e: IOException,
  )

  /**
   * Called when the HTTP response was successfully returned by the remote server. The callback may
   * proceed to read the response body with [Response.body]. The response is still live until its
   * response body is [closed][ResponseBody]. The recipient of the callback may consume the response
   * body on another thread.
   *

	// rewriting the C code.
	C.callback(unsafe.Pointer(&i))

	callbackMutex.Lock()
	delete(callbackFuncs, i)
	callbackMutex.Unlock()
}

//export goCallback
func goCallback(p unsafe.Pointer) {
	i := *(*int)(p)

	callbackMutex.Lock()
	f := callbackFuncs[i]
	callbackMutex.Unlock()

	if f == nil {
		panic("missing callback function")
	}
	f()
}

// Use of this source code is governed by a BSD-style
// license that can be found in the LICENSE file.

#include <string.h>

#include "_cgo_export.h"

void
callback(void *f)
{
	// use some stack space
	volatile char data[64*1024];

	data[0] = 0;
	goCallback(f);
        data[sizeof(data)-1] = 0;
}

void
callGoFoo(void)
{
	extern void goFoo(void);
	goFoo();
}

void
IntoC(void)
{

	}
	// Only frames in the test package are checked.
	want := []string{
		"test._Cfunc_backtrace",
		"test.testCallbackCallersSEH.func1.1",
		"test.testCallbackCallersSEH.func1",
		"test.goCallback",
		"test._Cfunc_callback",
		"test.nestedCall.func1",
		"test.nestedCall",
		"test.testCallbackCallersSEH",
		"test.TestCallbackCallersSEH",
	}
	pc := make([]uintptr, 100)
	n := 0
	nestedCall(func() {

Austin Clements <******@****.***> 1683224724 -0400

Austin Clements <******@****.***> 1683224724 -0400

class CustomModel(BaseModel):
    a: int


app = FastAPI()

callback_router = APIRouter(default_response_class=JSONResponse)


@callback_router.get(
    "{$callback_url}/callback/", responses={400: {"model": CustomModel}}
)
def callback_route():
    pass  # pragma: no cover


@app.post("/", callbacks=callback_router.routes)
def main_route(callback_url: HttpUrl):
    pass  # pragma: no cover

	var callbacks []*callback
	removedMap := map[string]bool{}
	for _, callback := range p.callbacks {
		if callback.match == nil || callback.match(p.db) {
			callbacks = append(callbacks, callback)
		}
		if callback.remove {
			removedMap[callback.name] = true
		}
	}

	if len(removedMap) > 0 {
		callbacks = removeCallbacks(callbacks, removedMap)
	}
	p.callbacks = callbacks

	updateCallback.Match(enableTransaction).Register("gorm:commit_or_rollback_transaction", CommitOrRollbackTransaction)
	updateCallback.Clauses = config.UpdateClauses

	rowCallback := db.Callback().Row()
	rowCallback.Register("gorm:row", RowQuery)
	rowCallback.Clauses = config.QueryClauses

	rawCallback := db.Callback().Raw()
	rawCallback.Register("gorm:raw", RawExec)
	rawCallback.Clauses = config.QueryClauses

Now use the parameter `callbacks` in *your API's path operation decorator* to pass the attribute `.routes` (that's actually just a `list` of routes/*path operations*) from that callback router:

```Python hl_lines="35"
{!../../../docs_src/openapi_callbacks/tutorial001.py!}
```

!!! tip