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 "SkAutoMalloc.h"
9 #include "SkEndian.h"
10 #include "SkFontStream.h"
11 #include "SkStream.h"
12 
13 struct SkSFNTHeader {
14     uint32_t    fVersion;
15     uint16_t    fNumTables;
16     uint16_t    fSearchRange;
17     uint16_t    fEntrySelector;
18     uint16_t    fRangeShift;
19 };
20 
21 struct SkTTCFHeader {
22     uint32_t    fTag;
23     uint32_t    fVersion;
24     uint32_t    fNumOffsets;
25     uint32_t    fOffset0;   // the first of N (fNumOffsets)
26 };
27 
28 union SkSharedTTHeader {
29     SkSFNTHeader    fSingle;
30     SkTTCFHeader    fCollection;
31 };
32 
33 struct SkSFNTDirEntry {
34     uint32_t    fTag;
35     uint32_t    fChecksum;
36     uint32_t    fOffset;
37     uint32_t    fLength;
38 };
39 
read(SkStream * stream,void * buffer,size_t amount)40 static bool read(SkStream* stream, void* buffer, size_t amount) {
41     return stream->read(buffer, amount) == amount;
42 }
43 
skip(SkStream * stream,size_t amount)44 static bool skip(SkStream* stream, size_t amount) {
45     return stream->skip(amount) == amount;
46 }
47 
48 /** Return the number of tables, or if this is a TTC (collection), return the
49     number of tables in the first element of the collection. In either case,
50     if offsetToDir is not-null, set it to the offset to the beginning of the
51     table headers (SkSFNTDirEntry), relative to the start of the stream.
52 
53     On an error, return 0 for number of tables, and ignore offsetToDir
54  */
count_tables(SkStream * stream,int ttcIndex,size_t * offsetToDir)55 static int count_tables(SkStream* stream, int ttcIndex, size_t* offsetToDir) {
56     SkASSERT(ttcIndex >= 0);
57 
58     SkAutoSMalloc<1024> storage(sizeof(SkSharedTTHeader));
59     SkSharedTTHeader* header = (SkSharedTTHeader*)storage.get();
60 
61     if (!read(stream, header, sizeof(SkSharedTTHeader))) {
62         return 0;
63     }
64 
65     // by default, SkSFNTHeader is at the start of the stream
66     size_t offset = 0;
67 
68     // if we're really a collection, the first 4-bytes will be 'ttcf'
69     uint32_t tag = SkEndian_SwapBE32(header->fCollection.fTag);
70     if (SkSetFourByteTag('t', 't', 'c', 'f') == tag) {
71         unsigned count = SkEndian_SwapBE32(header->fCollection.fNumOffsets);
72         if ((unsigned)ttcIndex >= count) {
73             return 0;
74         }
75 
76         if (ttcIndex > 0) { // need to read more of the shared header
77             stream->rewind();
78             size_t amount = sizeof(SkSharedTTHeader) + ttcIndex * sizeof(uint32_t);
79             header = (SkSharedTTHeader*)storage.reset(amount);
80             if (!read(stream, header, amount)) {
81                 return 0;
82             }
83         }
84         // this is the offset to the local SkSFNTHeader
85         offset = SkEndian_SwapBE32((&header->fCollection.fOffset0)[ttcIndex]);
86         stream->rewind();
87         if (!skip(stream, offset)) {
88             return 0;
89         }
90         if (!read(stream, header, sizeof(SkSFNTHeader))) {
91             return 0;
92         }
93     }
94 
95     if (offsetToDir) {
96         // add the size of the header, so we will point to the DirEntries
97         *offsetToDir = offset + sizeof(SkSFNTHeader);
98     }
99     return SkEndian_SwapBE16(header->fSingle.fNumTables);
100 }
101 
102 ///////////////////////////////////////////////////////////////////////////////
103 
104 struct SfntHeader {
SfntHeaderSfntHeader105     SfntHeader() : fCount(0), fDir(nullptr) {}
~SfntHeaderSfntHeader106     ~SfntHeader() { sk_free(fDir); }
107 
108     /** If it returns true, then fCount and fDir are properly initialized.
109         Note: fDir will point to the raw array of SkSFNTDirEntry values,
110         meaning they will still be in the file's native endianness (BE).
111 
112         fDir will be automatically freed when this object is destroyed
113      */
initSfntHeader114     bool init(SkStream* stream, int ttcIndex) {
115         stream->rewind();
116 
117         size_t offsetToDir;
118         fCount = count_tables(stream, ttcIndex, &offsetToDir);
119         if (0 == fCount) {
120             return false;
121         }
122 
123         stream->rewind();
124         if (!skip(stream, offsetToDir)) {
125             return false;
126         }
127 
128         size_t size = fCount * sizeof(SkSFNTDirEntry);
129         fDir = reinterpret_cast<SkSFNTDirEntry*>(sk_malloc_throw(size));
130         return read(stream, fDir, size);
131     }
132 
133     int             fCount;
134     SkSFNTDirEntry* fDir;
135 };
136 
137 ///////////////////////////////////////////////////////////////////////////////
138 
CountTTCEntries(SkStream * stream)139 int SkFontStream::CountTTCEntries(SkStream* stream) {
140     stream->rewind();
141 
142     SkSharedTTHeader shared;
143     if (!read(stream, &shared, sizeof(shared))) {
144         return 0;
145     }
146 
147     // if we're really a collection, the first 4-bytes will be 'ttcf'
148     uint32_t tag = SkEndian_SwapBE32(shared.fCollection.fTag);
149     if (SkSetFourByteTag('t', 't', 'c', 'f') == tag) {
150         return SkEndian_SwapBE32(shared.fCollection.fNumOffsets);
151     } else {
152         return 1;   // normal 'sfnt' has 1 dir entry
153     }
154 }
155 
GetTableTags(SkStream * stream,int ttcIndex,SkFontTableTag tags[])156 int SkFontStream::GetTableTags(SkStream* stream, int ttcIndex,
157                                SkFontTableTag tags[]) {
158     SfntHeader  header;
159     if (!header.init(stream, ttcIndex)) {
160         return 0;
161     }
162 
163     if (tags) {
164         for (int i = 0; i < header.fCount; i++) {
165             tags[i] = SkEndian_SwapBE32(header.fDir[i].fTag);
166         }
167     }
168     return header.fCount;
169 }
170 
GetTableData(SkStream * stream,int ttcIndex,SkFontTableTag tag,size_t offset,size_t length,void * data)171 size_t SkFontStream::GetTableData(SkStream* stream, int ttcIndex,
172                                   SkFontTableTag tag,
173                                   size_t offset, size_t length, void* data) {
174     SfntHeader  header;
175     if (!header.init(stream, ttcIndex)) {
176         return 0;
177     }
178 
179     for (int i = 0; i < header.fCount; i++) {
180         if (SkEndian_SwapBE32(header.fDir[i].fTag) == tag) {
181             size_t realOffset = SkEndian_SwapBE32(header.fDir[i].fOffset);
182             size_t realLength = SkEndian_SwapBE32(header.fDir[i].fLength);
183             // now sanity check the caller's offset/length
184             if (offset >= realLength) {
185                 return 0;
186             }
187             // if the caller is trusting the length from the file, then a
188             // hostile file might choose a value which would overflow offset +
189             // length.
190             if (offset + length < offset) {
191                 return 0;
192             }
193             if (length > realLength - offset) {
194                 length = realLength - offset;
195             }
196             if (data) {
197                 // skip the stream to the part of the table we want to copy from
198                 stream->rewind();
199                 size_t bytesToSkip = realOffset + offset;
200                 if (!skip(stream, bytesToSkip)) {
201                     return 0;
202                 }
203                 if (!read(stream, data, length)) {
204                     return 0;
205                 }
206             }
207             return length;
208         }
209     }
210     return 0;
211 }
212