--- a/src/java.base/share/classes/java/io/InputStream.java Wed Dec 05 19:17:22 2018 +0100
+++ b/src/java.base/share/classes/java/io/InputStream.java Wed Dec 05 15:58:46 2018 -0800
@@ -64,8 +64,8 @@
* <p> While the stream is open, the {@code available()}, {@code read()},
* {@code read(byte[])}, {@code read(byte[], int, int)},
* {@code readAllBytes()}, {@code readNBytes(byte[], int, int)},
- * {@code readNBytes(int)}, {@code skip(long)}, and
- * {@code transferTo()} methods all behave as if end of stream has been
+ * {@code readNBytes(int)}, {@code skip(long)}, {@code skipNBytes(long)},
+ * and {@code transferTo()} methods all behave as if end of stream has been
* reached. After the stream has been closed, these methods all throw
* {@code IOException}.
*
@@ -139,6 +139,14 @@
}
@Override
+ public void skipNBytes(long n) throws IOException {
+ ensureOpen();
+ if (n > 0) {
+ throw new EOFException();
+ }
+ }
+
+ @Override
public long transferTo(OutputStream out) throws IOException {
Objects.requireNonNull(out);
ensureOpen();
@@ -513,11 +521,11 @@
* For instance, the implementation may depend on the ability to seek.
*
* @param n the number of bytes to be skipped.
- * @return the actual number of bytes skipped.
+ * @return the actual number of bytes skipped which might be zero.
* @throws IOException if an I/O error occurs.
+ * @see java.io.InputStream#skipNBytes(long)
*/
public long skip(long n) throws IOException {
-
long remaining = n;
int nr;
@@ -539,6 +547,65 @@
}
/**
+ * Skips over and discards exactly {@code n} bytes of data from this input
+ * stream. If {@code n} is zero, then no bytes are skipped.
+ * If {@code n} is negative, then no bytes are skipped.
+ * Subclasses may handle the negative value differently.
+ *
+ * <p> This method blocks until the requested number of bytes have been
+ * skipped, end of file is reached, or an exception is thrown.
+ *
+ * <p> If end of stream is reached before the stream is at the desired
+ * position, then an {@code EOFException} is thrown.
+ *
+ * <p> If an I/O error occurs, then the input stream may be
+ * in an inconsistent state. It is strongly recommended that the
+ * stream be promptly closed if an I/O error occurs.
+ *
+ * @implNote
+ * Subclasses are encouraged to provide a more efficient implementation
+ * of this method.
+ *
+ * @implSpec
+ * If {@code n} is zero or negative, then no bytes are skipped.
+ * If {@code n} is positive, the default implementation of this method
+ * invokes {@link #skip(long) skip()} with parameter {@code n}. If the
+ * return value of {@code skip(n)} is non-negative and less than {@code n},
+ * then {@link #read()} is invoked repeatedly until the stream is {@code n}
+ * bytes beyond its position when this method was invoked or end of stream
+ * is reached. If the return value of {@code skip(n)} is negative or
+ * greater than {@code n}, then an {@code IOException} is thrown. Any
+ * exception thrown by {@code skip()} or {@code read()} will be propagated.
+ *
+ * @param n the number of bytes to be skipped.
+ * @throws EOFException if end of stream is encountered before the
+ * stream can be positioned {@code n} bytes beyond its position
+ * when this method was invoked.
+ * @throws IOException if the stream cannot be positioned properly or
+ * if an I/O error occurs.
+ * @see java.io.InputStream#skip(long)
+ */
+ public void skipNBytes(long n) throws IOException {
+ if (n > 0) {
+ long ns = skip(n);
+ if (ns >= 0 && ns < n) { // skipped too few bytes
+ // adjust number to skip
+ n -= ns;
+ // read until requested number skipped or EOS reached
+ while (n > 0 && read() != -1) {
+ n--;
+ }
+ // if not enough skipped, then EOFE
+ if (n != 0) {
+ throw new EOFException();
+ }
+ } else if (ns != n) { // skipped negative or too many bytes
+ throw new IOException("Unable to skip exactly");
+ }
+ }
+ }
+
+ /**
* Returns an estimate of the number of bytes that can be read (or skipped
* over) from this input stream without blocking, which may be 0, or 0 when
* end of stream is detected. The read might be on the same thread or
--- a/test/jdk/java/io/InputStream/Skip.java Wed Dec 05 19:17:22 2018 +0100
+++ b/test/jdk/java/io/InputStream/Skip.java Wed Dec 05 15:58:46 2018 -0800
@@ -1,5 +1,5 @@
/*
- * Copyright (c) 1997, Oracle and/or its affiliates. All rights reserved.
+ * Copyright (c) 1997, 2018 Oracle and/or its affiliates. All rights reserved.
* DO NOT ALTER OR REMOVE COPYRIGHT NOTICES OR THIS FILE HEADER.
*
* This code is free software; you can redistribute it and/or modify it
@@ -21,24 +21,22 @@
* questions.
*/
-
-/* @test
- @bug 4016710
- @summary check for correct implementation of InputStream.skip
- */
-
-import java.io.*;
-
+/**
+ * @test
+ * @bug 4016710 6516099
+ * @summary check for correct implementation of InputStream.skip{NBytes}
+ */
-public class Skip{
+import java.io.EOFException;
+import java.io.InputStream;
+import java.io.IOException;
- private static void dotest(InputStream in , int curpos ,
- long total , long toskip , long expected)
- throws Exception
- {
+public class Skip {
+ private static final int EOF = -1;
+ private static void dotest(InputStream in, int curpos, long total,
+ long toskip, long expected) throws Exception {
try {
-
System.err.println("\n\nCurrently at pos = " + curpos +
"\nTotal bytes in the Stream = " + total +
"\nNumber of bytes to skip = " + toskip +
@@ -50,43 +48,69 @@
System.err.println("actual number skipped: "+ skipped);
if ((skipped < 0) || (skipped > expected)) {
- throw new RuntimeException("Unexpected number of bytes skipped");
+ throw new RuntimeException("Unexpected byte count skipped");
}
-
} catch (IOException e) {
- System.err.println("IOException is thrown - possible result");
+ System.err.println("IOException is thrown: " + e);
} catch (Throwable e) {
- throw new RuntimeException("Unexpected "+e+" is thrown!");
+ throw new RuntimeException("Unexpected " + e + " is thrown!");
}
+ }
+ private static void dotestExact(MyInputStream in, long curpos, long total,
+ long toskip, boolean expectIOE, boolean expectEOFE) {
+
+ System.err.println("\n\nCurrently at pos = " + curpos +
+ "\nTotal bytes in the Stream = " + total +
+ "\nNumber of bytes to skip = " + toskip);
+
+ try {
+ long pos = in.position();
+ assert pos == curpos : pos + " != " + curpos;
+ in.skipNBytes(toskip);
+ if (in.position() != pos + (toskip < 0 ? 0 : toskip)) {
+ throw new RuntimeException((in.position() - pos) +
+ " bytes skipped; expected " + toskip);
+ }
+ } catch (EOFException eofe) {
+ if (!expectEOFE) {
+ throw new RuntimeException("Unexpected EOFException", eofe);
+ }
+ System.err.println("Caught expected EOFException");
+ } catch (IOException ioe) {
+ if (!expectIOE) {
+ throw new RuntimeException("Unexpected IOException", ioe);
+ }
+ System.err.println("Caught expected IOException");
+ }
}
public static void main( String argv[] ) throws Exception {
-
MyInputStream in = new MyInputStream(11);
- /* test for negative skip */
+ // test for negative skip
dotest(in, 0, 11, -23, 0);
- /* check for skip beyond EOF starting from before EOF */
+ // check for skip beyond EOF starting from before EOF
dotest(in, 0, 11, 20, 11);
- /* check for skip after EOF */
- dotest(in, -1, 11, 20, 0);
+ // check for skip after EOF
+ dotest(in, EOF, 11, 20, 0);
in = new MyInputStream(9000);
- /* check for skip equal to the read chunk size in InputStream.java */
+
+ // check for skip equal to the read chunk size in InputStream.java
dotest(in, 0, 9000, 2048, 2048);
- /* check for skip greater than the read chunk size in InputStream.java */
+ // check for skip larger than the read chunk size in InputStream.java
dotest(in, 2048, 9000, 5000, 5000);
- /* check for skip beyond EOF starting from before EOF */
+ // check for skip beyond EOF starting from before EOF
dotest(in, 7048, 9000, 5000, 1952);
in = new MyInputStream(5000);
- /* check for multiple chunk reads */
+ // check for multiple chunk reads
dotest(in, 0, 5000, 6000, 5000);
/*
@@ -98,23 +122,86 @@
* dotest(in, 0, total, toskip, toskip);
*/
+ // tests for skipping an exact number of bytes
+
+ final long streamLength = Long.MAX_VALUE;
+ in = new MyInputStream(streamLength);
+
+ // negative skip: OK
+ dotestExact(in, 0, streamLength, -1, false, false);
+
+ // negative skip at EOF: OK
+ in.position(streamLength);
+ dotestExact(in, streamLength, streamLength, -1, false, false);
+ in.position(0);
+
+ // zero skip: OK
+ dotestExact(in, 0, streamLength, 0, false, false);
+
+ // zero skip at EOF: OK
+ in.position(streamLength);
+ dotestExact(in, streamLength, streamLength, 0, false, false);
+
+ // skip(1) at EOF: EOFE
+ dotestExact(in, streamLength, streamLength, 1, false, true);
+ in.position(0);
+
+ final long n = 31; // skip count
+ long pos = 0;
+
+ // skip(n) returns negative value: IOE
+ in.setState(-1, 100);
+ dotestExact(in, pos, streamLength, n, true, false);
+
+ // skip(n) returns n + 1: IOE
+ in.setState(n + 1, 100);
+ dotestExact(in, pos, streamLength, n, true, false);
+ pos += n + 1;
+
+ // skip(n) returns n/2 but only n/4 subsequent reads succeed: EOFE
+ in.setState(n/2, n/2 + n/4);
+ dotestExact(in, pos, streamLength, n, false, true);
+ pos += n/2 + n/4;
+
+ // skip(n) returns n/2 but n - n/2 subsequent reads succeed: OK
+ in.setState(n/2, n);
+ dotestExact(in, pos, streamLength, n, false, false);
+ pos += n;
}
-
}
class MyInputStream extends InputStream {
+ private static final int EOF = -1;
- private int readctr = 0;
- private long endoffile;
+ private final long endoffile;
+
+ private long readctr = 0;
+
+ private boolean isStateSet = false;
+ private long skipReturn;
+ private long readLimit;
public MyInputStream(long endoffile) {
this.endoffile = endoffile;
}
- public int read() {
+ /**
+ * Limits the behavior of skip() and read().
+ *
+ * @param skipReturn the value to be returned by skip()
+ * @param maxReads the maximum number of reads past the current position
+ * before EOF is reached
+ */
+ public void setState(long skipReturn, long maxReads) {
+ this.skipReturn = skipReturn;
+ this.readLimit = readctr + maxReads;
+ isStateSet = true;
+ }
- if (readctr == endoffile) {
- return -1;
+ public int read() {
+ if (readctr == endoffile ||
+ (isStateSet && readctr >= readLimit)) {
+ return EOF;
}
else {
readctr++;
@@ -123,4 +210,19 @@
}
public int available() { return 0; }
+
+ public long position() { return readctr; }
+
+ public void position(long pos) {
+ readctr = pos < 0 ? 0 : Math.min(pos, endoffile);
+ }
+
+ public long skip(long n) throws IOException {
+ if (isStateSet) {
+ return skipReturn < 0 ? skipReturn : super.skip(skipReturn);
+ }
+
+ // InputStream skip implementation.
+ return super.skip(n); // readctr is implicitly incremented
+ }
}