runtime/connection.h

//===-- runtime/connection.h ------------------------------------*- C++ -*-===//
//
// Part of the LLVM Project, under the Apache License v2.0 with LLVM Exceptions.
// See https://llvm.org/LICENSE.txt for license information.
// SPDX-License-Identifier: Apache-2.0 WITH LLVM-exception
//
//===----------------------------------------------------------------------===//

// Fortran I/O connection state (abstracted over internal & external units)

#ifndef FORTRAN_RUNTIME_IO_CONNECTION_H_
#define FORTRAN_RUNTIME_IO_CONNECTION_H_

#include "format.h"
#include <cinttypes>
#include <optional>

namespace Fortran::runtime::io {

enum class Direction { Output, Input };
enum class Access { Sequential, Direct, Stream };

inline bool IsRecordFile(Access a) { return a != Access::Stream; }

// These characteristics of a connection are immutable after being
// established in an OPEN statement.
struct ConnectionAttributes {
  Access access{Access::Sequential}; // ACCESS='SEQUENTIAL', 'DIRECT', 'STREAM'
  std::optional<bool> isUnformatted; // FORM='UNFORMATTED' if true
  bool isUTF8{false}; // ENCODING='UTF-8'
  bool isFixedRecordLength{false}; // RECL= on OPEN
  std::optional<std::int64_t> recordLength; // RECL= or current record
};

struct ConnectionState : public ConnectionAttributes {
  bool IsAtEOF() const; // true when read has hit EOF or endfile record
  std::size_t RemainingSpaceInRecord() const;
  bool NeedAdvance(std::size_t) const;
  void HandleAbsolutePosition(std::int64_t);
  void HandleRelativePosition(std::int64_t);

  void BeginRecord() {
    positionInRecord = 0;
    furthestPositionInRecord = 0;
    leftTabLimit.reset();
  }

  // Positions in a record file (sequential or direct, not stream)
  std::int64_t currentRecordNumber{1}; // 1 is first
  std::int64_t positionInRecord{0}; // offset in current record
  std::int64_t furthestPositionInRecord{0}; // max(position+bytes)

  // Set at end of non-advancing I/O data transfer
  std::optional<std::int64_t> leftTabLimit; // offset in current record

  // currentRecordNumber value captured after ENDFILE/REWIND/BACKSPACE statement
  // or an end-of-file READ condition on a sequential access file
  std::optional<std::int64_t> endfileRecordNumber;

  // Set when processing repeated items during list-directed & NAMELIST input
  // in order to keep a span of records in frame on a non-positionable file,
  // so that backspacing to the beginning of the repeated item doesn't require
  // repositioning the external storage medium when that's impossible.
  std::optional<std::int64_t> resumptionRecordNumber;

  // Mutable modes set at OPEN() that can be overridden in READ/WRITE & FORMAT
  MutableModes modes; // BLANK=, DECIMAL=, SIGN=, ROUND=, PAD=, DELIM=, kP
};

// Utility class for capturing and restoring a position in an input stream.
class SavedPosition {
public:
  explicit SavedPosition(ConnectionState &c)
      : connection_{c}, positionInRecord_{c.positionInRecord},
        furthestPositionInRecord_{c.furthestPositionInRecord},
        leftTabLimit_{c.leftTabLimit}, previousResumptionRecordNumber_{
                                           c.resumptionRecordNumber} {
    c.resumptionRecordNumber = c.currentRecordNumber;
  }
  ~SavedPosition() {
    connection_.currentRecordNumber = *connection_.resumptionRecordNumber;
    connection_.resumptionRecordNumber = previousResumptionRecordNumber_;
    connection_.leftTabLimit = leftTabLimit_;
    connection_.furthestPositionInRecord = furthestPositionInRecord_;
    connection_.positionInRecord = positionInRecord_;
  }

private:
  ConnectionState &connection_;
  std::int64_t positionInRecord_;
  std::int64_t furthestPositionInRecord_;
  std::optional<std::int64_t> leftTabLimit_;
  std::optional<std::int64_t> previousResumptionRecordNumber_;
};

} // namespace Fortran::runtime::io
#endif // FORTRAN_RUNTIME_IO_CONNECTION_H_