如何在Go中接收具有多部分/表单数据边界的POSTed参数

Question

I'm using HayaGeek's jQuery file upload plugin, and successfully post a request that can be seen on the chrome's developer tool:

/* General */
Remote Address:127.0.0.1:80
Request URL:http://127.0.0.1/profile/edit
Request Method:POST
Status Code:200 OK

/* Response Headers */
Connection:keep-alive
Content-Length:101
Content-Type:application/json
Date:Fri, 24 Apr 2015 02:04:51 GMT
Server:nginx/1.6.2
Set-Cookie:SK=A; Path=/; Expires=Fri, 24 Apr 2015 04:04:51 UTC

/* Request Headers */
Accept:*/*
Accept-Encoding:gzip, deflate
Accept-Language:en-US,en;q=0.8,id;q=0.6
Connection:keep-alive
Content-Length:12855
Content-Type:multipart/form-data; boundary=----WebKitFormBoundarydlN4BAQWeDyF512h
Cookie:SK=A
Host:127.0.0.1
Origin:http://127.0.0.1
Referer:http://127.0.0.1/profile/edit
User-Agent:Mozilla/5.0 (X11; Linux x86_64) AppleWebKit/537.36 (KHTML, like Gecko) Chrome/42.0.2311.90 Safari/537.36
X-Requested-With:XMLHttpRequest

/* Request Payload */
------WebKitFormBoundarydlN4BAQWeDyF512h
Content-Disposition: form-data; name="file"; filename="screen-2015-04-23-21-01-51.png"
Content-Type: image/png


------WebKitFormBoundarydlN4BAQWeDyF512h
Content-Disposition: form-data; name="a"

file_upload
------WebKitFormBoundarydlN4BAQWeDyF512h
Content-Disposition: form-data; name="key"

transcript
------WebKitFormBoundarydlN4BAQWeDyF512h
Content-Disposition: form-data; name="id"

379
------WebKitFormBoundarydlN4BAQWeDyF512h
Content-Disposition: form-data; name=""

undefined
------WebKitFormBoundarydlN4BAQWeDyF512h--

There are no problem getting the uploaded file, using this command:

file, header, err := request.FormFile(`file`) 
// `request` is `*http.Request`

But I'm getting trouble getting the rest of the POSTed parameters, I've tried these but get no luck:

 a := request.FormValue(`a`) // should be: `file_upload`
 id := request.FormValue(`id`) // should be: `transcript`
 key := request.FormValue(`key`) // should be: `379`
 // normally it's works fine, but for this plugin it doesn't work

A normal post request (without boundary, without that plugin) would give something like this, that the POSTed parameter can be retrieved normally using the command above:

/* General */
Remote Address:127.0.0.1:80
Request URL:http://127.0.0.1/profile/edit
Request Method:POST
Status Code:200 OK

/* Response Headers */
Connection:keep-alive
Content-Length:297
Content-Type:application/json
Date:Fri, 24 Apr 2015 02:17:31 GMT
Server:nginx/1.6.2
Set-Cookie:SK=A; Path=/; Expires=Fri, 24 Apr 2015 04:17:31 UTC

- Request Headers
Accept:*/*
Accept-Encoding:gzip, deflate
Accept-Language:en-US,en;q=0.8,id;q=0.6
Connection:keep-alive
Content-Length:23
Content-Type:application/x-www-form-urlencoded; charset=UTF-8
Cookie:SK=A
Host:127.0.0.1
Origin:http://127.0.0.1
Referer:http://127.0.0.1/profile/edit
User-Agent:Mozilla/5.0 (X11; Linux x86_64) AppleWebKit/537.36 (KHTML, like Gecko) Chrome/42.0.2311.90 Safari/537.36
X-Requested-With:XMLHttpRequest

/* Form Data */
a:show
id:379
key:transcript

Answer 1

Ah, we should parse MultipartForm first, for example:

err := request.ParseMultipartForm(1024 * 1024 * 16) // max 16 MB
// then we could access using:
request.MultipartForm.Value[`a`][0]
request.MultipartForm.Value[`key`][0]
request.MultipartForm.Value[`id`][0]
request.MultipartForm.File[`file`]