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#lang racket/base
(require racket/contract/base)
(provide log-level/c)
(define log-level/c (or/c 'none 'fatal 'error 'warning 'info 'debug))
(define log-spec? (listof (or/c symbol? #f)))
(define log-event? (vector-immutable/c log-level/c string? any/c (or/c symbol? #f)))
(provide/contract [with-intercepted-logging
(->* ((-> log-event? any)
(-> any)
(#:logger logger?)
#:rest log-spec?
(->* (output-port? (-> any) log-level/c)
(#:logger logger?)
#:rest log-spec?
(define (receiver-thread receiver stop-chan intercept)
(lambda ()
(define (clear-events)
(let ([l (sync/timeout 0 receiver)])
(when l ; still something to read
(intercept l) ; interceptor gets the whole vector
(let loop ()
(let ([l (sync receiver stop-chan)])
(cond [(eq? l 'stop)
;; we received all the events we were supposed
;; to get, read them all (w/o waiting), then
;; stop
[else ; keep going
(intercept l)
(define (with-intercepted-logging interceptor proc #:logger [logger #f]
. log-spec)
(let* ([orig-logger (current-logger)]
;; Unless we're provided with an explicit logger to monitor we
;; use a local logger to avoid getting messages that didn't
;; originate from proc. Since it's a child of the original logger,
;; the rest of the program still sees the log entries.
[logger (or logger (make-logger #f orig-logger))]
[receiver (apply make-log-receiver logger log-spec)]
[stop-chan (make-channel)]
[t (receiver-thread receiver stop-chan interceptor)])
(parameterize ([current-logger logger])
(channel-put stop-chan 'stop) ; stop the receiver thread
(thread-wait t))))
(define (with-logging-to-port port proc #:logger [logger #f] . log-spec)
(apply with-intercepted-logging
#:logger logger
(lambda (l) (displayln (vector-ref l 1) ; actual message