Deprecate automatic cache invalidation in Request#{GET,POST}

Add Request#clear_{GET,POST} for users to perform manual cache
invalidation when replacing env['QUERY_STRING'] or env['rack.input'].

With this invalidation, env[RACK_REQUEST_QUERY_STRING] and
env[RACK_REQUEST_FORM_INPUT] are unnecessary.

It appears as though env[RACK_REQUEST_FORM_VARS] is already
unnecessary, as the value is set but never accessed, dating back to
its introduction in 6c80c6c.
However, even though it is never used by Rack, it apparently is
used by Rails.  However, Rails usage appears to be limited to
parameter filtering, and if the RACK_REQUEST_FORM_VARS key wasn't
set, there would be nothing to filter.  So it's possible Rails
could be changed so that if the key was missing, there are no
problems (maybe it works like that already, and only the Rails
tests need updates).

CHANGELOG.md

@@ -15,6 +15,7 @@ All notable changes to this project will be documented in this file. For info on
 - MIME type for JavaScript files (`.js`) changed from `application/javascript` to `text/javascript` ([`1bd0f15`](https://github.com/rack/rack/commit/1bd0f1597d8f4a90d47115f3e156a8ce7870c9c8))
 - Add `.mjs` MIME type ([#2057](https://github.com/rack/rack/pull/2057), [@axilleas])
 - Update MIME types associated to `.ttf`, `.woff`, `.woff2` and `.otf` extensions to use mondern `font/*` types. ([#2065](https://github.com/rack/rack/pull/2065), [@davidstosik])
+- Deprecate automatic cache invalidation in `Request#{GET,POST}` and add `Request#clear_{GET,POST}` for manual cache invalidation ([@jeremyevans])
 
 ## [3.0.7] - 2023-03-16
 

lib/rack/request.rb

@@ -480,11 +480,34 @@ def parseable_data?
         PARSEABLE_DATA_MEDIA_TYPES.include?(media_type)
       end
 
+      # Clear cached data related to GET/query string parameters.
+      # Should be called if modifying env["QUERY_STRING"].
+      def clear_GET
+        env.delete(RACK_REQUEST_QUERY_STRING) # Remove in Rack 3.2
+        env.delete(RACK_REQUEST_QUERY_HASH)
+        @params = nil
+      end
+
+      # Clear cached data related to POST/request body parameters.
+      # Should be called if modifying env["rack.input"].
+      def clear_POST
+        env.delete(RACK_REQUEST_FORM_INPUT) # Remove in Rack 3.2
+        env.delete(RACK_REQUEST_FORM_VARS)
+        env.delete(RACK_REQUEST_FORM_HASH)
+        env.delete(RACK_REQUEST_FORM_ERROR)
+        @params = nil
+      end
+
       # Returns the data received in the query string.
       def GET
-        if get_header(RACK_REQUEST_QUERY_STRING) == query_string
+        rr_query_string = get_header(RACK_REQUEST_QUERY_STRING)
+        query_string = self.query_string
+        if rr_query_string == query_string
           get_header(RACK_REQUEST_QUERY_HASH)
         else
+          if rr_query_string
+            warn "Cached query string different from current query string. Starting in Rack 3.2, you must call clear_GET when modifying env[\"QUERY_STRING\"]", uplevel: 1
+          end
           query_hash = parse_query(query_string, '&')
           set_header(RACK_REQUEST_QUERY_STRING, query_string)
           set_header(RACK_REQUEST_QUERY_HASH, query_hash)
@@ -505,9 +528,12 @@ def POST
 
           # If the form hash was already memoized:
           if form_hash = get_header(RACK_REQUEST_FORM_HASH)
+            form_input = get_header(RACK_REQUEST_FORM_INPUT)
             # And it was memoized from the same input:
-            if get_header(RACK_REQUEST_FORM_INPUT).equal?(rack_input)
+            if form_input.equal?(rack_input)
               return form_hash
+            elsif form_input
+              warn "Cached input stream value different from current input stream. Starting in Rack 3.2, you must call clear_POST when modifying env[\"#{RACK_INPUT}\"]", uplevel: 1
             end
           end
 

test/spec_request.rb

@@ -911,7 +911,7 @@ def initialize(*)
     req.media_type.must_be_nil
   end
 
-  it "cache, but invalidates the cache" do
+  deprecated "cache, but invalidates the cache" do
     req = make_request \
       Rack::MockRequest.env_for("/?foo=quux",
         "CONTENT_TYPE" => "application/x-www-form-urlencoded",
@@ -929,6 +929,29 @@ def initialize(*)
     req.POST.must_equal "foo" => "bla", "quux" => "bar"
   end
 
+  it "support manual cache invalidation via clear_GET and clear_POST" do
+    req = make_request \
+      Rack::MockRequest.env_for("/?foo=quux",
+        "CONTENT_TYPE" => "application/x-www-form-urlencoded",
+        :input => "foo=bar&quux=bla")
+    req.GET.must_equal "foo" => "quux"
+    req.GET.must_equal "foo" => "quux"
+    req.POST.must_equal "foo" => "bar", "quux" => "bla"
+    req.POST.must_equal "foo" => "bar", "quux" => "bla"
+
+    req.set_header("QUERY_STRING", "bla=foo")
+    req.clear_GET
+    req.GET.must_equal "bla" => "foo"
+    req.GET.must_equal "bla" => "foo"
+    req.params.must_equal "bla" => "foo", "foo" => "bar", "quux" => "bla"
+
+    req.set_header("rack.input", StringIO.new("foo=bla&quux=bar"))
+    req.clear_POST
+    req.POST.must_equal "foo" => "bla", "quux" => "bar"
+    req.POST.must_equal "foo" => "bla", "quux" => "bar"
+    req.params.must_equal "bla" => "foo", "foo" => "bla", "quux" => "bar"
+  end
+
   it "figure out if called via XHR" do
     req = make_request(Rack::MockRequest.env_for(""))
     req.wont_be :xhr?