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.我遇到的问题是将文档发送回客户端 MVC 应用程序.剩下的就是关于所发生的一切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.

我编写的代码成功地将这两种格式转换为 C# 代码，然后(返回)为 PDF 格式.我已经成功传输了一个应该代表这些文档之一的字节数组，但我无法让它在浏览器中显示(在一个新选项卡中).我总是收到某种无法显示"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，我做了一个方法来查看服务器端的文档，以确保我至少可以让它这样做.它将文档放入代码中并用它创建一个 FileStreamResult，然后它作为(隐式转换)ActionResult 返回.我得到它返回到服务器端 MVC 控制器并将其放入一个简单的返回(无视图)中，在浏览器中显示 PDF 就好了.但是，尝试直接使用 Web API 函数只会返回看起来像 FileStreamResult 的 JSON 表示的内容.

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.

当我尝试让它正确返回到我的客户端 MVC 应用程序时，它告诉我无法直接设置_buffer".一些错误消息，表明某些返回并抛出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 PDF 的字节数组表示，当转换为 base64 字符串时，其字符数似乎与 FileStreamResult 在 JSON 中返回的_buffer"字符串的字符数不同.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.

有关如何让此 PDF 正确返回的任何想法?如有必要，我可以提供代码，但必须有一些已知的方法将 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.

附言我确实知道客户端"应用程序在技术上不在客户端.它也将是一个服务器应用程序，但在这种情况下应该无关紧要.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();
}

MVC 应用程序中的代码随着时间的推移发生了很大变化.现在的方式，它没有达到它试图在浏览器中显示的阶段.在此之前它会出错.

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>();
}

我直接从 Web API 控制器运行该方法得到的 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)

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 System.Web.Mvc.ActionResult 类型的实例.类型是接口或抽象类，不能被实例化.路径文件流".

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'.

以前我拿空的pdf阅读器(阅读器是空白的.没有文件)的时候，我用了这个代码:

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);
    }

注释掉的是来自其他一些尝试的代码.当我使用该代码时，我从服务器返回了一个字节数组.它看起来像:

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

返回 PDF (Web Api) 的一些服务器端代码.

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;
}

在我的视图上你可以做这样的事情

On my a View you could do something like this

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

这将调用 web api 并在浏览器的新选项卡中打开 PDF 文档.

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

这是我基本上从 MVC 控制器做同样的事情

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));
}

希望能帮到你

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