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package panda.net.io;
import java.io.BufferedReader;
import java.io.IOException;
import java.io.Reader;
/**
* 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
* begining 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.
*
* 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.
*
* 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.
*
* @version $Id: DotTerminatedMessageReader.java 1301276 2012-03-15 23:51:31Z sebb $
*/
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(Reader reader) {
super(reader);
// Assumes input is at start of message
atBeginning = true;
eof = 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.
* @exception IOException If an error occurs while reading the underlying stream.
*/
@Override
public int read() throws IOException {
synchronized (lock) {
if (eof) {
return -1; // Don't allow read past EOF
}
int chint = super.read();
if (chint == -1) { // True EOF
eof = true;
return -1;
}
if (atBeginning) {
atBeginning = false;
if (chint == DOT) { // Have DOT
mark(2); // need to check for CR LF or DOT
chint = super.read();
if (chint == -1) { // Should not happen
// new Throwable("Trailing DOT").printStackTrace();
eof = true;
return DOT; // return the trailing DOT
}
if (chint == DOT) { // Have DOT DOT
// no need to reset as we want to lose the first DOT
return chint; // i.e. DOT
}
if (chint == CR) { // Have DOT CR
chint = super.read();
if (chint == -1) { // 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 -1;
}
}
// 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.
* @exception IOException If an error occurs in reading the underlying stream.
*/
@Override
public int read(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.
* @exception IOException If an error occurs in reading the underlying stream.
*/
@Override
public int read(char[] buffer, int offset, int length) throws IOException {
if (length < 1) {
return 0;
}
int ch;
synchronized (lock) {
if ((ch = read()) == -1) {
return -1;
}
int off = offset;
do {
buffer[offset++] = (char)ch;
}
while (--length > 0 && (ch = read()) != -1);
return (offset - off);
}
}
/**
* 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.
*
* 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.
*
* @exception 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;
}
}
/**
* Read 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.
*/
@Override
public String readLine() throws IOException {
StringBuilder sb = new StringBuilder();
int intch;
synchronized (lock) { // make thread-safe (hopefully!)
while ((intch = read()) != -1) {
if (intch == LF && atBeginning) {
return sb.substring(0, sb.length() - 1);
}
sb.append((char)intch);
}
}
String string = sb.toString();
if (string.length() == 0) { // immediate EOF
return null;
}
// Should not happen - EOF without CRLF
// new Throwable(string).printStackTrace();
return string;
}
}