formats/png/hasher.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_PNG_HASHER_H_
#define THIRD_PARTY_CREDENTIO_FORMATS_PNG_HASHER_H_

#include <cstdint>
#include <optional>
#include <vector>

#include "absl/functional/function_ref.h"
#include "absl/status/statusor.h"
#include "crypto/algorithms.h"
#include "formats/byte_range.h"
#include "formats/png/reader.h"
#include "proto/data_hash_assertion.pb.h"
#include "riegeli/bytes/reader.h"

namespace credentio {

struct DigestPngResult {
  DataHashAssertion assertion;
  int64_t insertion_offset;
  std::optional<int64_t> existing_c2pa_length;
};

// Determines byte ranges within a given PNG chunk to be excluded from hashing.
// Returned ByteRange offsets must be absolute file offsets within
// [chunk.offset, chunk.offset + chunk.length).
using PngExclusionProcessor =
    absl::FunctionRef<absl::StatusOr<std::vector<ByteRange>>(
        riegeli::Reader& reader, const PngChunk& chunk)>;

// Digests the given PNG image and returns DigestPngResult that can be used to
// generate a C2PA manifest store. It is assumed that a C2PA manifest store will
// be inserted immediately before the first IDAT chunk or already appears
// somewhere before the first IDAT chunk.
//
// If `exclusion_processor` is provided, it is invoked for chunks to identify
// byte ranges to exclude from hashing.
absl::StatusOr<DigestPngResult> DigestPng(
    riegeli::Reader& input, HashAlgorithm alg,
    std::optional<PngExclusionProcessor> exclusion_processor = std::nullopt);
}  // namespace credentio

#endif  // THIRD_PARTY_CREDENTIO_FORMATS_PNG_HASHER_H_