FIX stdio URL bug with proxyMode

[slyt3]

Problem

So deploying an MCPServer with transport: stdio and proxyMode: streamable-http, the status URL shows incorectly returns /sse endpoint instead of /mcp

Example

apiVersion: toolhive.stacklok.dev/v1alpha1
kind: MCPServer
metadata:
  name: arxiv
  namespace: toolhive-system
spec:
  image: ghcr.io/stacklok/dockyard/uvx/arxiv-mcp-server:0.3.1
  transport: stdio
  proxyMode: streamable-http
  proxyPort: 8080

Expected status URL:

http://arxiv.toolhive-system.svc.cluster.local:8080/mcp

Actual status URL:

http://arxiv.toolhive-system.svc.cluster.local:8080/sse#arxiv

---

Root Cause

The bug is in pkg/transport/url.go

This code is old and it shows that its treating stdio same as sse and ignoring proxyMode

isSSE := transportType == types.TransportTypeSSE.String() || 
         transportType == types.TransportTypeStdio.String()

So thinking logically we should assume that stdio always use SSE endpoint but stdio can use it either

• proxyMode: sse → /sse endpoint
• proxyMode: streamable-http → /mcp endpoint (default)

And the controller at cmd/thv-operator/controllers/mcpserver_controller.go:395 only passes Transport, never ProxyMode:

OLD CODE TOO missing proxyMode parameter

mcpServer.Status.URL = transport.GenerateMCPServerURL(
    mcpServer.Spec.Transport,
    host,
    int(mcpServer.GetProxyPort()),
    mcpServer.Name,
    "",
)

---

Solution

So I Added proxyMode parameter to GenerateMCPServerURL() function:

func GenerateMCPServerURL(transportType string, proxyMode string, host string, 
    port int, containerName, remoteURL string) string

Logic:

1. For stdio transport: Use proxyMode to easily determine endpoint

   • proxyMode: "streamable-http" → /mcp
   • proxyMode: "sse" → /sse#name
   • proxyMode: "" (empty) → defaults to /mcp (matches CRD default)

2. For other transports: JUST Ignore proxyMode its behaviour doesnt change xD

   • sse transport → always /sse#name
   • streamable-http transport → always /mcp

Type Conversions

Added string() conversions where ProxyMode is a typed string (was stuck on this one for whole night, was going crazy i just needed to convert ProxyMode string to function call, so proxyMode is defined as type ProxyMode string:

string(r.Config.ProxyMode)  

---

Testing

Unit Tests (15/15 passing)

$ go test ./pkg/transport/... -v -run TestGenerateMCPServerURL

Key test cases covering the bug:

Test	Transport	ProxyMode	Expected	Result
Bug case	stdio	streamable-http	/mcp	✅ PASS
Edge case	stdio	sse	/sse#name	✅ PASS
Default	stdio	"" (empty)	/mcp	✅ PASS
Unchanged	sse	(ignored)	/sse#name	✅ PASS
Unchanged	streamable-http	(ignored)	/mcp	✅ PASS

All 15 tests pass including targetURI path handling.

---

Changes

7 files changed:

• pkg/transport/url.go - Added proxyMode parameter and logic
• pkg/transport/url_test.go - Added comprehensive test coverage
• cmd/thv-operator/controllers/mcpserver_controller.go - Updated call site
• pkg/runner/runner.go - Updated call site with type conversion
• pkg/workloads/manager.go - Updated call site with type conversion
• pkg/workloads/types/types.go - Updated call site with empty string default
• pkg/vmcp/workloads/k8s.go - Updated call site with type conversion

Build status:

$ go build ./...

---

Impact

This fix ensures stdio transport respects the proxyMode setting:

Config	Before (Bug)	After (Fixed)
stdio + streamable-http	/sse ❌	/mcp ✅
stdio + sse	/sse ✅	/sse ✅
stdio + (empty)	/sse ❌	/mcp ✅
sse transport	/sse ✅	/sse ✅
streamable-http transport	/mcp ✅	/mcp ✅

Soooo since CRD is default for proxyMode is streamable-http` bug affects the default stdio configuration

---

Fixes #2920

[codecov]

Codecov Report

❌ Patch coverage is 73.68421% with 5 lines in your changes missing coverage. Please review.
✅ Project coverage is 56.37%. Comparing base (28797fa) to head (8f11963).
⚠️ Report is 4 commits behind head on main.

Files with missing lines	Patch %	Lines
...d/thv-operator/controllers/mcpserver_controller.go	0.00%	1 Missing ⚠️
pkg/runner/runner.go	0.00%	1 Missing ⚠️
pkg/vmcp/workloads/k8s.go	0.00%	1 Missing ⚠️
pkg/workloads/manager.go	0.00%	1 Missing ⚠️
pkg/workloads/types/types.go	0.00%	1 Missing ⚠️

Additional details and impacted files

@@           Coverage Diff           @@
##             main    #2935   +/-   ##
=======================================
  Coverage   56.36%   56.37%           
=======================================
  Files         323      323           
  Lines       31763    31777   +14     
=======================================
+ Hits        17904    17915   +11     
- Misses      12330    12333    +3     
  Partials     1529     1529           

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