Add LinuxEntropySource (#208)

wasi-emscripten-host/src/linuxMain/kotlin/EmbedderHost.linux.kt

@@ -27,5 +27,5 @@ internal actual fun createDefaultEmbedderHost(builder: Builder): EmbedderHost =
     clock = builder.clock ?: CommonClock(),
     localTimeFormatter = builder.localTimeFormatter ?: LinuxLocalTimeFormatter,
     timeZoneInfo = builder.timeZoneInfo ?: LinuxTimeZoneInfoProvider,
-    entropySource = builder.entropySource ?: LinuxEntropySource(),
+    entropySource = builder.entropySource ?: LinuxEntropySource,
 )

wasi-emscripten-host/src/linuxMain/kotlin/linux/LinuxEmbedderHost.kt

@@ -31,5 +31,5 @@ public class LinuxEmbedderHost(
     override val clock: Clock = CommonClock(),
     override val localTimeFormatter: LocalTimeFormatter = LinuxLocalTimeFormatter,
     override val timeZoneInfo: TimeZoneInfoProvider = LinuxTimeZoneInfoProvider,
-    override val entropySource: EntropySource = LinuxEntropySource(),
+    override val entropySource: EntropySource = LinuxEntropySource,
 ) : EmbedderHost

wasi-emscripten-host/src/linuxMain/kotlin/linux/LinuxEntropySource.kt

@@ -6,10 +6,27 @@
 
 package ru.pixnews.wasm.sqlite.open.helper.host.linux
 
+import kotlinx.cinterop.addressOf
+import kotlinx.cinterop.usePinned
+import platform.linux.SYS_getrandom
+import platform.posix.errno
+import platform.posix.syscall
 import ru.pixnews.wasm.sqlite.open.helper.host.EmbedderHost.EntropySource
 
-internal class LinuxEntropySource : EntropySource {
+internal object LinuxEntropySource : EntropySource {
     override fun generateEntropy(size: Int): ByteArray {
-        TODO("Not yet implemented")
+        val bytes = ByteArray(size)
+        var bytesLeft: Int = size
+        bytes.usePinned {
+            while (bytesLeft != 0) {
+                val startPosition = size - bytesLeft
+                val bytesWritten = syscall(SYS_getrandom.toLong(), it.addressOf(startPosition), bytesLeft.toULong(), 0U)
+                if (bytesWritten < 0) {
+                    error("Can not generate entropy. Errno: $errno")
+                }
+                bytesLeft -= bytesWritten.toInt()
+            }
+        }
+        return bytes
     }
 }

wasi-emscripten-host/src/linuxTest/kotlin/linux/LinuxEntropySourceTest.kt

@@ -0,0 +1,21 @@
+/*
+ * Copyright 2024, the wasm-sqlite-open-helper project authors and contributors. Please see the AUTHORS file
+ * for details. Use of this source code is governed by the Apache 2.0 license that can be found in the LICENSE file.
+ * SPDX-License-Identifier: Apache-2.0
+ */
+
+package ru.pixnews.wasm.sqlite.open.helper.host.linux
+
+import assertk.assertThat
+import assertk.assertions.isFalse
+import kotlin.test.Test
+
+class LinuxEntropySourceTest {
+    @Test
+    @Suppress("MagicNumber")
+    fun entropy_source_should_work() {
+        val entropy = LinuxEntropySource.generateEntropy(102400)
+        // XXX may be a more appropriate test
+        assertThat(entropy.all { it == 0.toByte() }).isFalse()
+    }
+}