dfx::Magic::Context Class Reference

RAII wrapper around a libmagic "magic_set" context. More...

#include <dfx-magic/Context.hpp>

Public Member Functions
	Context (int flags=-1, fs::path const &magicDb={})
	Construct a libmagic context and load the magic database.
	Context (Context &&other) noexcept
	Move-construct a context.
	~Context ()
	Destroy the context and release the underlying libmagic handle.
	DISABLE_COPY (Context)
	Copying is disabled (single owner of the libmagic handle).
Context &	operator= (Context &&other) noexcept
	Move-assign a context.
bool	isReady () const noexcept
	Whether the context is initialized and ready to be used.
std::string	lastError () const
	Retrieve the last error message from libmagic.
std::string	get (int fd) const
	Identify content from an open file descriptor.
std::string	get (fs::path const &path) const
	Identify content from a filesystem path.
std::string	get (std::span< uint8_t > const &data) const
	Identify content from an in-memory buffer.

Static Public Attributes
static int	defaultFlags
	Default libmagic flags used when the constructor argument flags is -1.

Detailed Description

RAII wrapper around a libmagic "magic_set" context.

This class manages a libmagic context used to detect file types / MIME types from:

• an open file descriptor,
• a filesystem path,
• an in-memory buffer.

It owns the underlying libmagic handle and releases it in the destructor. Copying is disabled (libmagic contexts are not trivially copyable), but moving is supported.

Typical usage:

dfx::Magic::Context ctx;           // uses Context::defaultFlags by default
if (!ctx.isReady())
    throw std::runtime_error(ctx.lastError());
 
std::string t1 = ctx.get("/bin/ls");
std::string t2 = ctx.get(fd);
std::string t3 = ctx.get(std::span<uint8_t const>(data, size)); // if you have const bytes, copy to uint8_t or adjust overloads

Note

"Magic" refers to the Linux libmagic library (the one behind the file command).

Constructor & Destructor Documentation

Context() [1/2]

dfx::Magic::Context::Context	(	int	flags = -1,
		fs::path const &	magicDb = {} )

Construct a libmagic context and load the magic database.

Parameters

flags	libmagic flags passed to magic_open(). If flags is -1 (default), the value of defaultFlags is used.
magicDb	Optional path to a specific magic database file (or directory, depending on how your implementation loads it). If empty, the system default database resolution is used (typically magic_load(ctx, nullptr)).

After construction, check isReady() to know whether initialization and database loading succeeded.

Context() [2/2]

dfx::Magic::Context::Context ( Context && other )

noexcept

Move-construct a context.

~Context()

dfx::Magic::Context::~Context

(

)

Destroy the context and release the underlying libmagic handle.

Member Function Documentation

DISABLE_COPY()

dfx::Magic::Context::DISABLE_COPY

(

Context

)

Copying is disabled (single owner of the libmagic handle).

get() [1/3]

std::string dfx::Magic::Context::get

(

fs::path const &

path

)

const

Identify content from a filesystem path.

Parameters

path	Path to an existing file.

Returns

A description string as produced by libmagic, or an empty string on failure

get() [2/3]

std::string dfx::Magic::Context::get

(

int

fd

)

const

Identify content from an open file descriptor.

Parameters

fd	An open file descriptor. The descriptor must remain valid for the duration of the call.

Returns

A description string as produced by libmagic (e.g. "ELF 64-bit LSB executable ...") or an empty string on failure

get() [3/3]

std::string dfx::Magic::Context::get

(

std::span< uint8_t > const &

data

)

const

Identify content from an in-memory buffer.

Parameters

data	Byte span containing the data to analyze.

Returns

A description string as produced by libmagic, or an empty string on failure

isReady()

bool dfx::Magic::Context::isReady ( ) const

inlinenoexcept

Whether the context is initialized and ready to be used.

A context is considered ready when:

• the underlying libmagic handle is non-null, and
• the magic database was successfully loaded

Returns

true if ready; false otherwise.

lastError()

std::string dfx::Magic::Context::lastError

(

)

const

Retrieve the last error message from libmagic.

Typically wraps magic_error(_ctx) when available, or returns an empty string if no detailed error is available.

Returns

Human-readable error string describing the last libmagic failure.

Note

If the context is not ready, this is the preferred way to diagnose why.

operator=()

Context & dfx::Magic::Context::operator= ( Context && other )

noexcept

Move-assign a context.

Member Data Documentation

defaultFlags

int dfx::Magic::Context::defaultFlags

static

Default libmagic flags used when the constructor argument flags is -1.

This value is intended to be configured by the application (e.g. enabling MIME output, following symlinks, preserving access time, etc.). By default it is set to MAGIC_MIME_TYPE | MAGIC_NO_CHECK_COMPRESS | MAGIC_NO_CHECK_ELF | MAGIC_NO_CHECK_ENCODING

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The documentation for this class was generated from the following file:

• lib/dfx-magic/Context.hpp