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POHow to Rescue from ActionDispatch::ParamsParser::ParseError in Rails 4
 

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  1. POHow to Rescue from ActionDispatch::ParamsParser::ParseError in Rails 4
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    <p>Rails 4 adds an exception <strong>ActionDispatch::ParamsParser::ParseError</strong> exception but since its in the middleware stack it appears it can't be rescued in the normal controller environment. In a json API application I want respond with a standard error format.</p> <p>This <a href="https://gist.github.com/elarkin/4709748">gist</a> shows a strategy for inserting middleware to intercept and respond. Following this pattern I have:</p> <p><strong>application.rb:</strong></p> <pre><code>module Traphos class Application &lt; Rails::Application .... config.middleware.insert_before ActionDispatch::ParamsParser, "JSONParseError" end end </code></pre> <p><strong>And the middleware is:</strong></p> <pre><code>class JSONParseError def initialize(app) @app = app end def call(env) begin @app.call(env) rescue ActionDispatch::ParamsParser::ParseError =&gt; e [422, {}, ['Parse Error']] end end end </code></pre> <p>If I run my test without the middleware I get (spec):</p> <pre><code>Failures: 1) Photo update attributes with non-parseable json Failure/Error: patch update_url, {:description =&gt; description}, "CONTENT_TYPE" =&gt; content_type, "HTTP_ACCEPT" =&gt; accepts, "HTTP_AUTHORIZATION" =&gt; @auth ActionDispatch::ParamsParser::ParseError: 399: unexpected token at 'description=Test+New+Description]' </code></pre> <p>Which is exactly what I would expect (ParseError that I can't rescue_from).</p> <p>Now with the only change to add in the middleware above:</p> <pre><code> 2) Photo update attributes with non-parseable json Failure/Error: response.status.should eql(422) expected: 422 got: 200 </code></pre> <p>And the log shows that the standard controller action is being executed and returning a normal response (although since it didn't receive any parameters it didn't update anything).</p> <p>My questions:</p> <ol> <li><p>How can rescue from ParseError and return a custom response. Feels like I'm on the right track but not quite there.</p></li> <li><p>I can't work out why, when the exception is raised and rescued, that the controller action still proceeds.</p></li> </ol> <p>Help much appreciated, --Kip</p>
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    1. COis there some other middleware that changes the return status? did you do some debugging with pry or something?
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