libbz2-rs-sys-cdylib

A drop-in replacement for the libbz2 dynamic library

# build the cdylib
# using `cargo build` will work but has limitations, see below
cargo build --release

# the extension of a cdylib varies per platform
cc bzpipe.c -o bzpipe target/release/libbz2_rs.so -I ../

# verify the implementation can compress and decompress our Cargo.toml
./bzpipe < Cargo.toml | ./bzpipe -d

By default this build uses libc malloc/free to (de)allocate memory, and only depends on the rust core library. See below for the available feature flags.

Feature Flags

Allocators

We provide three options for the default allocator

c-allocator

cargo build --release --no-default-features --features "c-allocator"

Uses the libc malloc and free functions for memory allocation.

rust-allocator

cargo build --release --no-default-features --features "std,rust-allocator"

Uses the rust standard library global allocator for memory allocation.

no allocator

cargo build --release --no-default-features

No allocator is configured automatically. This means that, before BZ2_bzCompressInit or BZ2_bzDecompressInit are called, the user must set the bzalloc and bzfree fields of the bz_stream to valid allocation and deallocation functions, and the opaque field to either NULL or a pointer expected by the (de)allocation functions.

If no allocator is configured, the initialization functions will return BZ_PARAM_ERROR.

Symbol Prefix

Symbols in C programs all live in the same namespace. A common solution to prevent names from clashing is to prefix all of a library's symbols with a prefix. We support prefixing the name at build time with the custom-prefix feature flag. When enabled, the value of the LIBBZ2_RS_SYS_PREFIX is used as a prefix for all exported symbols. For example:

> LIBBZ2_RS_SYS_PREFIX="MY_CUSTOM_PREFIX_" cargo build --release --features=custom-prefix

   Compiling libbz2-rs-sys v0.0.0 (libbz2-rs/libbz2-rs-sys)
   Compiling libz-rs-sys-cdylib v0.0.0 (libbz2-rs/libbz2-rs-sys-cdylib)
    Finished `release` profile [optimized] target(s) in 0.97s
> objdump -tT target/release/libbz2_rs.so | grep "BZ2_bzCompressInit"
000000000002f300 l     F .text	0000000000000441              .hidden _ZN15libbz2_rs_sys5bzlib22BZ2_bzCompressInitHelp17hac60bda3d983fe05E
000000000002f2e0 g     F .text	000000000000001a              MY_CUSTOM_PREFIX_BZ2_bzCompressInit
000000000002f2e0 g    DF .text	000000000000001a  Base        MY_CUSTOM_PREFIX_BZ2_bzCompressInit

#![no_std]

The dynamic library can be built without the rust std crate, e.g. for embedded devices that don't support it. Disabling the standard library has the following limitations:

• The rust-allocator should not be used. It internally enables the standard library, causing issues. Using c-allocator or not providing an allocator at build time is still supported.On embedded it is most common to provide a custom allocator that "allocates" into a custom array.

Build for Distribution

A cargo build currently does not set some fields that are required or useful when using a dynamic library from C. For instance, the soname and version are not set by a standard cargo build.

To build a proper, installable dynamic library, we recommend cargo-c:

cargo install cargo-c

This tool deals with setting fields (soname, version) that a normal cargo build does not set (today). It's configuration is in the Cargo.toml, where e.g. the library name or version can be changed.

> cargo cbuild --release
   Compiling libc v0.2.167
   Compiling libbz2-rs-sys v0.0.0 (libbz2-rs/libbz2-rs-sys)
   Compiling libz-rs-sys-cdylib v0.0.0 (libbz2-rs/libbz2-rs-sys-cdylib)
    Finished `release` profile [optimized] target(s) in 1.63s
    Building pkg-config files
> tree target
target
├── CACHEDIR.TAG
└── x86_64-unknown-linux-gnu
    ├── CACHEDIR.TAG
    └── release
        ├── examples
        ├── incremental
        ├── libbz2_rs.a
        ├── libbz2_rs.d
        ├── libbz2_rs.pc
        ├── libbz2_rs.so
        └── libbz2_rs-uninstalled.pc