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Standard Widget Toolkit for GTK on ppc64le
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/*******************************************************************************
* Copyright (c) 2000, 2017 IBM Corporation and others.
*
* This program and the accompanying materials
* are made available under the terms of the Eclipse Public License 2.0
* which accompanies this distribution, and is available at
* https://www.eclipse.org/legal/epl-2.0/
*
* SPDX-License-Identifier: EPL-2.0
*
* Contributors:
* IBM Corporation - initial API and implementation
*******************************************************************************/
package org.eclipse.swt.internal;
import java.io.*;
import java.nio.*;
import java.nio.charset.*;
import org.eclipse.swt.internal.gtk.*;
/**
* About this class:
* #################
* This class implements the conversions between unicode characters
* and the platform supported representation for characters.
*
* Note that, unicode characters which can not be found in the platform
* encoding will be converted to an arbitrary platform specific character.
*
* This class is tested via: org.eclipse.swt.tests.gtk.Test_GtkTextEncoding
*
* About JNI & string conversion:
* #############################
* - Regular JNI String conversion usually uses a modified UTF-8, see: https://en.wikipedia.org/wiki/UTF-8#Modified_UTF-8
* - And in JNI, normally (env*)->GetStringUTFChars(..) is used to convert a javaString into a C string.
* See: http://docs.oracle.com/javase/8/docs/technotes/guides/jni/spec/functions.html#GetStringUTFChars
*
* However, the modified UTF-8 only works well with C system functions as it doesn't contain embedded nulls
* and is null terminated.
*
* But because the modified UTF-8 only supports up to 3 bytes (and not up to 4 as regular UTF-8), characters
* that require 4 bytes (e.g emojos) are not translated properly from Java to C.
*
* To work around this issue, we convert the Java string to a byte array on the Java side manually and then pass it to C.
* See: http://stackoverflow.com/questions/32205446/getting-true-utf-8-characters-in-java-jni
*
* Note:
* Java uses UTF-16 Wide characters internally to represent a string.
* C uses UTF-8 Multibyte characters (null terminated) to represent a string.
*
* About encoding on Linux/Gtk & it's relevance to SWT:
* ####################################################
*
* UTF-* = variable length encoding.
*
* UTF-8 = minimum is 8 bits, max is 6 bytes, but rarely goes beyond 4 bytes. Gtk & most of web uses this.
* UTF-16 = minimum is 16 bits. Java's string are stored this way.
* UTF-16 can be
* Big Endian : 65 = 00000000 01000001 # Human friendly, reads left to right.
* Little Endian : 65 = 01000001 00000000 # Intel x86 and also AMD64 / x86-64 series of processors use the little-endian [1]
* # i.e, we in SWT often have to deal with UTF-16 LE
* Some terminology:
* - "Code point" is the numerical value of unicode character.
* - All of UTF-* have the same letter to code-point mapping,
* but UTF-8/16/32 have different "back-ends".
*
* Illustration:
* (char) = (code point) = (back end).
* A = 65 = 01000001 UTF-8
* = 00000000 01000001 UTF-16 BE
* = 01000001 00000000 UTF-16 LE
*
* - Byte Order Marks (BOM) are a few bytes at the start of a *file* indicating which endianess is used.
* Problem: Gtk/webkit often don't give us BOM's.
* (further reading *3)
*
* - We can reliably encode character to a backend (A -> UTF-8/16), but the other way round is
* guess work since byte order marks are often missing and UTF-16 bits are technically valid UTF-8.
* (see Converter.heuristic for details).
* We could improve our heuristic by using something like http://jchardet.sourceforge.net/.
*
* - Glib has some conversion functions:
* g_utf16_to_utf8
* g_utf8_to_utf16
*
* - So does java: (e.g null terminated UTF-8)
* ("myString" + '\0').getBytes(StandardCharsets.UTF-8)
*
* - I suggest using Java functions where possible to avoid memory leaks.
* (Yes, they happen and are big-pain-in-the-ass to find https://bugs.eclipse.org/bugs/show_bug.cgi?id=533995)
*
*
* Learning about encoding:
* #########################
* I suggest the following 3 videos to understand ASCII/UTF-8/UTF-16[LE|BE]/UTF-32 encoding:
* Overview: https://www.youtube.com/watch?v=MijmeoH9LT4
* Details:
* Part-1: https://www.youtube.com/watch?v=B1Sf1IhA0j4
* Part-2: https://www.youtube.com/watch?v=-oYfv794R9s
* Part-3: https://www.youtube.com/watch?v=vLBtrd9Ar28
*
* Also read all of this:
* http://kunststube.net/encoding/
* and this:
* https://www.joelonsoftware.com/2003/10/08/the-absolute-minimum-every-software-developer-absolutely-positively-must-know-about-unicode-and-character-sets-no-excuses/
*
* And lastly, good utf-8 reference: https://en.wikipedia.org/wiki/UTF-8#Description
*
* You should now be a master of encoding. I wish you luck on your journey.
*
* [1] https://en.wikipedia.org/wiki/Endianness
* [2] https://en.wikipedia.org/wiki/Byte_order_mark
* [3] BOM's: http://unicode.org/faq/utf_bom.html#BOM
*/
public final class Converter {
public static final byte [] NullByteArray = new byte [1];
public static final byte [] EmptyByteArray = new byte [0];
public static final char [] EmptyCharArray = new char [0];
/**
* Convert a "C" multibyte UTF-8 string byte array into a Java UTF-16 Wide character array.
*
* @param buffer - byte buffer with C bytes representing a string.
* @return char array representing the string. Usually used for String construction like: new String(mbcsToWcs(..))
*/
public static char [] mbcsToWcs (byte [] buffer) {
long [] items_written = new long [1];
long ptr = OS.g_utf8_to_utf16 (buffer, buffer.length, null, items_written, null);
if (ptr == 0) return EmptyCharArray;
int length = (int)items_written [0];
char [] chars = new char [length];
C.memmove (chars, ptr, length * 2);
OS.g_free (ptr);
return chars;
}
/**
* Convert a Java UTF-16 Wide character string into a C UTF-8 Multibyte byte array.
*
* This algorithm stops when it finds the first NULL character. I.e, if your Java String has embedded NULL
* characters, then the returned string will only go up to the first NULL character.
*
*
* @param string - a regular Java String
* @param terminate - if true the byte buffer should be terminated with a null character.
* @return byte array that can be passed to a native function.
*/
public static byte [] wcsToMbcs (String string, boolean terminate) {
int length = string.length ();
char [] buffer = new char [length];
string.getChars (0, length, buffer, 0);
return wcsToMbcs (buffer, terminate);
}
/**
* Given a java String, convert it to a regular null terimnated C string,
* to be used when calling a native C function.
* @param string A java string.
* @return a pointer to a C String. In C, this would be a 'char *'
*/
public static byte [] javaStringToCString (String string) {
return wcsToMbcs(string, true);
}
/**
* This method takes a 'C' pointer (char *) or (gchar *), reads characters up to the terminating symbol '\0' and
* converts it into a Java String.
*
* Note: In SWT we don't use JNI's native String functions because of the 3 vs 4 byte issue explained in Class description.
* Instead we pass a character pointer from C to java and convert it to a String in Java manually.
*
* @param cCharPtr - A char * or a gchar *. Which will be freed up afterwards.
* @param freecCharPtr - "true" means free up memory pointed to by cCharPtr.
* CAREFUL! If this string is part of a struct (ex GError), and a specialized
* free function (like g_error_free(..) is called on the whole struct, then you
* should not free up individual struct members with this function,
* as otherwise you can get unpredictable behavior).
* @return a Java String object.
*/
public static String cCharPtrToJavaString(long cCharPtr, boolean freecCharPtr) {
int length = C.strlen (cCharPtr);
byte[] buffer = new byte [length];
C.memmove (buffer, cCharPtr, length);
if (freecCharPtr) {
OS.g_free (cCharPtr);
}
return new String (mbcsToWcs (buffer));
}
/**
* Convert a Java UTF-16 Wide character array into a C UTF-8 Multibyte byte array.
*
* This algorithm stops when it finds the first NULL character. I.e, if your Java String has embedded NULL
* characters, then the returned string will only go up to the first NULL character.
*
* @param chars - a regular Java String
* @param terminate - if true the byte buffer should be terminated with a null character.
* @return byte array that can be passed to a native function.
*/
public static byte [] wcsToMbcs (char [] chars, boolean terminate) {
long [] items_read = new long [1], items_written = new long [1];
/*
* Note that g_utf16_to_utf8() stops converting
* when it finds the first NULL.
*/
long ptr = OS.g_utf16_to_utf8 (chars, chars.length, items_read, items_written, null);
if (ptr == 0) return terminate ? NullByteArray : EmptyByteArray;
int written = (int)items_written [0];
byte [] bytes = new byte [written + (terminate ? 1 : 0)];
C.memmove (bytes, ptr, written);
OS.g_free (ptr);
return bytes;
}
/**
* Convert a Java UTF-16 Wide character into a single C UTF-8 Multibyte character
* that you can pass to a native function.
* @param ch - Java UTF-16 wide character.
* @return C UTF-8 Multibyte character.
*/
public static char wcsToMbcs (char ch) {
int key = ch & 0xFFFF;
if (key <= 0x7F) return ch;
byte [] buffer = wcsToMbcs (new char [] {ch}, false);
if (buffer.length == 1) return (char) buffer [0];
if (buffer.length == 2) {
return (char) (((buffer [0] & 0xFF) << 8) | (buffer [1] & 0xFF));
}
return 0;
}
/**
* Convert C UTF-8 Multibyte character into a Java UTF-16 Wide character.
*
* @param ch - C Multibyte UTF-8 character
* @return Java UTF-16 Wide character
*/
public static char mbcsToWcs (char ch) {
int key = ch & 0xFFFF;
if (key <= 0x7F) return ch;
byte [] buffer;
if (key <= 0xFF) {
buffer = new byte [1];
buffer [0] = (byte) key;
} else {
buffer = new byte [2];
buffer [0] = (byte) ((key >> 8) & 0xFF);
buffer [1] = (byte) (key & 0xFF);
}
char [] result = mbcsToWcs (buffer);
if (result.length == 0) return 0;
return result [0];
}
/**
* Given a byte array with unknown encoding, try to decode it via (relatively simple) heuristic.
* This is useful when we're not provided the encoding by OS/library.
*
* Current implementation only supports standard java charsets but can be extended as needed.
* This method could be improved by using http://jchardet.sourceforge.net/
*
* Run time is O(a * n) where a is a constant that varies depending on the size of input n, but roughly 1-20)
*
* @param bytes raw bits from the OS.
* @return String based on the most pop
*/
public static String byteToStringViaHeuristic(byte [] bytes) {
/*
* Technical notes:
* - Given a sequence of bytes, UTF-8 and UTF-16 cannot determined deterministically (1*).
* - However, UTF-16 has a lot of null bytes when code points are mostly in the 0-255 range (using only 2nd byte),
* a byte sequence with many null bytes is likely UTF-16.
* - Valid UTF-8 technically can contain null bytes, but it's rare.
*
* Some times it can get confused if it receives two non-null bytes. e.g (E with two dots on top) = (UTF-16 [01,04])
* It can either mean a valid set of UTF-8 characters or a single UTF-16 character.
* This issue typically only occurs for very short sequences 1-5 characters of very special characters).
* Improving the heuristic for such corner cases is complicated. We'd have to implement a mechanism
* that would be aware of character frequencies and assign a score to the probability of each mapping.
*
* [1] https://softwareengineering.stackexchange.com/questions/187169/how-to-detect-the-encoding-of-a-file
*/
// Base cases
if ((bytes.length == 0) ||
(bytes.length == 1 && bytes[0] == 0)) {
return "";
}
// Test if it's valid UTF-8.
// Note, ASCII is a subset of UTF-8.
try {
CharsetDecoder charDecoder = StandardCharsets.UTF_8.newDecoder();
charDecoder.onMalformedInput(CodingErrorAction.REPORT);
charDecoder.onUnmappableCharacter(CodingErrorAction.REPORT);
String text = charDecoder.decode(ByteBuffer.wrap(bytes)).toString();
// No exception thrown means that we have valid UTF-8 "bit string". However, valid UTF-8 bit string doesn't mean it's the corect decoding.
// We have assert correctness via an educated guess
boolean probablyUTF8 = true;
{
// Problem 1: It might be UTF-16 since at the binary level UTF-16 can be valid UTF-8. (null is a valid utf-8 character).
// Solution: Count nulls to try to guess if it's UTF-16.
// Verified via
// org.eclipse.swt.tests.gtk.Test_GtkConverter.test_HeuristicUTF16_letters()
// org.eclipse.swt.tests.gtk.Test_GtkConverter.test_HeuristicUTF16_letter()
double nullBytePercentageForUtf16 = 0.01; // if more than this % null bytes, then it's probably utf-16.
int nullCount = 0;
for (byte b : bytes) {
if (b == 0)
nullCount++;
}
double nullPercentage = (double) nullCount / (double) bytes.length;
if (nullPercentage > nullBytePercentageForUtf16) {
probablyUTF8 = false;
}
}
// Problem 2: Valid UTF-8 bit string can map to invalid code points (i.e undefined unicode)
// Solution 2: verify that every character is a valid code point.
if (probablyUTF8) {
char [] chars = text.toCharArray();
for (int i = 0; i < chars.length; i++) {
int codePoint = Character.codePointAt(chars, i);
if (!Character.isValidCodePoint(codePoint)) {
probablyUTF8 = false;
break;
}
}
}
// Problem 3: Short 2-byte sequences are very ambiguous.
// E.g Unicode Hyphen U+2010 (which looks like a '-') ( which btw different from the ascii U+002D '-' Hyphen-Minus)
// can be miss-understood as 16 (Synchronous Idle) & 32 (Space).
// Solution: Unless we have two valid alphabet characters, it's probably a single utf-16 character.
// However, this leads to the problem that single non-alphabetic unicode characters are not recognized correctly.
// Below code is left in case recognizing alphabetic characters is of higher priority than exotic unicode once.
// if (probablyUTF8) {
// if (bytes.length == 2) {
// char [] chars = text.toCharArray();
// for (int i = 0; i < chars.length; i++) {
// int codePoint = Character.codePointAt(chars, i);
// if (!Character.isAlphabetic(codePoint)) {
// probablyUTF8 = false;
// break;
// }
// }
// }
// }
if (!probablyUTF8) {
return new String (bytes, StandardCharsets.UTF_16LE);
} else {
return text;
}
} catch (CharacterCodingException e) {
}
// Invalid UTF-8. Try other character sets.
Charset [] commonWebCharSets = new Charset[] {StandardCharsets.UTF_16LE, StandardCharsets.ISO_8859_1, StandardCharsets.UTF_16BE, StandardCharsets.UTF_16};
for (Charset setToTry : commonWebCharSets) {
try {
CharsetDecoder charDecoder = setToTry.newDecoder();
charDecoder.onMalformedInput(CodingErrorAction.REPORT);
charDecoder.onUnmappableCharacter(CodingErrorAction.REPORT);
return charDecoder.decode(ByteBuffer.wrap(bytes)).toString();
} catch (CharacterCodingException e) {}
}
// Could not determine encoding.
// Return error string with stack trace to help users determine which function lead to a failed decoding.
StringWriter sw = new StringWriter();
new Throwable("").printStackTrace(new PrintWriter(sw));
return "SWT: Failed to decode byte buffer. Encoding is not ASCII/UTF-8/UTF-16[LE|BE|BOM]/ISO_8859_1. Stack trace:\n" + sw.toString();
}
}
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