如何使用httr发布多部分/相关内容(适用于Google Drive API)

Question

我使用httr将简单文件上传到Google云端硬盘.问题是每个文档都被上传为"无标题",我必须修补元数据以设置标题.PATCH请求偶尔会失败.

根据API,我应该能够进行分段上传,允许我将标题指定为上传文件的同一POST请求的一部分.

res<-POST(
  "https://www.googleapis.com/upload/drive/v2/files?convert=true",
  config(token=google_token),
  body=list(y=upload_file(file))
)
id<-fromJSON(rawToChar(res$content))$id
if(is.null(id)) stop("Upload failed")
url<-paste(
  "https://www.googleapis.com/drive/v2/files/",
  id,
  sep=""
)
title<-strsplit(basename(file), "\\.")[[1]][1]
Sys.sleep(2)
res<-PATCH(url,
  config(token=google_token),
  body=paste('{"title": "',title,'"}', sep = ""),
  add_headers("Content-Type" = "application/json; charset=UTF-8")
)
stopifnot(res$status_code==200)
cat(id)

我想做的是这样的事情:

res<-POST(
  "https://www.googleapis.com/upload/drive/v2/files?uploadType=multipart&convert=true",
  config(token=google_token),
  body=list(y=upload_file(file),
            #add_headers("Content-Disposition" = "text/json"),
            json=toJSON(data.frame(title))
  ),
  encode="multipart",
  add_headers("Content-Type" = "multipart/related"),
  verbose()
)

我得到的输出显示各个部分的内容编码是错误的,它导致400错误:

-> POST /upload/drive/v2/files?uploadType=multipart&convert=true HTTP/1.1
-> User-Agent: curl/7.19.7 Rcurl/1.96.0 httr/0.6.1
-> Host: www.googleapis.com
-> Accept-Encoding: gzip
-> Accept: application/json, text/xml, application/xml, */*
-> Authorization: Bearer ya29.ngGLGA9iiOrEFt0ycMkPw7CZq23e6Dgx3Syjt3SXwJaQuH4B6dkDdFXyIC6roij2se7Fs-Ue_A9lfw
-> Content-Length: 371
-> Expect: 100-continue
-> Content-Type: multipart/related; boundary=----------------------------938934c053c6
-> 
<- HTTP/1.1 100 Continue
>> ------------------------------938934c053c6
>> Content-Disposition: form-data; name="y"; filename="db_biggest_tables.csv"
>> Content-Type: application/octet-stream
>> 

>> table    rows    DATA    idx total_size  idxfrac

>> 
>> ------------------------------938934c053c6
>> Content-Disposition: form-data; name="json"
>> 
>> {"title":"db_biggest_tables"}
>> ------------------------------938934c053c6--

<- HTTP/1.1 400 Bad Request
<- Vary: Origin
<- Vary: X-Origin
<- Content-Type: application/json; charset=UTF-8
<- Content-Length: 259
<- Date: Fri, 26 Jun 2015 18:50:38 GMT
<- Server: UploadServer
<- Alternate-Protocol: 443:quic,p=1
<- 

有没有办法为各个部分正确设置内容编码？例如,第二部分应该是"text/json".

我已经通过R文档,Hadley在Github的httr项目页面,这个网站和一些一般的谷歌搜索.我找不到任何关于如何进行分段上传和设置内容编码的示例.

Answer 1

你应该使用curl::form_file或别名来做这件事httr::upload_file.另见卷曲小插图.按照Google API文档中的示例操作:

library(httr)

media <- tempfile()
png(media, with = 800, height = 600)
plot(cars)
dev.off()

metadata <- tempfile()
writeLines(jsonlite::toJSON(list(title = unbox("My file"))), metadata)

#post
req <- POST("https://httpbin.org/post",
  body = list(
    metadata = upload_file(metadata, type = "application/json; charset=UTF-8"),
    media = upload_file(media, type = "image/png")
  ),
  add_headers("Content-Type" = "multipart/related"),
  verbose()
)

unlink(media)
unlink(metadata)

这里唯一的区别是curl会自动Content-Disposition为每个文件添加一个标题,这是必需的,multipart/form-data但不是multipart/related.在这种情况下,服务器可能只是忽略这个冗余头.

目前,如果不将内容写入文件,则无法实现此目的.也许我们可以在httr/curl的未来版本中添加类似的东西,尽管之前没有出现过.