How to return a PDF from a Web API application
<p>I have a Web API project that is running on a server. It is supposed to return PDFs from two different kinds of sources: an actual portable document file (PDF), and a base64 string stored in a database. The trouble I'm having is sending the document back to a client MVC application. The rest of this is the details on everything that's happened and that I've already tried.</p>

<p>I have written code that successfully translates those two formats into C# code and then (back) to PDF form. I have successfully transferred a byte array that was supposed to represent one of those documents, but I can't get it to display in browser (in a new tab by itself). I always get some kind of "cannot be displayed" error.</p>

<p>Recently, I made a way to view the documents on the server side to make sure I can at least get it to do that. It gets the document into the code and creates a FileStreamResult with it that it then returns as an (implicit cast) ActionResult. I got that to return to a server side MVC controller and threw it into a simple return (no view) that displays the PDF just fine in the browser. However, trying to simply go straight to the Web API function simply returns what looks like a JSON representation of a FileStreamResult.</p>

<p>When I try to get that to return properly to my client MVC application, it tells me that "_buffer" can't be directly set. Some error message to the effect that some of the properties being returned and thrown into an object are private and can't be accessed.</p>

<p>The aforementioned byte-array representation of the PDF, when translated to a base64 string, doesn't seem to have the same number of characters as the "_buffer" string returned in the JSON by a FileStreamResult. It's missing about 26k 'A's at the end.</p>

<p>Any ideas about how to get this PDF to return correctly? I can provide code if necessary, but there has to be some known way to return a PDF from a server-side Web API application to a client-side MVC application and display it as a web page in a browser.</p>

<p>P.S. I do know that the "client-side" application isn't technically on the client side. It will also be a server application, but that shouldn't matter in this case. Relative to the Web API server, my MVC application is "client-side".</p>

<p><strong>Code</strong>
For getting pdf:</p>

<pre><code>private System.Web.Mvc.ActionResult GetPDF()
{
    int bufferSize = 100;
    int startIndex = 0;
    long retval;
    byte[] buffer = new byte[bufferSize];
    MemoryStream stream = new MemoryStream();
    SqlCommand command;
    SqlConnection sqlca;
    SqlDataReader reader;

    using (sqlca = new SqlConnection(CONNECTION_STRING))
    {
        command = new SqlCommand((LINQ_TO_GET_FILE).ToString(), sqlca);
        sqlca.Open();
        reader = command.ExecuteReader(CommandBehavior.SequentialAccess);
        try
        {
            while (reader.Read())
            {
                do
                {
                    retval = reader.GetBytes(0, startIndex, buffer, 0, bufferSize);
                    stream.Write(buffer, 0, bufferSize);
                    startIndex += bufferSize;
                } while (retval == bufferSize);
            }
        }
        finally
        {
            reader.Close();
            sqlca.Close();
        }
    }
    stream.Position = 0;
    System.Web.Mvc.FileStreamResult fsr = new System.Web.Mvc.FileStreamResult(stream, "application/pdf");
    return fsr;
}
</code></pre>

<p>API Function that gets from GetPDF:</p>

<pre><code>    [AcceptVerbs("GET","POST")]
    public System.Web.Mvc.ActionResult getPdf()
    {
        System.Web.Mvc.ActionResult retVal = GetPDF();
        return retVal;
    }
</code></pre>

<p>For displaying PDF server-side:</p>

<pre><code>public ActionResult getChart()
{
    return new PDFController().GetPDF();
}
</code></pre>

<p>The code in the MVC application has changed a lot over time. The way it is right now, it doesn't get to the stage where it tries to display in browser. It gets an error before that.</p>

<pre><code>public async Task&lt;ActionResult&gt; get_pdf(args,keys)
{
    JObject jObj;
    StringBuilder argumentsSB = new StringBuilder();
    if (args.Length != 0)
    {
        argumentsSB.Append("?");
        argumentsSB.Append(keys[0]);
        argumentsSB.Append("=");
        argumentsSB.Append(args[0]);
        for (int i = 1; i &lt; args.Length; i += 1)
        {
            argumentsSB.Append("&amp;");
            argumentsSB.Append(keys[i]);
            argumentsSB.Append("=");
            argumentsSB.Append(args[i]);
        }
    }
    else
    {
        argumentsSB.Append("");
    }
    var arguments = argumentsSB.ToString();
    using (var client = new HttpClient())
    {
        client.DefaultRequestHeaders.Accept.Clear();
        client.DefaultRequestHeaders.Accept.Add(new MediaTypeWithQualityHeaderValue("application/json"));
        var response = await client.GetAsync(URL_OF_SERVER+"api/pdf/getPdf/" + arguments).ConfigureAwait(false);
        jObj = (JObject)JsonConvert.DeserializeObject(response.Content.ReadAsStringAsync().Result);
    }
    return jObj.ToObject&lt;ActionResult&gt;();
}
</code></pre>

<p>The JSON I get from running the method directly from the Web API controller is:</p>

<pre><code>{
    "FileStream":{
        "_buffer":"JVBER...NjdENEUxAA...AA==",
        "_origin":0,
        "_position":0,
        "_length":45600,
        "_capacity":65536,
        "_expandable":true,
        "_writable":true,
        "_exposable":true,
        "_isOpen":true,
        "__identity":null},
    "ContentType":"application/pdf",
    "FileDownloadName":""
}
</code></pre>

<p>I shortened "_buffer" because it's ridiculously long.
I currently get the error message below on the return line of get_pdf(args,keys)</p>

<p>Exception Details: Newtonsoft.Json.JsonSerializationException: Could not create an instance of type System.Web.Mvc.ActionResult. Type is an interface or abstract class and cannot be instantiated. Path 'FileStream'.</p>

<p>Back when I used to get a blank pdf reader (the reader was blank. no file), I used this code:</p>

<pre><code>public async Task&lt;ActionResult&gt; get_pdf(args,keys)
{
    byte[] retArr;
    StringBuilder argumentsSB = new StringBuilder();
    if (args.Length != 0)
    {
        argumentsSB.Append("?");
        argumentsSB.Append(keys[0]);
        argumentsSB.Append("=");
        argumentsSB.Append(args[0]);
        for (int i = 1; i &lt; args.Length; i += 1)
        {
            argumentsSB.Append("&amp;");
            argumentsSB.Append(keys[i]);
            argumentsSB.Append("=");
            argumentsSB.Append(args[i]);
        }
    }
    else
    {
        argumentsSB.Append("");
    }
    var arguments = argumentsSB.ToString();
    using (var client = new HttpClient())
    {
        client.DefaultRequestHeaders.Accept.Clear();
        client.DefaultRequestHeaders.Accept.Add(new MediaTypeWithQualityHeaderValue("application/pdf"));
        var response = await client.GetAsync(URL_OF_SERVER+"api/webservice/" + method + "/" + arguments).ConfigureAwait(false);
        retArr = await response.Content.ReadAsByteArrayAsync().ConfigureAwait(false);
    }
    var x = retArr.Skip(1).Take(y.Length-2).ToArray();
    /*Response.Clear();
    Response.ClearContent();
    Response.ClearHeaders();
    Response.ContentType = "application/pdf";
    Response.AppendHeader("Content-Disposition", "inline;filename=document.pdf");
    Response.BufferOutput = true;
    Response.BinaryWrite(x);
    Response.Flush();
    Response.End();*/
    return new FileStreamResult(new MemoryStream(x),MediaTypeNames.Application.Pdf);
    }
</code></pre>

<p>Commented out is code from some other attempts. When I was using that code, I was returning a byte array from the server. It looked like:</p>

<pre><code>JVBER...NjdENEUx
</code></pre>