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📄 CHANGELOG.md # CHANGELOG ## v0.4.1 - [Bug Fix] [commit](https://github.com/mdlayher/socket/commit/2a14ceef4da279de1f957c5761fffcc6c87bbd3b): ensure `socket.Conn` can be used with non-socket file descriptors by handling `ENOTSOCK` in the constructor. ## v0.4.0 This is the first release of package socket that only supports Go 1.18+. Users on older versions of Go must use v0.3.0. - [Improvement]: drop support for older versions of Go so we can begin using modern versions of `x/sys` and other dependencies. ## v0.3.0 This is the last release of package socket that supports Go 1.17 and below. - [New API/API change] [PR](https://github.com/mdlayher/socket/pull/8): numerous `socket.Conn` methods now support context cancelation. Future releases will continue adding support as needed. - New `ReadContext` and `WriteContext` methods. - `Connect`, `Recvfrom`, `Recvmsg`, `Sendmsg`, and `Sendto` methods now accept a context. - `Sendto` parameter order was also fixed to match the underlying syscall. ## v0.2.3 - [New API] [commit](https://github.com/mdlayher/socket/commit/a425d96e0f772c053164f8ce4c9c825380a98086): `socket.Conn` has new `Pidfd` methods for wrapping the `pidfd_(2)` family of system calls. ## v0.2.2 - [New API] [commit](https://github.com/mdlayher/socket/commit/a2429f1dfe8ec2586df5a09f50ead865276cd027): `socket.Conn` has new `IoctlKCM*` methods for wrapping `ioctl(2)` for `AF_KCM` operations. ## v0.2.1 - [New API] [commit](https://github.com/mdlayher/socket/commit/b18ddbe9caa0e34552b4409a3aa311cb460d2f99): `socket.Conn` has a new `SetsockoptPacketMreq` method for wrapping `setsockopt(2)` for `AF_PACKET` socket options. ## v0.2.0 - [New API] [commit](https://github.com/mdlayher/socket/commit/6e912a68523c45e5fd899239f4b46c402dd856da): `socket.FileConn` can be used to create a `socket.Conn` from an existing `os.File`, which may be provided by systemd socket activation or another external mechanism. - [API change] [commit](https://github.com/mdlayher/socket/commit/66d61f565188c23fe02b24099ddc856d538bf1a7): `socket.Conn.Connect` now returns the `unix.Sockaddr` value provided by `getpeername(2)`, since we have to invoke that system call anyway to verify that a connection to a remote peer was successfully established. - [Bug Fix] [commit](https://github.com/mdlayher/socket/commit/b60b2dbe0ac3caff2338446a150083bde8c5c19c): check the correct error from `unix.GetsockoptInt` in the `socket.Conn.Connect` method. Thanks @vcabbage! ## v0.1.2 - [Bug Fix]: `socket.Conn.Connect` now properly checks the `SO_ERROR` socket option value after calling `connect(2)` to verify whether or not a connection could successfully be established. This means that `Connect` should now report an error for an `AF_INET` TCP connection refused or `AF_VSOCK` connection reset by peer. - [New API]: add `socket.Conn.Getpeername` for use in `Connect`, but also for use by external callers. ## v0.1.1 - [New API]: `socket.Conn` now has `CloseRead`, `CloseWrite`, and `Shutdown` methods. - [Improvement]: internal rework to more robustly handle various errors. ## v0.1.0 - Initial unstable release. Most functionality has been developed and ported from package [`netlink`](https://github.com/mdlayher/netlink).	3.22 KB	2025-05-25 12:27
📄 LICENSE.md # MIT License Copyright (C) 2021 Matt Layher Permission is hereby granted, free of charge, to any person obtaining a copy of this software and associated documentation files (the "Software"), to deal in the Software without restriction, including without limitation the rights to use, copy, modify, merge, publish, distribute, sublicense, and/or sell copies of the Software, and to permit persons to whom the Software is furnished to do so, subject to the following conditions: The above copyright notice and this permission notice shall be included in all copies or substantial portions of the Software. THE SOFTWARE IS PROVIDED "AS IS", WITHOUT WARRANTY OF ANY KIND, EXPRESS OR IMPLIED, INCLUDING BUT NOT LIMITED TO THE WARRANTIES OF MERCHANTABILITY, FITNESS FOR A PARTICULAR PURPOSE AND NONINFRINGEMENT. IN NO EVENT SHALL THE AUTHORS OR COPYRIGHT HOLDERS BE LIABLE FOR ANY CLAIM, DAMAGES OR OTHER LIABILITY, WHETHER IN AN ACTION OF CONTRACT, TORT OR OTHERWISE, ARISING FROM, OUT OF OR IN CONNECTION WITH THE SOFTWARE OR THE USE OR OTHER DEALINGS IN THE SOFTWARE.	1.04 KB	2025-05-25 12:27
📄 README.md # socket [![Test Status](https://github.com/mdlayher/socket/workflows/Test/badge.svg)](https://github.com/mdlayher/socket/actions) [![Go Reference](https://pkg.go.dev/badge/github.com/mdlayher/socket.svg)](https://pkg.go.dev/github.com/mdlayher/socket) [![Go Report Card](https://goreportcard.com/badge/github.com/mdlayher/socket)](https://goreportcard.com/report/github.com/mdlayher/socket) Package `socket` provides a low-level network connection type which integrates with Go's runtime network poller to provide asynchronous I/O and deadline support. MIT Licensed. This package focuses on UNIX-like operating systems which make use of BSD sockets system call APIs. It is meant to be used as a foundation for the creation of operating system-specific socket packages, for socket families such as Linux's `AF_NETLINK`, `AF_PACKET`, or `AF_VSOCK`. This package should not be used directly in end user applications. Any use of package socket should be guarded by build tags, as one would also use when importing the `syscall` or `golang.org/x/sys` packages. ## Stability See the [CHANGELOG](./CHANGELOG.md) file for a description of changes between releases. This package only supports the two most recent major versions of Go, mirroring Go's own release policy. Older versions of Go may lack critical features and bug fixes which are necessary for this package to function correctly.	1.36 KB	2025-05-25 12:27
📄 accept.go //go:build !dragonfly && !freebsd && !illumos && !linux // +build !dragonfly,!freebsd,!illumos,!linux package socket import ( "fmt" "runtime" "golang.org/x/sys/unix" ) const sysAccept = "accept" // accept wraps accept(2). func accept(fd, flags int) (int, unix.Sockaddr, error) { if flags != 0 { // These operating systems have no support for flags to accept(2). return 0, nil, fmt.Errorf("socket: Conn.Accept flags are ineffective on %s", runtime.GOOS) } return unix.Accept(fd) }	496 B	2025-05-25 12:27
📄 accept4.go //go:build dragonfly \|\| freebsd \|\| illumos \|\| linux // +build dragonfly freebsd illumos linux package socket import ( "golang.org/x/sys/unix" ) const sysAccept = "accept4" // accept wraps accept4(2). func accept(fd, flags int) (int, unix.Sockaddr, error) { return unix.Accept4(fd, flags) }	296 B	2025-05-25 12:27
📄 conn.go package socket import ( "context" "errors" "io" "os" "sync" "sync/atomic" "syscall" "time" "golang.org/x/sys/unix" ) // Lock in an expected public interface for convenience. var _ interface { io.ReadWriteCloser syscall.Conn SetDeadline(t time.Time) error SetReadDeadline(t time.Time) error SetWriteDeadline(t time.Time) error } = &Conn{} // A Conn is a low-level network connection which integrates with Go's runtime // network poller to provide asynchronous I/O and deadline support. // // Many of a Conn's blocking methods support net.Conn deadlines as well as // cancelation via context. Note that passing a context with a deadline set will // override any of the previous deadlines set by calls to the SetDeadline family // of methods. type Conn struct { // Indicates whether or not Conn.Close has been called. Must be accessed // atomically. Atomics definitions must come first in the Conn struct. closed uint32 // A unique name for the Conn which is also associated with derived file // descriptors such as those created by accept(2). name string // facts contains information we have determined about Conn to trigger // alternate behavior in certain functions. facts facts // Provides access to the underlying file registered with the runtime // network poller, and arbitrary raw I/O calls. fd os.File rc syscall.RawConn } // facts contains facts about a Conn. type facts struct { // isStream reports whether this is a streaming descriptor, as opposed to a // packet-based descriptor like a UDP socket. isStream bool // zeroReadIsEOF reports Whether a zero byte read indicates EOF. This is // false for a message based socket connection. zeroReadIsEOF bool } // A Config contains options for a Conn. type Config struct { // NetNS specifies the Linux network namespace the Conn will operate in. // This option is unsupported on other operating systems. // // If set (non-zero), Conn will enter the specified network namespace and an // error will occur in Socket if the operation fails. // // If not set (zero), a best-effort attempt will be made to enter the // network namespace of the calling thread: this means that any changes made // to the calling thread's network namespace will also be reflected in Conn. // If this operation fails (due to lack of permissions or because network // namespaces are disabled by kernel configuration), Socket will not return // an error, and the Conn will operate in the default network namespace of // the process. This enables non-privileged use of Conn in applications // which do not require elevated privileges. // // Entering a network namespace is a privileged operation (root or // CAP_SYS_ADMIN are required), and most applications should leave this set // to 0. NetNS int } // High-level methods which provide convenience over raw system calls. // Close closes the underlying file descriptor for the Conn, which also causes // all in-flight I/O operations to immediately unblock and return errors. Any // subsequent uses of Conn will result in EBADF. func (c Conn) Close() error { // The caller has expressed an intent to close the socket, so immediately // increment s.closed to force further calls to result in EBADF before also // closing the file descriptor to unblock any outstanding operations. // // Because other operations simply check for s.closed != 0, we will permit // double Close, which would increment s.closed beyond 1. if atomic.AddUint32(&c.closed, 1) != 1 { // Multiple Close calls. return nil } return os.NewSyscallError("close", c.fd.Close()) } // CloseRead shuts down the reading side of the Conn. Most callers should just // use Close. func (c Conn) CloseRead() error { return c.Shutdown(unix.SHUT_RD) } // CloseWrite shuts down the writing side of the Conn. Most callers should just // use Close. func (c Conn) CloseWrite() error { return c.Shutdown(unix.SHUT_WR) } // Read reads directly from the underlying file descriptor. func (c Conn) Read(b []byte) (int, error) { return c.fd.Read(b) } // ReadContext reads from the underlying file descriptor with added support for // context cancelation. func (c Conn) ReadContext(ctx context.Context, b []byte) (int, error) { if c.facts.isStream && len(b) > maxRW { b = b[:maxRW] } n, err := readT(c, ctx, "read", func(fd int) (int, error) { return unix.Read(fd, b) }) if n == 0 && err == nil && c.facts.zeroReadIsEOF { return 0, io.EOF } return n, os.NewSyscallError("read", err) } // Write writes directly to the underlying file descriptor. func (c Conn) Write(b []byte) (int, error) { return c.fd.Write(b) } // WriteContext writes to the underlying file descriptor with added support for // context cancelation. func (c Conn) WriteContext(ctx context.Context, b []byte) (int, error) { var ( n, nn int err error ) doErr := c.write(ctx, "write", func(fd int) error { max := len(b) if c.facts.isStream && max-nn > maxRW { max = nn + maxRW } n, err = unix.Write(fd, b[nn:max]) if n > 0 { nn += n } if nn == len(b) { return err } if n == 0 && err == nil { err = io.ErrUnexpectedEOF return nil } return err }) if doErr != nil { return 0, doErr } return nn, os.NewSyscallError("write", err) } // SetDeadline sets both the read and write deadlines associated with the Conn. func (c Conn) SetDeadline(t time.Time) error { return c.fd.SetDeadline(t) } // SetReadDeadline sets the read deadline associated with the Conn. func (c Conn) SetReadDeadline(t time.Time) error { return c.fd.SetReadDeadline(t) } // SetWriteDeadline sets the write deadline associated with the Conn. func (c Conn) SetWriteDeadline(t time.Time) error { return c.fd.SetWriteDeadline(t) } // ReadBuffer gets the size of the operating system's receive buffer associated // with the Conn. func (c Conn) ReadBuffer() (int, error) { return c.GetsockoptInt(unix.SOL_SOCKET, unix.SO_RCVBUF) } // WriteBuffer gets the size of the operating system's transmit buffer // associated with the Conn. func (c Conn) WriteBuffer() (int, error) { return c.GetsockoptInt(unix.SOL_SOCKET, unix.SO_SNDBUF) } // SetReadBuffer sets the size of the operating system's receive buffer // associated with the Conn. // // When called with elevated privileges on Linux, the SO_RCVBUFFORCE option will // be used to override operating system limits. Otherwise SO_RCVBUF is used // (which obeys operating system limits). func (c Conn) SetReadBuffer(bytes int) error { return c.setReadBuffer(bytes) } // SetWriteBuffer sets the size of the operating system's transmit buffer // associated with the Conn. // // When called with elevated privileges on Linux, the SO_SNDBUFFORCE option will // be used to override operating system limits. Otherwise SO_SNDBUF is used // (which obeys operating system limits). func (c Conn) SetWriteBuffer(bytes int) error { return c.setWriteBuffer(bytes) } // SyscallConn returns a raw network connection. This implements the // syscall.Conn interface. // // SyscallConn is intended for advanced use cases, such as getting and setting // arbitrary socket options using the socket's file descriptor. If possible, // those operations should be performed using methods on Conn instead. // // Once invoked, it is the caller's responsibility to ensure that operations // performed using Conn and the syscall.RawConn do not conflict with each other. func (c Conn) SyscallConn() (syscall.RawConn, error) { if atomic.LoadUint32(&c.closed) != 0 { return nil, os.NewSyscallError("syscallconn", unix.EBADF) } // TODO(mdlayher): mutex or similar to enforce syscall.RawConn contract of // FD remaining valid for duration of calls? return c.rc, nil } // Socket wraps the socket(2) system call to produce a Conn. domain, typ, and // proto are passed directly to socket(2), and name should be a unique name for // the socket type such as "netlink" or "vsock". // // The cfg parameter specifies optional configuration for the Conn. If nil, no // additional configuration will be applied. // // If the operating system supports SOCK_CLOEXEC and SOCK_NONBLOCK, they are // automatically applied to typ to mirror the standard library's socket flag // behaviors. func Socket(domain, typ, proto int, name string, cfg Config) (Conn, error) { if cfg == nil { cfg = &Config{} } if cfg.NetNS == 0 { // Non-Linux or no network namespace. return socket(domain, typ, proto, name) } // Linux only: create Conn in the specified network namespace. return withNetNS(cfg.NetNS, func() (Conn, error) { return socket(domain, typ, proto, name) }) } // socket is the internal, cross-platform entry point for socket(2). func socket(domain, typ, proto int, name string) (Conn, error) { var ( fd int err error ) for { fd, err = unix.Socket(domain, typ\|socketFlags, proto) switch { case err == nil: // Some OSes already set CLOEXEC with typ. if !flagCLOEXEC { unix.CloseOnExec(fd) } // No error, prepare the Conn. return New(fd, name) case !ready(err): // System call interrupted or not ready, try again. continue case err == unix.EINVAL, err == unix.EPROTONOSUPPORT: // On Linux, SOCK_NONBLOCK and SOCK_CLOEXEC were introduced in // 2.6.27. On FreeBSD, both flags were introduced in FreeBSD 10. // EINVAL and EPROTONOSUPPORT check for earlier versions of these // OSes respectively. // // Mirror what the standard library does when creating file // descriptors: avoid racing a fork/exec with the creation of new // file descriptors, so that child processes do not inherit socket // file descriptors unexpectedly. // // For a more thorough explanation, see similar work in the Go tree: // func sysSocket in net/sock_cloexec.go, as well as the detailed // comment in syscall/exec_unix.go. syscall.ForkLock.RLock() fd, err = unix.Socket(domain, typ, proto) if err != nil { syscall.ForkLock.RUnlock() return nil, os.NewSyscallError("socket", err) } unix.CloseOnExec(fd) syscall.ForkLock.RUnlock() return New(fd, name) default: // Unhandled error. return nil, os.NewSyscallError("socket", err) } } } // FileConn returns a copy of the network connection corresponding to the open // file. It is the caller's responsibility to close the file when finished. // Closing the Conn does not affect the File, and closing the File does not // affect the Conn. func FileConn(f os.File, name string) (Conn, error) { // First we'll try to do fctnl(2) with F_DUPFD_CLOEXEC because we can dup // the file descriptor and set the flag in one syscall. fd, err := unix.FcntlInt(f.Fd(), unix.F_DUPFD_CLOEXEC, 0) switch err { case nil: // OK, ready to set up non-blocking I/O. return New(fd, name) case unix.EINVAL: // The kernel rejected our fcntl(2), fall back to separate dup(2) and // setting close on exec. // // Mirror what the standard library does when creating file descriptors: // avoid racing a fork/exec with the creation of new file descriptors, // so that child processes do not inherit socket file descriptors // unexpectedly. syscall.ForkLock.RLock() fd, err := unix.Dup(fd) if err != nil { syscall.ForkLock.RUnlock() return nil, os.NewSyscallError("dup", err) } unix.CloseOnExec(fd) syscall.ForkLock.RUnlock() return New(fd, name) default: // Any other errors. return nil, os.NewSyscallError("fcntl", err) } } // New wraps an existing file descriptor to create a Conn. name should be a // unique name for the socket type such as "netlink" or "vsock". // // Most callers should use Socket or FileConn to construct a Conn. New is // intended for integrating with specific system calls which provide a file // descriptor that supports asynchronous I/O. The file descriptor is immediately // set to nonblocking mode and registered with Go's runtime network poller for // future I/O operations. // // Unlike FileConn, New does not duplicate the existing file descriptor in any // way. The returned Conn takes ownership of the underlying file descriptor. func New(fd int, name string) (Conn, error) { // All Conn I/O is nonblocking for integration with Go's runtime network // poller. Depending on the OS this might already be set but it can't hurt // to set it again. if err := unix.SetNonblock(fd, true); err != nil { return nil, os.NewSyscallError("setnonblock", err) } // os.NewFile registers the non-blocking file descriptor with the runtime // poller, which is then used for most subsequent operations except those // that require raw I/O via SyscallConn. // // See also: https://golang.org/pkg/os/#NewFile f := os.NewFile(uintptr(fd), name) rc, err := f.SyscallConn() if err != nil { return nil, err } c := &Conn{ name: name, fd: f, rc: rc, } // Probe the file descriptor for socket settings. sotype, err := c.GetsockoptInt(unix.SOL_SOCKET, unix.SO_TYPE) switch { case err == nil: // File is a socket, check its properties. c.facts = facts{ isStream: sotype == unix.SOCK_STREAM, zeroReadIsEOF: sotype != unix.SOCK_DGRAM && sotype != unix.SOCK_RAW, } case errors.Is(err, unix.ENOTSOCK): // File is not a socket, treat it as a regular file. c.facts = facts{ isStream: true, zeroReadIsEOF: true, } default: return nil, err } return c, nil } // Low-level methods which provide raw system call access. // Accept wraps accept(2) or accept4(2) depending on the operating system, but // returns a Conn for the accepted connection rather than a raw file descriptor. // // If the operating system supports accept4(2) (which allows flags), // SOCK_CLOEXEC and SOCK_NONBLOCK are automatically applied to flags to mirror // the standard library's socket flag behaviors. // // If the operating system only supports accept(2) (which does not allow flags) // and flags is not zero, an error will be returned. // // Accept obeys context cancelation and uses the deadline set on the context to // cancel accepting the next connection. If a deadline is set on ctx, this // deadline will override any previous deadlines set using SetDeadline or // SetReadDeadline. Upon return, the read deadline is cleared. func (c Conn) Accept(ctx context.Context, flags int) (Conn, unix.Sockaddr, error) { type ret struct { nfd int sa unix.Sockaddr } r, err := readT(c, ctx, sysAccept, func(fd int) (ret, error) { // Either accept(2) or accept4(2) depending on the OS. nfd, sa, err := accept(fd, flags\|socketFlags) return ret{nfd, sa}, err }) if err != nil { // internal/poll, context error, or user function error. return nil, nil, err } // Successfully accepted a connection, wrap it in a Conn for use by the // caller. ac, err := New(r.nfd, c.name) if err != nil { return nil, nil, err } return ac, r.sa, nil } // Bind wraps bind(2). func (c Conn) Bind(sa unix.Sockaddr) error { return c.control(context.Background(), "bind", func(fd int) error { return unix.Bind(fd, sa) }) } // Connect wraps connect(2). In order to verify that the underlying socket is // connected to a remote peer, Connect calls getpeername(2) and returns the // unix.Sockaddr from that call. // // Connect obeys context cancelation and uses the deadline set on the context to // cancel connecting to a remote peer. If a deadline is set on ctx, this // deadline will override any previous deadlines set using SetDeadline or // SetWriteDeadline. Upon return, the write deadline is cleared. func (c Conn) Connect(ctx context.Context, sa unix.Sockaddr) (unix.Sockaddr, error) { const op = "connect" // TODO(mdlayher): it would seem that trying to connect to unbound vsock // listeners by calling Connect multiple times results in ECONNRESET for the // first and nil error for subsequent calls. Do we need to memoize the // error? Check what the stdlib behavior is. var ( // Track progress between invocations of the write closure. We don't // have an explicit WaitWrite call like internal/poll does, so we have // to wait until the runtime calls the closure again to indicate we can // write. progress uint32 // Capture closure sockaddr and error. rsa unix.Sockaddr err error ) doErr := c.write(ctx, op, func(fd int) error { if atomic.AddUint32(&progress, 1) == 1 { // First call: initiate connect. return unix.Connect(fd, sa) } // Subsequent calls: the runtime network poller indicates fd is // writable. Check for errno. errno, gerr := c.GetsockoptInt(unix.SOL_SOCKET, unix.SO_ERROR) if gerr != nil { return gerr } if errno != 0 { // Connection is still not ready or failed. If errno indicates // the socket is not ready, we will wait for the next write // event. Otherwise we propagate this errno back to the as a // permanent error. uerr := unix.Errno(errno) err = uerr return uerr } // According to internal/poll, it's possible for the runtime network // poller to spuriously wake us and return errno 0 for SO_ERROR. // Make sure we are actually connected to a peer. peer, err := c.Getpeername() if err != nil { // internal/poll unconditionally goes back to WaitWrite. // Synthesize an error that will do the same for us. return unix.EAGAIN } // Connection complete. rsa = peer return nil }) if doErr != nil { // internal/poll or context error. return nil, doErr } if err == unix.EISCONN { // TODO(mdlayher): is this block obsolete with the addition of the // getsockopt SO_ERROR check above? // // EISCONN is reported if the socket is already established and should // not be treated as an error. // - Darwin reports this for at least TCP sockets // - Linux reports this for at least AF_VSOCK sockets return rsa, nil } return rsa, os.NewSyscallError(op, err) } // Getsockname wraps getsockname(2). func (c Conn) Getsockname() (unix.Sockaddr, error) { return controlT(c, context.Background(), "getsockname", unix.Getsockname) } // Getpeername wraps getpeername(2). func (c Conn) Getpeername() (unix.Sockaddr, error) { return controlT(c, context.Background(), "getpeername", unix.Getpeername) } // GetsockoptInt wraps getsockopt(2) for integer values. func (c Conn) GetsockoptInt(level, opt int) (int, error) { return controlT(c, context.Background(), "getsockopt", func(fd int) (int, error) { return unix.GetsockoptInt(fd, level, opt) }) } // Listen wraps listen(2). func (c Conn) Listen(n int) error { return c.control(context.Background(), "listen", func(fd int) error { return unix.Listen(fd, n) }) } // Recvmsg wraps recvmsg(2). func (c Conn) Recvmsg(ctx context.Context, p, oob []byte, flags int) (int, int, int, unix.Sockaddr, error) { type ret struct { n, oobn, recvflags int from unix.Sockaddr } r, err := readT(c, ctx, "recvmsg", func(fd int) (ret, error) { n, oobn, recvflags, from, err := unix.Recvmsg(fd, p, oob, flags) return ret{n, oobn, recvflags, from}, err }) if r.n == 0 && err == nil && c.facts.zeroReadIsEOF { return 0, 0, 0, nil, io.EOF } return r.n, r.oobn, r.recvflags, r.from, err } // Recvfrom wraps recvfrom(2). func (c Conn) Recvfrom(ctx context.Context, p []byte, flags int) (int, unix.Sockaddr, error) { type ret struct { n int addr unix.Sockaddr } out, err := readT(c, ctx, "recvfrom", func(fd int) (ret, error) { n, addr, err := unix.Recvfrom(fd, p, flags) return ret{n, addr}, err }) if out.n == 0 && err == nil && c.facts.zeroReadIsEOF { return 0, nil, io.EOF } return out.n, out.addr, err } // Sendmsg wraps sendmsg(2). func (c Conn) Sendmsg(ctx context.Context, p, oob []byte, to unix.Sockaddr, flags int) (int, error) { return writeT(c, ctx, "sendmsg", func(fd int) (int, error) { return unix.SendmsgN(fd, p, oob, to, flags) }) } // Sendto wraps sendto(2). func (c Conn) Sendto(ctx context.Context, p []byte, flags int, to unix.Sockaddr) error { return c.write(ctx, "sendto", func(fd int) error { return unix.Sendto(fd, p, flags, to) }) } // SetsockoptInt wraps setsockopt(2) for integer values. func (c Conn) SetsockoptInt(level, opt, value int) error { return c.control(context.Background(), "setsockopt", func(fd int) error { return unix.SetsockoptInt(fd, level, opt, value) }) } // Shutdown wraps shutdown(2). func (c Conn) Shutdown(how int) error { return c.control(context.Background(), "shutdown", func(fd int) error { return unix.Shutdown(fd, how) }) } // Conn low-level read/write/control functions. These functions mirror the // syscall.RawConn APIs but the input closures return errors rather than // booleans. // read wraps readT to execute a function and capture its error result. This is // a convenience wrapper for functions which don't return any extra values. func (c Conn) read(ctx context.Context, op string, f func(fd int) error) error { _, err := readT(c, ctx, op, func(fd int) (struct{}, error) { return struct{}{}, f(fd) }) return err } // write executes f, a write function, against the associated file descriptor. // op is used to create an os.SyscallError if the file descriptor is closed. func (c Conn) write(ctx context.Context, op string, f func(fd int) error) error { _, err := writeT(c, ctx, op, func(fd int) (struct{}, error) { return struct{}{}, f(fd) }) return err } // readT executes c.rc.Read for op using the input function, returning a newly // allocated result T. func readT[T any](c Conn, ctx context.Context, op string, f func(fd int) (T, error)) (T, error) { return rwT(c, rwContext[T]{ Context: ctx, Type: read, Op: op, Do: f, }) } // writeT executes c.rc.Write for op using the input function, returning a newly // allocated result T. func writeT[T any](c Conn, ctx context.Context, op string, f func(fd int) (T, error)) (T, error) { return rwT(c, rwContext[T]{ Context: ctx, Type: write, Op: op, Do: f, }) } // readWrite indicates if an operation intends to read or write. type readWrite bool // Possible readWrite values. const ( read readWrite = false write readWrite = true ) // An rwContext provides arguments to rwT. type rwContext[T any] struct { // The caller's context passed for cancelation. Context context.Context // The type of an operation: read or write. Type readWrite // The name of the operation used in errors. Op string // The actual function to perform. Do func(fd int) (T, error) } // rwT executes c.rc.Read or c.rc.Write (depending on the value of rw.Type) for // rw.Op using the input function, returning a newly allocated result T. // // It obeys context cancelation and the rw.Context must not be nil. func rwT[T any](c Conn, rw rwContext[T]) (T, error) { if atomic.LoadUint32(&c.closed) != 0 { // If the file descriptor is already closed, do nothing. return new(T), os.NewSyscallError(rw.Op, unix.EBADF) } if err := rw.Context.Err(); err != nil { // Early exit due to context cancel. return new(T), os.NewSyscallError(rw.Op, err) } var ( // The read or write function used to access the runtime network poller. poll func(func(uintptr) bool) error // The read or write function used to set the matching deadline. deadline func(time.Time) error ) if rw.Type == write { poll = c.rc.Write deadline = c.SetWriteDeadline } else { poll = c.rc.Read deadline = c.SetReadDeadline } var ( // Whether or not the context carried a deadline we are actively using // for cancelation. setDeadline bool // Signals for the cancelation watcher goroutine. wg sync.WaitGroup doneC = make(chan struct{}) // Atomic: reports whether we have to disarm the deadline. // // TODO(mdlayher): switch back to atomic.Bool when we drop support for // Go 1.18. needDisarm int64 ) // On cancel, clean up the watcher. defer func() { close(doneC) wg.Wait() }() if d, ok := rw.Context.Deadline(); ok { // The context has an explicit deadline. We will use it for cancelation // but disarm it after poll for the next call. if err := deadline(d); err != nil { return new(T), err } setDeadline = true atomic.AddInt64(&needDisarm, 1) } else { // The context does not have an explicit deadline. We have to watch for // cancelation so we can propagate that signal to immediately unblock // the runtime network poller. // // TODO(mdlayher): is it possible to detect a background context vs a // context with possible future cancel? wg.Add(1) go func() { defer wg.Done() select { case <-rw.Context.Done(): // Cancel the operation. Make the caller disarm after poll // returns. atomic.AddInt64(&needDisarm, 1) _ = deadline(time.Unix(0, 1)) case <-doneC: // Nothing to do. } }() } var ( t T err error ) pollErr := poll(func(fd uintptr) bool { t, err = rw.Do(int(fd)) return ready(err) }) if atomic.LoadInt64(&needDisarm) > 0 { _ = deadline(time.Time{}) } if pollErr != nil { if rw.Context.Err() != nil \|\| (setDeadline && errors.Is(pollErr, os.ErrDeadlineExceeded)) { // The caller canceled the operation or we set a deadline internally // and it was reached. // // Unpack a plain context error. We wait for the context to be done // to synchronize state externally. Otherwise we have noticed I/O // timeout wakeups when we set a deadline but the context was not // yet marked done. <-rw.Context.Done() return new(T), os.NewSyscallError(rw.Op, rw.Context.Err()) } // Error from syscall.RawConn methods. Conventionally the standard // library does not wrap internal/poll errors in os.NewSyscallError. return new(T), pollErr } // Result from user function. return t, os.NewSyscallError(rw.Op, err) } // control executes Conn.control for op using the input function. func (c Conn) control(ctx context.Context, op string, f func(fd int) error) error { _, err := controlT(c, ctx, op, func(fd int) (struct{}, error) { return struct{}{}, f(fd) }) return err } // controlT executes c.rc.Control for op using the input function, returning a // newly allocated result T. func controlT[T any](c Conn, ctx context.Context, op string, f func(fd int) (T, error)) (T, error) { if atomic.LoadUint32(&c.closed) != 0 { // If the file descriptor is already closed, do nothing. return new(T), os.NewSyscallError(op, unix.EBADF) } var ( t T err error ) doErr := c.rc.Control(func(fd uintptr) { // Repeatedly attempt the syscall(s) invoked by f until completion is // indicated by the return value of ready or the context is canceled. // // The last values for t and err are captured outside of the closure for // use when the loop breaks. for { if err = ctx.Err(); err != nil { // Early exit due to context cancel. return } t, err = f(int(fd)) if ready(err) { return } } }) if doErr != nil { // Error from syscall.RawConn methods. Conventionally the standard // library does not wrap internal/poll errors in os.NewSyscallError. return new(T), doErr } // Result from user function. return t, os.NewSyscallError(op, err) } // ready indicates readiness based on the value of err. func ready(err error) bool { switch err { case unix.EAGAIN, unix.EINPROGRESS, unix.EINTR: // When a socket is in non-blocking mode, we might see a variety of errors: // - EAGAIN: most common case for a socket read not being ready // - EINPROGRESS: reported by some sockets when first calling connect // - EINTR: system call interrupted, more frequently occurs in Go 1.14+ // because goroutines can be asynchronously preempted // // Return false to let the poller wait for readiness. See the source code // for internal/poll.FD.RawRead for more details. return false default: // Ready regardless of whether there was an error or no error. return true } } // Darwin and FreeBSD can't read or write 2GB+ files at a time, // even on 64-bit systems. // The same is true of socket implementations on many systems. // See golang.org/issue/7812 and golang.org/issue/16266. // Use 1GB instead of, say, 2GB-1, to keep subsequent reads aligned. const maxRW = 1 << 30	27.46 KB	2025-05-25 12:27
📄 conn_linux.go //go:build linux // +build linux package socket import ( "context" "os" "unsafe" "golang.org/x/net/bpf" "golang.org/x/sys/unix" ) // IoctlKCMClone wraps ioctl(2) for unix.KCMClone values, but returns a Conn // rather than a raw file descriptor. func (c Conn) IoctlKCMClone() (Conn, error) { info, err := controlT(c, context.Background(), "ioctl", unix.IoctlKCMClone) if err != nil { return nil, err } // Successful clone, wrap in a Conn for use by the caller. return New(int(info.Fd), c.name) } // IoctlKCMAttach wraps ioctl(2) for unix.KCMAttach values. func (c Conn) IoctlKCMAttach(info unix.KCMAttach) error { return c.control(context.Background(), "ioctl", func(fd int) error { return unix.IoctlKCMAttach(fd, info) }) } // IoctlKCMUnattach wraps ioctl(2) for unix.KCMUnattach values. func (c Conn) IoctlKCMUnattach(info unix.KCMUnattach) error { return c.control(context.Background(), "ioctl", func(fd int) error { return unix.IoctlKCMUnattach(fd, info) }) } // PidfdGetfd wraps pidfd_getfd(2) for a Conn which wraps a pidfd, but returns a // Conn rather than a raw file descriptor. func (c Conn) PidfdGetfd(targetFD, flags int) (Conn, error) { outFD, err := controlT(c, context.Background(), "pidfd_getfd", func(fd int) (int, error) { return unix.PidfdGetfd(fd, targetFD, flags) }) if err != nil { return nil, err } // Successful getfd, wrap in a Conn for use by the caller. return New(outFD, c.name) } // PidfdSendSignal wraps pidfd_send_signal(2) for a Conn which wraps a Linux // pidfd. func (c Conn) PidfdSendSignal(sig unix.Signal, info unix.Siginfo, flags int) error { return c.control(context.Background(), "pidfd_send_signal", func(fd int) error { return unix.PidfdSendSignal(fd, sig, info, flags) }) } // SetBPF attaches an assembled BPF program to a Conn. func (c Conn) SetBPF(filter []bpf.RawInstruction) error { // We can't point to the first instruction in the array if no instructions // are present. if len(filter) == 0 { return os.NewSyscallError("setsockopt", unix.EINVAL) } prog := unix.SockFprog{ Len: uint16(len(filter)), Filter: (unix.SockFilter)(unsafe.Pointer(&filter[0])), } return c.SetsockoptSockFprog(unix.SOL_SOCKET, unix.SO_ATTACH_FILTER, &prog) } // RemoveBPF removes a BPF filter from a Conn. func (c Conn) RemoveBPF() error { // 0 argument is ignored. return c.SetsockoptInt(unix.SOL_SOCKET, unix.SO_DETACH_FILTER, 0) } // SetsockoptPacketMreq wraps setsockopt(2) for unix.PacketMreq values. func (c Conn) SetsockoptPacketMreq(level, opt int, mreq unix.PacketMreq) error { return c.control(context.Background(), "setsockopt", func(fd int) error { return unix.SetsockoptPacketMreq(fd, level, opt, mreq) }) } // SetsockoptSockFprog wraps setsockopt(2) for unix.SockFprog values. func (c Conn) SetsockoptSockFprog(level, opt int, fprog unix.SockFprog) error { return c.control(context.Background(), "setsockopt", func(fd int) error { return unix.SetsockoptSockFprog(fd, level, opt, fprog) }) } // GetsockoptTpacketStats wraps getsockopt(2) for unix.TpacketStats values. func (c Conn) GetsockoptTpacketStats(level, name int) (unix.TpacketStats, error) { return controlT(c, context.Background(), "getsockopt", func(fd int) (unix.TpacketStats, error) { return unix.GetsockoptTpacketStats(fd, level, name) }) } // GetsockoptTpacketStatsV3 wraps getsockopt(2) for unix.TpacketStatsV3 values. func (c Conn) GetsockoptTpacketStatsV3(level, name int) (unix.TpacketStatsV3, error) { return controlT(c, context.Background(), "getsockopt", func(fd int) (unix.TpacketStatsV3, error) { return unix.GetsockoptTpacketStatsV3(fd, level, name) }) } // Waitid wraps waitid(2). func (c Conn) Waitid(idType int, info unix.Siginfo, options int, rusage unix.Rusage) error { return c.read(context.Background(), "waitid", func(fd int) error { return unix.Waitid(idType, fd, info, options, rusage) }) }	3.83 KB	2025-05-25 12:27
📄 conn_linux_test.go //go:build linux // +build linux package socket_test import ( "context" "errors" "fmt" "math" "net" "os" "runtime" "testing" "github.com/google/go-cmp/cmp" "github.com/mdlayher/socket" "github.com/mdlayher/socket/internal/sockettest" "golang.org/x/sync/errgroup" "golang.org/x/sys/unix" ) func TestLinuxConnBuffers(t testing.T) { t.Parallel() // This test isn't necessarily Linux-specific but it's easiest to verify on // Linux because we can rely on the kernel's documented buffer size // manipulation behavior. c, err := socket.Socket(unix.AF_INET, unix.SOCK_STREAM, 0, "tcpv4", nil) if err != nil { t.Fatalf("failed to open socket: %v", err) } defer c.Close() const ( set = 8192 // Per socket(7): // // "The kernel doubles this value (to allow space for // book‐keeping overhead) when it is set using setsockopt(2), // and this doubled value is returned by getsockopt(2)."" want = set 2 ) if err := c.SetReadBuffer(set); err != nil { t.Fatalf("failed to set read buffer size: %v", err) } if err := c.SetWriteBuffer(set); err != nil { t.Fatalf("failed to set write buffer size: %v", err) } // Now that we've set the buffers, we can check the size by asking the // kernel using SyscallConn and getsockopt. rcv, err := c.ReadBuffer() if err != nil { t.Fatalf("failed to get read buffer size: %v", err) } snd, err := c.WriteBuffer() if err != nil { t.Fatalf("failed to get write buffer size: %v", err) } if diff := cmp.Diff(want, rcv); diff != "" { t.Fatalf("unexpected read buffer size (-want +got):\n%s", diff) } if diff := cmp.Diff(want, snd); diff != "" { t.Fatalf("unexpected write buffer size (-want +got):\n%s", diff) } } func TestLinuxNetworkNamespaces(t testing.T) { t.Parallel() l, err := sockettest.Listen(0, nil) if err != nil { t.Fatalf("failed to create listener: %v", err) } defer l.Close() addrC := make(chan net.Addr, 1) var eg errgroup.Group eg.Go(func() error { // We are poisoning this thread by creating a new anonymous network // namespace. Do not unlock the OS thread so that the runtime will kill // this thread when the goroutine exits. runtime.LockOSThread() if err := unix.Unshare(unix.CLONE_NEWNET); err != nil { // Explicit wrap to check for permission denied. return fmt.Errorf("failed to unshare network namespace: %w", err) } ns, err := socket.ThreadNetNS() if err != nil { return fmt.Errorf("failed to get listener thread's network namespace: %v", err) } // This OS thread has been moved to a different network namespace and // thus we should also be able to start a listener on the same port. l, err := sockettest.Listen( l.Addr().(net.TCPAddr).Port, &socket.Config{NetNS: ns.FD()}, ) if err != nil { return fmt.Errorf("failed to create listener in network namespace: %v", err) } defer l.Close() addrC <- l.Addr() return nil }) if err := eg.Wait(); err != nil { if errors.Is(err, os.ErrPermission) { t.Skipf("skipping, permission denied: %v", err) } t.Fatalf("failed to run listener thread: %v", err) } select { case addr := <-addrC: if diff := cmp.Diff(l.Addr(), addr); diff != "" { t.Fatalf("unexpected network address (-want +got):\n%s", diff) } default: t.Fatal("listener thread did not return its local address") } } func TestLinuxDialVsockNoListener(t testing.T) { t.Parallel() // See https://github.com/mdlayher/vsock/issues/47 and // https://github.com/lxc/lxd/pull/9894 for context on this test. c, err := socket.Socket(unix.AF_VSOCK, unix.SOCK_STREAM, 0, "vsock", nil) if err != nil { t.Fatalf("failed to open socket: %v", err) } defer c.Close() // Given a (hopefully) non-existent listener on localhost, expect // ECONNRESET. _, err = c.Connect(context.Background(), &unix.SockaddrVM{ CID: unix.VMADDR_CID_LOCAL, Port: math.MaxUint32, }) if err == nil { // See https://github.com/mdlayher/socket/issues/4. t.Skipf("skipping, expected error but vsock successfully connected to local service") } want := os.NewSyscallError("connect", unix.ECONNRESET) if diff := cmp.Diff(want, err); diff != "" { t.Fatalf("unexpected connect error (-want +got):\n%s", diff) } } func TestLinuxOpenPIDFD(t testing.T) { // Verify we can use regular files with socket by properly handling // ENOTSOCK, as is the case with pidfds. fd, err := unix.PidfdOpen(1, unix.PIDFD_NONBLOCK) if err != nil { t.Fatalf("failed to open pidfd for init: %v", err) } c, err := socket.New(fd, "pidfd") if err != nil { t.Fatalf("failed to open Conn for pidfd: %v", err) } _ = c.Close() }	4.52 KB	2025-05-25 12:27
📄 conn_test.go package socket_test import ( "bytes" "context" "errors" "fmt" "io" "math" "net" "net/netip" "os" "runtime" "sync" "testing" "time" "github.com/google/go-cmp/cmp" "github.com/google/go-cmp/cmp/cmpopts" "github.com/mdlayher/socket/internal/sockettest" "golang.org/x/net/nettest" "golang.org/x/sync/errgroup" "golang.org/x/sys/unix" ) func TestConn(t testing.T) { t.Parallel() tests := []struct { name string pipe nettest.MakePipe }{ // Standard library plumbing. { name: "basic", pipe: makePipe( func() (net.Listener, error) { return sockettest.Listen(0, nil) }, func(addr net.Addr) (net.Conn, error) { return sockettest.Dial(context.Background(), addr, nil) }, ), }, // Our own implementations which have context cancelation support. { name: "context", pipe: makePipe( func() (net.Listener, error) { l, err := sockettest.Listen(0, nil) if err != nil { return nil, err } return l.Context(context.Background()), nil }, func(addr net.Addr) (net.Conn, error) { ctx := context.Background() c, err := sockettest.Dial(ctx, addr, nil) if err != nil { return nil, err } return c.Context(ctx), nil }, ), }, } for _, tt := range tests { tt := tt t.Run(tt.name, func(t testing.T) { t.Parallel() nettest.TestConn(t, tt.pipe) // Our own extensions to TestConn. t.Run("CloseReadWrite", func(t testing.T) { timeoutWrapper(t, tt.pipe, testCloseReadWrite) }) }) } } func TestDialTCPNoListener(t testing.T) { t.Parallel() // See https://github.com/mdlayher/vsock/issues/47 and // https://github.com/lxc/lxd/pull/9894 for context on this test. // // // Given a (hopefully) non-existent listener on localhost, expect // ECONNREFUSED. _, err := sockettest.Dial(context.Background(), &net.TCPAddr{ IP: net.IPv6loopback, Port: math.MaxUint16, }, nil) want := os.NewSyscallError("connect", unix.ECONNREFUSED) if diff := cmp.Diff(want, err); diff != "" { t.Fatalf("unexpected connect error (-want +got):\n%s", diff) } } func TestDialTCPContextCanceledBefore(t testing.T) { t.Parallel() // Context is canceled before any dialing can take place. ctx, cancel := context.WithCancel(context.Background()) cancel() _, err := sockettest.Dial(ctx, &net.TCPAddr{ IP: net.IPv6loopback, Port: math.MaxUint16, }, nil) if diff := cmp.Diff(context.Canceled, err, cmpopts.EquateErrors()); diff != "" { t.Fatalf("unexpected connect error (-want +got):\n%s", diff) } } var ipTests = []struct { name string ip netip.Addr }{ // It appears we can dial addresses in the documentation range and // connect will hang, which is perfect for this test case. { name: "IPv4", ip: netip.MustParseAddr("192.0.2.1"), }, { name: "IPv6", ip: netip.MustParseAddr("2001:db8::1"), }, } func TestDialTCPContextCanceledDuring(t testing.T) { t.Parallel() for _, tt := range ipTests { tt := tt t.Run(tt.name, func(t testing.T) { t.Parallel() // Context is canceled during a blocking operation but without an // explicit deadline passed on the context. ctx, cancel := context.WithCancel(context.Background()) defer cancel() go func() { time.Sleep(1 time.Second) cancel() }() _, err := sockettest.Dial(ctx, &net.TCPAddr{ IP: tt.ip.AsSlice(), Port: math.MaxUint16, }, nil) if errors.Is(err, unix.ENETUNREACH) \|\| errors.Is(err, unix.EHOSTUNREACH) { t.Skipf("skipping, no outbound %s connectivity: %v", tt.name, err) } if diff := cmp.Diff(context.Canceled, err, cmpopts.EquateErrors()); diff != "" { t.Fatalf("unexpected connect error (-want +got):\n%s", diff) } }) } } func TestDialTCPContextDeadlineExceeded(t testing.T) { t.Parallel() for _, tt := range ipTests { tt := tt t.Run(tt.name, func(t testing.T) { t.Parallel() // Dialing is canceled after the deadline passes. ctx, cancel := context.WithTimeout(context.Background(), 1time.Second) defer cancel() _, err := sockettest.Dial(ctx, &net.TCPAddr{ IP: tt.ip.AsSlice(), Port: math.MaxUint16, }, nil) if errors.Is(err, unix.ENETUNREACH) \|\| errors.Is(err, unix.EHOSTUNREACH) { t.Skipf("skipping, no outbound %s connectivity: %v", tt.name, err) } if diff := cmp.Diff(context.DeadlineExceeded, err, cmpopts.EquateErrors()); diff != "" { t.Fatalf("unexpected connect error (-want +got):\n%s", diff) } }) } } func TestListenerAcceptTCPContextCanceledBefore(t testing.T) { t.Parallel() l, err := sockettest.Listen(0, nil) if err != nil { t.Fatalf("failed to listen: %v", err) } defer l.Close() // Context is canceled before accept can take place. ctx, cancel := context.WithCancel(context.Background()) cancel() _, err = l.Context(ctx).Accept() if diff := cmp.Diff(context.Canceled, err, cmpopts.EquateErrors()); diff != "" { t.Fatalf("unexpected accept error (-want +got):\n%s", diff) } } func TestListenerAcceptTCPContextCanceledDuring(t testing.T) { t.Parallel() l, err := sockettest.Listen(0, nil) if err != nil { t.Fatalf("failed to listen: %v", err) } defer l.Close() // Context is canceled during a blocking operation but without an // explicit deadline passed on the context. ctx, cancel := context.WithCancel(context.Background()) defer cancel() go func() { time.Sleep(1 time.Second) cancel() }() _, err = l.Context(ctx).Accept() if diff := cmp.Diff(context.Canceled, err, cmpopts.EquateErrors()); diff != "" { t.Fatalf("unexpected accept error (-want +got):\n%s", diff) } } func TestListenerAcceptTCPContextDeadlineExceeded(t testing.T) { t.Parallel() l, err := sockettest.Listen(0, nil) if err != nil { t.Fatalf("failed to listen: %v", err) } defer l.Close() // Accept is canceled after the deadline passes. ctx, cancel := context.WithTimeout(context.Background(), 1time.Second) defer cancel() _, err = l.Context(ctx).Accept() if diff := cmp.Diff(context.DeadlineExceeded, err, cmpopts.EquateErrors()); diff != "" { t.Fatalf("unexpected accept error (-want +got):\n%s", diff) } } func TestListenerConnTCPContextCanceled(t testing.T) { t.Parallel() l, err := sockettest.Listen(0, nil) if err != nil { t.Fatalf("failed to open listener: %v", err) } defer l.Close() // Accept a single connection. var eg errgroup.Group eg.Go(func() error { c, err := l.Accept() if err != nil { return fmt.Errorf("failed to accept: %v", err) } defer c.Close() // Context is canceled during recvfrom. ctx, cancel := context.WithTimeout(context.Background(), 1time.Second) defer cancel() b := make([]byte, 1024) _, _, err = c.(sockettest.Conn).Conn.Recvfrom(ctx, b, 0) return err }) c, err := net.Dial(l.Addr().Network(), l.Addr().String()) if err != nil { t.Fatalf("failed to dial listener: %v", err) } defer c.Close() // Client never sends data, so we wait until ctx cancel and errgroup return. if diff := cmp.Diff(context.DeadlineExceeded, eg.Wait(), cmpopts.EquateErrors()); diff != "" { t.Fatalf("unexpected recvfrom error (-want +got):\n%s", diff) } } func TestListenerConnTCPContextDeadlineExceeded(t testing.T) { t.Parallel() l, err := sockettest.Listen(0, nil) if err != nil { t.Fatalf("failed to open listener: %v", err) } defer l.Close() // Accept a single connection. var eg errgroup.Group eg.Go(func() error { c, err := l.Accept() if err != nil { return fmt.Errorf("failed to accept: %v", err) } defer c.Close() // Context is canceled before recvfrom can take place. ctx, cancel := context.WithCancel(context.Background()) cancel() b := make([]byte, 1024) _, _, err = c.(sockettest.Conn).Conn.Recvfrom(ctx, b, 0) return err }) c, err := net.Dial(l.Addr().Network(), l.Addr().String()) if err != nil { t.Fatalf("failed to dial listener: %v", err) } defer c.Close() // Client never sends data, so we wait until ctx cancel and errgroup return. if diff := cmp.Diff(context.Canceled, eg.Wait(), cmpopts.EquateErrors()); diff != "" { t.Fatalf("unexpected recvfrom error (-want +got):\n%s", diff) } } func TestFileConn(t testing.T) { t.Parallel() // Use raw system calls to set up the socket since we assume anything being // passed into a FileConn is set up by another system, such as systemd's // socket activation. fd, err := unix.Socket(unix.AF_INET6, unix.SOCK_STREAM, 0) if err != nil { t.Fatalf("failed to open socket: %v", err) } // Bind to loopback, any available port. sa := &unix.SockaddrInet6{Addr: [16]byte{15: 0x01}} if err := unix.Bind(fd, sa); err != nil { t.Fatalf("failed to bind: %v", err) } if err := unix.Listen(fd, unix.SOMAXCONN); err != nil { t.Fatalf("failed to listen: %v", err) } // The socket should be ready, create a blocking file which is ready to be // passed into FileConn via the FileListener helper. f := os.NewFile(uintptr(fd), "tcpv6-listener") defer f.Close() l, err := sockettest.FileListener(f) if err != nil { t.Fatalf("failed to open file listener: %v", err) } defer l.Close() // To exercise the listener, attempt to accept and then immediately close a // single TCPv6 connection. Dial to the listener from the main goroutine and // wait for everything to finish. var eg errgroup.Group eg.Go(func() error { c, err := l.Accept() if err != nil { return fmt.Errorf("failed to accept: %v", err) } _ = c.Close() return nil }) c, err := net.Dial(l.Addr().Network(), l.Addr().String()) if err != nil { t.Fatalf("failed to dial listener: %v", err) } _ = c.Close() if err := eg.Wait(); err != nil { t.Fatalf("failed to wait for listener goroutine: %v", err) } } // Use our TCP net.Listener and net.Conn implementations backed by socket.Conn // and run compliance tests with nettest.TestConn. // // This nettest.MakePipe function is adapted from nettest's own tests: // https://github.com/golang/net/blob/master/nettest/conntest_test.go // // Copyright 2016 The Go Authors. All rights reserved. Use of this source // code is governed by a BSD-style license that can be found in the LICENSE // file. func makePipe( listen func() (net.Listener, error), dial func(addr net.Addr) (net.Conn, error), ) nettest.MakePipe { return func() (c1, c2 net.Conn, stop func(), err error) { ln, err := listen() if err != nil { return nil, nil, nil, err } // Start a connection between two endpoints. var err1, err2 error done := make(chan bool) go func() { c2, err2 = ln.Accept() close(done) }() c1, err1 = dial(ln.Addr()) <-done stop = func() { if err1 == nil { c1.Close() } if err2 == nil { c2.Close() } ln.Close() } switch { case err1 != nil: stop() return nil, nil, nil, err1 case err2 != nil: stop() return nil, nil, nil, err2 default: return c1, c2, stop, nil } } } // Copied from x/net/nettest, pending acceptance of: // https://go-review.googlesource.com/c/net/+/372815 type connTester func(t testing.T, c1, c2 net.Conn) func timeoutWrapper(t testing.T, mp nettest.MakePipe, f connTester) { t.Helper() c1, c2, stop, err := mp() if err != nil { t.Fatalf("unable to make pipe: %v", err) } var once sync.Once defer once.Do(func() { stop() }) timer := time.AfterFunc(time.Minute, func() { once.Do(func() { t.Error("test timed out; terminating pipe") stop() }) }) defer timer.Stop() f(t, c1, c2) } // testCloseReadWrite tests that net.Conns which also implement the optional // CloseRead and CloseWrite methods can be half-closed correctly. func testCloseReadWrite(t testing.T, c1, c2 net.Conn) { // TODO(mdlayher): investigate why Mac/Windows errors are so different. if runtime.GOOS != "linux" { t.Skip("skipping, not supported on non-Linux platforms") } type closerConn interface { net.Conn CloseRead() error CloseWrite() error } cc1, ok1 := c1.(closerConn) cc2, ok2 := c2.(closerConn) if !ok1 \|\| !ok2 { // Both c1 and c2 must implement closerConn to proceed. return } var wg sync.WaitGroup wg.Add(2) defer wg.Wait() go func() { defer wg.Done() // Writing succeeds at first but should result in a permanent "broken // pipe" error after closing the write side of the net.Conn. b := make([]byte, 64) if err := chunkedCopy(cc1, bytes.NewReader(b)); err != nil { t.Errorf("unexpected initial cc1.Write error: %v", err) } if err := cc1.CloseWrite(); err != nil { t.Errorf("unexpected cc1.CloseWrite error: %v", err) } _, err := cc1.Write(b) if nerr, ok := err.(net.Error); !ok \|\| nerr.Timeout() { t.Errorf("unexpected final cc1.Write error: %v", err) } }() go func() { defer wg.Done() // Reading succeeds at first but should result in an EOF error after // closing the read side of the net.Conn. if err := chunkedCopy(io.Discard, cc2); err != nil { t.Errorf("unexpected initial cc2.Read error: %v", err) } if err := cc2.CloseRead(); err != nil { t.Errorf("unexpected cc2.CloseRead error: %v", err) } if _, err := cc2.Read(make([]byte, 64)); err != io.EOF { t.Errorf("unexpected final cc2.Read error: %v", err) } }() } // chunkedCopy copies from r to w in fixed-width chunks to avoid // causing a Write that exceeds the maximum packet size for packet-based // connections like "unixpacket". // We assume that the maximum packet size is at least 1024. func chunkedCopy(w io.Writer, r io.Reader) error { b := make([]byte, 1024) _, err := io.CopyBuffer(struct{ io.Writer }{w}, struct{ io.Reader }{r}, b) return err }	13.25 KB	2025-05-25 12:27
📄 doc.go // Package socket provides a low-level network connection type which integrates // with Go's runtime network poller to provide asynchronous I/O and deadline // support. // // This package focuses on UNIX-like operating systems which make use of BSD // sockets system call APIs. It is meant to be used as a foundation for the // creation of operating system-specific socket packages, for socket families // such as Linux's AF_NETLINK, AF_PACKET, or AF_VSOCK. This package should not // be used directly in end user applications. // // Any use of package socket should be guarded by build tags, as one would also // use when importing the syscall or golang.org/x/sys packages. package socket	690 B	2025-05-25 12:27
📄 export_linux_test.go //go:build linux // +build linux package socket // A NetNS is an exported wrapper for netNS for tests. type NetNS struct{ netNS } // ThreadNetNS is an exported wrapper for threadNetNS for tests. func ThreadNetNS() (NetNS, error) { ns, err := threadNetNS() if err != nil { return nil, err } return &NetNS{ns}, nil }	327 B	2025-05-25 12:27
📄 go.mod module github.com/mdlayher/socket go 1.20 require ( github.com/google/go-cmp v0.5.9 golang.org/x/net v0.9.0 golang.org/x/sync v0.1.0 golang.org/x/sys v0.7.0 )	165 B	2025-05-25 12:27
📄 go.sum github.com/google/go-cmp v0.5.9 h1:O2Tfq5qg4qc4AmwVlvv0oLiVAGB7enBSJ2x2DqQFi38= github.com/google/go-cmp v0.5.9/go.mod h1:17dUlkBOakJ0+DkrSSNjCkIjxS6bF9zb3elmeNGIjoY= golang.org/x/net v0.9.0 h1:aWJ/m6xSmxWBx+V0XRHTlrYrPG56jKsLdTFmsSsCzOM= golang.org/x/net v0.9.0/go.mod h1:d48xBJpPfHeWQsugry2m+kC02ZBRGRgulfHnEXEuWns= golang.org/x/sync v0.1.0 h1:wsuoTGHzEhffawBOhz5CYhcrV4IdKZbEyZjBMuTp12o= golang.org/x/sync v0.1.0/go.mod h1:RxMgew5VJxzue5/jJTE5uejpjVlOe/izrB70Jof72aM= golang.org/x/sys v0.7.0 h1:3jlCCIQZPdOYu1h8BkNvLz8Kgwtae2cagcG/VamtZRU= golang.org/x/sys v0.7.0/go.mod h1:oPkhp1MJrh7nUepCBck5+mAzfO9JrbApNNgaTdGDITg=	622 B	2025-05-25 12:27
📁 internal	-	2025-05-25 12:27
📄 netns_linux.go //go:build linux // +build linux package socket import ( "errors" "fmt" "os" "runtime" "golang.org/x/sync/errgroup" "golang.org/x/sys/unix" ) // errNetNSDisabled is returned when network namespaces are unavailable on // a given system. var errNetNSDisabled = errors.New("socket: Linux network namespaces are not enabled on this system") // withNetNS invokes fn within the context of the network namespace specified by // fd, while also managing the logic required to safely do so by manipulating // thread-local state. func withNetNS(fd int, fn func() (Conn, error)) (Conn, error) { var ( eg errgroup.Group conn Conn ) eg.Go(func() error { // Retrieve and store the calling OS thread's network namespace so the // thread can be reassigned to it after creating a socket in another network // namespace. runtime.LockOSThread() ns, err := threadNetNS() if err != nil { // No thread-local manipulation, unlock. runtime.UnlockOSThread() return err } defer ns.Close() // Beyond this point, the thread's network namespace is poisoned. Do not // unlock the OS thread until all network namespace manipulation completes // to avoid returning to the caller with altered thread-local state. // Assign the current OS thread the goroutine is locked to to the given // network namespace. if err := ns.Set(fd); err != nil { return err } // Attempt Conn creation and unconditionally restore the original namespace. c, err := fn() if nerr := ns.Restore(); nerr != nil { // Failed to restore original namespace. Return an error and allow the // runtime to terminate the thread. if err == nil { _ = c.Close() } return nerr } // No more thread-local state manipulation; return the new Conn. runtime.UnlockOSThread() conn = c return nil }) if err := eg.Wait(); err != nil { return nil, err } return conn, nil } // A netNS is a handle that can manipulate network namespaces. // // Operations performed on a netNS must use runtime.LockOSThread before // manipulating any network namespaces. type netNS struct { // The handle to a network namespace. f os.File // Indicates if network namespaces are disabled on this system, and thus // operations should become a no-op or return errors. disabled bool } // threadNetNS constructs a netNS using the network namespace of the calling // thread. If the namespace is not the default namespace, runtime.LockOSThread // should be invoked first. func threadNetNS() (netNS, error) { return fileNetNS(fmt.Sprintf("/proc/self/task/%d/ns/net", unix.Gettid())) } // fileNetNS opens file and creates a netNS. fileNetNS should only be called // directly in tests. func fileNetNS(file string) (netNS, error) { f, err := os.Open(file) switch { case err == nil: return &netNS{f: f}, nil case os.IsNotExist(err): // Network namespaces are not enabled on this system. Use this signal // to return errors elsewhere if the caller explicitly asks for a // network namespace to be set. return &netNS{disabled: true}, nil default: return nil, err } } // Close releases the handle to a network namespace. func (n netNS) Close() error { return n.do(func() error { return n.f.Close() }) } // FD returns a file descriptor which represents the network namespace. func (n netNS) FD() int { if n.disabled { // No reasonable file descriptor value in this case, so specify a // non-existent one. return -1 } return int(n.f.Fd()) } // Restore restores the original network namespace for the calling thread. func (n netNS) Restore() error { return n.do(func() error { return n.Set(n.FD()) }) } // Set sets a new network namespace for the current thread using fd. func (n netNS) Set(fd int) error { return n.do(func() error { return os.NewSyscallError("setns", unix.Setns(fd, unix.CLONE_NEWNET)) }) } // do runs fn if network namespaces are enabled on this system. func (n *netNS) do(fn func() error) error { if n.disabled { return errNetNSDisabled } return fn() }	3.93 KB	2025-05-25 12:27
📄 netns_others.go //go:build !linux // +build !linux package socket import ( "fmt" "runtime" ) // withNetNS returns an error on non-Linux systems. func withNetNS(_ int, _ func() (Conn, error)) (Conn, error) { return nil, fmt.Errorf("socket: Linux network namespace support is not available on %s", runtime.GOOS) }	304 B	2025-05-25 12:27
📄 setbuffer_linux.go //go:build linux // +build linux package socket import "golang.org/x/sys/unix" // setReadBuffer wraps the SO_RCVBUF{,FORCE} setsockopt(2) options. func (c Conn) setReadBuffer(bytes int) error { err := c.SetsockoptInt(unix.SOL_SOCKET, unix.SO_RCVBUFFORCE, bytes) if err != nil { err = c.SetsockoptInt(unix.SOL_SOCKET, unix.SO_RCVBUF, bytes) } return err } // setWriteBuffer wraps the SO_SNDBUF{,FORCE} setsockopt(2) options. func (c Conn) setWriteBuffer(bytes int) error { err := c.SetsockoptInt(unix.SOL_SOCKET, unix.SO_SNDBUFFORCE, bytes) if err != nil { err = c.SetsockoptInt(unix.SOL_SOCKET, unix.SO_SNDBUF, bytes) } return err }	651 B	2025-05-25 12:27
📄 setbuffer_others.go //go:build !linux // +build !linux package socket import "golang.org/x/sys/unix" // setReadBuffer wraps the SO_RCVBUF setsockopt(2) option. func (c Conn) setReadBuffer(bytes int) error { return c.SetsockoptInt(unix.SOL_SOCKET, unix.SO_RCVBUF, bytes) } // setWriteBuffer wraps the SO_SNDBUF setsockopt(2) option. func (c Conn) setWriteBuffer(bytes int) error { return c.SetsockoptInt(unix.SOL_SOCKET, unix.SO_SNDBUF, bytes) }	433 B	2025-05-25 12:27
📄 typ_cloexec_nonblock.go //go:build !darwin // +build !darwin package socket import "golang.org/x/sys/unix" const ( // These operating systems support CLOEXEC and NONBLOCK socket options. flagCLOEXEC = true socketFlags = unix.SOCK_CLOEXEC \| unix.SOCK_NONBLOCK )	243 B	2025-05-25 12:27
📄 typ_none.go //go:build darwin // +build darwin package socket const ( // These operating systems do not support CLOEXEC and NONBLOCK socket // options. flagCLOEXEC = false socketFlags = 0 )	184 B	2025-05-25 12:27

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