Codereview request for 6995537: different behavior in iso-2022-jp encoding between jdk131/140/141 and jdk142/5/6/7 (original) (raw)

Xueming Shen xueming.shen at oracle.com
Thu Feb 9 06:26:54 UTC 2012

Hi

This is a long standing "regression" from 1.3.1 on how OutputStreamWriter.flush()/flushBuffer() handles escape or shift sequence in some of the charset/encoding, for example the ISO-2022-JP.

ISO-2022-JP is encoding that starts with ASCII mode and then switches between ASCII andJapanese characters through an escape sequence. For example, the escape sequence ESC $ B (0x1B, 0x24 0x42) is used to indicate the following bytes are Japanese (switch from ASCII mode to Japanese mode), and the ESC ( B (0x1b 0x28 0x42) is used to switch back to ASCII.

In Java's sun.io.CharToByteConvert (old generation charset converter) and the nio.io.charset.CharsetEncoder usually switches back forth between ASCII and Japanese modes based on the input character sequence (for example, if you are in ASCII mode, and your next input character is a Japanese, you add the ESC $ B into the output first and then followed the converted input character, or if you are in Japanese mode and your next input is ASCII, you output ESC ( B first to switch the mode and then the ASCII) and switch back to ASCII mode (if the last mode is non-Japanese) if either the encoding is ending or the flush() method gets invoked.

In JDK1.3.1, OutputStreamWriter.flushBuffer() explicitly invokes sun.io.c2b's flushAny() to switch back to ASCII mode every time the flush() or flushBuffer() (from PrintStream) gets invoked, as showed at the end of this email. For example, as showed below, the code uses OutputStreamWriter to "write" a Japanese character \u6700 to the underlying stream with iso-2022jp,

ByteArrayOutputStream bos = new ByteArrayOutputStream();
     String str = "\u6700";
OutputStreamWriter osw = new OutputStreamWriter(bos, "iso-2022-jp");
osw.write(str, 0, str.length());

Since the iso-2022-jp starts with ASCII mode, we now have a Japanese, so we need to switch into Japanese mode first (the first 3 bytes) and then the encoded Japanese character (the following 2 bytes)

0x1b 0x24 0x42 0x3a 0x47

and then the code invokes

     osw.flush();

since we are now in Japanese, the writer continues to write out

0x1b 0x28 0x 42

to switch back to ASCII mode. The total output is 8 bytes after write() and flush().

However, when all encoidng/charset related codes were migrated from 1.3.1's sun.io based to 1.4's java.nio.charset based implementation (1.4, 1.4.1 and 1.4.2, we gradually migrated from sun.io to java.nio.charset), the "c2b.flushAny()" invocation obviously was dropped in sun.nio.cs.StreamEncoder. It results in that the "switch back to ASCII mode" sequence is no longer output when OutputStreamWriter.flush() or PrintStream.write(String) is invoked.

This does not trigger problem for most use scenario, if the "stream" finally gets closed (in which the StreamEncoder does invoke encoder's flush() to output the escape sequence to switch back to ASCII) or PrintStream.println(String) is used (in which it outputs a \n character, since this \n is in ASCII range, it "accidentally " switches the mode back to ASCII).

But it obviously causes problem when you can't not close the OutputStreamWriter after you're done your iso2022-jp writing (for example, you need continue to use the underlying OutputStream for other writing, but not "this" osw), for 1.3.1, these apps invoke osw.flush() to force the output switch back to ASCII, this no longer works when we switch to java.nio.charset in jdk1.4.2. (we migrated iso-2022-jp to nio.charset in 1.4.2). This is what happened in JavaMail, as described in the bug report.

The solution is to re-store the "flush the encoder" mechanism in StreamEncoder's flushBuffer().

I have been hesitated to make this change for a while, mostly because this regressed behavior has been their for 3 releases, and the change triggers yet another "behavior change". But given there is no obvious workaround and it only changes the behavior of the charsets with this shift in/out mechanism, mainly the iso-2022 family and those IBM EBCDIC_DBCS charsets, I decided to give it a try.

Here is the webreview

http://cr.openjdk.java.net/~sherman/6995537/webrev

Sherman

---------------------------------1.3.1 OutputStreamWriter----------------------- /** * Flush the output buffer to the underlying byte stream, without flushing * the byte stream itself. This method is non-private only so that it may * be invoked by PrintStream. */ void flushBuffer() throws IOException { synchronized (lock) { ensureOpen();

     for (;;) {
     try {
         nextByte += ctb.flushAny(bb, nextByte, nBytes);
     }
     catch (ConversionBufferFullException x) {
         nextByte = ctb.nextByteIndex();
     }
     if (nextByte == 0)
         break;
     if (nextByte > 0) {
         out.write(bb, 0, nextByte);
         nextByte = 0;
     }
     }
 }
 }

 /**
  * Flush the stream.
  *
  * @exception  IOException  If an I/O error occurs
  */
 public void flush() throws IOException {
 synchronized (lock) {
     flushBuffer();
     out.flush();
 }
 }

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