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      1 /*
      2  * Copyright 2011 Google Inc.
      3  *
      4  * Use of this source code is governed by a BSD-style license that can be
      5  * found in the LICENSE file.
      6  */
      7 
      8 #include "SkEndian.h"
      9 #include "SkFontStream.h"
     10 #include "SkStream.h"
     11 
     12 struct SkSFNTHeader {
     13     uint32_t    fVersion;
     14     uint16_t    fNumTables;
     15     uint16_t    fSearchRange;
     16     uint16_t    fEntrySelector;
     17     uint16_t    fRangeShift;
     18 };
     19 
     20 struct SkTTCFHeader {
     21     uint32_t    fTag;
     22     uint32_t    fVersion;
     23     uint32_t    fNumOffsets;
     24     uint32_t    fOffset0;   // the first of N (fNumOffsets)
     25 };
     26 
     27 union SkSharedTTHeader {
     28     SkSFNTHeader    fSingle;
     29     SkTTCFHeader    fCollection;
     30 };
     31 
     32 struct SkSFNTDirEntry {
     33     uint32_t    fTag;
     34     uint32_t    fChecksum;
     35     uint32_t    fOffset;
     36     uint32_t    fLength;
     37 };
     38 
     39 static bool read(SkStream* stream, void* buffer, size_t amount) {
     40     return stream->read(buffer, amount) == amount;
     41 }
     42 
     43 static bool skip(SkStream* stream, size_t amount) {
     44     return stream->skip(amount) == amount;
     45 }
     46 
     47 /** Return the number of tables, or if this is a TTC (collection), return the
     48     number of tables in the first element of the collection. In either case,
     49     if offsetToDir is not-null, set it to the offset to the beginning of the
     50     table headers (SkSFNTDirEntry), relative to the start of the stream.
     51 
     52     On an error, return 0 for number of tables, and ignore offsetToDir
     53  */
     54 static int count_tables(SkStream* stream, int ttcIndex, size_t* offsetToDir) {
     55     SkASSERT(ttcIndex >= 0);
     56 
     57     SkAutoSMalloc<1024> storage(sizeof(SkSharedTTHeader));
     58     SkSharedTTHeader* header = (SkSharedTTHeader*)storage.get();
     59 
     60     if (!read(stream, header, sizeof(SkSharedTTHeader))) {
     61         return 0;
     62     }
     63 
     64     // by default, SkSFNTHeader is at the start of the stream
     65     size_t offset = 0;
     66 
     67     // if we're really a collection, the first 4-bytes will be 'ttcf'
     68     uint32_t tag = SkEndian_SwapBE32(header->fCollection.fTag);
     69     if (SkSetFourByteTag('t', 't', 'c', 'f') == tag) {
     70         unsigned count = SkEndian_SwapBE32(header->fCollection.fNumOffsets);
     71         if ((unsigned)ttcIndex >= count) {
     72             return 0;
     73         }
     74 
     75         if (ttcIndex > 0) { // need to read more of the shared header
     76             stream->rewind();
     77             size_t amount = sizeof(SkSharedTTHeader) + ttcIndex * sizeof(uint32_t);
     78             header = (SkSharedTTHeader*)storage.reset(amount);
     79             if (!read(stream, header, amount)) {
     80                 return 0;
     81             }
     82         }
     83         // this is the offset to the local SkSFNTHeader
     84         offset = SkEndian_SwapBE32((&header->fCollection.fOffset0)[ttcIndex]);
     85         stream->rewind();
     86         if (!skip(stream, offset)) {
     87             return 0;
     88         }
     89         if (!read(stream, header, sizeof(SkSFNTHeader))) {
     90             return 0;
     91         }
     92     }
     93 
     94     if (offsetToDir) {
     95         // add the size of the header, so we will point to the DirEntries
     96         *offsetToDir = offset + sizeof(SkSFNTHeader);
     97     }
     98     return SkEndian_SwapBE16(header->fSingle.fNumTables);
     99 }
    100 
    101 ///////////////////////////////////////////////////////////////////////////////
    102 
    103 struct SfntHeader {
    104     SfntHeader() : fCount(0), fDir(NULL) {}
    105     ~SfntHeader() { sk_free(fDir); }
    106 
    107     /** If it returns true, then fCount and fDir are properly initialized.
    108         Note: fDir will point to the raw array of SkSFNTDirEntry values,
    109         meaning they will still be in the file's native endianness (BE).
    110 
    111         fDir will be automatically freed when this object is destroyed
    112      */
    113     bool init(SkStream* stream, int ttcIndex) {
    114         stream->rewind();
    115 
    116         size_t offsetToDir;
    117         fCount = count_tables(stream, ttcIndex, &offsetToDir);
    118         if (0 == fCount) {
    119             return false;
    120         }
    121 
    122         stream->rewind();
    123         if (!skip(stream, offsetToDir)) {
    124             return false;
    125         }
    126 
    127         size_t size = fCount * sizeof(SkSFNTDirEntry);
    128         fDir = reinterpret_cast<SkSFNTDirEntry*>(sk_malloc_throw(size));
    129         return read(stream, fDir, size);
    130     }
    131 
    132     int             fCount;
    133     SkSFNTDirEntry* fDir;
    134 };
    135 
    136 ///////////////////////////////////////////////////////////////////////////////
    137 
    138 int SkFontStream::CountTTCEntries(SkStream* stream) {
    139     stream->rewind();
    140 
    141     SkSharedTTHeader shared;
    142     if (!read(stream, &shared, sizeof(shared))) {
    143         return 0;
    144     }
    145 
    146     // if we're really a collection, the first 4-bytes will be 'ttcf'
    147     uint32_t tag = SkEndian_SwapBE32(shared.fCollection.fTag);
    148     if (SkSetFourByteTag('t', 't', 'c', 'f') == tag) {
    149         return SkEndian_SwapBE32(shared.fCollection.fNumOffsets);
    150     } else {
    151         return 1;   // normal 'sfnt' has 1 dir entry
    152     }
    153 }
    154 
    155 int SkFontStream::GetTableTags(SkStream* stream, int ttcIndex,
    156                                SkFontTableTag tags[]) {
    157     SfntHeader  header;
    158     if (!header.init(stream, ttcIndex)) {
    159         return 0;
    160     }
    161 
    162     if (tags) {
    163         for (int i = 0; i < header.fCount; i++) {
    164             tags[i] = SkEndian_SwapBE32(header.fDir[i].fTag);
    165         }
    166     }
    167     return header.fCount;
    168 }
    169 
    170 size_t SkFontStream::GetTableData(SkStream* stream, int ttcIndex,
    171                                   SkFontTableTag tag,
    172                                   size_t offset, size_t length, void* data) {
    173     SfntHeader  header;
    174     if (!header.init(stream, ttcIndex)) {
    175         return 0;
    176     }
    177 
    178     for (int i = 0; i < header.fCount; i++) {
    179         if (SkEndian_SwapBE32(header.fDir[i].fTag) == tag) {
    180             size_t realOffset = SkEndian_SwapBE32(header.fDir[i].fOffset);
    181             size_t realLength = SkEndian_SwapBE32(header.fDir[i].fLength);
    182             // now sanity check the caller's offset/length
    183             if (offset >= realLength) {
    184                 return 0;
    185             }
    186             // if the caller is trusting the length from the file, then a
    187             // hostile file might choose a value which would overflow offset +
    188             // length.
    189             if (offset + length < offset) {
    190                 return 0;
    191             }
    192             if (length > realLength - offset) {
    193                 length = realLength - offset;
    194             }
    195             if (data) {
    196                 // skip the stream to the part of the table we want to copy from
    197                 stream->rewind();
    198                 size_t bytesToSkip = realOffset + offset;
    199                 if (!skip(stream, bytesToSkip)) {
    200                     return 0;
    201                 }
    202                 if (!read(stream, data, length)) {
    203                     return 0;
    204                 }
    205             }
    206             return length;
    207         }
    208     }
    209     return 0;
    210 }
    211