mirror of
https://github.com/xiaoqidun/ofdgo.git
synced 2026-10-29 16:44:23 +08:00
107 lines
3.5 KiB
Go
107 lines
3.5 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 pdf
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import (
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"bytes"
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"context"
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"crypto/sha256"
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"reflect"
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"github.com/xiaoqidun/pdfgo"
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)
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// imageValueBudget 限制图像描述的检查深度和保留字节数
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type imageValueBudget struct {
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nodes int
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bytes int
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}
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// ImageDigest 对无间接依赖的小图像生成编码摘要，超预算时不参与内容缓存
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// 入参: ctx 取消上下文, source 图像描述
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// 返回: [32]byte 编码摘要, bool 是否可复用, error 取消错误
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func ImageDigest(ctx context.Context, source *pdfgo.Image) ([32]byte, bool, error) {
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if source == nil || source.Stream == nil || len(source.Stream.Data) > 1<<20 {
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return [32]byte{}, false, nil
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}
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budget := imageValueBudget{nodes: 256, bytes: 65536}
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for _, value := range []pdfgo.Object{source.Stream.Dictionary, source.ColorSpace, source.Decode, source.Mask, source.SoftMask} {
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if !imageDirectValue(value, &budget) {
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return [32]byte{}, false, ctx.Err()
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}
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}
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hash := sha256.New()
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data := source.Stream.Data
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for len(data) != 0 {
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if err := ctx.Err(); err != nil {
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return [32]byte{}, false, err
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}
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n := min(len(data), 65536)
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hash.Write(data[:n])
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data = data[n:]
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}
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var result [32]byte
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hash.Sum(result[:0])
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return result, true, ctx.Err()
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}
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// SameImage 核对完整编码与有效图像属性，不以摘要相同代替内容相同
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// 入参: left 已缓存图像, right 待复用图像，二者须包含有效编码流
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// 返回: bool 是否可使用同一图像资源
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func SameImage(left, right *pdfgo.Image) bool {
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return left.Width == right.Width && left.Height == right.Height && left.BitsPerComponent == right.BitsPerComponent &&
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left.ImageMask == right.ImageMask && left.Interpolate == right.Interpolate &&
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bytes.Equal(left.Stream.Data, right.Stream.Data) && reflect.DeepEqual(left.Stream.Dictionary, right.Stream.Dictionary) &&
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reflect.DeepEqual(left.ColorSpace, right.ColorSpace) && reflect.DeepEqual(left.Decode, right.Decode) &&
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reflect.DeepEqual(left.Mask, right.Mask) && reflect.DeepEqual(left.SoftMask, right.SoftMask)
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}
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// imageDirectValue 检查图像描述是否完全独立，拒绝间接引用和嵌套流
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// 入参: value 描述值, budget 描述检查预算
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// 返回: bool 是否不依赖阅读器资源
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func imageDirectValue(value pdfgo.Object, budget *imageValueBudget) bool {
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if budget.nodes <= 0 || budget.bytes < 64 {
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return false
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}
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budget.nodes--
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budget.bytes -= 64
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switch v := value.(type) {
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case nil, pdfgo.Boolean, pdfgo.Integer, pdfgo.Real:
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return true
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case pdfgo.Name:
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budget.bytes -= len(v)
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return budget.bytes >= 0
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case pdfgo.String:
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budget.bytes -= len(v)
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return budget.bytes >= 0
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case pdfgo.Array:
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for _, child := range v {
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if !imageDirectValue(child, budget) {
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return false
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}
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}
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return true
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case pdfgo.Dictionary:
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for key, child := range v {
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budget.bytes -= len(key)
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if !imageDirectValue(child, budget) {
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return false
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}
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}
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return true
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}
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return false
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}
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