Sling 
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 to learn how to compose a Sling into your API client.
Features
- 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
Install
go get github.com/dghubble/sling
Documentation
Read GoDoc
Usage
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()
client.Do(req)
Path
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")
Headers
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()
Query
QueryStruct
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()
Body
JSON Body
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().
Sending
Receive
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))
client.Do(req)
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
- Digits dghubble/go-digits
- GoSquared drinkin/go-gosquared
- Kala ajvb/kala
- Parse fergstar/go-parse
- Swagger Generator swagger-api/swagger-codegen
- Twitter dghubble/go-twitter
- Stacksmith jesustinoco/go-smith
Create a Pull Request to add a link to your own API.
Motivation
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.
Contributing
See the Contributing Guide.