Connect

Connect is a slim library for building browser and gRPC-compatible HTTP APIs. You write a short Protocol Buffer schema and implement your application logic, and Connect generates code to handle marshaling, routing, compression, and content type negotiation. It also generates an idiomatic, type-safe client. Handlers and clients support three protocols: gRPC, gRPC-Web, and Connect's own protocol.

The Connect protocol is a simple, POST-only protocol that works over HTTP/1.1 or HTTP/2. It takes the best portions of gRPC and gRPC-Web, including streaming, and packages them into a protocol that works equally well in browsers, monoliths, and microservices. Calling a Connect API is as easy as using curl. Try it with our live demo:

curl \
    --header "Content-Type: application/json" \
    --data '{"sentence": "I feel happy."}' \
    https://demo.connect.build/buf.connect.demo.eliza.v1.ElizaService/Say

Handlers and clients also support the gRPC and gRPC-Web protocols, including streaming, headers, trailers, and error details. gRPC-compatible server reflection and health checks are available as standalone packages. Instead of cURL, we could call our API with grpcurl:

go install github.com/fullstorydev/grpcurl/cmd/grpcurl@latest
grpcurl \
    -d '{"sentence": "I feel happy."}' \
    demo.connect.build:443 \
    buf.connect.demo.eliza.v1.ElizaService/Say

Under the hood, Connect is just Protocol Buffers and the standard library: no custom HTTP implementation, no new name resolution or load balancing APIs, and no surprises. Everything you already know about net/http still applies, and any package that works with an http.Server, http.Client, or http.Handler also works with Connect.

For more on Connect, see the announcement blog post, the documentation on connect.build (especially the Getting Started guide for Go), the demo service, or the protocol specification.

A small example

Curious what all this looks like in practice? From a Protobuf schema, we generate a small RPC package. Using that package, we can build a server:

package main

import (
  "context"
  "log"
  "net/http"

  "github.com/bufbuild/connect-go"
  pingv1 "github.com/bufbuild/connect-go/internal/gen/connect/ping/v1"
  "github.com/bufbuild/connect-go/internal/gen/connect/ping/v1/pingv1connect"
  "golang.org/x/net/http2"
  "golang.org/x/net/http2/h2c"
)

type PingServer struct {
  pingv1connect.UnimplementedPingServiceHandler // returns errors from all methods
}

func (ps *PingServer) Ping(
  ctx context.Context,
  req *connect.Request[pingv1.PingRequest],
) (*connect.Response[pingv1.PingResponse], error) {
  // connect.Request and connect.Response give you direct access to headers and
  // trailers. No context-based nonsense!
  log.Println(req.Header().Get("Some-Header"))
  res := connect.NewResponse(&pingv1.PingResponse{
    // req.Msg is a strongly-typed *pingv1.PingRequest, so we can access its
    // fields without type assertions.
    Number: req.Msg.Number,
  })
  res.Header().Set("Some-Other-Header", "hello!")
  return res, nil
}

func main() {
  mux := http.NewServeMux()
  // The generated constructors return a path and a plain net/http
  // handler.
  mux.Handle(pingv1connect.NewPingServiceHandler(&PingServer{}))
  err := http.ListenAndServe(
    "localhost:8080",
    // For gRPC clients, it's convenient to support HTTP/2 without TLS. You can
    // avoid x/net/http2 by using http.ListenAndServeTLS.
    h2c.NewHandler(mux, &http2.Server{}),
  )
  log.Fatalf("listen failed: %v", err)
}

With that server running, you can make requests with any gRPC or Connect client. To write a client using connect-go,

package main

import (
  "context"
  "log"
  "net/http"

  "github.com/bufbuild/connect-go"
  pingv1 "github.com/bufbuild/connect-go/internal/gen/connect/ping/v1"
  "github.com/bufbuild/connect-go/internal/gen/connect/ping/v1/pingv1connect"
)

func main() {
  client := pingv1connect.NewPingServiceClient(
    http.DefaultClient,
    "http://localhost:8080/",
  )
  req := connect.NewRequest(&pingv1.PingRequest{
    Number: 42,
  })
  req.Header().Set("Some-Header", "hello from connect")
  res, err := client.Ping(context.Background(), req)
  if err != nil {
    log.Fatalln(err)
  }
  log.Println(res.Msg)
  log.Println(res.Header().Get("Some-Other-Header"))
}

Of course, http.ListenAndServe and http.DefaultClient aren't fit for production use! See Connect's deployment docs for a guide to configuring timeouts, connection pools, observability, and h2c.

Ecosystem

connect-grpchealth-go: gRPC-compatible health checks
connect-grpcreflect-go: gRPC-compatible server reflection
connect-demo: demonstration service powering demo.connect.build, including bidi streaming
connect-web: TypeScript clients for web browsers
Buf Studio: web UI for ad-hoc RPCs
connect-crosstest: gRPC and gRPC-Web interoperability tests

Status

This module is a beta: we rely on it in production, but we may make a few changes as we gather feedback from early adopters. We're planning to tag a stable v1 in October, soon after the Go 1.19 release.

Support and versioning

connect-go supports:

The two most recent major releases of Go, with a minimum of Go 1.18.
APIv2 of Protocol Buffers in Go (google.golang.org/protobuf).

Within those parameters, Connect follows semantic versioning.

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