title: Endless HTTP Stream Observable not emitting anything but data transferred
body: <p>I've been digging an issue with Angular 4 and RxJS. Here is my code, the issue is, the <code>http.post</code> request Observable is not emitting anything to the next of the chain, the <code>map()</code>. The POST just get an endless response, it's a stream of Motion JPEG data. Now I have to deal with the data, say each 500KB transferred. My problem is that I cannot do anything with the data if the Observable not emitting anything.</p>
  
  <p>So how to make such angular HTTP feature emit to the next of the chain each chunk of data transferred?</p>
  
  <pre><code>postActionGivenDataBinaryResponse(url:string, data:string) : Observable&lt;any&gt;{
      let headers = new Headers ({
          'Content-Type' : 'application/json;charset=utf-8'
      }) ;
      let options = new RequestOptions({
          headers : headers,
          responseType: ResponseContentType.ArrayBuffer
      }) ;
  
      //return binary data as is no json
      return this.http.post(url, data, options) //suspecting here is not emitting anything due to unknown configuration issue.
                      .map(this.extractBinaryData)
                      .catch(this.handleError) ;
  }
  
  private extractBinaryData(res:Response){
      console.log('Dealing with data in the com service.') ; // this never runs
      return res ;
  }
  </code></pre>
  
  <p>I call the above function like this, the post response is an endless binary data, I need to process it as string array.</p>
  
  <pre><code>this.mySubscription = this.comService.postActionGivenDataBinaryResponse(myurl,mydata)
    .do(()=&gt;{
                console.log('Observable Passed data.') ; //this never runs.
            })
    .bufferCount(128000)
    .map((data)=&gt;{//process the data each 128kb chunk})
    .subscribe();
  </code></pre>