Quick and dirty HTTP proxy in R

proxy.R

library(curl)
library(httpuv)

req_rook_to_curl <- function(req, host) {
  # browser()
  # Rename headers. Example: HTTP_CACHE_CONTROL => Cache-Control
  r <- as.list(req)

  # Uncomment to print out request headers
  cat("== Original ==\n")
  cat(capture.output(print(str(r))), sep = "\n")
  
  r <- r[grepl("^HTTP_", names(r))]
  nms <- names(r)
  nms <- sub("^HTTP_", "", nms)
  nms <- tolower(nms)
  nms <- gsub("_", "-", nms, fixed = TRUE)
  nms <- gsub("\\b([a-z])", "\\U\\1", nms, perl = TRUE)
  names(r) <- nms

  # Overwrite host field
  r$Host <- host
  # Uncomment to print out modified request headers
  cat("== Modified ==\n")
  cat(capture.output(print(str(r))), sep = "\n")
  r
}


resp_httr_to_rook <- function(resp) {
  # browser()
  status <- as.integer(sub("^HTTP\\S+ (\\d+).*", "\\1", curl::parse_headers(resp$headers)[1]))
  list(
    status = status,
    headers = parse_headers_list(resp$headers),
    body = resp$content
  )
}


s <- startServer("0.0.0.0", 5002,
  list(
    call = function(req) {
      host <- "beta.rstudioconnect.com"
      
      req_curl <- req_rook_to_curl(req, host)
      h <- new_handle()
      do.call(handle_setheaders, c(h, req_curl))

      resp_curl <- curl_fetch_memory(paste0("http://", host, req$PATH_INFO), handle = h)

      resp_httr_to_rook(resp_curl)
    }
  )
)

# Stop the server
stopServer(s)