[DavidCozens]

Closes #892

What #892 found

The new tls_reconnect.feature failed on bdd-cmsis-qemu-lwip: 2 of 5 records arrived, and the three logged during the outage were reported Sent and lost.

When the collector ends a TLS session it sends a close_notify alert and then a FIN. Neither TLS stream looked at what the peer had sent before writing, so SSL_write / mbedtls_ssl_write took the record. On that lane the transport beneath, SolidSyslogLwipSocketTcpStream, peeks one byte to detect a closed peer. It saw the alert's unread bytes, took them for a live peer, and let the write through.

Investigating why the other lanes passed turned up the same gap one layer down:

• LwipRaw and PlusTcp see the FIN from the stack's connection state.
• SolidSyslogPosixTcpStream and SolidSyslogWinsockTcpStream had no closed-peer check at all, for TLS or plain TCP. They pass only on timing. The StreamSender writes each record as two Send calls: the octet-count prefix, then the message. After a FIN the prefix goes through, the collector answers with a reset, and on a local bridge or loopback that reset arrives before the second write, which fails. On a link with a real round trip both writes go out first, and the record is lost. This is the failure S35.03 fixed for LwipSocket, whose QEMU slirp hop adds enough delay to lose the race.

A probe against the oracle confirmed the stimulus is a genuine FIN on the host lanes, not a reset. Over TLS 1.3 the client receives 24 bytes (the encrypted alert) and then the FIN.

The fix

TLS streams (OpenSSL, Mbed TLS). Before writing, each reads what is waiting, through its existing Read, which already closes on any terminal result:

• an alert, an unexpected EOF or a transport teardown closes the session, and Send returns false, so the record stays with the caller;
• application data, which a collector should not send, is discarded;
• WANT_READ means the session is intact, and the write goes ahead;
• a peer that keeps sending is plainly alive, so the drain is bounded at 8 reads and the write then proceeds.

The same read consumes TLS 1.3 post-handshake messages, which would otherwise sit unread in front of a later close.

TCP streams (POSIX, Winsock). Before send, each peeks one byte with MSG_PEEK, the same check LwipSocket already makes. End-of-stream or a stack fault fails the send and closes. Data waiting, or would-block, means the peer is there, and the bytes stay for a later Read.

Fakes. SSL_read / mbedtls_ssl_read gained per-call return sequences. The Mbed TLS fake's ssl_read, SocketFake's recv and WinsockFake's recv now default to what an idle non-blocking session returns (would-block); each used to default to 0, which reads as end-of-stream.

CodeRabbit's finding (a repeated closed-session setup in the OpenSSL tests) is fixed with a fixture helper.

Known limitation, documented rather than fixed. The TCP peek cannot see a close behind bytes the peer sent that nothing has read; this applies to the POSIX, Winsock, lwIP sockets and VxWorks 6.4 streams alike. Discarding those bytes in Send would break the TLS handshake layered on top, so they are kept. In practice the queue is empty: a collector sends nothing back over TCP, and the TLS streams now drain before every write. The comments on all four checks and the four platform pages say so.

Scenario count

81 -> 82 (one new scenario, tls_reconnect.feature, @tls @buffered), as agreed on #892.

Local evidence

• bdd-cmsis-qemu-lwip, cross-built and run on QEMU (TLS fixes only): full lane set, 72 passed, 0 failed (it was 71 passed and 1 failed in CI before the fix).
• Linux BDD at the final commit: every @tcp, @udp, @tls and @mtls scenario, 82 passed, 0 failed.
• Windows BDD at the final commit, native MSVC with the OTel collector: the lane's full tag set, 80 passed, 0 failed.
• Unit tests: Linux debug, all ctest suites including OpenSslIntegrationTests; freertos-host, the Mbed TLS suites including MbedTlsIntegrationTests; native MSVC, 1682 tests.
• clang-format reflow and misra_renumber.py --apply done. Two 11.5 suppressions were moved by hand to the casts they cover, which now sit inside the new if.

Not demonstrated: a host lane losing a record over a real round trip. netem is not available in Docker Desktop's kernel, so the race argument rests on the LwipSocket history and the code, not a reproduction. The FreeRTOS+TCP and FreeRTOS on lwIP QEMU lanes were not run locally.

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Summary by CodeRabbit

• Bug Fixes
  • TLS and TCP streams now check for peer shutdown before sending. If a closed connection is detected, the send is rejected and the connection is closed rather than attempting to write.
• Tests
  • Added coverage for buffered message delivery during a TLS reconnect, including checks for all five messages and their sequence IDs.
  • Expanded checks for sending after TLS shutdown, while peer data is pending, and when TCP peers have disconnected.
• Documentation
  • Clarified how peer-close checks work and their limitations, including closes during a send or behind unread peer data.

Local review before the final push

/code-review high over the branch raised seven findings. Fixed: the OpenSSL and Mbed TLS platform pages now state the pre-write read, that it discards what it meets, and its 128-byte bound; both fakes' read-return sequences count from the moment they are installed rather than from the first read of the test; a test per TLS pack pins the bound (8 reads of 16 bytes). Three were not acted on:

• Drain loop duplicated across the two TLS packs. A shared helper would need a public header in Core/Interface for a twelve-line loop; the packs are separate by design.
• OpenSSL fake's SSL_read still answers num by default, so existing Send tests pass through the bound rather than the idle path. Changing it also changes the SSL_get_error default the handshake tests rely on; left for a test-support change of its own.
• Over TLS on POSIX and Windows a record now costs a TLS read, a TCP peek and a send. The peek is one non-blocking recv on a socket the TLS read has just drained; accepted.

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Walkthrough

TCP and TLS stream sends now check peer status before writing. Tests cover peer shutdown, queued data, and non-blocking read results. A TLS BDD scenario checks delivery of five messages with contiguous sequence IDs around a pause in connection acceptance.

Changes

TCP and TLS peer checks

Layer / File(s)	Summary
TCP peer probes before send Platform/Posix/Source/SolidSyslogPosixTcpStream.c, Platform/Windows/Source/SolidSyslogWinsockTcpStream.c, Tests/SolidSyslogPosixTcpStreamTest.cpp, Tests/SolidSyslogWinsockTcpStreamTest.cpp, Tests/Support/SocketFake.*, Tests/Support/WinsockFake.*, Tests/SocketFakeTest.cpp, Tests/WinsockFakeTest.cpp, Platform/LwipSocket/Source/SolidSyslogLwipSocketTcpStream.c, Platform/VxWorks64/Source/SolidSyslogVxWorks64TcpStream.c, docs/platforms/{lwipsocket,posix,vxworks64,windows}/index.md, misra_suppressions.txt	POSIX and Windows TCP send paths probe the peer with MSG_PEEK before sending. Tests and fakes cover available data, idle sockets, EOF, and errors. Platform notes describe probe limits. MISRA suppression references are updated.
TLS reads before writes Platform/{MbedTls,OpenSsl}/Source/*Stream.c, Tests/MbedTls/SolidSyslogMbedTlsStreamTest.cpp, Tests/SolidSyslogOpenSslStreamTest.cpp, Tests/Support/{MbedTlsFake,OpenSslFake}.*, docs/platforms/{mbedtls,openssl}/index.md, misra_suppressions.txt	Both TLS send paths read and discard data in 16-byte chunks, for up to eight reads, before writing. Tests cover shutdown and other read results. Fake TLS reads support configured return sequences.
TLS reconnect scenario Bdd/features/tls_reconnect.feature	Adds a scenario that sends one message before the acceptance pause, three during it, and one after acceptance resumes. It expects five messages over TLS with contiguous sequence IDs.

Priority: ➖ Normal

Estimated code review effort: 3 (Moderate) | ~30 minutes

Change: Bug fix · Severity of issue fixed: Medium

Possibly related issues

• cososo-ltd/solid-syslog#1055: The PR updates platform documentation about pre-send checks, record replay, and TCP and TLS limitations.

Merge Risk: 🟡 Moderate · up to 5413c

TCP streams may acknowledge records after peer closure in queued-data cases, causing record loss without replay; this should be resolved before merging.

Pre-merge checks: 2 · 1 · 1

Failed checks: 1 warning · 1 inconclusive

Check name	Status	Explanation	Resolution
Out of Scope Changes check		Issue #892 explicitly excludes an audit of the four plain-TCP transports. The PR changes SolidSyslogPosixTcpStream and SolidSyslogWinsockTcpStream, adds their production peer checks, tests, fake b…	Remove the POSIX and Winsock production changes and their supporting tests, fake changes, and documentation, unless a separate active issue adds that scope.
Linked Issues check		The PR adds the required @tls @buffered outage-and-recovery scenario in Bdd/features/tls_reconnect.feature. Both TLS production streams perform bounded pre-write reads, and the TLS tests cover pee…	Provide reviewable pass results for every lane that runs TLS, including the two unrun QEMU lanes, or confirm that those lanes do not run TLS.

Passed checks: 2 passed

Check name	Status	Explanation
Description check		The description explains the defect, implementation, tests, affected platforms, scenario-count change, limitations, and local evidence. It does not use the exact template headings, but it provides the…
Title check		The title uses Conventional Commits format and clearly states the primary change: preventing a stream from accepting a record after the collector closes the connection.

Full details: Description check

Explanation

The description explains the defect, implementation, tests, affected platforms, scenario-count change, limitations, and local evidence. It does not use the exact template headings, but it provides the required information in equivalent sections.

Full details: Out of Scope Changes check

Explanation

Issue #892 explicitly excludes an audit of the four plain-TCP transports. The PR changes SolidSyslogPosixTcpStream and SolidSyslogWinsockTcpStream, adds their production peer checks, tests, fake behaviour, and platform documentation. These changes extend beyond the linked issue's TLS scenario. The supplied evidence does not establish a separate linked requirement for them.

Resolution

Remove the POSIX and Winsock production changes and their supporting tests, fake changes, and documentation, unless a separate active issue adds that scope.

Full details: Linked Issues check

Explanation

The PR adds the required @tls @buffered outage-and-recovery scenario in Bdd/features/tls_reconnect.feature. Both TLS production streams perform bounded pre-write reads, and the TLS tests cover peer closure, discarded data, and the eight-read bound. The supplied evidence does not establish a passing result for every TLS-running lane. It states that the FreeRTOS+TCP and FreeRTOS-on-lwIP QEMU lanes were not run locally.

Resolution

Provide reviewable pass results for every lane that runs TLS, including the two unrun QEMU lanes, or confirm that those lanes do not run TLS.

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Actionable comments posted: 1

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Inline comments:
Review comments at @Tests/SolidSyslogOpenSslStreamTest.cpp:
- Around line 1389-1394: Extract the repeated immediate-peer-close setup into a
helper on the existing TEST_GROUP and use it in the separate send-refusal,
no-write, and resource-closure tests, including
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Review comments at @Platform/Posix/Source/SolidSyslogPosixTcpStream.c:
- Line 498: Update PosixTcpStream_Send so it detects a peer FIN even when input
data is queued, without discarding bytes needed by SolidSyslogStream_Read; use a
non-destructive mechanism or preserve any consumed bytes for later reads. Add
coverage for queued input followed by EOF, verifying sends return false after
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Review comments at @Platform/Windows/Source/SolidSyslogWinsockTcpStream.c:
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🟠 Major · Do not discard positive reads in the liveness probe. · SolidSyslogMbedTlsStream.c:911-918

Platform/MbedTls/Source/SolidSyslogMbedTlsStream.c:911-918
🗄️ Data Integrity & Integration | 🟠 Major | 🏗️ Heavy lift

Do not discard positive reads in the liveness probe.

When peer application data is pending, MbedTlsStream_SessionIsStillOpen calls MbedTlsStream_Read(base, discard, sizeof(discard)) and drops the returned bytes before MbedTlsStream_Send writes. A subsequent caller of Read cannot recover them. OpenSslStream_SessionIsStillOpen has the same defect.

Store positive probe results in adapter-owned pending data and return them from the next Read. Implement this correction independently in both TLS adapters because their Read and Send implementations are separate.

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Review comment at @Platform/MbedTls/Source/SolidSyslogMbedTlsStream.c around
lines 911 - 918:
Update MbedTlsStream_SessionIsStillOpen and OpenSslStream_SessionIsStillOpen so
liveness probes preserve positive reads instead of discarding peer application
data. Store probed bytes in adapter-owned pending data and make each adapter’s
next Read return them before reading more from the TLS stream; implement this
independently in both adapters, keeping their separate Read and Send paths.

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Outside diff comments:
Review comments at @Platform/MbedTls/Source/SolidSyslogMbedTlsStream.c:
- Around line 911-918: Update MbedTlsStream_SessionIsStillOpen and
OpenSslStream_SessionIsStillOpen so liveness probes preserve positive reads
instead of discarding peer application data. Store probed bytes in adapter-owned
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[DavidCozens]

On the review-body finding at SolidSyslogMbedTlsStream.c 911-918 (the TLS pre-write read discards application data; same in OpenSslStream_SessionIsStillOpen):

Confirmed, and declined on the same ground as the two TCP threads. Nothing in the library reads a TLS stream in production: StreamSender never calls Read, and the only Read callers are the TLS adapters' BIO callbacks, on the transport beneath them. Syslog over TLS (RFC 5425) carries nothing from collector to device, so the bytes the probe would buffer never arrive. Holding them in each adapter would be state for an input no deployment produces.

The probe exists to notice a close_notify or a torn-down transport before writing, which the CMSIS lane showed the write alone does not. Application data it meets on the way is discarded by design.

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Review comments at @docs/platforms/mbedtls/index.md:
- Around line 168-169: Update the read-limit description in the mbedTLS and
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16 bytes each, rather than implying it always reads 128 bytes; keep the stated
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☀️   Quality Summary

     build-linux-gcc (Whole Project): ✅ successful — 2075 passed
     build-freertos-host-tdd-plustcp (Whole Project): ✅ successful — 2960 passed
     build-linux-clang (Whole Project): ✅ successful — 1904 passed
     sanitize-linux-gcc (Whole Project): ✅ successful — 1904 passed
     integration-linux-openssl (Whole Project): ✅ successful — 45 passed
     integration-linux-mbedtls (Whole Project): ✅ successful — 69 passed
     integration-linux-littlefs (Whole Project): ✅ successful — 14 passed
     integration-windows-openssl (Whole Project): ✅ successful — 45 passed
     bdd-linux-syslog-ng (Whole Project): ✅ successful — 82 passed, 3 skipped
     bdd-windows-otel (Whole Project): ✅ successful — 80 passed, 5 skipped
     bdd-freertos-qemu-plustcp (Whole Project): ✅ successful — 72 passed, 13 skipped
     bdd-freertos-qemu-lwip (Whole Project): ✅ successful — 72 passed, 13 skipped
     bdd-cmsis-qemu-lwip (Whole Project): ✅ successful — 72 passed, 13 skipped
     build-windows-msvc (Whole Project): ✅ successful — 1712 passed
     build-linux-tunable-override (Whole Project): ✅ successful — 1904 passed
     vxworks64-host (Whole Project): ✅ successful — 2082 passed
   ⚠️   Clang-Tidy (Whole Project): No warnings
   ⚠️   CPPCheck (Whole Project): No warnings

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