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//! Decompression chain building.
//!
//! This module provides functions for building decoder chains for
//! various compression methods and filter combinations.
use std::io::{Cursor, Read, Write};
use crate::format::streams::Folder;
use crate::{Error, READ_BUFFER_SIZE, Result, codec};
#[cfg(feature = "aes")]
use super::entries;
use super::{Archive, ExtractionLimits, map_io_error};
impl<R: Read + std::io::Seek> Archive<R> {
/// Decompresses a standard (non-BCJ2) entry to a sink.
///
/// Handles both solid and non-solid entries by dispatching to the appropriate
/// decompression method. This helper eliminates code duplication between
/// cfg(feature = "lzma") and cfg(not(feature = "lzma")) paths.
#[allow(clippy::too_many_arguments)]
pub(crate) fn decompress_standard_entry(
&mut self,
packed_data: Vec<u8>,
folder: &Folder,
folder_idx: usize,
stream_index: Option<usize>,
entry_size: u64,
sink: &mut impl Write,
limits: &ExtractionLimits,
) -> Result<()> {
if self.is_solid_block(folder_idx) {
self.decompress_to_sink_solid(
packed_data,
folder,
folder_idx,
stream_index.unwrap_or(0),
sink,
limits,
)?;
} else {
self.decompress_to_sink_non_solid(packed_data, folder, entry_size, sink, limits)?;
}
Ok(())
}
/// Decompresses non-solid entry to a sink.
pub(crate) fn decompress_to_sink_non_solid(
&self,
packed_data: Vec<u8>,
folder: &Folder,
expected_size: u64,
sink: &mut impl Write,
limits: &ExtractionLimits,
) -> Result<u64> {
if folder.coders.is_empty() {
return Err(Error::InvalidFormat("folder has no coders".into()));
}
let uncompressed_size = folder.final_unpack_size().unwrap_or(expected_size);
let compressed_size = packed_data.len() as u64;
let cursor = Cursor::new(packed_data);
// Build decoder chain - handles both single coders and filter+codec chains
let decoder = self.build_decoder_chain(cursor, folder, uncompressed_size)?;
// Wrap decoder with LimitedReader for resource limit enforcement
let mut limited_decoder = limits.wrap_reader(decoder, compressed_size);
let mut total = 0u64;
let mut buf = [0u8; READ_BUFFER_SIZE];
loop {
let n = limited_decoder.read(&mut buf).map_err(map_io_error)?;
if n == 0 {
break;
}
sink.write_all(&buf[..n]).map_err(Error::Io)?;
total += n as u64;
}
Ok(total)
}
/// Builds a decoder chain for a folder, handling filter+codec combinations
/// and encrypted folders.
///
/// For single-coder folders, returns a simple decoder.
/// For two-coder folders (filter + codec), chains them in correct order:
/// packed_data -> codec -> filter -> output
///
/// For encrypted folders, uses the stored password to decrypt.
pub(crate) fn build_decoder_chain<T: Read + Send + 'static>(
&self,
input: T,
folder: &Folder,
uncompressed_size: u64,
) -> Result<Box<dyn Read + Send>> {
// Check if the folder uses AES encryption
#[cfg(feature = "aes")]
if entries::folder_uses_encryption(folder) {
let password = self.password.as_ref().ok_or(Error::PasswordRequired)?;
let decoder =
codec::build_encrypted_folder_decoder(input, folder, uncompressed_size, password)?;
return Ok(Box::new(decoder));
}
match folder.coders.len() {
0 => Err(Error::InvalidFormat("folder has no coders".into())),
1 => {
// Single coder - simple case
let coder = &folder.coders[0];
let decoder = codec::build_decoder(input, coder, uncompressed_size)?;
Ok(Box::new(decoder))
}
2 => {
// Two coders - typically filter + codec
// In 7z, the coder order in the list is: [filter, codec]
// But data flows: packed -> codec -> filter -> output
// The bind_pair connects them: filter's input comes from codec's output
let filter_coder = &folder.coders[0];
let codec_coder = &folder.coders[1];
// Check if first coder is a filter (BCJ, Delta)
let is_filter = self.is_filter_method(&filter_coder.method_id);
if is_filter {
// First decompress with the codec
let codec_output_size = folder
.unpack_sizes
.get(1)
.copied()
.unwrap_or(uncompressed_size);
let codec_decoder =
codec::build_decoder(input, codec_coder, codec_output_size)?;
// Then apply the filter
let filter_decoder =
codec::build_decoder(codec_decoder, filter_coder, uncompressed_size)?;
Ok(Box::new(filter_decoder))
} else {
// Not a standard filter chain - try sequential decoding
// First coder processes packed data
let first_output_size = folder
.unpack_sizes
.first()
.copied()
.unwrap_or(uncompressed_size);
let first_decoder =
codec::build_decoder(input, filter_coder, first_output_size)?;
// Second coder processes first decoder's output
let second_decoder =
codec::build_decoder(first_decoder, codec_coder, uncompressed_size)?;
Ok(Box::new(second_decoder))
}
}
_ => {
// Complex chains with 3+ coders need special handling
// For now, fall back to first coder only (BCJ2 handled separately)
let coder = &folder.coders[0];
let decoder = codec::build_decoder(input, coder, uncompressed_size)?;
Ok(Box::new(decoder))
}
}
}
/// Checks if a method ID represents a filter (not a compression codec).
pub(crate) fn is_filter_method(&self, method_id: &[u8]) -> bool {
codec::method::is_filter(method_id)
}
/// Decompresses solid block entry to a sink.
///
/// Supports filter+codec combinations (e.g., BCJ + LZMA2) in solid blocks
/// by building a full decoder chain.
pub(crate) fn decompress_to_sink_solid(
&self,
packed_data: Vec<u8>,
folder: &Folder,
folder_idx: usize,
stream_index: usize,
sink: &mut impl Write,
limits: &ExtractionLimits,
) -> Result<u64> {
if folder.coders.is_empty() {
return Err(Error::InvalidFormat("folder has no coders".into()));
}
let entry_sizes = self.get_solid_block_entry_sizes(folder_idx)?;
if stream_index >= entry_sizes.len() {
return Err(Error::InvalidFormat(format!(
"stream index {} out of range for solid block",
stream_index
)));
}
let uncompressed_size = folder.final_unpack_size().unwrap_or(0);
let compressed_size = packed_data.len() as u64;
let cursor = Cursor::new(packed_data);
// Build decoder chain to handle filter+codec combinations (e.g., BCJ + LZMA2)
let mut decoder = codec::build_decoder_chain(cursor, folder, uncompressed_size)?;
// Skip entries before the target (no limit enforcement on skipped data)
for &skip_size in entry_sizes.iter().take(stream_index) {
let mut remaining = skip_size;
let mut buf = [0u8; READ_BUFFER_SIZE];
while remaining > 0 {
let to_read = buf.len().min(remaining as usize);
let n = decoder.read(&mut buf[..to_read]).map_err(Error::Io)?;
if n == 0 {
break;
}
remaining -= n as u64;
}
}
// Read the target entry to sink with limit enforcement
let target_size = entry_sizes[stream_index];
let mut limited_decoder = limits.wrap_reader(&mut decoder, compressed_size);
let mut remaining = target_size;
let mut total = 0u64;
let mut buf = [0u8; READ_BUFFER_SIZE];
while remaining > 0 {
let to_read = buf.len().min(remaining as usize);
let n = limited_decoder
.read(&mut buf[..to_read])
.map_err(map_io_error)?;
if n == 0 {
break;
}
sink.write_all(&buf[..n]).map_err(Error::Io)?;
total += n as u64;
remaining -= n as u64;
}
Ok(total)
}
}