Add new APNG renderer, just for internal users for now.

core/util-jvm/src/main/java/org/signal/core/util/ByteArrayExtensions.kt

@@ -0,0 +1,17 @@
+/*
+ * Copyright 2024 Signal Messenger, LLC
+ * SPDX-License-Identifier: AGPL-3.0-only
+ */
+
+package org.signal.core.util
+
+import java.nio.ByteBuffer
+import java.nio.ByteOrder
+
+fun ByteArray.toUInt(): UInt {
+  return ByteBuffer.wrap(this).order(ByteOrder.BIG_ENDIAN).int.toUInt()
+}
+
+fun ByteArray.toUShort(): UShort {
+  return ByteBuffer.wrap(this).order(ByteOrder.BIG_ENDIAN).getShort().toUShort()
+}

core/util-jvm/src/main/java/org/signal/core/util/InputStreamExtensions.kt

@@ -10,6 +10,7 @@ import java.io.ByteArrayOutputStream
 import java.io.IOException
 import java.io.InputStream
 import java.io.OutputStream
+import kotlin.jvm.Throws
 import kotlin.math.min
 
 /**
@@ -107,6 +108,13 @@ fun InputStream.readLength(): Long {
   return count
 }
 
+/**
+ * Reads a 32-bit unsigned integer from the stream.
+ */
+fun InputStream.readUInt(): UInt {
+  return this.readNBytesOrThrow(4).toUInt()
+}
+
 /**
  * Reads the contents of the stream and discards them.
  */

core/util-jvm/src/main/java/org/signal/core/util/OutputStreamExtensions.kt

@@ -6,6 +6,8 @@
 package org.signal.core.util
 
 import java.io.OutputStream
+import java.nio.ByteBuffer
+import java.nio.ByteOrder
 
 /**
  * Writes a 32-bit variable-length integer to the stream.
@@ -30,3 +32,11 @@ fun OutputStream.writeVarInt32(value: Int) {
     }
   }
 }
+
+/**
+ * Writes a 32-bit unsigned integer to the stream.
+ */
+fun OutputStream.writeUInt(value: UInt) {
+  // Note that casting to an int here is fine, because at the end of the day, we're just writing 4 bytes to the stream
+  this.write(ByteBuffer.allocate(4).order(ByteOrder.BIG_ENDIAN).putInt(value.toInt()).array())
+}

core/util-jvm/src/main/java/org/signal/core/util/stream/Crc32OutputStream.kt

@@ -0,0 +1,34 @@
+/*
+ * Copyright 2024 Signal Messenger, LLC
+ * SPDX-License-Identifier: AGPL-3.0-only
+ */
+
+package org.signal.core.util.stream
+
+import java.io.FilterOutputStream
+import java.io.OutputStream
+import java.util.zip.CRC32
+
+/**
+ * A simple pass-through stream that calculates a CRC32 as data is written to the target [OutputStream].
+ */
+class Crc32OutputStream(private val wrapped: OutputStream) : FilterOutputStream(wrapped) {
+  private val crc32 = CRC32()
+
+  val currentCrc32: Long
+    get() = crc32.value
+
+  override fun write(byte: Int) {
+    wrapped.write(byte)
+    crc32.update(byte)
+  }
+
+  override fun write(data: ByteArray) {
+    write(data, 0, data.size)
+  }
+
+  override fun write(data: ByteArray, offset: Int, length: Int) {
+    wrapped.write(data, offset, length)
+    crc32.update(data, offset, length)
+  }
+}