rest-builder

by Lin Jen-Shin (godfat)

LINKS:

• github
• rubygems
• rdoc
• issues (feel free to ask for support)

DESCRIPTION:

Modular Ruby clients interface for REST APIs.

Build your own API clients for less dependencies, less codes, less memory, less conflicts, and run faster. Checkout rest-core for pre-built middleware and rest-more for pre-built clients.

FEATURES:

• Modular interface for REST clients similar to WSGI/Rack for servers.
• Concurrent requests with synchronous or asynchronous interfaces with threads via promise_pool.

WHY?

This was extracted from rest-core because rest-core itself is getting too complex, and this would be the new core of rest-core. Naming it rest-core-core is a bit silly, and due to compatibility reason, rest-core should work as is.

REQUIREMENTS:

Mandatory:

• Tested with MRI (official CRuby) and JRuby.
• gem promise_pool
• gem timers
• gem httpclient
• gem mime-types

INSTALLATION:

gem install rest-builder

Or if you want development version, put this in Gemfile:

gem 'rest-builder', :git => 'git://github.com/godfat/rest-builder.git',
                    :submodules => true

If you want to use pre-built middleware instead of rolling your own, please checkout rest-core.

If you just want to use Facebook or Twitter clients, please take a look at rest-more which has a lot of clients built with rest-core.

Basic Usage:

Use RestBuilder::Builder to build your own clients like Rack::Builder to build your application. The client you built this way would be a class which you could then make client instances from. This way, each instance could carry different configuration, e.g. different cache time or timeout time.

require 'rest-builder'

YourClient = RestBuilder::Builder.client do
  # use ...
  # use ...
  # run ...
end
client = YourClient.new
client.get('http://example.com/') # make a request to http://example.com/

Build Your Own Middleware:

How We Pick the Default Value:

There are a number of ways to specify a default value, each with different priorities. Suppose we have a middleware which remembers an integer:

class HP
  def self.members; [:hp]; end
  include RestBuilder::Middleware
  def call env, &k
    puts "HP: #{hp(env)}"
    app.call(env, &k)
  end
end
Mage = RestBuilder::Builder.client do
  use HP, 5 # the very last default
end
mage = Mage.new

1. The one passed to the request directly gets the first priority, e.g.

mage.get('http://example.com/', {}, :hp => 1) # prints HP: 1

2. The one saved as an instance variable in the client gets the 2nd place.

mage.hp = 2
mage.get('http://example.com/')               # prints HP: 2
mage.get('http://example.com/', {}, :hp => 1) # prints HP: 1
mage.hp         # still 2
mage.hp = false # disable hp
mage.hp = nil   # reset to default

3. The method defined in the client instance named default_hp gets the 3rd.

class Mage
  def default_hp
    3
  end
end
mage.get('http://example.com/')               # prints HP: 3
mage.hp       # 3
mage.hp = nil # reset default
Mage.send(:remove_method, :default_hp)

4. The method defined in the client class named default_hp gets the 4rd. P.S. In rest-more, with RestCore::Config it would generate a DefaultAttributes module which defines this kind of default method and then is extended into the client class. You could still define this method to override the default though.

class Mage
  def self.default_hp
    4
  end
end
mage.get('http://example.com/')               # prints HP: 4
mage.hp       # 4
mage.hp = nil # reset to default
Mage.singleton_class.send(:remove_method, :default_hp)

5. The one defined in the middleware gets the last place.

mage.get('http://example.com/')               # prints HP: 5
mage.hp       # 5
mage.hp = nil # reset to default

You can find all the details in client.rb and middleware.rb. See the included method hooks.

Concurrent Requests with Futures:

You can also make concurrent requests easily: (see "Advanced Concurrent HTTP Requests -- Embrace the Future" for detail)

a = [client.get('http://example.com/a'), client.get('http://example.com/b')]
puts "It's not blocking... but doing concurrent requests underneath"
p a # Here we want the values, so it blocks here
puts "DONE"

Exception Handling for Futures:

Note that since the API call would only block whenever you're looking at the response, it won't raise any exception at the time the API was called. So if you want to block and handle the exception at the time API was called, you would do something like this:

begin
  response = client.get('http://nonexist/').itself # itself is the point
  do_the_work(response)
rescue => e
  puts "Got an exception: #{e}"
end

The trick here is forcing the future immediately give you the exact response, so that rest-builder could see the response and raise the exception. You can call whatever methods on the future to force this behaviour, but since itself is a method from Kernel (which is included in Object), it's always available and would return the original value, so it is the easiest method to be remembered and used.

If you know the response must be a string, then you can also use to_s. Like this:

begin
  response = client.get('http://nonexist/').to_s
  do_the_work(response)
rescue => e
  puts "Got an exception: #{e}"
end

Or you can also do this:

begin
  response = client.get('http://nonexist/')
  response.class # simply force it to load
  do_the_work(response)
rescue => e
  puts "Got an exception: #{e}"
end

The point is simply making a method call to force it load, whatever method should work.

Concurrent Requests with Callbacks:

On the other hand, callback mode also available:

client.get('http://example.com/'){ |v| p v }
puts "It's not blocking... but doing concurrent requests underneath"
client.wait # we block here to wait for the request done
puts "DONE"

Exception Handling for Callbacks:

What about exception handling in callback mode? You know that we cannot raise any exception in the case of using a callback. So rest-builder would pass the exception object into your callback. You can handle the exception like this:

client.get('http://nonexist/') do |response|
  if response.kind_of?(Exception)
    puts "Got an exception: #{response}"
  else
    do_the_work(response)
  end
end
puts "It's not blocking... but doing concurrent requests underneath"
client.wait # we block here to wait for the request done
puts "DONE"

Thread Pool / Connection Pool

Underneath, rest-builder would spawn a thread for each request, freeing you from blocking. However, occasionally we would not want this behaviour, giving that we might have limited resource and cannot maximize performance.

For example, maybe we could not afford so many threads running concurrently, or the target server cannot accept so many concurrent connections. In those cases, we would want to have limited concurrent threads or connections.

YourClient.pool_size = 10
YourClient.pool_idle_time = 60

This could set the thread pool size to 10, having a maximum of 10 threads running together, growing from requests. Each threads idled more than 60 seconds would be shut down automatically.

Note that pool_size should at least be larger than 4, or it might be very likely to have deadlock if you're using nested callbacks and having a large number of concurrent calls.

Also, setting pool_size to -1 would mean we want to make blocking requests, without spawning any threads. This might be useful for debugging.

Gracefully shutdown

To shutdown gracefully, consider shutdown the thread pool (if we're using it), and wait for all requests for a given client. For example, we'll do this when we're shutting down:

YourClient.shutdown

We could put them in at_exit callback like this:

at_exit do
  YourClient.shutdown
end

If you're using unicorn, you probably want to put that in the config.

Random Asynchronous Tasks

Occasionally we might want to do some asynchronous tasks which could take the advantage of the concurrency facilities inside rest-builder, for example, using wait and shutdown. You could do this with defer for a particular client. For example:

YourClient.defer do
  sleep(1)
  puts "Slow task done"
end

YourClient.wait

Persistent connections (keep-alive connections)

Since we're using httpclient by default now, we would reuse connections, making it much faster for hitting the same host repeatedly.

Streaming Requests

Suppose we want to POST a file, instead of trying to read all the contents in memory and send them, we could stream it from the file system directly.

client.post('path', File.open('README.md'))

Basically, payloads could be any IO object. Check out RestBuilder::Payload for more information.

Streaming Responses

This one is much harder then streaming requests, since all built-in middleware actually assume the responses should be blocking and buffered. Say, some JSON parser could not really parse from streams.

We solve this issue similarly to the way Rack solves it. That is, we hijack the socket. This would be how we're doing:

sock = client.get('path', {}, RestBuilder::HIJACK => true)
p sock.read(10)
p sock.read(10)
p sock.read(10)

Of course, if we don't want to block in order to get the socket, we could always use the callback form:

client.get('path', {}, RestBuilder::HIJACK => true) do |sock|
  p sock.read(10)
  p sock.read(10)
  p sock.read(10)
end

Note that since the socket would be put inside RestBuilder::RESPONSE_SOCKET instead of RestBuilder::RESPONSE_BODY, not all middleware would handle the socket. In the case of hijacking, RestBuilder::RESPONSE_BODY would always be mapped to an empty string, as it does not make sense to store the response in this case.

SSE (Server-Sent Events)

Not only JavaScript could receive server-sent events, any languages could. Doing so would establish a keep-alive connection to the server, and receive data periodically. We'll take Firebase as an example:

If you are using Firebase, please consider rest-firebase instead.

require 'rest-builder'

# Streaming over 'users/tom.json'
cl = RestBuilder::Builder.client.new
ph = 'https://SampleChat.firebaseIO-demo.com/users/tom.json'
es = cl.event_source(ph, {}, # this is query, none here
                     RestBuilder::REQUEST_HEADERS =>
                       {'Accept' => 'text/event-stream'})

@reconnect = true

es.onopen   { |sock| p sock } # Called when connected
es.onmessage{ |event, data, sock| p event, data } # Called for each message
es.onerror  { |error, sock| p error } # Called whenever there's an error
# Extra: If we return true in onreconnect callback, it would automatically
#        reconnect the node for us if disconnected.
es.onreconnect{ |error, sock| p error; @reconnect }

# Start making the request
es.start

# Try to close the connection and see it reconnects automatically
es.close

# Update users/tom.json
p cl.put(ph, '{"some":"data"}')
p cl.post(ph, '{"some":"other"}')
p cl.get(ph)
p cl.delete(ph)

# Need to tell onreconnect stops reconnecting, or even if we close
# the connection manually, it would still try to reconnect again.
@reconnect = false

# Close the connection to gracefully shut it down.
es.close

Those callbacks would be called in a separate background thread, so we don't have to worry about blocking it. If we want to wait for the connection to be closed, we could call wait:

es.wait # This would block until the connection is closed

More Control with request_full:

You can also use request_full to retrieve everything including response status, response headers, and also other rest-builder options. But since using this interface is like using Rack directly, you have to build the env manually. To help you build the env manually, everything has a default, including the path.

client.request_full(RestBuilder::REQUEST_PATH =>
                      'http://example.com/')[RestBuilder::RESPONSE_BODY]
client.request_full(RestBuilder::REQUEST_PATH =>
                      'http://example.com/')[RestBuilder::RESPONSE_STATUS]
client.request_full(RestBuilder::REQUEST_PATH =>
                      'http://example.com/')[RestBuilder::RESPONSE_HEADERS]
# Headers are normalized with all upper cases and
# dashes are replaced by underscores.

# To make POST (or any other request methods) request:
client.request_full(RestBuilder::REQUEST_PATH   => 'http://example.com/',
                    RestBuilder::REQUEST_METHOD =>
                      :post)[RestBuilder::RESPONSE_STATUS] # 404

Advanced Concurrent HTTP Requests -- Embrace the Future

The Interface

There are a number of different ways to make concurrent requests in rest-builder. They could be roughly categorized to two different forms. One is using the well known callbacks, while the other one is using through a technique called future. Basically, it means it would return you a promise, which would eventually become the real value (response here) you were asking for whenever you really want it. Otherwise, the program keeps running until the value is evaluated, and blocks there if the computation (response) hasn't been done yet. If the computation is already done, then it would simply return you the result.

Here's a very simple example for using futures:

client = YourClient.new
puts "httpclient with threads doing concurrent requests"
a = [client.get('http://example.com/a'), client.get('http://example.com/b')]
puts "It's not blocking... but doing concurrent requests underneath"
p a # Here we want the values, so it blocks here
puts "DONE"

And here's a corresponded version for using callbacks:

client = YourClient.new
puts "httpclient with threads doing concurrent requests"
client.get('http://example.com/a'){ |v|
         p v
       }.
       get('http://example.com/b'){ |v|
         p v
       }
puts "It's not blocking... but doing concurrent requests underneath"
client.wait # until all requests are done
puts "DONE"

You can pick whatever works for you.

Configure the underlying HTTP engine

Occasionally we might want to configure the underlying HTTP engine, which for now is httpclient. For example, we might not want to decompress gzip automatically, (rest-core configures httpclient to request and decompress gzip automatically). or we might want to skip verifying SSL in some situation. (e.g. making requests against a self-signed testing server)

In such cases, we could use config_engine option to configure the underlying engine. This could be set with request based, client instance based, or client class based. Please refer to: How We Pick the Default Value, except that there's no middleware for config_engine.

Here are some examples:

# class based:
def YourClient.default_config_engine
  lambda do |engine|
    # disable auto-gzip:
    engine.transparent_gzip_decompression = false

    # disable verifying SSL
    engine.ssl_config.verify_mode = OpenSSL::SSL::VERIFY_NONE
  end
end

# instance based:
client = YourClient.new(:config_engine => lambda do |engine|
  # disable auto-gzip:
  engine.transparent_gzip_decompression = false

  # disable verifying SSL
  engine.ssl_config.verify_mode = OpenSSL::SSL::VERIFY_NONE
end)

# request based:
client.get('http://example.com/', {}, :config_engine => lambda do |engine|
  # disable auto-gzip:
  engine.transparent_gzip_decompression = false

  # disable verifying SSL
  engine.ssl_config.verify_mode = OpenSSL::SSL::VERIFY_NONE
end)

As we stated in How We Pick the Default Value, the priority here is:

0. request based
1. instance based
2. class based

CONTRIBUTORS:

• Lin Jen-Shin (@godfat)

LICENSE:

Apache License 2.0 (Apache-2.0)

Copyright (c) 2016-2023, Lin Jen-Shin (godfat)

Licensed under the Apache License, Version 2.0 (the "License"); you may not use this file except in compliance with the License. You may obtain a copy of the License at

https://www.apache.org/licenses/LICENSE-2.0

Unless required by applicable law or agreed to in writing, software distributed under the License is distributed on an "AS IS" BASIS, WITHOUT WARRANTIES OR CONDITIONS OF ANY KIND, either express or implied. See the License for the specific language governing permissions and limitations under the License.