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fix(ssh): tear down tunnel relay on socket hangup instead of busy-spinning (#1769) #1772

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Merged
datlechin merged 2 commits into from
Jun 27, 2026
Merged

fix(ssh): tear down tunnel relay on socket hangup instead of busy-spinning (#1769) #1772

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71806a4
fix(ssh): tear down tunnel relay on socket hangup instead of busy-spi…
datlechin Jun 26, 2026
442bf4f
refactor(ssh): detect transport EOF directly and propagate write-path…
datlechin Jun 26, 2026
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4 changes: 4 additions & 0 deletions CHANGELOG.md
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Expand Up @@ -7,6 +7,10 @@ and this project adheres to [Semantic Versioning](https://semver.org/spec/v2.0.0

## [Unreleased]

### Fixed

- SSH tunnels no longer pin a CPU core after the connection drops. A dropped tunnel is now detected and torn down instead of spinning in its relay loop. (#1769)

## [0.53.0] - 2026-06-25

### Added
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41 changes: 41 additions & 0 deletions TablePro/Core/SSH/LibSSH2ChannelIO.swift
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@@ -0,0 +1,41 @@
//
// LibSSH2ChannelIO.swift
// TablePro
//

import Foundation

import CLibSSH2

/// Routes channel reads/writes through the serial `sessionQueue` because libssh2
/// is not thread-safe per session. Maps libssh2 return codes to the transport
/// agnostic results consumed by `SSHChannelRelay`.
internal struct LibSSH2ChannelIO: SSHChannelIO {
let channel: OpaquePointer
let session: OpaquePointer
let sessionQueue: DispatchQueue

func read(into buffer: UnsafeMutablePointer<CChar>, count: Int) -> ChannelReadResult {
let result = sessionQueue.sync { Int(tablepro_libssh2_channel_read(channel, buffer, count)) }
if result > 0 { return .bytes(result) }
if result == 0 { return .closed }
if sessionQueue.sync(execute: { libssh2_channel_eof(channel) }) != 0 { return .closed }
if result == Int(LIBSSH2_ERROR_EAGAIN) { return .wouldBlock }
return .closed
}

func write(_ buffer: UnsafePointer<CChar>, count: Int) -> ChannelWriteResult {
let result = sessionQueue.sync { Int(tablepro_libssh2_channel_write(channel, buffer, count)) }
if result > 0 { return .bytes(result) }
if result == Int(LIBSSH2_ERROR_EAGAIN) { return .wouldBlock }
return .closed
}

func blockDirections() -> RelayDirections {
let directions = sessionQueue.sync { libssh2_session_block_directions(session) }
var result: RelayDirections = []
if directions & LIBSSH2_SESSION_BLOCK_INBOUND != 0 { result.insert(.inbound) }
if directions & LIBSSH2_SESSION_BLOCK_OUTBOUND != 0 { result.insert(.outbound) }
return result
}
}
89 changes: 17 additions & 72 deletions TablePro/Core/SSH/LibSSH2Tunnel.swift
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Expand Up @@ -350,82 +350,27 @@ internal final class LibSSH2Tunnel: @unchecked Sendable {

/// Blocking relay loop. Runs on `relayQueue`; libssh2 calls go through `sessionQueue`.
private func runRelay(clientFD: Int32, channel: OpaquePointer) {
let buffer = UnsafeMutablePointer<CChar>.allocate(capacity: Self.relayBufferSize)
defer {
buffer.deallocate()
Darwin.close(clientFD)
if self.isRunning {
sessionQueue.sync {
libssh2_channel_close(channel)
libssh2_channel_free(channel)
}
}
}
let relay = SSHChannelRelay(
localFD: clientFD,
transportFD: socketFD,
channelIO: LibSSH2ChannelIO(channel: channel, session: session, sessionQueue: sessionQueue),
bufferSize: Self.relayBufferSize,
isActive: { [weak self] in self?.isRunning ?? false }
)

while self.isRunning {
var pollFDs = [
pollfd(fd: clientFD, events: Int16(POLLIN), revents: 0),
pollfd(fd: self.socketFD, events: Int16(POLLIN), revents: 0),
]
let termination = relay.run()

let pollResult = poll(&pollFDs, 2, 500) // 500ms timeout
if pollResult < 0 { break }
Darwin.close(clientFD)
guard self.isRunning else { return }

// Read from SSH channel when the SSH socket has data or on timeout
// (libssh2 may have internally buffered data)
if pollFDs[1].revents & Int16(POLLIN) != 0 || pollResult == 0 {
let readResult: Int = sessionQueue.sync {
Int(tablepro_libssh2_channel_read(channel, buffer, Self.relayBufferSize))
}
if readResult > 0 {
var totalSent = 0
while totalSent < readResult {
let sent = send(
clientFD,
buffer.advanced(by: totalSent),
readResult - totalSent,
0
)
if sent <= 0 { return }
totalSent += sent
}
} else if readResult == 0 || sessionQueue.sync(execute: { libssh2_channel_eof(channel) }) != 0 {
return
} else if readResult != Int(LIBSSH2_ERROR_EAGAIN) {
return
}
}
sessionQueue.sync {
libssh2_channel_close(channel)
libssh2_channel_free(channel)
}

// Read from client -> write to SSH channel
if pollFDs[0].revents & Int16(POLLIN) != 0 {
let clientRead = recv(clientFD, buffer, Self.relayBufferSize, 0)
if clientRead <= 0 { return }

var totalWritten = 0
while totalWritten < Int(clientRead) {
let written: Int = sessionQueue.sync {
Int(tablepro_libssh2_channel_write(
channel,
buffer.advanced(by: totalWritten),
Int(clientRead) - totalWritten
))
}
if written > 0 {
totalWritten += written
} else if written == Int(LIBSSH2_ERROR_EAGAIN) {
let directions = sessionQueue.sync {
libssh2_session_block_directions(self.session)
}
_ = self.waitForSocketDirections(
directions: directions,
socketFD: self.socketFD,
timeoutMs: 1_000
)
} else {
return
}
}
}
if termination == .transportHangup {
Self.logger.info("SSH transport hung up, marking tunnel dead for \(self.connectionId)")
markDead()
}
}

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82 changes: 15 additions & 67 deletions TablePro/Core/SSH/LibSSH2TunnelFactory.swift
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Expand Up @@ -735,75 +735,23 @@ internal enum LibSSH2TunnelFactory {
return Task.detached {
await withCheckedContinuation { (continuation: CheckedContinuation<Void, Never>) in
relayQueue.async {
let bufferSize = 32_768
let buffer = UnsafeMutablePointer<CChar>.allocate(capacity: bufferSize)
defer {
buffer.deallocate()
Darwin.close(socketFD)
continuation.resume()
}

while !Task.isCancelled {
var pollFDs = [
pollfd(fd: socketFD, events: Int16(POLLIN), revents: 0),
pollfd(fd: sshSocketFD, events: Int16(POLLIN), revents: 0),
]
let relay = SSHChannelRelay(
localFD: socketFD,
transportFD: sshSocketFD,
channelIO: LibSSH2ChannelIO(
channel: channel,
session: session,
sessionQueue: sessionQueue
),
bufferSize: 32_768,
isActive: { !Task.isCancelled }
)

let pollResult = poll(&pollFDs, 2, 500)
if pollResult < 0 { break }
_ = relay.run()

// Channel -> socketpair (serialized libssh2 call)
if pollFDs[1].revents & Int16(POLLIN) != 0 || pollResult == 0 {
let channelRead: Int = sessionQueue.sync {
Int(tablepro_libssh2_channel_read(channel, buffer, bufferSize))
}
if channelRead > 0 {
var totalSent = 0
while totalSent < channelRead {
let sent = send(
socketFD,
buffer.advanced(by: totalSent),
channelRead - totalSent,
0
)
if sent <= 0 { return }
totalSent += sent
}
} else if channelRead == 0
|| sessionQueue.sync(execute: { libssh2_channel_eof(channel) }) != 0 {
return
} else if channelRead != Int(LIBSSH2_ERROR_EAGAIN) {
return
}
}

// Socketpair -> channel
if pollFDs[0].revents & Int16(POLLIN) != 0 {
let socketRead = recv(socketFD, buffer, bufferSize, 0)
if socketRead <= 0 { return }

var totalWritten = 0
while totalWritten < Int(socketRead) {
let written: Int = sessionQueue.sync {
Int(tablepro_libssh2_channel_write(
channel,
buffer.advanced(by: totalWritten),
Int(socketRead) - totalWritten
))
}
if written > 0 {
totalWritten += written
} else if written == Int(LIBSSH2_ERROR_EAGAIN) {
var writePollFD = pollfd(
fd: sshSocketFD, events: Int16(POLLOUT), revents: 0
)
_ = poll(&writePollFD, 1, 1_000)
} else {
return
}
}
}
}
shutdown(socketFD, SHUT_RDWR)
Darwin.close(socketFD)
continuation.resume()
}
}
}
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20 changes: 20 additions & 0 deletions TablePro/Core/SSH/RelayPollState.swift
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@@ -0,0 +1,20 @@
//
// RelayPollState.swift
// TablePro
//

import Foundation

internal enum RelayFDState: Equatable {
case idle
case readable
case drainThenStop
case stop
}

internal func relayFDState(_ revents: Int16) -> RelayFDState {
if revents & Int16(POLLERR | POLLNVAL) != 0 { return .stop }
if revents & Int16(POLLHUP) != 0 { return .drainThenStop }
if revents & Int16(POLLIN) != 0 { return .readable }
return .idle
}
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