From 6244511c38ffc4153bf1a0d32e75893ff8946d9a Mon Sep 17 00:00:00 2001
From: aikaterna <20862007+aikaterna@users.noreply.github.com>
Date: Mon, 12 Jul 2021 13:33:29 -0700
Subject: [PATCH] [TrackDecoder] Initial commit

---
 README.md                    |   2 +
 trackdecoder/__init__.py     |   5 ++
 trackdecoder/info.json       |   9 +++
 trackdecoder/trackdecoder.py | 106 +++++++++++++++++++++++++++++++++++
 4 files changed, 122 insertions(+)
 create mode 100644 trackdecoder/__init__.py
 create mode 100644 trackdecoder/info.json
 create mode 100644 trackdecoder/trackdecoder.py

diff --git a/README.md b/README.md
index e50f047..b31bf67 100644
--- a/README.md
+++ b/README.md
@@ -61,6 +61,8 @@ snacktime - A v3 port of irdumb's snacktime cog. Now with friends!
 
 timezone - A v3 port of Fishyfing's timezone cog with a few improvements.
 
+trackdecoder - A dev utility cog to resolve Lavalink Track information from a b64 string.
+
 trickortreat - A trick or treat-based competitive candy eating game with a leaderboard and other fun commands like stealing candy from guildmates.
 
 tools - A collection of mod and admin tools, ported from my v2 version. Sitryk is responsible for a lot of the code in tools... thanks for the help with this cog.
diff --git a/trackdecoder/__init__.py b/trackdecoder/__init__.py
new file mode 100644
index 0000000..1755712
--- /dev/null
+++ b/trackdecoder/__init__.py
@@ -0,0 +1,5 @@
+from .trackdecoder import TrackDecoder
+
+
+def setup(bot):
+    bot.add_cog(TrackDecoder(bot))
diff --git a/trackdecoder/info.json b/trackdecoder/info.json
new file mode 100644
index 0000000..e08a6f2
--- /dev/null
+++ b/trackdecoder/info.json
@@ -0,0 +1,9 @@
+{
+    "author": ["aikaterna", "devoxin#0001"],
+    "description": "Utility cog for decoding b64 encoded Lavalink Track strings.",
+    "install_msg": "Thanks for installing.",
+    "short": "Utility cog for decoding b64 encoded Lavalink Track strings.",
+    "tags": ["lavalink"],
+    "type": "COG",
+    "end_user_data_statement": "This cog does not persistently store data or metadata about users."
+}
\ No newline at end of file
diff --git a/trackdecoder/trackdecoder.py b/trackdecoder/trackdecoder.py
new file mode 100644
index 0000000..0d043b5
--- /dev/null
+++ b/trackdecoder/trackdecoder.py
@@ -0,0 +1,106 @@
+from base64 import b64decode
+import json
+from io import BytesIO
+import struct
+from types import SimpleNamespace
+
+from redbot.core import checks, commands
+from redbot.core.utils.chat_formatting import box
+
+
+class TrackDecoder(commands.Cog):
+    """Decodes a b64 encoded audio track string."""
+
+    def __init__(self, bot):
+        self.bot = bot
+
+    @checks.is_owner()
+    @commands.command()
+    @commands.guild_only()
+    async def trackdecode(self, ctx: commands.Context, *, track: str):
+        """
+        Decodes a b64 encoded audio track string.
+
+        This command is possible thanks to devoxin#0001's work.
+        `https://github.com/Devoxin/Lavalink.py`
+        """
+        decoded = self.decode_track(track)
+        if not decoded:
+            return await ctx.send(f"Not a valid track.")
+
+        msg = (
+            f"[Title]:      {decoded.title}\n"
+            f"[Author]:     {decoded.author}\n"
+            f"[URL]:        {decoded.uri}\n"
+            f"[Identifier]: {decoded.identifier}\n"
+            f"[Source]:     {decoded.source}\n"
+            f"[Length]:     {decoded.length}\n"
+            f"[Stream]:     {decoded.is_stream}\n"
+            f"[Position]:   {decoded.position}\n"
+        )
+
+        await ctx.send(box(msg, lang="ini"))
+
+    @staticmethod
+    def decode_track(track, decode_errors="ignore"):
+        """
+        Source is derived from:
+        https://github.com/Devoxin/Lavalink.py/blob/3688fe6aff265ff53928ec811279177a88aa9664/lavalink/utils.py
+        """
+        reader = DataReader(track)
+
+        try:
+            flags = (reader.read_int() & 0xC0000000) >> 30
+        except struct.error:
+            return None
+
+        (version,) = struct.unpack("B", reader.read_byte()) if flags & 1 != 0 else 1
+
+        track = SimpleNamespace(
+            title=reader.read_utf().decode(errors=decode_errors),
+            author=reader.read_utf().decode(),
+            length=reader.read_long(),
+            identifier=reader.read_utf().decode(),
+            is_stream=reader.read_boolean(),
+            uri=reader.read_utf().decode() if reader.read_boolean() else None,
+            source=reader.read_utf().decode(),
+            position=reader.read_long(),
+        )
+
+        return track
+
+
+class DataReader:
+    """
+    Source is from:
+    https://github.com/Devoxin/Lavalink.py/blob/3688fe6aff265ff53928ec811279177a88aa9664/lavalink/datarw.py
+    """
+
+    def __init__(self, ts):
+        self._buf = BytesIO(b64decode(ts))
+
+    def _read(self, n):
+        return self._buf.read(n)
+
+    def read_byte(self):
+        return self._read(1)
+
+    def read_boolean(self):
+        (result,) = struct.unpack("B", self.read_byte())
+        return result != 0
+
+    def read_unsigned_short(self):
+        (result,) = struct.unpack(">H", self._read(2))
+        return result
+
+    def read_int(self):
+        (result,) = struct.unpack(">i", self._read(4))
+        return result
+
+    def read_long(self):
+        (result,) = struct.unpack(">Q", self._read(8))
+        return result
+
+    def read_utf(self):
+        text_length = self.read_unsigned_short()
+        return self._read(text_length)