如何从Web API应用程序返回PDF [英] How to return a PDF from a Web API application

问题描述

我有一个在服务器上运行的Web API项目.它应该从两种不同的来源返回PDF:实际的便携式文档文件(PDF)和存储在数据库中的base64字符串.我遇到的麻烦是将文档发送回客户端MVC应用程序.剩下的就是所有发生的事情以及我已经尝试过的细节.

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.

我已经编写了将这两种格式成功转换为C#代码，然后(返回)为PDF格式的代码.我已经成功地传输了一个字节数组，该字节数组应该代表这些文档之一，但是我无法在浏览器中显示它(仅在一个新标签中).我总是会遇到某种无法显示"的错误.

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.

最近，我提出了一种在服务器端查看文档的方法，以确保至少可以做到这一点.它将文档放入代码中，并使用它创建一个FileStreamResult，然后将其作为(隐式强制转换)ActionResult返回.我得到了返回到服务器端MVC控制器的信息，并将其放入一个简单的返回(无视图)中，该返回在浏览器中显示PDF很好.但是，尝试直接使用Web API函数只会返回类似于FileStreamResult的JSON表示形式.

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.

当我尝试使它正确返回到客户端MVC应用程序时，它告诉我不能直接设置"_buffer".一些错误消息，表明某些返回并扔到对象中的属性是私有的，无法访问.

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.

上述的PDF字节数组表示形式，当转换为base64字符串时，似乎不具有与FileStreamResult在JSON中返回的"_buffer"字符串相同的字符数.最后缺少大约26k'A'.

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.

关于如何正确获取此PDF的任何想法?我可以根据需要提供代码，但是必须有一种已知的方法将PDF从服务器端Web API应用程序返回到客户端MVC应用程序，并在浏览器中将其显示为网页.

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.S.我确实知道客户端"应用程序在技术上不是客户端.它也将是一个服务器应用程序，但是在这种情况下这无关紧要.相对于Web API服务器，我的MVC应用程序是客户端".

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".

代码 要获取pdf:

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;
}

从GetPDF获取的API函数:

API Function that gets from GetPDF:

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

用于显示PDF服务器端:

For displaying PDF server-side:

public ActionResult getChart()
{
    return new PDFController().GetPDF();
}

随着时间的流逝，MVC应用程序中的代码发生了很大的变化.现在的方式并没有进入尝试在浏览器中显示的阶段.在此之前会出现错误.

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.

public async Task<ActionResult> 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 < args.Length; i += 1)
        {
            argumentsSB.Append("&");
            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<ActionResult>();
}

直接从Web API控制器运行方法得到的JSON是:

The JSON I get from running the method directly from the Web API controller is:

{
    "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":""
}

我缩短了"_buffer"，因为它太长了. 我目前在get_pdf(args，keys)返回行上收到以下错误消息

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

异常详细信息:Newtonsoft.Json.JsonSerializationException:无法创建类型为System.Web.Mvc.ActionResult的实例.类型是接口或抽象类，无法实例化.路径"FileStream".

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'.

返回时，我曾经使用空白的pdf阅读器(阅读器为空白.没有文件)，我使用了以下代码:

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

public async Task<ActionResult> 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 < args.Length; i += 1)
        {
            argumentsSB.Append("&");
            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);
    }

注释是来自其他一些尝试的代码.当我使用该代码时，我是从服务器返回一个字节数组.看起来像:

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:

JVBER...NjdENEUx

推荐答案

某些服务器端代码可返回PDF(Web Api).

Some Server side code to return PDF (Web Api).

[HttpGet]
[Route("documents/{docid}")]
public HttpResponseMessage Display(string docid) {
    HttpResponseMessage response = Request.CreateResponse(HttpStatusCode.BadRequest);
    var documents = reader.GetDocument(docid);
    if (documents != null && documents.Length == 1) {
        var document = documents[0];
        docid = document.docid;
        byte[] buffer = new byte[0];
        //generate pdf document
        MemoryStream memoryStream = new MemoryStream();
        MyPDFGenerator.New().PrintToStream(document, memoryStream);
        //get buffer
        buffer = memoryStream.ToArray();
        //content length for use in header
        var contentLength = buffer.Length;
        //200
        //successful
        var statuscode = HttpStatusCode.OK;
        response = Request.CreateResponse(statuscode);
        response.Content = new StreamContent(new MemoryStream(buffer));
        response.Content.Headers.ContentType = new MediaTypeHeaderValue("application/pdf");
        response.Content.Headers.ContentLength = contentLength;
        ContentDispositionHeaderValue contentDisposition = null;
        if (ContentDispositionHeaderValue.TryParse("inline; filename=" + document.Name + ".pdf", out contentDisposition)) {
            response.Content.Headers.ContentDisposition = contentDisposition;
        }
    } else {
        var statuscode = HttpStatusCode.NotFound;
        var message = String.Format("Unable to find resource. Resource \"{0}\" may not exist.", docid);
        var responseData = responseDataFactory.CreateWithOnlyMetadata(statuscode, message);
        response = Request.CreateResponse((HttpStatusCode)responseData.meta.code, responseData);
    }
    return response;
}

在我看来，您可以执行以下操作

On my a View you could do something like this

<a href="api/documents/1234" target = "_blank" class = "btn btn-success" >View document</a>

它将调用Web api，并在浏览器的新标签页中打开PDF文档.

which will call the web api and open the PDF document in a new tab in the browser.

这是我基本上是通过MVC控制器执行相同操作的方式

Here is how i basically do the same thing but from a MVC controller

// NOTE: Original return type: FileContentResult, Changed to ActionResult to allow for error results
[Route("{docid}/Label")]
public ActionResult Label(Guid docid) {
    var timestamp = DateTime.Now;
    var shipment = objectFactory.Create<Document>();
    if (docid!= Guid.Empty) {
        var documents = reader.GetDocuments(docid);
        if (documents.Length > 0)
            document = documents[0];

            MemoryStream memoryStream = new MemoryStream();
            var printer = MyPDFGenerator.New();
            printer.PrintToStream(document, memoryStream);

            Response.AppendHeader("Content-Disposition", "inline; filename=" + timestamp.ToString("yyyyMMddHHmmss") + ".pdf");
            return File(memoryStream.ToArray(), "application/pdf");
        } else {
            return this.RedirectToAction(c => c.Details(id));
        }
    }
    return this.RedirectToAction(c => c.Index(null, null));
}

希望这会有所帮助

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