No longer use stat in timezone database implementations (#385)

<https://developer.apple.com/documentation/bundleresources/privacy_manifest_files/describing_use_of_required_reason_api>
states that Apple will require the apps to declare all usages of
`stat`, as it can be used to check the file timestamps.

core/androidNative/src/internal/TzdbBionic.kt

@@ -26,9 +26,8 @@ internal fun TzdbBionic(): TimeZoneDatabase = TzdbBionic(buildMap<String, TzdbBi
         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 content = path.readBytes() ?: continue // this file does not exist
         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)" }

core/tzdbOnFilesystem/src/internal/TzdbOnFilesystem.kt

@@ -7,19 +7,28 @@ package kotlinx.datetime.internal
 
 internal class TzdbOnFilesystem(defaultTzdbPath: Path? = null): TimeZoneDatabase {
 
-    private val tzdbPath = tzdbPaths(defaultTzdbPath).find {
-        it.chaseSymlinks().check()?.isDirectory == true
+    internal val tzdbPath = tzdbPaths(defaultTzdbPath).find { path ->
+        tabPaths.any { path.containsFile(it) }
     } ?: throw IllegalStateException("Could not find the path to the timezone database")
 
-    override fun rulesForId(id: String): TimeZoneRules =
-        readTzFile(tzdbPath.resolve(Path.fromString(id)).readBytes()).toTimeZoneRules()
+    override fun rulesForId(id: String): TimeZoneRules {
+        val idAsPath = Path.fromString(id)
+        require(!idAsPath.isAbsolute) { "Timezone ID '$idAsPath' must not begin with a '/'" }
+        require(idAsPath.components.none { it == ".." }) { "'$idAsPath' must not contain '..' as a component" }
+        val file = Path(tzdbPath.isAbsolute, tzdbPath.components + idAsPath.components)
+        val contents = file.readBytes() ?: throw RuntimeException("File '$file' not found")
+        return readTzFile(contents).toTimeZoneRules()
+    }
 
     override fun availableTimeZoneIds(): Set<String> = buildSet {
-        tzdbPath.traverseDirectory(exclude = tzdbUnneededFiles) { add(it.toString()) }
+        tzdbPath.tryTraverseDirectory(exclude = tzdbUnneededFiles) { add(it.toString()) }
     }
 
 }
 
+// taken from https://github.com/tzinfo/tzinfo/blob/9953fc092424d55deaea2dcdf6279943f3495724/lib/tzinfo/data_sources/zoneinfo_data_source.rb#L354
+private val tabPaths = listOf("zone1970.tab", "zone.tab", "tab/zone_sun.tab")
+
 /** The files that sometimes lie in the `zoneinfo` directory but aren't actually time zones. */
 private val tzdbUnneededFiles = setOf(
     // taken from https://github.com/tzinfo/tzinfo/blob/9953fc092424d55deaea2dcdf6279943f3495724/lib/tzinfo/data_sources/zoneinfo_data_source.rb#L88C29-L97C21
@@ -51,7 +60,7 @@ internal fun tzdbPaths(defaultTzdbPath: Path?) = sequence {
 
 // taken from https://github.com/HowardHinnant/date/blob/ab37c362e35267d6dee02cb47760f9e9c669d3be/src/tz.cpp#L3951-L3952
 internal fun pathToSystemDefault(): Pair<Path, Path>? {
-    val info = Path(true, listOf("etc", "localtime")).chaseSymlinks()
+    val info = chaseSymlinks("/etc/localtime") ?: return null
     val i = info.components.indexOf("zoneinfo")
     if (!info.isAbsolute || i == -1 || i == info.components.size - 1) return null
     return Pair(

core/tzdbOnFilesystem/src/internal/filesystem.kt

@@ -9,35 +9,37 @@ package kotlinx.datetime.internal
 import kotlinx.cinterop.*
 import platform.posix.*
 
-internal fun Path.chaseSymlinks(maxDepth: Int = 100): Path {
-    var realPath = this
-    var depth = maxDepth
-    while (true) {
-        realPath = realPath.readLink() ?: break
-        if (depth-- == 0) throw RuntimeException("Too many levels of symbolic links")
-    }
-    return realPath
+internal fun chaseSymlinks(name: String): Path? = memScoped {
+    val buffer = allocArray<ByteVar>(PATH_MAX)
+    realpath(name, buffer)?.let { Path.fromString(it.toKString()) }
 }
 
-internal fun Path.traverseDirectory(exclude: Set<String> = emptySet(), stripLeadingComponents: Int = this.components.size, actionOnFile: (Path) -> Unit) {
-    val handler = opendir(this.toString()) ?: return
+internal fun Path.containsFile(file: String): Boolean = access("$this/$file", F_OK) == 0
+
+internal fun Path.tryTraverseDirectory(
+    exclude: Set<String> = emptySet(),
+    stripLeadingComponents: Int = this.components.size,
+    maxDepth: Int = 100,
+    actionOnFile: (Path) -> Unit
+): Boolean {
+    if (maxDepth <= 0) throw IllegalStateException("Max depth reached: $this")
+    val handler = opendir(this.toString()) ?: return false
     try {
         while (true) {
             val entry = readdir(handler) ?: break
             val name = entry.pointed.d_name.toKString()
             if (name == "." || name == "..") continue
             if (name in exclude) continue
             val path = Path(isAbsolute, components + name)
-            val info = path.check() ?: continue // skip broken symlinks
-            if (info.isDirectory) {
-                if (!info.isSymlink) {
-                    path.traverseDirectory(exclude, stripLeadingComponents, actionOnFile)
-                }
-            } else {
+            val isDirectory = path.tryTraverseDirectory(
+                exclude, stripLeadingComponents, maxDepth = maxDepth - 1, actionOnFile
+            )
+            if (!isDirectory) {
                 actionOnFile(Path(false, path.components.drop(stripLeadingComponents)))
             }
         }
     } finally {
         closedir(handler)
     }
+    return true
 }

core/tzdbOnFilesystem/test/TimeZoneRulesCompleteTest.kt

@@ -16,12 +16,10 @@ class TimeZoneRulesCompleteTest {
     @OptIn(ExperimentalEncodingApi::class)
     @Test
     fun iterateOverAllTimezones() {
-        val root = Path.fromString("/usr/share/zoneinfo")
-        val tzdb = TzdbOnFilesystem(root)
+        val tzdb = TzdbOnFilesystem()
         for (id in tzdb.availableTimeZoneIds()) {
-            val file = root.resolve(Path.fromString(id))
             val rules = tzdb.rulesForId(id)
-            runUnixCommand("env LOCALE=C zdump -V $file").windowed(size = 2, step = 2).forEach { (line1, line2) ->
+            runUnixCommand("env LOCALE=C zdump -V ${tzdb.tzdbPath}/$id").windowed(size = 2, step = 2).forEach { (line1, line2) ->
                 val beforeTransition = parseZdumpLine(line1)
                 val afterTransition = parseZdumpLine(line2)
                 try {
@@ -51,7 +49,7 @@ class TimeZoneRulesCompleteTest {
                 } catch (e: Throwable) {
                     println(beforeTransition)
                     println(afterTransition)
-                    println(Base64.encode(file.readBytes()))
+                    println(Base64.encode(Path.fromString("${tzdb.tzdbPath}/$id").readBytes()!!))
                     throw e
                 }
             }

core/tzfile/src/internal/filesystem.kt

@@ -10,29 +10,6 @@ import kotlinx.cinterop.*
 import platform.posix.*
 
 internal class Path(val isAbsolute: Boolean, val components: List<String>) {
-    fun check(): PathInfo? = memScoped {
-        val stat = alloc<stat>()
-        val err = stat(this@Path.toString(), stat.ptr)
-        if (err != 0) return null
-        object : PathInfo {
-            override val isDirectory: Boolean = stat.st_mode.toInt() and S_IFMT == S_IFDIR // `inode(7)`, S_ISDIR
-            override val isSymlink: Boolean = stat.st_mode.toInt() and S_IFMT == S_IFLNK // `inode(7)`, S_ISLNK
-        }
-    }
-
-    fun readLink(): Path? = memScoped {
-        val buffer = allocArray<ByteVar>(PATH_MAX)
-        val err = readlink(this@Path.toString(), buffer, PATH_MAX.convert<size_t>())
-        if (err == (-1).convert<ssize_t>()) return null
-        buffer[err] = 0
-        fromString(buffer.toKString())
-    }
-
-    fun resolve(other: Path): Path = when {
-        other.isAbsolute -> other
-        else -> Path(isAbsolute, components + other.components)
-    }
-
     override fun toString(): String = buildString {
         if (isAbsolute) append("/")
         if (components.isNotEmpty()) {
@@ -53,14 +30,8 @@ internal class Path(val isAbsolute: Boolean, val components: List<String>) {
     }
 }
 
-// `stat(2)` lists the other available fields
-internal interface PathInfo {
-    val isDirectory: Boolean
-    val isSymlink: Boolean
-}
-
-internal fun Path.readBytes(): ByteArray {
-    val handler = fopen(this.toString(), "rb") ?: throw RuntimeException("Cannot open file $this")
+internal fun Path.readBytes(): ByteArray? {
+    val handler = fopen(this.toString(), "rb") ?: return null
     try {
         var err = fseek(handler, 0, SEEK_END)
         if (err == -1) throw RuntimeException("Cannot jump to the end of $this: $errnoString")