Add display, simple-format and format variants

Which call put-bytevector for performing output. When used in
combination with an unbuffered port, this should be safer than using
the normal Guile procedures, as I think it'll avoid writing to the
buffers, while still avoiding single character at a time output.

More research is needed though in to how to output to stdout/stderr
when using fibers with a parallelism greater than 1.

knots.scm

@@ -1,7 +1,9 @@
 (define-module (knots)
   #:use-module (srfi srfi-1)
   #:use-module (ice-9 match)
+  #:use-module (ice-9 binary-ports)
   #:use-module (ice-9 suspendable-ports)
+  #:use-module (rnrs bytevectors)
   #:use-module (fibers)
   #:use-module (fibers conditions)
   #:use-module (system repl debug)
@@ -11,6 +13,10 @@
 
             call-with-sigint
 
+            display/knots
+            simple-format/knots
+            format/knots
+
             &knots-exception
             make-knots-exception
             knots-exception?
@@ -51,6 +57,34 @@
             ;; restore original C handler.
             (sigaction SIGINT #f))))))
 
+(define* (display/knots obj #:optional (port (current-output-port)))
+  (put-bytevector
+   port
+   (string->utf8
+    (call-with-output-string
+      (lambda (port)
+        (display obj port))))))
+
+(define (simple-format/knots port s . args)
+  (let ((str (apply simple-format #f s args)))
+    (if (eq? #f port)
+        str
+        (display/knots
+         str
+         (if (eq? #t port)
+             (current-output-port)
+             port)))))
+
+(define (format/knots port s . args)
+  (let ((str (apply format #f s args)))
+    (if (eq? #f port)
+        str
+        (display/knots
+         str
+         (if (eq? #t port)
+             (current-output-port)
+             port)))))
+
 (define &knots-exception
   (make-exception-type '&knots-exception
                        &exception
@@ -135,13 +169,19 @@
          (error-string
           (with-exception-handler
               (lambda (exn)
-                (display (get-output-string string-port)
+                (display/knots (get-output-string string-port)
                                port)
                 (close-output-port string-port)
-                (display "\n\n" port)
+                (display/knots "\n\n" port)
 
-                (backtrace port)
-                (simple-format
+                (let* ((stack (make-stack #t))
+                       (backtrace
+                        (call-with-output-string
+                          (lambda (port)
+                            (display-backtrace stack port)
+                            (newline port)))))
+                  (display/knots backtrace))
+                (simple-format/knots
                  port
                  "\nexception in print-backtrace-and-exception/knots: ~A\n"
                  exn)
@@ -151,14 +191,14 @@
               (let ((str (get-output-string string-port)))
                 (close-output-port string-port)
                 str)))))
-    (display error-string port)))
+    (display/knots error-string port)))
 
 (define* (spawn-fiber/knots thunk #:optional scheduler #:key parallel?)
   (spawn-fiber
    (lambda ()
      (with-exception-handler
          (lambda (exn)
-           (display "Uncaught exception in task:\n"
+           (display/knots "Uncaught exception in task:\n"
                           (current-error-port))
            (print-backtrace-and-exception/knots exn))
        (lambda ()

knots/resource-pool.scm

@@ -90,7 +90,7 @@
 (set-record-type-printer!
  <resource-pool>
  (lambda (resource-pool port)
-   (display
+   (display/knots
     (simple-format #f "#<resource-pool name: \"~A\">"
                    (resource-pool-name resource-pool))
     port)))
@@ -488,7 +488,7 @@
                             (stack-ref stack 3)
                             '%exception
                             (list exn))))))
-                 (display error-string
+                 (display/knots error-string
                                 (current-error-port)))
                (raise-exception exn))
            (lambda ()
@@ -1146,7 +1146,7 @@
                             (stack-ref stack 3)
                             '%exception
                             (list exn))))))
-                 (display error-string
+                 (display/knots error-string
                                 (current-error-port)))
                (raise-exception exn))
            (lambda ()

knots/web-server.scm

@@ -289,7 +289,7 @@ on the procedure being called at any particular time."
   (not (memq 'close (response-connection response))))
 
 (define (default-read-request-exception-handler exn)
-  (display "While reading request:\n" (current-error-port))
+  (display/knots "While reading request:\n" (current-error-port))
   (print-exception
    (current-error-port)
    #f
@@ -302,12 +302,12 @@ on the procedure being called at any particular time."
   (if (and (exception-with-origin? exn)
            (string=? (exception-origin exn)
                      "fport_write"))
-      (simple-format
+      (simple-format/knots
        (current-error-port)
        "~A ~A: error replying to client\n"
        (request-method request)
        (uri-path (request-uri request)))
-      (simple-format
+      (simple-format/knots
        (current-error-port)
        "knots web server: ~A ~A: exception replying to client: ~A\n"
        (request-method request)
@@ -329,7 +329,7 @@ on the procedure being called at any particular time."
               (print-backtrace-and-exception/knots
                exn
                #:port port)))))
-    (display error-string
+    (display/knots error-string
                    (current-error-port)))
 
   (values (build-response #:code 500)
@@ -476,13 +476,17 @@ on the procedure being called at any particular time."
             (unless (and (exception-with-origin? exn)
                          (string=? (exception-origin exn)
                                    "fport_read"))
-              (display "knots web-server, exception in client loop:\n"
+              (display/knots "knots web-server, exception in client loop:\n"
                              (current-error-port))
+              (display/knots
+               (call-with-output-string
+                 (lambda (port)
                    (print-exception
-               (current-error-port)
+                    port
                     #f
                     '%exception
-               (list exn)))
+                    (list exn))))
+               (current-error-port)))
             #t)
         (lambda ()
           (or