Http

+++ title = "HTTP" description = "Call and listen to webhooks asynchronously" date = 2019-07-06T22:30:00+02:00 bref = "Call and listen to webhooks asynchronously" weight = 60 +++

The HTTP subscriber listens to HTTP requests (for example - webhooks) and outputs them as messages. You can then post them to any Publisher. Here is an example with sending HTTP messages to Kafka.

The HTTP publisher sends HTTP requests as specified in its configuration. Here is an example with transforming Kafka messages into HTTP webhook requests.

Installation

go get github.com/ThreeDotsLabs/watermill-http/v2

Characteristics

Subscriber configuration

Subscriber configuration is done via the config struct passed to the constructor:

{{% load-snippet-partial file="src-link/watermill-http/pkg/http/subscriber.go" first_line_contains="type SubscriberConfig struct" last_line_contains="}" %}}

You can use the Router config option to SubscriberConfig to pass your own chi.Router (see chi). This may be helpful if you'd like to add your own HTTP handlers (e.g. a health check endpoint).

Publisher configuration

Publisher configuration is done via the config struct passed to the constructor:

{{% load-snippet-partial file="src-link/watermill-http/pkg/http/publisher.go" first_line_contains="type PublisherConfig struct" last_line_contains="}" %}}

How the message topic and body translate into the URL, method, headers, and payload of the HTTP request is highly configurable through the use of MarshalMessageFunc. Use the provided DefaultMarshalMessageFunc to send POST requests to a specific url:

{{% load-snippet-partial file="src-link/watermill-http/pkg/http/publisher.go" first_line_contains="// MarshalMessageFunc" last_line_contains="return req, nil" padding_after="2" %}}

You can pass your own http.Client to execute the requests or use Golang's default client.

Running

To run HTTP subscriber you need to run StartHTTPServer(). It needs to be run after Subscribe().

When using with the router, you should wait for the router to start.

<-r.Running()
httpSubscriber.StartHTTPServer()

Subscribing

{{% load-snippet-partial file="src-link/watermill-http/pkg/http/subscriber.go" first_line_contains="// Subscribe adds" last_line_contains="func (s *Subscriber) Subscribe" %}}

Custom HTTP status codes

To specify a custom HTTP status code, which will returned as response, you can use following call during message handling:

// msg is a *message.Message
http.SetResponseStatusCode(msg, http.StatusForbidden)
msg.Nack()