class mrpt::io::CCompressedInputStream

Overview

Transparently reads from a compressed file, automatically detecting the compression format from the file magic signature.

Supports:

Uncompressed files
Gzip compressed files (.gz)
Zstandard compressed files (.zst)

The compression type is detected automatically when opening the file.

#include <mrpt/io/CCompressedInputStream.h>

class CCompressedInputStream: public mrpt::io::CStream
{
public:
    // structs

    struct Impl;

    // construction

    CCompressedInputStream();
    CCompressedInputStream(const std::string& fileName);
    CCompressedInputStream(const CCompressedInputStream&);

    // methods

    CCompressedInputStream& operator = (const CCompressedInputStream&);
    virtual std::string getStreamDescription() const;
    bool open(const std::string& fileName, mrpt::optional_ref<std::string> error_msg = std::nullopt);
    void close();
    bool fileOpenCorrectly() const;
    bool is_open();
    bool checkEOF();
    std::string filePathAtUse() const;
    CompressionType getCompressionType() const;
    virtual uint64_t getTotalBytesCount() const;
    virtual uint64_t getPosition() const;
    uint64_t getUncompressedSize() const;
    double getCompressionRatio() const;
    uint64_t getUncompressedPosition() const;
    virtual uint64_t Seek(int64_t Offset, CStream::TSeekOrigin Origin);
    virtual size_t Read(void* Buffer, size_t Count);
    virtual size_t Write(const void* Buffer, size_t Count);
};

Inherited Members

public:
    // methods

    virtual size_t Read(void* Buffer, size_t Count) = 0;
    virtual size_t Write(const void* Buffer, size_t Count) = 0;
    virtual uint64_t getTotalBytesCount() const = 0;
    virtual uint64_t getPosition() const = 0;

Construction

CCompressedInputStream()

Constructor without open.

CCompressedInputStream(const std::string& fileName)

Constructor and open.

Parameters:

fileName	The file to be opened in this stream
std::exception	If there’s an error opening the file.

Methods

virtual std::string getStreamDescription() const

Returns a human-friendly description of the stream, e.g.

a filename.

bool open(const std::string& fileName, mrpt::optional_ref<std::string> error_msg = std::nullopt)

Opens the file for reading.

Automatically detects compression format.

Parameters:

fileName	The file to be opened in this stream
error_msg	Optional output parameter for error message

Returns:

false if there’s an error opening the file, true otherwise

void close()

Closes the file.

bool fileOpenCorrectly() const

Returns true if the file was opened without errors.

bool is_open()

Returns true if the file was opened without errors.

bool checkEOF()

Will be true if EOF has been already reached.

std::string filePathAtUse() const

Returns the path of the filename passed to open(), or empty if none.

CompressionType getCompressionType() const

Returns the detected compression type for the opened file.

virtual uint64_t getTotalBytesCount() const

Method for getting the total number of compressed bytes in the file (the physical size of the file on disk).

virtual uint64_t getPosition() const

Method for getting the current cursor position in the compressed data, where 0 is the first byte and TotalBytesCount-1 the last one.

For uncompressed files, this equals the position in uncompressed data. For compressed files, this is an approximation based on the compressed stream position.

uint64_t getUncompressedSize() const

Attempts to estimate the total uncompressed size of the file.

For Gzip files, this reads the size from the footer if available. For Zstd files with frame content size, returns that value. For uncompressed files, returns the actual file size. If the exact size is not available, returns an estimate based on the compression ratio measured so far (compressed bytes read vs uncompressed bytes served). This estimate improves as more data is read. Returns 0 only if no data has been read yet and no size hint is available.

Returns:

Estimated uncompressed size, or 0 if it cannot be determined.

double getCompressionRatio() const

Returns the compression ratio measured so far.

This is the ratio: uncompressed_bytes / compressed_bytes. A ratio of 3.0 means the data compressed to 1/3 of its original size.

Returns:

Ratio of uncompressed to compressed bytes, or 0.0 if no data read.

uint64_t getUncompressedPosition() const

Estimates the current position in the uncompressed data stream.

This is an estimate and may not be accurate for all compression formats.

Returns:

Estimated position in uncompressed data, or 0 if it cannot be determined.

virtual uint64_t Seek(int64_t Offset, CStream::TSeekOrigin Origin)

This method is not implemented in this class.

virtual size_t Read(void* Buffer, size_t Count)

Introduces a pure virtual method responsible for reading from the stream.

virtual size_t Write(const void* Buffer, size_t Count)

Introduces a pure virtual method responsible for writing to the stream.

Write attempts to write up to Count bytes to Buffer, and returns the number of bytes actually written.