SkFontStream.cpp revision 64334352cc3f29f52dfa07225d65eb218d2fd830 
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
12struct SkSFNTHeader {
13    uint32_t    fVersion;
14    uint16_t    fNumTables;
15    uint16_t    fSearchRange;
16    uint16_t    fEntrySelector;
17    uint16_t    fRangeShift;
18};
19
20struct SkTTCFHeader {
21    uint32_t    fTag;
22    uint32_t    fVersion;
23    uint32_t    fNumOffsets;
24    uint32_t    fOffset0;   // the first of N (fNumOffsets)
25};
26
27union SkSharedTTHeader {
28    SkSFNTHeader    fSingle;
29    SkTTCFHeader    fCollection;
30};
31
32struct 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 */
46static int count_tables(SkStream* stream, int ttcIndex, size_t* offsetToDir) {
47    SkASSERT(ttcIndex >= 0);
48
49    SkSharedTTHeader shared;
50    if (stream->read(&shared, sizeof(shared)) != sizeof(shared)) {
51        return 0;
52    }
53
54    // by default, SkSFNTHeader is at the start of the stream
55    size_t offset = 0;
56
57    // if we're really a collection, the first 4-bytes will be 'ttcf'
58    uint32_t tag = SkEndian_SwapBE32(shared.fCollection.fTag);
59    if (SkSetFourByteTag('t', 't', 'c', 'f') == tag) {
60        unsigned count = SkEndian_SwapBE32(shared.fCollection.fNumOffsets);
61        if ((unsigned)ttcIndex >= count) {
62            return 0;
63        }
64
65        if (ttcIndex > 0) { // need to read more of the shared header
66            stream->rewind();
67            size_t amount = sizeof(shared) + ttcIndex * sizeof(uint32_t);
68            if (stream->read(&shared, amount) != amount) {
69                return 0;
70            }
71        }
72        // this is the offset to the local SkSFNTHeader
73        offset = SkEndian_SwapBE32((&shared.fCollection.fOffset0)[ttcIndex]);
74        stream->rewind();
75        if (stream->skip(offset) != offset) {
76            return 0;
77        }
78        if (stream->read(&shared, sizeof(shared)) != sizeof(shared)) {
79            return 0;
80        }
81    }
82
83    if (offsetToDir) {
84        // add the size of the header, so we will point to the DirEntries
85        *offsetToDir = offset + sizeof(SkSFNTHeader);
86    }
87    return SkEndian_SwapBE16(shared.fSingle.fNumTables);
88}
89
90///////////////////////////////////////////////////////////////////////////////
91
92struct SfntHeader {
93    SfntHeader() : fCount(0), fDir(NULL) {}
94    ~SfntHeader() { sk_free(fDir); }
95
96    /** If it returns true, then fCount and fDir are properly initialized.
97        Note: fDir will point to the raw array of SkSFNTDirEntry values,
98        meaning they will still be in the file's native endianness (BE).
99
100        fDir will be automatically freed when this object is destroyed
101     */
102    bool init(SkStream* stream, int ttcIndex) {
103        stream->rewind();
104
105        size_t offsetToDir;
106        fCount = count_tables(stream, ttcIndex, &offsetToDir);
107        if (0 == fCount) {
108            return false;
109        }
110
111        stream->rewind();
112        if (stream->skip(offsetToDir) != offsetToDir) {
113            return false;
114        }
115
116        size_t size = fCount * sizeof(SkSFNTDirEntry);
117        fDir = reinterpret_cast<SkSFNTDirEntry*>(sk_malloc_throw(size));
118        return stream->read(fDir, size) == size;
119    }
120
121    int             fCount;
122    SkSFNTDirEntry* fDir;
123};
124
125///////////////////////////////////////////////////////////////////////////////
126
127int SkFontStream::CountTTCEntries(SkStream* stream) {
128    stream->rewind();
129
130    SkSharedTTHeader shared;
131    if (stream->read(&shared, sizeof(shared)) != sizeof(shared)) {
132        return 0;
133    }
134
135    // if we're really a collection, the first 4-bytes will be 'ttcf'
136    uint32_t tag = SkEndian_SwapBE32(shared.fCollection.fTag);
137    if (SkSetFourByteTag('t', 't', 'c', 'f') == tag) {
138        return SkEndian_SwapBE32(shared.fCollection.fNumOffsets);
139    } else {
140        return 0;
141    }
142}
143
144int SkFontStream::GetTableTags(SkStream* stream, int ttcIndex,
145                               SkFontTableTag tags[]) {
146    SfntHeader  header;
147    if (!header.init(stream, ttcIndex)) {
148        return 0;
149    }
150
151    if (tags) {
152        for (int i = 0; i < header.fCount; i++) {
153            tags[i] = SkEndian_SwapBE32(header.fDir[i].fTag);
154        }
155    }
156    return header.fCount;
157}
158
159size_t SkFontStream::GetTableData(SkStream* stream, int ttcIndex,
160                                  SkFontTableTag tag,
161                                  size_t offset, size_t length, void* data) {
162    SfntHeader  header;
163    if (!header.init(stream, ttcIndex)) {
164        return 0;
165    }
166
167    for (int i = 0; i < header.fCount; i++) {
168        if (SkEndian_SwapBE32(header.fDir[i].fTag) == tag) {
169            size_t realOffset = SkEndian_SwapBE32(header.fDir[i].fOffset);
170            size_t realLength = SkEndian_SwapBE32(header.fDir[i].fLength);
171            // now sanity check the caller's offset/length
172            if (offset >= realLength) {
173                return 0;
174            }
175            // if the caller is trusting the length from the file, then a
176            // hostile file might choose a value which would overflow offset +
177            // length.
178            if (offset + length < offset) {
179                return 0;
180            }
181            if (length > realLength - offset) {
182                length = realLength - offset;
183            }
184            if (data) {
185                // skip the stream to the part of the table we want to copy from
186                stream->rewind();
187                size_t bytesToSkip = realOffset + offset;
188                if (stream->skip(bytesToSkip) != bytesToSkip) {
189                    return 0;
190                }
191                if (stream->read(data, length) != length) {
192                    return 0;
193                }
194            }
195            return length;
196        }
197    }
198    return 0;
199}
200