Post request using cookies with cURL, RCurl and httr

Question

In Windows cURL I can post a web request similar to this:

curl  --dump-header cook.txt ^
  --data "RURL=http=//www.example.com/r&user=bob&password=hello" ^
  --user-agent  "Mozilla/5.0"  ^
  http://www.example.com/login

With type cook.txt I get a response similar to this:

HTTP/1.1 302 Found                                                 
Date: Thu, ******
Server: Microsoft-IIS/6.0                                          
SERVER: ******                                                  
X-Powered-By: ASP.NET                                              
X-AspNet-Version: 1.1.4322                                         
Location: ******
Set-Cookie: Cookie1=; domain=******; expires=****** ******
******
******
Cache-Control: private                                             
Content-Type: text/html; charset=iso-8859-1                        
Content-Length: 189

I can manually read cookie lines like: Set-Cookie: AuthCode=ABC... (I could script this of course). So I can use AuthCode for subsequent requests.

I am trying do the same in R with RCurl and/or httr (still don't know which one is better for my task).

When I try:

library(httr)

POST("http://www.example.com/login",
     body= list(RURL="http=//www.example.com/r",
                user="bob", password="hello"),
     user_agent("Mozilla/5.0"))  

I get a response similar to this:

Response [http://www.example.com/error]
  Status: 411
  Content-type: text/html
<h1>Length Required</h1> 

By and large I know about 411-error and I could try to fix the request; but I do not get it in cURL, so I am doing something wrong with the POST command.

Can you help me in translating my cURL command to RCurl and/or httr?

Answer 1

httr automatically preserves cookies across calls to the same site, as illustrated by these two calls to http://httpbin.org

GET("http://httpbin.org/cookies/set?a=1")
# Response [http://httpbin.org/cookies]
#   Status: 200
#   Content-type: application/json
# {
#    "cookies": {
#     "a": "1"
#   }
# } 

GET("http://httpbin.org/cookies")
# Response [http://httpbin.org/cookies]
#   Status: 200
#   Content-type: application/json
# {
#   "cookies": {
#     "a": "1"
#   }
# } 

Perhaps the problem is that you're sending your data as application/x-www-form-urlencoded, but the default in httr is multipart/form-data, so use multipart = FALSE in your POST call.

Answer 2

Based on Juba suggestion, here is a working RCurl template.

The code emulates a browser behaviour, as it:

1. retrieves cookies on a login screen and
2. reuses them on the following page requests containing the actual data.

### RCurl login and browse private pages ###

library("RCurl")

loginurl ="http=//www.*****"
mainurl  ="http=//www.*****"
agent    ="Mozilla/5.0"

#User account data and other login pars
pars=list(
     RURL="http=//www.*****",
     Username="*****",
     Password="*****"
)

#RCurl pars     
curl = getCurlHandle()
curlSetOpt(cookiejar="cookiesk.txt",  useragent = agent, followlocation = TRUE, curl=curl)
#or simply
#curlSetOpt(cookiejar="", useragent = agent, followlocation = TRUE, curl=curl)

#post login form
web=postForm(loginurl, .params = pars, curl=curl)

#go to main url with real data
web=getURL(mainurl, curl=curl)

#parse/print content of web
#..... etc. etc.


#This has the side effect of saving cookie data to the cookiejar file 
rm(curl)
gc()

Answer 3

Here is a way to create a post request, keep and reuse the resulting cookies with RCurl, for example to get web pages when authentication is required :

library(RCurl)
curl <- getCurlHandle()
curlSetOpt(cookiejar="/tmp/cookies.txt", curl=curl)
postForm("http://example.com/login", login="mylogin", passwd="mypasswd", curl=curl)
getURL("http://example.com/anotherpage", curl=curl)