HTTP Client

Syntax#

resp, err := http.Get(url) // Makes a HTTP GET request with the default HTTP client. A non-nil error is returned if the request fails.
resp, err := http.Post(url, bodyType, body) // Makes a HTTP POST request with the default HTTP client. A non-nil error is returned if the request fails.
resp, err := http.PostForm(url, values) // Makes a HTTP form POST request with the default HTTP client. A non-nil error is returned if the request fails.

Parameters#

Parameter	Details
resp	A response of type `*http.Response` to an HTTP request
err	An `error`. If not nil, it represents an error that occured when the function was called.
url	A URL of type `string` to make a HTTP request to.
bodyType	The MIME type of type `string` of the body payload of a POST request.
body	An `io.Reader` (implements `Read()`) which will be read from until an error is reached to be submitted as the body payload of a POST request.
values	A key-value map of type `url.Values`. The underlying type is a `map[string][]string`.
## Remarks#
It is important to `defer resp.Body.Close()` after every HTTP request that does not return a non-nil error, else resources will be leaked.
## Basic GET
Perform a basic GET request and prints the contents of a site (HTML).

package main

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

func main() {
    resp, err := http.Get("https://example.com/")
    if err != nil {
        panic(err)
    }

    // It is important to defer resp.Body.Close(), else resource leaks will occur.
    defer resp.Body.Close()

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

    // Will print site contents (HTML) to output
    fmt.Println(string(data))
}

GET with URL parameters and a JSON response

A request for the top 10 most recently active StackOverflow posts using the Stack Exchange API.

package main

import (
    "encoding/json"
    "fmt"
    "net/http"
    "net/url"
)

const apiURL = "https://api.stackexchange.com/2.2/posts?"

// Structs for JSON decoding
type postItem struct {
    Score int    `json:"score"`
    Link  string `json:"link"`
}

type postsType struct {
    Items []postItem `json:"items"`
}

func main() {
    // Set URL parameters on declaration
    values := url.Values{
        "order": []string{"desc"},
        "sort":  []string{"activity"},
        "site":  []string{"stackoverflow"},
    }

    // URL parameters can also be programmatically set
    values.Set("page", "1")
    values.Set("pagesize", "10")

    resp, err := http.Get(apiURL + values.Encode())
    if err != nil {
        panic(err)
    }

    defer resp.Body.Close()

    // To compare status codes, you should always use the status constants
    // provided by the http package.
    if resp.StatusCode != http.StatusOK {
        panic("Request was not OK: " + resp.Status)
    }

    // Example of JSON decoding on a reader.
    dec := json.NewDecoder(resp.Body)
    var p postsType
    err = dec.Decode(&p)
    if err != nil {
        panic(err)
    }

    fmt.Println("Top 10 most recently active StackOverflow posts:")
    fmt.Println("Score", "Link")
    for _, post := range p.Items {
        fmt.Println(post.Score, post.Link)
    }
}

Time out request with a context

1.7+

Timing out an HTTP request with a context can be accomplished with only the standard library (not the subrepos) in 1.7+:

import (
    "context"
    "net/http"
    "time"
)

req, err := http.NewRequest("GET", `https://example.net`, nil)
ctx, _ := context.WithTimeout(context.TODO(), 200 * time.Milliseconds)
resp, err := http.DefaultClient.Do(req.WithContext(ctx))
// Be sure to handle errors.
defer resp.Body.Close()

Before 1.7

import (
    "net/http"
    "time"

    "golang.org/x/net/context"
    "golang.org/x/net/context/ctxhttp"
)

ctx, err := context.WithTimeout(context.TODO(), 200 * time.Milliseconds)
resp, err := ctxhttp.Get(ctx, http.DefaultClient, "https://www.example.net")
// Be sure to handle errors.
defer resp.Body.Close()

Further Reading

For more information on the context package see https://stackoverflow.com/documentation/go/2743/context#t=201607241737444114694.

PUT request of JSON object

The following updates a User object via a PUT request and prints the status code of the request:

package main

import (
    "bytes"
    "encoding/json"
    "fmt"
    "net/http"
)

type User struct {
    Name  string
    Email string
}

func main() {
    user := User{
        Name:  "John Doe",
        Email: "johndoe@example.com",
    }

    // initialize http client
    client := &http.Client{}

    // marshal User to json
    json, err := json.Marshal(user)
    if err != nil {
        panic(err)
    }

    // set the HTTP method, url, and request body
    req, err := http.NewRequest(http.MethodPut, "https://api.example.com/v1/user", bytes.NewBuffer(json))
    if err != nil {
        panic(err)
    }

    // set the request header Content-Type for json
    req.Header.Set("Content-Type", "application/json; charset=utf-8")
    resp, err := client.Do(req)
    if err != nil {
        panic(err)
    }

    fmt.Println(resp.StatusCode)
}