api2 – Our Solution to Facilitate API Development

Usage

Organize your code in services. Each service provides some domain specific functionality. It is a Go type whose methods correspond to exposed RPCs of the API. Each method has the following signature:

func(ctx, *Request) (*Response, error)

Let’s define a service Foo with method Bar.

type Foo struct {
 ...
}
type BarRequest struct {
 // These fields are stored in JSON format in body.
 Name string `json:"name"`
 // These fields are GET parameters.
 UserID int `query:"user_id"`
 // These fields are headers.
 FileHash string `header:"file_hash"`
 // These fields are cookies.
 Foo string `cookie:"foo"`
 // These fields are skipped.
 SkippedField int `json:"-"`
}
type BarResponse struct {
 // These fields are stored in JSON format in body.
 FileSize int `json:"file_size"`
 // These fields are headers.
 FileHash string `header:"file_hash"`
 // These fields are skipped.
 SkippedField int `json:"-"`
}
func (s *Foo) Bar(ctx context.Context, req *BarRequest) (*BarResponse, error) {
 ...
}

A field must not have more than one of tags: json, query, header, cookie. Fields in query, header and cookie parts are encoded and decoded with fmt.Sprintf and fmt.Sscanf. Strings are not decoded with fmt.Sscanf, but passed as is. Types implementing encoding.TextMarshaler and encoding.TextUnmarshaler are encoded and decoded using it. If no JSON field is in the struct, then HTTP body is skipped.

If you need the top-level type matching body JSON to not be a struct, but of some other kind (e.g. slice or map), you should provide a field in your struct with tag use_as_body:"true":

type FooRequest struct {
	// Body of the request is JSON array of strings: ["abc", "eee", ...].
	Body []string `use_as_body:"true"`

	// You can add 'header', 'query' and 'cookie' fields here, but not 'json'.
}

If you use use_as_body:"true", you can also set is_protobuf:"true" and put a protobuf type (convertible to proto.Message) in that field. It will be sent over wire as protobuf binary form.

Now let’s write the function that generates the table of routes:

func GetRoutes(s *Foo) []api2.Route {
	return []api2.Route{
		{
			Method:    http.MethodPost,
			Path:      "/v1/foo/bar",
			Handler:   s.Bar,
			Transport: &api2.JsonTransport{},
		},
	}
}

You can add multiple routes with the same path, but in this case their HTTP methods must be different so that they can be distinguished.

If Transport is not set, DefaultTransport is used which is defined as &api2.JsonTransport{}.

In the server you need a real instance of service Foo to pass to GetRoutes. Then just bind the routes to http.ServeMux and run the server:

// Server.
foo := NewFoo(...)
routes := GetRoutes(foo)
api2.BindRoutes(http.DefaultServeMux, routes)
log.Fatal(http.ListenAndServe(":8080", nil))

The server is running. It serves foo.Bar function on path /v1/foo/bar with HTTP method Post.

Now let’s create the client:

// Client.
routes := GetRoutes(nil)
client := api2.NewClient(routes, "http://127.0.0.1:8080")
barRes := &BarResponse{}
err := client.Call(context.Background(), barRes, &BarRequest{
	...
})
if err != nil {
	panic(err)
}
// Server's response is in variable barRes.

Note that you don’t have to pass a real service object to GetRoutes on client side. You can pass nil, it is sufficient to pass all needed information about request and response types in the routes table, that is used by client to find a proper route.

You can make GetRoutes accepting an interface instead of a concrete Service type. In this case you can not get method handlers by s.Bar, because this code panics if s is nil interface. As a workaround api2 provides function Method(service pointer, methodName) which you can use:

type Service interface {
	Bar(ctx context.Context, req *BarRequest) (*BarResponse, error)
}

func GetRoutes(s Service) []api2.Route {
	return []api2.Route{
		{Method: http.MethodPost, Path: "/v1/foo/bar", Handler: api2.Method(&s, "Bar"), Transport: &api2.JsonTransport{}},
	}
}

If you have function GetRoutes in package foo as above you can generate static client for it in file client.go located near the file in which GetRoutes is defined:

api2.GenerateClient(foo.GetRoutes)

You can find an example in directory example. To build and run it:

$ go get github.com/starius/api2/example/...
$ server &
$ client
test
87672h0m0s

Code generation code is located in directory example/gen. To regenerate file client.go run: