Programming language: Go
Tags: Utilities    
Latest version: v1.3.0

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Sling Build Status GoDoc

Sling is a Go HTTP client library for creating and sending API requests.

Slings store HTTP Request properties to simplify sending requests and decoding responses. Check usage or the [examples](examples) to learn how to compose a Sling into your API client.


  • Method Setters: Get/Post/Put/Patch/Delete/Head
  • Add or Set Request Headers
  • Base/Path: Extend a Sling for different endpoints
  • Encode structs into URL query parameters
  • Encode a form or JSON into the Request Body
  • Receive JSON success or failure responses


go get github.com/dghubble/sling


Read GoDoc


Use a Sling to set path, method, header, query, or body properties and create an http.Request.

type Params struct {
    Count int `url:"count,omitempty"`
params := &Params{Count: 5}

req, err := sling.New().Get("https://example.com").QueryStruct(params).Request()


Use Path to set or extend the URL for created Requests. Extension means the path will be resolved relative to the existing URL.

// creates a GET request to https://example.com/foo/bar
req, err := sling.New().Base("https://example.com/").Path("foo/").Path("bar").Request()

Use Get, Post, Put, Patch, Delete, Head, Options, Trace, or Connect which are exactly the same as Path except they set the HTTP method too.

req, err := sling.New().Post("http://upload.com/gophers")


Add or Set headers for requests created by a Sling.

s := sling.New().Base(baseUrl).Set("User-Agent", "Gophergram API Client")
req, err := s.New().Get("gophergram/list").Request()



Define url tagged structs. Use QueryStruct to encode a struct as query parameters on requests.

// Github Issue Parameters
type IssueParams struct {
    Filter    string `url:"filter,omitempty"`
    State     string `url:"state,omitempty"`
    Labels    string `url:"labels,omitempty"`
    Sort      string `url:"sort,omitempty"`
    Direction string `url:"direction,omitempty"`
    Since     string `url:"since,omitempty"`
githubBase := sling.New().Base("https://api.github.com/").Client(httpClient)

path := fmt.Sprintf("repos/%s/%s/issues", owner, repo)
params := &IssueParams{Sort: "updated", State: "open"}
req, err := githubBase.New().Get(path).QueryStruct(params).Request()



Define JSON tagged structs. Use BodyJSON to JSON encode a struct as the Body on requests.

type IssueRequest struct {
    Title     string   `json:"title,omitempty"`
    Body      string   `json:"body,omitempty"`
    Assignee  string   `json:"assignee,omitempty"`
    Milestone int      `json:"milestone,omitempty"`
    Labels    []string `json:"labels,omitempty"`
githubBase := sling.New().Base("https://api.github.com/").Client(httpClient)
path := fmt.Sprintf("repos/%s/%s/issues", owner, repo)

body := &IssueRequest{
    Title: "Test title",
    Body:  "Some issue",
req, err := githubBase.New().Post(path).BodyJSON(body).Request()

Requests will include an application/json Content-Type header.

Form Body

Define url tagged structs. Use BodyForm to form url encode a struct as the Body on requests.

type StatusUpdateParams struct {
    Status             string   `url:"status,omitempty"`
    InReplyToStatusId  int64    `url:"in_reply_to_status_id,omitempty"`
    MediaIds           []int64  `url:"media_ids,omitempty,comma"`
tweetParams := &StatusUpdateParams{Status: "writing some Go"}
req, err := twitterBase.New().Post(path).BodyForm(tweetParams).Request()

Requests will include an application/x-www-form-urlencoded Content-Type header.

Plain Body

Use Body to set a plain io.Reader on requests created by a Sling.

body := strings.NewReader("raw body")
req, err := sling.New().Base("https://example.com").Body(body).Request()

Set a content type header, if desired (e.g. Set("Content-Type", "text/plain")).

Extend a Sling

Each Sling creates a standard http.Request (e.g. with some path and query params) each time Request() is called. You may wish to extend an existing Sling to minimize duplication (e.g. a common client or base url).

Each Sling instance provides a New() method which creates an independent copy, so setting properties on the child won't mutate the parent Sling.

const twitterApi = "https://api.twitter.com/1.1/"
base := sling.New().Base(twitterApi).Client(authClient)

// statuses/show.json Sling
tweetShowSling := base.New().Get("statuses/show.json").QueryStruct(params)
req, err := tweetShowSling.Request()

// statuses/update.json Sling
tweetPostSling := base.New().Post("statuses/update.json").BodyForm(params)
req, err := tweetPostSling.Request()

Without the calls to base.New(), tweetShowSling and tweetPostSling would reference the base Sling and POST to "https://api.twitter.com/1.1/statuses/show.json/statuses/update.json", which is undesired.

Recap: If you wish to extend a Sling, create a new child copy with New().



Define a JSON struct to decode a type from 2XX success responses. Use ReceiveSuccess(successV interface{}) to send a new Request and decode the response body into successV if it succeeds.

// Github Issue (abbreviated)
type Issue struct {
    Title  string `json:"title"`
    Body   string `json:"body"`
issues := new([]Issue)
resp, err := githubBase.New().Get(path).QueryStruct(params).ReceiveSuccess(issues)
fmt.Println(issues, resp, err)

Most APIs return failure responses with JSON error details. To decode these, define success and failure JSON structs. Use Receive(successV, failureV interface{}) to send a new Request that will automatically decode the response into the successV for 2XX responses or into failureV for non-2XX responses.

type GithubError struct {
    Message string `json:"message"`
    Errors  []struct {
        Resource string `json:"resource"`
        Field    string `json:"field"`
        Code     string `json:"code"`
    } `json:"errors"`
    DocumentationURL string `json:"documentation_url"`
issues := new([]Issue)
githubError := new(GithubError)
resp, err := githubBase.New().Get(path).QueryStruct(params).Receive(issues, githubError)
fmt.Println(issues, githubError, resp, err)

Pass a nil successV or failureV argument to skip JSON decoding into that value.

Modify a Request

Sling provides the raw http.Request so modifications can be made using standard net/http features. For example, in Go 1.7+ , add HTTP tracing to a request with a context:

req, err := sling.New().Get("https://example.com").QueryStruct(params).Request()
// handle error

trace := &httptrace.ClientTrace{
   DNSDone: func(dnsInfo httptrace.DNSDoneInfo) {
      fmt.Printf("DNS Info: %+v\n", dnsInfo)
   GotConn: func(connInfo httptrace.GotConnInfo) {
      fmt.Printf("Got Conn: %+v\n", connInfo)

req = req.WithContext(httptrace.WithClientTrace(req.Context(), trace))

Build an API

APIs typically define an endpoint (also called a service) for each type of resource. For example, here is a tiny Github IssueService which lists repository issues.

const baseURL = "https://api.github.com/"

type IssueService struct {
    sling *sling.Sling

func NewIssueService(httpClient *http.Client) *IssueService {
    return &IssueService{
        sling: sling.New().Client(httpClient).Base(baseURL),

func (s *IssueService) ListByRepo(owner, repo string, params *IssueListParams) ([]Issue, *http.Response, error) {
    issues := new([]Issue)
    githubError := new(GithubError)
    path := fmt.Sprintf("repos/%s/%s/issues", owner, repo)
    resp, err := s.sling.New().Get(path).QueryStruct(params).Receive(issues, githubError)
    if err == nil {
        err = githubError
    return *issues, resp, err

Example APIs using Sling

Create a Pull Request to add a link to your own API.


Many client libraries follow the lead of google/go-github (our inspiration!), but do so by reimplementing logic common to all clients.

This project borrows and abstracts those ideas into a Sling, an agnostic component any API client can use for creating and sending requests.


See the Contributing Guide.


[MIT License](LICENSE)

*Note that all licence references and agreements mentioned in the sling README section above are relevant to that project's source code only.