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README.md

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+# ROS 2 Middleware Implementation for eProsima's Fast-RTPS
+
+`rmw_fastrtps` constitutes __[ROS 2](https://index.ros.org/doc/ros2/) default middleware implementation__, providing an interface between ROS 2 and [eProsima's](https://www.eprosima.com/index.php) [Fast-RTPS](https://github.com/eProsima/Fast-RTPS) middleware.
+
+## Getting started
+This implementation is available in all ROS 2 distributions, both from binaries and from sources.
+You do not need to do anything in order to use Fast-RTPS as your ROS 2 middleware layer (since it is the default implementation).
+However, you can still specify it in two different ways:
+
+1. Exporting `RMW_IMPLEMENTATION` environment variable:
+ ```bash
+ export RMW_IMPLEMENTATION=rmw_fastrtps_cpp
+ ```
+1. When launching your ROS 2 application:
+ ```bash
+ RMW_IMPLEMENTATION=rmw_fastrtps_cpp ros2 run <your_package> <your application>
+ ```
+
+## Two different RMW implementations
+
+`rmw_fastrtps` actually provides not one but two different ROS 2 middleware implementations, both of them using Fast-RTPS as middleware layer: `rmw_fastrtps_cpp` and `rmw_fastrtps_dynamic_cpp` (note that directory `rmw_fastrtps_shared_cpp` just contains the code that the two implementations share, and does not constitute a layer on its own).
+
+The main difference between the two is that `rmw_fastrtps_dynamic_cpp` uses introspection typesupport at run time to decide on the serialization/deserialization mechanism.
+On the other hand, `rmw_fastrtps_cpp` uses its own typesupport, which generates the mapping for each message type at build time.
+
+Mind that the default ROS 2 RMW implementation is `rmw_fastrtps_cpp`.
+You can however set it to `rmw_fastrtps_dynamic_cpp` using the environment variable `RMW_IMPLEMENTATION` as described above.
+
+## Advance usage
+
+`rmw_fastrtps` sets some of the Fast-RTPS configurable parameters:
+* History memory policy: `PREALLOCATED_WITH_REALLOC_MEMORY_MODE`
+* Publication mode: `ASYNCHRONOUS_PUBLISH_MODE`
+
+However, it is possible to fully configure Fast-RTPS (including the history memory policy and the publication mode) using an XML file as described in [Fast-RTPS documentation](https://eprosima-fast-rtps.readthedocs.io/en/latest/xmlprofiles.html).
+Then, you just need to set environment variable `RMW_FASTRTPS_USE_QOS_FROM_XML` to 1 (it is set to 0 by default).
+This tells `rmw_fastrtps` that it should not override neither the history memory policy nor the publication mode.
+
+You have two ways of telling you ROS 2 application which XML to use:
+1. Placing your XML file in the running directory under the name `DEFAULT_FASTRTPS_PROFILES.xml`.
+2. Setting environment variable `FASTRTPS_DEFAULT_PROFILES_FILE` to your XML file.
+
+## Example
+
+The following example configures Fast-RTPS to publish synchronously, and to have a pre-allocated history that can be expanded whenever it gets filled.
+
+1. Create a Fast-RTPS XML file with:
+
+ ```XML
+ <?xml version="1.0" encoding="UTF-8"?>
+ <dds xmlns="http://www.eprosima.com/XMLSchemas/fastRTPS_Profiles">
+ <profiles>
+ <publisher profile_name="publisher profile" is_default_profile="true">
+ <qos>
+ <publishMode>
+ <kind>SYNCHRONOUS</kind>
+ </publishMode>
+ </qos>
+ <historyMemoryPolicy>PREALLOCATED_WITH_REALLOC</historyMemoryPolicy>
+ </publisher>
+
+ <subscriber profile_name="subscriber profile" is_default_profile="true">
+ <historyMemoryPolicy>PREALLOCATED_WITH_REALLOC</historyMemoryPolicy>
+ </subscriber>
+ </profiles>
+ </dds>
+ ```
+
+1. Run the talker/listener ROS 2 demo:
+ 1. In one terminal
+
+ ```bash
+ FASTRTPS_DEFAULT_PROFILES_FILE=<path_to_xml_file> RMW_FASTRTPS_USE_QOS_FROM_XML=1 RMW_IMPLEMENTATION=rmw_fastrtps_cpp ros2 run demo_nodes_cpp talker
+ ```
+
+ 1. In another terminal
+
+ ```bash
+ FASTRTPS_DEFAULT_PROFILES_FILE=<path_to_xml_file> RMW_FASTRTPS_USE_QOS_FROM_XML=1 RMW_IMPLEMENTATION=rmw_fastrtps_cpp ros2 run demo_nodes_cpp listener
+ ```