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// Copyright 2009 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.
/*
Package net provides a portable interface for network I/O, including
TCP/IP, UDP, domain name resolution, and Unix domain sockets.
Although the package provides access to low-level networking
primitives, most clients will need only the basic interface provided
by the Dial, Listen, and Accept functions and the associated
Conn and Listener interfaces. The crypto/tls package uses
the same interfaces and similar Dial and Listen functions.
The Dial function connects to a server:
conn, err := net.Dial("tcp", "google.com:80")
if err != nil {
// handle error
}
fmt.Fprintf(conn, "GET / HTTP/1.0\r\n\r\n")
status, err := bufio.NewReader(conn).ReadString('\n')
// ...
The Listen function creates servers:
ln, err := net.Listen("tcp", ":8080")
if err != nil {
// handle error
}
for {
conn, err := ln.Accept()
if err != nil {
// handle error
}
go handleConnection(conn)
}
*/
package net
import (
"errors"
"io"
"os"
"syscall"
"time"
)
// Addr represents a network end point address.
type Addr interface {
Network() string // name of the network
String() string // string form of address
}
// Conn is a generic stream-oriented network connection.
//
// Multiple goroutines may invoke methods on a Conn simultaneously.
type Conn interface {
// Read reads data from the connection.
// Read can be made to time out and return a Error with Timeout() == true
// after a fixed time limit; see SetDeadline and SetReadDeadline.
Read(b []byte) (n int, err error)
// Write writes data to the connection.
// Write can be made to time out and return a Error with Timeout() == true
// after a fixed time limit; see SetDeadline and SetWriteDeadline.
Write(b []byte) (n int, err error)
// Close closes the connection.
// Any blocked Read or Write operations will be unblocked and return errors.
Close() error
// LocalAddr returns the local network address.
LocalAddr() Addr
// RemoteAddr returns the remote network address.
RemoteAddr() Addr
// SetDeadline sets the read and write deadlines associated
// with the connection. It is equivalent to calling both
// SetReadDeadline and SetWriteDeadline.
//
// A deadline is an absolute time after which I/O operations
// fail with a timeout (see type Error) instead of
// blocking. The deadline applies to all future I/O, not just
// the immediately following call to Read or Write.
//
// An idle timeout can be implemented by repeatedly extending
// the deadline after successful Read or Write calls.
//
// A zero value for t means I/O operations will not time out.
SetDeadline(t time.Time) error
// SetReadDeadline sets the deadline for future Read calls.
// A zero value for t means Read will not time out.
SetReadDeadline(t time.Time) error
// SetWriteDeadline sets the deadline for future Write calls.
// Even if write times out, it may return n > 0, indicating that
// some of the data was successfully written.
// A zero value for t means Write will not time out.
SetWriteDeadline(t time.Time) error
}
type conn struct {
fd *netFD
}
func (c *conn) ok() bool { return c != nil && c.fd != nil }
// Implementation of the Conn interface.
// Read implements the Conn Read method.
func (c *conn) Read(b []byte) (int, error) {
if !c.ok() {
return 0, syscall.EINVAL
}
return c.fd.Read(b)
}
// Write implements the Conn Write method.
func (c *conn) Write(b []byte) (int, error) {
if !c.ok() {
return 0, syscall.EINVAL
}
return c.fd.Write(b)
}
// Close closes the connection.
func (c *conn) Close() error {
if !c.ok() {
return syscall.EINVAL
}
return c.fd.Close()
}
// LocalAddr returns the local network address.
// The Addr returned is shared by all invocations of LocalAddr, so
// do not modify it.
func (c *conn) LocalAddr() Addr {
if !c.ok() {
return nil
}
return c.fd.laddr
}
// RemoteAddr returns the remote network address.
// The Addr returned is shared by all invocations of RemoteAddr, so
// do not modify it.
func (c *conn) RemoteAddr() Addr {
if !c.ok() {
return nil
}
return c.fd.raddr
}
// SetDeadline implements the Conn SetDeadline method.
func (c *conn) SetDeadline(t time.Time) error {
if !c.ok() {
return syscall.EINVAL
}
return c.fd.setDeadline(t)
}
// SetReadDeadline implements the Conn SetReadDeadline method.
func (c *conn) SetReadDeadline(t time.Time) error {
if !c.ok() {
return syscall.EINVAL
}
return c.fd.setReadDeadline(t)
}
// SetWriteDeadline implements the Conn SetWriteDeadline method.
func (c *conn) SetWriteDeadline(t time.Time) error {
if !c.ok() {
return syscall.EINVAL
}
return c.fd.setWriteDeadline(t)
}
// SetReadBuffer sets the size of the operating system's
// receive buffer associated with the connection.
func (c *conn) SetReadBuffer(bytes int) error {
if !c.ok() {
return syscall.EINVAL
}
return setReadBuffer(c.fd, bytes)
}
// SetWriteBuffer sets the size of the operating system's
// transmit buffer associated with the connection.
func (c *conn) SetWriteBuffer(bytes int) error {
if !c.ok() {
return syscall.EINVAL
}
return setWriteBuffer(c.fd, bytes)
}
// File sets the underlying os.File to blocking mode and returns a copy.
// It is the caller's responsibility to close f when finished.
// Closing c does not affect f, and closing f does not affect c.
//
// The returned os.File's file descriptor is different from the connection's.
// Attempting to change properties of the original using this duplicate
// may or may not have the desired effect.
func (c *conn) File() (f *os.File, err error) { return c.fd.dup() }
// An Error represents a network error.
type Error interface {
error
Timeout() bool // Is the error a timeout?
Temporary() bool // Is the error temporary?
}
// PacketConn is a generic packet-oriented network connection.
//
// Multiple goroutines may invoke methods on a PacketConn simultaneously.
type PacketConn interface {
// ReadFrom reads a packet from the connection,
// copying the payload into b. It returns the number of
// bytes copied into b and the return address that
// was on the packet.
// ReadFrom can be made to time out and return
// an error with Timeout() == true after a fixed time limit;
// see SetDeadline and SetReadDeadline.
ReadFrom(b []byte) (n int, addr Addr, err error)
// WriteTo writes a packet with payload b to addr.
// WriteTo can be made to time out and return
// an error with Timeout() == true after a fixed time limit;
// see SetDeadline and SetWriteDeadline.
// On packet-oriented connections, write timeouts are rare.
WriteTo(b []byte, addr Addr) (n int, err error)
// Close closes the connection.
// Any blocked ReadFrom or WriteTo operations will be unblocked and return errors.
Close() error
// LocalAddr returns the local network address.
LocalAddr() Addr
// SetDeadline sets the read and write deadlines associated
// with the connection.
SetDeadline(t time.Time) error
// SetReadDeadline sets the deadline for future Read calls.
// If the deadline is reached, Read will fail with a timeout
// (see type Error) instead of blocking.
// A zero value for t means Read will not time out.
SetReadDeadline(t time.Time) error
// SetWriteDeadline sets the deadline for future Write calls.
// If the deadline is reached, Write will fail with a timeout
// (see type Error) instead of blocking.
// A zero value for t means Write will not time out.
// Even if write times out, it may return n > 0, indicating that
// some of the data was successfully written.
SetWriteDeadline(t time.Time) error
}
var listenerBacklog = maxListenerBacklog()
// A Listener is a generic network listener for stream-oriented protocols.
//
// Multiple goroutines may invoke methods on a Listener simultaneously.
type Listener interface {
// Accept waits for and returns the next connection to the listener.
Accept() (c Conn, err error)
// Close closes the listener.
// Any blocked Accept operations will be unblocked and return errors.
Close() error
// Addr returns the listener's network address.
Addr() Addr
}
// Various errors contained in OpError.
var (
// For connection setup and write operations.
errMissingAddress = errors.New("missing address")
// For both read and write operations.
errTimeout error = &timeoutError{}
errClosing = errors.New("use of closed network connection")
ErrWriteToConnected = errors.New("use of WriteTo with pre-connected connection")
)
// OpError is the error type usually returned by functions in the net
// package. It describes the operation, network type, and address of
// an error.
type OpError struct {
// Op is the operation which caused the error, such as
// "read" or "write".
Op string
// Net is the network type on which this error occurred,
// such as "tcp" or "udp6".
Net string
// Addr is the network address on which this error occurred.
Addr Addr
// Err is the error that occurred during the operation.
Err error
}
func (e *OpError) Error() string {
if e == nil {
return "<nil>"
}
s := e.Op
if e.Net != "" {
s += " " + e.Net
}
if e.Addr != nil {
s += " " + e.Addr.String()
}
s += ": " + e.Err.Error()
return s
}
type temporary interface {
Temporary() bool
}
func (e *OpError) Temporary() bool {
t, ok := e.Err.(temporary)
return ok && t.Temporary()
}
var noDeadline = time.Time{}
type timeout interface {
Timeout() bool
}
func (e *OpError) Timeout() bool {
t, ok := e.Err.(timeout)
return ok && t.Timeout()
}
type timeoutError struct{}
func (e *timeoutError) Error() string { return "i/o timeout" }
func (e *timeoutError) Timeout() bool { return true }
func (e *timeoutError) Temporary() bool { return true }
type AddrError struct {
Err string
Addr string
}
func (e *AddrError) Error() string {
if e == nil {
return "<nil>"
}
s := e.Err
if e.Addr != "" {
s += " " + e.Addr
}
return s
}
func (e *AddrError) Temporary() bool {
return false
}
func (e *AddrError) Timeout() bool {
return false
}
type UnknownNetworkError string
func (e UnknownNetworkError) Error() string { return "unknown network " + string(e) }
func (e UnknownNetworkError) Temporary() bool { return false }
func (e UnknownNetworkError) Timeout() bool { return false }
type InvalidAddrError string
func (e InvalidAddrError) Error() string { return string(e) }
func (e InvalidAddrError) Timeout() bool { return false }
func (e InvalidAddrError) Temporary() bool { return false }
// DNSConfigError represents an error reading the machine's DNS configuration.
type DNSConfigError struct {
Err error
}
func (e *DNSConfigError) Error() string {
return "error reading DNS config: " + e.Err.Error()
}
func (e *DNSConfigError) Timeout() bool { return false }
func (e *DNSConfigError) Temporary() bool { return false }
type writerOnly struct {
io.Writer
}
// Fallback implementation of io.ReaderFrom's ReadFrom, when sendfile isn't
// applicable.
func genericReadFrom(w io.Writer, r io.Reader) (n int64, err error) {
// Use wrapper to hide existing r.ReadFrom from io.Copy.
return io.Copy(writerOnly{w}, r)
}
// Limit the number of concurrent cgo-using goroutines, because
// each will block an entire operating system thread. The usual culprit
// is resolving many DNS names in separate goroutines but the DNS
// server is not responding. Then the many lookups each use a different
// thread, and the system or the program runs out of threads.
var threadLimit = make(chan struct{}, 500)
// Using send for acquire is fine here because we are not using this
// to protect any memory. All we care about is the number of goroutines
// making calls at a time.
func acquireThread() {
threadLimit <- struct{}{}
}
func releaseThread() {
<-threadLimit
}