add basic apigateway example which discovers services on demand from consul and forwards rpc calls to discovered endpoints
Marcel Hauf
7 years ago
| 0 | package main | |
| 1 | ||
| 2 | import ( | |
| 3 | "bytes" | |
| 4 | "encoding/json" | |
| 5 | "io" | |
| 6 | "io/ioutil" | |
| 7 | "log" | |
| 8 | "net/http" | |
| 9 | "net/url" | |
| 10 | "strings" | |
| 11 | ||
| 12 | "golang.org/x/net/context" | |
| 13 | ||
| 14 | "github.com/gorilla/mux" | |
| 15 | ||
| 16 | "github.com/go-kit/kit/endpoint" | |
| 17 | "github.com/go-kit/kit/loadbalancer" | |
| 18 | "github.com/go-kit/kit/loadbalancer/consul" | |
| 19 | klog "github.com/go-kit/kit/log" | |
| 20 | httptransport "github.com/go-kit/kit/transport/http" | |
| 21 | ||
| 22 | "github.com/hashicorp/consul/api" | |
| 23 | ) | |
| 24 | ||
| 25 | var ( | |
| 26 | discoveryClient consul.Client | |
| 27 | ctx = context.Background() | |
| 28 | ) | |
| 29 | ||
| 30 | func main() { | |
| 31 | ||
| 32 | consulConfig := api.DefaultConfig() | |
| 33 | consulClient, err := api.NewClient(consulConfig) | |
| 34 | if err != nil { | |
| 35 | log.Fatal(err) | |
| 36 | } | |
| 37 | discoveryClient = consul.NewClient(consulClient) | |
| 38 | ||
| 39 | r := mux.NewRouter() | |
| 40 | r.HandleFunc("/api/{service}/{method}", apiGateway) | |
| 41 | ||
| 42 | http.ListenAndServe(":8000", r) | |
| 43 | } | |
| 44 | ||
| 45 | func apiGateway(w http.ResponseWriter, r *http.Request) { | |
| 46 | vars := mux.Vars(r) | |
| 47 | service := vars["service"] | |
| 48 | method := vars["method"] | |
| 49 | e, err := getEndpoint(service, method) | |
| 50 | if err != nil { | |
| 51 | log.Print(err) | |
| 52 | return | |
| 53 | } | |
| 54 | ||
| 55 | var val interface{} | |
| 56 | dec := json.NewDecoder(r.Body) | |
| 57 | err = dec.Decode(&val) | |
| 58 | if err != nil { | |
| 59 | log.Print(err) | |
| 60 | return | |
| 61 | } | |
| 62 | ||
| 63 | resp, err := e(ctx, val) | |
| 64 | if err != nil { | |
| 65 | log.Print(err) | |
| 66 | return | |
| 67 | } | |
| 68 | enc := json.NewEncoder(w) | |
| 69 | err = enc.Encode(resp) | |
| 70 | if err != nil { | |
| 71 | log.Print(err) | |
| 72 | return | |
| 73 | } | |
| 74 | } | |
| 75 | ||
| 76 | var services = make(map[string]service) | |
| 77 | ||
| 78 | type service map[string]loadbalancer.LoadBalancer | |
| 79 | ||
| 80 | func getEndpoint(se string, method string) (endpoint.Endpoint, error) { | |
| 81 | if s, ok := services[se]; ok { | |
| 82 | if m, ok := s[method]; ok { | |
| 83 | return m.Endpoint() | |
| 84 | } | |
| 85 | } | |
| 86 | ||
| 87 | publisher, err := consul.NewPublisher(discoveryClient, factory(ctx, method), klog.NewLogfmtLogger(&klog.StdlibWriter{}), se) | |
| 88 | if err != nil { | |
| 89 | return nil, err | |
| 90 | } | |
| 91 | rr := loadbalancer.NewRoundRobin(publisher) | |
| 92 | ||
| 93 | if _, ok := services[se]; ok { | |
| 94 | services[se][method] = rr | |
| 95 | } else { | |
| 96 | services[se] = service{method: rr} | |
| 97 | } | |
| 98 | ||
| 99 | return rr.Endpoint() | |
| 100 | } | |
| 101 | ||
| 102 | func factory(ctx context.Context, method string) loadbalancer.Factory { | |
| 103 | return func(service string) (endpoint.Endpoint, io.Closer, error) { | |
| 104 | var e endpoint.Endpoint | |
| 105 | e = makeProxy(ctx, service, method) | |
| 106 | return e, nil, nil | |
| 107 | } | |
| 108 | } | |
| 109 | ||
| 110 | func makeProxy(ctx context.Context, service, method string) endpoint.Endpoint { | |
| 111 | if !strings.HasPrefix(service, "http") { | |
| 112 | service = "http://" + service | |
| 113 | } | |
| 114 | u, err := url.Parse(service) | |
| 115 | if err != nil { | |
| 116 | panic(err) | |
| 117 | } | |
| 118 | if u.Path == "" { | |
| 119 | u.Path = "/" + method | |
| 120 | } | |
| 121 | ||
| 122 | return httptransport.NewClient( | |
| 123 | "GET", | |
| 124 | u, | |
| 125 | encodeRequest, | |
| 126 | decodeResponse, | |
| 127 | ).Endpoint() | |
| 128 | } | |
| 129 | ||
| 130 | func encodeRequest(r *http.Request, request interface{}) error { | |
| 131 | log.Printf("encode req: %v", request) | |
| 132 | var buf bytes.Buffer | |
| 133 | if err := json.NewEncoder(&buf).Encode(request); err != nil { | |
| 134 | log.Print(err) | |
| 135 | return err | |
| 136 | } | |
| 137 | r.Body = ioutil.NopCloser(&buf) | |
| 138 | return nil | |
| 139 | } | |
| 140 | ||
| 141 | func decodeResponse(r *http.Response) (interface{}, error) { | |
| 142 | var response interface{} | |
| 143 | if err := json.NewDecoder(r.Body).Decode(&response); err != nil { | |
| 144 | return nil, err | |
| 145 | } | |
| 146 | return response, nil | |
| 147 | } |