IO: add ByteReadChannel.cancel

Author: Sergey Mashkov

core/kotlinx-coroutines-io/src/main/kotlin/kotlinx/coroutines/experimental/io/ByteBufferChannel.kt

@@ -95,6 +95,10 @@ internal class ByteBufferChannel(
         return true
     }
 
+    suspend override fun cancel(cause: Throwable?): Boolean {
+        return close(cause ?: CancellationException("Channel has been cancelled"))
+    }
+
     private fun flushImpl(minReadSize: Int, minWriteSize: Int) {
         joining?.delegatedTo?.flush()
 

core/kotlinx-coroutines-io/src/main/kotlin/kotlinx/coroutines/experimental/io/ByteReadChannel.kt

@@ -144,6 +144,8 @@ public interface ByteReadChannel {
      * @param block to be invoked when at least [min] bytes available for read
      */
     suspend fun read(min: Int = 1, block: (ByteBuffer) -> Unit)
+
+    suspend fun cancel(cause: Throwable?): Boolean
 }
 
 suspend fun ByteReadChannel.joinTo(dst: ByteWriteChannel, closeOnEnd: Boolean) {