Render a redirect message as the plain text it claims to be

CHANGELOG.md

@@ -55,6 +55,7 @@
 * [#2827](https://github.com/ruby-grape/grape/pull/2827): Make the `cascade` DSL getter return the configured value (`cascade false` read back as `true`) - [@ericproulx](https://github.com/ericproulx).
 * [#2829](https://github.com/ruby-grape/grape/pull/2829): Fix a cascading route handing over only to the last route registered for the path, making a middle version (3+ mounted versions with a catch-all) answer 406 - [@ericproulx](https://github.com/ericproulx).
 * [#2826](https://github.com/ruby-grape/grape/pull/2826): Fix `api.version` not being set for the root route of a path-versioned API (`GET /v1`) - [@ericproulx](https://github.com/ericproulx).
+* [#2845](https://github.com/ruby-grape/grape/pull/2845): Render a `redirect` message as the plain text its content type announces, instead of letting the API's formatter re-encode it - [@ericproulx](https://github.com/ericproulx).
 * Your contribution here.
 
 ### 3.3.5 (2026-07-30)

lib/grape/dsl/inside_route.rb

@@ -52,7 +52,12 @@ def redirect(url, permanent: false, body: nil)
           body_message ||= "This resource has been moved temporarily to #{url}."
         end
         header 'Location', url
+        # The message is plain text, so say so and render it as such. Setting
+        # only the header left the body to the API's own formatter, which on a
+        # JSON API returned the sentence wrapped in quotes under a text/plain
+        # content type.
         content_type 'text/plain'
+        api_format :txt
         body body_message
       end
 

spec/grape/endpoint_spec.rb

@@ -667,6 +667,38 @@ def handle_argument_error
       get '/hey'
       expect(last_response.body).to eq 'test body'
     end
+
+    # The message is announced as text/plain, so it has to be rendered as such
+    # whatever the API's own format is. Left to the JSON formatter it came back
+    # as a quoted JSON string under a text/plain content type.
+    context 'when the API declares a format of its own' do
+      before do
+        subject.format :json
+        subject.get('/hey') { redirect '/ha' }
+      end
+
+      it 'renders the message as plain text' do
+        get '/hey'
+
+        expect(last_response.headers[Rack::CONTENT_TYPE]).to eq('text/plain')
+        expect(last_response.body).to eq 'This resource has been moved temporarily to /ha.'
+      end
+
+      it 'renders an overridden body as plain text too' do
+        subject.get('/there') { redirect '/ha', body: 'go away' }
+
+        get '/there'
+        expect(last_response.body).to eq 'go away'
+      end
+
+      it 'leaves the format of other routes alone' do
+        subject.get('/plain') { { a: 1 } }
+
+        get '/plain'
+        expect(last_response.headers[Rack::CONTENT_TYPE]).to eq('application/json')
+        expect(last_response.body).to eq({ a: 1 }.to_json)
+      end
+    end
   end
 
   describe 'NameError' do