Source/core/fetch/TextResourceDecoder.cpp

/*
    Copyright (C) 1999 Lars Knoll (knoll@mpi-hd.mpg.de)
    Copyright (C) 2003, 2004, 2005, 2006, 2007, 2008, 2009, 2012 Apple Inc. All rights reserved.
    Copyright (C) 2005, 2006, 2007 Alexey Proskuryakov (ap@nypop.com)

    This library is free software; you can redistribute it and/or
    modify it under the terms of the GNU Library General Public
    License as published by the Free Software Foundation; either
    version 2 of the License, or (at your option) any later version.

    This library is distributed in the hope that it will be useful,
    but WITHOUT ANY WARRANTY; without even the implied warranty of
    MERCHANTABILITY or FITNESS FOR A PARTICULAR PURPOSE.  See the GNU
    Library General Public License for more details.

    You should have received a copy of the GNU Library General Public License
    along with this library; see the file COPYING.LIB.  If not, write to
    the Free Software Foundation, Inc., 51 Franklin Street, Fifth Floor,
    Boston, MA 02110-1301, USA.
*/


#include "config.h"
#include "core/fetch/TextResourceDecoder.h"

#include "HTMLNames.h"
#include "core/dom/DOMImplementation.h"
#include "core/html/parser/HTMLMetaCharsetParser.h"
#include "platform/text/TextEncodingDetector.h"
#include "wtf/StringExtras.h"
#include "wtf/text/TextCodec.h"
#include "wtf/text/TextEncodingRegistry.h"

using namespace WTF;

namespace WebCore {

using namespace HTMLNames;

static inline bool bytesEqual(const char* p, char b0, char b1, char b2, char b3, char b4)
{
    return p[0] == b0 && p[1] == b1 && p[2] == b2 && p[3] == b3 && p[4] == b4;
}

static inline bool bytesEqual(const char* p, char b0, char b1, char b2, char b3, char b4, char b5)
{
    return p[0] == b0 && p[1] == b1 && p[2] == b2 && p[3] == b3 && p[4] == b4 && p[5] == b5;
}

static inline bool bytesEqual(const char* p, char b0, char b1, char b2, char b3, char b4, char b5, char b6, char b7)
{
    return p[0] == b0 && p[1] == b1 && p[2] == b2 && p[3] == b3 && p[4] == b4 && p[5] == b5 && p[6] == b6 && p[7] == b7;
}

static inline bool bytesEqual(const char* p, char b0, char b1, char b2, char b3, char b4, char b5, char b6, char b7, char b8, char b9)
{
    return p[0] == b0 && p[1] == b1 && p[2] == b2 && p[3] == b3 && p[4] == b4 && p[5] == b5 && p[6] == b6 && p[7] == b7 && p[8] == b8 && p[9] == b9;
}

// You might think we should put these find functions elsewhere, perhaps with the
// similar functions that operate on UChar, but arguably only the decoder has
// a reason to process strings of char rather than UChar.

static int find(const char* subject, size_t subjectLength, const char* target)
{
    size_t targetLength = strlen(target);
    if (targetLength > subjectLength)
        return -1;
    for (size_t i = 0; i <= subjectLength - targetLength; ++i) {
        bool match = true;
        for (size_t j = 0; j < targetLength; ++j) {
            if (subject[i + j] != target[j]) {
                match = false;
                break;
            }
        }
        if (match)
            return i;
    }
    return -1;
}

static WTF::TextEncoding findTextEncoding(const char* encodingName, int length)
{
    Vector<char, 64> buffer(length + 1);
    memcpy(buffer.data(), encodingName, length);
    buffer[length] = '\0';
    return buffer.data();
}

TextResourceDecoder::ContentType TextResourceDecoder::determineContentType(const String& mimeType)
{
    if (equalIgnoringCase(mimeType, "text/css"))
        return CSS;
    if (equalIgnoringCase(mimeType, "text/html"))
        return HTML;
    if (DOMImplementation::isXMLMIMEType(mimeType))
        return XML;
    return PlainText;
}

const WTF::TextEncoding& TextResourceDecoder::defaultEncoding(ContentType contentType, const WTF::TextEncoding& specifiedDefaultEncoding)
{
    // Despite 8.5 "Text/xml with Omitted Charset" of RFC 3023, we assume UTF-8 instead of US-ASCII
    // for text/xml. This matches Firefox.
    if (contentType == XML)
        return UTF8Encoding();
    if (!specifiedDefaultEncoding.isValid())
        return Latin1Encoding();
    return specifiedDefaultEncoding;
}

TextResourceDecoder::TextResourceDecoder(const String& mimeType, const WTF::TextEncoding& specifiedDefaultEncoding, bool usesEncodingDetector)
    : m_contentType(determineContentType(mimeType))
    , m_encoding(defaultEncoding(m_contentType, specifiedDefaultEncoding))
    , m_source(DefaultEncoding)
    , m_hintEncoding(0)
    , m_checkedForBOM(false)
    , m_checkedForCSSCharset(false)
    , m_checkedForXMLCharset(false)
    , m_checkedForMetaCharset(false)
    , m_useLenientXMLDecoding(false)
    , m_sawError(false)
    , m_usesEncodingDetector(usesEncodingDetector)
{
}

TextResourceDecoder::~TextResourceDecoder()
{
}

void TextResourceDecoder::setEncoding(const WTF::TextEncoding& encoding, EncodingSource source)
{
    // In case the encoding didn't exist, we keep the old one (helps some sites specifying invalid encodings).
    if (!encoding.isValid())
        return;

    // When encoding comes from meta tag (i.e. it cannot be XML files sent via XHR),
    // treat x-user-defined as windows-1252 (bug 18270)
    if (source == EncodingFromMetaTag && !strcasecmp(encoding.name(), "x-user-defined"))
        m_encoding = "windows-1252";
    else if (source == EncodingFromMetaTag || source == EncodingFromXMLHeader || source == EncodingFromCSSCharset)
        m_encoding = encoding.closestByteBasedEquivalent();
    else
        m_encoding = encoding;

    m_codec.clear();
    m_source = source;
}

// Returns the position of the encoding string.
static int findXMLEncoding(const char* str, int len, int& encodingLength)
{
    int pos = find(str, len, "encoding");
    if (pos == -1)
        return -1;
    pos += 8;

    // Skip spaces and stray control characters.
    while (pos < len && str[pos] <= ' ')
        ++pos;

    // Skip equals sign.
    if (pos >= len || str[pos] != '=')
        return -1;
    ++pos;

    // Skip spaces and stray control characters.
    while (pos < len && str[pos] <= ' ')
        ++pos;

    // Skip quotation mark.
    if (pos >= len)
        return - 1;
    char quoteMark = str[pos];
    if (quoteMark != '"' && quoteMark != '\'')
        return -1;
    ++pos;

    // Find the trailing quotation mark.
    int end = pos;
    while (end < len && str[end] != quoteMark)
        ++end;
    if (end >= len)
        return -1;

    encodingLength = end - pos;
    return pos;
}

size_t TextResourceDecoder::checkForBOM(const char* data, size_t len)
{
    // Check for UTF-16/32 or UTF-8 BOM mark at the beginning, which is a sure sign of a Unicode encoding.
    // We let it override even a user-chosen encoding.
    ASSERT(!m_checkedForBOM);

    size_t lengthOfBOM = 0;

    size_t bufferLength = m_buffer.size();

    size_t buf1Len = bufferLength;
    size_t buf2Len = len;
    const unsigned char* buf1 = reinterpret_cast<const unsigned char*>(m_buffer.data());
    const unsigned char* buf2 = reinterpret_cast<const unsigned char*>(data);
    unsigned char c1 = buf1Len ? (--buf1Len, *buf1++) : buf2Len ? (--buf2Len, *buf2++) : 0;
    unsigned char c2 = buf1Len ? (--buf1Len, *buf1++) : buf2Len ? (--buf2Len, *buf2++) : 0;
    unsigned char c3 = buf1Len ? (--buf1Len, *buf1++) : buf2Len ? (--buf2Len, *buf2++) : 0;
    unsigned char c4 = buf2Len ? (--buf2Len, *buf2++) : 0;

    // Check for the BOM.
    if (c1 == 0xFF && c2 == 0xFE) {
        if (c3 || c4) {
            setEncoding(UTF16LittleEndianEncoding(), AutoDetectedEncoding);
            lengthOfBOM = 2;
        } else {
            setEncoding(UTF32LittleEndianEncoding(), AutoDetectedEncoding);
            lengthOfBOM = 4;
        }
    } else if (c1 == 0xEF && c2 == 0xBB && c3 == 0xBF) {
        setEncoding(UTF8Encoding(), AutoDetectedEncoding);
        lengthOfBOM = 3;
    } else if (c1 == 0xFE && c2 == 0xFF) {
        setEncoding(UTF16BigEndianEncoding(), AutoDetectedEncoding);
        lengthOfBOM = 2;
    } else if (!c1 && !c2 && c3 == 0xFE && c4 == 0xFF) {
        setEncoding(UTF32BigEndianEncoding(), AutoDetectedEncoding);
        lengthOfBOM = 4;
    }

    if (lengthOfBOM || bufferLength + len >= 4)
        m_checkedForBOM = true;

    return lengthOfBOM;
}

bool TextResourceDecoder::checkForCSSCharset(const char* data, size_t len, bool& movedDataToBuffer)
{
    if (m_source != DefaultEncoding && m_source != EncodingFromParentFrame) {
        m_checkedForCSSCharset = true;
        return true;
    }

    size_t oldSize = m_buffer.size();
    m_buffer.grow(oldSize + len);
    memcpy(m_buffer.data() + oldSize, data, len);

    movedDataToBuffer = true;

    if (m_buffer.size() <= 13) // strlen('@charset "x";') == 13
        return false;

    const char* dataStart = m_buffer.data();
    const char* dataEnd = dataStart + m_buffer.size();

    if (bytesEqual(dataStart, '@', 'c', 'h', 'a', 'r', 's', 'e', 't', ' ', '"')) {
        dataStart += 10;
        const char* pos = dataStart;

        while (pos < dataEnd && *pos != '"')
            ++pos;
        if (pos == dataEnd)
            return false;

        int encodingNameLength = pos - dataStart;

        ++pos;

        if (*pos == ';')
            setEncoding(findTextEncoding(dataStart, encodingNameLength), EncodingFromCSSCharset);
    }

    m_checkedForCSSCharset = true;
    return true;
}

bool TextResourceDecoder::checkForXMLCharset(const char* data, size_t len, bool& movedDataToBuffer)
{
    if (m_source != DefaultEncoding && m_source != EncodingFromParentFrame) {
        m_checkedForXMLCharset = true;
        return true;
    }

    // This is not completely efficient, since the function might go
    // through the HTML head several times.

    size_t oldSize = m_buffer.size();
    m_buffer.grow(oldSize + len);
    memcpy(m_buffer.data() + oldSize, data, len);

    movedDataToBuffer = true;

    const char* ptr = m_buffer.data();
    const char* pEnd = ptr + m_buffer.size();

    // Is there enough data available to check for XML declaration?
    if (m_buffer.size() < 8)
        return false;

    // Handle XML declaration, which can have encoding in it. This encoding is honored even for HTML documents.
    // It is an error for an XML declaration not to be at the start of an XML document, and it is ignored in HTML documents in such case.
    if (bytesEqual(ptr, '<', '?', 'x', 'm', 'l')) {
        const char* xmlDeclarationEnd = ptr;
        while (xmlDeclarationEnd != pEnd && *xmlDeclarationEnd != '>')
            ++xmlDeclarationEnd;
        if (xmlDeclarationEnd == pEnd)
            return false;
        // No need for +1, because we have an extra "?" to lose at the end of XML declaration.
        int len = 0;
        int pos = findXMLEncoding(ptr, xmlDeclarationEnd - ptr, len);
        if (pos != -1)
            setEncoding(findTextEncoding(ptr + pos, len), EncodingFromXMLHeader);
        // continue looking for a charset - it may be specified in an HTTP-Equiv meta
    } else if (bytesEqual(ptr, '<', 0, '?', 0, 'x', 0)) {
        setEncoding(UTF16LittleEndianEncoding(), AutoDetectedEncoding);
    } else if (bytesEqual(ptr, 0, '<', 0, '?', 0, 'x')) {
        setEncoding(UTF16BigEndianEncoding(), AutoDetectedEncoding);
    } else if (bytesEqual(ptr, '<', 0, 0, 0, '?', 0, 0, 0)) {
        setEncoding(UTF32LittleEndianEncoding(), AutoDetectedEncoding);
    } else if (bytesEqual(ptr, 0, 0, 0, '<', 0, 0, 0, '?')) {
        setEncoding(UTF32BigEndianEncoding(), AutoDetectedEncoding);
    }

    m_checkedForXMLCharset = true;
    return true;
}

void TextResourceDecoder::checkForMetaCharset(const char* data, size_t length)
{
    if (m_source == UserChosenEncoding || m_source == EncodingFromHTTPHeader || m_source == AutoDetectedEncoding) {
        m_checkedForMetaCharset = true;
        return;
    }

    if (!m_charsetParser)
        m_charsetParser = HTMLMetaCharsetParser::create();

    if (!m_charsetParser->checkForMetaCharset(data, length))
        return;

    setEncoding(m_charsetParser->encoding(), EncodingFromMetaTag);
    m_charsetParser.clear();
    m_checkedForMetaCharset = true;
    return;
}

// We use the encoding detector in two cases:
//   1. Encoding detector is turned ON and no other encoding source is
//      available (that is, it's DefaultEncoding).
//   2. Encoding detector is turned ON and the encoding is set to
//      the encoding of the parent frame, which is also auto-detected.
//   Note that condition #2 is NOT satisfied unless parent-child frame
//   relationship is compliant to the same-origin policy. If they're from
//   different domains, |m_source| would not be set to EncodingFromParentFrame
//   in the first place.
bool TextResourceDecoder::shouldAutoDetect() const
{
    // Just checking m_hintEncoding suffices here because it's only set
    // in setHintEncoding when the source is AutoDetectedEncoding.
    return m_usesEncodingDetector
        && (m_source == DefaultEncoding || (m_source == EncodingFromParentFrame && m_hintEncoding));
}

String TextResourceDecoder::decode(const char* data, size_t len)
{
    size_t lengthOfBOM = 0;
    if (!m_checkedForBOM)
        lengthOfBOM = checkForBOM(data, len);

    bool movedDataToBuffer = false;

    if (m_contentType == CSS && !m_checkedForCSSCharset) {
        if (!checkForCSSCharset(data, len, movedDataToBuffer))
            return emptyString();
    }

    if ((m_contentType == HTML || m_contentType == XML) && !m_checkedForXMLCharset) {
        if (!checkForXMLCharset(data, len, movedDataToBuffer))
            return emptyString();
    }

    const char* dataForDecode = data + lengthOfBOM;
    size_t lengthForDecode = len - lengthOfBOM;

    if (!m_buffer.isEmpty()) {
        if (!movedDataToBuffer) {
            size_t oldSize = m_buffer.size();
            m_buffer.grow(oldSize + len);
            memcpy(m_buffer.data() + oldSize, data, len);
        }

        dataForDecode = m_buffer.data() + lengthOfBOM;
        lengthForDecode = m_buffer.size() - lengthOfBOM;
    }

    if (m_contentType == HTML && !m_checkedForMetaCharset)
        checkForMetaCharset(dataForDecode, lengthForDecode);

    if (shouldAutoDetect()) {
        WTF::TextEncoding detectedEncoding;
        if (detectTextEncoding(data, len, m_hintEncoding, &detectedEncoding))
            setEncoding(detectedEncoding, EncodingFromContentSniffing);
    }

    ASSERT(m_encoding.isValid());

    if (!m_codec)
        m_codec = newTextCodec(m_encoding);

    String result = m_codec->decode(dataForDecode, lengthForDecode, false, m_contentType == XML && !m_useLenientXMLDecoding, m_sawError);

    m_buffer.clear();
    return result;
}

String TextResourceDecoder::flush()
{
    // If we can not identify the encoding even after a document is completely
    // loaded, we need to detect the encoding if other conditions for
    // autodetection is satisfied.
    if (m_buffer.size() && shouldAutoDetect()
        && ((!m_checkedForXMLCharset && (m_contentType == HTML || m_contentType == XML)) || (!m_checkedForCSSCharset && (m_contentType == CSS)))) {
        WTF::TextEncoding detectedEncoding;
        if (detectTextEncoding(m_buffer.data(), m_buffer.size(), m_hintEncoding, &detectedEncoding))
            setEncoding(detectedEncoding, EncodingFromContentSniffing);
    }

    if (!m_codec)
        m_codec = newTextCodec(m_encoding);

    String result = m_codec->decode(m_buffer.data(), m_buffer.size(), true, m_contentType == XML && !m_useLenientXMLDecoding, m_sawError);
    m_buffer.clear();
    m_codec.clear();
    m_checkedForBOM = false; // Skip BOM again when re-decoding.
    return result;
}

}