In Alamofire.UploadRequest, how to log httpBody of wrapped URLRequest?

Question

The answer to this seemingly simple question is eluding me.

I am using Alamofire version 5.6.1.

I am trying to extract httpBody of Foundation's URLRequest and put it into an NSLog statement. However, the URLRequest is generated and wrapped by an Alamofire.UploadRequest.

Alamofire.UploadRequest seems to delay creation of the URLRequest until deep in the bowels of Alamofire. Currently, I have breakpoints in Alamofire.Session.performUploadRequest and the URLRequest still has not been fully assembled.

I tried logging from our app's data fetcher where the response comes back. The response type is Alamofire.DataResponse and that has a reference to the original URLRequest. However, at this point, the URLRequest is reported as having httpBody of nil and this is simply false because the call is succeeding and the data used to configure the Alamofire.UploadRequest which must eventually become the httpBody of a URLRequest, is arriving successfully at the backend service.

Regarding how far I have gotten, as I wrote, I can see the data still separate from a URLRequest contained within a Alamofire.UploadRequest at Alamofire.Session.performUploadRequest. Here is the code for that:

func performUploadRequest(_ request: UploadRequest) {
        dispatchPrecondition(condition: .onQueue(requestQueue))
        performSetupOperations(for: request, convertible: request.convertible) {
            do {
                let uploadable = try request.upload.createUploadable()
                // START of code I added.
                switch uploadable {
                case .data(let d):
                    let s = String(data: d, encoding: .utf8)
                    NSLog("YOJEFF uploadable case data = \(String(describing: s))")
                default:
                    NSLog("YOJEFF uploadable case is not data")
                }
                // END of code I added.
                self.rootQueue.async { request.didCreateUploadable(uploadable) }

And that shows the data which will eventually become httpBody of a URLRequest but I want to log the data from the actual URLRequest passed to a URLSession.

How much deeper into Alamofire must I go? Or am I missing some property further up?

I already have a logger that I wrote that conform to Alamofire.EventMonitor, and it is injected into Alamofire.Session but why that is not working on this particular network call is a separate puzzle.

Answer 1

URLSessionUploadTasks, which Alamofire uses under the upload functionality, don't use the httpBody property. Instead, it attaches to the httpBodyStream of the URLRequest after it's passed into the URLSession issuing the request. Currently Alamofire doesn't have any events that occur when this happens (URLSession is generally a blackbox at that level) but you can access request.task.currentRequest to get the current state of the URLRequest as URLSession operates. In fact, this value is key value observable, so you could even get a live observation from that:

session.upload(...)
  .onURLSessionTaskCreation { task in
    <store observation> = task.observe(\.currentRequest) { task, change in
      debugPrint(task.currentRequest?.httpBodyStream)
    }
  }

In my testing this value actually changes a few times under URLSession, which is one of the reasons Alamofire offers no built-in hooks here.

However, it may be simpler to log your upload before it's passed to the request in the first place, especially if all you're trying to do is confirm its value. You could do this before creating the upload at all or by implementing the request(_ request:didCreateUploadable:) event.