Github user srowen commented on a diff in the pull request:
https://github.com/apache/spark/pull/2321#discussion_r17260492
--- Diff:
core/src/main/scala/org/apache/spark/util/io/LengthBoundedInputStream.scala ---
@@ -0,0 +1,69 @@
+/*
+ * Licensed to the Apache Software Foundation (ASF) under one or more
+ * contributor license agreements. See the NOTICE file distributed with
+ * this work for additional information regarding copyright ownership.
+ * The ASF licenses this file to You under the Apache License, Version 2.0
+ * (the "License"); you may not use this file except in compliance with
+ * the License. You may obtain a copy of the License at
+ *
+ * http://www.apache.org/licenses/LICENSE-2.0
+ *
+ * Unless required by applicable law or agreed to in writing, software
+ * distributed under the License is distributed on an "AS IS" BASIS,
+ * WITHOUT WARRANTIES OR CONDITIONS OF ANY KIND, either express or implied.
+ * See the License for the specific language governing permissions and
+ * limitations under the License.
+ */
+
+package org.apache.spark.util.io
+
+import java.io.InputStream
+
+
+/**
+ * An InputStream that decorator that limits the number of bytes returned
from the underlying
+ * InputStream. If the underlying InputStream returns end of stream (-1
value in read) before
+ * the limit is reached, then the end of stream is properly returned to
the caller as well.
+ *
+ * One use case is to read a segment of a file (FileInputStream always
reads until the end of a
+ * file, whereas caller can use this one to limit it to stop before the
end of the file).
+ *
+ * @param underlying Underlying InputStream to read from
+ * @param limit number of bytes to read before returning EOF
+ */
+final class LengthBoundedInputStream(underlying: InputStream, limit: Long)
extends InputStream {
+
+ private[this] var pos: Long = 0L
+
+ override def close(): Unit = underlying.close()
+
+ override def read(): Int = {
+ if (pos >= limit) {
+ -1
+ } else {
+ val buf = underlying.read()
+ pos += 1
+ buf
+ }
+ }
+
+ override def read(b: Array[Byte], off: Int, len: Int): Int = {
+ if (pos >= limit) {
+ -1
+ } else {
+ val bytesRead = underlying.read(b, off, math.min(limit - pos,
len).toInt)
+ if (bytesRead == -1) {
+ -1
+ } else {
+ pos += bytesRead
+ bytesRead
+ }
+ }
+ }
+
+ override def available(): Int = throw new UnsupportedOperationException
--- End diff --
It seems like you could implement these 3 methods without much trouble, no?
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