NP created COMPRESS-595:
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Summary: IOUtils.readRange() reads more than len when input.read()
returns < len (ie. rewind() makes no sense)
Key: COMPRESS-595
URL: https://issues.apache.org/jira/browse/COMPRESS-595
Project: Commons Compress
Issue Type: Bug
Affects Versions: 1.21
Reporter: NP
When `input.read(b)` returns `readNow` < `len`, then it means
`input.read(b)` will need to be called again with the same
buffer, whose `remaining()` is now the old `remaining()` - `readNow`.
This way the ReadableByteChannel knows how many bytes are to be
read in subsequent iterations of the `while (read < len)` loop.
This is currently not the case, because there is a call to rewind()
which results in a buffer whose remaining() is reset to `len` if
`readNow` < `len`.
I suspect the readRange() method has only been used with channels that never do
partial reads (such as File Channels), and hence the problem has not been
experienced until now.
Here is a test case that exhibits the bug:
```kotlin
import org.apache.commons.compress.utils.IOUtils
import org.junit.jupiter.api.Assertions.assertArrayEquals
import org.junit.jupiter.api.Assertions.assertEquals
import org.junit.jupiter.api.Test
import java.nio.ByteBuffer
import java.nio.channels.ReadableByteChannel
class IOUtilsTest {
private class ReadableBytePerByteChannel: ReadableByteChannel {
val data = byteArrayOf(0x03, 0x02, 0x01)
val dataBuffer = ByteBuffer.wrap(data)!!
override fun close(): Unit = TODO("Not needed")
override fun isOpen(): Boolean = TODO("Not needed")
override fun read(dst: ByteBuffer): Int {
if (! dataBuffer.hasRemaining()) return -1
val bytesAvailableForReading = dataBuffer.remaining()
for (bytesReadSoFar in 1..bytesAvailableForReading) {
val nextByte: Byte = dataBuffer.get()
dst.put(nextByte)
// first read() call reads 1 byte, less than requested(2)
if (0x03.toByte() == nextByte) return bytesReadSoFar
}
return bytesAvailableForReading
}
}
@Test
fun readRangeShouldHandlePartialReads() {
val channel = ReadableBytePerByteChannel()
// should result in two calls to read()
val actual = IOUtils.readRange(channel, 2)
val expected = byteArrayOf(0x03, 0x02)
assertArrayEquals(expected, actual)
assertEquals(1, channel.dataBuffer.remaining())
}
}
```
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