From 258893a291963894ba4d202b90d02fbcfab441e4 Mon Sep 17 00:00:00 2001
From: David Thompson <dthompson2@worcester.edu>
Date: Sat, 7 Nov 2015 16:26:19 -0500
Subject: Add (web socket server) module.

---
 web/socket/server.scm | 116 ++++++++++++++++++++++++++++++++++++++++++++++++++
 1 file changed, 116 insertions(+)
 create mode 100644 web/socket/server.scm

(limited to 'web')

diff --git a/web/socket/server.scm b/web/socket/server.scm
new file mode 100644
index 0000000..b7d541c
--- /dev/null
+++ b/web/socket/server.scm
@@ -0,0 +1,116 @@
+(define-module (web socket server)
+  #:use-module (ice-9 match)
+  #:use-module (rnrs bytevectors)
+  #:use-module (base64)
+  #:use-module (sha-1)
+  #:use-module (web request)
+  #:use-module (web response)
+  #:use-module (web uri)
+  #:use-module (web socket frame)
+  #:export (make-server-socket
+            run-server))
+
+;; See section 4.2 for explanation of the handshake.
+(define (handshake client-key)
+  "Translate the base64 encoded CLIENT-KEY string into a base64
+encoded acceptance key."
+  (base64-encode
+   (sha-1->bytevector
+    (sha-1
+     (string->utf8
+      (string-append (string-trim-both client-key)
+                     "258EAFA5-E914-47DA-95CA-C5AB0DC85B11"))))))
+
+(define (read-handshake-request client-socket)
+  "Read HTTP request from CLIENT-SOCKET that should contain the
+headers required for a WebSocket handshake."
+  ;; See section 4.2.1.
+  (read-request client-socket))
+
+(define (make-handshake-response client-key)
+  "Return an HTTP response object for upgrading to a WebSocket
+connection for the client whose key is CLIENT-KEY, a base64 encoded
+string."
+  ;; See section 4.2.2.
+  (let ((accept-key (handshake client-key)))
+    (build-response #:code 101
+                    #:headers `((upgrade . ("websocket"))
+                                (connection . (upgrade))
+                                (sec-websocket-accept . ,accept-key)))))
+
+(define* (make-server-socket #:key
+                             (host #f)
+                             (addr (if host (inet-aton host) INADDR_LOOPBACK))
+                             (port 8080))
+  (let ((sock (socket PF_INET SOCK_STREAM 0)))
+    (setsockopt sock SOL_SOCKET SO_REUSEADDR 1)
+    (bind sock AF_INET addr port)
+    sock))
+
+(define (accept-new-client server-socket)
+  (match (accept server-socket)
+    ((client-socket . _) client-socket)))
+
+(define (serve-client client-socket handler)
+  "Serve client connected via CLIENT-SOCKET by performing the HTTP
+handshake and listening for control and data frames.  HANDLER is
+called for each complete message that is received."
+  (define (handle-data-frame type data)
+    (let ((result (handler (match type
+                            ('text   (utf8->string data))
+                            ('binary data)))))
+      (write-frame (cond
+                    ((string? result)
+                     (make-text-frame result))
+                    ((bytevector? result)
+                     (make-binary-frame result)))
+                   client-socket)))
+
+  ;; Perform the HTTP handshake and upgrade to WebSocket protocol.
+  (let* ((request (read-handshake-request client-socket))
+         (client-key (assoc-ref (request-headers request) 'sec-websocket-key))
+         (response (make-handshake-response client-key)))
+    (write-response response client-socket)
+    (let loop ((fragments '())
+               (type #f))
+      (let ((frame (read-frame client-socket)))
+        (cond
+         ;; Per section 5.4, control frames may appear interspersed
+         ;; along with a fragmented message.
+         ((close-frame? frame)
+          ;; Per section 5.5.1, echo the close frame back to the
+          ;; client before closing the socket.
+          (write-frame (make-close-frame (frame-data frame)) client-socket)
+          (close-port client-socket))
+         ((ping-frame? frame)
+          ;; Per section 5.5.3, a pong frame must include the exact
+          ;; same data as the ping frame.
+          (write-frame (make-pong-frame (frame-data frame)) client-socket)
+          (loop fragments type))
+         ((pong-frame? frame) ; silently ignore pongs
+          (loop fragments type))
+         ((first-fragment-frame? frame) ; begin accumulating fragments
+          (loop (list frame) (frame-type frame)))
+         ((final-fragment-frame? frame) ; concatenate all fragments
+          (handle-data-frame type (frame-concatenate (reverse fragments)))
+          (loop '() #f))
+         ((fragment-frame? frame) ; add a fragment
+          (loop (cons frame fragments) type))
+         ((data-frame? frame) ; unfragmented data frame
+          (handle-data-frame (frame-type frame) (frame-data frame))
+          (loop '() #f)))))))
+
+(define* (run-server handler #:optional (server-socket (make-server-socket)))
+  "Run WebSocket server on SERVER-SOCKET.  HANDLER, a procedure that
+accepts a single argument, is called for each complete message that
+the server receives from a client.  When the message is in text
+format, HANDLER is passed a string.  When the message is in binary
+format, HANDLER is passed a bytevector.  HANDLER must return either a
+string, bytevector, or #f.  Strings and bytevectors are sent to the
+client in response to their message, and #f indicates that nothing
+should be sent back."
+  ;; TODO: Handle multiple simultaneous clients.
+  (listen server-socket 1)
+  (let loop ()
+    (serve-client (accept-new-client server-socket) handler)
+    (loop)))
-- 
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