto_file);
     }
+    (void)fuzzed_auto_file.fclose();
 }

src/test/fuzz/utxo_snapshot.cpp

@@ -150,6 +150,7 @@ void utxo_snapshot_fuzz(FuzzBufferType buffer)
             WriteCompactSize(outfile, 999); // index of coin
             outfile << Coin{coinbase->vout[0], /*nHeightIn=*/999, /*fCoinBaseIn=*/0};
         }
+        assert(outfile.fclose() == 0);
     }
 
     const auto ActivateFuzzedSnapshot{[&] {

src/test/streams_tests.cpp

@@ -39,6 +39,7 @@ BOOST_AUTO_TEST_CASE(xor_file)
 #endif
         AutoFile xor_file{raw_file(mode), xor_pat};
         xor_file << test1 << test2;
+        BOOST_REQUIRE_EQUAL(xor_file.fclose(), 0);
     }
     {
         // Read raw from disk
@@ -379,8 +380,8 @@ BOOST_AUTO_TEST_CASE(streams_buffered_file)
     // by the rewind window (relative to our farthest read position, 40).
     BOOST_CHECK(bf.GetPos() <= 30U);
 
-    // We can explicitly close the file, or the destructor will do it.
-    file.fclose();
+    // Explicitly close the file and check that the close succeeds.
+    BOOST_REQUIRE_EQUAL(file.fclose(), 0);
 
     fs::remove(streams_test_filename);
 }
@@ -430,7 +431,7 @@ BOOST_AUTO_TEST_CASE(streams_buffered_file_skip)
     bf.SkipTo(13);
     BOOST_CHECK_EQUAL(bf.GetPos(), 13U);
 
-    file.fclose();
+    BOOST_REQUIRE_EQUAL(file.fclose(), 0);
     fs::remove(streams_test_filename);
 }
 
@@ -551,6 +552,7 @@ BOOST_AUTO_TEST_CASE(streams_buffered_file_rand)
             if (maxPos < currentPos)
                 maxPos = currentPos;
         }
+        BOOST_REQUIRE_EQUAL(file.fclose(), 0);
     }
     fs::remove(streams_test_filename);
 }
@@ -566,7 +568,9 @@ BOOST_AUTO_TEST_CASE(buffered_reader_matches_autofile_random_content)
 
     // Write out the file with random content
     {
-        AutoFile{test_file.Open(pos, /*read_only=*/false), obfuscation}.write(m_rng.randbytes<std::byte>(file_size));
+        AutoFile f{test_file.Open(pos, /*read_only=*/false), obfuscation};
+        f.write(m_rng.randbytes<std::byte>(file_size));
+        BOOST_REQUIRE_EQUAL(f.fclose(), 0);
     }
     BOOST_CHECK_EQUAL(fs::file_size(test_file.FileName(pos)), file_size);
 
@@ -623,6 +627,7 @@ BOOST_AUTO_TEST_CASE(buffered_writer_matches_autofile_random_content)
         AutoFile direct_file{test_direct.Open(pos, /*read_only=*/false), obfuscation};
 
         AutoFile buffered_file{test_buffered.Open(pos, /*read_only=*/false), obfuscation};
+        {
             BufferedWriter buffered{buffered_file, buf_size};
 
             for (size_t total_written{0}; total_written < file_size;) {
@@ -634,7 +639,9 @@ BOOST_AUTO_TEST_CASE(buffered_writer_matches_autofile_random_content)
 
                 total_written += write_size;
             }
-        // Destructors of AutoFile and BufferedWriter will flush/close here
+        }
+        BOOST_REQUIRE_EQUAL(buffered_file.fclose(), 0);
+        BOOST_REQUIRE_EQUAL(direct_file.fclose(), 0);
     }
 
     // Compare the resulting files

src/test/util/chainstate.h

@@ -48,7 +48,7 @@ CreateAndActivateUTXOSnapshot(
     AutoFile auto_outfile{outfile};
 
     UniValue result = CreateUTXOSnapshot(
-        node, node.chainman->ActiveChainstate(), auto_outfile, snapshot_path, snapshot_path);
+        node, node.chainman->ActiveChainstate(), auto_outfile, snapshot_path, snapshot_path); // Will close auto_outfile.
     LogPrintf(
         "Wrote UTXO snapshot to %s: %s\n", fs::PathToString(snapshot_path.make_preferred()), result.write());
 

src/wallet/test/fuzz/wallet_bdb_parser.cpp

@@ -45,6 +45,7 @@ FUZZ_TARGET(wallet_bdb_parser, .init = initialize_wallet_bdb_parser)
     {
         AutoFile outfile{fsbridge::fopen(wallet_path, "wb")};
         outfile << std::span{buffer};
+        assert(outfile.fclose() == 0);
     }
 
     const DatabaseOptions options{};