how to get data from the WTO API in R - r

Question

library(httr)
library(jsonlite)
headers = c(
# Request headers
'Ocp-Apim-Subscription-Key' = '{subscription key}'
)
params = list()
# Request parameters
params['countries[]'] = '{array}'
resp <- GET(paste0("https://api.wto.org/tfad/transparency/procedures_contacts_single_window?"
, paste0(names(params),'=',params,collapse = "&")),
add_headers(headers))
if(!http_error(resp)){
jsonRespText<-fromJSON(rawToChar(content(resp,encoding = 'UTF-8')))$Dataset
jsonRespText
}else{
stop('Error in Response')
}
I don't know how to get response from an API in R. I have executed this code but the server is not responding...

Answer 1

If you examine the value of the resp object after running your code you'll notice a status code:
> resp
Response [https://tfadatabase.org/api/transparency/procedures_contacts_single_window?countries[]=%7Barray%7D]
Date: 2020-04-17 19:25
Status: 422
Content-Type: application/json
Size: 77 B
So the server actually did respond, it just didn't give you what you were hoping for. In the API documentation we can look up this code:
422 Unprocessable Entity
If a member cannot be found, or the request parameters are poorly
formed.
So I just went to the Query Builder and looked for a valid request URL and updated the code. It ran fine - i.e. Status 200.
This was the URL I used in the code:
https://api.wto.org/timeseries/v1/data?i=TP_A_0100&r=000&fmt=json&mode=full&lang=1&meta=false
and the value of resp was
Date: 2020-04-17 19:30
Status: 200
Content-Type: application/json; charset=utf-8
Size: 88 B
I cut out the subscription key in my results above. You can find the Query Builder here. Incidentally, in the Query Builder it automatically includes the subscription key and other "header" info in the URL. You can either remove that first and re-add it in your code, or just change your code to run GET() directly on their version of the URL.