Automate multiple requests to a web search form using R - r

Question

I am trying to create a dataframe of combinations of place of residence and tax using https://swisstaxcalculator.estv.admin.ch/#/calculator/income-wealth-tax
I have seen How to automate multiple requests to a web search form using R and Scrape tables by passing multiple search requests using R but both those cases work by building new URLs and I don't think this works for admin.ch (the URL always stays the same).
Using the browser inspector I can extract query from a random calculation and it looks like this:
curl 'https://swisstaxcalculator.estv.admin.ch/delegate/ost-integration/v1/lg-proxy/operation/c3b67379_ESTV/API_calculateSimpleTaxes' \
-H 'Connection: keep-alive' \
-H 'Accept: application/json, text/plain, */*' \
-H 'User-Agent: Mozilla/5.0 (Windows NT 10.0; Win64; x64) AppleWebKit/537.36 (KHTML, like Gecko) Chrome/86.0.4240.75 Safari/537.36' \
-H 'Content-Type: application/json;charset=UTF-8' \
-H 'Origin: https://swisstaxcalculator.estv.admin.ch' \
-H 'Sec-Fetch-Site: same-origin' \
-H 'Sec-Fetch-Mode: cors' \
-H 'Sec-Fetch-Dest: empty' \
-H 'Referer: https://swisstaxcalculator.estv.admin.ch/' \
-H 'Accept-Language: en-GB,en-US;q=0.9,en;q=0.8,fr;q=0.7' \
-H 'Cookie: SCDID_S=ji-7X06i9sLI29sYA_JLmUSOd6JpMHsgFG_8ilp1l6EZz8h7y2PMjA$$' \
--data-binary '{"SimKey":null,"TaxYear":2019,"TaxLocationID":100000000,"Relationship":1,"Confession1":5,"Children":[],"Confession2":0,"TaxableIncomeCanton":30000,"TaxableIncomeFed":30000,"TaxableFortune":0}' \
--compressed
It's quite clear I should change the part after --data-binary so I create a vector of taxable incomes and then a vector of --data-binary:
taxable_inc <- seq(30000, 150000, by = 1000)
data <- paste0('{"SimKey":null,"TaxYear":2019,"TaxLocationID":100000000,"Relationship":1,"Confession1":5,"Children":[],"Confession2":0,"TaxableIncomeCanton":',
taxable_inc,
',"TaxableIncomeFed":',
taxable_inc,
',"TaxableFortune":0}')
The next part would be to pass/execute this query and capture the answer but I do not know how to to this. Since the query starts with curl I looked at packages curl and RCurl but I really do not understand the link between handles, urls and queries....

Answer 1

You can use httr to make the call and specify encode = "json" to automatically set the header Content-Type: application/json like in curl and encode the body parameter as a JSON object :
library(httr)
url <- 'https://swisstaxcalculator.estv.admin.ch/delegate/ost-integration/v1/lg-proxy/operation/c3b67379_ESTV/API_calculateSimpleTaxes'
r <- POST(url, body = list(
SimKey = NULL,
TaxYear = 2019,
TaxLocationID = 100000000,
Relationship = 1,
Confession1 = 5,
Children = array(),
Confession2 = 0,
TaxableIncomeCanton = 30000,
TaxableIncomeFed = 30000,
TaxableFortune = 0
), encode = "json", verbose())
data = content(r, "parsed")
print(str(data))
which gives :
{"response":{"IncomeSimpleTaxCanton":1747,"FortuneTaxCanton":0,"IncomeSimpleTaxCity":1747,"IncomeTaxChurch":0,"IncomeTaxCity":1380,"IncomeSimpleTaxFed":119,"PersonalTax":0,"FortuneTaxCity":0,"FortuneSimpleTaxCanton":0,"IncomeTaxFed":119,"FortuneSimpleTaxCity":0,"IncomeTaxCanton":2699,"Location":{"TaxLocationID":100000000,"ZipCode":"1000","BfsID":5586,"CantonID":23,"BfsName":"Lausanne","City":"Lausanne","Canton":"VD"},"FortuneTaxChurch":0}}