Add support for more methods in TruncatingInputStream.

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

@@ -5,8 +5,10 @@
 
 package org.signal.core.util
 
+import java.io.ByteArrayOutputStream
 import java.io.IOException
 import java.io.InputStream
+import kotlin.math.min
 
 /**
  * Reads a 32-bit variable-length integer from the stream.
@@ -68,6 +70,29 @@ fun InputStream.readNBytesOrThrow(length: Int): ByteArray {
   return buffer
 }
 
+/**
+ * Read at most [byteLimit] bytes from the stream.
+ */
+fun InputStream.readAtMostNBytes(byteLimit: Int): ByteArray {
+  val buffer = ByteArrayOutputStream()
+  val readBuffer = ByteArray(4096)
+
+  var remaining = byteLimit
+  while (remaining > 0) {
+    val bytesToRead = min(remaining, readBuffer.size)
+    val read = this.read(readBuffer, 0, bytesToRead)
+
+    if (read == -1) {
+      break
+    }
+
+    buffer.write(readBuffer, 0, read)
+    remaining -= read
+  }
+
+  return buffer.toByteArray()
+}
+
 @Throws(IOException::class)
 fun InputStream.readLength(): Long {
   val buffer = ByteArray(4096)

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

@@ -5,9 +5,12 @@
 
 package org.signal.core.util.stream
 
+import org.signal.core.util.readAtMostNBytes
+import org.signal.core.util.readFully
 import java.io.FilterInputStream
 import java.io.InputStream
 import java.lang.UnsupportedOperationException
+import kotlin.math.min
 
 /**
  * An [InputStream] that will read from the target [InputStream] until it reaches the end, or until it has read [maxBytes] bytes.
@@ -15,6 +18,7 @@ import java.lang.UnsupportedOperationException
 class TruncatingInputStream(private val wrapped: InputStream, private val maxBytes: Long) : FilterInputStream(wrapped) {
 
   private var bytesRead: Long = 0
+  private var lastMark = -1L
 
   override fun read(): Int {
     if (bytesRead >= maxBytes) {
@@ -48,11 +52,58 @@ class TruncatingInputStream(private val wrapped: InputStream, private val maxByt
     return bytesRead
   }
 
-  override fun skip(n: Long): Long {
+  override fun skip(requestedSkipCount: Long): Long {
-    throw UnsupportedOperationException()
+    val bytesRemaining: Long = maxBytes - bytesRead
+    val bytesToSkip: Long = min(bytesRemaining, requestedSkipCount)
+
+    return super.skip(bytesToSkip).also { bytesSkipped ->
+      if (bytesSkipped > 0) {
+        this.bytesRead += bytesSkipped
+      }
+    }
+  }
+
+  override fun available(): Int {
+    val bytesRemaining = Math.toIntExact(maxBytes - bytesRead)
+    return min(bytesRemaining, wrapped.available())
+  }
+
+  override fun markSupported(): Boolean {
+    return wrapped.markSupported()
+  }
+
+  override fun mark(readlimit: Int) {
+    if (!markSupported()) {
+      throw UnsupportedOperationException("Mark not supported")
+    }
+
+    wrapped.mark(readlimit)
+    lastMark = bytesRead
   }
 
   override fun reset() {
-    throw UnsupportedOperationException()
+    if (!markSupported()) {
+      throw UnsupportedOperationException("Mark not supported")
+    }
+
+    if (lastMark == -1L) {
+      throw UnsupportedOperationException("Mark not set")
+    }
+
+    wrapped.reset()
+    bytesRead = lastMark
+  }
+
+  /**
+   * If the stream has been fully read, this will return all bytes that were truncated from the stream.
+   *
+   * @param byteLimit The maximum number of truncated bytes to read. Defaults to no limit.
+   */
+  fun readTruncatedBytes(byteLimit: Int = -1): ByteArray {
+    return if (byteLimit < 0) {
+      wrapped.readFully()
+    } else {
+      wrapped.readAtMostNBytes(byteLimit)
+    }
   }
 }

core-util-jvm/src/test/java/org/signal/core/util/stream/TruncatingInputStreamTest.kt

@@ -8,6 +8,7 @@ package org.signal.core.util.stream
 import org.junit.Assert.assertEquals
 import org.junit.Test
 import org.signal.core.util.readFully
+import org.signal.core.util.readNBytesOrThrow
 
 class TruncatingInputStreamTest {
 
@@ -32,4 +33,84 @@ class TruncatingInputStreamTest {
 
     assertEquals(75, count)
   }
+
+  @Test
+  fun `when I skip past the maxBytes, I should get -1`() {
+    val inputStream = TruncatingInputStream(ByteArray(100).inputStream(), maxBytes = 75)
+
+    val skipCount = inputStream.skip(100)
+    val read = inputStream.read()
+
+    assertEquals(75, skipCount)
+    assertEquals(-1, read)
+  }
+
+  @Test
+  fun `when I skip, I should still truncate correctly afterwards`() {
+    val inputStream = TruncatingInputStream(ByteArray(100).inputStream(), maxBytes = 75)
+
+    val skipCount = inputStream.skip(50)
+    val data = inputStream.readFully()
+
+    assertEquals(50, skipCount)
+    assertEquals(25, data.size)
+  }
+
+  @Test
+  fun `when I skip more than maxBytes, I only skip maxBytes`() {
+    val inputStream = TruncatingInputStream(ByteArray(100).inputStream(), maxBytes = 75)
+
+    val skipCount = inputStream.skip(100)
+
+    assertEquals(75, skipCount)
+  }
+
+  @Test
+  fun `when I finish reading the stream, getTruncatedBytes gives me the rest`() {
+    val inputStream = TruncatingInputStream(ByteArray(100).inputStream(), maxBytes = 75)
+    inputStream.readFully()
+
+    val truncatedBytes = inputStream.readTruncatedBytes()
+    assertEquals(25, truncatedBytes.size)
+  }
+
+  @Test
+  fun `when I finish reading the stream, getTruncatedBytes gives me the rest, respecting the byte limit`() {
+    val inputStream = TruncatingInputStream(ByteArray(100).inputStream(), maxBytes = 75)
+    inputStream.readFully()
+
+    val truncatedBytes = inputStream.readTruncatedBytes(byteLimit = 10)
+    assertEquals(10, truncatedBytes.size)
+  }
+
+  @Test
+  fun `when I call available, it should respect the maxBytes`() {
+    val inputStream = TruncatingInputStream(ByteArray(100).inputStream(), maxBytes = 75)
+    val available = inputStream.available()
+
+    assertEquals(75, available)
+  }
+
+  @Test
+  fun `when I call available after reading some bytes, it should respect the maxBytes`() {
+    val inputStream = TruncatingInputStream(ByteArray(100).inputStream(), maxBytes = 75)
+    inputStream.readNBytesOrThrow(50)
+
+    val available = inputStream.available()
+
+    assertEquals(25, available)
+  }
+
+  @Test
+  fun `when I mark and reset, it should jump back to the correct position`() {
+    val inputStream = TruncatingInputStream(ByteArray(100).inputStream(), maxBytes = 75)
+
+    inputStream.mark(100)
+    inputStream.readNBytesOrThrow(10)
+    inputStream.reset()
+
+    val data = inputStream.readFully()
+
+    assertEquals(75, data.size)
+  }
 }

core-util/src/test/java/org/signal/core/util/InputStreamExtensionTests.kt

@@ -19,4 +19,20 @@ class InputStreamExtensionTests {
       assertEquals(bytes.size.toLong(), length)
     }
   }
+
+  @Test
+  fun `when I call readAtMostNBytes, I only read that many bytes`() {
+    val bytes = ByteArray(100)
+    val inputStream = bytes.inputStream()
+    val readBytes = inputStream.readAtMostNBytes(50)
+    assertEquals(50, readBytes.size)
+  }
+
+  @Test
+  fun `when I call readAtMostNBytes, it will return at most the length of the stream`() {
+    val bytes = ByteArray(100)
+    val inputStream = bytes.inputStream()
+    val readBytes = inputStream.readAtMostNBytes(200)
+    assertEquals(100, readBytes.size)
+  }
 }