diff --git a/Cargo.lock b/Cargo.lock
index d51970db471..9600a51ba68 100644
--- a/Cargo.lock
+++ b/Cargo.lock
@@ -3326,6 +3326,7 @@ dependencies = [
  "ascii",
  "base64",
  "bitflags 2.13.1",
+ "bzip2",
  "crc32fast",
  "getrandom 0.4.3",
  "itertools 0.15.0",
@@ -3571,7 +3572,6 @@ dependencies = [
  "adler32",
  "ascii",
  "blake2",
- "bzip2",
  "constant_time_eq",
  "crossbeam-utils",
  "csv-core",
diff --git a/Lib/test/test_bz2.py b/Lib/test/test_bz2.py
index bcd4e033b59..64293d75733 100644
--- a/Lib/test/test_bz2.py
+++ b/Lib/test/test_bz2.py
@@ -1032,7 +1032,6 @@ def test_failure(self):
         # Previously, a second call could crash due to internal inconsistency
         self.assertRaises(Exception, bzd.decompress, self.BAD_DATA * 30)
 
-    @unittest.expectedFailure  # TODO: RUSTPYTHON; Wrong error message
     def test_decompress_after_data_error(self):
         data = bytes.fromhex(
             "425a6839314159265359000000000000007fffff000000000000000000000000"
diff --git a/crates/common/Cargo.toml b/crates/common/Cargo.toml
index 21b700a5526..72d7ce4a6f7 100644
--- a/crates/common/Cargo.toml
+++ b/crates/common/Cargo.toml
@@ -11,6 +11,7 @@ license.workspace = true
 [features]
 default = ["std"]
 binascii = ["dep:base64", "dep:crc32fast"]
+bz2 = ["std", "dep:bzip2"]
 cjk-codecs = []
 inet = ["std"]
 json = ["dep:memchr", "std"]
@@ -28,6 +29,7 @@ rustpython-wtf8 = { workspace = true }
 ascii = { workspace = true }
 base64 = { workspace = true, optional = true }
 bitflags = { workspace = true }
+bzip2 = { workspace = true, optional = true }
 crc32fast = { workspace = true, optional = true }
 getrandom = { workspace = true }
 itertools = { workspace = true }
diff --git a/crates/common/src/compression/bz2.rs b/crates/common/src/compression/bz2.rs
new file mode 100644
index 00000000000..d346ce4bd9c
--- /dev/null
+++ b/crates/common/src/compression/bz2.rs
@@ -0,0 +1,324 @@
+// spell-checker:ignore chunker libbz
+//! VM-independent bzip2 stream engine.
+//!
+//! The engine owns its native stream state and reports plain Rust errors so
+//! interpreter and embedding layers can provide their own object and exception
+//! adapters.
+
+use bzip2::{Action, Compress, Compression, Decompress, Error, Status};
+
+use super::Chunker;
+
+const INITIAL_BUFFER_SIZE: usize = 8192;
+const BIGCHUNK: usize = 512 * 1024;
+
+/// Double the output block until `BIGCHUNK`, then keep the size fixed.
+const fn new_buffer_size(current_size: usize) -> usize {
+    if current_size < BIGCHUNK {
+        current_size + current_size
+    } else {
+        current_size
+    }
+}
+
+/// Stream errors reported by the bzip2 engine. Exception mapping belongs to
+/// the interpreter adapter.
+#[derive(Clone, Copy, PartialEq, Eq, Debug)]
+pub enum Bz2Error {
+    /// `BZ_PARAM_ERROR`
+    Param,
+    /// `BZ_DATA_ERROR` / `BZ_DATA_ERROR_MAGIC`
+    Data,
+    /// `BZ_SEQUENCE_ERROR`
+    Sequence,
+    /// `BZ_MEM_ERROR`
+    Mem,
+}
+
+impl From<Error> for Bz2Error {
+    fn from(error: Error) -> Self {
+        match error {
+            Error::Param => Self::Param,
+            Error::Data | Error::DataMagic => Self::Data,
+            Error::Sequence => Self::Sequence,
+        }
+    }
+}
+
+/// Incremental compressor. After `flush`, the stream is finished and must
+/// not be used again.
+pub struct Compressor {
+    compress: Compress,
+    flushed: bool,
+}
+
+impl Compressor {
+    /// Create a compressor. Returns `None` when `compresslevel` is outside
+    /// `1..=9`. A zero work factor selects libbz2's default of 30.
+    pub fn new(compresslevel: i64) -> Option<Self> {
+        let level = u32::try_from(compresslevel)
+            .ok()
+            .and_then(Compression::try_new)?;
+        Some(Self {
+            compress: Compress::new(level, 0),
+            flushed: false,
+        })
+    }
+
+    #[must_use]
+    pub fn is_flushed(&self) -> bool {
+        self.flushed
+    }
+
+    /// Compress `data` without finishing the stream.
+    pub fn compress(&mut self, data: &[u8]) -> Result<Vec<u8>, Bz2Error> {
+        self.run(data, Action::Run)
+    }
+
+    /// Finish the stream. The compressor must not be used again.
+    pub fn flush(&mut self) -> Result<Vec<u8>, Bz2Error> {
+        self.flushed = true;
+        self.run(&[], Action::Finish)
+    }
+
+    /// One pass over the input with the requested action, growing the output
+    /// block whenever libbz2 fills it.
+    fn run(&mut self, mut input: &[u8], action: Action) -> Result<Vec<u8>, Bz2Error> {
+        let mut out = Vec::new();
+        let mut block = vec![0u8; INITIAL_BUFFER_SIZE];
+        loop {
+            // In regular compression mode, stop when input data is exhausted.
+            if action == Action::Run && input.is_empty() {
+                break;
+            }
+            let previous_in = self.compress.total_in();
+            let previous_out = self.compress.total_out();
+            let status = self.compress.compress(input, &mut block, action)?;
+            let consumed = (self.compress.total_in() - previous_in) as usize;
+            let produced = (self.compress.total_out() - previous_out) as usize;
+            out.extend_from_slice(&block[..produced]);
+            input = &input[consumed..];
+            // In flushing mode, stop when all buffered data has been flushed.
+            if action == Action::Finish && status == Status::StreamEnd {
+                break;
+            }
+            if produced == block.len() {
+                block = vec![0u8; new_buffer_size(block.len())];
+            }
+        }
+        out.shrink_to_fit();
+        Ok(out)
+    }
+}
+
+/// Incremental decompressor. The first failure is latched so later calls
+/// can be refused by the caller; re-entering the native stream after a
+/// failure can write out of bounds.
+pub struct Decompressor {
+    decompress: Decompress,
+    eof: bool,
+    failed: bool,
+    needs_input: bool,
+    unused_data: Vec<u8>,
+    /// Input handed to `decompress` that libbz2 has not consumed yet.
+    input_buffer: Vec<u8>,
+}
+
+impl Decompressor {
+    /// Create a decompressor using the fast (non-`small`) algorithm.
+    #[must_use]
+    pub fn new() -> Self {
+        Self {
+            decompress: Decompress::new(false),
+            eof: false,
+            failed: false,
+            needs_input: true,
+            unused_data: Vec::new(),
+            input_buffer: Vec::new(),
+        }
+    }
+
+    #[must_use]
+    pub fn eof(&self) -> bool {
+        self.eof
+    }
+
+    #[must_use]
+    pub fn failed(&self) -> bool {
+        self.failed
+    }
+
+    #[must_use]
+    pub fn needs_input(&self) -> bool {
+        self.needs_input
+    }
+
+    #[must_use]
+    pub fn unused_data(&self) -> &[u8] {
+        &self.unused_data
+    }
+
+    /// Decompress from new input and any bytes buffered by an earlier call.
+    /// `max_length` of `None` means unlimited output.
+    pub fn decompress(
+        &mut self,
+        data: &[u8],
+        max_length: Option<usize>,
+    ) -> Result<Vec<u8>, Bz2Error> {
+        let max_length = max_length.unwrap_or(usize::MAX);
+        let mut out = Vec::new();
+        let mut block = vec![0u8; INITIAL_BUFFER_SIZE.min(max_length)];
+
+        let mut failed = None;
+        let mut stream_end = false;
+        let leftover = {
+            let mut chunks = Chunker::chain(&self.input_buffer, data);
+            loop {
+                let chunk = chunks.chunk();
+                let previous_in = self.decompress.total_in();
+                let previous_out = self.decompress.total_out();
+                let status = self.decompress.decompress(chunk, &mut block);
+                let consumed = (self.decompress.total_in() - previous_in) as usize;
+                let produced = (self.decompress.total_out() - previous_out) as usize;
+                chunks.advance(consumed);
+                out.extend_from_slice(&block[..produced]);
+                match status {
+                    Err(error) => {
+                        failed = Some(error.into());
+                        break;
+                    }
+                    Ok(Status::MemNeeded) => {
+                        failed = Some(Bz2Error::Mem);
+                        break;
+                    }
+                    Ok(Status::StreamEnd) => {
+                        stream_end = true;
+                        break;
+                    }
+                    Ok(_) => {}
+                }
+                if chunks.is_empty() {
+                    break;
+                }
+                if produced == block.len() {
+                    // The output block is full: grow it unless `max_length`
+                    // has already been reached.
+                    if out.len() == max_length {
+                        break;
+                    }
+                    block = vec![0u8; new_buffer_size(block.len()).min(max_length - out.len())];
+                }
+            }
+            if chunks.is_empty() {
+                None
+            } else {
+                Some(chunks.to_vec())
+            }
+        };
+
+        if let Some(error) = failed {
+            return Err(self.fail(error));
+        }
+
+        if stream_end {
+            self.eof = true;
+            self.needs_input = false;
+            self.input_buffer.clear();
+            if let Some(unused) = leftover {
+                self.unused_data = unused;
+            }
+        } else if let Some(remaining) = leftover {
+            self.needs_input = false;
+            self.input_buffer = remaining;
+        } else {
+            self.needs_input = true;
+            self.input_buffer.clear();
+        }
+        out.shrink_to_fit();
+        Ok(out)
+    }
+
+    /// Latch the first failure and drop the pending input with it.
+    fn fail(&mut self, error: Bz2Error) -> Bz2Error {
+        self.failed = true;
+        self.needs_input = false;
+        self.input_buffer = Vec::new();
+        error
+    }
+}
+
+impl Default for Decompressor {
+    fn default() -> Self {
+        Self::new()
+    }
+}
+
+#[cfg(test)]
+mod tests {
+    use super::*;
+
+    fn roundtrip(data: &[u8], level: i64) -> Vec<u8> {
+        let mut compressor = Compressor::new(level).unwrap();
+        let mut encoded = compressor.compress(data).unwrap();
+        encoded.extend(compressor.flush().unwrap());
+        let mut decompressor = Decompressor::new();
+        let out = decompressor.decompress(&encoded, None).unwrap();
+        assert!(decompressor.eof());
+        out
+    }
+
+    #[test]
+    fn invalid_level_is_rejected() {
+        assert!(Compressor::new(0).is_none());
+        assert!(Compressor::new(10).is_none());
+        assert!(Compressor::new(-1).is_none());
+    }
+
+    #[test]
+    fn streaming_roundtrip() {
+        let data = b"the quick brown fox jumps over the lazy dog".repeat(50);
+        assert_eq!(roundtrip(&data, 9), data);
+    }
+
+    #[test]
+    fn unused_data_after_stream_end() {
+        let mut compressor = Compressor::new(9).unwrap();
+        let mut encoded = compressor.compress(b"hello").unwrap();
+        encoded.extend(compressor.flush().unwrap());
+        encoded.extend_from_slice(b"trailing");
+
+        let mut decompressor = Decompressor::new();
+        let out = decompressor.decompress(&encoded, None).unwrap();
+        assert_eq!(out, b"hello");
+        assert!(decompressor.eof());
+        assert!(!decompressor.needs_input());
+        assert_eq!(decompressor.unused_data(), b"trailing");
+    }
+
+    #[test]
+    fn max_length_leaves_unconsumed_input() {
+        let data = b"abcdefghij".repeat(20);
+        let mut compressor = Compressor::new(9).unwrap();
+        let mut encoded = compressor.compress(&data).unwrap();
+        encoded.extend(compressor.flush().unwrap());
+
+        let mut decompressor = Decompressor::new();
+        let first = decompressor.decompress(&encoded, Some(5)).unwrap();
+        assert_eq!(first.len(), 5);
+        assert!(!decompressor.eof());
+        assert!(!decompressor.needs_input());
+        let rest = decompressor.decompress(&[], None).unwrap();
+        assert_eq!([first, rest].concat(), data);
+        assert!(decompressor.eof());
+    }
+
+    #[test]
+    fn bad_data_latches_failure() {
+        let mut decompressor = Decompressor::new();
+        let err = decompressor.decompress(b"not a bz2 stream", None);
+        assert_eq!(err, Err(Bz2Error::Data));
+        assert!(decompressor.failed());
+        assert!(!decompressor.needs_input());
+        assert!(!decompressor.eof());
+    }
+}
diff --git a/crates/common/src/compression/mod.rs b/crates/common/src/compression/mod.rs
index f0d2b7b5f19..9f84d2590dd 100644
--- a/crates/common/src/compression/mod.rs
+++ b/crates/common/src/compression/mod.rs
@@ -69,6 +69,8 @@ impl<'a> Chunker<'a> {
     }
 }
 
+#[cfg(feature = "bz2")]
+pub mod bz2;
 #[cfg(all(
     feature = "lzma",
     not(any(target_os = "android", target_arch = "wasm32"))
diff --git a/crates/common/src/lib.rs b/crates/common/src/lib.rs
index 575bf64e365..ddf0cf91558 100644
--- a/crates/common/src/lib.rs
+++ b/crates/common/src/lib.rs
@@ -11,7 +11,7 @@ pub mod binascii;
 pub mod borrow;
 pub mod boxvec;
 pub mod cformat;
-#[cfg(any(feature = "lzma", feature = "zlib"))]
+#[cfg(any(feature = "bz2", feature = "lzma", feature = "zlib"))]
 pub mod compression;
 pub mod encodings;
 pub mod float_ops;
diff --git a/crates/stdlib/Cargo.toml b/crates/stdlib/Cargo.toml
index cd955597d94..794b8eee176 100644
--- a/crates/stdlib/Cargo.toml
+++ b/crates/stdlib/Cargo.toml
@@ -30,7 +30,7 @@ __ssl-rustls = ["ssl", "rustls", "rustls-native-certs", "rustls-pemfile", "rustl
 # rustpython crates
 rustpython-derive = { workspace = true }
 rustpython-vm = { workspace = true, default-features = false, features = ["compiler"]}
-rustpython-common = { workspace = true, features = ["binascii", "cjk-codecs", "inet", "json", "lzma", "zlib"] }
+rustpython-common = { workspace = true, features = ["binascii", "bz2", "cjk-codecs", "inet", "json", "lzma", "zlib"] }
 rustpython-host_env = { workspace = true }
 rustpython-unicode = { workspace = true }
 
@@ -79,7 +79,6 @@ constant_time_eq = { workspace = true }
 
 # compression
 adler32 = { workspace = true }
-bzip2 = { workspace = true }
 
 # tkinter
 jiff = { workspace = true }
diff --git a/crates/stdlib/src/bz2.rs b/crates/stdlib/src/bz2.rs
index fcde54057e5..25efa228d60 100644
--- a/crates/stdlib/src/bz2.rs
+++ b/crates/stdlib/src/bz2.rs
@@ -4,54 +4,50 @@ pub(crate) use _bz2::module_def;
 
 #[pymodule]
 mod _bz2 {
-    use crate::compression::{
-        DecompressArgs, DecompressError, DecompressState, DecompressStatus, Decompressor,
-    };
+    use crate::compression::DecompressArgs;
     use crate::vm::{
         Py, VirtualMachine,
-        builtins::{PyBytesRef, PyType},
+        builtins::{PyBaseExceptionRef, PyBytesRef, PyType},
         common::lock::PyMutex,
         function::{ArgBytesLike, OptionalArg},
         object::PyResult,
         types::Constructor,
     };
     use alloc::fmt;
-    use bzip2::{Decompress, Status, write::BzEncoder};
-    use core::mem;
-    use rustpython_vm::convert::ToPyException;
-    use std::io::Write;
-
-    const BUFSIZ: usize = 8192;
+    use rustpython_common::compression::bz2 as backend;
 
-    #[pyattr]
-    #[pyclass(name = "BZ2Decompressor")]
-    #[derive(PyPayload)]
-    struct BZ2Decompressor {
-        state: PyMutex<DecompressState<Decompress>>,
+    fn map_bz2_error(error: backend::Bz2Error, vm: &VirtualMachine) -> PyBaseExceptionRef {
+        match error {
+            backend::Bz2Error::Param => {
+                vm.new_value_error("Internal error - invalid parameters passed to libbzip2")
+            }
+            backend::Bz2Error::Data => vm.new_os_error("Invalid data stream"),
+            backend::Bz2Error::Sequence => vm.new_runtime_error(
+                "Internal error - Invalid sequence of commands sent to libbzip2",
+            ),
+            backend::Bz2Error::Mem => vm.new_memory_error("out of memory"),
+        }
     }
 
-    impl Decompressor for Decompress {
-        type Flush = ();
-        type Status = Status;
-        type Error = bzip2::Error;
+    struct PyBZ2DecompressorInner {
+        decompress: backend::Decompressor,
+        unused_data: PyBytesRef,
+    }
 
-        fn total_in(&self) -> u64 {
-            self.total_in()
-        }
-        fn decompress_vec(
-            &mut self,
-            input: &[u8],
-            output: &mut Vec<u8>,
-            (): Self::Flush,
-        ) -> Result<Self::Status, Self::Error> {
-            self.decompress_vec(input, output)
+    impl PyBZ2DecompressorInner {
+        fn sync_visible_state(&mut self, vm: &VirtualMachine) {
+            if self.unused_data.as_bytes() != self.decompress.unused_data() {
+                self.unused_data = vm.ctx.new_bytes(self.decompress.unused_data().to_vec());
+            }
         }
     }
 
-    impl DecompressStatus for Status {
-        fn is_stream_end(&self) -> bool {
-            *self == Self::StreamEnd
-        }
+    #[pyattr]
+    #[pyclass(name = "BZ2Decompressor", traverse)]
+    #[derive(PyPayload)]
+    struct BZ2Decompressor {
+        #[pytraverse(skip)]
+        inner: PyMutex<PyBZ2DecompressorInner>,
     }
 
     impl fmt::Debug for BZ2Decompressor {
@@ -65,7 +61,10 @@ mod _bz2 {
 
         fn py_new(_cls: &Py<PyType>, _args: Self::Args, vm: &VirtualMachine) -> PyResult<Self> {
             Ok(Self {
-                state: PyMutex::new(DecompressState::new(Decompress::new(false), vm)),
+                inner: PyMutex::new(PyBZ2DecompressorInner {
+                    decompress: backend::Decompressor::new(),
+                    unused_data: vm.ctx.empty_bytes.clone(),
+                }),
             })
         }
     }
@@ -77,50 +76,44 @@ mod _bz2 {
             let max_length = args.max_length();
             let data = &*args.data();
 
-            let mut state = self.state.lock();
-            state
-                .decompress(data, max_length, BUFSIZ, vm)
-                .map_err(|e| match e {
-                    DecompressError::Decompress(err) => vm.new_os_error(err.to_string()),
-                    DecompressError::Eof(err) => err.to_pyexception(vm),
-                })
+            let mut inner = self.inner.lock();
+            if inner.decompress.eof() {
+                return Err(vm.new_eof_error("End of stream already reached"));
+            }
+            if inner.decompress.failed() {
+                return Err(vm.new_value_error("Decompressor is unusable after a previous error"));
+            }
+            let result = inner.decompress.decompress(data, max_length);
+            inner.sync_visible_state(vm);
+            result.map_err(|error| map_bz2_error(error, vm))
         }
 
         #[pygetset]
         fn eof(&self) -> bool {
-            self.state.lock().eof()
+            self.inner.lock().decompress.eof()
         }
 
         #[pygetset]
         fn unused_data(&self) -> PyBytesRef {
-            self.state.lock().unused_data()
+            self.inner.lock().unused_data.clone()
         }
 
         #[pygetset]
         fn needs_input(&self) -> bool {
-            // False if the decompress() method can provide more
-            // decompressed data before requiring new uncompressed input.
-            self.state.lock().needs_input()
+            self.inner.lock().decompress.needs_input()
         }
 
         #[pymethod(name = "__reduce__")]
         fn reduce(&self, vm: &VirtualMachine) -> PyResult<()> {
             Err(vm.new_type_error("cannot pickle '_bz2.BZ2Decompressor' object"))
         }
-
-        // TODO: mro()?
-    }
-
-    struct CompressorState {
-        flushed: bool,
-        encoder: Option<BzEncoder<Vec<u8>>>,
     }
 
     #[pyattr]
     #[pyclass(name = "BZ2Compressor")]
     #[derive(PyPayload)]
     struct BZ2Compressor {
-        state: PyMutex<CompressorState>,
+        state: PyMutex<backend::Compressor>,
     }
 
     impl fmt::Debug for BZ2Compressor {
@@ -137,21 +130,11 @@ mod _bz2 {
             (compresslevel,): Self::Args,
             vm: &VirtualMachine,
         ) -> PyResult<Self> {
-            // TODO: seriously?
-            // compresslevel.unwrap_or(bzip2::Compression::best().level().try_into().unwrap());
             let compresslevel = compresslevel.unwrap_or(9);
-            let level = match compresslevel {
-                valid_level @ 1..=9 => bzip2::Compression::new(valid_level as u32),
-                _ => {
-                    return Err(vm.new_value_error("compresslevel must be between 1 and 9"));
-                }
-            };
-
+            let compressor = backend::Compressor::new(i64::from(compresslevel))
+                .ok_or_else(|| vm.new_value_error("compresslevel must be between 1 and 9"))?;
             Ok(Self {
-                state: PyMutex::new(CompressorState {
-                    flushed: false,
-                    encoder: Some(BzEncoder::new(Vec::new(), level)),
-                }),
+                state: PyMutex::new(compressor),
             })
         }
     }
@@ -159,34 +142,22 @@ mod _bz2 {
     #[pyclass(with(Constructor))]
     impl BZ2Compressor {
         #[pymethod]
-        fn compress(&self, data: ArgBytesLike, vm: &VirtualMachine) -> PyResult<PyBytesRef> {
-            let mut state = self.state.lock();
-            if state.flushed {
+        fn compress(&self, data: ArgBytesLike, vm: &VirtualMachine) -> PyResult<Vec<u8>> {
+            let mut compressor = self.state.lock();
+            if compressor.is_flushed() {
                 return Err(vm.new_value_error("Compressor has been flushed"));
             }
-
-            let CompressorState { encoder, .. } = &mut *state;
-            let encoder = encoder.as_mut().unwrap();
-            data.with_ref(|input_bytes| encoder.write_all(input_bytes).unwrap());
-            // BzEncoder writes its pending output at the start of the next write.
-            assert_eq!(encoder.write(&[]).unwrap(), 0);
-            Ok(vm.ctx.new_bytes(mem::take(encoder.get_mut())))
+            data.with_ref(|input| compressor.compress(input))
+                .map_err(|error| map_bz2_error(error, vm))
         }
 
         #[pymethod]
-        fn flush(&self, vm: &VirtualMachine) -> PyResult<PyBytesRef> {
-            let mut state = self.state.lock();
-            if state.flushed {
+        fn flush(&self, vm: &VirtualMachine) -> PyResult<Vec<u8>> {
+            let mut compressor = self.state.lock();
+            if compressor.is_flushed() {
                 return Err(vm.new_value_error("Repeated call to flush()"));
             }
-
-            // let CompressorState { flushed, encoder } = &mut *state;
-            let CompressorState { encoder, .. } = &mut *state;
-
-            // TODO: handle Err
-            let out = encoder.take().unwrap().finish().unwrap();
-            state.flushed = true;
-            Ok(vm.ctx.new_bytes(out.to_vec()))
+            compressor.flush().map_err(|error| map_bz2_error(error, vm))
         }
 
         #[pymethod(name = "__reduce__")]
diff --git a/crates/stdlib/src/compression.rs b/crates/stdlib/src/compression.rs
index 563a32f7b35..3ca8c6d10eb 100644
--- a/crates/stdlib/src/compression.rs
+++ b/crates/stdlib/src/compression.rs
@@ -1,14 +1,6 @@
-// spell-checker:ignore chunker
-
 //! internal shared module for compression libraries
 
 use crate::vm::function::{ArgBytesLike, ArgSize, OptionalArg};
-use crate::vm::{
-    VirtualMachine,
-    builtins::{PyBaseExceptionRef, PyBytesRef},
-    convert::ToPyException,
-};
-use rustpython_common::compression::Chunker;
 
 #[derive(FromArgs)]
 pub(crate) struct DecompressArgs {
@@ -33,189 +25,3 @@ impl DecompressArgs {
             .and_then(|ArgSize { value }| usize::try_from(value).ok())
     }
 }
-
-pub(crate) trait Decompressor {
-    type Flush: DecompressFlushKind;
-    type Status: DecompressStatus;
-    type Error;
-
-    fn total_in(&self) -> u64;
-    fn decompress_vec(
-        &mut self,
-        input: &[u8],
-        output: &mut Vec<u8>,
-        flush: Self::Flush,
-    ) -> Result<Self::Status, Self::Error>;
-    fn maybe_set_dict(&mut self, err: Self::Error) -> Result<(), Self::Error> {
-        Err(err)
-    }
-}
-
-pub(crate) trait DecompressStatus {
-    fn is_stream_end(&self) -> bool;
-}
-
-pub(crate) trait DecompressFlushKind: Copy {
-    const SYNC: Self;
-}
-
-impl DecompressFlushKind for () {
-    const SYNC: Self = ();
-}
-
-pub(crate) const fn flush_sync<T: DecompressFlushKind>(_final_chunk: bool) -> T {
-    T::SYNC
-}
-
-pub(crate) fn _decompress_chunks<D: Decompressor>(
-    data: &mut Chunker<'_>,
-    d: &mut D,
-    bufsize: usize,
-    max_length: Option<usize>,
-    calc_flush: impl Fn(bool) -> D::Flush,
-) -> Result<(Vec<u8>, bool), D::Error> {
-    if data.is_empty() {
-        return Ok((Vec::new(), true));
-    }
-    let max_length = max_length.unwrap_or(usize::MAX);
-    let mut buf = Vec::new();
-
-    'outer: loop {
-        let chunk = data.chunk();
-        let flush = calc_flush(chunk.len() == data.len());
-        loop {
-            let additional = core::cmp::min(bufsize, max_length - buf.capacity());
-            if additional == 0 {
-                return Ok((buf, false));
-            }
-            buf.reserve_exact(additional);
-
-            let prev_in = d.total_in();
-            let res = d.decompress_vec(chunk, &mut buf, flush);
-            let consumed = d.total_in() - prev_in;
-
-            data.advance(consumed as usize);
-
-            match res {
-                Ok(status) => {
-                    let stream_end = status.is_stream_end();
-                    if stream_end || data.is_empty() {
-                        // we've reached the end of the stream, we're done
-                        buf.shrink_to_fit();
-                        return Ok((buf, stream_end));
-                    } else if !chunk.is_empty() && consumed == 0 {
-                        // we're gonna need a bigger buffer
-                        continue;
-                    }
-                    // next chunk
-                    continue 'outer;
-                }
-                Err(e) => {
-                    d.maybe_set_dict(e)?;
-                    // now try the next chunk
-                    continue 'outer;
-                }
-            };
-        }
-    }
-}
-
-#[derive(Debug)]
-pub(crate) struct DecompressState<D> {
-    decompress: D,
-    unused_data: PyBytesRef,
-    input_buffer: Vec<u8>,
-    eof: bool,
-    needs_input: bool,
-}
-
-impl<D: Decompressor> DecompressState<D> {
-    pub(crate) fn new(decompress: D, vm: &VirtualMachine) -> Self {
-        Self {
-            decompress,
-            unused_data: vm.ctx.empty_bytes.clone(),
-            input_buffer: Vec::new(),
-            eof: false,
-            needs_input: true,
-        }
-    }
-
-    pub(crate) const fn eof(&self) -> bool {
-        self.eof
-    }
-
-    pub(crate) fn unused_data(&self) -> PyBytesRef {
-        self.unused_data.clone()
-    }
-
-    pub(crate) const fn needs_input(&self) -> bool {
-        self.needs_input
-    }
-
-    pub(crate) fn decompress(
-        &mut self,
-        data: &[u8],
-        max_length: Option<usize>,
-        bufsize: usize,
-        vm: &VirtualMachine,
-    ) -> Result<Vec<u8>, DecompressError<D::Error>> {
-        if self.eof {
-            return Err(DecompressError::Eof(EofError));
-        }
-
-        let input_buffer = &mut self.input_buffer;
-        let d = &mut self.decompress;
-
-        let mut chunks = Chunker::chain(input_buffer, data);
-
-        let prev_len = chunks.len();
-        let (ret, stream_end) =
-            match _decompress_chunks(&mut chunks, d, bufsize, max_length, flush_sync) {
-                Ok((buf, stream_end)) => (Ok(buf), stream_end),
-                Err(err) => (Err(err), false),
-            };
-        let consumed = prev_len - chunks.len();
-
-        self.eof |= stream_end;
-
-        if self.eof {
-            self.needs_input = false;
-            if !chunks.is_empty() {
-                self.unused_data = vm.ctx.new_bytes(chunks.to_vec());
-            }
-        } else if chunks.is_empty() {
-            input_buffer.clear();
-            self.needs_input = true;
-        } else {
-            self.needs_input = false;
-            if let Some(n_consumed_from_data) = consumed.checked_sub(input_buffer.len()) {
-                input_buffer.clear();
-                input_buffer.extend_from_slice(&data[n_consumed_from_data..]);
-            } else {
-                input_buffer.drain(..consumed);
-                input_buffer.extend_from_slice(data);
-            }
-        }
-
-        ret.map_err(DecompressError::Decompress)
-    }
-}
-
-pub(crate) enum DecompressError<E> {
-    Decompress(E),
-    Eof(EofError),
-}
-
-impl<E> From<E> for DecompressError<E> {
-    fn from(err: E) -> Self {
-        Self::Decompress(err)
-    }
-}
-
-pub(crate) struct EofError;
-
-impl ToPyException for EofError {
-    fn to_pyexception(&self, vm: &VirtualMachine) -> PyBaseExceptionRef {
-        vm.new_eof_error("End of stream already reached")
-    }
-}