docs: update readme about cli solution

Cargo.lock

@@ -434,6 +434,7 @@ dependencies = [
  "anyhow",
  "clap",
  "umc_kuwo",
+ "umc_ncm",
  "umc_qmc",
  "umc_utils",
 ]

README.MD

@@ -6,9 +6,10 @@
 
 ```text
 lib_um_crypto_rust
-├── um_crypto       子目录存放具体算法的代码
-├── um_wasm         将 um_crypto 包装为能从 JavaScript 层调用的代码
-└── um_wasm_loader  打包 `um_wasm` 到 npm 包的代码
+├── um_cli          用于调试的 CLI 方案。
+├── um_crypto/*     子目录存放具体算法的代码。
+├── um_wasm         将 um_crypto 包装为能从 JavaScript 层调用的代码。
+└── um_wasm_loader  打包 `um_wasm` 到 npm 包的代码。
 ```
 
 ## 授权协议

um_cli/Cargo.toml

@@ -8,4 +8,5 @@ anyhow = "1.0.86"
 clap = { version = "4.5.17", features = ["derive"] }
 umc_kuwo = { path = "../um_crypto/kuwo" }
 umc_qmc = { path = "../um_crypto/qmc" }
+umc_ncm = { path = "../um_crypto/ncm" }
 umc_utils = { path = "../um_crypto/utils" }

um_cli/src/cmd/mod.rs

@@ -1,5 +1,6 @@
 use clap::Subcommand;
 
+pub mod ncm;
 pub mod qmc1;
 pub mod qmc2;
 
@@ -9,4 +10,6 @@ pub enum Commands {
     QMCv1(qmc1::ArgsQMCv1),
     #[command(name = "qmc2")]
     QMCv2(qmc2::ArgsQMCv2),
+    #[command(name = "ncm")]
+    NCM(ncm::ArgsNCM),
 }

um_cli/src/cmd/ncm.rs

@@ -0,0 +1,90 @@
+use crate::Cli;
+use clap::Args;
+use std::fs::File;
+use std::io::{Read, Seek, SeekFrom, Write};
+use std::path::PathBuf;
+use umc_ncm::header::NCMFile;
+
+/// Decrypt a NCM file (NetEase Cloud Music)
+#[derive(Args)]
+pub struct ArgsNCM {
+    /// Path to output file, e.g. /export/Music/song.flac
+    #[arg(short, long)]
+    output: Option<PathBuf>,
+
+    /// Path to input file, e.g. /export/Music/song.ncm
+    #[arg(name = "input")]
+    input: PathBuf,
+
+    /// Path to export cover image. Could be either JPG or PNG.
+    /// File will not be created if not found.
+    #[arg(short)]
+    cover: Option<PathBuf>,
+
+    /// Path to export metadata. JSON string.
+    #[arg(short)]
+    metadata: Option<PathBuf>,
+}
+
+impl ArgsNCM {
+    fn write_metadata(&self, cli: &Cli, ncm: &NCMFile) -> anyhow::Result<()> {
+        if let Some(metadata_path) = &self.metadata {
+            if !ncm.metadata.is_empty() {
+                let metadata = ncm.get_metadata()?;
+                File::create(metadata_path)?.write_all(&metadata)?;
+                if cli.verbose {
+                    let metadata_path = metadata_path.display();
+                    let len = metadata.len();
+                    println!("metadata written to {metadata_path} ({len} bytes)");
+                }
+            } else {
+                println!("metadata is empty, skip.");
+            }
+        }
+        Ok(())
+    }
+
+    fn write_cover(&self, cli: &Cli, ncm: &NCMFile) -> anyhow::Result<()> {
+        if let Some(cover_path) = &self.cover {
+            if let Some(cover) = &ncm.image1 {
+                File::create(cover_path)?.write_all(&cover)?;
+                if cli.verbose {
+                    let cover_path = cover_path.display();
+                    let len = cover.len();
+                    println!("cover written to {cover_path} ({len} bytes)");
+                }
+            } else {
+                println!("cover#1 is empty, skip.");
+            }
+        }
+        Ok(())
+    }
+
+    pub fn run(&self, cli: &Cli) -> anyhow::Result<i32> {
+        let mut file_input = File::open(&self.input)?;
+        let ncm = NCMFile::new_from_readable(&mut file_input)?;
+
+        self.write_metadata(cli, &ncm)?;
+        self.write_cover(cli, &ncm)?;
+
+        if let Some(output_path) = &self.output {
+            file_input.seek(SeekFrom::Start(ncm.audio_data_offset as u64))?;
+            let mut file_output = File::create(output_path)?;
+
+            let mut offset = 0usize;
+            let mut buffer = vec![0u8; cli.buffer_size].into_boxed_slice();
+
+            while let Ok(n) = file_input.read(&mut buffer) {
+                if n == 0 {
+                    break;
+                }
+
+                ncm.decrypt(&mut buffer[..n], offset);
+                file_output.write_all(&buffer[..n])?;
+                offset += n;
+            }
+        }
+
+        Ok(0)
+    }
+}

um_cli/src/cmd/qmc1.rs

@@ -5,7 +5,7 @@ use std::fs::File;
 use std::io::{Read, Write};
 use std::path::PathBuf;
 
-/// Decrypt a QMCv1 file
+/// Decrypt a QMCv1 file (QQMusic)
 #[derive(Args)]
 pub struct ArgsQMCv1 {
     /// Path to output file, e.g. /export/Music/song.flac

um_cli/src/cmd/qmc2.rs

@@ -8,7 +8,7 @@ use std::path::PathBuf;
 use umc_qmc::{footer, QMCv2Cipher};
 use umc_utils::base64;
 
-/// Decrypt a QMCv2 file
+/// Decrypt a QMCv2 file (QQMusic)
 #[derive(Args)]
 pub struct ArgsQMCv2 {
     /// Path to output file, e.g. /export/Music/song.flac

um_cli/src/main.rs

@@ -29,6 +29,7 @@ fn run_command(cli: &Cli) -> Result<i32> {
     match &cli.command {
         Some(Commands::QMCv1(cmd)) => cmd.run(&cli),
         Some(Commands::QMCv2(cmd)) => cmd.run(&cli),
+        Some(Commands::NCM(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");

um_crypto/ncm/src/header.rs

@@ -1,20 +1,26 @@
-use crate::{content_key, NetEaseCryptoError as Error};
+use crate::{content_key, metadata, NetEaseCryptoError as Error, NetEaseCryptoError};
 use byteorder::{ByteOrder, LE};
+use std::cmp::max;
+use std::io::Read;
 
 const CRC32: crc::Crc<u32> = crc::Crc::<u32>::new(&crc::CRC_32_ISO_HDLC);
 
-struct NCMFile {
+#[derive(Debug, PartialEq, Clone)]
+pub struct NCMFile {
+    audio_rc4_key_stream: [u8; 256],
+
+    /// NCM File format version, 0x01
     pub ncm_version: u8,
+    /// CloudMusic client version (guess)
     pub client_version: u8,
-    /// Encrypted content key
+    /// Encrypted content key.
     pub content_key: Vec<u8>,
     /// Encrypted metadata.
     pub metadata: Vec<u8>,
-    /// Cover image 1
+    /// Cover image 1, usually jpg.
     pub image1: Option<Vec<u8>>,
     /// Cover image 2, format unknown
     pub image2: Option<Vec<u8>>,
-    audio_rc4_key_stream: [u8; 256],
     pub audio_data_offset: usize,
 }
 
@@ -34,6 +40,7 @@ fn build_audio_rc4_key_stream(enciphered_content_key: &[u8]) -> Result<[u8; 256]
 
     let mut key = [0u8; 256];
     for (i, k) in key.iter_mut().enumerate() {
+        let i = (i + 1) & 0xff;
         let j = s[i].wrapping_add(i as u8);
         let idx = s[i].wrapping_add(s[j as usize]);
         *k = s[idx as usize];
@@ -92,10 +99,10 @@ impl NCMFile {
         let offset = offset + 1;
 
         let cover_frame_len = LE::read_u32(&header[offset..offset + 4]) as usize;
+        let offset = offset + 4;
         if header.len() < offset + cover_frame_len + 4 {
             Err(Error::HeaderTooSmall(offset + cover_frame_len + 4))?;
         }
-        let offset = offset + 4;
 
         let image1_len = LE::read_u32(&header[offset..offset + 4]) as usize;
         if image1_len > cover_frame_len {
@@ -105,6 +112,7 @@ impl NCMFile {
             })?;
         }
         let offset = offset + 4;
+
         let image2_len = cover_frame_len - image1_len;
         let image1 = match image1_len {
             0 => None,
@@ -129,35 +137,92 @@ impl NCMFile {
             audio_data_offset: offset,
         })
     }
+
+    pub fn new_from_readable<T>(file: &mut T) -> Result<Self, Error>
+    where
+        T: Read + ?Sized,
+    {
+        let mut total_bytes_read = 0;
+        let mut next_read_len = 4096;
+        let mut header = vec![];
+
+        let ncm = loop {
+            header.resize(total_bytes_read + next_read_len, 0);
+            let this_read = file
+                .read(&mut header[total_bytes_read..])
+                .map_err(NetEaseCryptoError::FileIOError)?;
+            if this_read == 0 {
+                Err(NetEaseCryptoError::FileIOErrorReadZero)?;
+            }
+            total_bytes_read += this_read;
+
+            match NCMFile::new(&header) {
+                Ok(ncm) => break ncm,
+                Err(NetEaseCryptoError::HeaderTooSmall(expected_len)) => {
+                    next_read_len = max(expected_len - total_bytes_read, 4096);
+                }
+                Err(err) => Err(err)?,
+            };
+        };
+
+        Ok(ncm)
+    }
+
+    pub fn get_metadata(&self) -> Result<Vec<u8>, Error> {
+        metadata::decrypt(&self.metadata)
+    }
+
+    /// Decrypt audio data.
+    ///
+    /// # Arguments
+    ///
+    /// * `data`: The data to decrypt
+    /// * `offset`: Offset of the data in file, subtract `self.audio_data_offset`
+    pub fn decrypt<T>(&self, data: &mut T, offset: usize)
+    where
+        T: AsMut<[u8]> + ?Sized,
+    {
+        let key_stream = self.audio_rc4_key_stream.iter().cycle().skip(offset & 0xff);
+        for (datum, &key) in data.as_mut().iter_mut().zip(key_stream) {
+            *datum ^= key;
+        }
+    }
 }
 
 #[test]
 fn test_load_ncm() -> Result<(), Error> {
     let ncm_header = include_bytes!("__fixture__/ncm_test1.bin");
     let ncm = NCMFile::new(ncm_header)?;
-    let sbox = [
-        0x08, 0x67, 0x20, 0xF0, 0x5C, 0xAC, 0xAF, 0x1B, 0x74, 0x0D, 0x26, 0x40, 0xBE, 0x85, 0x61,
-        0x45, 0x0D, 0xA8, 0x69, 0xAE, 0x78, 0xEC, 0xB8, 0x14, 0x79, 0x53, 0xC4, 0x74, 0xF2, 0x9F,
-        0xE1, 0x18, 0xE2, 0xF9, 0xC0, 0x7D, 0x1E, 0x5A, 0xBA, 0x4A, 0xB3, 0x11, 0x36, 0xD9, 0xAA,
-        0xD2, 0x13, 0xEE, 0x92, 0x45, 0x4B, 0x57, 0xE6, 0xF1, 0x13, 0x90, 0xE9, 0xE5, 0x2F, 0xBE,
-        0x6E, 0x16, 0x01, 0xBF, 0x10, 0x81, 0x5C, 0x68, 0x1C, 0xE3, 0xEB, 0xDF, 0x5A, 0xC7, 0xC3,
-        0x3F, 0x9C, 0xD7, 0x28, 0x3A, 0x81, 0x2B, 0x1F, 0xF3, 0x6F, 0x27, 0x15, 0x7E, 0x53, 0xD3,
-        0xF0, 0xFA, 0x50, 0x9F, 0xC7, 0xF0, 0x7F, 0xA6, 0xA7, 0x24, 0x80, 0x87, 0x39, 0x55, 0xA5,
-        0x0B, 0x2B, 0x8B, 0x00, 0x19, 0x82, 0xA8, 0x40, 0xA5, 0x77, 0x9C, 0x93, 0x3B, 0xEE, 0x27,
-        0x70, 0x0F, 0xA2, 0xEB, 0xA5, 0x6F, 0x58, 0xFB, 0xEB, 0x57, 0x1B, 0xC3, 0x61, 0x10, 0x6D,
-        0x95, 0x2C, 0xAA, 0xC6, 0x58, 0x88, 0xD5, 0x9E, 0x33, 0x9A, 0x5A, 0xD1, 0xB5, 0xD2, 0x17,
-        0x44, 0xD6, 0xDB, 0xAB, 0xED, 0x7C, 0xFC, 0x5C, 0x37, 0xB9, 0x16, 0xB8, 0xA5, 0x77, 0xFB,
-        0x58, 0x35, 0x36, 0xE7, 0x51, 0xD0, 0x03, 0xBB, 0x2A, 0x88, 0x24, 0x84, 0x1D, 0x28, 0xB1,
-        0xE1, 0xA0, 0xA5, 0xA0, 0xDD, 0x15, 0x66, 0xBB, 0x4F, 0x7E, 0xBC, 0x99, 0x76, 0x1A, 0xD2,
-        0xEF, 0xBE, 0xD9, 0x79, 0xA0, 0x33, 0xD5, 0x96, 0x6C, 0xD9, 0xEF, 0x42, 0x7E, 0x11, 0x45,
-        0x1F, 0x99, 0x96, 0x1A, 0x90, 0x0C, 0x75, 0xBC, 0x01, 0xE2, 0xC8, 0xEF, 0x16, 0x98, 0x9A,
-        0x09, 0xEB, 0xD8, 0xA1, 0xEA, 0x62, 0xE7, 0x92, 0x20, 0x8F, 0x6F, 0x72, 0xDE, 0x14, 0xFE,
-        0xBF, 0xCD, 0xBA, 0x97, 0xDE, 0xA3, 0x3B, 0x67, 0xD4, 0x0B, 0xF4, 0xD3, 0x97, 0x25, 0xBA,
-        0xCA,
+    let key_stream = [
+        0x67, 0x20, 0xF0, 0x5C, 0xAC, 0xAF, 0x1B, 0x74, 0x0D, 0x26, 0x40, 0xBE, 0x85, 0x61, 0x45,
+        0x0D, 0xA8, 0x69, 0xAE, 0x78, 0xEC, 0xB8, 0x14, 0x79, 0x53, 0xC4, 0x74, 0xF2, 0x9F, 0xE1,
+        0x18, 0xE2, 0xF9, 0xC0, 0x7D, 0x1E, 0x5A, 0xBA, 0x4A, 0xB3, 0x11, 0x36, 0xD9, 0xAA, 0xD2,
+        0x13, 0xEE, 0x92, 0x45, 0x4B, 0x57, 0xE6, 0xF1, 0x13, 0x90, 0xE9, 0xE5, 0x2F, 0xBE, 0x6E,
+        0x16, 0x01, 0xBF, 0x10, 0x81, 0x5C, 0x68, 0x1C, 0xE3, 0xEB, 0xDF, 0x5A, 0xC7, 0xC3, 0x3F,
+        0x9C, 0xD7, 0x28, 0x3A, 0x81, 0x2B, 0x1F, 0xF3, 0x6F, 0x27, 0x15, 0x7E, 0x53, 0xD3, 0xF0,
+        0xFA, 0x50, 0x9F, 0xC7, 0xF0, 0x7F, 0xA6, 0xA7, 0x24, 0x80, 0x87, 0x39, 0x55, 0xA5, 0x0B,
+        0x2B, 0x8B, 0x00, 0x19, 0x82, 0xA8, 0x40, 0xA5, 0x77, 0x9C, 0x93, 0x3B, 0xEE, 0x27, 0x70,
+        0x0F, 0xA2, 0xEB, 0xA5, 0x6F, 0x58, 0xFB, 0xEB, 0x57, 0x1B, 0xC3, 0x61, 0x10, 0x6D, 0x95,
+        0x2C, 0xAA, 0xC6, 0x58, 0x88, 0xD5, 0x9E, 0x33, 0x9A, 0x5A, 0xD1, 0xB5, 0xD2, 0x17, 0x44,
+        0xD6, 0xDB, 0xAB, 0xED, 0x7C, 0xFC, 0x5C, 0x37, 0xB9, 0x16, 0xB8, 0xA5, 0x77, 0xFB, 0x58,
+        0x35, 0x36, 0xE7, 0x51, 0xD0, 0x03, 0xBB, 0x2A, 0x88, 0x24, 0x84, 0x1D, 0x28, 0xB1, 0xE1,
+        0xA0, 0xA5, 0xA0, 0xDD, 0x15, 0x66, 0xBB, 0x4F, 0x7E, 0xBC, 0x99, 0x76, 0x1A, 0xD2, 0xEF,
+        0xBE, 0xD9, 0x79, 0xA0, 0x33, 0xD5, 0x96, 0x6C, 0xD9, 0xEF, 0x42, 0x7E, 0x11, 0x45, 0x1F,
+        0x99, 0x96, 0x1A, 0x90, 0x0C, 0x75, 0xBC, 0x01, 0xE2, 0xC8, 0xEF, 0x16, 0x98, 0x9A, 0x09,
+        0xEB, 0xD8, 0xA1, 0xEA, 0x62, 0xE7, 0x92, 0x20, 0x8F, 0x6F, 0x72, 0xDE, 0x14, 0xFE, 0xBF,
+        0xCD, 0xBA, 0x97, 0xDE, 0xA3, 0x3B, 0x67, 0xD4, 0x0B, 0xF4, 0xD3, 0x97, 0x25, 0xBA, 0xCA,
+        0x08,
     ];
-    assert_eq!(ncm.audio_rc4_key_stream, sbox);
+    assert_eq!(ncm.audio_rc4_key_stream, key_stream);
     assert_eq!(ncm.image1, Some(b"img#1".to_vec()));
     assert_eq!(ncm.image2, Some(b"IMAGE#2".to_vec()));
 
+    let mut audio_data = ncm_header[ncm.audio_data_offset..].to_vec();
+    ncm.decrypt(&mut audio_data, 0);
+    let actual = vec![
+        0x49, 0x44, 0x33, 0x03, 0x00, 0x00, 0x00, 0x00, 0x01, 0x73, 0x54, 0x50, 0x45, 0x31, 0x00,
+    ];
+    assert_eq!(audio_data, actual);
+
     Ok(())
 }

um_crypto/ncm/src/lib.rs

@@ -11,6 +11,11 @@ pub enum NetEaseCryptoError {
     #[error("Header need at least {0} more bytes")]
     HeaderTooSmall(usize),
 
+    #[error("File I/O Error: {0}")]
+    FileIOError(std::io::Error),
+    #[error("File I/O Error: Read 0 bytes")]
+    FileIOErrorReadZero,
+
     #[error("Not a NCM file")]
     NotNCMFile,
     #[error("Invalid NCM checksum. Expected {expected:08x}, actual: {expected:08x}")]
@@ -34,4 +39,6 @@ pub enum NetEaseCryptoError {
     MetadataDecryptError(UnpadError),
     #[error("Metadata: Decode metadata failed: {0}")]
     MetadataDecodeError(base64::DecodeError),
+    #[error("Metadata: Invalid prefix on final json: {0}")]
+    MetadataInvalidJsonPrefix(String),
 }

um_crypto/ncm/src/metadata.rs

@@ -35,6 +35,12 @@ where
     let metadata = aes
         .decrypt_padded::<Pkcs7>(&mut data[..])
         .map_err(NetEaseCryptoError::MetadataDecryptError)?;
+    let metadata = match metadata.strip_prefix(b"music:") {
+        None => Err(NetEaseCryptoError::MetadataInvalidJsonPrefix(
+            String::from_utf8_lossy(metadata).to_string(),
+        ))?,
+        Some(stripped) => stripped,
+    };
     Ok(Vec::from(metadata))
 }
 
@@ -100,6 +106,6 @@ fn test_decrypt_metadata() -> Result<(), NetEaseCryptoError> {
         0x25, 0x1B, 0x37, 0x48, 0x57, 0x53, 0x2A, 0x22, 0x3A, 0x00, 0x34, 0x53, 0x24, 0x12,
     ];
     let key = decrypt(enciphered_metadata)?;
-    assert_eq!(&key[..6], b"music:");
+    assert_eq!(key[0], b'{');
     Ok(())
 }