websockets: Initial HyBi support

libvncserver/rfbserver.c

@@ -365,8 +365,6 @@ rfbNewTCPOrUDPClient(rfbScreenInfoPtr rfbScreen,
 #ifdef LIBVNCSERVER_WITH_WEBSOCKETS
       cl->webSockets       = FALSE;
       cl->webSocketsBase64 = FALSE;
-      cl->dblen= 0;
-      cl->carrylen = 0;
 #endif
 
 #if defined(LIBVNCSERVER_HAVE_LIBZ) || defined(LIBVNCSERVER_HAVE_LIBPNG)

libvncserver/sockets.c

@@ -647,11 +647,12 @@ rfbWriteExact(rfbClientPtr cl,
 
 #ifdef LIBVNCSERVER_WITH_WEBSOCKETS
     if (cl->webSockets) {
-        if ((len = webSocketsEncode(cl, buf, len)) < 0) {
+        char *tmp = NULL;
+        if ((len = webSocketsEncode(cl, buf, len, &tmp)) < 0) {
             rfbErr("WriteExact: WebSockets encode error\n");
             return -1;
         }
-        buf = cl->encodeBuf;
+        buf = tmp;
     }
 #endif
 

libvncserver/websockets.c

@@ -32,12 +32,90 @@
 #include <errno.h>
 
 #include <md5.h>
+#include <byteswap.h>
+#include "rfbconfig.h"
 #include "rfbssl.h"
 
+#if defined(__BYTE_ORDER) && defined(__BIG_ENDIAN) && __BYTE_ORDER == __BIG_ENDIAN
+#define WS_NTOH64(n) (n)
+#define WS_NTOH32(n) (n)
+#define WS_NTOH16(n) (n)
+#define WS_HTON64(n) (n)
+#define WS_HTON16(n) (n)
+#else
+#define WS_NTOH64(n) bswap_64(n)
+#define WS_NTOH32(n) bswap_32(n)
+#define WS_NTOH16(n) bswap_16(n)
+#define WS_HTON64(n) bswap_64(n)
+#define WS_HTON16(n) bswap_16(n)
+#endif
+
+#define B64LEN(__x) (((__x + 2) / 3) * 12 / 3)
+#define WSHLENMAX 14  /* 2 + sizeof(uint64_t) + sizeof(uint32_t) */
+
+enum {
+  WEBSOCKETS_VERSION_HIXIE,
+  WEBSOCKETS_VERSION_HYBI
+};
+
+#include <sys/syscall.h>
+static int gettid() {
+    return (int)syscall(SYS_gettid);
+}
+
+typedef struct ws_ctx_s {
+    char encodeBuf[B64LEN(UPDATE_BUF_SIZE) + WSHLENMAX]; /* base64 + maximum frame header length */
+    char decodeBuf[8192];                  /* TODO: what makes sense? */
+    char readbuf[8192];
+    int readbufstart;
+    int readbuflen;
+    int dblen;
+    char carryBuf[3];                      /* For base64 carry-over */
+    int carrylen;
+    int version;
+} ws_ctx_t;
+
+typedef union ws_mask_s {
+  char c[4];
+  uint32_t u;
+} ws_mask_t;
+
+typedef struct __attribute__ ((__packed__)) ws_header_s {
+  unsigned char b0;
+  unsigned char b1;
+  union {
+    struct __attribute__ ((__packed__)) {
+      uint16_t l16;
+      ws_mask_t m16;
+    };
+    struct __attribute__ ((__packed__)) {
+      uint64_t l64;
+      ws_mask_t m64;
+    };
+    ws_mask_t m;
+  };
+} ws_header_t;
+
+enum
+{
+    WS_OPCODE_CONTINUATION = 0x0,
+    WS_OPCODE_TEXT_FRAME,
+    WS_OPCODE_BINARY_FRAME,
+    WS_OPCODE_CLOSE = 0x8,
+    WS_OPCODE_PING,
+    WS_OPCODE_PONG
+};
+
 #define FLASH_POLICY_RESPONSE "<cross-domain-policy><allow-access-from domain=\"*\" to-ports=\"*\" /></cross-domain-policy>\n"
 #define SZ_FLASH_POLICY_RESPONSE 93
 
-#define WEBSOCKETS_HANDSHAKE_RESPONSE "HTTP/1.1 101 Web Socket Protocol Handshake\r\n\
+/*
+ * draft-ietf-hybi-thewebsocketprotocol-10
+ * 5.2.2. Sending the Server's Opening Handshake
+ */
+#define GUID "258EAFA5-E914-47DA-95CA-C5AB0DC85B11"
+
+#define SERVER_HANDSHAKE_HIXIE "HTTP/1.1 101 Web Socket Protocol Handshake\r\n\
 Upgrade: WebSocket\r\n\
 Connection: Upgrade\r\n\
 %sWebSocket-Origin: %s\r\n\
@@ -45,6 +123,14 @@ Connection: Upgrade\r\n\
 %sWebSocket-Protocol: %s\r\n\
 \r\n%s"
 
+#define SERVER_HANDSHAKE_HYBI "HTTP/1.1 101 Switching Protocols\r\n\
+Upgrade: websocket\r\n\
+Connection: Upgrade\r\n\
+Sec-WebSocket-Accept: %s\r\n\
+Sec-WebSocket-Protocol: %s\r\n\
+\r\n"
+
+
 #define WEBSOCKETS_CLIENT_CONNECT_WAIT_MS 100
 #define WEBSOCKETS_CLIENT_SEND_WAIT_MS 100
 #define WEBSOCKETS_MAX_HANDSHAKE_LEN 4096
@@ -65,6 +151,24 @@ min (int a, int b) {
     return a < b ? a : b;
 }
 
+#ifdef LIBVNCSERVER_WITH_CLIENT_GCRYPT
+#else
+#include <openssl/sha.h>
+
+static void webSocketsGenSha1Key(char *target, int size, char *key)
+{
+    SHA_CTX c;
+    unsigned char tmp[SHA_DIGEST_LENGTH];
+
+    SHA1_Init(&c);
+    SHA1_Update(&c, key, strlen(key));
+    SHA1_Update(&c, GUID, sizeof(GUID) - 1);
+    SHA1_Final(tmp, &c);
+    if (-1 == __b64_ntop(tmp, SHA_DIGEST_LENGTH, target, size))
+	rfbErr("b64_ntop failed\n");
+}
+#endif
+
 /*
  * rfbWebSocketsHandshake is called to handle new WebSockets connections
  */
@@ -126,6 +230,9 @@ webSocketsHandshake(rfbClientPtr cl, char *scheme)
     char prefix[5], trailer[17];
     char *path = NULL, *host = NULL, *origin = NULL, *protocol = NULL;
     char *key1 = NULL, *key2 = NULL, *key3 = NULL;
+    char *sec_ws_origin = NULL;
+    char *sec_ws_key = NULL;
+    char sec_ws_version = 0;
 
     buf = (char *) malloc(WEBSOCKETS_MAX_HANDSHAKE_LEN);
     if (!buf) {
@@ -198,16 +305,28 @@ webSocketsHandshake(rfbClientPtr cl, char *scheme)
                 key2 = line+20;
                 buf[len-2] = '\0';
                 /* rfbLog("Got key2: %s\n", key2); */
-            } else if ((strncasecmp("sec-websocket-protocol: ", line, min(llen,24))) == 0) {
+            /* HyBI */
+
+	    } else if ((strncasecmp("sec-websocket-protocol: ", line, min(llen,24))) == 0) {
                 protocol = line+24;
                 buf[len-2] = '\0';
-                /* rfbLog("Got protocol: %s\n", protocol); */
-            }
+                rfbLog("Got protocol: %s\n", protocol);
+            } else if ((strncasecmp("sec-websocket-origin: ", line, min(llen,22))) == 0) {
+		sec_ws_origin = line+22;
+                buf[len-2] = '\0';
+            } else if ((strncasecmp("sec-websocket-key: ", line, min(llen,19))) == 0) {
+		sec_ws_key = line+19;
+                buf[len-2] = '\0';
+            } else if ((strncasecmp("sec-websocket-version: ", line, min(llen,23))) == 0) {
+		sec_ws_version = strtol(line+23, NULL, 10);
+                buf[len-2] = '\0';
+	    }
+
             linestart = len;
         }
     }
 
-    if (!(path && host && origin)) {
+    if (!(path && host && (origin || sec_ws_origin))) {
         rfbErr("webSocketsHandshake: incomplete client handshake\n");
         free(response);
         free(buf);
@@ -228,27 +347,40 @@ webSocketsHandshake(rfbClientPtr cl, char *scheme)
      * by the client.
      */
 
-    if (!(key1 && key2 && key3)) {
-        rfbLog("  - WebSockets client version 75\n");
-        prefix[0] = '\0';
-        trailer[0] = '\0';
+    if (sec_ws_version) {
+	char accept[SHA_DIGEST_LENGTH * 3];
+	rfbLog("  - WebSockets client version hybi-%02d\n", sec_ws_version);
+	webSocketsGenSha1Key(accept, sizeof(accept), sec_ws_key);
+	len = snprintf(response, WEBSOCKETS_MAX_HANDSHAKE_LEN,
+		 SERVER_HANDSHAKE_HYBI, accept, protocol);
     } else {
-        rfbLog("  - WebSockets client version 76\n");
-        snprintf(prefix, 5, "Sec-");
-        webSocketsGenMd5(trailer, key1, key2, key3);
+	/* older hixie handshake, this could be removed if
+	 * a final standard is established */
+	if (!(key1 && key2 && key3)) {
+	    rfbLog("  - WebSockets client version hixie-75\n");
+	    prefix[0] = '\0';
+	    trailer[0] = '\0';
+	} else {
+	    rfbLog("  - WebSockets client version hixie-76\n");
+	    snprintf(prefix, 5, "Sec-");
+	    webSocketsGenMd5(trailer, key1, key2, key3);
+	}
+	len = snprintf(response, WEBSOCKETS_MAX_HANDSHAKE_LEN,
+		 SERVER_HANDSHAKE_HIXIE, prefix, origin, prefix, scheme,
+		 host, path, prefix, protocol, trailer);
     }
 
-    snprintf(response, WEBSOCKETS_MAX_HANDSHAKE_LEN,
-             WEBSOCKETS_HANDSHAKE_RESPONSE, prefix, origin, prefix, scheme,
-             host, path, prefix, protocol, trailer);
-
-    if (rfbWriteExact(cl, response, strlen(response)) < 0) {
+    if (rfbWriteExact(cl, response, len) < 0) {
         rfbErr("webSocketsHandshake: failed sending WebSockets response\n");
         free(response);
         free(buf);
         return FALSE;
     }
-    /* rfbLog("webSocketsHandshake: handshake complete\n"); */
+    rfbLog("webSocketsHandshake: %s\n", response);
+    free(response);
+    free(buf);
+    cl->wsctx = (wsCtx *)calloc(1, sizeof(ws_ctx_t));
+    ((ws_ctx_t *)cl->wsctx)->version = sec_ws_version ? WEBSOCKETS_VERSION_HYBI : WEBSOCKETS_VERSION_HIXIE;
     return TRUE;
 }
 
@@ -299,13 +431,15 @@ webSocketsGenMd5(char * target, char *key1, char *key2, char *key3)
 }
 
 int
-webSocketsEncode(rfbClientPtr cl, const char *src, int len)
+webSocketsEncodeHixie(rfbClientPtr cl, const char *src, int len, char **dst)
 {
     int i, sz = 0;
     unsigned char chr;
-    cl->encodeBuf[sz++] = '\x00';
+    ws_ctx_t *wsctx = (ws_ctx_t *)cl->wsctx;
+
+    wsctx->encodeBuf[sz++] = '\x00';
     if (cl->webSocketsBase64) {
-        len = __b64_ntop((unsigned char *)src, len, cl->encodeBuf+sz, UPDATE_BUF_SIZE*2);
+        len = __b64_ntop((unsigned char *)src, len, wsctx->encodeBuf+sz, sizeof(wsctx->encodeBuf) - (sz + 1));
         if (len < 0) {
             return len;
         }
@@ -315,24 +449,24 @@ webSocketsEncode(rfbClientPtr cl, const char *src, int len)
             chr = src[i];
             if (chr < 128) {
                 if (chr == 0x00) {
-                    cl->encodeBuf[sz++] = '\xc4';
-                    cl->encodeBuf[sz++] = '\x80';
+                    wsctx->encodeBuf[sz++] = '\xc4';
+                    wsctx->encodeBuf[sz++] = '\x80';
                 } else {
-                    cl->encodeBuf[sz++] = chr;
+                    wsctx->encodeBuf[sz++] = chr;
                 }
             } else {
                 if (chr < 192) {
-                    cl->encodeBuf[sz++] = '\xc2';
-                    cl->encodeBuf[sz++] = chr;
+                    wsctx->encodeBuf[sz++] = '\xc2';
+                    wsctx->encodeBuf[sz++] = chr;
                 } else {
-                    cl->encodeBuf[sz++] = '\xc3';
-                    cl->encodeBuf[sz++] = chr - 64;
+                    wsctx->encodeBuf[sz++] = '\xc3';
+                    wsctx->encodeBuf[sz++] = chr - 64;
                 }
             }
         }
     }
-    cl->encodeBuf[sz++] = '\xff';
-    /* rfbLog("<< webSocketsEncode: %d\n", len); */
+    wsctx->encodeBuf[sz++] = '\xff';
+    *dst = wsctx->encodeBuf;
     return sz;
 }
 
@@ -361,18 +495,19 @@ ws_peek(rfbClientPtr cl, char *buf, int len)
 }
 
 int
-webSocketsDecode(rfbClientPtr cl, char *dst, int len)
+webSocketsDecodeHixie(rfbClientPtr cl, char *dst, int len)
 {
     int retlen = 0, n, i, avail, modlen, needlen, actual;
     char *buf, *end = NULL;
     unsigned char chr, chr2;
+    ws_ctx_t *wsctx = (ws_ctx_t *)cl->wsctx;
 
-    buf = cl->decodeBuf;
+    buf = wsctx->decodeBuf;
 
     n = ws_peek(cl, buf, len*2+2);
 
     if (n <= 0) {
-        rfbErr("%s: recv of %d\n", __func__, n);
+        rfbErr("%s: peek of %d\n", __func__, n);
         return n;
     }
 
@@ -406,7 +541,7 @@ webSocketsDecode(rfbClientPtr cl, char *dst, int len)
         }
         avail = end - buf;
 
-        len -= cl->carrylen;
+        len -= wsctx->carrylen;
 
         /* Determine how much base64 data we need */
         modlen = len + (len+2)/3;
@@ -422,9 +557,9 @@ webSocketsDecode(rfbClientPtr cl, char *dst, int len)
         }
 
         /* Any carryover from previous decode */
-        for (i=0; i < cl->carrylen; i++) {
-	    /* rfbLog("Adding carryover %d\n", cl->carryBuf[i]); */
-            dst[i] = cl->carryBuf[i];
+        for (i=0; i < wsctx->carrylen; i++) {
+	    /* rfbLog("Adding carryover %d\n", wsctx->carryBuf[i]); */
+            dst[i] = wsctx->carryBuf[i];
             retlen += 1;
         }
 
@@ -442,11 +577,11 @@ webSocketsDecode(rfbClientPtr cl, char *dst, int len)
         /* Consume the data from socket */
         i = ws_read(cl, buf, needlen);
 
-        cl->carrylen = n - len;
-        retlen -= cl->carrylen;
-        for (i=0; i < cl->carrylen; i++) {
+        wsctx->carrylen = n - len;
+        retlen -= wsctx->carrylen;
+        for (i=0; i < wsctx->carrylen; i++) {
             /* rfbLog("Saving carryover %d\n", dst[retlen + i]); */
-            cl->carryBuf[i] = dst[retlen + i];
+            wsctx->carryBuf[i] = dst[retlen + i];
         }
     } else {
         /* UTF-8 encoded WebSockets stream */
@@ -509,3 +644,216 @@ webSocketsDecode(rfbClientPtr cl, char *dst, int len)
     /* rfbLog("<< webSocketsDecode, retlen: %d\n", retlen); */
     return retlen;
 }
+
+int
+webSocketsDecodeHybi(rfbClientPtr cl, char *dst, int len)
+{
+    char *buf, *payload, *rbuf;
+    int ret = -1, result = -1;
+    int total = 0;
+    ws_mask_t mask;
+    ws_header_t *header;
+    int i, j;
+    unsigned char opcode;
+    ws_ctx_t *wsctx = (ws_ctx_t *)cl->wsctx;
+    int flength, fin, fhlen, blen;
+
+    // rfbLog(" <== %s[%d]: %d cl: %p, wsctx: %p-%p (%d)\n", __func__, gettid(), len, cl, wsctx, (char *)wsctx + sizeof(ws_ctx_t), sizeof(ws_ctx_t));
+
+    if (wsctx->readbuflen) {
+      /* simply return what we have */
+      if (wsctx->readbuflen > len) {
+	memcpy(dst, wsctx->readbuf +  wsctx->readbufstart, len);
+	result = len;
+	wsctx->readbuflen -= len;
+	wsctx->readbufstart += len;
+      } else {
+	memcpy(dst, wsctx->readbuf +  wsctx->readbufstart, wsctx->readbuflen);
+	result = wsctx->readbuflen;
+	wsctx->readbuflen = 0;
+	wsctx->readbufstart = 0;
+      }
+      goto spor;
+    }
+
+    buf = wsctx->decodeBuf;
+    header = (ws_header_t *)wsctx->decodeBuf;
+
+    if (-1 == (ret = ws_peek(cl, buf, B64LEN(len) + WSHLENMAX))) {
+      rfbErr("%s: peek; %m\n", __func__);
+      goto spor;
+    }
+
+    if (ret < 2) {
+	rfbErr("%s: peek; got %d bytes\n", __func__, ret);
+	goto spor; /* Incomplete frame header */
+    }
+
+    opcode = header->b0 & 0x0f;
+    fin = (header->b0 & 0x80) >> 7;
+    flength = header->b1 & 0x7f;
+
+    /*
+     * 4.3. Client-to-Server Masking
+     *
+     * The client MUST mask all frames sent to the server.  A server MUST
+     * close the connection upon receiving a frame with the MASK bit set to 0.
+    **/
+    if (!(header->b1 & 0x80)) {
+	rfbErr("%s: got frame without mask\n", __func__, ret);
+	errno = EIO;
+	goto spor;
+    }
+
+    if (flength < 126) {
+	fhlen = 2;
+	mask = header->m;
+    } else if (flength == 126 && 4 <= ret) {
+	flength = WS_NTOH16(header->l16);
+	fhlen = 4;
+	mask = header->m16;
+    } else if (flength == 127 && 10 <= ret) {
+	flength = WS_NTOH64(header->l64);
+	fhlen = 10;
+	mask = header->m64;
+    } else {
+      /* Incomplete frame header */
+      rfbErr("%s: incomplete frame header\n", __func__, ret);
+      errno = EIO;
+      goto spor;
+    }
+
+    /* absolute length of frame */
+    total = fhlen + flength + 4;
+    payload = buf + fhlen + 4; /* header length + mask */
+
+    if (-1 == (ret = ws_read(cl, buf, total))) {
+      rfbErr("%s: read; %m", __func__);
+      return ret;
+    } else if (ret < total) {
+      /* TODO: hmm? */
+      rfbLog("%s: read; got partial data\n", __func__);
+    } else {
+      buf[ret] = '\0';
+    }
+
+    /* process 1 frame */
+    for (i = 0; i < flength; i++) {
+	j = i % 4;
+	payload[i] ^= mask.c[j];
+    }
+
+    switch (opcode) {
+      case WS_OPCODE_CLOSE:
+	rfbLog("got closure, reason %d\n", WS_NTOH16(((uint16_t *)payload)[0]));
+	errno = ECONNRESET;
+	break;
+      case WS_OPCODE_TEXT_FRAME:
+	if (-1 == (flength = __b64_pton(payload, (unsigned char *)wsctx->decodeBuf, sizeof(wsctx->decodeBuf)))) {
+	  rfbErr("%s: Base64 decode error; %m\n", __func__);
+	  break;
+	}
+	payload = wsctx->decodeBuf;
+	/* fall through */
+      case WS_OPCODE_BINARY_FRAME:
+	if (flength > len) {
+	  memcpy(wsctx->readbuf, payload + len, flength - len);
+	  wsctx->readbufstart = 0;
+	  wsctx->readbuflen = flength - len;
+	  flength = len;
+	}
+	memcpy(dst, payload, flength);
+	result = flength;
+	break;
+      default:
+	rfbErr("unhandled opcode %d, b0: %02x, b1: %02x\n", (int)opcode, header->b0, header->b1);
+    }
+
+    /* single point of return, if someone has questions :-) */
+spor:
+    /* rfbLog("%s: ret: %d/%d\n", __func__, result, len); */
+    return result;
+}
+
+int
+webSocketsEncodeHybi(rfbClientPtr cl, const char *src, int len, char **dst)
+{
+    int blen, ret = -1, sz = 0;
+    unsigned char opcode = '\0'; /* TODO: option! */
+    ws_header_t *header;
+    ws_ctx_t *wsctx = (ws_ctx_t *)cl->wsctx;
+
+
+    /* Optional opcode:
+     *   0x0 - continuation
+     *   0x1 - text frame (base64 encode buf)
+     *   0x2 - binary frame (use raw buf)
+     *   0x8 - connection close
+     *   0x9 - ping
+     *   0xA - pong
+    **/
+    if (!len) {
+	  rfbLog("%s: nothing to encode\n", __func__);
+	  return 0;
+    }
+
+    header = (ws_header_t *)wsctx->encodeBuf;
+
+    if (cl->webSocketsBase64) {
+	opcode = WS_OPCODE_TEXT_FRAME;
+	/* calculate the resulting size */
+	blen = B64LEN(len);
+    } else {
+	blen = len;
+    }
+
+    header->b0 = 0x80 | (opcode & 0x0f);
+    if (blen <= 125) {
+      header->b1 = (uint8_t)blen;
+      sz = 2;
+    } else if (blen <= 65536) {
+      header->b1 = 0x7e;
+      header->l16 = WS_HTON16((uint16_t)blen);
+      sz = 4;
+    } else {
+      header->b1 = 0x7f;
+      header->l64 = WS_HTON64(blen);
+      sz = 10;
+    }
+
+    if (cl->webSocketsBase64) {
+        if (-1 == (ret = __b64_ntop((unsigned char *)src, len, wsctx->encodeBuf + sz, sizeof(wsctx->encodeBuf) - sz))) {
+	  rfbErr("%s: Base 64 encode failed\n", __func__);
+	} else {
+	  if (ret != blen)
+	    rfbErr("%s: Base 64 encode; something weird happened\n", __func__);
+	  ret += sz;
+	}
+    } else {
+      memcpy(wsctx->encodeBuf + sz, src, len);
+      ret =  sz + len;
+    }
+
+    *dst = wsctx->encodeBuf;
+    return ret;
+}
+
+int
+webSocketsEncode(rfbClientPtr cl, const char *src, int len, char **dst)
+{
+    ws_ctx_t *wsctx = (ws_ctx_t *)cl->wsctx;
+    if (wsctx->version == WEBSOCKETS_VERSION_HIXIE)
+	return webSocketsEncodeHixie(cl, src, len, dst);
+    else
+	return webSocketsEncodeHybi(cl, src, len, dst);
+}
+
+int
+webSocketsDecode(rfbClientPtr cl, char *dst, int len)
+{
+    ws_ctx_t *wsctx = (ws_ctx_t *)cl->wsctx;
+    if (wsctx->version == WEBSOCKETS_VERSION_HIXIE)
+	return webSocketsDecodeHixie(cl, dst, len);
+    else
+	return webSocketsDecodeHybi(cl, dst, len);
+}

rfb/rfb.h

@@ -419,6 +419,7 @@ typedef struct _rfbStatList {
 } rfbStatList;
 
 typedef struct _rfbSslCtx rfbSslCtx;
+typedef struct _wsCtx wsCtx;
 
 typedef struct _rfbClientRec {
 
@@ -640,17 +641,10 @@ typedef struct _rfbClientRec {
 
 #ifdef LIBVNCSERVER_WITH_WEBSOCKETS
     rfbBool webSockets;
-    rfbBool webSocketsSSL;
     rfbBool webSocketsBase64;
-
     rfbSslCtx *sslctx;
-
+    wsCtx     *wsctx;
     char *wspath;                          /* Requests path component */
-    char encodeBuf[UPDATE_BUF_SIZE*2 + 2]; /* UTF-8 could double it + framing */
-    char decodeBuf[8192];                  /* TODO: what makes sense? */
-    int dblen;
-    char carryBuf[3];                      /* For base64 carry-over */
-    int carrylen;
 #endif
 } rfbClientRec, *rfbClientPtr;
 
@@ -718,7 +712,7 @@ extern rfbBool rfbSetNonBlocking(int sock);
 /* websockets.c */
 
 extern rfbBool webSocketsCheck(rfbClientPtr cl);
-extern int webSocketsEncode(rfbClientPtr cl, const char *src, int len);
+extern int webSocketsEncode(rfbClientPtr cl, const char *src, int len, char **dst);
 extern int webSocketsDecode(rfbClientPtr cl, char *dst, int len);
 #endif