[kgm] feat #2: basic kgm support

um_cli/src/cmd/kgm.rs

@@ -0,0 +1,44 @@
+use crate::Cli;
+use clap::Args;
+use std::fs::File;
+use std::io::{Read, Seek, SeekFrom, Write};
+use std::path::PathBuf;
+use umc_kgm::header::Header;
+
+/// Decrypt a KGM/VPR file (Kugou Music)
+#[derive(Args)]
+pub struct ArgsKGM {
+    /// Path to output file, e.g. /export/Music/song.flac
+    #[arg(short, long)]
+    output: PathBuf,
+
+    /// Path to input file, e.g. /export/Music/song.kgm
+    #[arg(name = "input")]
+    input: PathBuf,
+}
+
+impl ArgsKGM {
+    pub fn run(&self, cli: &Cli) -> anyhow::Result<i32> {
+        let mut file_input = File::open(&self.input)?;
+        let mut header = [0u8; 0x40];
+        file_input.read_exact(&mut header)?;
+        let kgm_header = Header::from_buffer(&mut header)?;
+        let decipher = kgm_header.make_decipher()?;
+        file_input.seek(SeekFrom::Start(kgm_header.offset_to_data as u64))?;
+
+        let mut offset = 0usize;
+        let mut buffer = vec![0u8; cli.buffer_size].into_boxed_slice();
+        let mut file_output = File::create(&self.output)?;
+        while let Ok(n) = file_input.read(&mut buffer) {
+            if n == 0 {
+                break;
+            }
+
+            decipher.decrypt(&mut buffer[..n], offset);
+            file_output.write_all(&buffer[..n])?;
+            offset += n;
+        }
+
+        Ok(0)
+    }
+}

um_cli/src/cmd/mod.rs

@@ -1,5 +1,6 @@
 use clap::Subcommand;
 
+pub mod kgm;
 pub mod ncm;
 pub mod qmc1;
 pub mod qmc2;
@@ -12,4 +13,6 @@ pub enum Commands {
     QMCv2(qmc2::ArgsQMCv2),
     #[command(name = "ncm")]
     NCM(ncm::ArgsNCM),
+    #[command(name = "kgm")]
+    KGM(kgm::ArgsKGM),
 }

um_cli/src/cmd/qmc2.rs

@@ -30,7 +30,7 @@ pub struct ArgsQMCv2 {
     info_only: bool,
 }
 
-fn read_ekey(ekey: &str) -> Result<Box<[u8]>> {
+fn read_ekey(ekey: &str) -> Result<Vec<u8>> {
     let mut external_file = false;
     let mut decrypt_ekey = true;
 
@@ -54,7 +54,7 @@ fn read_ekey(ekey: &str) -> Result<Box<[u8]>> {
     let ekey = ekey.trim();
     let ekey = match decrypt_ekey {
         true => umc_qmc::ekey::decrypt(ekey)?,
-        false => base64::decode(ekey)?.into_boxed_slice(),
+        false => base64::decode(ekey)?,
     };
     Ok(ekey)
 }

um_cli/src/main.rs

@@ -30,6 +30,7 @@ fn run_command(cli: &Cli) -> Result<i32> {
         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),
         None => {
             // https://github.com/clap-rs/clap/issues/3857#issuecomment-1161796261
             todo!("implement a sensible default command, similar to um/cli");