rust/hg-cpython/src/dirstate/copymap.rs

stream-clone: smoothly detect and handle a case were a revlog is split

This detect and handle the most common case for a race condition around stream
and revlog splitting. The one were the revlog is split between the initial
collection of data and the time were we start considering stream that data.

In such case, we repatch an inlined version of that revlog together when this
happens. This is necessary as stream-v2 promised a specific number of bytes and
a specific number of files to the client. In stream-v3, we will have the
opportunity to just send a split revlog instead.

Getting a better version of the protocol for stream-v3 is still useful, but it
is no longer a blocket to fix that race condition.

Note that another, rarer race condition exist, were the revlog is split while
we creating the revlog and extracing content from it. This can be dealt with
later.

// copymap.rs
//
// Copyright 2019 Raphaël Gomès <[e-mail]>
//
// This software may be used and distributed according to the terms of the
// GNU General Public License version 2 or any later version.

//! Bindings for `hg::dirstate::dirstate_map::CopyMap` provided by the
//! `hg-core` package.

use cpython::{
    PyBytes, PyClone, PyDict, PyObject, PyResult, Python, UnsafePyLeaked,
};
use std::cell::RefCell;

use crate::dirstate::dirstate_map::v2_error;
use crate::dirstate::dirstate_map::DirstateMap;
use hg::dirstate::CopyMapIter;
use hg::dirstate_tree::on_disk::DirstateV2ParseError;
use hg::utils::hg_path::HgPath;

py_class!(pub class CopyMap |py| {
    data dirstate_map: DirstateMap;

    def __getitem__(&self, key: PyObject) -> PyResult<PyBytes> {
        (*self.dirstate_map(py)).copymapgetitem(py, key)
    }

    def __len__(&self) -> PyResult<usize> {
        self.dirstate_map(py).copymaplen(py)
    }

    def __contains__(&self, key: PyObject) -> PyResult<bool> {
        self.dirstate_map(py).copymapcontains(py, key)
    }

    def get(
        &self,
        key: PyObject,
        default: Option<PyObject> = None
    ) -> PyResult<Option<PyObject>> {
        self.dirstate_map(py).copymapget(py, key, default)
    }

    def pop(
        &self,
        key: PyObject,
        default: Option<PyObject> = None
    ) -> PyResult<Option<PyObject>> {
        self.dirstate_map(py).copymappop(py, key, default)
    }

    def __iter__(&self) -> PyResult<CopyMapKeysIterator> {
        self.dirstate_map(py).copymapiter(py)
    }

    // Python's `dict()` builtin works with either a subclass of dict
    // or an abstract mapping. Said mapping needs to implement `__getitem__`
    // and `keys`.
    def keys(&self) -> PyResult<CopyMapKeysIterator> {
        self.dirstate_map(py).copymapiter(py)
    }

    def items(&self) -> PyResult<CopyMapItemsIterator> {
        self.dirstate_map(py).copymapitemsiter(py)
    }

    def iteritems(&self) -> PyResult<CopyMapItemsIterator> {
        self.dirstate_map(py).copymapitemsiter(py)
    }

    def __setitem__(
        &self,
        key: PyObject,
        item: PyObject
    ) -> PyResult<()> {
        self.dirstate_map(py).copymapsetitem(py, key, item)?;
        Ok(())
    }

    def copy(&self) -> PyResult<PyDict> {
        self.dirstate_map(py).copymapcopy(py)
    }

});

impl CopyMap {
    pub fn from_inner(py: Python, dm: DirstateMap) -> PyResult<Self> {
        Self::create_instance(py, dm)
    }
    fn translate_key(
        py: Python,
        res: Result<(&HgPath, &HgPath), DirstateV2ParseError>,
    ) -> PyResult<Option<PyBytes>> {
        let (k, _v) = res.map_err(|e| v2_error(py, e))?;
        Ok(Some(PyBytes::new(py, k.as_bytes())))
    }
    fn translate_key_value(
        py: Python,
        res: Result<(&HgPath, &HgPath), DirstateV2ParseError>,
    ) -> PyResult<Option<(PyBytes, PyBytes)>> {
        let (k, v) = res.map_err(|e| v2_error(py, e))?;
        Ok(Some((
            PyBytes::new(py, k.as_bytes()),
            PyBytes::new(py, v.as_bytes()),
        )))
    }
}

py_shared_iterator!(
    CopyMapKeysIterator,
    UnsafePyLeaked<CopyMapIter<'static>>,
    CopyMap::translate_key,
    Option<PyBytes>
);

py_shared_iterator!(
    CopyMapItemsIterator,
    UnsafePyLeaked<CopyMapIter<'static>>,
    CopyMap::translate_key_value,
    Option<(PyBytes, PyBytes)>
);