Host networking lies about the MCP url #2317
Description
Bug description
Host networking support was introduced in toolhive in order to support the MCP-optimizer use case. This solved the root cause of networking issues that made it impossible for MCP-optimizer to reach MCP servers while running in. native containers.
However, for some reason thv still attempts to bind random ports and reports that the MCP server can be accessed on that port. This is not true, the MCP is accessible on whatever host port it decides to bind itself to (mcp-optimizer respects MCP_PORT)
Steps to reproduce
Using native containers (Linux)
❯ thv run python:3-slim --name test-bug --network host --target-port 8000 --transport streamable-http --detach -- python3 -m http.server 8000
❯ thv list | grep test-bug
A new version of ToolHive is available: v0.4.2
Currently running: v0.4.2-3-g392db5b9
test-bug python:3-slim running http://127.0.0.1:18178/mcp 18178 mcp default 2025-10-24 10:47:05.770908242 +0200 CEST
❯ curl -I http://127.0.0.1:18178/mcp
HTTP/1.1 502 Bad Gateway
Date: Fri, 24 Oct 2025 08:48:28 GMT
❯ curl -I http://127.0.0.1:18178/
HTTP/1.1 502 Bad Gateway
Date: Fri, 24 Oct 2025 08:48:48 GMT
❯ curl -I http://127.0.0.1:8000/mcp
HTTP/1.0 404 File not found
Server: SimpleHTTP/0.6 Python/3.14.0
Date: Fri, 24 Oct 2025 08:49:03 GMT
Connection: close
Content-Type: text/html;charset=utf-8
Content-Length: 460
❯ curl -I http://127.0.0.1:8000/
HTTP/1.0 200 OK
Server: SimpleHTTP/0.6 Python/3.14.0
Date: Fri, 24 Oct 2025 08:49:14 GMT
Content-type: text/html; charset=utf-8
Content-Length: 946
Expected behavior
- MCP accessible through URL reported by
thv ls - Host networking ignored when it's not applicable
Actual behavior
- MCP NOT accessible through URL reported by
thv ls - Host networking seemingly enabled, even when it's not truly possible?
Environment (if relevant)
Linux with any container engine using native containers. I tested with Docker.