RCurl get response body when it errors out - r

Question

I'm just trying to get the response body when the post request fails using RCurl. When I'm running it through R, I only get the response error and it fails out.
Error: Unprocessable Entity
when I post the same request with the UI interface for testing, it gives
{
"reason": [
"Can not create Data with Name: DataTest. Data Name should be unique."
],
"singleReason": "Can not create Data with Name: DataTest. Data Name should be unique."
}
Any help on how to get response bodies on 4XX errors is appreciated. TIA.
Post request
postdata.json <- '{"name":"DataTest","description":"Test Payload","algorithm":{"name":"DataTest","version":"0.1.0"}}'
post.result <- httpPOST(url=SERVER, postfields = postdata.json, verbose = T,
httpheader=c(Authorization=access.token, 'Content-Type'='application/json', Accept='application/json'))
RStudio output
* About to connect() to SERVER port 80 (#0)
* Trying SERVER... * connected
* Connected to SERVER port 80 (#0)
> POST /api/test HTTP/1.1
Host: SERVER
Authorization: AUTHENTICATION
Content-Type: application/json
Accept: application/json
Content-Length: 171
< HTTP/1.1 422 Unprocessable Entity
< Content-Type: application/json;charset=UTF-8
< Date: Thu, 13 Nov 2014 16:31:42 GMT
< Server: Apache-Coyote/1.1
< Content-Length: 215
< Connection: keep-alive
<
* Connection #0 to host SERVER left intact
Show Traceback
Rerun with Debug
Error: Unprocessable Entity
n.b. I'm okay with it failing and returning an Error. That's expected. I'm just trying to get the response body associated with the error code.

Answer 1

Here's one approach with httr:
library(httr)
postdata.json <- '{"name":"DataTest","description":"Test Payload","algorithm":{"name":"DataTest","version":"0.1.0"}}'
res <- POST(SERVER,
body = postdata.json,
add_headers(
Authorization = access.token,
'Content-Type' = 'application/json',
Accept = 'application/json'
)
)
http_status(res)
content(res)

Answer 2

I was able to get the response body using RCurl by adding a basicTextGatherer() and a writefunction.
reader <- basicTextGatherer()
post.result <- httpPOST(url=SERVER, postfields = postdata.json, verbose = T,
writefunction = reader$update,
httpheader=c(Authorization=access.token,
'Content-Type'='application/json',
Accept='application/json')
)
return(body=reader$value())
but Hadley's solution is simpler to work with and doesn't error out.