抑制302 httr POST返回的错误

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我使用R httr POST函数向jSON发送一个API。 API正确地返回一个302：Found消息，但httr正在退出该函数，然后我才能抓住响应的主体（这是一个jSON主体，有一些关键的信息）。

使用Verbose（）参数运行httr，以下是响应：

; - HTTP / 1.1 302 Found < - Cache-Control：no-cache < - Pragma：no-cache < - Content-Length：47 < ; - Content-Type：application / json; charset = utf-8 < - Expires：-1 函数中出现错误（类型，msg，asError = TRUE）：不能进行必要的数据回退

我已经从终端运行相同的cURL文章，并且可以确认我发送的是从API产生回复302和所需的身体。

为了参考，我的R代码如下。 （注意：y是jSON格式的主体）

POST（https：// thewebsite，authenticate（myusername mypassword，type =basic）， add_headers（Content-Type=application / json）， body = y，verbose（））

有关如何绕过错误并捕获302消息内容的任何想法？

解决方案

我刚刚花了一些时间与这个问题自己。问题出在HTTP规范（这基本上是RCurl坚持）和什么浏览器实际上做的不同。

事件的顺序是这样：

您向服务器发出POST请求

服务器处理请求并将您重定向到新网址

RCurl将此类似于像POST这样的新请求对待，并尝试重放正文。 （浏览器不尝试重新发送数据）

它不能重新发送数据，因为底层的RCurl不是这样构造的，这是可能的（这就是为什么curl抱怨： 必要的数据倒转不可能）

解决方案很简单 - 禁用以下重定向与 config（followlocation = 0L）：

POST（https：// thewebsite， authenticate（myusername，mypassword）， content_type_json（）， config（followlocation = 0L）， body = y，） b $ b＃PS with httr 0.4你可以简化为 POST（https：// thewebsite， authenticate（myusername，mypassword）， config（followlocation = 0L ）， body = x，encode =json）

然后需要查看位置字段的内容，并自己执行重定向。

有关基本问题的更多讨论，请参阅：

• HTTP：POST请求接收到302，如果重定向请求为GET？
• programmers.stackexchange/questions/99894

I'm using the R httr POST function to send a body of jSON to an API. The API is, properly, returning a 302: Found message, but httr is exiting the function before I'm able to grab the body of response (which is a jSON body, with some key bits of info.)

Running httr with the Verbose() argument, the following is the response:

<- HTTP/1.1 302 Found <- Cache-Control: no-cache <- Pragma: no-cache <- Content-Length: 47 <- Content-Type: application/json; charset=utf-8 <- Expires: -1 Error in function (type, msg, asError = TRUE) : necessary data rewind wasn't possible

I've run the same cURL post from terminal, and can confirm what I'm sending produces a reply from the API with both the 302 and the desired body.

For reference my R code follows. (note: y is the jSON formatted body)

POST("thewebsite",authenticate("myusername","mypassword",type="basic"), add_headers("Content-Type" = "application/json"), body = y, verbose())

Any thoughts on how to bypass the error and capture the 302 message content?

解决方案

I just spent some time battling with this issue myself. The problem comes down to a difference in the HTTP spec (which is basically what RCurl adheres to) and what browsers actually do.

The sequence of events is this:

You issue POST request to server

Server handles request and issues you a redirect to a new url

RCurl treats this like new request like a POST, and tries to replay the body. (Browser don't try and resend the data)

It can't resend the data because the underlying RCurl isn't constructed in such a way this is possible (that's why curl complains: "necessary data rewind wasn't possible")

The solution is simple - disable the following of redirects with config(followlocation = 0L):

POST("thewebsite", authenticate("myusername","mypassword"), content_type_json(), config(followlocation = 0L), body = y, ) # PS with httr 0.4 you can simplify to POST("thewebsite", authenticate("myusername","mypassword"), config(followlocation = 0L), body = x, encode = "json" )

You'll then need to look at the contents of the location field, and do the redirect yourself.

For more discussion of the underlying issue, see:

• HTTP: POST request receives a 302, should the redirect-request be a GET?
• programmers.stackexchange/questions/99894