formats/pdf/reader.h

// Copyright 2026 Google LLC
//
// 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
//
//    https://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.
//

#ifndef THIRD_PARTY_CREDENTIO_FORMATS_PDF_READER_H_
#define THIRD_PARTY_CREDENTIO_FORMATS_PDF_READER_H_

#include <cstdint>
#include <memory>
#include <utility>

#include "absl/base/nullability.h"
#include "absl/container/btree_map.h"
#include "absl/container/btree_set.h"
#include "absl/status/statusor.h"
#include "formats/pdf/objects.h"
#include "riegeli/bytes/reader.h"

namespace credentio {

// PDF reader for C2PA, holds onto a reference to a `riegeli::Reader` which
// must outlive the reader.
class PdfReader {
 public:
  // Creates and initializes a PdfReader.
  static absl::StatusOr<std::unique_ptr<PdfReader>> Create(
      riegeli::Reader* absl_nonnull input);

  // Returns true if there is a next PDF object to read.
  bool HasNext();

  // Reads the next PDF object from the input.
  absl::StatusOr<IndirectObject> Next();

  // Returns the file trailer dictionary.
  const Object::Dictionary& file_trailer_dictionary() const {
    return file_trailer_dictionary_;
  }

  // Returns the ordered set of free object entries in the cross-reference
  // table.
  const absl::btree_set<Object::IndirectReference>& free_entries() const {
    return free_entries_;
  }

  // Returns the byte offset of the PDF object with the given object number and
  // generation number. If the object is not found, returns a NOT_FOUND error.
  absl::StatusOr<uint64_t> GetObjectOffset(uint32_t object_number,
                                           uint32_t generation_number);

  // Returns the PDF object with the given object number and generation number.
  // If the object is not found, returns a NOT_FOUND error.
  absl::StatusOr<IndirectObject> GetObject(uint32_t object_number,
                                           uint32_t generation_number);

 private:
  explicit PdfReader(
      riegeli::Reader* absl_nonnull input,
      absl::btree_map<Object::IndirectReference, uint64_t>&& xref_table,
      absl::btree_set<Object::IndirectReference>&& free_entries,
      Object::Dictionary&& file_trailer_dict)
      : input_(*input),
        xref_table_(std::move(xref_table)),
        current_it_(xref_table_.begin()),
        free_entries_(std::move(free_entries)),
        file_trailer_dictionary_(std::move(file_trailer_dict)) {}

  riegeli::Reader& input_;

  // Cross-reference table mapping in-use object references to their byte
  // offsets in the input stream.
  const absl::btree_map<Object::IndirectReference, uint64_t> xref_table_;
  absl::btree_map<Object::IndirectReference, uint64_t>::const_iterator
      current_it_;

  // Set of free object entries in the cross-reference table.
  const absl::btree_set<Object::IndirectReference> free_entries_;

  // File trailer dictionary.
  const Object::Dictionary file_trailer_dictionary_;

  // Active objects during indirect reference resolution to detect cycles.
  absl::btree_set<Object::IndirectReference> active_objects_;
};
}  // namespace credentio
#endif  // THIRD_PARTY_CREDENTIO_FORMATS_PDF_READER_H_