Using httr to place orders through BitMex API - r

Question

I'm trying to use the httr R package to place orders on BitMex through their API.
I found some guidance over here, and after specifying both my API key and secret in respectively the objects K and S, I've tried the following
verb <- 'POST'
expires <- floor(as.numeric(Sys.time() + 10000))
path <- '/api/v1/order'
data <- '{"symbol":"XBTUSD","price":4500,"orderQty":10}'
body <- paste0(verb, path, expires, data)
signature <- hmac(S, body, algo = 'sha256')
body_l <- list(verb = verb, expires = expires, path = path, data = data)
And then both:
msg <- POST('https://www.bitmex.com/api/v1/order', encode = 'json', body = body_l, add_headers('api-key' = K, 'api-signature' = signature, 'api-expires' = expires))
and:
msg <- POST('https://www.bitmex.com/api/v1/order', body = body, add_headers('api-key' = K, 'api-signature' = signature, 'api-expires' = expires))
Give me the same error message when checked:
rawToChar(msg$content)
[1] "{\"error\":{\"message\":\"Signature not valid.\",\"name\":\"HTTPError\"}}"
I've tried to set it up according to how BitMex explains to use their API, but I appear to be missing something. They list out a couple of issues that might underly my invalid signature issue, but they don't seem to help me out. When following their example I get the exact same hashes, so that seems to be in order.

Answer 1

bit late to the party here but hopefully this helps!
Your POST call just needs some minor changes:
add content_type_json()
include .headers = c('the headers') in add_headers(). See example below:
library(httr)
library(digest)
S <- "your api secret"
K <- "your api key"
verb <- 'POST'
expires <- floor(as.numeric(Sys.time() + 10))
path <- '/api/v1/order'
data <- '{"symbol":"XBTUSD","price":4500,"orderQty":10}'
body <- paste0(verb, path, expires, data)
signature <- hmac(S, body, algo = 'sha256')
msg <- POST('https://www.bitmex.com/api/v1/order',
encode = 'json',
body = data,
content_type_json(),
add_headers(.headers = c('api-key' = K,
'api-signature' = signature,
'api-expires' = expires)))
content(msg, "text")
I have a package on CRAN - bitmexr - that provides a wrapper around the majority of BitMEX's API endpoints that you might be interested in. Still quite a "young" package so I would welcome any feedback!