Can AngularJS set the responseType after a response has been received?

Question

I have an Angular 1.x application that is expecting to receive a binary file download (pdf) using a $http.post() call. The problem is, I'd like to alternatively get a processing error message that's sent as json. I can do this with the config

headers: {
  'Accept': 'application/pdf, application/json'
}

The problem is I have have to set responseType: 'arraybuffer', otherwise the pdf binary is escaped (or altered such that it doesn't load). However, that prevents the json from being read or interpreted correctly.

How can I have both?

Edit: I'm going to try to clarify; perhaps my understanding is incorrect.

$http({
    method: 'POST',
    url: "/myresource",
    headers: {
        'Accept': 'application/pdf, application/json'
    },
    responseType: 'arraybuffer'
})
.then(
    function(response) {
        // handle pdf download via `new Blob([data])`
    }, function(response) {
        // pop up a message based on response.data
    }
)

In a scenario where I return a pdf data block and a http status of 200, the first function handles the response and prompts the user to save the file. However if the status is an error (422), the response.data is undefined. I assume this is because the responseType is preventing the json from being handled correctly.

If I remove the responseType line, the error data is correctly read, but when the pdf is saved, some of the file bytes aren't correct and it's effectively corrupted. I assume this is because the file is being encoded because javascript was expecting a string.

Answer 1

An XHR responseType property can not be changed after a response has been loaded. But an arraybuffer can be decoded and parsed depending on Content-Type:

 var config = {
    responseType: "arraybuffer",
    transformResponse: jsonBufferToObject,
  };

  function jsonBufferToObject (data, headersGetter, status) {
      var type = headersGetter("Content-Type");
      if (!type.startsWith("application/json")) {
        return data;
      };
      var decoder = new TextDecoder("utf-8");
      var domString = decoder.decode(data);
      var json = JSON.parse(domString);
      return json;
  };

  $http.get(url, config);

The above example sets the XHR to return an arraybuffer and uses a transformResponse function to detect Content-Type: application/json and convert it if necessary.

The DEMO on PLNKR