Go HTTP client example with context cancellation + sensible timeouts, returning response body safely (idiomatic net/http).

go-http-client-timeout-context.go

package main

import (
	"context"
	"fmt"
	"io"
	"log"
	"net"
	"net/http"
	"time"
)

// newHTTPClient returns an HTTP client with sensible defaults.
//
// Notes:
// - http.Client.Timeout covers the full request (connect + redirects + reading body).
// - Transport timeouts provide more granular control.
func newHTTPClient() *http.Client {
	transport := &http.Transport{
		Proxy: http.ProxyFromEnvironment,
		DialContext: (&net.Dialer{
			Timeout:   5 * time.Second,  // TCP connect timeout
			KeepAlive: 30 * time.Second, // keepalive
		}).DialContext,
		TLSHandshakeTimeout:   5 * time.Second,
		ResponseHeaderTimeout: 10 * time.Second,
		ExpectContinueTimeout: 1 * time.Second,
		IdleConnTimeout:       90 * time.Second,
		MaxIdleConns:          100,
	}

	return &http.Client{
		Transport: transport,
		Timeout:   15 * time.Second, // hard upper bound for whole request
	}
}

// get performs a GET request with a context.
// It returns the response body as bytes and fails if status is not 2xx.
func get(ctx context.Context, client *http.Client, url string) ([]byte, error) {
	req, err := http.NewRequestWithContext(ctx, http.MethodGet, url, nil)
	if err != nil {
		return nil, fmt.Errorf("new request: %w", err)
	}

	req.Header.Set("User-Agent", "go-http-client-timeout-context/1.0")
	req.Header.Set("Accept", "application/json")

	resp, err := client.Do(req)
	if err != nil {
		return nil, fmt.Errorf("do request: %w", err)
	}
	defer resp.Body.Close()

	// Optional but recommended: limit response body size
	const maxBodySize = 2 << 20 // 2MB
	body, err := io.ReadAll(io.LimitReader(resp.Body, maxBodySize))
	if err != nil {
		return nil, fmt.Errorf("read body: %w", err)
	}

	if resp.StatusCode < 200 || resp.StatusCode >= 300 {
		return nil, fmt.Errorf("http status %d: %s", resp.StatusCode, string(body))
	}

	return body, nil
}

func main() {
	client := newHTTPClient()

	// Context timeout (cancels the request if it exceeds this time)
	ctx, cancel := context.WithTimeout(context.Background(), 3*time.Second)
	defer cancel()

	url := "https://httpbin.org/json"

	body, err := get(ctx, client, url)
	if err != nil {
		log.Fatalf("request failed: %v", err)
	}

	fmt.Println(string(body))
}