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listener.go
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/
listener.go
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// Copyright 2022 Namespace Labs Inc; All rights reserved.
// Licensed under the Apache License, Version 2.0 (the "License");
// you may not use this file except in compliance with the License.
package fnnet
import (
"context"
"fmt"
"net"
"strings"
)
func ListenPort(ctx context.Context, localAddr string, localPort, containerPort int) (net.Listener, error) {
host := localAddr
if isIPv6 := strings.Count(localAddr, ":") >= 2; isIPv6 {
host = fmt.Sprintf("[%s]", localAddr)
}
var cfg net.ListenConfig
if localPort == 0 && containerPort != 0 {
// First we try to listen on a local port that matches the container port.
lst, err := cfg.Listen(ctx, "tcp", fmt.Sprintf("%s:%d", host, containerPort))
if err == nil {
return lst, nil
}
// Any failures fallback to the open any port path.
}
return cfg.Listen(ctx, "tcp", fmt.Sprintf("%s:%d", host, localPort))
}