util: add a file object proxy that can read at most N bytes
Sometimes we have data of a known size within a stream. For
performance reasons, we don't want to pre-read this data (we want
to allow consumers to read on demand). For simplicitly reasons,
we don't want callers to necessarily know their data is coming
from within an outer stream and there is a limit to how much
they should read.
The class introduced by this commit provides a very simple proxy
around an underlying file object that allows the consumer to
.read() up to N bytes from the file object. Attempts to read
past this many bytes results in a simulated EOF.
Differential Revision: https://phab.mercurial-scm.org/D2377
# Rust builds with a modern MSVC and uses a newer CRT.
# Python 2.7 has a shared library dependency on an older CRT (msvcr90.dll).
# We statically link the modern CRT to avoid multiple msvcr*.dll libraries
# being loaded and Python possibly picking up symbols from the newer runtime
# (which would be loaded first).
[target.'cfg(target_os = "windows")']
rustflags = ["-Ctarget-feature=+crt-static"]