Add 2 crystal LibIPC examples.

crystal/.gitignore

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+/docs/
+/lib/
+/bin/
+/.shards/
+*.dwarf
+shard.lock

crystal/README.md

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+# LibIPC examples
+
+Crystal LibIPC examples, using [libipc bindings shard][bindings].
+
+## Installation
+
+```sh
+# Compiles all examples.
+shards build
+```
+
+Currently there are 2 examples:
+- pongd (server): repeating every message
+- pong (client): sending a message to the pong service and waiting for response
+
+## Usage
+
+```sh
+# Run the service
+./bin/pongd # run the service
+./bin/pong  # run the client
+```
+
+# LICENCE
+
+ISC
+
+[bindings]: https://git.baguette.netlib.re/Baguette/ipc.cr

crystal/shard.yml

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+name: libipc-examples
+version: 0.1.0
+
+authors:
+  - Philippe Pittoli <karchnu@karchnu.fr>
+
+description: |
+  Examples of applications using libipc.
+
+targets:
+  pong:
+    main: src/pong.cr
+  pongd:
+    main: src/pongd.cr
+
+dependencies:
+  ipc:
+    git: https://git.baguette.netlib.re/Baguette/ipc.cr
+    branch: master
+
+crystal: 1.7.1
+
+license: ISC

crystal/src/pong.cr

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+require "ipc"
+
+ipc = IPC.new
+ipc.timer 5000 # timer event every 5 seconds
+fd = ipc.connect "pong" # 'pong' service
+
+# Schedule a message to send to a particular file descriptor
+ipc.schedule fd, "Hello this is me!"
+
+ipc.loop do |event|
+  case event.type
+  when LibIPC::EventType::MessageRx
+    m = event.message
+    if m.nil?
+      puts "Err, should have received smth :("
+      exit 1
+    else
+      received = String.new(m.to_unsafe, m.size)
+      puts "msg received: #{received}"
+      if "Hello this is me!".compare(received) == 0
+        puts "All good! Goodbye!"
+        exit 0
+      end
+      puts "Received message isn't what was expected!"
+      exit 1
+    end
+  when LibIPC::EventType::MessageTx
+    puts "A message has been sent"
+  when LibIPC::EventType::Connection
+    puts "A client just connected #JOY"
+  when LibIPC::EventType::Disconnection
+    puts "A client just disconnected #SAD"
+  when LibIPC::EventType::Timer
+    STDOUT.write "\rTimer!".to_slice
+  else
+    puts "Unexpected: #{event.type}"
+    exit 1
+  end
+end

crystal/src/pongd.cr

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+require "ipc"
+
+ipc = IPC.new
+ipc.timer 5000 # timer event every 5 seconds
+fd = ipc.service_init "pong"
+
+ipc.loop do |event|
+  case event.type
+  when LibIPC::EventType::MessageRx
+    m = event.message
+    if m.nil?
+      puts "No message"
+    else
+      received = String.new(m.to_unsafe, m.size)
+      pp! received
+      ipc.schedule event.fd, m, m.size
+    end
+  when LibIPC::EventType::MessageTx
+    puts "A message has been sent"
+  when LibIPC::EventType::Connection
+    puts "A client just connected #JOY"
+  when LibIPC::EventType::Disconnection
+    puts "A client just disconnected #SAD"
+  when LibIPC::EventType::Timer
+    STDOUT.write "\rTimer!".to_slice
+  else
+    puts "Unexpected: #{event.type}"
+    exit 1
+  end
+end