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October 3, 2015 08:01
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An experiment towards a nice http api in Go
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| // An experiment towards a nice http api in Go | |
| // | |
| // What is a "pretty" api? | |
| // | |
| // - content negotiation (including errors) | |
| // - public vs internal errors | |
| // - extensible (i.e. additional formats can be added easily) | |
| // | |
| // The current implementation has the first two, but not the last. | |
| package main | |
| import ( | |
| "encoding/json" | |
| "fmt" | |
| "github.com/golang/gddo/httputil" | |
| "html/template" | |
| "log" | |
| "net/http" | |
| ) | |
| // # The Spec | |
| // | |
| // GET /list -> html | |
| // GET /list (application/json) -> json | |
| // GET /list (oops) -> "unsupported media type" as text | |
| // | |
| // GET /error -> "internal server error" as html, actual error logged | |
| // GET /error (application/json) -> "internal server error" as json, actual error logged | |
| // GET /error (oops) -> "unsupported media type" as text, actual error logged? | |
| // | |
| // GET /public-error -> error as html | |
| // GET /public-error (application/json) -> error as json | |
| // GET /public-error (oops) -> "unsupported media type as text | |
| type Renderable struct { | |
| Status int | |
| Metadata map[string]interface{} | |
| Data interface{} | |
| Template *template.Template | |
| } | |
| func (r Renderable) MarshalJSON() ([]byte, error) { | |
| return json.Marshal(r.Data) | |
| } | |
| func main() { | |
| http.HandleFunc("/list", handleRequest(ListAll)) | |
| http.HandleFunc("/error", handleRequest(ErrorExample)) | |
| http.HandleFunc("/public-error", handleRequest(PublicError)) | |
| log.Println("Running on http://localhost:12345") | |
| err := http.ListenAndServe("localhost:12345", nil) | |
| if err != nil { | |
| log.Fatal(err) | |
| } | |
| } | |
| type Post struct { | |
| Title string `json:"title"` | |
| Content string `json:"content"` | |
| } | |
| func ListAll(w http.ResponseWriter, req *http.Request) (interface{}, error) { | |
| posts := []Post{ | |
| Post{"Hello, World!", "This is my first post!!!"}, | |
| } | |
| return Renderable{ | |
| Metadata: map[string]interface{}{ | |
| "Title": "All posts", | |
| }, | |
| Data: posts, | |
| Template: template.Must(template.New("").Parse(listAllTemplate)), | |
| }, nil | |
| } | |
| var listAllTemplate = `<!doctype html> | |
| <html> | |
| <head> | |
| <meta charset="utf-8" /> | |
| <title>{{ .Metadata.Title }}</title> | |
| </head> | |
| <body> | |
| <h1>{{ .Metadata.Title }}</h1> | |
| {{ range .Data }} | |
| <article class="post"> | |
| <h2>{{ .Title }}</h2> | |
| <p>{{ .Content }}</p> | |
| </article> | |
| {{ end }} | |
| </body> | |
| </html> | |
| ` | |
| func ErrorExample(w http.ResponseWriter, req *http.Request) (interface{}, error) { | |
| return nil, fmt.Errorf("this is an error...") | |
| } | |
| func PublicError(w http.ResponseWriter, req *http.Request) (interface{}, error) { | |
| return RenderableStatus(http.StatusNotImplemented), nil | |
| } | |
| func handleRequest(handler func(http.ResponseWriter, *http.Request) (interface{}, error)) func(http.ResponseWriter, *http.Request) { | |
| return func(w http.ResponseWriter, req *http.Request) { | |
| contentType := httputil.NegotiateContentType(req, []string{"text/html", "application/json"}, "") | |
| data, err := handler(w, req) | |
| if err != nil { | |
| log.Printf("Error: %s: %s\n", req.URL.Path, err) | |
| render(w, req, contentType, RenderableStatus(http.StatusInternalServerError)) | |
| return | |
| } | |
| renderable, ok := data.(Renderable) | |
| if !ok { | |
| panic("not implemented") | |
| } | |
| render(w, req, contentType, renderable) | |
| } | |
| } | |
| func render(w http.ResponseWriter, req *http.Request, contentType string, renderable Renderable) { | |
| if renderable.Status == 0 { | |
| renderable.Status = 200 | |
| } | |
| w.WriteHeader(renderable.Status) | |
| switch contentType { | |
| case "text/html": | |
| if renderable.Template != nil { | |
| err := renderable.Template.Execute(w, renderable) | |
| if err != nil { | |
| // FIXME: we might be in a partial response here, i.e. we | |
| // probably didn't return valid html. | |
| log.Printf("Error: rendering %s: %s\n", req.URL.Path, err) | |
| } | |
| } else { | |
| fmt.Fprint(w, http.StatusText(renderable.Status)) | |
| } | |
| case "application/json": | |
| var err error | |
| pretty := req.URL.Query().Get("pretty") == "true" | |
| if pretty { | |
| data, err := json.MarshalIndent(renderable.Data, "", " ") | |
| if err == nil { | |
| w.Write(data) | |
| w.Write([]byte{'\n'}) | |
| } | |
| } else { | |
| encoder := json.NewEncoder(w) | |
| err = encoder.Encode(renderable.Data) | |
| } | |
| if err != nil { | |
| log.Printf("Error: rendering %s: %s\n", req.URL.Path, err) | |
| } | |
| default: | |
| status := http.StatusUnsupportedMediaType | |
| http.Error(w, http.StatusText(status), status) | |
| } | |
| } | |
| func RenderableStatus(status int) Renderable { | |
| return Renderable{ | |
| Status: status, | |
| Data: httpStatus{ | |
| Status: status, | |
| Message: http.StatusText(status), | |
| }, | |
| } | |
| } | |
| type httpStatus struct { | |
| Status int `json:"status"` | |
| Message string `json:"message"` | |
| } |
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