How do I set headers for HTTP requests and use a specific IP address with http.Client and http.Transport?

Setting Headers for Requests with http.Client and http.Transport

When making HTTP requests with multiple available IP addresses, it is necessary to specify the desired IP for outgoing connections. This can be accomplished using the http.Client and http.Transport structures.

Creating a Dialer with a Specific IP

First, create a net.Dialer instance and set the LocalAddr field to the desired IP address. In your code, you have:

<code class="go">tcpAddr := &net.TCPAddr{
    IP: addrs[3].(*net.IPNet).IP, // Choosing ip address number 3
}
d := net.Dialer{LocalAddr: tcpAddr}</code>

Customizing the http.Transport

Next, create an http.Transport instance and configure its Dial field with the custom dialer:

<code class="go">transport := &http.Transport{
    Dial:                (&net.Dialer{LocalAddr: tcpAddr}).Dial,
    TLSHandshakeTimeout: 10 * time.Second,
}</code>

Creating the http.Client

Finally, create an http.Client instance and set its Transport field to the customized transport:

<code class="go">client := &http.Client{
    Transport: transport,
}</code>

Setting Request Headers

To set headers for a specific request, you need to create an http.Request object and use the Set method on its Header field:

<code class="go">req, err := http.NewRequest("GET", "https://www.whatismyip.com/", nil)
if err != nil {
    // Handle error
}

req.Header.Set("name", "value")</code>

Using the Configured Client

Once you have set the headers, you can use the Do method of the client instance to execute the request:

<code class="go">resp, err := client.Do(req)
if err != nil {
    // Handle error
}

// Handle the response</code>

By following these steps, you can set headers for HTTP requests while using a specific IP address for outgoing connections.

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