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