在Web响应中返回的PDF内容，如何在本地保存?

Question

我通过一个将文件转换的API得到一个网络响应(在本例中，Powerpoint演示文稿到PDF(。

我确实在字符串中得到响应，但是当将此字符串保存到文件或流(无论如何最终都会保存在文件中(时，我总是以一个空白文件结束，它的大小总是远远超过 0 字节。

下面是调用 API 的类：

public class CloudConvert
{
private string apiKey;
private static object ProcessResponse;
public CloudConvert(string apiKey)
{
this.apiKey = apiKey;
}
public async Task<string> Convert(string inputFormat, string outputFormat, string fileUrl)
{
var processUrl = await CreateProcess(inputFormat, outputFormat);
return await Upload(processUrl, fileUrl, outputFormat);
}
private async Task<string> CreateProcess(string inputFormat, string outputFormat)
{
var request = new
{
apikey = apiKey,
inputformat = inputFormat,
outputformat = outputFormat
};
var json = await PostJson("https://api.cloudconvert.com/process", request);
dynamic obj = JObject.Parse(json);
ProcessResponse = obj;
return "https:" + obj.url;
}
private static async Task<string> Upload(string processUrl,
string fileUrl, string outputFormat)
{
var request = new
{
input = "download",
file = fileUrl,
outputformat = outputFormat,
download = "false",
wait = "true",
save = "false"
};
return await PostJson(processUrl, request);
}

private static async Task<string> PostJson(string url, object data)
{
var parameters = JsonConvert.SerializeObject(data);
using (var wc = new WebClient())
{
wc.Headers[HttpRequestHeader.ContentType] = "application/json";
try
{
return await wc.UploadStringTaskAsync(url, "POST", parameters);
}
catch (WebException ex)
{
return string.Empty;
}
}
}
}

以及我如何调用它：

Task<string> task = Task.Run(async () =>
{
return await cloudConvert.Convert("ppt", "pdf", "http://host.com/myfile.ppt");
});
//I have the PDF in the response, as a string.
var pdfContent = task.Result;
//I think it's here that I'm not handling the resulting string 
//properly, ending in a blank file. I've tried writing it to a local file as well, same issue.
using (MemoryStream stream = new MemoryStream())
{
StreamWriter writer = new StreamWriter(stream);
writer.Write(pdfContent);
writer.Flush();
stream.Seek(0, SeekOrigin.Begin);
//This below is something that saves to an Azure storage container...
//filePath = fileStorage.SaveFile($"{fileGeneratedName}.pdf", stream);
//But this fails as well. Blank file 
using (FileStream fs = new FileStream(@"c:tmpoutput.pdf", FileMode.OpenOrCreate))
{
stream.CopyTo(fs);
fs.Flush();
}
}

因此，无论我如何尝试保存返回的内容，似乎我的编码都是错误的。我注意到生成的空白文件始终具有与输入Powerpoint演示文稿相同的页数。

有什么想法吗？

Answer 1

让你的转换函数返回一个 HttpResponseMessage：

public async Task<HttpResponseMessage> convert()

将转换为内存流，然后：

var result = new HttpResponseMessage(HttpStatusCode.OK)
{
Content = new ByteArrayContent(outStream.GetBuffer(),0,(int)outStream.Length)
};
result.Content.Headers.ContentDisposition =
new System.Net.Http.Headers.ContentDispositionHeaderValue("attachment")
{
FileName = fname
};
result.Content.Headers.ContentType = new MediaTypeHeaderValue("application/pdf");
return result;