formats/pdf/object_writer.cc

// 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.
//

#include "formats/pdf/object_writer.h"

#include <cstddef>
#include <cstdint>
#include <string>
#include <variant>

#include "absl/status/status.h"
#include "absl/status/status_macros.h"
#include "absl/status/statusor.h"
#include "absl/strings/str_cat.h"
#include "absl/strings/str_format.h"
#include "absl/strings/string_view.h"
#include "formats/pdf/number_validator.h"
#include "formats/pdf/objects.h"
#include "riegeli/bytes/string_writer.h"
#include "riegeli/bytes/writer.h"

namespace credentio {
namespace {

constexpr absl::string_view kTrue = "true";
constexpr absl::string_view kFalse = "false";
constexpr absl::string_view kNull = "null";

absl::Status WriteObject(const Object::Boolean& obj, riegeli::Writer& output) {
  std::string buffer = obj.value ? std::string(kTrue) : std::string(kFalse);
  if (!output.Write(buffer)) {
    return output.status();
  }
  return absl::OkStatus();
}

absl::Status WriteObject(const Object::Integer& obj, riegeli::Writer& output) {
  std::string buffer = absl::StrCat(obj.value);
  if (!output.Write(buffer)) {
    return output.status();
  }
  return absl::OkStatus();
}

absl::Status WriteObject(const Object::RealNumber& obj,
                         riegeli::Writer& output) {
  if (!IsValidRealNumber(obj.raw_value)) {
    return absl::InvalidArgumentError(
        absl::StrCat("Invalid real number: ", obj.raw_value));
  }
  std::string buffer = obj.raw_value;
  if (!output.Write(buffer)) {
    return output.status();
  }
  return absl::OkStatus();
}

absl::Status WriteObject(const Object::LiteralString& obj,
                         riegeli::Writer& output) {
  std::string buffer = "(";
  for (const char c : obj.raw_value) {
    if (c == '(' || c == ')' || c == '\\') {
      buffer += '\\';
      buffer += c;
    } else {
      buffer += c;
    }
  }
  buffer += ')';
  if (!output.Write(buffer)) {
    return output.status();
  }
  return absl::OkStatus();
}

absl::Status WriteObject(const Object::HexadecimalString& obj,
                         riegeli::Writer& output) {
  if (!IsValidHexadecimalString(obj.raw_value)) {
    return absl::InvalidArgumentError(
        absl::StrCat("Invalid hexadecimal string: ", obj.raw_value));
  }
  std::string buffer = absl::StrCat("<", obj.raw_value, ">");
  if (!output.Write(buffer)) {
    return output.status();
  }
  return absl::OkStatus();
}

absl::Status WriteObject(const Object::Name& obj, riegeli::Writer& output) {
  std::string buffer = "/";
  for (const char c : obj.value) {
    // Escape control characters, non-ASCII, slash, and any PDF delimiter
    // character. Delimiters include: (, ), <, >, [, ], {, }, %, #, /
    if (c < 0x21 || c > 0x7e || c == 0x2f || c == '(' || c == ')' || c == '<' ||
        c == '>' || c == '[' || c == ']' || c == '{' || c == '}' || c == '%' ||
        c == '#') {
      absl::StrAppendFormat(&buffer, "#%02x", static_cast<unsigned char>(c));
    } else {
      buffer += c;
    }
  }
  if (!output.Write(buffer)) {
    return output.status();
  }
  return absl::OkStatus();
}

absl::Status WriteObject(const Object::Array& obj, riegeli::Writer& output) {
  // Write the open bracket.
  std::string delimiter = "[";
  if (!output.Write(delimiter)) {
    return output.status();
  }

  // Write the elements separated by spaces.
  std::string space = " ";
  for (auto i = 0; i < obj.objects.size(); ++i) {
    ABSL_RETURN_IF_ERROR(WriteObject(obj.objects[i], output));
    // Write the space as a delimiter when necessary.
    if (i < obj.objects.size() - 1) {
      if (!output.Write(space)) {
        return output.status();
      }
    }
  }
  // Write the close bracket.
  delimiter = "]";
  if (!output.Write(delimiter)) {
    return output.status();
  }
  return absl::OkStatus();
}

absl::Status WriteObject(const Object::Dictionary& obj,
                         riegeli::Writer& output) {
  // Write the open brackets.
  std::string delimiter = "<<";
  if (!output.Write(delimiter)) {
    return output.status();
  }

  // Write the entries separated by spaces.
  std::string space = " ";
  int entries_written = 0;
  for (const auto& [key, value] : obj.entries) {
    // Write the key as a Name object.
    auto key_obj = Object{.value = Object::Name{.value = key}};
    ABSL_RETURN_IF_ERROR(WriteObject(key_obj, output));

    // Write the space as a delimiter.
    if (!output.Write(space)) {
      return output.status();
    }

    // Write the value object.
    ABSL_RETURN_IF_ERROR(WriteObject(value, output));

    // Write the space as a delimiter when necessary.
    if (entries_written < obj.entries.size() - 1) {
      if (!output.Write(space)) {
        return output.status();
      }
    }
    ++entries_written;
  }
  delimiter = ">>";
  if (!output.Write(delimiter)) {
    return output.status();
  }
  return absl::OkStatus();
}

absl::Status WriteObject(const Object::Stream& obj, riegeli::Writer& output) {
  std::string buffer = "stream\n";
  if (!output.Write(buffer)) {
    return output.status();
  }

  buffer = obj.raw_value;
  if (!output.Write(buffer)) {
    return output.status();
  }

  buffer = "\nendstream";
  if (!output.Write(buffer)) {
    return output.status();
  }
  return absl::OkStatus();
}

absl::Status WriteObject(const Object::Null& obj, riegeli::Writer& output) {
  std::string buffer = std::string(kNull);
  if (!output.Write(buffer)) {
    return output.status();
  }
  return absl::OkStatus();
}

absl::Status WriteObject(const Object::IndirectReference& obj,
                         riegeli::Writer& output) {
  std::string buffer =
      absl::StrCat(obj.object_number, " ", obj.generation_number, " R");
  if (!output.Write(buffer)) {
    return output.status();
  }
  return absl::OkStatus();
}

}  // namespace

absl::Status WriteObject(const Object& obj, riegeli::Writer& output) {
  if (std::holds_alternative<Object::Stream>(obj.value)) {
    return absl::InvalidArgumentError(
        "Stream must be written as an indirect object. Call "
        "WriteIndirectObject() instead.");
  }
  return std::visit(
      [&output](const auto& obj) { return WriteObject(obj, output); },
      obj.value);
}

absl::Status WriteIndirectObject(const IndirectObject& obj,
                                 riegeli::Writer& output, bool is_measurement) {
  // Write the object header.
  std::string buffer =
      absl::StrCat(obj.object_number, " ", obj.generation_number, " obj\n");
  if (!output.Write(buffer)) {
    return output.status();
  }
  if (obj.stream_dictionary.has_value()) {
    ABSL_ASSIGN_OR_RETURN(auto obj_stream,
                          Object::As<Object::Stream>(obj.object));
    Object::Dictionary serialized_dict = *obj.stream_dictionary;

    if (!obj_stream.raw_value.empty()) {
      serialized_dict.entries["Length"] =
          Object{.value = Object::Integer{.value = static_cast<int64_t>(
                                              obj_stream.raw_value.length())}};
    } else if (!is_measurement) {
      // Safely lock genuinely empty streams to /Length 0 to prevent smuggling.
      serialized_dict.entries["Length"] =
          Object{.value = Object::Integer{.value = 0}};
    }
    ABSL_RETURN_IF_ERROR(WriteObject(Object{.value = serialized_dict}, output));

    // Write a newline to separate the stream dictionary from the stream.
    buffer = "\n";
    if (!output.Write(buffer)) {
      return output.status();
    }
    ABSL_RETURN_IF_ERROR(WriteObject(obj_stream, output));
  } else {
    ABSL_RETURN_IF_ERROR(WriteObject(obj.object, output));
  }

  // Write the end-of-object marker.
  buffer = "\nendobj\n";
  if (!output.Write(buffer)) {
    return output.status();
  }
  return absl::OkStatus();
}

absl::StatusOr<int64_t> ComputeIndirectStreamHeaderByteSize(
    const IndirectObject& indirect_stream_obj) {
  if (!std::holds_alternative<Object::Stream>(
          indirect_stream_obj.object.value)) {
    return absl::InvalidArgumentError(
        "The object is not an indirect stream object.");
  }
  // Create a copy of the indirect stream object with only the header info to
  // avoid serializing the entire stream.
  IndirectObject indirect_stream_obj_copy;
  indirect_stream_obj_copy.object_number = indirect_stream_obj.object_number;
  indirect_stream_obj_copy.generation_number =
      indirect_stream_obj.generation_number;
  indirect_stream_obj_copy.stream_dictionary =
      indirect_stream_obj.stream_dictionary;
  indirect_stream_obj_copy.object = Object{.value = Object::Stream{}};

  std::string serialized_obj;
  riegeli::StringWriter<> output(&serialized_obj);
  ABSL_RETURN_IF_ERROR(WriteIndirectObject(indirect_stream_obj_copy, output,
                                           /*is_measurement=*/true));
  if (!output.Close()) {
    return output.status();
  }

  size_t pos = serialized_obj.length();
  while ((pos = serialized_obj.rfind("stream\n", pos)) != std::string::npos) {
    if (pos >= 3 && serialized_obj.substr(pos - 3, 3) == "end") {
      if (pos == 0) break;
      pos--;
      continue;
    }
    return pos + 7;
  }

  return absl::InternalError(
      "Failed to find the stream marker in the serialized object.");
}
}  // namespace credentio