Add concurrent web server

* fibers.texi (Concurrent Web Server): New section.
* fibers/web/server.scm: Add web server that can run handlers
  concurrently.
* examples/concurrent-web-hello.scm: New file.
* Makefile.am (SOURCES): Add (fibers web server).

4 files changed, 335 insertions, 7 deletions

diff --git a/Makefile.am b/Makefile.am
index fe8eb67..7e203a4 100644
--- a/Makefile.am
+++ b/Makefile.am
@@ -40,6 +40,7 @@ SOURCES = \
 	fibers/stack.scm \
 	fibers/repl.scm \
 	fibers/timers.scm \
+	fibers/web/server.scm \
 	web/server/fibers.scm
 
 extlibdir = $(libdir)/guile/$(GUILE_EFFECTIVE_VERSION)/extensions
diff --git a/examples/concurrent-web-hello.scm b/examples/concurrent-web-hello.scm
new file mode 100644
index 0000000..29ed102
--- /dev/null
+++ b/examples/concurrent-web-hello.scm
@@ -0,0 +1,7 @@
+(use-modules (fibers web server))
+
+(define (handler request body)
+  (values '((content-type . (text/plain)))
+          "Hello, World!"))
+
+(run-server handler)
diff --git a/fibers.texi b/fibers.texi
index c6833c1..3a1f78f 100644
--- a/fibers.texi
+++ b/fibers.texi
@@ -1092,9 +1092,10 @@ fiber while it owns any mutex.
 Here are some small examples to get you started.
 
 @menu
-* Ping::                An echo server and client.
-* Memcached::           A simple memcached server and client.
-* Web Server::          Guile's non-blocking web server.
+* Ping::                  An echo server and client.
+* Memcached::             A simple memcached server and client.
+* Web Server Backend::    A backend for Guile's web server.
+* Concurrent Web Server:: A more concurrent web server.
 @end menu
 
 More examples would be great, especially demonstrating interesting
@@ -1260,12 +1261,18 @@ sys	0m1.456s
 Here we see a throughput of around 12000 puts plus 12000 gets per
 second; pretty good for a basic implementation.
 
-@node Web Server
-@section Web Server
+@node Web Server Backend
+@section Web Server Backend
 
 Fibers includes a ``backend'' for Guile's built-in web server that
-uses fibers.  To run a web server that serves each client from fibers,
-specify the @code{fibers} backend when running your web server:
+uses non-blocking fibers to read requests and write responses.  Fibers
+also includes a standalone web server that uses Guile's HTTP
+facilities, but not its web server framework.  @xref{Concurrent Web
+Server}, for more on the standalone web server.
+
+To run a web server that serves each client from
+fibers, specify the @code{fibers} backend when running your web
+server:
 
 @example
 (use-modules (web server))
@@ -1335,6 +1342,37 @@ request (or the client), so it's at this point that we introduce work
 sharing to our system, allowing us to naturally take advantage of
 multiple cores on our server.
 
+@node Concurrent Web Server
+@section Concurrent Web Server
+
+Guile's web server framework single-threads all web request handling.
+The handler procedure can be passed a number of additional ``state''
+arguments, and is expected to return a corresponding number of
+additional values to use as the next state.  This is sometimes what
+you want, but it does limit concurrency; instead it would be nice to
+be able to not only the input and output running concurrently, but
+also handlers too.
+
+For this reason, Fibers includes a simple standalone web server that
+uses Guile's Guile's HTTP facilities, but not its web server
+framework.  To run a standalone web server, use the @code{(fibers web
+server)} module:
+
+@example
+(use-modules (fibers web server))
+
+(define (handler request body)
+  (values '((content-type . (text/plain)))
+          "Hello, World!"))
+
+(run-server handler)
+@end example
+
+Compared to the Fibers web server backend (@pxref{Web Server
+Backend}), using the standalone fibers web server enables more
+parallelism, as the handlers can run in parallel when you have
+multiple cores.
+
 @node Status
 @chapter Project status
 
diff --git a/fibers/web/server.scm b/fibers/web/server.scm
new file mode 100644
index 0000000..9f50277
--- /dev/null
+++ b/fibers/web/server.scm
@@ -0,0 +1,282 @@
+;;; Fibers web server
+
+;; Copyright (C)  2010-2013,2015,2017 Free Software Foundation, Inc.
+
+;; This library is free software; you can redistribute it and/or
+;; modify it under the terms of the GNU Lesser General Public
+;; License as published by the Free Software Foundation; either
+;; version 3 of the License, or (at your option) any later version.
+;;
+;; This library is distributed in the hope that it will be useful,
+;; but WITHOUT ANY WARRANTY; without even the implied warranty of
+;; MERCHANTABILITY or FITNESS FOR A PARTICULAR PURPOSE.  See the GNU
+;; Lesser General Public License for more details.
+;;
+;; You should have received a copy of the GNU Lesser General Public
+;; License along with this library; if not, write to the Free Software
+;; Foundation, Inc., 51 Franklin Street, Fifth Floor, Boston, MA
+;; 02110-1301 USA
+
+;;; Commentary:
+;;;
+;;; (web server) is a web server implementation using Fibers.  Unlike
+;;; the standard Guile web server implementation which threads all
+;;; handler calls through a single thread, this implementation
+;;; allows multiple concurrent handler threads.
+;;;
+;;; Code:
+
+(define-module (fibers web server)
+  #:use-module (fibers)
+  #:use-module (fibers conditions)
+  #:use-module (rnrs bytevectors)
+  #:use-module (ice-9 binary-ports)
+  #:use-module (ice-9 iconv)
+  #:use-module (ice-9 match)
+  #:use-module ((srfi srfi-9 gnu) #:select (set-field))
+  #:use-module (system repl error-handling)
+  #:use-module (web request)
+  #:use-module (web response)
+  #:export (run-server))
+
+(define (set-nonblocking! port)
+  (fcntl port F_SETFL (logior O_NONBLOCK (fcntl port F_GETFL)))
+  (setvbuf port 'block 1024))
+
+(define (make-default-socket family addr port)
+  (let ((sock (socket PF_INET SOCK_STREAM 0)))
+    (setsockopt sock SOL_SOCKET SO_REUSEADDR 1)
+    (fcntl sock F_SETFD FD_CLOEXEC)
+    (bind sock family addr port)
+    (set-nonblocking! sock)
+    sock))
+
+(define (extend-response r k v . additional)
+  (define (extend-alist alist k v)
+    (let ((pair (assq k alist)))
+      (acons k v (if pair (delq pair alist) alist))))
+  (let ((r (set-field r (response-headers)
+                      (extend-alist (response-headers r) k v))))
+    (if (null? additional)
+        r
+        (apply extend-response r additional))))
+
+;; -> response body
+(define (sanitize-response request response body)
+  "\"Sanitize\" the given response and body, making them appropriate for
+the given request.
+
+As a convenience to web handler authors, RESPONSE may be given as
+an alist of headers, in which case it is used to construct a default
+response.  Ensures that the response version corresponds to the request
+version.  If BODY is a string, encodes the string to a bytevector,
+in an encoding appropriate for RESPONSE.  Adds a
+‘content-length’ and ‘content-type’ header, as necessary.
+
+If BODY is a procedure, it is called with a port as an argument,
+and the output collected as a bytevector.  In the future we might try to
+instead use a compressing, chunk-encoded port, and call this procedure
+later, in the write-client procedure.  Authors are advised not to rely
+on the procedure being called at any particular time."
+  (cond
+   ((list? response)
+    (sanitize-response request
+                       (build-response #:version (request-version request)
+                                       #:headers response)
+                       body))
+   ((not (equal? (request-version request) (response-version response)))
+    (sanitize-response request
+                       (adapt-response-version response
+                                               (request-version request))
+                       body))
+   ((not body)
+    (values response #vu8()))
+   ((string? body)
+    (let* ((type (response-content-type response
+                                        '(text/plain)))
+           (declared-charset (assq-ref (cdr type) 'charset))
+           (charset (or declared-charset "utf-8")))
+      (sanitize-response
+       request
+       (if declared-charset
+           response
+           (extend-response response 'content-type
+                            `(,@type (charset . ,charset))))
+       (string->bytevector body charset))))
+   ((procedure? body)
+    (let* ((type (response-content-type response
+                                        '(text/plain)))
+           (declared-charset (assq-ref (cdr type) 'charset))
+           (charset (or declared-charset "utf-8")))
+      (sanitize-response
+       request
+       (if declared-charset
+           response
+           (extend-response response 'content-type
+                            `(,@type (charset . ,charset))))
+       (call-with-encoded-output-string charset body))))
+   ((not (bytevector? body))
+    (error "unexpected body type"))
+   ((and (response-must-not-include-body? response)
+         body
+         ;; FIXME make this stricter: even an empty body should be prohibited.
+         (not (zero? (bytevector-length body))))
+    (error "response with this status code must not include body" response))
+   (else
+    ;; check length; assert type; add other required fields?
+    (values (let ((rlen (response-content-length response))
+                  (blen (bytevector-length body)))
+              (cond
+               (rlen (if (= rlen blen)
+                         response
+                         (error "bad content-length" rlen blen)))
+               (else (extend-response response 'content-length blen))))
+            (if (eq? (request-method request) 'HEAD)
+                ;; Responses to HEAD requests must not include bodies.
+                ;; We could raise an error here, but it seems more
+                ;; appropriate to just do something sensible.
+                #f
+                body)))))
+
+(define (with-stack-and-prompt thunk)
+  (call-with-prompt (default-prompt-tag)
+                    (lambda () (start-stack #t (thunk)))
+                    (lambda (k proc)
+                      (with-stack-and-prompt (lambda () (proc k))))))
+
+;; -> response body
+(define (handle-request handler request body)
+  (cond
+   ((not request)
+    ;; Bad request.
+    (values (build-response #:version '(1 . 0) #:code 400
+                            #:headers '((content-length . 0)))
+            #vu8()))
+   (else
+    (call-with-error-handling
+      (lambda ()
+        (call-with-values (lambda ()
+                            (with-stack-and-prompt
+                             (lambda ()
+                               (handler request body))))
+          (lambda (response body)
+            (sanitize-response request response body))))
+      #:on-error 'backtrace
+      #:post-error (lambda _
+                     (values (build-response #:code 500) #f))))))
+
+(define (keep-alive? response)
+  (let ((v (response-version response)))
+    (and (or (< (response-code response) 400)
+             (= (response-code response) 404))
+         (case (car v)
+           ((1)
+            (case (cdr v)
+              ((1) (not (memq 'close (response-connection response))))
+              ((0) (memq 'keep-alive (response-connection response)))))
+           (else #f)))))
+
+(define (client-loop client handler)
+  (with-throw-handler #t
+    (lambda ()
+      (let loop ()
+        (cond
+         ((eof-object? (lookahead-u8 client))
+          (close-port client))
+         (else
+          (call-with-values
+              (lambda ()
+                (catch #t
+                  (lambda ()
+                    (let* ((request (read-request client))
+                           (body (read-request-body request)))
+                      (values request body)))
+                  (lambda (key . args)
+                    (display "While reading request:\n" (current-error-port))
+                    (print-exception (current-error-port) #f key args)
+                    (values #f #f))))
+            (lambda (request body)
+              (call-with-values (lambda ()
+                                  (handle-request handler request body))
+                (lambda (response body)
+                  (write-response response client)
+                  (when body
+                    (put-bytevector client body))
+                  (force-output client)
+                  (if (and (keep-alive? response)
+                           (not (eof-object? (lookahead-u8 client))))
+                      (loop)
+                      (close-port client))))))))))
+    (lambda (k . args)
+      (close-port client))))
+
+(define (socket-loop socket handler)
+  (let loop ()
+    (match (accept socket)
+      ((client . sockaddr)
+       ;; From "HOP, A Fast Server for the Diffuse Web", Serrano.
+       (setsockopt client SOL_SOCKET SO_SNDBUF (* 12 1024))
+       (set-nonblocking! client)
+       ;; Always disable Nagle's algorithm, as we handle buffering
+       ;; ourselves.  Ignore exceptions if it's not a TCP port, or
+       ;; TCP_NODELAY is not defined on this platform.
+       (false-if-exception
+        (setsockopt client IPPROTO_TCP TCP_NODELAY 0))
+       (spawn-fiber (lambda () (client-loop client handler))
+                    #:parallel? #t)
+       (loop)))))
+
+(define (call-with-sigint thunk cvar)
+  (let ((handler #f))
+    (dynamic-wind
+      (lambda ()
+        (set! handler
+          (sigaction SIGINT (lambda (sig) (signal-condition! cvar)))))
+      thunk
+      (lambda ()
+        (if handler
+            ;; restore Scheme handler, SIG_IGN or SIG_DFL.
+            (sigaction SIGINT (car handler) (cdr handler))
+            ;; restore original C handler.
+            (sigaction SIGINT #f))))))
+
+(define* (run-server handler #:key
+                     (host #f)
+                     (family AF_INET)
+                     (addr (if host
+                               (inet-pton family host)
+                               INADDR_LOOPBACK))
+                     (port 8080)
+                     (socket (make-default-socket family addr port)))
+  "Run the fibers web server.
+
+HANDLER should be a procedure that takes two arguments, the HTTP request
+and request body, and returns two values, the response and response
+body.
+
+For example, here is a simple \"Hello, World!\" server:
+
+@example
+ (define (handler request body)
+   (values '((content-type . (text/plain)))
+           \"Hello, World!\"))
+ (run-server handler)
+@end example
+
+The response and body will be run through ‘sanitize-response’
+before sending back to the client."
+  ;; We use a large backlog by default.  If the server is suddenly hit
+  ;; with a number of connections on a small backlog, clients won't
+  ;; receive confirmation for their SYN, leading them to retry --
+  ;; probably successfully, but with a large latency.
+  (listen socket 1024)
+  (set-nonblocking! socket)
+  (sigaction SIGPIPE SIG_IGN)
+  (let ((finished? (make-condition)))
+    (call-with-sigint
+     (lambda ()
+       (run-fibers
+        (lambda ()
+          (spawn-fiber (lambda () (socket-loop socket handler)))
+          (wait finished?))))
+     finished?)))