tinygo-org
Runtime error "Server error: Netdev not set" in wasip2
I could compile a MCP server using mcp-go to wasip2 target, with the wasi-http-go interface and disabling the stdio transport due to #4865. However, when I run this component on wasmtime with wasi-http capability, I got a runtime error saying "server error: netdev not set". Would love some help on figuring out why is a netdev even being used in the first place.
wasmtime run -Shttp main.wasm
2025/05/01 19:25:03 SSE server listening on :8080
2025/05/01 19:25:03 Server error: Netdev not set
https://github.com/tinygo-org/net/blob/main/netdev.go#L147
What did you do to get the example building?
(I've fixed the os/signal issues but adding wasi-http-go I get
~/go/src/github.com/mark3labs/mcp-go/examples/everything $ tinygo build -target=wasip2
error: failed to encode a component from module
Caused by:
0: failed to decode world from module
1: module was not valid
2: module requires an import interface named `wasi:http/[email protected]`
`wasm-tools component new` failed: exit status 1
~/go/src/github.com/mark3labs/mcp-go/examples/everything $ git diff .
diff --git a/examples/everything/main.go b/examples/everything/main.go
index fa1c304..90f69ec 100644
--- a/examples/everything/main.go
+++ b/examples/everything/main.go
@@ -9,6 +9,8 @@ import (
"github.com/mark3labs/mcp-go/mcp"
"github.com/mark3labs/mcp-go/server"
+
+ _ "github.com/ydnar/wasi-http-go/wasihttp"
)
type ToolName string
Sorry, you need a WIT file for wasi-http. I've pushed my changes to a forked branch and you may see the diff here. To run it, run the following command
cd examples/everything
tinygo build -target=wasip2.json main.go
wasmtime run -Shttp main.wasm
where wasip2.json is
{
"inherits": ["wasip2"],
"wit-package": "./wit/proxy.wit",
"wit-world": "go:http/proxy",
"emulator": "wasmtime serve -Scli --dir={tmpDir}::/tmp {}"
}
That is not working for me:
~/go/src/github.com/mark3labs/mcp-go/examples/everything $ git show |head -1
commit 78fa3977d55f5f3cc2e3a6e6225833af122c0915
~/go/src/github.com/mark3labs/mcp-go/examples/everything $ tinygo build -target=wasip2.json main.go
error: expected `world`, `interface` or `use`, found keyword `package`
--> ./wit/proxy.wit:38:1
|
38 | package wasi:[email protected] {
| ^------
`wasm-tools component embed` failed: exit status 1
I think my wasip2 build stuff is broken at the moment. I'll fix it and come back to this.
From diving into the source code, it appears we need a driver in https://github.com/tinygo-org/drivers (or elsewhere) that calls https://pkg.go.dev/tinygo.org/x/drivers/netdev#UseNetdev . Without that, the network device is left as https://github.com/tinygo-org/net/blob/main/netdev.go#L149 which always returns errors.
