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Middleware
em-http provides a simple mechanism to inject custom pre and post processing steps for each connection, or globally, through a middleware interface.
First, when the request is issued, em-http will initialize the headers, and then pass control back to your middleware (request(client, headers, body)
) where you can inject your own custom logic to modify the headers or body (ex: OAuth headers, encode the body, etc). Once the response is fulfilled, the response(request)
callback will be called, where you will have control over the response object before it is passed to the regular callbacks.
require 'json'
class JSONify
def response(resp)
resp.response = JSON.parse(resp.response)
end
end
EventMachine.run do
conn = EventMachine::HttpRequest.new('http://twitter.com/igrigorik.json')
conn.use JSONify
req = conn.get
req.callback {
req.response # => { ... twitter data as a Ruby hash ... }
}
end
In the example above, the JSONify
parses the response JSON body before returning control to our regular callback. In similar fashion, you can modify the outbound headers or body of the original request, or do whatever you wish with the response object before you regular code gets to it.
Different middleware filters can be applied on a per connection basis, or, you can specify global middleware filters which will span all requests (ex: insert a custom header across all requests, or parse all returned bodies with custom logic).
EventMachine.run do
EM::HttpRequest.use GlobalMiddleware
conn = EventMachine::HttpRequest.new('http://www.website.com/')
conn.use ConnectionMiddleware
conn.use OAuthMiddleware, {:config_data => {}} do
# .. custom signing logic
end
req = conn.get
req.callback { }
end
Any class that responds to request(client, headers, body)
and response(resp)
methods is a valid middleware:
class JSONify
def request(client, head, body)
[head, body]
end
def response(resp)
resp.response = JSON.parse(resp.response)
end
end
Note that request
must return the headers and the body when called.
Middleware filters will be executed in the order you’ve added them through HttpRequest.use
or connection.use
. First, global middleware will be executed, then connection specific middleware, and only then will the regular callbacks fire.