File Downloads using HttpClient

This post is just a little reminder to me and some of you might compassionately smile. But I have recently spent hours racking my brains why I only get “empty” files when I download a “simple” PDF using HttpClient in a Business Central AL extension (although file-size and general sizing of the pdf files were ok). I didn’t consider saving the response stream directly into an InStream instead of using a Text variable which i then stored in a blob field.

Why? Because I forgot about my own post about method overloading. ResponseMessage.Content.ReadAs(…) has an overload accepting either Text or InStream.

The result is a working file with correct content…

procedure WebserviceCall(var ResponseInStream: InStream): Text
var
    ...
begin
    //File Downloads using HttpClient
    //WebClient call downloading a file
    //...

    //Check response headers to decide how to proceed
    ResponseMessage.Content.GetHeaders(ResponseHeader);
    ResponseHeader.GetValues('Content-Type', ResponseHeaders);
    case ResponseHeaders[1] of
        'application/pdf', 'application/octet-stream':
            begin                    
                //Store response stream directly
                ResponseMessage.Content.ReadAs(ResponseInStream);   
                exit;         
            end;
        else
            ResponseMessage.Content.ReadAs(ResponseText);
    end;

    //Otherwise return response as text
    exit(ResponseText);
end;

Now you could directly proceed using the InStream… This might be persisting in a Blob field or downloading it to the client using DownloadFromStream(…)

... is a technical consultant and developer at Comsol Unternehmenslösungen AG in Kronberg/Taunus. Major tasks are the architecture and implementation of complex, usually cross-system applications in and around Microsoft Dynamics 365 Business Central.

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