capybara/util.rkt

#lang racket/base

(require racket/format racket/string racket/port)

(provide ~r/pad run-external)

(define (~r/pad num pad-to)
  (~r num #:min-width pad-to #:pad-string "0"))

(define (run-external argv source)
  (printf "running external program: ~a\n" argv)
  (define-values [proc out in err]
    (apply subprocess #f #f #f "/usr/bin/env" argv))
  (define out-str #f)
  (define err-str "")
  (define out-reader (thread (λ () (set! out-str (port->string out)))))
  (define err-reader (thread (λ () (set! err-str (port->string err)))))

  (write-string source in)
  (flush-output in)
  (close-output-port in)

  (subprocess-wait proc)
  (thread-wait out-reader)
  (thread-wait err-reader)

  (define err-trimmed (string-trim err-str))
  (unless (string=? "" err-trimmed)
    (error "child process raised error!" err-trimmed))

  (unless out-str
    (error "child process didn't return anything!"))

  out-str)