dial.go

Documentation: golang.org/x/net/proxy

     1  // Copyright 2019 The Go Authors. All rights reserved.
     2  // Use of this source code is governed by a BSD-style
     3  // license that can be found in the LICENSE file.
     4  
     5  package proxy
     6  
     7  import (
     8  	"context"
     9  	"net"
    10  )
    11  
    12  // A ContextDialer dials using a context.
    13  type ContextDialer interface {
    14  	DialContext(ctx context.Context, network, address string) (net.Conn, error)
    15  }
    16  
    17  // Dial works like DialContext on net.Dialer but using a dialer returned by FromEnvironment.
    18  //
    19  // The passed ctx is only used for returning the Conn, not the lifetime of the Conn.
    20  //
    21  // Custom dialers (registered via RegisterDialerType) that do not implement ContextDialer
    22  // can leak a goroutine for as long as it takes the underlying Dialer implementation to timeout.
    23  //
    24  // A Conn returned from a successful Dial after the context has been cancelled will be immediately closed.
    25  func Dial(ctx context.Context, network, address string) (net.Conn, error) {
    26  	d := FromEnvironment()
    27  	if xd, ok := d.(ContextDialer); ok {
    28  		return xd.DialContext(ctx, network, address)
    29  	}
    30  	return dialContext(ctx, d, network, address)
    31  }
    32  
    33  // WARNING: this can leak a goroutine for as long as the underlying Dialer implementation takes to timeout
    34  // A Conn returned from a successful Dial after the context has been cancelled will be immediately closed.
    35  func dialContext(ctx context.Context, d Dialer, network, address string) (net.Conn, error) {
    36  	var (
    37  		conn net.Conn
    38  		done = make(chan struct{}, 1)
    39  		err  error
    40  	)
    41  	go func() {
    42  		conn, err = d.Dial(network, address)
    43  		close(done)
    44  		if conn != nil && ctx.Err() != nil {
    45  			conn.Close()
    46  		}
    47  	}()
    48  	select {
    49  	case <-ctx.Done():
    50  		err = ctx.Err()
    51  	case <-done:
    52  	}
    53  	return conn, err
    54  }
    55
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