WIP: Socket.IO protocol on top of Engine.IO

CLAUDE.md

@@ -9,13 +9,19 @@ Task-based async (`Task`, `IAsyncEnumerable`, `Channel<T>`) rather than the even
 .NET Socket.IO clients. Prefer an `await`-able or `await foreach`-able API over an `event` when adding surface area.
 
 The Engine.IO layer is implemented (HTTP polling transport, WebSocket transport with upgrade, plain-text and binary
-packets). The Socket.IO layer on top of it — namespaces, payload send/receive — is not yet written; see the TODOs in
-`README.md`.
+packets). The Socket.IO layer on top of it is half written: `src/SocketIO.Client` encodes packets and sends them, but
+nothing parses an inbound one yet, so namespaces and acknowledgements are still open. See the TODOs in `README.md`.
 
 Protocol references:
 - Engine.IO: https://socket.io/docs/v4/engine-io-protocol
 - Socket.IO: https://socket.io/docs/v4/socket-io-protocol
 
+The reference implementation is in `node_modules` once `npm install` has run, and it is the arbiter when a question is
+about what the wire actually accepts: `node_modules/socket.io-parser` decodes a string the C# side produced, which is a
+faster and surer check than reading the spec. Its rules are stricter than they look — a binary packet must announce at
+least one attachment, an event may not be named after a reserved one, and a decode error costs the whole connection
+rather than the one packet.
+
 ## Commands
 
 ```bash
@@ -33,6 +39,7 @@ Running the sample end to end needs the Node test server, which lives in an npm
 ```bash
 npm install                        # once, from the repo root
 npm run start:server               # Engine.IO server on http://127.0.0.1:9854 (scripts/run-server.sh wraps this)
+npm run start:socket-server        # Socket.IO server on http://127.0.0.1:9855
 dotnet run --project samples/PingPong
 ```
 
@@ -78,9 +85,11 @@ values being the *ASCII byte* of the digit (`Open = 0x30`, i.e. `'0'`) so parsin
 - `.editorconfig` is authoritative and unusually strict: `end_of_line = crlf`, `insert_final_newline = false`,
   `var` is disallowed where the type is not apparent, and `using` groups are separated with `System` first. Run
   `dotnet format` rather than hand-matching it.
-- `AssemblyInfo.cs` grants `InternalsVisibleTo("EngineIO.Client.Tests")`. Transports expose `internal` constructors that
-  accept an injected `HttpClient` purely so tests can supply a mocked `HttpMessageHandler` — follow that pattern for new
-  transports instead of adding public seams.
+- `AssemblyInfo.cs` grants `InternalsVisibleTo` to the matching test project, and `EngineIO.Client` also grants it to
+  `SocketIO.Client` so the layer above can reach the same seam. `Engine`, `IO` and the transports expose `internal`
+  constructors that accept an injected `HttpClient` purely so tests can supply a stubbed handler — follow that pattern
+  instead of adding public seams. `EngineIO.Client.Tests` mocks the handler with Moq; `SocketIO.Client.Tests` takes no
+  such dependency and uses the hand-rolled `FakePollingServer`.
 - Logging is optional throughout: `ILoggerFactory` is nullable everywhere and callers may pass nothing.
 
 ## Other agent configs present

README.md

@@ -15,8 +15,11 @@ The client implements `Engine.IO` and `Socket.IO` core protocols.
 
 - **Socket.IO Client**
 
+- [x] Packet model and wire-format serialization (events, acks, binary attachments)
+- [x] Send plain text, JSON and binary payloads
+- [ ] Packet parsing (receiving)
 - [ ] Namespaces support
-- [ ] Send and receive plain text and binary payloads
+- [ ] Acknowledgement correlation
 
 ## Resources
 

SocketIO.sln

@@ -15,6 +15,10 @@ Project("{2150E333-8FDC-42A3-9474-1A3956D46DE8}") = "tests", "tests", "{D8B5DE1E
 EndProject
 Project("{FAE04EC0-301F-11D3-BF4B-00C04F79EFBC}") = "EngineIO.Client.Tests", "tests\EngineIO.Client.Tests\EngineIO.Client.Tests.csproj", "{5D824F05-5793-4768-99DF-E4D993F16B75}"
 EndProject
+Project("{FAE04EC0-301F-11D3-BF4B-00C04F79EFBC}") = "SocketIO.Client", "src\SocketIO.Client\SocketIO.Client.csproj", "{222889F5-6A36-4A8A-8C78-A910E40D4F82}"
+EndProject
+Project("{FAE04EC0-301F-11D3-BF4B-00C04F79EFBC}") = "SocketIO.Client.Tests", "tests\SocketIO.Client.Tests\SocketIO.Client.Tests.csproj", "{E0C636E7-91B0-44AE-9752-F08326C7C5F2}"
+EndProject
 Global
 	GlobalSection(SolutionConfigurationPlatforms) = preSolution
 		Debug|Any CPU = Debug|Any CPU
@@ -36,10 +40,20 @@ Global
 		{5D824F05-5793-4768-99DF-E4D993F16B75}.Debug|Any CPU.Build.0 = Debug|Any CPU
 		{5D824F05-5793-4768-99DF-E4D993F16B75}.Release|Any CPU.ActiveCfg = Release|Any CPU
 		{5D824F05-5793-4768-99DF-E4D993F16B75}.Release|Any CPU.Build.0 = Release|Any CPU
+		{222889F5-6A36-4A8A-8C78-A910E40D4F82}.Debug|Any CPU.ActiveCfg = Debug|Any CPU
+		{222889F5-6A36-4A8A-8C78-A910E40D4F82}.Debug|Any CPU.Build.0 = Debug|Any CPU
+		{222889F5-6A36-4A8A-8C78-A910E40D4F82}.Release|Any CPU.ActiveCfg = Release|Any CPU
+		{222889F5-6A36-4A8A-8C78-A910E40D4F82}.Release|Any CPU.Build.0 = Release|Any CPU
+		{E0C636E7-91B0-44AE-9752-F08326C7C5F2}.Debug|Any CPU.ActiveCfg = Debug|Any CPU
+		{E0C636E7-91B0-44AE-9752-F08326C7C5F2}.Debug|Any CPU.Build.0 = Debug|Any CPU
+		{E0C636E7-91B0-44AE-9752-F08326C7C5F2}.Release|Any CPU.ActiveCfg = Release|Any CPU
+		{E0C636E7-91B0-44AE-9752-F08326C7C5F2}.Release|Any CPU.Build.0 = Release|Any CPU
 	EndGlobalSection
 	GlobalSection(NestedProjects) = preSolution
 		{D1C745FE-52AF-4145-8243-9FCA91BE7916} = {80C612B0-98E1-4E6B-AF10-5BB3087F0864}
 		{4F6177C5-3234-4897-B61C-49C44D3E2EF8} = {577735D4-BC7E-464A-BC9B-93AD8B5B6738}
 		{5D824F05-5793-4768-99DF-E4D993F16B75} = {D8B5DE1E-C83F-40A9-9D27-D2FBB3866F0A}
+		{222889F5-6A36-4A8A-8C78-A910E40D4F82} = {577735D4-BC7E-464A-BC9B-93AD8B5B6738}
+		{E0C636E7-91B0-44AE-9752-F08326C7C5F2} = {D8B5DE1E-C83F-40A9-9D27-D2FBB3866F0A}
 	EndGlobalSection
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