How to Resolve \"Accept: Invalid Argument\" Error When Creating HTTP Server on TCP Socket in Go?

HTTP Server from TCP Socket in Go: Troubleshooting an "Accept: Invalid Argument" Error

This issue arises when attempting to create an HTTP server on a TCP socket within a specific VRF interface. Despite correctly binding the socket to the VRF, starting the HTTP server results in an error indicating "accept tcp 127.0.0.1:80: accept: invalid argument."

Understanding the Problem

This error suggests that the socket configuration may be incorrect or defective. However, it is essential to note that the VRF binding is not directly causing the problem but is simply included in the provided code for context.

Resolution

To resolve this issue, it is necessary to ensure that the socket is configured correctly according to the requirements of the net package. A net.ListenConfig can be utilized to specify the desired socket options before calling syscall.Bind.

Code Example

The following code demonstrates the use of net.ListenConfig to resolve the socket configuration issue:

<code class="go">import (
    "context"
    "fmt"
    "log"
    "net"
    syscall
)

func main() {
    lc := net.ListenConfig{Control: controlOnConnSetup}

    ln, err := lc.Listen(context.Background(), "tcp", "127.0.0.1:80")
    if err != nil {
        log.Fatal(err)
    }

    // ... Do something with the listener

    ln.Close()
}

func controlOnConnSetup(network string, address string, c syscall.RawConn) error {
    var operr error
    fn := func(fd uintptr) {
        operr = syscall.SetsockoptString(int(fd), syscall.SOL_SOCKET, syscall.SO_BINDTODEVICE, "vrfiface")
    }
    if err := c.Control(fn); err != nil {
        return err
    }
    if operr != nil {
        return operr
    }
    return nil
}</code>

Explanation

The ListenConfig.Control function provides access to the syscall.RawConn, which allows manipulation of the underlying file descriptor before the actual socket binding is performed. The Control function is invoked with a closure that specifies the desired socket option, in this case, binding to a specific VRF interface.

By utilizing the ListenConfig, the socket configuration process is properly synchronized with the expectations of the net package, ensuring that the socket is set up correctly for HTTP server operation.

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