Using Rack::Utils to parse query string.

Author: dblock

CHANGELOG.markdown

@@ -13,6 +13,7 @@ Next Release
 * [#204](https://github.com/intridea/grape/pull/204): Added ability to declare shared parameters at namespace level - [@tim-vandecasteele](https://github.com/tim-vandecasteele).
 * [#208](https://github.com/intridea/grape/pull/208): `Entity#serializable_hash` must also check if attribute is generated by a user supplied block - [@ppadron](https://github.com/ppadron).
 * [#234](https://github.com/intridea/grape/pull/234): Adds a DSL for creating entities via mixin - [@mbleigh](https://github.com/mbleigh).
+* [#240](https://github.com/intridea/grape/pull/240): Define API response format from a query string `format` parameter, if specified - [@neetiraj](https://github.com/neetiraj).
 
 0.2.1 (7/11/2012)
 =================

README.markdown

@@ -538,7 +538,7 @@ By default, Grape supports _XML_, _JSON_, _Atom_, _RSS_, and _text_ content-type
 Serialization takes place automatically.
 
 Your API can declare additional types to support. Response format is determined by the
-request's extension or `Accept` header.
+request's extension, an explicit `format` parameter in the query string, or `Accept` header.
 
 ``` ruby
 class Twitter::API < Grape::API
@@ -549,7 +549,8 @@ end
 You can also set the default format. The order for choosing the format is the following.
 
 * Use the file extension, if specified. If the file is .json, choose the JSON format.
-* Use the format, if specified by the `format` option.
+* Use the value of the format parameter in the query string, if specified.
+* Use the format set by the `format` option, if specified.
 * Attempt to find an acceptable format from the `Accept` header.
 * Use the default format, if specified by the `default_format` option.
 * Default to `:txt` otherwise.

lib/grape/middleware/formatter.rb

@@ -51,12 +51,8 @@ def format_from_extension
       end
 
       def format_from_params
-        if env['QUERY_STRING']
-          format_query = env['QUERY_STRING'].split('&').reject{|q| !q.include?('format=')} 
-          return format_query[0].split('=').last.to_sym if (format_query && !format_query.empty?)
-        else
-          nil
-        end 
+        fmt = Rack::Utils.parse_nested_query(env['QUERY_STRING'])["format"]
+        fmt ? fmt.to_sym : nil
       end
 
       def format_from_header