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fuss:metaverse_viewer [2022/09/22 06:43] – [Hide the User Interface] officefuss:metaverse_viewer [2022/09/22 18:17] – [Solving the Local Typing Issue with Viewer AOs] office
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 If everything was done correctly, then the UI to configure the viewer AO should reflect the change and the ''Default Typing'' drop down box should be blank. Now, when typing on local chat, the avatar should not animate anymore. If everything was done correctly, then the UI to configure the viewer AO should reflect the change and the ''Default Typing'' drop down box should be blank. Now, when typing on local chat, the avatar should not animate anymore.
 +
 +====== Reverse-Engineering the Script Message API ======
 +
 +Amongst many other debug settings (following the menu items ''Advanced->Debug settings...'') there are two settings, namely:
 +
 +  * ''ScriptMessageAPI'', and
 +  * ''ScriptMessageAPIKey''
 +
 +{{fuss:fuss_metaverse_viewer_script_message_api_debug_settings.png}}
 +
 +for which there is no documentation to be found.
 +
 +In brief, these settings can be traced down to some code within the viewer meant to emit messages on a chosen channel number whenever certain events occur. 
 +
 +The ''ScriptMessageAPI'' setting allows the user to define a channel number where the messages will be received and ''ScriptMessageAPIKey'' is an encryption key used to encrypt the message being sent. The "encryption" is really a character-by-character XOR between the message generated by the viewer and the key provided by the ''ScriptMessageAPIKey'' that is linearly shifted to the length of the message. In order words, the final message that will be sent to the channel defined by the ''ScriptMessageAPI'' could be expressed as follows.
 +
 +Given a key $k$ of any arbitrary length $\gt 0$, and a message $M$ containing characters $m_{i..n}$ then the encrypted message $E$ will consists of corresponding characters $e_{i..n}$ where each character $e_{i}$ can be computed as:
 +\begin{eqnarray*}
 +e_{i} &=& m_{i} \oplus k[i_{c} \% length(k)]
 +\end{eqnarray*}
 +The encrypted message $E$ is then converted to Base64 and sent on the channel specified by the ''ScriptMessageAPI'' debug setting.
 +
 +The code responsible for encrypting the message can be found in the source inside the file ''llimprocessing.cpp'' in Snowglobe-based viewers defined within the ''script_msg_api'' function:
 +
 +<code cpp>
 +void script_msg_api(const std::string& msg)
 +{
 +        static const LLCachedControl<S32> channel("ScriptMessageAPI");
 +        if (!channel) return;
 +        static const LLCachedControl<std::string> key("ScriptMessageAPIKey");
 +        std::string str;
 +        for (size_t i = 0, keysize = key().size(); i != msg.size(); ++i)
 +                str += msg[i] ^ key()[i%keysize];
 +        send_chat_from_viewer(LLBase64::encode(reinterpret_cast<const U8*>(str.c_str()), str.size()), CHAT_TYPE_WHISPER, channel);
 +}
 +</code>
 +
 +The actual messages being sent by the viewer have the following format:
 +<code bash>
 +UUID + ", " + n
 +</code>
 +where:
 +  * UUID is the key of the avatar generating the message,
 +  * ''n'' is a single digit number corresponding to the event type.
 +
 +The single digit number ''n'' corresponds to certain events that are spread out through ''llimprocessing.cpp'' and some in ''llviewermessage.cpp''.
 +
 +^ n ^ Event ^ Example Message ^
 +| 0 | instant message | ''bcb678be-cddc-a470-8fd7-845fefb4a853, 0'' |
 +| 1 | inventory item offered | ''f0e9f375-e2de-9853-4a0b-ebb8a0e9da54, 1'' |
 +| 2 | teleport lure received | ''67a469f5-0692-4524-92d9-f3c340af6ba9, 2'' |
 +| 3 | teleport lure sent | ''91b45476-d316-4755-b667-9819441e13e6, 3'' |
 +| 4 | start typing | ''ea7f05b7-aaf1-4e7c-ae08-d96f9af131d5, 4'' |
 +| 5 | stop typing | ''62ef45a0-4642-4b9a-ac2b-46a2fb5e79ca, 5'' |
 +| 6 | message from object | ''9da01e7f-c82b-4ca1-b7dd-345afc473ff7, 6'' |
 +| 7 | group message | ''52bd6c1e-9b04-419c-be5a-f39ce898e9ee, 7'' |
 +
 +Obtaining the plaintext message from the viewer can be done in LSL. Unfortunately, a well-chosen key is an easy choice to work around the limitations of ''llBase64ToString''; namely, ''llBase64ToString'' will display a placeholder (''?'') for all non-printable characters meaning that performing a XOR between two values that would yield an unprintable character cannot be converted back using ''llBase64ToString''. As a workaround, and knowing that all the messages sent by the "Script Message API" have a character set restricted to ''[0-9a-f]'', then the key to be chosen could consist of only upper-case characters (''[A-Z]'') in order to avoid that the XOR operation produces unprintable characters.
 +
 +{{fuss:fuss_metaverse_viewer_script_message_api_decrypting_the_messages.png}}
 +
 +The following script is more or less a verbatim translation of the algorithm implemented in ''llimprocessing.cpp'' using ''Ord'' and ''Chr'' by Pedro Oval for elegance:
 +<code lsl2>
 +///////////////////////////////////////////////////////////////////////////
 +//  Copyright (C) Wizardry and Steamworks 2022 - License: GNU GPLv3      //
 +///////////////////////////////////////////////////////////////////////////
 +
 +// Chr() function, written by Pedro Oval, 2010-05-28
 +// Auxiliary function UrlCode, which returns the hex code of the given integer
 +// (which must be in range 0-255) with a "%" prepended.
 +string UrlCode(integer b)
 +{
 +    string hexd = "0123456789ABCDEF";
 +    return "%" + llGetSubString(hexd, b>>4, b>>4)
 +               + llGetSubString(hexd, b&15, b&15);
 +}
 +
 +// Chr function itself, which implements Unicode to UTF-8 conversion and uses
 +// llUnescapeURL to do its job.
 +string Chr(integer ord)
 +{
 +    if (ord <= 0)
 +        return "";
 +    if (ord < 0x80)
 +        return llUnescapeURL(UrlCode(ord));
 +    if (ord < 0x800)
 +        return llUnescapeURL(UrlCode((ord >> 6) | 0xC0)
 +                            +UrlCode(ord & 0x3F | 0x80));
 +    if (ord < 0x10000)
 +        return llUnescapeURL(UrlCode((ord >> 12) | 0xE0)
 +                            +UrlCode((ord >> 6) & 0x3F | 0x80)
 +                            +UrlCode(ord & 0x3F | 0x80));
 +    return llUnescapeURL(UrlCode((ord >> 18) | 0xF0)
 +                        +UrlCode((ord >> 12) & 0x3F | 0x80)
 +                        +UrlCode((ord >> 6) & 0x3F | 0x80)
 +                        +UrlCode(ord & 0x3F | 0x80));
 +}
 +
 +// Ord() function, written by Pedro Oval, 2010-05-28
 +// This function works by using llEscapeURL to find the corresponding UTF-8
 +// string then converts it to the Unicode code. In cases where llEscapeURL
 +// doesn't help, a combination of llStringToBase64 and llBase64ToInteger
 +// does the job instead.
 +integer Ord(string chr)
 +{
 +    if (chr == "")
 +        return 0;
 +    chr = llGetSubString(chr, 0, 0);
 +    string hex = llEscapeURL(chr);
 +    if (llGetSubString(hex, 0, 0) != "%")
 +    {
 +        // Regular character - we can't take advantage of llEscapeURL in this case,
 +        // so we use llStringToBase64/llBase64ToInteger instead.
 +        return llBase64ToInteger("AAAA" + llStringToBase64(chr));
 +    }
 +    integer b = (integer)("0x" + llGetSubString(hex, 1, 2));
 +    if (b < 194 || b > 244)
 +        return b;
 +    if (b < 224)
 +        return ((b & 0x1F) << 6) | (integer)("0x" + llGetSubString(hex, 4, 5)) & 0x3F;
 +    integer cp;
 +    if (b < 240)
 +    {
 +        cp = (b & 0x0F) << 12;
 +        cp += ((integer)("0x" + llGetSubString(hex, 4, 5)) & 0x3F) << 6;
 +        cp += (integer)("0x" + llGetSubString(hex, 7, 8)) & 0x3F;
 +        return cp;
 +    }
 +    cp = (b & 0x07) << 18;
 +    cp += ((integer)("0x" + llGetSubString(hex, 4, 5)) & 0x3F) << 12;
 +    cp += ((integer)("0x" + llGetSubString(hex, 7, 8)) & 0x3F) << 6;
 +    cp += (integer)("0x" + llGetSubString(hex, 10, 11)) & 0x3F;
 +    return cp;
 +}
 +
 +default
 +{
 +    state_entry() {
 +        // Listen on the channel number specified by the ScriptMessageAPI debug setting.
 +        llListen(1, "", "", "");
 +    }
 +
 +    listen(integer channel, string name, key id, string message) {
 +        // Define the encryption key specified by the ScriptMessageAPIKey debug setting.
 +        string enc = "ABRACADABRA";
 +        
 +        // Dump all listen() parameters.
 +        llOwnerSay("CHANNEL: " + (string)channel);
 +        llOwnerSay("NAME: " + name);
 +        llOwnerSay("KEY: " + (string)id);
 +        
 +        // Convert the message from Base64 to its string equivalent.
 +        message = llBase64ToString(message);
 +        
 +        // Reproduce the algorith verbatim as defined by the viewer in the script_msg_api() 
 +        // function within the llimprocessing.cpp file.
 +        string output = "";
 +        integer i;
 +        integer size;
 +        for(i = 0, size = llStringLength(enc); i != llStringLength(message); ++i) {
 +            output += Chr(Ord(llGetSubString(message, i, i)) ^ Ord(llGetSubString(enc, i % size, i % size)));
 +        }
 +        
 +        // Print out the converted message.
 +        llOwnerSay("MESSAGE: " + output);
 +    }
 +}
 +</code>
 +
 +
 +
 +
 +
 +
 +
fuss/metaverse_viewer.txt · Last modified: 2023/05/27 07:37 by office
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