DotTerminatedMessageReader.java
/*
* 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
*
* https://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.commons.net.io;
import java.io.BufferedReader;
import java.io.IOException;
import java.io.Reader;
import org.apache.commons.net.util.NetConstants;
/**
* DotTerminatedMessageReader is a class used to read messages from a server that are terminated by a single dot followed by a <CR><LF> sequence and
* with double dots appearing at the beginning of lines which do not signal end of message yet start with a dot. Various Internet protocols such as
* NNTP and POP3 produce messages of this type.
* <p>
* This class handles stripping of the duplicate period at the beginning of lines starting with a period, and ensures you cannot read past the end of the
* message.
* </p>
* <p>
* Note: versions since 3.0 extend BufferedReader rather than Reader, and no longer change the CRLF into the local EOL. Also, only DOT CR LF acts as EOF.
* </p>
*/
public final class DotTerminatedMessageReader extends BufferedReader {
private static final char LF = '\n';
private static final char CR = '\r';
private static final int DOT = '.';
private boolean atBeginning;
private boolean eof;
private boolean seenCR; // was last character CR?
/**
* Creates a DotTerminatedMessageReader that wraps an existing Reader input source.
*
* @param reader The Reader input source containing the message.
*/
public DotTerminatedMessageReader(final Reader reader) {
super(reader);
// Assumes input is at start of message
atBeginning = true;
eof = false;
}
/**
* Closes the message for reading. This doesn't actually close the underlying stream. The underlying stream may still be used for communicating with the
* server and therefore is not closed.
* <p>
* If the end of the message has not yet been reached, this method will read the remainder of the message until it reaches the end, so that the underlying
* stream may continue to be used properly for communicating with the server. If you do not fully read a message, you MUST close it, otherwise your program
* will likely hang or behave improperly.
* </p>
*
* @throws IOException If an error occurs while reading the underlying stream.
*/
@Override
public void close() throws IOException {
synchronized (lock) {
if (!eof) {
while (read() != -1) {
// read to EOF
}
}
eof = true;
atBeginning = false;
}
}
/**
* Reads and returns the next character in the message. If the end of the message has been reached, returns -1. Note that a call to this method may result
* in multiple reads from the underlying input stream to decode the message properly (removing doubled dots and so on). All of this is transparent to the
* programmer and is only mentioned for completeness.
*
* @return The next character in the message. Returns -1 if the end of the message has been reached.
* @throws IOException If an error occurs while reading the underlying stream.
*/
@Override
public int read() throws IOException {
synchronized (lock) {
if (eof) {
return NetConstants.EOS; // Don't allow read past EOF
}
int chint = super.read();
if (chint == NetConstants.EOS) { // True EOF
eof = true;
return NetConstants.EOS;
}
if (atBeginning) {
atBeginning = false;
if (chint == DOT) { // Have DOT
mark(2); // need to check for CR LF or DOT
chint = super.read();
switch (chint) {
case NetConstants.EOS:
// new Throwable("Trailing DOT").printStackTrace();
eof = true;
return DOT; // return the trailing DOT
case DOT:
// no need to reset as we want to lose the first DOT
return chint; // i.e. DOT
case CR:
chint = super.read();
if (chint == NetConstants.EOS) { // Still only DOT CR - should not happen
// new Throwable("Trailing DOT CR").printStackTrace();
reset(); // So CR is picked up next time
return DOT; // return the trailing DOT
}
if (chint == LF) { // DOT CR LF
atBeginning = true;
eof = true;
// Do we need to clear the mark somehow?
return NetConstants.EOS;
}
break;
default:
break;
}
// Should not happen - lone DOT at beginning
// new Throwable("Lone DOT followed by "+(char)chint).printStackTrace();
reset();
return DOT;
} // have DOT
} // atBeginning
// Handle CRLF in normal flow
if (seenCR) {
seenCR = false;
if (chint == LF) {
atBeginning = true;
}
}
if (chint == CR) {
seenCR = true;
}
return chint;
}
}
/**
* Reads the next characters from the message into an array and returns the number of characters read. Returns -1 if the end of the message has been
* reached.
*
* @param buffer The character array in which to store the characters.
* @return The number of characters read. Returns -1 if the end of the message has been reached.
* @throws IOException If an error occurs in reading the underlying stream.
*/
@Override
public int read(final char[] buffer) throws IOException {
return read(buffer, 0, buffer.length);
}
/**
* Reads the next characters from the message into an array and returns the number of characters read. Returns -1 if the end of the message has been
* reached. The characters are stored in the array starting from the given offset and up to the length specified.
*
* @param buffer The character array in which to store the characters.
* @param offset The offset into the array at which to start storing characters.
* @param length The number of characters to read.
* @return The number of characters read. Returns -1 if the end of the message has been reached.
* @throws IOException If an error occurs in reading the underlying stream.
*/
@Override
public int read(final char[] buffer, int offset, int length) throws IOException {
if (length < 1) {
return 0;
}
int ch;
synchronized (lock) {
if ((ch = read()) == -1) {
return NetConstants.EOS;
}
final int off = offset;
do {
buffer[offset++] = (char) ch;
} while (--length > 0 && (ch = read()) != -1);
return offset - off;
}
}
/**
* Reads a line of text. A line is considered to be terminated by carriage return followed immediately by a linefeed. This contrasts with BufferedReader
* which also allows other combinations.
*
* @since 3.0
*/
@Override
public String readLine() throws IOException {
final StringBuilder sb = new StringBuilder();
int intch;
synchronized (lock) { // make thread-safe (hopefully!)
while ((intch = read()) != NetConstants.EOS) {
if (intch == LF && atBeginning) {
return sb.substring(0, sb.length() - 1);
}
sb.append((char) intch);
}
}
final String string = sb.toString();
if (string.isEmpty()) { // immediate EOF
return null;
}
// Should not happen - EOF without CRLF
// new Throwable(string).printStackTrace();
return string;
}
}