rpc

README

RPC

Calling Golang backend should be simple.

• no dependencies
• 100% test coverage
• simple and efficient

This project was created within one night after my frustration while writing yet another service which basically exposes DB operations as an HTTP endpoint. The problem is that most of the current approaches offer some kind of framework lock. Once you write your business logic, you will, basically, have to duplicate the method, which will just accept values from an HTTP request and proxy it to the business function.

This project allows you to expose almost any kind of structure method as HTTP endpoints.

Supports:

• Any input and output arguments as soon as it is supported by JSON encoder/decoder
  • (optionally) First argument can be context.Context and it will be wired to request.Context()
• Value and/or error output. Example:
  • Foo(...)
  • Foo(...) error
  • Foo(...) int64
  • Foo(...) (int64, error)

Simplest possible example:

package main

type Service struct{}

func (srv *Service) Sum(a, b int64) int64 {
	return a + b
}

func main() {
	http.Handle("/api/", http.StripPrefix("/api", rpc.New(&Service{})))
	http.ListenAndServe("127.0.0.1:8080", nil)
}

In JS side (you can just copy-and-paste)

function RPC(baseURL = "") {
    return new Proxy({}, {
        get(obj, method) {
            method = method.toLowerCase();
            if (method in obj) {
                return obj[method]
            }

            const url = baseURL + "/" + encodeURIComponent(method)
            const fn = async function () {
                const args = Array.prototype.slice.call(arguments);
                const res = await fetch(url, {
                    method: "POST",
                    body: JSON.stringify(args),
                    headers: {
                        "Content-Type": "application/json"
                    }
                })
                if (!res.ok) {
                    const errMessage = await res.text();
                    throw new Error(errMessage);
                }
                return await res.json()
            }
            return obj[method] = fn
        }
    })
}

And use it as:

const api = RPC("/api");

const amount = await api.sum(123, 456)

Alternative is to use CDN (seriously? for 375 bytes?)

<script type="module">
    import RPC from "https://cdn.jsdelivr.net/gh/reddec/rpc@1/js/rpc.min.js"

    const API = RPC("/api");
    const total = await API.sum(123, 456);
</script>

Dynamic session

In some cases you may need to prepare session, based on request: find user, authenticate it and so on. For that use Builder.

Builder will invoke factory on each request and use returned value as API session object.

For example:

package main

import (
	"net/http"
	"github.com/reddec/rpc"
)

type userSession struct {
	user string
}

func (us *userSession) Greet() string { // this will be an exported method
	return "Hello, " + us.user + "!"
}

type server struct{}

func (srv *server) newSession(r *http.Request) (*userSession, error) {
	user := r.Header.Get("X-User") // mimic real authorization
	return &userSession{
		user: user,
	}, nil
}

func main() {
	var srv server // initialize it!
	http.Handle("/api/", http.StripPrefix("/api", rpc.Builder(srv.newSession)))
	http.ListenAndServe("127.0.0.1:8080", nil)
}

Now, on call api.greet(), first will be executed newSession and then userSession.Greet

Documentation

Index

• func Builder[T any](factory func(r *http.Request) (T, error)) http.Handler
• func Index(object interface{}) map[string]*ExposedMethod
• func New(object interface{}) http.Handler
• func Router(index map[string]*ExposedMethod) http.Handler
• type ExposedMethod
  • func (em *ExposedMethod) ServeHTTP(writer http.ResponseWriter, request *http.Request)

Functions

func Builder

func Builder[T any](factory func(r *http.Request) (T, error)) http.Handler

Builder creates new path-based, POST-only router, with custom receiver (aka session) for each request.

type API struct {
    User string // to be filled by Server
}
type Server struct {}
func (srv *Server) newAPI(r *http.Request) (*API, error) {}

// ...
var server Server
handler := Builder(server.newAPI)

Handler will return

400 Bad Request in case payload can not be unmarshalled to arguments or number of arguments not enough.

404 Not Found in case method is not known (case-insensitive).

500 Internal Server Error in case method returned an error or factory returned error. Response payload will be error message (plain text)

200 OK in case everything fine

func Index

func Index(object interface{}) map[string]*ExposedMethod

Index object's (usually pointer to struct) method. Matched public methods will be wrapped to http handler, which parses request body as JSON array and passes it to function. Result will be returned also as json.

Criteria for matching methods: no return values, or single return value/error, or two return values, where second one must be an error. First input argument could be context.Context which will be automatically wired from request.Context().

Foo()                                          // OK
Foo(ctx context.Context)                       // OK
Foo(ctx context.Context, bar int, baz SomeObj) // OK
Foo(bar int, baz string)                       // OK

Foo(...) error        // OK
Foo(...) int          // OK
Foo(...) (int, error) // OK
Foo(...) (int, int)   // NOT ok - last argument is not an error

Handler will return

400 Bad Request in case payload can not be unmarshalled to arguments or number of arguments not enough.

500 Internal Server Error in case method returned an error. Response payload will be error message (plain text)

200 OK in case everything fine

func New

func New(object interface{}) http.Handler

New exposes matched methods of object as HTTP endpoints. It's shorthand for Router(Index(object)).

func Router

func Router(index map[string]*ExposedMethod) http.Handler

Router creates mux handler which exposes all indexed method with name as path, in lower case, and only for POST method.

http.Handle("/api/", http.StripPrefix("/api", Router(...)))

MyFoo(..) -> POST /myfoo

Types

type ExposedMethod

type ExposedMethod struct {
	// contains filtered or unexported fields
}

func (*ExposedMethod) ServeHTTP

func (em *ExposedMethod) ServeHTTP(writer http.ResponseWriter, request *http.Request)