golemcloud/golem/golem-add-cors-go

Configuring CORS on Go HTTP Endpoints

Overview

CORS allowed-origin patterns are declared on the agent definition: mount-wide with Mount.CORS, or per route with golem.EndpointCORS. Origins declared at both levels are unioned for that route. CORS is metadata only — declaring it advertises the origins the platform will allow; the gateway handles preflight automatically.

Steps

1. Set mount-level origins with Mount.CORS to cover every endpoint.
2. Add per-endpoint origins with golem.EndpointCORS(patterns...); they union with the mount list.
3. Use `"*"` to allow all origins.

Mount-level CORS

Mount.CORS is a []string of allowed-origin patterns applied to all endpoints:

type ID struct{ Name string }
 
var Agent = golem.DefineAgent[ID](golem.Spec{
	Name: "MyAgent",
	HTTP: &golem.Mount{
		Path: "/api/{name}",
		CORS: []string{"https://app.example.com"}, // all endpoints
	},
})
 
// GET /api/{name}/data  — allows https://app.example.com
var GetData = Agent.Method[golem.Unit, Data]("getData", golem.HTTP(golem.GET("/data")))

Endpoint-level CORS

golem.EndpointCORS(patterns...) adds origins for one route. They are unioned with the mount-level list, not replaced:

var Agent = golem.DefineAgent[ID](golem.Spec{
	Name: "MyAgent",
	HTTP: &golem.Mount{Path: "/api/{name}", CORS: []string{"https://app.example.com"}},
})
 
var (
	// Allows BOTH https://app.example.com AND * (all origins)
	GetData = Agent.Method[golem.Unit, Data]("getData", golem.HTTP(golem.GET("/data", golem.EndpointCORS("*"))))
 
	// Inherits mount-level only: https://app.example.com
	GetOther = Agent.Method[golem.Unit, Data]("getOther", golem.HTTP(golem.GET("/other")))
)

Wildcard

Use "*" to allow all origins:

var Agent = golem.DefineAgent[ID](golem.Spec{
	Name: "PublicAgent",
	HTTP: &golem.Mount{Path: "/public/{name}", CORS: []string{"*"}},
})

CORS preflight

The platform handles OPTIONS preflight requests automatically for endpoints that have CORS configured — you do not declare an OPTIONS route yourself. The preflight response carries Access-Control-Allow-Origin, Access-Control-Allow-Methods, and Access-Control-Allow-Headers.

Key Constraints

• Mount.CORS and golem.EndpointCORS(patterns...) both take origin patterns; the effective set for a route is the union of the two.
• An empty CORS means no cross-origin access is allowed for that scope.
• CORS declared in code still requires the agent to be served behind an httpApi deployment (see golem-add-http-endpoint-go).

Related Skills