How to configure Go programs to utilize a custom proxy?

Customizing Proxy Usage in Go Programs

To automatically configure Go programs to utilize a proxy, the http.Client type provides a ProxyFromEnvironment method. This method examines the HTTP_PROXY and HTTPS_PROXY environment variables to determine the appropriate proxy URL.

In the code snippet provided:

<code class="go">tr := &http.Transport{
    TLSClientConfig: &tls.Config{InsecureSkipVerify: true},
}
client := &http.Client{Transport: tr}
resp, err := client.Get(url)</code>

the transport created does not consider proxy settings. To enable proxy usage, utilize the ProxyFromEnvironment method:

<code class="go">var PTransport = &http.Transport{
  Proxy: http.ProxyFromEnvironment,
}
client := http.Client{
  Transport: PTransport,
}</code>

ProxyFromEnvironment returns the proxy URL derived from the environment variables, prioritizing HTTPS_PROXY for HTTPS requests.

To utilize a custom proxy, define the environment variables as follows:

export http_proxy='http://user:password@prox-server:3128'
export https_proxy='http://user:password@prox-server:3128'
export HTTP_PROXY='http://user:password@prox-server:3128'
export HTTPS_PROXY='http://user:password@prox-server:3128'

The provided code sample, which performs a GET request against a remote API, demonstrates the successful integration of proxy settings:

<code class="go">package main

import (
  "fmt"
  "net/http"
  "io/ioutil"
)

func main() {

  var PTransport = & http.Transport {
    Proxy: http.ProxyFromEnvironment
  }
  client: = http.Client {
    Transport: PTransport
  }
  req, err: = http.NewRequest("GET", "https://jsonplaceholder.typicode.com/todos/1", nil)
  req.Header.Add("If-None-Match", `some value`)
  resp, err: = client.Do(req)
  if err != nil {
    panic(err)
  }
  defer resp.Body.Close()

  bodyBytes, err: = ioutil.ReadAll(resp.Body)
  if err != nil {
    panic(err)
  }

  bodyString: = string(bodyBytes)
  fmt.Printf("GET Response = %s \n", string(bodyString))


}</code>

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