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