venv/lib/python3.10/site-packages/pyarrow/include/arrow/io/interfaces.h

// Licensed to the Apache Software Foundation (ASF) under one
// or more contributor license agreements.  See the NOTICE file
// distributed with this work for additional information
// regarding copyright ownership.  The ASF licenses this file
// to you 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.

#pragma once

#include <cstdint>
#include <memory>
#include <string>
#include <string_view>
#include <vector>

#include "arrow/io/type_fwd.h"
#include "arrow/type_fwd.h"
#include "arrow/util/cancel.h"
#include "arrow/util/macros.h"
#include "arrow/util/type_fwd.h"
#include "arrow/util/visibility.h"

namespace arrow {
namespace io {

struct ReadRange {
  int64_t offset;
  int64_t length;

  friend bool operator==(const ReadRange& left, const ReadRange& right) {
    return (left.offset == right.offset && left.length == right.length);
  }
  friend bool operator!=(const ReadRange& left, const ReadRange& right) {
    return !(left == right);
  }

  bool Contains(const ReadRange& other) const {
    return (offset <= other.offset && offset + length >= other.offset + other.length);
  }
};

/// EXPERIMENTAL: options provider for IO tasks
///
/// Includes an Executor (which will be used to execute asynchronous reads),
/// a MemoryPool (which will be used to allocate buffers when zero copy reads
/// are not possible), and an external id (in case the executor receives tasks from
/// multiple sources and must distinguish tasks associated with this IOContext).
struct ARROW_EXPORT IOContext {
  // No specified executor: will use a global IO thread pool
  IOContext() : IOContext(default_memory_pool(), StopToken::Unstoppable()) {}

  explicit IOContext(StopToken stop_token)
      : IOContext(default_memory_pool(), std::move(stop_token)) {}

  explicit IOContext(MemoryPool* pool, StopToken stop_token = StopToken::Unstoppable());

  explicit IOContext(MemoryPool* pool, ::arrow::internal::Executor* executor,
                     StopToken stop_token = StopToken::Unstoppable(),
                     int64_t external_id = -1)
      : pool_(pool),
        executor_(executor),
        external_id_(external_id),
        stop_token_(std::move(stop_token)) {}

  explicit IOContext(::arrow::internal::Executor* executor,
                     StopToken stop_token = StopToken::Unstoppable(),
                     int64_t external_id = -1)
      : pool_(default_memory_pool()),
        executor_(executor),
        external_id_(external_id),
        stop_token_(std::move(stop_token)) {}

  MemoryPool* pool() const { return pool_; }

  ::arrow::internal::Executor* executor() const { return executor_; }

  // An application-specific ID, forwarded to executor task submissions
  int64_t external_id() const { return external_id_; }

  StopToken stop_token() const { return stop_token_; }

 private:
  MemoryPool* pool_;
  ::arrow::internal::Executor* executor_;
  int64_t external_id_;
  StopToken stop_token_;
};

class ARROW_EXPORT FileInterface : public std::enable_shared_from_this<FileInterface> {
 public:
  virtual ~FileInterface() = 0;

  /// \brief Close the stream cleanly
  ///
  /// For writable streams, this will attempt to flush any pending data
  /// before releasing the underlying resource.
  ///
  /// After Close() is called, closed() returns true and the stream is not
  /// available for further operations.
  virtual Status Close() = 0;

  /// \brief Close the stream asynchronously
  ///
  /// By default, this will just submit the synchronous Close() to the
  /// default I/O thread pool. Subclasses may implement this in a more
  /// efficient manner.
  virtual Future<> CloseAsync();

  /// \brief Close the stream abruptly
  ///
  /// This method does not guarantee that any pending data is flushed.
  /// It merely releases any underlying resource used by the stream for
  /// its operation.
  ///
  /// After Abort() is called, closed() returns true and the stream is not
  /// available for further operations.
  virtual Status Abort();

  /// \brief Return the position in this stream
  virtual Result<int64_t> Tell() const = 0;

  /// \brief Return whether the stream is closed
  virtual bool closed() const = 0;

  FileMode::type mode() const { return mode_; }

 protected:
  FileInterface() : mode_(FileMode::READ) {}
  FileMode::type mode_;
  void set_mode(FileMode::type mode) { mode_ = mode; }

 private:
  ARROW_DISALLOW_COPY_AND_ASSIGN(FileInterface);
};

class ARROW_EXPORT Seekable {
 public:
  virtual ~Seekable() = default;
  virtual Status Seek(int64_t position) = 0;
};

class ARROW_EXPORT Writable {
 public:
  virtual ~Writable() = default;

  /// \brief Write the given data to the stream
  ///
  /// This method always processes the bytes in full.  Depending on the
  /// semantics of the stream, the data may be written out immediately,
  /// held in a buffer, or written asynchronously.  In the case where
  /// the stream buffers the data, it will be copied.  To avoid potentially
  /// large copies, use the Write variant that takes an owned Buffer.
  virtual Status Write(const void* data, int64_t nbytes) = 0;

  /// \brief Write the given data to the stream
  ///
  /// Since the Buffer owns its memory, this method can avoid a copy if
  /// buffering is required.  See Write(const void*, int64_t) for details.
  virtual Status Write(const std::shared_ptr<Buffer>& data);

  /// \brief Flush buffered bytes, if any
  virtual Status Flush();

  Status Write(std::string_view data);
};

class ARROW_EXPORT Readable {
 public:
  virtual ~Readable() = default;

  /// \brief Read data from current file position.
  ///
  /// Read at most `nbytes` from the current file position into `out`.
  /// The number of bytes read is returned.
  virtual Result<int64_t> Read(int64_t nbytes, void* out) = 0;

  /// \brief Read data from current file position.
  ///
  /// Read at most `nbytes` from the current file position. Less bytes may
  /// be read if EOF is reached. This method updates the current file position.
  ///
  /// In some cases (e.g. a memory-mapped file), this method may avoid a
  /// memory copy.
  virtual Result<std::shared_ptr<Buffer>> Read(int64_t nbytes) = 0;

  /// EXPERIMENTAL: The IOContext associated with this file.
  ///
  /// By default, this is the same as default_io_context(), but it may be
  /// overridden by subclasses.
  virtual const IOContext& io_context() const;
};

class ARROW_EXPORT OutputStream : virtual public FileInterface, public Writable {
 protected:
  OutputStream() = default;
};

class ARROW_EXPORT InputStream : virtual public FileInterface, virtual public Readable {
 public:
  /// \brief Advance or skip stream indicated number of bytes
  /// \param[in] nbytes the number to move forward
  /// \return Status
  Status Advance(int64_t nbytes);

  /// \brief Return zero-copy string_view to upcoming bytes.
  ///
  /// Do not modify the stream position.  The view becomes invalid after
  /// any operation on the stream.  May trigger buffering if the requested
  /// size is larger than the number of buffered bytes.
  ///
  /// May return NotImplemented on streams that don't support it.
  ///
  /// \param[in] nbytes the maximum number of bytes to see
  virtual Result<std::string_view> Peek(int64_t nbytes);

  /// \brief Return true if InputStream is capable of zero copy Buffer reads
  ///
  /// Zero copy reads imply the use of Buffer-returning Read() overloads.
  virtual bool supports_zero_copy() const;

  /// \brief Read and return stream metadata
  ///
  /// If the stream implementation doesn't support metadata, empty metadata
  /// is returned.  Note that it is allowed to return a null pointer rather
  /// than an allocated empty metadata.
  virtual Result<std::shared_ptr<const KeyValueMetadata>> ReadMetadata();

  /// \brief Read stream metadata asynchronously
  virtual Future<std::shared_ptr<const KeyValueMetadata>> ReadMetadataAsync(
      const IOContext& io_context);
  Future<std::shared_ptr<const KeyValueMetadata>> ReadMetadataAsync();

 protected:
  InputStream() = default;
};

class ARROW_EXPORT RandomAccessFile : public InputStream, public Seekable {
 public:
  /// Necessary because we hold a std::unique_ptr
  ~RandomAccessFile() override;

  /// \brief Create an isolated InputStream that reads a segment of a
  /// RandomAccessFile. Multiple such stream can be created and used
  /// independently without interference
  /// \param[in] file a file instance
  /// \param[in] file_offset the starting position in the file
  /// \param[in] nbytes the extent of bytes to read. The file should have
  /// sufficient bytes available
  static Result<std::shared_ptr<InputStream>> GetStream(
      std::shared_ptr<RandomAccessFile> file, int64_t file_offset, int64_t nbytes);

  /// \brief Return the total file size in bytes.
  ///
  /// This method does not read or move the current file position, so is safe
  /// to call concurrently with e.g. ReadAt().
  virtual Result<int64_t> GetSize() = 0;

  /// \brief Read data from given file position.
  ///
  /// At most `nbytes` bytes are read.  The number of bytes read is returned
  /// (it can be less than `nbytes` if EOF is reached).
  ///
  /// This method can be safely called from multiple threads concurrently.
  /// It is unspecified whether this method updates the file position or not.
  ///
  /// The default RandomAccessFile-provided implementation uses Seek() and Read(),
  /// but subclasses may override it with a more efficient implementation
  /// that doesn't depend on implicit file positioning.
  ///
  /// \param[in] position Where to read bytes from
  /// \param[in] nbytes The number of bytes to read
  /// \param[out] out The buffer to read bytes into
  /// \return The number of bytes read, or an error
  virtual Result<int64_t> ReadAt(int64_t position, int64_t nbytes, void* out);

  /// \brief Read data from given file position.
  ///
  /// At most `nbytes` bytes are read, but it can be less if EOF is reached.
  ///
  /// \param[in] position Where to read bytes from
  /// \param[in] nbytes The number of bytes to read
  /// \return A buffer containing the bytes read, or an error
  virtual Result<std::shared_ptr<Buffer>> ReadAt(int64_t position, int64_t nbytes);

  /// EXPERIMENTAL: Read data asynchronously.
  virtual Future<std::shared_ptr<Buffer>> ReadAsync(const IOContext&, int64_t position,
                                                    int64_t nbytes);

  /// EXPERIMENTAL: Read data asynchronously, using the file's IOContext.
  Future<std::shared_ptr<Buffer>> ReadAsync(int64_t position, int64_t nbytes);

  /// EXPERIMENTAL: Explicit multi-read.
  /// \brief Request multiple reads at once
  ///
  /// The underlying filesystem may optimize these reads by coalescing small reads into
  /// large reads or by breaking up large reads into multiple parallel smaller reads.  The
  /// reads should be issued in parallel if it makes sense for the filesystem.
  ///
  /// One future will be returned for each input read range.  Multiple returned futures
  /// may correspond to a single read.  Or, a single returned future may be a combined
  /// result of several individual reads.
  ///
  /// \param[in] ranges The ranges to read
  /// \return A future that will complete with the data from the requested range is
  /// available
  virtual std::vector<Future<std::shared_ptr<Buffer>>> ReadManyAsync(
      const IOContext&, const std::vector<ReadRange>& ranges);

  /// EXPERIMENTAL: Explicit multi-read, using the file's IOContext.
  std::vector<Future<std::shared_ptr<Buffer>>> ReadManyAsync(
      const std::vector<ReadRange>& ranges);

  /// EXPERIMENTAL: Inform that the given ranges may be read soon.
  ///
  /// Some implementations might arrange to prefetch some of the data.
  /// However, no guarantee is made and the default implementation does nothing.
  /// For robust prefetching, use ReadAt() or ReadAsync().
  virtual Status WillNeed(const std::vector<ReadRange>& ranges);

 protected:
  RandomAccessFile();

 private:
  struct ARROW_NO_EXPORT Impl;
  std::unique_ptr<Impl> interface_impl_;
};

class ARROW_EXPORT WritableFile : public OutputStream, public Seekable {
 public:
  virtual Status WriteAt(int64_t position, const void* data, int64_t nbytes) = 0;

 protected:
  WritableFile() = default;
};

class ARROW_EXPORT ReadWriteFileInterface : public RandomAccessFile, public WritableFile {
 protected:
  ReadWriteFileInterface() { RandomAccessFile::set_mode(FileMode::READWRITE); }
};

/// \brief Return an iterator on an input stream
///
/// The iterator yields a fixed-size block on each Next() call, except the
/// last block in the stream which may be smaller.
/// Once the end of stream is reached, Next() returns nullptr
/// (unlike InputStream::Read() which returns an empty buffer).
ARROW_EXPORT
Result<Iterator<std::shared_ptr<Buffer>>> MakeInputStreamIterator(
    std::shared_ptr<InputStream> stream, int64_t block_size);

}  // namespace io
}  // namespace arrow