- (log-debug "uri-download ~v into ~v" u cached-object-path)
- (define-values (status-line headers body-input)
- ; TODO Timeout. Currently hangs on slow connections.
- (http-sendrecv/url u #:headers (list (format "User-Agent: ~a" user-agent))))
- (log-debug "headers: ~v" headers)
- (log-debug "status-line: ~v" status-line)
- (define status
- (string->number (second (string-split (bytes->string/utf-8 status-line)))))
- (log-debug "status: ~v" status)
- ; TODO Handle redirects
- (match status
- [200
- (let ([etag (header-get headers #"ETag")]
- [lmod (header-get headers #"Last-Modified")])
- (if (and etag
- (file-exists? cached-etag-path)
- (bytes=? etag (file->bytes cached-etag-path)))
- (log-info "ETags match, skipping the rest of ~v" (url->string u))
- (begin
- (log-info
- "Downloading the rest of ~v. ETag: ~a, Last-Modified: ~v"
- (url->string u) etag lmod)
- (make-parent-directory* cached-object-path)
- (make-parent-directory* cached-etag-path)
- (make-parent-directory* cached-lmod-path)
- (call-with-output-file cached-object-path
- (curry copy-port body-input)
- #:exists 'replace)
- (when etag
- (display-to-file etag cached-etag-path #:exists 'replace))
- (when lmod
- (display-to-file etag cached-lmod-path #:exists 'replace))))
- (close-input-port body-input))]
- [_
- (raise status)]))
+ (define etag (header-get headers #"ETag"))
+ (define lmod (header-get headers #"Last-Modified"))
+ (define lmod-curr (if lmod (rfc2822->epoch lmod) #f))
+ (define lmod-prev (if (file-exists? cached-lmod-path)
+ (rfc2822->epoch (file->bytes cached-lmod-path))
+ #f))
+ (log-debug "lmod-curr:~v lmod-prev:~v" lmod-curr lmod-prev)
+ (define cached?
+ (or (and etag
+ (file-exists? cached-etag-path)
+ (bytes=? etag (file->bytes cached-etag-path))
+ (begin
+ (log-debug "ETags match, skipping the rest of ~v" u-str)
+ #t))
+ (and lmod-curr
+ lmod-prev
+ (<= lmod-curr lmod-prev)
+ (begin
+ (log-debug "Last-Modified <= current skipping the rest of ~v" u-str)
+ #t))))
+ (if (not cached?)
+ (begin
+ (log-debug
+ "Downloading the rest of ~v. ETag: ~a, Last-Modified: ~v"
+ u-str etag lmod)
+ (make-parent-directory* cached-object-path)
+ (make-parent-directory* cached-etag-path)
+ (make-parent-directory* cached-lmod-path)
+ (call-with-output-file cached-object-path
+ (curry copy-port body-input)
+ #:exists 'replace)
+ (when etag
+ (display-to-file etag cached-etag-path #:exists 'replace))
+ (when lmod
+ (display-to-file lmod cached-lmod-path #:exists 'replace))
+ 'downloaded-new)
+ 'skipped-cached))
+
+(: uri-download
+ (-> Positive-Float Url
+ (Result (U 'skipped-cached 'downloaded-new)
+ Any))) ; TODO Maybe more-precise error type?
+(define (uri-download timeout u)
+ (define u-str (url->string u))
+ (define timeout-chan (make-channel))
+ (define result-chan (make-channel))
+ (define timeout-thread
+ (thread (λ ()
+ ; Doing this instead of sync/timeout to distinguish error values,
+ ; rather than just have #f to work with.
+ (sleep timeout)
+ (channel-put timeout-chan '(error . timeout)))))
+ (define result-thread
+ (thread (λ ()
+ ; XXX We timeout getting a response, but body download could
+ ; also take a long time and we might want to time that out as
+ ; well, but then we may end-up with partially downloaded
+ ; objects. But that could happen anyway if the server drops the
+ ; connection for whatever reason.
+ ;
+ ; Maybe that is OK once we start treating the
+ ; downloaded object as an addition to the stored set of
+ ; messages, rather than the final set of messages.
+
+ ; TODO message db
+ ; - 1st try can just be an in-memory set that gets written-to
+ ; and read-from disk as a whole.
+ (define result
+ (with-handlers
+ ; TODO Maybe name each known errno? (exn:fail:network:errno-errno e)
+ ([exn:fail:network?
+ (λ (e) `(error . (net-error . ,e)))]
+ [exn?
+ (λ (e) `(error . (other . ,e)))])
+ (define-values (status-line headers body-input)
+ (http-sendrecv/url
+ u
+ #:headers (list (format "User-Agent: ~a" user-agent))))
+ `(ok . ,(Resp status-line headers body-input))))
+ (channel-put result-chan result))))
+ (define result
+ (sync timeout-chan
+ result-chan))
+ (kill-thread result-thread)
+ (kill-thread timeout-thread)
+ (match result
+ [(cons 'error _)
+ result]
+ [(cons 'ok (Resp status-line headers body-input))
+ (log-debug "headers: ~v" headers)
+ (log-debug "status-line: ~v" status-line)
+ (define status
+ (string->number (second (string-split (bytes->string/utf-8 status-line)))))
+ (log-debug "status: ~v" status)
+ ; TODO Handle redirects. Should be within same timeout as req and body.
+ (let ([result
+ (match status
+ [200
+ `(ok . ,(uri-download-from-port u headers body-input))]
+ [_
+ `(error . (http . ,status))])])
+ (close-input-port body-input)
+ result)]))