Guacamole 源码分析与 VNC 中 RFB 协议的坑

# 装依赖
sudo apt-get install libpng12-dev libjpeg-dev libcairo2-dev libossp-uuid-dev libpulse-dev libvncserver-dev libcairo2-dev freerdp-x11 libfreerdp-dev libvorbis-dev libssh-dev libpulse-dev tomcat7 tomcat7-admin libpango1.0-dev autoconf libossp-uuid-dev libtelnet-dev libvncserver-dev build-essential default-jre default-jdk  maven vnc4server

# 然后去官网把源码下下来, 进到 /src 内:
./configure
./configure --with-init-dir=/etc/init.d
sudo make
sudo make install
sudo ldconfig

sudo mkdir -p /var/lib/guacamole/classpath
sudo wget -q --span-hosts http://sourceforge.net/projects/guacamole/files/current/binary/guacamole-0.9.9.war -P /var/lib/guacamole
cd /var/lib/tomcat7/webapps
sudo rm -rf ROOT
sudo ln -s /var/lib/guacamole/guacamole-0.9.9.war ./ROOT.war
sudo mkdir /etc/guacamole
sudo ln -s /etc/guacamole /usr/share/tomcat7/.guacamole
sudo vim /etc/guacamole/guacamole.properties

## 配置内容如下
#tname and port of guacamole proxy
guacd-hostname: 127.0.0.1
guacd-port:     4822
enable-websocket: true

# Authentication provider class
# auth-provider: net.sourceforge.guacamole.net.basic.BasicFileAuthenticationProvider
lib-drectory: /var/lib/guacamole/classpath
auth-provider: com.stephensugden.guacamole.net.hmac.HmacAuthenticationProvider
secret-key: for-test
timestamp-age-limit: 42000000

sudo /etc/init.d/guacd start
sudo /etc/init.d/tomcat7 start
vnc4server :1

/**
 * Sets the clipboard of the remote client to the given text data.
 *
 * @deprecated Use createClipboardStream() instead. 
 * @param {String} data The data to send as the clipboard contents.
 */
this.setClipboard = function(data) {
    // Do not send requests if not connected
    if (!isConnected())
        return;
    // Open stream
    var stream = guac_client.createClipboardStream("text/plain");
    var writer = new Guacamole.StringWriter(stream);
    // Send text chunks
    for (var i=0; i<data.length; i += 4096)
        writer.sendText(data.substring(i, i+4096));
    // Close stream
    writer.sendEnd();
};

/**
 * Sends the given text.
 * 
 * @param {String} text The text to send.
 */
this.sendText = function(text) {
    if (text.length)
        array_writer.sendData(__encode_utf8(text));
};

// Guacamole Client 字符转码

var buffer = new Uint8Array(8192);
var length = 0;

function __expand(bytes) {

    // Resize buffer if more space needed
    if (length+bytes >= buffer.length) {
        var new_buffer = new Uint8Array((length+bytes)*2);
        new_buffer.set(buffer);
        buffer = new_buffer;
    }

    length += bytes;

}

function __append_utf8(codepoint) {

    var mask;
    var bytes;

    // 1 byte
    if (codepoint <= 0x7F) {
        mask = 0x00;
        bytes = 1;
    }
    // 2 byte
    else if (codepoint <= 0x7FF) {
        mask = 0xC0;
        bytes = 2;
    }
    // 3 byte
    else if (codepoint <= 0xFFFF) {
        mask = 0xE0;
        bytes = 3;
    }
    // 4 byte
    else if (codepoint <= 0x1FFFFF) {
        mask = 0xF0;
        bytes = 4;
    }
    // If invalid codepoint, append replacement character
    else {
        __append_utf8(0xFFFD);
        return;
    }
    // Offset buffer by size
    __expand(bytes);
    var offset = length - 1;
    // Add trailing bytes, if any
    for (var i=1; i<bytes; i++) {
        buffer[offset--] = 0x80 | (codepoint & 0x3F);
        codepoint >>= 6;
    }
    // Set initial byte
    buffer[offset] = mask | codepoint;
}

function __encode_utf8(text) {

    // Fill buffer with UTF-8
    // 使用 UTF-8 填充缓冲区
    for (var i=0; i<text.length; i++) {
        var codepoint = text.charCodeAt(i);
        __append_utf8(codepoint);
    }
    // Flush buffer
    if (length > 0) {
        var out_buffer = buffer.subarray(0, length);
        length = 0;
        return out_buffer;
    }

}

// 『你好』的 UTF-8 编码
// E4 BD A0
// 1110 0100 1011 1101 1010 0000
// E5 A5 BD
// 1110 0101 1010 0101 1011 1101
console.log(__encode_utf8("你好"));

#include "unicode.h"
int main() {
    // 这里保存了『你好』的 UTF-8 编码
    char str[] = {0xE4, 0xBD, 0xA0, 0xE5, 0xA5, 0xBD, 0};
    guac_utf8_write(str[0], str, 6);
    printf("%s", str);
}

void guac_common_clipboard_reset(guac_common_clipboard* clipboard, const char* mimetype) {
    clipboard->length = 0;
    strncpy(clipboard->mimetype, mimetype, sizeof(clipboard->mimetype)-1);
}

int guac_vnc_clipboard_handler(guac_user* user, guac_stream* stream,
        char* mimetype) {

    /* Clear clipboard and prepare for new data */
    guac_vnc_client* vnc_client = (guac_vnc_client*) user->client->data;
    // 设置剪切板的类型
    guac_common_clipboard_reset(vnc_client->clipboard, mimetype);

    // 设置剪切板内容的处理方法
    /* Set handlers for clipboard stream */
    stream->blob_handler = guac_vnc_clipboard_blob_handler;
    stream->end_handler = guac_vnc_clipboard_end_handler;

    return 0;
}
int guac_vnc_clipboard_blob_handler(guac_user* user, guac_stream* stream,
        void* data, int length) {

    // 将数据拼接到剪切板中
    /* Append new data */
    guac_vnc_client* vnc_client = (guac_vnc_client*) user->client->data;
    guac_common_clipboard_append(vnc_client->clipboard, (char*) data, length);

    return 0;
}
void guac_vnc_cut_text(rfbClient* client, const char* text, int textlen) {

    guac_client* gc = rfbClientGetClientData(client, GUAC_VNC_CLIENT_KEY);
    guac_vnc_client* vnc_client = (guac_vnc_client*) gc->data;

    char received_data[GUAC_VNC_CLIPBOARD_MAX_LENGTH];

    const char* input = text;
    char* output = received_data;
    guac_iconv_read* reader = vnc_client->clipboard_reader;

    /* Convert clipboard contents */
    guac_iconv(reader, &input, textlen,
               GUAC_WRITE_UTF8, &output, sizeof(received_data));

    // 在这里设置剪切板内容
    /* Send converted data */
    guac_common_clipboard_reset(vnc_client->clipboard, "text/plain");
    guac_common_clipboard_append(vnc_client->clipboard, received_data, output - received_data);
    guac_common_clipboard_send(vnc_client->clipboard, gc);

}

+--------------+--------------+--------------+
| No. of bytes | Type [Value] | Description  |
+--------------+--------------+--------------+
| 1            | U8 [6]       | message-type |
| 3            |              | padding      |
| 4            | U32          | length       |
| length       | U8 array     | text         |
+--------------+--------------+--------------+

```> **7.6.4.  ServerCutText**
>
> The server has new ISO 8859-1 (Latin-1) text in its cut buffer.  Ends of lines are represented by the newline character (hex 0a) alone.  No carriage-return (hex 0d) is used.  There is no way to transfer text outside the Latin-1 character set.

在这两个消息的设计中，所有的内容均按照 `text/plain` 的方式进行传输，彻底忽略了剪切板中的 `minetype`，最终导致了无法传输除了 `ISO 8859-1` 标准规定以外的字符。## 一些扩展的思考

VNC 是个烂协议，这么烂的协议居然活到了 2016 年，那么我们有什么办法可以解决它呢？要知道，guacamole 本身实现的服务端 `guacd` 就可以将其称之为 `guacamole` 协议了。从最开始的架构图就可以看到，`guacd`本身并不仅仅只和 VNC 打交道，它还支持 `RDP` 这种远比 `VNC` 复杂得多也好得多的协议。但是，为什么我们还是希望用 `VNC`？因为 `VNC` 支持会话共享，而这正是  `RDP` 所做不到的事情。理论上看，我们可以在 `guacd` 底层动刀，复制出一个数据流，从而间接的支持会话共享，当然，这都是后话了。

关于会话共享，我们以后有时间再研究，这里有一个 `issue`：

- [Screen sharing support within Guacamole core](https://glyptodon.org/jira/browse/GUAC-844)