File.cc File Reference

#include "File.h"
#include <spdlog/fmt/fmt.h>
#include <fstream>
#include <regex>
#include "String.h"

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Functions
uint32_t	GetMagicNumber (const std::string &filename)
	Reads the magic number from the beginning of a file.
bool	IsCompressedFits (const std::string &filename)
	Checks whether a given file is a compressed FITS file.
bool	IsRemoteHttpFile (const std::string &filename)
	Checks whether a given filename represents a remote HTTP or HTTPS URL.
bool	IsGzMagicNumber (uint32_t magic_number)
	Determines if a given magic number corresponds to a gzip-compressed file.
int	GetNumItems (const std::string &path)
	Counts the number of items in a given directory.
fs::path	SearchPath (std::string filename)
	Searches for a file in the system's PATH environment variable.
CARTA::FileType	GuessImageType (const std::string &path_string, bool check_content)
	Determines the image file type based on its content or extension.
CARTA::FileType	GuessRegionType (const std::string &path_string, bool check_content)
	Determines the region file type based on its content or extension.
CARTA::CatalogFileType	GuessTableType (const std::string &path_string, bool check_content)
	Determines the catalog table file type based on its content or file extension.

Function Documentation

GetMagicNumber()

uint32_t GetMagicNumber

(

const std::string &

filename

)

Reads the magic number from the beginning of a file.

This function opens the specified file and reads the first 4 bytes as a uint32_t magic number.

Note

• The function assumes the file's magic number is stored in the first 4 bytes.
• Reads the file in binary mode would be safer to avoid unwanted conversions.
• The byte order (endianness) of the magic number depends on the system architecture.

Warning

• If the file does not exist or is not readable, the function returns 0 without error messages.

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GetNumItems()

int GetNumItems

(

const std::string &

path

)

Counts the number of items in a given directory.

This function iterates over the contents of the specified directory and counts the number of files and subdirectories present. If the directory does not exist or cannot be accessed, the function returns -1.

Note

This function does not distinguish between files and subdirectories; it counts both.

Warning

If the path is invalid or inaccessible, an exception is caught internally, and -1 is returned.

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GuessImageType()

CARTA::FileType GuessImageType	(	const std::string &	path_string,
		bool	check_content
	)

Determines the image file type based on its content or extension.

This function attempts to identify the type of an image file either by checking its magic number (file signature) or examining its file extension. If check_content is set to true, the function inspects the file's magic number to classify it as FITS or HDF5. If check_content is false, it relies on common file extensions.

Note

When check_content is enabled, compressed FITS files (.fits.gz) are identified by their decompressed filename extension.

Warning

Checking the file content requires reading the file's magic number, which may introduce additional I/O overhead.

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GuessRegionType()

CARTA::FileType GuessRegionType	(	const std::string &	path_string,
		bool	check_content
	)

Determines the region file type based on its content or extension.

This function attempts to identify the type of a region file used in astronomical imaging analysis by either checking its file content or examining its file extension. If check_content is true, it reads the first line of the file to identify known headers (e.g., #CRTF or # Region file format: DS9). Otherwise, it determines the file type based on its extension.

Note

CRTF files typically start with #CRTF, while DS9 region files may include # Region file format: DS9 as an optional header.

Warning

Checking file content requires reading the first line, which may introduce a slight I/O overhead.

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GuessTableType()

CARTA::CatalogFileType GuessTableType	(	const std::string &	path_string,
		bool	check_content
	)

Determines the catalog table file type based on its content or file extension.

This function attempts to classify the type of a catalog table file (e.g., FITS table or VOTable) either by checking its magic number (if check_content is true) or, if content checking is disabled, by inspecting the file extension.

Note

If check_content is enabled, the function may attempt to read the file's magic number. Ensure the file is accessible to avoid potential I/O errors.

Warning

This function does not validate file integrity; it only determines type based on basic signature matching or filename extensions.

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IsCompressedFits()

bool IsCompressedFits

(

const std::string &

filename

)

Checks whether a given file is a compressed FITS file.

This function first determines if the file is gzip-compressed by examining its magic number. If the file is gzip-compressed, it then checks whether the original filename (before compression) has a .fits extension.

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IsGzMagicNumber()

bool IsGzMagicNumber

(

uint32_t

magic_number

)

Determines if a given magic number corresponds to a gzip-compressed file.

This function checks whether the provided 32-bit magic number matches the gzip file signature (0x1f8b). The magic number is formatted as a hexadecimal string and examined to see if it ends with "8b1f".

Note

This function assumes little-endian byte order for checking the magic number.

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IsRemoteHttpFile()

bool IsRemoteHttpFile

(

const std::string &

filename

)

Checks whether a given filename represents a remote HTTP or HTTPS URL.

This function uses a regular expression to determine if the provided filename starts with "http://" or "https://", indicating that it is a remote file accessible via HTTP.

Note

This function does not verify if the URL is accessible or valid beyond its prefix.

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SearchPath()

fs::path SearchPath

(

std::string

filename

)

Searches for a file in the system's PATH environment variable.

This function retrieves the PATH environment variable, splits it into individual directory paths, and searches for the specified file within those directories. If the file is found, its full path is returned. If not found or if an error occurs, an empty fs::path is returned.

Note

This function assumes that path entries in PATH are separated by colons (:), which is standard on UNIX-like systems.

Warning

If the PATH environment variable is not set, this function may behave unexpectedly.

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