mirror of
https://github.com/xiaoqidun/ofdgo.git
synced 2026-10-29 16:59:27 +08:00
249 lines
8.1 KiB
Go
249 lines
8.1 KiB
Go
// Copyright 2025-2026 肖其顿 (XIAO QI DUN)
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//
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// Licensed under the Apache License, Version 2.0 (the "License");
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// you may not use this file except in compliance with the License.
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// You may obtain a copy of the License at
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//
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// http://www.apache.org/licenses/LICENSE-2.0
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//
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// Unless required by applicable law or agreed to in writing, software
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// distributed under the License is distributed on an "AS IS" BASIS,
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// WITHOUT WARRANTIES OR CONDITIONS OF ANY KIND, either express or implied.
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// See the License for the specific language governing permissions and
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// limitations under the License.
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package font
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import (
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"bytes"
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"compress/zlib"
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"encoding/binary"
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"fmt"
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"io"
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"sort"
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"github.com/andybalholm/brotli"
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)
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// fontContainerLimit 限制压缩字体展开后的表数据总量
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const fontContainerLimit = 256 << 20
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// woff2Tags 保存WOFF2表目录的标准标签顺序
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var woff2Tags = [...]string{
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"cmap", "head", "hhea", "hmtx", "maxp", "name", "OS/2", "post",
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"cvt ", "fpgm", "glyf", "loca", "prep", "CFF ", "VORG", "EBDT",
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"EBLC", "gasp", "hdmx", "kern", "LTSH", "PCLT", "VDMX", "vhea",
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"vmtx", "BASE", "GDEF", "GPOS", "GSUB", "EBSC", "JSTF", "MATH",
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"CBDT", "CBLC", "COLR", "CPAL", "SVG ", "sbix", "acnt", "avar",
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"bdat", "bloc", "bsln", "cvar", "fdsc", "feat", "fmtx", "fvar",
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"gvar", "hsty", "just", "lcar", "mort", "morx", "opbd", "prop",
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"trak", "Zapf", "Silf", "Glat", "Gloc", "Feat", "Sill",
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}
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// DecodeWOFF2 展开未变换的WOFF2表，字体集合及字形变换交由绘图适配器处理
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// 入参: data WOFF2文件
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// 返回: []byte OpenType数据, bool 是否已处理, error 封装错误
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func DecodeWOFF2(data []byte) ([]byte, bool, error) {
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if len(data) < 48 || string(data[:4]) != "wOF2" || uint64(binary.BigEndian.Uint32(data[8:])) != uint64(len(data)) {
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return nil, true, fmt.Errorf("invalid WOFF2 header")
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}
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if string(data[4:8]) == "ttcf" {
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return nil, false, nil
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}
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count := int(binary.BigEndian.Uint16(data[12:]))
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if count == 0 || count > (len(data)-48)/2 {
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return nil, true, fmt.Errorf("invalid WOFF2 table count")
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}
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tags := make([]string, 0, count)
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sizes := make([]uint32, 0, count)
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table := make(map[string][]byte, count)
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pos, total, transformed := 48, uint64(0), false
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for range count {
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if pos >= len(data) {
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return nil, true, fmt.Errorf("truncated WOFF2 directory")
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}
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flags := data[pos]
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pos++
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var tag string
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if index := flags & 63; index == 63 {
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if len(data)-pos < 4 {
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return nil, true, fmt.Errorf("truncated WOFF2 tag")
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}
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tag = string(data[pos : pos+4])
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pos += 4
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} else {
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tag = woff2Tags[index]
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}
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if _, exists := table[tag]; exists {
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return nil, true, fmt.Errorf("duplicate WOFF2 table %q", tag)
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}
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table[tag] = nil
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size, err := readWOFF2Base128(data, &pos)
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if err != nil {
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return nil, true, err
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}
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version := flags >> 6
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changed := version != 0
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if tag == "glyf" || tag == "loca" {
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if version != 0 && version != 3 {
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return nil, true, fmt.Errorf("invalid WOFF2 glyph transform")
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}
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changed = version == 0
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} else if version != 0 && (tag != "hmtx" || version != 1) {
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return nil, true, fmt.Errorf("invalid WOFF2 table transform %q", tag)
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}
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if changed {
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transformed = true
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size, err = readWOFF2Base128(data, &pos)
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if err != nil {
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return nil, true, err
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}
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if tag == "loca" && size != 0 {
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return nil, true, fmt.Errorf("invalid WOFF2 loca length")
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}
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}
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total += uint64(size)
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if total+uint64(12+19*count) > fontContainerLimit {
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return nil, true, fmt.Errorf("WOFF2 font exceeds size limit")
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}
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tags = append(tags, tag)
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sizes = append(sizes, size)
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}
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end := uint64(pos) + uint64(binary.BigEndian.Uint32(data[20:]))
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if end > uint64(len(data)) {
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return nil, true, fmt.Errorf("invalid WOFF2 compressed length")
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}
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if err := validateWOFFBlocks(data, end, 28); err != nil {
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return nil, true, err
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}
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if transformed {
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return nil, false, nil
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}
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reader := brotli.NewReader(bytes.NewReader(data[pos:end]))
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body, err := io.ReadAll(io.LimitReader(reader, int64(total)+1))
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if err != nil {
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return nil, true, fmt.Errorf("decode WOFF2 data: %w", err)
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}
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if uint64(len(body)) != total {
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return nil, true, fmt.Errorf("invalid WOFF2 expanded length")
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}
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for i, tag := range tags {
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size := int(sizes[i])
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table[tag], body = body[:size], body[size:]
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}
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decoded, err := SerializeOTF(table)
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return decoded, true, err
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}
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// readWOFF2Base128 读取WOFF2无符号变长整数，拒绝溢出和前导零
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// 入参: data 编码数据, pos 当前读取位置
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// 返回: uint32 整数值, error 编码错误
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func readWOFF2Base128(data []byte, pos *int) (uint32, error) {
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var value uint32
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for i := range 5 {
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if *pos >= len(data) {
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return 0, fmt.Errorf("truncated WOFF2 integer")
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}
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b := data[*pos]
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*pos++
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if i == 0 && b == 0x80 || value > 0x1ffffff {
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return 0, fmt.Errorf("invalid WOFF2 integer")
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}
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value = value<<7 | uint32(b&127)
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if b&128 == 0 {
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return value, nil
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}
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}
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return 0, fmt.Errorf("invalid WOFF2 integer")
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}
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// DecodeWOFF 展开WOFF表数据，不解析或更改字体轮廓
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// 入参: data WOFF文件
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// 返回: []byte OpenType数据, error 封装错误
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func DecodeWOFF(data []byte) ([]byte, error) {
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if len(data) < 44 || uint64(binary.BigEndian.Uint32(data[8:])) != uint64(len(data)) || binary.BigEndian.Uint16(data[14:]) != 0 {
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return nil, fmt.Errorf("invalid WOFF header")
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}
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count := int(binary.BigEndian.Uint16(data[12:]))
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if count == 0 || count > (len(data)-44)/20 {
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return nil, fmt.Errorf("invalid WOFF table count")
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}
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table := make(map[string][]byte, count)
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ranges := make([][2]uint64, 0, count)
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total := uint64(12 + 16*count)
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for i := range count {
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record := data[44+i*20:]
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tag := string(record[:4])
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offset, packed, size := uint64(binary.BigEndian.Uint32(record[4:])), uint64(binary.BigEndian.Uint32(record[8:])), uint64(binary.BigEndian.Uint32(record[12:]))
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total += (size + 3) &^ 3
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if _, exists := table[tag]; exists || offset < uint64(44+20*count) || offset%4 != 0 || packed > size || offset+packed > uint64(len(data)) || total > fontContainerLimit {
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return nil, fmt.Errorf("invalid WOFF table %q", tag)
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}
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body := data[offset : offset+packed]
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if packed < size {
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reader, err := zlib.NewReader(bytes.NewReader(body))
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if err != nil {
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return nil, err
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}
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body, err = io.ReadAll(io.LimitReader(reader, int64(size)+1))
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reader.Close()
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if err != nil {
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return nil, err
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}
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if uint64(len(body)) != size {
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return nil, fmt.Errorf("invalid WOFF expanded length")
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}
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}
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table[tag] = body
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ranges = append(ranges, [2]uint64{offset, offset + packed})
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}
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if total != uint64(binary.BigEndian.Uint32(data[16:])) {
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return nil, fmt.Errorf("invalid WOFF SFNT size")
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}
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sort.Slice(ranges, func(i, j int) bool { return ranges[i][0] < ranges[j][0] })
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end := uint64(44 + 20*count)
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for _, interval := range ranges {
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if interval[0] != (end+3)&^3 {
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return nil, fmt.Errorf("invalid WOFF table ranges")
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}
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end = interval[1]
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}
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if err := validateWOFFBlocks(data, end, 24); err != nil {
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return nil, err
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}
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return SerializeOTF(table)
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}
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// validateWOFFBlocks 校验附加数据块的边界及对齐，字体元数据不写入输出
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// 入参: data 字体文件, end 字体数据结束位置, fields 元数据偏移字段位置
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// 返回: error 附加块错误
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func validateWOFFBlocks(data []byte, end uint64, fields int) error {
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for _, pos := range []int{fields, fields + 12} {
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offset, length := uint64(binary.BigEndian.Uint32(data[pos:])), uint64(binary.BigEndian.Uint32(data[pos+4:]))
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if offset == 0 {
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if length != 0 || pos == fields && binary.BigEndian.Uint32(data[pos+8:]) != 0 {
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return fmt.Errorf("invalid WOFF optional block")
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}
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continue
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}
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if length == 0 || offset != (end+3)&^3 || offset+length > uint64(len(data)) {
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return fmt.Errorf("invalid WOFF block range")
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}
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for _, b := range data[end:offset] {
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if b != 0 {
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return fmt.Errorf("invalid WOFF padding")
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}
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}
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end = offset + length
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}
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if end > uint64(len(data)) || uint64(len(data)) > (end+3)&^3 {
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return fmt.Errorf("invalid WOFF trailing data")
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}
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for _, b := range data[end:] {
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if b != 0 {
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return fmt.Errorf("invalid WOFF padding")
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}
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}
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return nil
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}
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