Handle invalid RSC frame lengths

Author: justin808

spec/requests/server_components_spec.rb

@@ -38,7 +38,7 @@ def parse_length_prefixed_chunk(body)
       raise "Malformed length-prefixed RSC payload: missing tab separator" unless content_length_hex
 
       content_start = header_end + 1
-      content_length = Integer(content_length_hex, 16)
+      content_length = parse_content_length(content_length_hex)
       content = body.byteslice(content_start, content_length)
       raise "Malformed length-prefixed RSC payload: truncated content" unless content&.bytesize == content_length
 
@@ -48,6 +48,12 @@ def parse_length_prefixed_chunk(body)
       ]
     end
 
+    def parse_content_length(content_length_hex)
+      Integer(content_length_hex, 16)
+    rescue ArgumentError
+      raise "Malformed length-prefixed RSC payload: invalid hex length '#{content_length_hex}'"
+    end
+
     def parse_payload_metadata(metadata_json, content)
       metadata = JSON.parse(metadata_json.force_encoding(Encoding::UTF_8))
       content.force_encoding(Encoding::UTF_8)
@@ -63,6 +69,13 @@ def expect_valid_rsc_payload
       expect(chunks.any? { |chunk| chunk.key?("html") }).to be(true)
     end
 
+    it "raises a malformed payload error for invalid hex content lengths" do
+      payload = { payloadType: "string" }.to_json
+
+      expect { parse_length_prefixed_chunk("#{payload}\tzz\ncontent".b) }
+        .to raise_error(RuntimeError, "Malformed length-prefixed RSC payload: invalid hex length 'zz'")
+    end
+
     it "streams a valid RSC payload for ServerComponentsPage" do
       get "/rsc_payload/ServerComponentsPage", params: { props: "{}" }
       expect_valid_rsc_payload