如何使用Yesod和Http-Conduit将FileInfo发布到Web服务？ [英] How can I post FileInfo to a web service using Yesod and Http-Conduit?

问题描述

我正在使用默认的Yesod scaffolding项目。

我创建了一个显示上传文件的简单表单的页面。

（该表单可能会创建客户端使用Javascript。）

为简洁起见，表单有一个文件输入：

 < form method =postaction = @ {UploadR}> 
< input type =filename =myfile> 
< button type =submit> 
  

我的目标是处理表单数据，然后将文件上传到Web服务。

我没有麻烦处理表单，我关心的是与web服务交互。

例如，给定以下的Yesod处理程序：

  postUploadR :: Handler Html 
 postUploadR = do 
 mgr<  -  fmap httpManager getYesod 
 fi<  -  runInputPost $ ireq fileFieldmyfile
 let fSource = fileSource fi 
 fName = fileName fi 
 req<  -  parseUrlhttp：// webservice / upload
 let areq = req {method = methodPost 
 ，requestBody = requestBodySourceChunked fSource 
} 
 res<  -  httpLbs areq mgr 
 defaultLayout $ do 
 setTitlefile uploaded
 [whamlet | 
< h3>成功
< p>您上传了＃{fName}。 
 $] 
  

web服务返回错误：失败发布内容长度，但其他一切按预期工作。也许服务器不支持分块请求体？

解决方案

我想你对分块请求体的猜测是正确的。您需要做的是：

• 将上传的内容传输到临时文件中。


• 使用 requestBodySource 并提供文件长度及其内容。

幸运的是，步骤（1）和（2）可以通过 sinkCacheLength 函数。您最终会得到如下结果：

 （fSize，fSource）<  -  fileSource fi $$ sinkCacheLength 
  

I am working with the default Yesod scaffolding project.
I have created a page that displays a simple form to upload files.
(The form will likely be created on the client using Javascript.)
For brevity, the form has a single file input:

<form method="post" action=@{UploadR}>
   <input type="file" name="myfile">
   <button type="submit">

My objective is to process the form data and then upload the file to a web service.
I have no trouble processing the form, my concern is interacting with the web service.
For example, given the following Yesod handler:

postUploadR :: Handler Html
postUploadR = do
    mgr <- fmap httpManager getYesod
    fi  <- runInputPost $ ireq fileField "myfile"
    let fSource = fileSource fi
        fName   = fileName fi
    req <- parseUrl "http://webservice/upload"
    let areq = req { method = methodPost
                   , requestBody = requestBodySourceChunked fSource
                   }
    res <- httpLbs areq mgr
    defaultLayout $ do
      setTitle "file uploaded"
      [whamlet|
       <h3> Success
       <p> You uploaded #{fName}.
      |]

The webservice returns the error: fail post content-length, but everything else works as expected. Perhaps the server doesn't support a chunked request body?

解决方案

I think your guess about chunked request body is correct. What you need to do is:

• Stream the uploaded contents into a temporary file.
• Get the size of that file.
• Use requestBodySource and provide the file length and its contents.

Fortunately, steps (1) and (2) can be handled quite easily by the sinkCacheLength function. You'll end up with something like:

(fSize, fSource) <- fileSource fi $$ sinkCacheLength

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