Write the Hook Code

We need to create a new plugin directory under pkg/rules/ and then write the plugin code, like this:

package mux

import _ "unsafe"
import "github.com/alibaba/loongsuite-go-agent/pkg/api"
import mux "github.com/gorilla/mux"

//go:linkname muxRoute130OnEnter github.com/gorilla/mux.muxRoute130OnEnter
func muxRoute130OnEnter(call api.CallContext, req *http.Request, route interface{}) {
    ...
}

There's no magic here — it's just regular Go code. A few interesting points:

• The hook function muxRoute130OnEnter must be annotated with the go:linkname directive.
• The first parameter of the hook function must be of type api.CallContext, and the remaining parameters should match those of the target function:
  • If the target function is func foo(a int, b string, c float) (d string, e error), then the onEnter hook function should be func hook(call api.CallContext, a int, b string, c float)
  • If the target function is func foo(a int, b string, c float) (d string, e error), then the onExit hook function should be func hook(call api.CallContext, d string, e error)
  • If you need to modify the parameters or return values of the target function, you can use CallContext.SetParam() or CallContext.SetReturnVal()

We need more documentation explaining all aspects of writing plugin code. For now, the best way is to refer to other plugin implementations, such as pkg/rules/mux or any other existing plugin.