Redmine

When I try your changes with Redmine 5.1.1 I get errors:

# Format: html
Started GET "/robots.html" for 192.168.2.26 at 2024-02-07 15:04:16 +0100

ActionController::RoutingError (No route matches [GET] "/robots.html"):

# Format: json 
Started GET "/robots.json" for 192.168.2.26 at 2024-02-07 15:04:27 +0100

ActionController::RoutingError (No route matches [GET] "/robots.json"):

Started GET "/robots" for 192.168.2.26 at 2024-02-07 15:04:46 +0100

# Format: html
Processing by WelcomeController#robots as HTML

Completed 500 Internal Server Error in 29ms (ActiveRecord: 16.1ms | Allocations: 6204)

ActionController::RespondToMismatchError (respond_to was called multiple times and matched with conflicting formats in this action. Please note that you may only call respond_to and match on a single format per action.):

app/controllers/application_controller.rb:585:in `render_error'
app/controllers/application_controller.rb:573:in `render_404'
app/controllers/application_controller.rb:597:in `missing_template'

Did you test with the master branch?

In my environment, the stable-5.1 branch with the patch works as expected as well. It successfully returns 404 for "/robots.html", "/robots.json", and "/robots".

Started GET "/robots.html" for 127.0.0.1 at 2024-02-08 09:07:07 +0900

ActionController::RoutingError (No route matches [GET] "/robots.html"):

Started GET "/robots.json" for 127.0.0.1 at 2024-02-08 09:07:13 +0900

ActionController::RoutingError (No route matches [GET] "/robots.json"):

Started GET "/robots" for 127.0.0.1 at 2024-02-08 09:07:20 +0900

ActionController::RoutingError (No route matches [GET] "/robots")

I have made a fresh install of Redmine 5.1.1 and only changed the robots route according to your suggestion.

Then I have run the instance in development and production but it stays the same as above.

This is my (production) environment:

Environment:
  Redmine version                5.1.1.stable
  Ruby version                   3.1.4-p223 (2023-03-30) [x86_64-linux-musl]
  Rails version                  6.1.7.6
  Environment                    production
  Database adapter               Mysql2
  Mailer queue                   ActiveJob::QueueAdapters::AsyncAdapter
  Mailer delivery                smtp
Redmine settings:
  Redmine theme                  Default
SCM:
  Subversion                     1.14.2
  Mercurial                      6.6
  Git                            2.43.0
  Filesystem                     
Redmine plugins:
  no plugin installed

I have just installed Redmine 5.1.1 using tarball https://www.redmine.org/releases/redmine-5.1.1.tar.gz and applied the patch in #note-1.

I cannot reproduce the error you encountered when you accessed /robots. Everything looks working fine. Redmine returns 404 for "/robots.html", "/robots.json", and "/robots" as expected.

$ curl --head http://localhost:3000/robots.html
HTTP/1.1 404 Not Found
Content-Type: text/html; charset=utf-8
X-Request-Id: ffb0a0ce-3672-4abc-8a90-017b0716f8df
X-Runtime: 0.099908
Content-Length: 252860

$ curl --head http://localhost:3000/robots.json
HTTP/1.1 404 Not Found
Content-Type: text/html; charset=utf-8
X-Request-Id: 5899aa24-bfb2-4b0d-8b56-a1d9ea13957a
X-Runtime: 0.068502
Content-Length: 252860

$ curl --head http://localhost:3000/robots
HTTP/1.1 404 Not Found
Content-Type: text/html; charset=utf-8
X-Request-Id: 8f8c654a-ecfc-471c-a13b-74b4d6c503eb
X-Runtime: 0.089086
Content-Length: 252855

Started HEAD "/robots.html" for ::1 at 2024-02-08 16:58:36 +0900

ActionController::RoutingError (No route matches [HEAD] "/robots.html"):

Started HEAD "/robots.json" for ::1 at 2024-02-08 16:58:38 +0900

ActionController::RoutingError (No route matches [HEAD] "/robots.json"):

Started HEAD "/robots" for ::1 at 2024-02-08 16:58:39 +0900

ActionController::RoutingError (No route matches [HEAD] "/robots"):

Environment:
  Redmine version                5.1.1.stable
  Ruby version                   3.1.4-p223 (2023-03-30) [arm64-darwin23]
  Rails version                  6.1.7.6
  Environment                    production
  Database adapter               SQLite
  Mailer queue                   ActiveJob::QueueAdapters::AsyncAdapter
  Mailer delivery                smtp
Redmine settings:
  Redmine theme                  Default
SCM:
  Subversion                     1.14.3
  Mercurial                      6.6.1
  Cvs                            1.12.13
  Bazaar                         3.3.4
  Git                            2.43.0
  Filesystem
Redmine plugins:
  no plugin installed

--- config/routes.rb.orig    2024-02-08 17:07:46
+++ config/routes.rb    2024-02-08 17:08:26
@@ -402,7 +402,7 @@

   match 'uploads', :to => 'attachments#upload', :via => :post

-  get 'robots', :to => 'welcome#robots'
+  get 'robots.:format', :to => 'welcome#robots', :constraints => {format: 'txt'}

   Redmine::Plugin.directory.glob("*/config/routes.rb").sort.each do |plugin_routes_path|
     instance_eval(plugin_routes_path.read, plugin_routes_path.to_s)

Update:

Tested also with 5.1-stable branch but the result is still the same with `GET /robots`:

Completed 500 Internal Server Error in 16ms (ActiveRecord: 3.0ms | Allocations: 4739)

ActionController::RespondToMismatchError (respond_to was called multiple times and matched with conflicting formats in this action. Please note that you may only call respond_to and match on a single format per action.):

app/controllers/application_controller.rb:585:in `render_error'
app/controllers/application_controller.rb:573:in `render_404'
app/controllers/application_controller.rb:597:in `missing_template'

Now I can confirm the behavior you described! :)

I missed the .:format in the fresh installs.

Your hint to test via curl was also insightful: Testing without .:format and via curl gives another result than testing via browser.

With .:format it is stable via both ways curl and browser. Therefore, I can fully agree to your solution.

Thank you very much for your help!