feat(文件归并): 归并PDF适配与解析逻辑

internal/codec/pdf/reference.go

@@ -0,0 +1,121 @@
+// Copyright 2025-2026 肖其顿 (XIAO QI DUN)
+//
+// Licensed under the Apache License, Version 2.0 (the "License");
+// you may not use this file except in compliance with the License.
+// You may obtain a copy of the License at
+//
+// http://www.apache.org/licenses/LICENSE-2.0
+//
+// Unless required by applicable law or agreed to in writing, software
+// distributed under the License is distributed on an "AS IS" BASIS,
+// WITHOUT WARRANTIES OR CONDITIONS OF ANY KIND, either express or implied.
+// See the License for the specific language governing permissions and
+// limitations under the License.
+
+package pdf
+
+import (
+	"bytes"
+	"context"
+	"crypto/sha256"
+	"errors"
+	"fmt"
+
+	"github.com/xiaoqidun/pdfgo"
+)
+
+// ReferenceCache 保存单次会话拥有的引用文档及页面，零值可用，须串行使用且使用后不应复制
+// Close只释放缓存自行打开的阅读器，不关闭来源文档或调用方提供的阅读器
+type ReferenceCache struct {
+	readers map[[32]byte]*pdfgo.Reader
+	streams map[*pdfgo.Stream]*pdfgo.Reader
+	pages   map[referencePageKey]*pdfgo.Page
+}
+
+// referencePageKey 区分目标文档、索引和文本标签，避免重复遍历页面树
+type referencePageKey struct {
+	reader  *pdfgo.Reader
+	index   int64
+	label   string
+	labeled bool
+}
+
+// Resolve 解析引用目标，目标不可用时按PDF标准保留代理内容
+// 入参: ctx 取消上下文, source 来源文档, reference 引用目标, fileResolver 外部文件读取, referenceResolver 调用方页面解析, warning 诊断回调
+// 返回: *pdfgo.Page 目标页面，不可用时为空, error 取消或调用方解析错误
+func (c *ReferenceCache) Resolve(ctx context.Context, source *pdfgo.Reader, reference pdfgo.ReferenceXObject, fileResolver pdfgo.FileResolver, referenceResolver pdfgo.ReferenceResolver, warning func(pdfgo.Diagnostic)) (*pdfgo.Page, error) {
+	if err := ctx.Err(); err != nil {
+		return nil, err
+	}
+	if referenceResolver != nil {
+		return referenceResolver(ctx, source, reference)
+	}
+	reader := c.streams[reference.File.Embedded]
+	if reader == nil {
+		if reference.File.Embedded == nil && fileResolver == nil {
+			return referenceProxy(ctx, fmt.Errorf("external reference file unavailable"), warning)
+		}
+		data, err := source.ReadFileData(ctx, reference.File, fileResolver)
+		if err != nil {
+			return referenceProxy(ctx, err, warning)
+		}
+		key := sha256.Sum256(data)
+		reader = c.readers[key]
+		if reader == nil {
+			reader, err = pdfgo.NewReaderWithOptions(bytes.NewReader(data), int64(len(data)), pdfgo.ReaderOptions{Warning: warning})
+			if err != nil {
+				return referenceProxy(ctx, err, warning)
+			}
+			if c.readers == nil {
+				c.readers = make(map[[32]byte]*pdfgo.Reader)
+			}
+			c.readers[key] = reader
+		}
+		if reference.File.Embedded != nil {
+			if c.streams == nil {
+				c.streams = make(map[*pdfgo.Stream]*pdfgo.Reader)
+			}
+			c.streams[reference.File.Embedded] = reader
+		}
+	}
+	key := referencePageKey{reader: reader, index: reference.PageIndex}
+	if reference.PageLabel != nil {
+		key.index, key.label, key.labeled = 0, *reference.PageLabel, true
+	}
+	if page := c.pages[key]; page != nil {
+		return page, ctx.Err()
+	}
+	page, err := reader.ResolveReferencePage(ctx, reference)
+	if err != nil {
+		return referenceProxy(ctx, err, warning)
+	}
+	if c.pages == nil {
+		c.pages = make(map[referencePageKey]*pdfgo.Page)
+	}
+	c.pages[key] = page
+	return page, ctx.Err()
+}
+
+// referenceProxy 记录目标不可用原因，不将合法的代理绘制视为转换失败
+// 入参: ctx 取消上下文, cause 目标不可用原因, warning 诊断回调
+// 返回: *pdfgo.Page 空目标, error 取消错误
+func referenceProxy(ctx context.Context, cause error, warning func(pdfgo.Diagnostic)) (*pdfgo.Page, error) {
+	if err := ctx.Err(); err != nil {
+		return nil, err
+	}
+	if errors.Is(cause, context.Canceled) || errors.Is(cause, context.DeadlineExceeded) {
+		return nil, cause
+	}
+	if warning != nil {
+		warning(pdfgo.Diagnostic{Message: "reference XObject proxy retained: " + cause.Error()})
+	}
+	return nil, nil
+}
+
+// Close 释放本次会话打开的引用文档并清空缓存，可重复调用，之后可重新解析
+func (c *ReferenceCache) Close() {
+	for _, reader := range c.readers {
+		reader.Close()
+	}
+	c.readers, c.streams, c.pages = nil, nil, nil
+}