[Kotlin][FlexBuffers] JSON support for Flexbuffers (#6417)

* [Kotlin][FlexBuffers] Add JSON support for FlexBuffers

* [Kotlin][Flexbuffers] Re-implement JSON parser with a tokenizer.

kotlin/benchmark/build.gradle.kts

@@ -5,6 +5,7 @@ plugins {
   id("org.jetbrains.kotlin.plugin.allopen") version "1.4.20"
   id("kotlinx.benchmark") version "0.2.0-dev-20"
   id("io.morethan.jmhreport") version "0.9.0"
+  id("de.undercouch.download") version "4.1.1"
 }
 
 // allOpen plugin is needed for the benchmark annotations.
@@ -32,6 +33,8 @@ benchmark {
       iterations = 5
       iterationTime = 300
       iterationTimeUnit = "ms"
+      // uncomment for benchmarking JSON op only
+      // include(".*JsonBenchmark.*")
     }
   }
   targets {
@@ -76,6 +79,11 @@ kotlin {
         implementation("org.jetbrains.kotlin:kotlin-stdlib-jdk8")
         implementation("org.jetbrains.kotlinx:kotlinx-coroutines-core-jvm:1.4.1")
 
+        //moshi
+        implementation("com.squareup.moshi:moshi-kotlin:1.11.0")
+
+        //gson
+        implementation("com.google.code.gson:gson:2.8.5")
       }
     }
 
@@ -88,3 +96,16 @@ kotlin {
     }
   }
 }
+
+// This task download all JSON files used for benchmarking
+tasks.register<de.undercouch.gradle.tasks.download.Download>("downloadMultipleFiles") {
+  // We are downloading json benchmark samples from serdes-rs project.
+  // see: https://github.com/serde-rs/json-benchmark/blob/master/data
+  val baseUrl = "https://github.com/serde-rs/json-benchmark/raw/master/data/"
+  src(listOf("$baseUrl/canada.json", "$baseUrl/twitter.json", "$baseUrl/citm_catalog.json"))
+  dest(File("${project.projectDir.absolutePath}/src/jvmMain/resources"))
+}
+
+project.tasks.named("compileKotlinJvm") {
+  dependsOn("downloadMultipleFiles")
+}

kotlin/benchmark/src/jvmMain/kotlin/com/google/flatbuffers/kotlin/benchmark/FlexBuffersBenchmark.kt

@@ -35,7 +35,7 @@ import java.util.concurrent.TimeUnit
 @BenchmarkMode(Mode.AverageTime)
 @OutputTimeUnit(TimeUnit.NANOSECONDS)
 @Measurement(iterations = 20, time = 1, timeUnit = TimeUnit.NANOSECONDS)
-class KotlinBenchmark {
+class FlexBuffersBenchmark {
 
   var initialCapacity = 1024
   var value: Double = 0.0

kotlin/benchmark/src/jvmMain/kotlin/com/google/flatbuffers/kotlin/benchmark/JsonBenchmark.kt

@@ -0,0 +1,121 @@
+/*
+ * Copyright 2021 Google Inc. All rights reserved.
+ *
+ * Licensed 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.
+ */
+package com.google.flatbuffers.kotlin.benchmark
+
+import com.google.flatbuffers.kotlin.ArrayReadBuffer
+import com.google.flatbuffers.kotlin.JSONParser
+import com.google.flatbuffers.kotlin.Reference
+import com.google.flatbuffers.kotlin.toJson
+import com.google.gson.Gson
+import com.google.gson.JsonObject
+import com.google.gson.JsonParser
+import com.squareup.moshi.Moshi
+import com.squareup.moshi.kotlin.reflect.KotlinJsonAdapterFactory
+import kotlinx.benchmark.Blackhole
+import okio.Buffer
+import org.openjdk.jmh.annotations.Benchmark
+import org.openjdk.jmh.annotations.BenchmarkMode
+import org.openjdk.jmh.annotations.Measurement
+import org.openjdk.jmh.annotations.Mode
+import org.openjdk.jmh.annotations.OutputTimeUnit
+import org.openjdk.jmh.annotations.Scope
+import org.openjdk.jmh.annotations.State
+import java.io.ByteArrayInputStream
+import java.io.InputStreamReader
+import java.util.concurrent.TimeUnit
+
+@State(Scope.Benchmark)
+@BenchmarkMode(Mode.AverageTime)
+@OutputTimeUnit(TimeUnit.MICROSECONDS)
+@Measurement(iterations = 100, time = 1, timeUnit = TimeUnit.MICROSECONDS)
+class JsonBenchmark {
+
+  final val moshi = Moshi.Builder()
+    .addLast(KotlinJsonAdapterFactory())
+    .build()
+  final val moshiAdapter = moshi.adapter(Map::class.java)
+
+  final val gson = Gson()
+  final val gsonParser = JsonParser()
+
+  val fbParser = JSONParser()
+
+  final val twitterData = this.javaClass.classLoader.getResourceAsStream("twitter.json")!!.readBytes()
+  final val canadaData = this.javaClass.classLoader.getResourceAsStream("canada.json")!!.readBytes()
+  final val citmData = this.javaClass.classLoader.getResourceAsStream("citm_catalog.json")!!.readBytes()
+
+  val fbCitmRef = JSONParser().parse(ArrayReadBuffer(citmData))
+  val moshiCitmRef = moshi.adapter(Map::class.java).fromJson(citmData.decodeToString())
+  val gsonCitmRef = gsonParser.parse(citmData.decodeToString())
+
+  fun readFlexBuffers(data: ByteArray): Reference = fbParser.parse(ArrayReadBuffer(data))
+
+  fun readMoshi(data: ByteArray): Map<*, *>? {
+    val buffer = Buffer().write(data)
+    return moshiAdapter.fromJson(buffer)
+  }
+
+  fun readGson(data: ByteArray): JsonObject {
+    val parser = JsonParser()
+    val jsonReader = InputStreamReader(ByteArrayInputStream(data))
+    return parser.parse(jsonReader).asJsonObject
+  }
+
+  // TWITTER
+  @Benchmark
+  fun readTwitterFlexBuffers(hole: Blackhole? = null) = hole?.consume(readFlexBuffers(twitterData))
+  @Benchmark
+  fun readTwitterMoshi(hole: Blackhole?) = hole?.consume(readMoshi(twitterData))
+  @Benchmark
+  fun readTwitterGson(hole: Blackhole?) = hole?.consume(readGson(twitterData))
+
+  @Benchmark
+  fun roundTripTwitterFlexBuffers(hole: Blackhole? = null) = hole?.consume(readFlexBuffers(twitterData).toJson())
+  @Benchmark
+  fun roundTripTwitterMoshi(hole: Blackhole?) = hole?.consume(moshiAdapter.toJson(readMoshi(twitterData)))
+  @Benchmark
+  fun roundTripTwitterGson(hole: Blackhole?) = hole?.consume(gson.toJson(readGson(twitterData)))
+
+  // CITM
+  @Benchmark
+  fun readCITMFlexBuffers(hole: Blackhole? = null) = hole?.consume(readFlexBuffers(citmData))
+  @Benchmark
+  fun readCITMMoshi(hole: Blackhole?) = hole?.consume(moshiAdapter.toJson(readMoshi(citmData)))
+  @Benchmark
+  fun readCITMGson(hole: Blackhole?) = hole?.consume(gson.toJson(readGson(citmData)))
+
+  @Benchmark
+  fun roundTripCITMFlexBuffers(hole: Blackhole? = null) = hole?.consume(readFlexBuffers(citmData).toJson())
+  @Benchmark
+  fun roundTripCITMMoshi(hole: Blackhole?) = hole?.consume(moshiAdapter.toJson(readMoshi(citmData)))
+  @Benchmark
+  fun roundTripCITMGson(hole: Blackhole?) = hole?.consume(gson.toJson(readGson(citmData)))
+
+  @Benchmark
+  fun writeCITMFlexBuffers(hole: Blackhole? = null) = hole?.consume(fbCitmRef.toJson())
+  @Benchmark
+  fun writeCITMMoshi(hole: Blackhole?) = hole?.consume(moshiAdapter.toJson(moshiCitmRef))
+  @Benchmark
+  fun writeCITMGson(hole: Blackhole?) = hole?.consume(gson.toJson(gsonCitmRef))
+
+  // CANADA
+  @Benchmark
+  fun readCanadaFlexBuffers(hole: Blackhole? = null) = hole?.consume(readFlexBuffers(canadaData))
+  @Benchmark
+  fun readCanadaMoshi(hole: Blackhole?) = hole?.consume(readMoshi(canadaData))
+  @Benchmark
+  fun readCanadaGson(hole: Blackhole?) = hole?.consume(readGson(canadaData))
+}