view tests/test-storage.py @ 47965:f9e6f2bb721d

rhg: Don’t compare ambiguous files one byte at a time

Even though the use of `BufReader` reduces the number of syscalls to read
the file from disk, `.bytes()` yields a separate `Result` for every byte.
Creating those results and dispatching on them is most likely costly.

Instead, this commit opts for simplicity by reading the entire file into memory
and comparing a single pair of byte strings. Note that memory already needs to
contain the entire previous contents of the file, as read from the filelog.
So with an extremely large file this doubles memory use but does not make it
grow by orders of magnitude.

At first I wrote code that still avoids reading the entire file into memory
and compares one buffer at a time with `BufReader`. Find this code below for
posterity. However its correctness is subtle. I ended up preferring the
simplicity of the obviously-correct single comparison.

```rust
let mut reader = BufReader::new(fobj);
let mut expected = &contents_in_p1[..];
loop {
    let buf = reader.fill_buf().when_reading_file(&fs_path)?;
    if buf.is_empty() {
        // Found EOF
        return Ok(expected.is_empty());
    } else if let Some(rest) = expected.drop_prefix(buf) {
        // What we read so far matches the expected content, continue reading
        let buf_len = buf.len();
        reader.consume(buf_len);
        expected = rest
    } else {
        // Found different content
        return Ok(false);
    }
}
```

Differential Revision: https://phab.mercurial-scm.org/D11412

# This test verifies the conformance of various classes to various
# storage interfaces.
from __future__ import absolute_import

import silenttestrunner

from mercurial import (
    error,
    filelog,
    revlog,
    transaction,
    ui as uimod,
    vfs as vfsmod,
)

from mercurial.testing import storage as storagetesting

try:
    from hgext import sqlitestore
except ImportError:
    sqlitestore = None

try:
    import sqlite3

    if sqlite3.sqlite_version_info < (3, 8, 3):
        # WITH clause not supported
        sqlitestore = None
except ImportError:
    pass

try:
    from mercurial import zstd

    zstd.__version__
except ImportError:
    zstd = None

STATE = {
    'lastindex': 0,
    'ui': uimod.ui(),
    'vfs': vfsmod.vfs(b'.', realpath=True),
}


def makefilefn(self):
    """Factory for filelog instances."""
    fl = filelog.filelog(STATE['vfs'], b'filelog-%d' % STATE['lastindex'])
    STATE['lastindex'] += 1
    return fl


def maketransaction(self):
    vfsmap = {b'plain': STATE['vfs'], b'store': STATE['vfs']}

    return transaction.transaction(
        STATE['ui'].warn, STATE['vfs'], vfsmap, b'journal', b'undo'
    )


def addrawrevision(
    self,
    fl,
    tr,
    node,
    p1,
    p2,
    linkrev,
    rawtext=None,
    delta=None,
    censored=False,
    ellipsis=False,
    extstored=False,
):
    flags = 0

    if censored:
        flags |= revlog.REVIDX_ISCENSORED
    if ellipsis:
        flags |= revlog.REVIDX_ELLIPSIS
    if extstored:
        flags |= revlog.REVIDX_EXTSTORED

    if rawtext is not None:
        fl._revlog.addrawrevision(rawtext, tr, linkrev, p1, p2, node, flags)
    elif delta is not None:
        fl._revlog.addrawrevision(
            rawtext, tr, linkrev, p1, p2, node, flags, cachedelta=delta
        )
    else:
        raise error.Abort('must supply rawtext or delta arguments')

    # We may insert bad data. Clear caches to prevent e.g. cache hits to
    # bypass hash verification.
    fl._revlog.clearcaches()


# Assigning module-level attributes that inherit from unittest.TestCase
# is all that is needed to register tests.
filelogindextests = storagetesting.makeifileindextests(
    makefilefn, maketransaction, addrawrevision
)
filelogdatatests = storagetesting.makeifiledatatests(
    makefilefn, maketransaction, addrawrevision
)
filelogmutationtests = storagetesting.makeifilemutationtests(
    makefilefn, maketransaction, addrawrevision
)


def makesqlitefile(self):
    path = STATE['vfs'].join(b'db-%d.db' % STATE['lastindex'])
    STATE['lastindex'] += 1

    db = sqlitestore.makedb(path)

    compression = b'zstd' if zstd else b'zlib'

    return sqlitestore.sqlitefilestore(db, b'dummy-path', compression)


def addrawrevisionsqlite(
    self,
    fl,
    tr,
    node,
    p1,
    p2,
    linkrev,
    rawtext=None,
    delta=None,
    censored=False,
    ellipsis=False,
    extstored=False,
):
    flags = 0

    if censored:
        flags |= sqlitestore.FLAG_CENSORED

    if ellipsis | extstored:
        raise error.Abort(
            b'support for ellipsis and extstored flags not ' b'supported'
        )

    if rawtext is not None:
        fl._addrawrevision(node, rawtext, tr, linkrev, p1, p2, flags=flags)
    elif delta is not None:
        fl._addrawrevision(
            node, rawtext, tr, linkrev, p1, p2, storedelta=delta, flags=flags
        )
    else:
        raise error.Abort(b'must supply rawtext or delta arguments')


if sqlitestore is not None:
    sqlitefileindextests = storagetesting.makeifileindextests(
        makesqlitefile, maketransaction, addrawrevisionsqlite
    )
    sqlitefiledatatests = storagetesting.makeifiledatatests(
        makesqlitefile, maketransaction, addrawrevisionsqlite
    )
    sqlitefilemutationtests = storagetesting.makeifilemutationtests(
        makesqlitefile, maketransaction, addrawrevisionsqlite
    )

if __name__ == '__main__':
    silenttestrunner.main(__name__)