Using RCurl postForm to gather JSON data - r

Question

I am trying to extract time series data from the BLS API using RCurl.
The BLS supplies the following sample code for command line extraction:
curl -i -X POST -H 'Content-Type: application/json'
-d '{"seriesid":["LEU0254555900", "APU0000701111"],
"startyear":"2002", "endyear":"2012"}'
http://api.bls.gov/publicAPI/v1/timeseries/data/
I have also confirmed that the specified files (i.e. series ids) are both present as the following both yield a JSON formatted object:
require(RCurl)
bls.content_test1 <- getURLContent("http://api.bls.gov/publicAPI/v1/timeseries/data/LEU0254555900")
bls.content_test2 <- getURLContent("http://api.bls.gov/publicAPI/v1/timeseries/data/APU0000701111")
Based on a variety of posts with the RCurl tag (and this post in particular), I have ported the command line script to the following chunk of code:
require(RJSONIO)
jsonbody <- toJSON(list("seriesid"=paste('"["CFU0000008000"', '[LEU0254555900"]"')
,"startyear"="2012"
,"endyear"="2013"))
httpheader <- c(Accept="application/json; charset=UTF-8",
"Content-Type"="application/json")
bls.content <- postForm("http://api.bls.gov/publicAPI/v1/timeseries/data/"
,.opts=list(httpheader=httpheader
,postfields=jsonbody))
Which yields:
[1] "{\"status\":\"REQUEST_FAILED\",\"responseTime\":0,\"message\":[\"Your request has failed, please check your input parameters and try your request again.\"],\"Results\":null}"
attr(,"Content-Type")
charset
"application/json" "UTF-8"
Does this appear to be a problem with my implementation of RCurl or does this appear to be a problem with the BLS API?

Answer 1

It's actually a problem with the way you are creating your json body. With your version if you do cat(jsonbody) you get
{
"seriesid": "\"[\"CFU0000008000\" [LEU0254555900\"]\"",
"startyear": "2012",
"endyear": "2013"
}
which has those extra escapes and brackets in there. It's not correct. Instead try
jsonbody <- toJSON(list("seriesid"=c("CFU0000008000", "LEU0254555900"),
startyear="2012",
endyear="2013"))
which gives
{
"seriesid": [ "CFU0000008000", "LEU0254555900" ],
"startyear": "2012",
"endyear": "2013"
}
which is valid JSON. Just changing that part and using the rest of the code as you had it gives me a REQUEST_SUCCEEDED message.

Answer 2

Here's an approach with httr:
library(httr)
library(jsonlite)
# Need unbox() to tell jsonlite() numbers are scalars, not vectors of length 1
body <- list(
seriesid = c("CFU0000008000", "LEU0254555900"),
startyear = unbox(2012),
endyear = unbox(2013)
)
r <- POST("http://api.bls.gov/publicAPI/v1/timeseries/data/", body = body, encode = "json")
stop_for_status(r)
# Need to specify type since site returns incorrect type of text/plain
str(content(r, type = "application/json"))