Eclipse Zenoh

The Eclipse Zenoh: Zero Overhead Pub/sub, Store/Query and Compute.

Zenoh (pronounce /zeno/) unifies data in motion, data at rest and computations. It carefully blends traditional pub/sub with geo-distributed storages, queries and computations, while retaining a level of time and space efficiency that is well beyond any of the mainstream stacks.

Check the website zenoh.io and the roadmap for more detailed information.

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C API

This repository provides a C binding based on the main Zenoh implementation written in Rust.

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How to build it

⚠️ WARNING ⚠️ : Zenoh and its ecosystem are under active development. When you build from git, make sure you also build from git any other Zenoh repository you plan to use (e.g. binding, plugin, backend, etc.). It may happen that some changes in git are not compatible with the most recent packaged Zenoh release (e.g. deb, docker, pip). We put particular effort in mantaining compatibility between the various git repositories in the Zenoh project.

1. Make sure that Rust is available on your platform. Please check here to learn how to install it.

2. Clone the source with git:

   git clone https://github.com/eclipse-zenoh/zenoh-c.git

3. Build:

Good CMake practice is to perform build outside of source directory, leaving source tree untouched. The examples below demonstrates this mode of building. On the other hand VScode by default creates build directory named 'build' inside source tree. In this case build script sligthly changes its behavior. See more about it in section 'VScode'.

By default build configuration is set to Release, it's not necessary to add -DCMAKE_BUILD_TYPE=Release option on configuration step. But if your platform uses multi-config generator by default (this is the case on Windows), you may need to add option --config Release on build step. See more in CMake build-configurations documenation. Option--config Release is skipped in further examples for brewity. It's actually necessary for Visual Studio generators only. For Ninja Multi-Config the build script is able to select Release as the default configuration.

$ mkdir -p build && cd build 
$ cmake ../zenoh-c
$ cmake --build . --config Release

The generator to use is selected with option -G. If Ninja is installed on your system, adding -GNinja to cmake command can greatly speed up the build time:

$ cmake ../zenoh-c -GNinja
$ cmake --build .

3. Install:

To install zenoh-c library into system just build target install. You need root privileges to do it, as the default install location is /usr/local.

$ cmake --build . --target install

If you want to install zenoh-c libraries locally, you can set the installation directory with CMAKE_INSTALL_PREFIX

$ cmake ../zenoh-c -DCMAKE_INSTALL_PREFIX=~/.local
$ cmake --build . --target install

By default only dynamic library is installed. Set ZENOHC_INSTALL_STATIC_LIBRARY variable to install static library also:

$ cmake ../zenoh-c -DCMAKE_INSTALL_PREFIX=~/.local -DZENOHC_INSTALL_STATIC_LIBRARY=TRUE
$ cmake --build . --target install

The result of installation is the header files in include directory, the library files in lib directory and cmake package configuration files for package zenohc in lib/cmake directory. The library later can be loaded with CMake command find_package(zenohc). Link to targets zenohc::lib for dynamic library and zenohc::static for static one in your CMakeLists.txt configuration file.

For Debug configuration the library package zenohc_debug is installed side-by-side with release zenohc library. Suffix d is added to names of library files (libzenohcd.so).

4. VScode

When zenoh-c project is opened in VSCode the build directory is set to build inside source tree (this is default behavior of Microsoft CMake Tools). The project build script detects this situation. In this case it places build files in target directory and Cargo.toml file (which is generated from Cargo.toml.in) into the root of source tree, as the rust developers used to and as the rust build tools expects by default. This behavior also can be explicitly enabled by setting ZENOHC_BUILD_IN_SOURCE_TREE variable to TRUE.

Building the Examples

The examples can be built in two ways. One is to select examples as a build target of zenoh-c project (assuming here that the current directory is side-by-side with zenoh-c directory):

$ cmake ../zenoh-c
$ cmake --build . --target examples

You may also use --target <example_name> if you wish to only build a specific example.

All build artifacts will be in the target/release/examples directory in this case.

Second way is to directly build examples as a root project:

$ cmake ../zenoh-c/examples
$ cmake --build .

In this case the examples executables will be built in the current directory.

As a root project the examples project links zenoh-c with CMake's add_subdirectory command by default. There are also other ways to link zenoh-c - with find_package or FetchContent:

Link with zenoh-c installed into default location in the system (with find_package):

$ cmake ../zenoh-c/examples -DZENOHC_SOURCE=PACKAGE

Link with zenoh-c installed in ~/.local directory:

$ cmake ../zenoh-c/examples -DZENOHC_SOURCE=PACKAGE -DCMAKE_INSTALL_PREFIX=~/.local

Download specific zenoh-c version from git with FetchContent:

$ cmake ../zenoh-c/examples -DZENOHC_SOURCE=GIT_URL -DZENOHC_GIT_TAG=0.8.0-rc

See also configure_include_project function in helpers.cmake for more information

Running the Examples

Basic Pub/Sub Example

$ ./target/release/examples/z_sub

$ ./target/release/examples/z_pub

Queryable and Query Example

$ ./target/release/examples/z_queryable

$ ./target/release/examples/z_get

Running the Throughput Examples

$ ./target/release/examples/z_sub_thgr

$ ./target/release/examples/z_pub_thgr

API conventions

Many of the types exposed by the zenoh-c API are types for which destruction is necessary. To help you spot these types, we named them with the convention that any destructible type must start by z_owned.

For maximum performance, we try to make as few copies as possible. Sometimes, this implies moving data that you z_owned. Any function that takes a non-const pointer to a z_owned type will perform its destruction. To make this pattern more obvious, we encourage you to use the z_move macro instead of a simple & to create these pointers. Rest assured that all z_owned types are double-free safe, and that you may check whether any z_owned_X_t typed value is still valid by using z_X_check(&val), or the z_check(val) macro if you're using C11.

We hope this convention will help you streamline your memory-safe usage of zenoh, as following it should make looking for leaks trivial: simply search for paths where a value of a z_owned type hasn't been passed to a function using z_move.

Functions that simply need to borrow your data will instead take values of the associated z_X_t type. You may construct them using z_X_loan(&val) (or the z_loan(val) generic macro with C11).

Note that some z_X_t typed values can be constructed without needing to z_borrow their owned variants. This allows you to reduce the amount of copies realized in your program.

The examples have been written with C11 in mind, using the conventions we encourage you to follow.

Finally, we strongly advise that you refrain from using structure field that starts with _:

• We try to maintain a common API between zenoh-c and zenoh-pico, such that porting code from one to the other is, ideally, trivial. However, some types must have distinct representations in either library, meaning that using these representations explicitly will get you in trouble when porting.
• We reserve the right to change the memory layout of any type which has _-prefixed fields, so trying to use them might cause your code to break on updates.

Logging

By default, zenoh-c enables Zenoh's logging library upon using the z_open or z_scout functions. This behaviour can be disabled by adding -DDISABLE_LOGGER_AUTOINIT:bool=true to the cmake configuration command. The logger may then be manually re-enabled with the zc_init_logger function.

Cross-Compilation

• The following alternative options have been introduced to facilitate cross-compilation.

⚠️ WARNING ⚠️ : Perhaps aditional efforts are neccesary, that will depend of your enviroment.

• -DZENOHC_CARGO_CHANNEL=nightly|beta|stable: refers to a specific rust toolchain release [rust-channels] https://rust-lang.github.io/rustup/concepts/channels.html
• -DZENOHC_CARGO_FLAGS: several optional flags can be used for compilation. [cargo flags] https://doc.rust-lang.org/cargo/commands/cargo-build.html
• -DZENOHC_CUSTOM_TARGET: specifies a crosscompilation target. Currently rust support several Tire-1, Tire-2 and Tire-3 targets [targets] https://doc.rust-lang.org/nightly/rustc/platform-support.html. But keep in mind that zenoh-c only have support for following targets: aarch64-unknown-linux-gnu, x86_64-unknown-linux-gnu, arm-unknown-linux-gnueabi

Lets put all together in an example: Assuming you want to crosscompile for aarch64-unknown-linux-gnu.

1. install required packages

• sudo apt install gcc-aarch64-linux-gnu

2. *(Only if you use nightly )

• rustup component add rust-src --toolchain nightly

3. Compile Zenoh-C. Assume that it's in 'zenoh-c' directory. Notice that build in this sample is performed outside of source directory

$ export RUSTFLAGS="-Clinker=aarch64-linux-gnu-gcc -Car=aarch64-linux-gnu-ar"
$ mkdir -p build && cd build
$ cmake ../zenoh-c  -DZENOHC_CARGO_CHANNEL=nightly -DZENOHC_CARGO_FLAGS="-Zbuild-std=std,panic_abort" -DZENOHC_CUSTOM_TARGET="aarch64-unknown-linux-gnu" -DCMAKE_INSTALL_PREFIX=../aarch64/stage
$ cmake --build . --target install

Additionaly you can use RUSTFLAGS enviroment variable for lead the compilation.

If all goes right the building files will be located at: /path/to/zenoh-c/target/aarch64-unknown-linux-gnu/release and release files will be located at /path/to/zenoh-c/target/aarch64-unknown-linux-gnu/release