Implement kotlinx-datetime for the Android native targets

To test, run an Android emulator, and then, in the command line,
./gradlew androidNativeArm64TestBinaries && adb push core/build/bin/androidNativeArm64/debugTest/test.kexe /data/local/tmp/ && adb shell /data/local/tmp/test.kexe

Change `Arm64` to another platfom (`X86`, `X64`, or `Arm32`)
as needed.

Author: dkhalanskyjb

core/android/src/internal/TimeZoneNative.kt

@@ -0,0 +1,27 @@
+/*
+ * Copyright 2019-2023 JetBrains s.r.o.
+ * Use of this source code is governed by the Apache 2.0 License that can be found in the LICENSE.txt file.
+ */
+
+@file:OptIn(ExperimentalForeignApi::class)
+package kotlinx.datetime.internal
+
+import kotlinx.cinterop.*
+import platform.posix.*
+
+internal actual val systemTzdb: TimeZoneDatabase get() = tzdb.getOrThrow()
+
+private val tzdb = runCatching { TzdbBionic() }
+
+internal actual fun currentSystemDefaultZone(): Pair<String, TimeZoneRules?> = memScoped {
+    val name = readSystemProperty("persist.sys.timezone")
+        ?: throw IllegalStateException("The system property 'persist.sys.timezone' should contain the system timezone")
+    return name to null
+}
+
+private fun readSystemProperty(name: String): String? = memScoped {
+    // see https://android.googlesource.com/platform/bionic/+/froyo/libc/include/sys/system_properties.h
+    val result = allocArray<ByteVar>(92)
+    val error = __system_property_get(name, result)
+    if (error == 0) null else result.toKString()
+}

core/android/src/internal/TzdbBionic.kt

@@ -0,0 +1,72 @@
+/*
+ * Copyright 2019-2024 JetBrains s.r.o. and contributors.
+ * Use of this source code is governed by the Apache 2.0 License that can be found in the LICENSE.txt file.
+ */
+/*
+ * Based on the bionic project.
+ * Copyright (C) 2017 The Android Open Source Project
+ */
+
+package kotlinx.datetime.internal
+
+private class TzdbBionic(private val rules: Map<String, Entry>) : TimeZoneDatabase {
+    override fun rulesForId(id: String): TimeZoneRules =
+        rules[id]?.readRules() ?: throw IllegalStateException("Unknown time zone $id")
+
+    override fun availableTimeZoneIds(): Set<String> = rules.keys
+
+    class Entry(val file: ByteArray, val offset: Int, val length: Int) {
+        fun readRules(): TimeZoneRules = readTzFile(file.copyOfRange(offset, offset + length)).toTimeZoneRules()
+    }
+}
+
+// see https://android.googlesource.com/platform/bionic/+/master/libc/tzcode/bionic.cpp for the format
+internal fun TzdbBionic(): TimeZoneDatabase = TzdbBionic(buildMap<String, TzdbBionic.Entry> {
+    for (path in listOf(
+        Path.fromString("/system/usr/share/zoneinfo/tzdata"), // immutable fallback tzdb
+        Path.fromString("/apex/com.android.tzdata/etc/tz/tzdata"), // an up-to-date tzdb, may not exist
+    )) {
+        if (path.check() == null) continue // the file does not exist
+        // be careful to only read each file a single time and keep many references to the same ByteArray in memory.
+        val content = path.readBytes()
+        val header = BionicTzdbHeader.parse(content)
+        val indexSize = header.data_offset - header.index_offset
+        check(indexSize % 52 == 0) { "Invalid index size: $indexSize (must be a multiple of 52)" }
+        val reader = BinaryDataReader(content, header.index_offset)
+        repeat(indexSize / 52) {
+            val name = reader.readNullTerminatedUtf8String(40)
+            val start = reader.readInt()
+            val length = reader.readInt()
+            reader.readInt() // unused
+            // intentionally overwrite the older entries
+            put(name, TzdbBionic.Entry(content, header.data_offset + start, length))
+        }
+    }
+})
+
+// bionic_tzdata_header_t
+private class BionicTzdbHeader(
+    val version: String,
+    val index_offset: Int,
+    val data_offset: Int,
+    val final_offset: Int,
+) {
+    override fun toString(): String =
+        "BionicTzdbHeader(version='$version', index_offset=$index_offset, " +
+            "data_offset=$data_offset, final_offset=$final_offset)"
+
+    companion object {
+        fun parse(content: ByteArray): BionicTzdbHeader =
+            with(BinaryDataReader(content)) {
+                BionicTzdbHeader(
+                    version = readNullTerminatedUtf8String(12),
+                    index_offset = readInt(),
+                    data_offset = readInt(),
+                    final_offset = readInt(),
+                )
+            }.apply {
+                check(version.startsWith("tzdata") && version.length < 12) { "Unknown tzdata version: $version" }
+                check(index_offset <= data_offset) { "Invalid data and index offsets: $data_offset and $index_offset" }
+            }
+    }
+}

core/android/test/Util.kt

@@ -0,0 +1,10 @@
+/*
+ * Copyright 2019-2024 JetBrains s.r.o. and contributors.
+ * Use of this source code is governed by the Apache 2.0 License that can be found in the LICENSE.txt file.
+ */
+
+package kotlinx.datetime.test
+
+import kotlin.test.Ignore
+
+actual typealias NoAndroid = Ignore

core/build.gradle.kts

@@ -47,13 +47,12 @@ kotlin {
                 // Tier 4 (deprecated, but still in demand)
                 target("linuxArm32Hfp")
             }
-            // the following targets are not supported, as we don't have timezone database implementations for them:
-            /*
-            target("androidNativeArm32")
-            target("androidNativeArm64")
-            target("androidNativeX86")
-            target("androidNativeX64")
-             */
+            common("android") {
+                target("androidNativeArm32")
+                target("androidNativeArm64")
+                target("androidNativeX86")
+                target("androidNativeX64")
+            }
             common("darwin") {
                 common("darwinDevices") {
                     // Tier 1
@@ -157,10 +156,11 @@ kotlin {
                     }
                 }
             }
-            konanTarget.family == org.jetbrains.kotlin.konan.target.Family.LINUX -> {
-                // do nothing special
-            }
-            konanTarget.family.isAppleFamily -> {
+
+            konanTarget.family == org.jetbrains.kotlin.konan.target.Family.LINUX ||
+                konanTarget.family == org.jetbrains.kotlin.konan.target.Family.ANDROID ||
+                konanTarget.family.isAppleFamily ->
+            {
                 // do nothing special
             }
             else -> {

core/common/src/internal/BinaryDataReader.kt

@@ -42,8 +42,17 @@ internal class BinaryDataReader(private val bytes: ByteArray, private var positi
             (bytes[position + 6].toLong() and 0xFF shl 8) or
             (bytes[position + 7].toLong() and 0xFF).also { position += 8 }
 
-    fun readUtf8String(length: Int) =
-        bytes.decodeToString(position, position + length).also { position += length }
+    fun readUtf8String(exactLength: Int) =
+        bytes.decodeToString(position, position + exactLength).also { position += exactLength }
+
+    fun readNullTerminatedUtf8String(fieldSize: Int): String {
+        var exactLength = 0
+        while (position + exactLength < bytes.size && bytes[position + exactLength] != 0.toByte() && exactLength < fieldSize) {
+            ++exactLength
+        }
+        return bytes.decodeToString(position, position + exactLength)
+            .also { position += fieldSize }
+    }
 
     fun readAsciiChar(): Char = readByte().toInt().toChar()
 

core/nix/test/TimeZoneRulesCompleteTest.kt

@@ -15,6 +15,7 @@ import kotlin.test.*
 class TimeZoneRulesCompleteTest {
     @OptIn(ExperimentalEncodingApi::class)
     @Test
+    @NoAndroid
     fun iterateOverAllTimezones() {
         val root = Path.fromString("/usr/share/zoneinfo")
         val tzdb = TzdbOnFilesystem(root)
@@ -67,7 +68,7 @@ private inline fun runUnixCommand(command: String): Sequence<String> = sequence
             // read line by line
             while (true) {
                 val linePtr = alloc<CPointerVar<ByteVar>>()
-                val nPtr = alloc<ULongVar>()
+                val nPtr = alloc<size_tVar>()
                 try {
                     val result = getline(linePtr.ptr, nPtr.ptr, pipe)
                     if (result != (-1).convert<ssize_t>()) {

core/nix/test/Util.kt

@@ -5,6 +5,10 @@
 
 package kotlinx.datetime.test
 
+@OptIn(ExperimentalMultiplatform::class)
+@OptionalExpectation
+expect annotation class NoAndroid()
+
 // od --format=x1 --output-duplicates --address-radix=n --width=16 /usr/share/zoneinfo/Europe/Berlin |
 // sed -e 's/\b\(\w\)/0x\1/g' -e 's/\(\w\)\b/\1,/g'
 // Do not remove the type annotation, otherwise the compiler slows down to a crawl for this file even more.

license/README.md

@@ -27,5 +27,8 @@ may apply:
       https://raw.githubusercontent.com/unicode-org/cldr/master/common/supplemental/windowsZones.xml
     - License: Unicode ([license/thirdparty/unicode_license.txt](thirdparty/unicode_license.txt))
 
+- Path: `core/android/src`
+    - Origin: implementation is based on the bionic project.
+    - License: BSD ([license/thirdparty/bionic_license.txt](thirdparty/bionic_license.txt))
 
 [threetenbp]: thirdparty/threetenbp_license.txt

license/thirdparty/bionic_license.txt

@@ -0,0 +1,25 @@
+Copyright (C) 2017 The Android Open Source Project
+All rights reserved.
+
+Redistribution and use in source and binary forms, with or without
+modification, are permitted provided that the following conditions
+are met:
+ * Redistributions of source code must retain the above copyright
+   notice, this list of conditions and the following disclaimer.
+ * Redistributions in binary form must reproduce the above copyright
+   notice, this list of conditions and the following disclaimer in
+   the documentation and/or other materials provided with the
+   distribution.
+
+THIS SOFTWARE IS PROVIDED BY THE COPYRIGHT HOLDERS AND CONTRIBUTORS
+"AS IS" AND ANY EXPRESS OR IMPLIED WARRANTIES, INCLUDING, BUT NOT
+LIMITED TO, THE IMPLIED WARRANTIES OF MERCHANTABILITY AND FITNESS
+FOR A PARTICULAR PURPOSE ARE DISCLAIMED. IN NO EVENT SHALL THE
+COPYRIGHT OWNER OR CONTRIBUTORS BE LIABLE FOR ANY DIRECT, INDIRECT,
+INCIDENTAL, SPECIAL, EXEMPLARY, OR CONSEQUENTIAL DAMAGES (INCLUDING,
+BUT NOT LIMITED TO, PROCUREMENT OF SUBSTITUTE GOODS OR SERVICES; LOSS
+OF USE, DATA, OR PROFITS; OR BUSINESS INTERRUPTION) HOWEVER CAUSED
+AND ON ANY THEORY OF LIABILITY, WHETHER IN CONTRACT, STRICT LIABILITY,
+OR TORT (INCLUDING NEGLIGENCE OR OTHERWISE) ARISING IN ANY WAY OUT
+OF THE USE OF THIS SOFTWARE, EVEN IF ADVISED OF THE POSSIBILITY OF
+SUCH DAMAGE.