discourse/lib/hijack.rb

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# frozen_string_literal: true
require_dependency 'method_profiler'
# This module allows us to hijack a request and send it to the client in the deferred job queue
# For cases where we are making remote calls like onebox or proxying files and so on this helps
# free up a unicorn worker while the remote IO is happening
module Hijack
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def hijack(&blk)
controller_class = self.class
if hijack = request.env['rack.hijack']
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request.env['discourse.request_tracker.skip'] = true
request_tracker = request.env['discourse.request_tracker']
# in the past unicorn would recycle env, this is not longer the case
env = request.env
# rack may clean up tempfiles unless we trick it and take control
tempfiles = env[Rack::RACK_TEMPFILES]
env[Rack::RACK_TEMPFILES] = nil
request_copy = ActionDispatch::Request.new(env)
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transfer_timings = MethodProfiler.transfer
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io = hijack.call
# duplicate headers so other middleware does not mess with it
# on the way down the stack
original_headers = response.headers.dup
Scheduler::Defer.later("hijack #{params["controller"]} #{params["action"]}") do
MethodProfiler.start(transfer_timings)
begin
Thread.current[Logster::Logger::LOGSTER_ENV] = env
# do this first to confirm we have a working connection
# before doing any work
io.write "HTTP/1.1 "
# this trick avoids double render, also avoids any litter that the controller hooks
# place on the response
instance = controller_class.new
response = ActionDispatch::Response.new
instance.response = response
instance.request = request_copy
original_headers&.each do |k, v|
instance.response.headers[k] = v
end
begin
instance.instance_eval(&blk)
rescue => e
# TODO we need to reuse our exception handling in ApplicationController
Discourse.warn_exception(e, message: "Failed to process hijacked response correctly", env: env)
end
unless instance.response_body || response.committed?
instance.status = 500
end
response.commit!
body = response.body
headers = response.headers
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# add cors if needed
if cors_origins = env[Discourse::Cors::ORIGINS_ENV]
Discourse::Cors.apply_headers(cors_origins, env, headers)
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end
headers['Content-Type'] ||= response.content_type || "text/plain"
headers['Content-Length'] = body.bytesize
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headers['Connection'] = "close"
status_string = Rack::Utils::HTTP_STATUS_CODES[response.status.to_i] || "Unknown"
io.write "#{response.status} #{status_string}\r\n"
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timings = MethodProfiler.stop
if timings && duration = timings[:total_duration]
headers["X-Runtime"] = "#{"%0.6f" % duration}"
end
headers.each do |name, val|
io.write "#{name}: #{val}\r\n"
end
io.write "\r\n"
io.write body
rescue Errno::EPIPE, IOError
# happens if client terminated before we responded, ignore
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io = nil
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ensure
MethodProfiler.clear
Thread.current[Logster::Logger::LOGSTER_ENV] = nil
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io.close if io rescue nil
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if request_tracker
status = response.status rescue 500
request_tracker.log_request_info(env, [status, headers || {}, []], timings)
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end
tempfiles&.each(&:close!)
end
end
# not leaked out, we use 418 ... I am a teapot to denote that we are hijacked
render plain: "", status: 418
else
blk.call
end
end
end