Input / output#

Interfaces#

class FileInterface : public std::enable_shared_from_this<FileInterface>#

Subclassed by arrow::io::InputStream, arrow::io::OutputStream

Public Functions

virtual Status Close() = 0#

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 Future CloseAsync()#

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 Status Abort()#

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 Result<int64_t> Tell() const = 0#: Return the position in this stream.

virtual bool closed() const = 0#: Return whether the stream is closed.

class Readable#

Subclassed by arrow::io::InputStream

Public Functions

virtual Result<int64_t> Read(int64_t nbytes, void *out) = 0#

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<std::shared_ptr<Buffer>> Read(int64_t nbytes) = 0#

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 const IOContext &io_context() const#

EXPERIMENTAL: The IOContext associated with this file.

By default, this is the same as default_io_context(), but it may be overridden by subclasses.

class Seekable#: Subclassed by arrow::io::RandomAccessFile, arrow::io::WritableFile

class Writable#

Subclassed by arrow::io::OutputStream

Public Functions

virtual Status Write(const void *data, int64_t nbytes) = 0#

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 std::shared_ptr<Buffer> &data)#

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 Flush()#: Flush buffered bytes, if any.

class InputStream : public virtual arrow::io::FileInterface, public virtual arrow::io::Readable #

Subclassed by arrow::io::SlowInputStreamBase< InputStream >, arrow::io::internal::InputStreamConcurrencyWrapper< CompressedInputStream >, arrow::io::internal::InputStreamConcurrencyWrapper< BufferedInputStream >, arrow::io::RandomAccessFile, arrow::io::StdinStream, arrow::io::TransformInputStream, arrow::io::internal::InputStreamConcurrencyWrapper< Derived >

Public Functions

Status Advance(int64_t nbytes)#

Advance or skip stream indicated number of bytes.

Parameters:: nbytes – [in] the number to move forward
Returns:: Status

virtual Result<std::string_view> Peek(int64_t nbytes)#

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.

Parameters:: nbytes – [in] the maximum number of bytes to see

virtual bool supports_zero_copy() const#

Return true if InputStream is capable of zero copy Buffer reads.

Zero copy reads imply the use of Buffer-returning Read() overloads.

virtual Result<std::shared_ptr<const KeyValueMetadata>> ReadMetadata()#

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 Future<std::shared_ptr<const KeyValueMetadata>> ReadMetadataAsync(const IOContext &io_context)#: Read stream metadata asynchronously.

class RandomAccessFile : public arrow::io::InputStream, public arrow::io::Seekable #

Subclassed by arrow::io::SlowInputStreamBase< RandomAccessFile >, arrow::io::internal::RandomAccessFileConcurrencyWrapper< ReadableFile >, arrow::io::internal::RandomAccessFileConcurrencyWrapper< CudaBufferReader >, arrow::io::internal::RandomAccessFileConcurrencyWrapper< BufferReader >, arrow::io::HdfsReadableFile, arrow::io::ReadWriteFileInterface, arrow::io::internal::RandomAccessFileConcurrencyWrapper< Derived >

Public Functions

~RandomAccessFile() override#: Necessary because we hold a std::unique_ptr.

virtual Result<int64_t> GetSize() = 0#

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> ReadAt(int64_t position, int64_t nbytes, void *out)#

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.

Parameters:

position – [in] Where to read bytes from
nbytes – [in] The number of bytes to read
out – [out] The buffer to read bytes into

Returns:

The number of bytes read, or an error

virtual Result<std::shared_ptr<Buffer>> ReadAt(int64_t position, int64_t nbytes)#

Read data from given file position.

At most nbytes bytes are read, but it can be less if EOF is reached.

Parameters:

position – [in] Where to read bytes from
nbytes – [in] The number of bytes to read

Returns:

A buffer containing the bytes read, or an error

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

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

virtual std::vector<Future<std::shared_ptr<Buffer>>> ReadManyAsync(const IOContext&, const std::vector<ReadRange> &ranges)#

EXPERIMENTAL: Explicit multi-read.

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.

Parameters:: ranges – [in] The ranges to read
Returns:: A future that will complete with the data from the requested range is available

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

virtual Status WillNeed(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().

Public Static Functions

static Result<std::shared_ptr<InputStream>> GetStream(std::shared_ptr<RandomAccessFile> file, int64_t file_offset, int64_t nbytes)#

Create an isolated InputStream that reads a segment of a RandomAccessFile.

Multiple such stream can be created and used independently without interference

Parameters:

file – [in] a file instance
file_offset – [in] the starting position in the file
nbytes – [in] the extent of bytes to read. The file should have sufficient bytes available

class OutputStream : public virtual arrow::io::FileInterface, public arrow::io::Writable #: Subclassed by arrow::io::BufferOutputStream, arrow::io::BufferedOutputStream, arrow::io::CompressedOutputStream, arrow::io::FileOutputStream, arrow::io::HdfsOutputStream, arrow::io::MockOutputStream, arrow::io::StderrStream, arrow::io::StdoutStream, arrow::io::WritableFile

class ReadWriteFileInterface : public arrow::io::RandomAccessFile, public arrow::io::WritableFile#: Subclassed by arrow::io::MemoryMappedFile

Concrete implementations#

In-memory streams#

class BufferReader : public arrow::io::internal::RandomAccessFileConcurrencyWrapper<BufferReader>#

Random access zero-copy reads on an arrow::Buffer.

Public Functions

explicit BufferReader(std::shared_ptr<Buffer> buffer)#

Instantiate from std::shared_ptr<Buffer>.

This is a zero-copy constructor.

explicit BufferReader(std::string_view data)#

Instantiate from std::string_view.

Does not own data

Deprecated:: Deprecated in 14.0.0. Use FromString or BufferReader(std::shared_ptr<Buffer> buffer) instead.

virtual bool closed() const override#: Return whether the stream is closed.

virtual bool supports_zero_copy() const override#

Return true if InputStream is capable of zero copy Buffer reads.

Zero copy reads imply the use of Buffer-returning Read() overloads.

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

virtual Status WillNeed(const std::vector<ReadRange> &ranges) override#

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().

Public Static Functions

static std::unique_ptr<BufferReader> FromString(std::string data)#: Instantiate from std::string. Owns data.

class MockOutputStream : public arrow::io::OutputStream #

A helper class to track the size of allocations.

Writes to this stream do not copy or retain any data, they just bump a size counter that can be later used to know exactly which data size needs to be allocated for actual writing.

Public Functions

virtual Status Close() override#

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 bool closed() const override#: Return whether the stream is closed.

virtual Result<int64_t> Tell() const override#: Return the position in this stream.

virtual Status Write(const void *data, int64_t nbytes) override#

Write the given data to the stream.

class BufferOutputStream : public arrow::io::OutputStream #

An output stream that writes to a resizable buffer.

Public Functions

virtual Status Close() override#: Close the stream, preserving the buffer (retrieve it with Finish()).

virtual bool closed() const override#: Return whether the stream is closed.

virtual Result<int64_t> Tell() const override#: Return the position in this stream.

virtual Status Write(const void *data, int64_t nbytes) override#

Write the given data to the stream.

Result<std::shared_ptr<Buffer>> Finish()#: Close the stream and return the buffer.

Status Reset(int64_t initial_capacity = 1024, MemoryPool *pool = default_memory_pool())#

Initialize state of OutputStream with newly allocated memory and set position to 0.

Parameters:

initial_capacity – [in] the starting allocated capacity
pool – [inout] the memory pool to use for allocations

Returns:

Status

Public Static Functions

static Result<std::shared_ptr<BufferOutputStream>> Create(int64_t initial_capacity = 4096, MemoryPool *pool = default_memory_pool())#

Create in-memory output stream with indicated capacity using a memory pool.

Parameters:

initial_capacity – [in] the initial allocated internal capacity of the OutputStream
pool – [inout] a MemoryPool to use for allocations

Returns:

the created stream

class FixedSizeBufferWriter : public arrow::io::WritableFile#

An output stream that writes into a fixed-size mutable buffer.

Public Functions

explicit FixedSizeBufferWriter(const std::shared_ptr<Buffer> &buffer)#: Input buffer must be mutable, will abort if not.

virtual Status Close() override#

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 bool closed() const override#: Return whether the stream is closed.

virtual Result<int64_t> Tell() const override#: Return the position in this stream.

virtual Status Write(const void *data, int64_t nbytes) override#

Write the given data to the stream.

Local files#

class ReadableFile : public arrow::io::internal::RandomAccessFileConcurrencyWrapper<ReadableFile>#

An operating system file open in read-only mode.

Reads through this implementation are unbuffered. If many small reads need to be issued, it is recommended to use a buffering layer for good performance.

Public Functions

virtual bool closed() const override#: Return whether the stream is closed.

virtual Status WillNeed(const std::vector<ReadRange> &ranges) override#

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().

Public Static Functions

static Result<std::shared_ptr<ReadableFile>> Open(const std::string &path, MemoryPool *pool = default_memory_pool())#

Open a local file for reading.

Parameters:

path – [in] with UTF8 encoding
pool – [in] a MemoryPool for memory allocations

Returns:

ReadableFile instance

static Result<std::shared_ptr<ReadableFile>> Open(int fd, MemoryPool *pool = default_memory_pool())#

Open a local file for reading.

The file descriptor becomes owned by the ReadableFile, and will be closed on Close() or destruction.

Parameters:

fd – [in] file descriptor
pool – [in] a MemoryPool for memory allocations

Returns:

ReadableFile instance

class FileOutputStream : public arrow::io::OutputStream #

An operating system file open in write-only mode.

Public Functions

virtual Status Close() override#

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 bool closed() const override#: Return whether the stream is closed.

virtual Result<int64_t> Tell() const override#: Return the position in this stream.

virtual Status Write(const void *data, int64_t nbytes) override#

Write the given data to the stream.

Public Static Functions

static Result<std::shared_ptr<FileOutputStream>> Open(const std::string &path, bool append = false)#

Open a local file for writing, truncating any existing file.

When opening a new file, any existing file with the indicated path is truncated to 0 bytes, deleting any existing data

Parameters:

path – [in] with UTF8 encoding
append – [in] append to existing file, otherwise truncate to 0 bytes

Returns:

an open FileOutputStream

static Result<std::shared_ptr<FileOutputStream>> Open(int fd)#

Open a file descriptor for writing.

The underlying file isn’t truncated.

The file descriptor becomes owned by the

OutputStream, and will be closed on Close() or destruction.

Parameters:: fd – [in] file descriptor
Returns:: an open FileOutputStream

class MemoryMappedFile : public arrow::io::ReadWriteFileInterface #

A file interface that uses memory-mapped files for memory interactions.

This implementation supports zero-copy reads. The same class is used for both reading and writing.

If opening a file in a writable mode, it is not truncated first as with FileOutputStream.

Public Functions

virtual Status Close() override#

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 bool closed() const override#: Return whether the stream is closed.

virtual Result<int64_t> Tell() const override#: Return the position in this stream.

virtual Result<int64_t> Read(int64_t nbytes, void *out) override#

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<std::shared_ptr<Buffer>> Read(int64_t nbytes) override#

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>> ReadAt(int64_t position, int64_t nbytes) override#

Read data from given file position.

At most nbytes bytes are read, but it can be less if EOF is reached.

Parameters:

position – [in] Where to read bytes from
nbytes – [in] The number of bytes to read

Returns:

A buffer containing the bytes read, or an error

virtual Result<int64_t> ReadAt(int64_t position, int64_t nbytes, void *out) override#

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.

Parameters:

position – [in] Where to read bytes from
nbytes – [in] The number of bytes to read
out – [out] The buffer to read bytes into

Returns:

The number of bytes read, or an error

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

virtual Status WillNeed(const std::vector<ReadRange> &ranges) override#

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 bool supports_zero_copy() const override#

Return true if InputStream is capable of zero copy Buffer reads.

Zero copy reads imply the use of Buffer-returning Read() overloads.

virtual Status Write(const void *data, int64_t nbytes) override#: Write data at the current position in the file. Thread-safe.

Status Resize(int64_t new_size)#: Set the size of the map to new_size.

virtual Status WriteAt(int64_t position, const void *data, int64_t nbytes) override#: Write data at a particular position in the file. Thread-safe.

virtual Result<int64_t> GetSize() override#

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().

Public Static Functions

static Result<std::shared_ptr<MemoryMappedFile>> Create(const std::string &path, int64_t size)#: Create new file with indicated size, return in read/write mode.

Buffering input / output wrappers#

class BufferedInputStream : public arrow::io::internal::InputStreamConcurrencyWrapper<BufferedInputStream>#

An InputStream that performs buffered reads from an unbuffered InputStream, which can mitigate the overhead of many small reads in some cases.

Public Functions

Status SetBufferSize(int64_t new_buffer_size)#

Resize internal read buffer; calls to Read(…) will read at least.

Parameters:: new_buffer_size – [in] the new read buffer size
Returns:: Status

int64_t bytes_buffered() const#: Return the number of remaining bytes in the read buffer.

int64_t buffer_size() const#: Return the current size of the internal buffer.

std::shared_ptr<InputStream> Detach()#

Release the raw InputStream.

Any data buffered will be discarded. Further operations on this object are invalid

Returns:: raw the underlying InputStream

std::shared_ptr<InputStream> raw() const#: Return the unbuffered InputStream.

virtual bool closed() const override#: Return whether the stream is closed.

virtual Result<std::shared_ptr<const KeyValueMetadata>> ReadMetadata() override#

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 Future<std::shared_ptr<const KeyValueMetadata>> ReadMetadataAsync(const IOContext &io_context) override#: Read stream metadata asynchronously.

Public Static Functions

static Result<std::shared_ptr<BufferedInputStream>> Create(int64_t buffer_size, MemoryPool *pool, std::shared_ptr<InputStream> raw, int64_t raw_read_bound = -1)#

Create a BufferedInputStream from a raw InputStream.

Parameters:

buffer_size – [in] the size of the temporary read buffer
pool – [in] a MemoryPool to use for allocations
raw – [in] a raw InputStream
raw_read_bound – [in] a bound on the maximum number of bytes to read from the raw input stream. The default -1 indicates that it is unbounded

Returns:

the created BufferedInputStream

class BufferedOutputStream : public arrow::io::OutputStream #

Public Functions

Status SetBufferSize(int64_t new_buffer_size)#

Resize internal buffer.

Parameters:: new_buffer_size – [in] the new buffer size
Returns:: Status

int64_t buffer_size() const#: Return the current size of the internal buffer.

int64_t bytes_buffered() const#: Return the number of remaining bytes that have not been flushed to the raw OutputStream.

Result<std::shared_ptr<OutputStream>> Detach()#

Flush any buffered writes and release the raw OutputStream.

Further operations on this object are invalid

Returns:: the underlying OutputStream

virtual Status Close() override#

Close the buffered output stream.

This implicitly closes the underlying raw output stream.

virtual Status Abort() override#

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 bool closed() const override#: Return whether the stream is closed.

virtual Result<int64_t> Tell() const override#: Return the position in this stream.

virtual Status Write(const void *data, int64_t nbytes) override#

Write the given data to the stream.

virtual Status Write(const std::shared_ptr<Buffer> &data) override#

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 Flush() override#: Flush buffered bytes, if any.

std::shared_ptr<OutputStream> raw() const#: Return the underlying raw output stream.

Public Static Functions

static Result<std::shared_ptr<BufferedOutputStream>> Create(int64_t buffer_size, MemoryPool *pool, std::shared_ptr<OutputStream> raw)#

Create a buffered output stream wrapping the given output stream.

Parameters:

buffer_size – [in] the size of the temporary write buffer
pool – [in] a MemoryPool to use for allocations
raw – [in] another OutputStream

Returns:

the created BufferedOutputStream

Compressed input / output wrappers#

class CompressedInputStream : public arrow::io::internal::InputStreamConcurrencyWrapper<CompressedInputStream>#

Public Functions

virtual bool closed() const override#: Return whether the stream is closed.

virtual Result<std::shared_ptr<const KeyValueMetadata>> ReadMetadata() override#

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 Future<std::shared_ptr<const KeyValueMetadata>> ReadMetadataAsync(const IOContext &io_context) override#: Read stream metadata asynchronously.

std::shared_ptr<InputStream> raw() const#: Return the underlying raw input stream.

Public Static Functions

static Result<std::shared_ptr<CompressedInputStream>> Make(util::Codec *codec, const std::shared_ptr<InputStream> &raw, MemoryPool *pool = default_memory_pool())#: Create a compressed input stream wrapping the given input stream.

class CompressedOutputStream : public arrow::io::OutputStream #

Public Functions

virtual Status Close() override#

Close the compressed output stream.

This implicitly closes the underlying raw output stream.

virtual Status Abort() override#

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 bool closed() const override#: Return whether the stream is closed.

virtual Result<int64_t> Tell() const override#: Return the position in this stream.

virtual Status Write(const void *data, int64_t nbytes) override#

Write the given data to the stream.

virtual Status Flush() override#: Flush buffered bytes, if any.

std::shared_ptr<OutputStream> raw() const#: Return the underlying raw output stream.

Public Static Functions

static Result<std::shared_ptr<CompressedOutputStream>> Make(util::Codec *codec, const std::shared_ptr<OutputStream> &raw, MemoryPool *pool = default_memory_pool())#: Create a compressed output stream wrapping the given output stream.

Transforming input wrapper#

class TransformInputStream : public arrow::io::InputStream #

Public Functions

virtual Status Close() override#

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 Abort() override#

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 bool closed() const override#: Return whether the stream is closed.

virtual Result<int64_t> Read(int64_t nbytes, void *out) override#

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<std::shared_ptr<Buffer>> Read(int64_t nbytes) override#

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<const KeyValueMetadata>> ReadMetadata() override#

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 Future<std::shared_ptr<const KeyValueMetadata>> ReadMetadataAsync(const IOContext &io_context) override#: Read stream metadata asynchronously.

virtual Result<int64_t> Tell() const override#: Return the position in this stream.