Fix Grape allowing invalid headers to be set

CHANGELOG.md

@@ -15,6 +15,7 @@
 * [#2506](https://github.com/ruby-grape/grape/pull/2506): Fix fetch_formatter api_format - [@ericproulx](https://github.com/ericproulx).
 * [#2507](https://github.com/ruby-grape/grape/pull/2507): Fix type: Set with values - [@nikolai-b](https://github.com/nikolai-b).
 * [#2510](https://github.com/ruby-grape/grape/pull/2510): Fix ContractScope's validator inheritance - [@ericproulx](https://github.com/ericproulx).
+* [#2511](https://github.com/ruby-grape/grape/pull/2511): Convert all header values to strings - [@SlakrHakr](https://github.com/SlakrHakr).
 * Your contribution here.
 
 ### 2.2.0 (2024-09-14)

README.md

@@ -2210,6 +2210,10 @@ get do
 end
 ```
 
+#### Header Value Types
+
+All header values are converted to strings to conform with the [rack specification](https://github.com/rack/rack/blob/main/SPEC.rdoc#the-headers-).
+
 #### Header Case Handling
 
 The above example may have been requested as follows:

lib/grape/dsl/headers.rb

@@ -10,7 +10,12 @@ module Headers
       # 4. Delete a specifc header key-value pair
       def header(key = nil, val = nil)
         if key
-          val ? header[key.to_s] = val : header.delete(key.to_s)
+          if val
+            warn "Header value for '#{key}' is not a string. Converting to string." unless val.is_a?(String)
+            header[key.to_s] = val.to_s
+          else
+            header.delete(key.to_s)
+          end
         else
           @header ||= Grape::Util::Header.new
         end

spec/grape/dsl/headers_spec.rb

@@ -56,4 +56,17 @@
       end
     end
   end
+
+  context 'when non-string headers are set' do
+    describe '#header' do
+      it 'converts non-string header values to strings' do
+        subject.header('integer key', 123)
+        expect(subject.header['integer key']).to eq '123'
+      end
+
+      it 'emits a warning if the header value is not a string' do
+        expect { subject.header('integer key', 123) }.to output("Header value for 'integer key' is not a string. Converting to string.\n").to_stderr
+      end
+    end
+  end
 end

spec/grape/dsl/inside_route_spec.rb

@@ -222,7 +222,7 @@ def initialize
         it 'set the correct headers' do
           expect(subject.header).to match(
             Rack::CACHE_CONTROL => 'cache',
-            Rack::CONTENT_LENGTH => 123,
+            Rack::CONTENT_LENGTH => '123',
             Grape::Http::Headers::TRANSFER_ENCODING => 'base64'
           )
         end