Add simple Ruby server example (#17)

fix apache/arrow#40479

Author: kou

http/get_simple/ruby/server/.gitignore

@@ -0,0 +1,18 @@
+# Licensed to the Apache Software Foundation (ASF) under one
+# or more contributor license agreements.  See the NOTICE file
+# distributed with this work for additional information
+# regarding copyright ownership.  The ASF licenses this file
+# to you under the Apache License, Version 2.0 (the
+# "License"); you may not use this file except in compliance
+# with the License.  You may obtain a copy of the License at
+#
+#   http://www.apache.org/licenses/LICENSE-2.0
+#
+# Unless required by applicable law or agreed to in writing,
+# software distributed under the License is distributed on an
+# "AS IS" BASIS, WITHOUT WARRANTIES OR CONDITIONS OF ANY
+# KIND, either express or implied.  See the License for the
+# specific language governing permissions and limitations
+# under the License.
+
+/Gemfile.lock

http/get_simple/ruby/server/Gemfile

@@ -0,0 +1,21 @@
+# Licensed to the Apache Software Foundation (ASF) under one
+# or more contributor license agreements.  See the NOTICE file
+# distributed with this work for additional information
+# regarding copyright ownership.  The ASF licenses this file
+# to you under the Apache License, Version 2.0 (the
+# "License"); you may not use this file except in compliance
+# with the License.  You may obtain a copy of the License at
+#
+#   http://www.apache.org/licenses/LICENSE-2.0
+#
+# Unless required by applicable law or agreed to in writing,
+# software distributed under the License is distributed on an
+# "AS IS" BASIS, WITHOUT WARRANTIES OR CONDITIONS OF ANY
+# KIND, either express or implied.  See the License for the
+# specific language governing permissions and limitations
+# under the License.
+
+source "https://rubygems.org/"
+
+gem "rackup"
+gem "red-arrow"

http/get_simple/ruby/server/README.md

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+<!---
+  Licensed to the Apache Software Foundation (ASF) under one
+  or more contributor license agreements.  See the NOTICE file
+  distributed with this work for additional information
+  regarding copyright ownership.  The ASF licenses this file
+  to you under the Apache License, Version 2.0 (the
+  "License"); you may not use this file except in compliance
+  with the License.  You may obtain a copy of the License at
+
+    http://www.apache.org/licenses/LICENSE-2.0
+
+  Unless required by applicable law or agreed to in writing,
+  software distributed under the License is distributed on an
+  "AS IS" BASIS, WITHOUT WARRANTIES OR CONDITIONS OF ANY
+  KIND, either express or implied.  See the License for the
+  specific language governing permissions and limitations
+  under the License.
+-->
+
+# HTTP GET Arrow Data: Simple Ruby Server Example
+
+This directory contains a minimal example of an HTTP server implemented in Ruby. The server:
+1. Creates a list of record batches and populates it with synthesized data.
+2. Listens for HTTP GET requests from clients.
+3. Upon receiving a request, sends an HTTP 200 response with the body containing an Arrow IPC stream of record batches.
+
+To run this example:
+
+```sh
+bundle install
+bundle exec rackup --port=8008
+```

http/get_simple/ruby/server/config.ru

@@ -0,0 +1,94 @@
+# Licensed to the Apache Software Foundation (ASF) under one
+# or more contributor license agreements.  See the NOTICE file
+# distributed with this work for additional information
+# regarding copyright ownership.  The ASF licenses this file
+# to you under the Apache License, Version 2.0 (the
+# "License"); you may not use this file except in compliance
+# with the License.  You may obtain a copy of the License at
+#
+#   http://www.apache.org/licenses/LICENSE-2.0
+#
+# Unless required by applicable law or agreed to in writing,
+# software distributed under the License is distributed on an
+# "AS IS" BASIS, WITHOUT WARRANTIES OR CONDITIONS OF ANY
+# KIND, either express or implied.  See the License for the
+# specific language governing permissions and limitations
+# under the License.
+
+require "arrow"
+
+class ArrowStreamGenerator
+  def initialize(env)
+    @env = env
+    @schema = Arrow::Schema.new(a: :int64,
+                                b: :int64,
+                                c: :int64,
+                                d: :int64)
+    generate_record_batches
+  end
+
+  def each(&block)
+    body = RackBody.new(block, need_manual_chunked?)
+    Gio::RubyOutputStream.open(body) do |gio_output|
+      Arrow::GIOOutputStream.open(gio_output) do |arrow_output|
+        Arrow::RecordBatchStreamWriter.open(arrow_output, @schema) do |writer|
+          @record_batches.each do |record_batch|
+            writer.write_record_batch(record_batch)
+          end
+        end
+      end
+    end
+  end
+
+  private
+  def need_manual_chunked?
+    not (@env["SERVER_SOFTWARE"] || "").start_with?("WEBrick")
+  end
+
+  def generate_record_batches
+    n_total_records = 100000000
+    n_columns = 4
+
+    n_rows = 4096
+    max_int64 = 2 ** 63 - 1
+    arrays = n_columns.times.collect do
+      Arrow::Int64Array.new(n_rows.times.collect {rand(max_int64)})
+    end
+
+    record_batch = Arrow::RecordBatch.new(@schema, n_rows, arrays)
+    @record_batches = [record_batch] * (n_total_records / n_rows)
+    n_remained_records = n_total_records % n_rows
+    if n_remained_records
+      @record_batches << record_batch.slice(0, n_remained_records)
+    end
+  end
+
+  class RackBody
+    def initialize(block, need_manual_chunked)
+      @block = block
+      @need_manual_chunked = need_manual_chunked
+    end
+
+    def write(buffer)
+      @block.call("#{buffer.bytesize.to_s(16)}\r\n") if @need_manual_chunked
+      @block.call(buffer)
+      @block.call("\r\n") if @need_manual_chunked
+      buffer.bytesize
+    end
+
+    def flush
+    end
+
+    def close
+      @block.call("0\r\n\r\n") if @need_manual_chunked
+    end
+  end
+end
+
+run do |env|
+  headers = {
+    "content-type" => "application/vnd.apache.arrow.stream",
+    "transfer-encoding" => "chunked",
+  }
+  [200, headers, ArrowStreamGenerator.new(env)]
+end