fixed: session data is not tracked correctly

Author: strowk

examples/streamable_http/README.md

@@ -1,3 +1,74 @@
-# 
+# Streamable HTTP Example
 
-mcp-autotest run -u http://localhost:8080/mcp testdata  -- go run main.go
+This is a simple example of how to use the streamable HTTP transport with the MCP server.
+
+You will need port 8080 to be free for this example to work.
+
+To start server, run this command:
+
+```bash
+go run main.go
+```
+
+Then try sending POST to see how server responds:
+
+```bash
+curl -X POST \
+  -H "Content-Type: application/json" \
+  -d '{"method":"tools/call", "params": {"name": "my-great-tool", "arguments": {}},"id":0}' \
+  http://localhost:8080/mcp
+```
+
+You can also autotest this example like this:
+
+```bash
+go test
+```
+
+, or with mcp-autotest:
+
+```bash
+mcp-autotest run -u http://localhost:8080/mcp testdata -- go run main.go
+```
+
+
+## Using session
+
+Try making such request to call the tool:
+
+```bash
+curl -X POST -i \
+  -H "Content-Type: application/json" \
+  -d '{"method":"tools/call", "params": {"name": "my-great-tool", "arguments": {}},"id":0}' \
+  http://localhost:8080/mcp
+```
+
+You should see output like this:
+
+```
+Content-Type: application/json
+Mcp-Session-Id: 25b4dda4-90dc-4616-a298-24a8a23e90ad
+Date: Mon, 31 Mar 2025 22:28:51 GMT
+Content-Length: 106
+
+{"jsonrpc":"2.0","result":{"content":[{"text":"Sup, saving greatness to session","type":"text"}]},"id":0}
+```
+
+Grab session id from the response header and use it in the next request:
+
+```bash
+curl -X POST -i \
+  -H "Content-Type: application/json" \
+  -H "Mcp-Session-Id: 25b4dda4-90dc-4616-a298-24a8a23e90ad" \
+  -d '{"method":"tools/call", "params": {"name": "my-great-tool", "arguments": {}},"id":1}' \
+  http://localhost:8080/mcp
+```
+
+This should print out different body:
+
+```json
+{"jsonrpc":"2.0","result":{"content":[{"text":"Sup, already great","type":"text"}]},"id":1}
+```
+
+The result is different for this session, but if you send another request without session id, it would give you the same result as before. 
+This is because of how tool keeps session state using SessionManager.

pkg/session/session_manager.go

@@ -52,22 +52,31 @@ func (sm *SessionManager) FindSessionById(sessionId uuid.UUID) (*Session, bool)
 	return session, ok
 }
 
-func (sm *SessionManager) ResolveSessionOrCreateNew(ctx context.Context, sessionId uuid.UUID) (context.Context, *Session, error) {
+func (sm *SessionManager) ResolveSessionOrCreateNew(
+	ctx context.Context,
+	sessionId uuid.UUID,
+) (context.Context, *Session, error) {
 	session, ok := sm.FindSessionById(sessionId)
 	if ok {
 		ctx = WithSession(ctx, session)
 		return ctx, session, nil
 	}
 
-	return sm.CreateNewSession(ctx)
+	return sm.CreateNewSession(ctx, &sessionId)
 }
 
 func (sm *SessionManager) DeleteSession(sessionId uuid.UUID) {
 	delete(sm.sessions, sessionId)
 }
 
-func (sm *SessionManager) CreateNewSession(ctx context.Context) (context.Context, *Session, error) {
+func (sm *SessionManager) CreateNewSession(
+	ctx context.Context,
+	sessionId *uuid.UUID,
+) (context.Context, *Session, error) {
 	session := NewSession()
+	if sessionId != nil {
+		session.SessionID = *sessionId
+	}
 	ctx = WithSession(ctx, session)
 	sm.saveSession(session)
 	return ctx, session, nil