[mg3d] feat #3: implement migu 3d decipher with improved key guessing

um_cli/src/cmd/mg3d.rs

@@ -0,0 +1,70 @@
+use crate::Cli;
+use anyhow::{bail, Result};
+use clap::Args;
+use std::fs::File;
+use std::io::{BufReader, BufWriter, Read, Seek, SeekFrom, Write};
+use std::path::PathBuf;
+use umc_mg3d::{guess_key, Decipher};
+
+/// Decrypt a mg3d file (Migu 3D Audio)
+#[derive(Args)]
+pub struct ArgsMigu3D {
+    /// Path to output file, e.g. /export/Music/song.wav
+    #[clap(short, long)]
+    output: PathBuf,
+
+    /// Path to input file, e.g. /export/Music/song.mg3d
+    #[arg(name = "input")]
+    input: PathBuf,
+
+    /// File key (androidFileKey/iosFileKey). Leave empty to guess the key.
+    #[clap(short = 'k', long = "file-key")]
+    file_key: Option<String>,
+}
+
+impl ArgsMigu3D {
+    pub fn run(&self, cli: &Cli) -> Result<i32> {
+        let mut reader = BufReader::with_capacity(cli.buffer_size, File::open(&self.input)?);
+        let mut writer = BufWriter::with_capacity(cli.buffer_size, File::create(&self.output)?);
+
+        let decipher = self.make_decipher(&mut reader)?;
+        if cli.verbose {
+            println!("final key: {}", hex::encode(decipher.get_key()));
+        }
+
+        let mut offset = 0usize;
+        let mut buffer = vec![0u8; cli.buffer_size];
+        loop {
+            let n = reader.read(&mut buffer[..])?;
+            if n == 0 {
+                break;
+            }
+            decipher.decrypt(&mut buffer[..n], offset);
+            writer.write_all(&buffer[..n])?;
+            offset += n;
+        }
+
+        Ok(0)
+    }
+
+    fn make_decipher<T>(&self, reader: &mut T) -> Result<Decipher>
+    where
+        T: Read + Seek + ?Sized,
+    {
+        let decipher = match &self.file_key {
+            None => {
+                let mut buffer = [0u8; 0x100];
+                reader.read_exact(&mut buffer)?;
+                reader.seek(SeekFrom::Current(-0x100))?;
+                let key = match guess_key(&buffer) {
+                    Some(key) => key,
+                    None => bail!("failed to guess a valid key"),
+                };
+                Decipher::new_from_final_key(&key)?
+            }
+            Some(key) => Decipher::new_from_file_key(key)?,
+        };
+
+        Ok(decipher)
+    }
+}

um_cli/src/cmd/mod.rs

@@ -2,6 +2,7 @@ use clap::Subcommand;
 
 pub mod joox;
 pub mod kgm;
+pub mod mg3d;
 pub mod ncm;
 pub mod qmc1;
 pub mod qmc2;
@@ -11,20 +12,29 @@ pub mod xmly;
 
 #[derive(Subcommand)]
 pub enum Commands {
+    #[command(name = "ncm")]
+    NCM(ncm::ArgsNCM),
+
+    #[command(name = "kgm")]
+    KGM(kgm::ArgsKGM),
+
+    #[command(name = "mg3d")]
+    Migu3D(mg3d::ArgsMigu3D),
+
+    #[command(name = "joox")]
+    JOOX(joox::ArgsJoox),
+
     #[command(name = "qmc1")]
     QMCv1(qmc1::ArgsQMCv1),
     #[command(name = "qmc2")]
     QMCv2(qmc2::ArgsQMCv2),
-    #[command(name = "ncm")]
-    NCM(ncm::ArgsNCM),
-    #[command(name = "kgm")]
-    KGM(kgm::ArgsKGM),
-    #[command(name = "joox")]
-    JOOX(joox::ArgsJoox),
-    #[command(name = "xmly")]
-    XMLY(xmly::ArgsXimalaya),
-    #[command(name = "xiami")]
-    Xiami(xiami::ArgsXiami),
+
     #[command(name = "qtfm")]
     QTFM(qtfm::ArgsQingTingFM),
+
+    #[command(name = "xiami")]
+    Xiami(xiami::ArgsXiami),
+
+    #[command(name = "xmly")]
+    XMLY(xmly::ArgsXimalaya),
 }

um_cli/src/main.rs

@@ -27,14 +27,15 @@ pub struct Cli {
 
 fn run_command(cli: &Cli) -> Result<i32> {
     match &cli.command {
+        Some(Commands::JOOX(cmd)) => cmd.run(&cli),
+        Some(Commands::KGM(cmd)) => cmd.run(&cli),
+        Some(Commands::Migu3D(cmd)) => cmd.run(&cli),
+        Some(Commands::NCM(cmd)) => cmd.run(&cli),
         Some(Commands::QMCv1(cmd)) => cmd.run(&cli),
         Some(Commands::QMCv2(cmd)) => cmd.run(&cli),
-        Some(Commands::NCM(cmd)) => cmd.run(&cli),
-        Some(Commands::KGM(cmd)) => cmd.run(&cli),
-        Some(Commands::JOOX(cmd)) => cmd.run(&cli),
-        Some(Commands::XMLY(cmd)) => cmd.run(&cli),
-        Some(Commands::Xiami(cmd)) => cmd.run(&cli),
         Some(Commands::QTFM(cmd)) => cmd.run(&cli),
+        Some(Commands::Xiami(cmd)) => cmd.run(&cli),
+        Some(Commands::XMLY(cmd)) => cmd.run(&cli),
         None => {
             // https://github.com/clap-rs/clap/issues/3857#issuecomment-1161796261
             todo!("implement a sensible default command, similar to um/cli");