LIBMAGIC

Section: C Library Functions (3)
Page Index

BSD mandoc

NAME

magic_open magic_close magic_error magic_errno magic_descriptor magic_buffer magic_getflags magic_setflags magic_check magic_compile magic_list magic_load magic_load_buffers magic_setparam magic_getparam magic_version - Magic number recognition library

LIBRARY

Lb libmagic

SYNOPSIS

In magic.h Ft magic_t Fn magic_open int flags Ft void Fn magic_close magic_t cookie Ft const char * Fn magic_error magic_t cookie Ft int Fn magic_errno magic_t cookie Ft const char * Fn magic_descriptor magic_t cookie int fd Ft const char * Fn magic_file magic_t cookie const char *filename Ft const char * Fn magic_buffer magic_t cookie const void *buffer size_t length Ft int Fn magic_getflags magic_t cookie Ft int Fn magic_setflags magic_t cookie int flags Ft int Fn magic_check magic_t cookie const char *filename Ft int Fn magic_compile magic_t cookie const char *filename Ft int Fn magic_list magic_t cookie const char *filename Ft int Fn magic_load magic_t cookie const char *filename Ft int Fn magic_load_buffers magic_t cookie void **buffers size_t *sizes size_t nbuffers Ft int Fn magic_getparam magic_t cookie int param void *value Ft int Fn magic_setparam magic_t cookie int param const void *value Ft int Fn magic_version void

DESCRIPTION

These functions operate on the magic database file which is described in magic(5).

The function Fn magic_open creates a magic cookie pointer and returns it. It returns NULL if there was an error allocating the magic cookie. The flags argument specifies how the other magic functions should behave:

MAGIC_NONE: No special handling.
MAGIC_DEBUG: Print debugging messages to stderr.
MAGIC_SYMLINK: If the file queried is a symlink, follow it.
MAGIC_COMPRESS: If the file is compressed, unpack it and look at the contents.
MAGIC_DEVICES: If the file is a block or character special device, then open the device and try to look in its contents.
MAGIC_MIME_TYPE: Return a MIME type string, instead of a textual description.
MAGIC_MIME_ENCODING: Return a MIME encoding, instead of a textual description.
MAGIC_MIME: A shorthand for MAGIC_MIME_TYPE | MAGIC_MIME_ENCODING.
MAGIC_CONTINUE: Return all matches, not just the first.
MAGIC_CHECK: Check the magic database for consistency and print warnings to stderr.
MAGIC_PRESERVE_ATIME: On systems that support utime(3) or utimes(2), attempt to preserve the access time of files analysed.
MAGIC_RAW: Don't translate unprintable characters to a \ooo octal representation.
MAGIC_ERROR: Treat operating system errors while trying to open files and follow symlinks as real errors, instead of printing them in the magic buffer.
MAGIC_APPLE: Return the Apple creator and type.
MAGIC_EXTENSION: Return a slash-separated list of extensions for this file type.
MAGIC_COMPRESS_TRANSP: Don't report on compression, only report about the uncompressed data.
MAGIC_NO_CHECK_APPTYPE: Don't check for EMX application type (only on EMX).
MAGIC_NO_CHECK_CDF: Don't get extra information on MS Composite Document Files.
MAGIC_NO_CHECK_COMPRESS: Don't look inside compressed files.
MAGIC_NO_CHECK_ELF: Don't print ELF details.
MAGIC_NO_CHECK_ENCODING: Don't check text encodings.
MAGIC_NO_CHECK_SOFT: Don't consult magic files.
MAGIC_NO_CHECK_TAR: Don't examine tar files.
MAGIC_NO_CHECK_TEXT: Don't check for various types of text files.
MAGIC_NO_CHECK_TOKENS: Don't look for known tokens inside ascii files.
MAGIC_NO_CHECK_JSON: Don't example JSON files.

The Fn magic_close function closes the magic(5) database and deallocates any resources used.

The Fn magic_error function returns a textual explanation of the last error, or NULL if there was no error.

The Fn magic_errno function returns the last operating system error number (errno(2) ) that was encountered by a system call.

The Fn magic_file function returns a textual description of the contents of the filename argument, or NULL if an error occurred. If the filename is NULL then stdin is used.

The Fn magic_descriptor function returns a textual description of the contents of the fd argument, or NULL if an error occurred.

The Fn magic_buffer function returns a textual description of the contents of the buffer argument with length bytes size.

The Fn magic_getflags functions returns a value representing current flags set.

The Fn magic_setflags function sets the flags described above. Note that using both MIME flags together can also return extra information on the charset.

The Fn magic_check function can be used to check the validity of entries in the colon separated database files passed in as filename or NULL for the default database. It returns 0 on success and -1 on failure.

The Fn magic_compile function can be used to compile the colon separated list of database files passed in as filename or NULL for the default database. It returns 0 on success and -1 on failure. The compiled files created are named from the basename(1) of each file argument with ``.mgc'' appended to it.

The Fn magic_list function dumps all magic entries in a human readable format, dumping first the entries that are matched against binary files and then the ones that match text files. It takes and optional Fa filename argument which is a colon separated list of database files, or NULL for the default database.

The Fn magic_load function must be used to load the colon separated list of database files passed in as filename or NULL for the default database file before any magic queries can performed.

The default database file is named by the MAGIC environment variable. If that variable is not set, the default database file name is /usr/share/misc/magic. Fn magic_load adds ``.mgc'' to the database filename as appropriate.

The Fn magic_load_buffers function takes an array of size Fa nbuffers of Fa buffers with a respective size for each in the array of Fa sizes loaded with the contents of the magic databases from the filesystem. This function can be used in environment where the magic library does not have direct access to the filesystem, but can access the magic database via shared memory or other IPC means.

The Fn magic_getparam and Fn magic_setparam allow getting and setting various limits related to the magic library.

Parameter Ta Type Ta Default
MAGIC_PARAM_INDIR_MAX Ta size_t Ta 15
MAGIC_PARAM_NAME_MAX Ta size_t Ta 30
MAGIC_PARAM_ELF_NOTES_MAX Ta size_t Ta 256
MAGIC_PARAM_ELF_PHNUM_MAX Ta size_t Ta 128
MAGIC_PARAM_ELF_SHNUM_MAX Ta size_t Ta 32768
MAGIC_PARAM_REGEX_MAX Ta size_t Ta 8192
MAGIC_PARAM_BYTES_MAX Ta size_t Ta 1048576

The MAGIC_PARAM_INDIR_RECURSION parameter controls how many levels of recursion will be followed for indirect magic entries.

The MAGIC_PARAM_NAME_RECURSION parameter controls how many levels of recursion will be followed for for name/use calls.

The MAGIC_PARAM_NAME_MAX parameter controls the maximum number of calls for name/use.

The MAGIC_PARAM_NOTES_MAX parameter controls how many ELF notes will be processed.

The MAGIC_PARAM_PHNUM_MAX parameter controls how many ELF program sections will be processed.

The MAGIC_PARAM_SHNUM_MAX parameter controls how many ELF sections will be processed.

The Fn magic_version command returns the version number of this library which is compiled into the shared library using the constant MAGIC_VERSION from In magic.h . This can be used by client programs to verify that the version they compile against is the same as the version that they run against.

RETURN VALUES

The function Fn magic_open returns a magic cookie on success and NULL on failure setting errno to an appropriate value. It will set errno to Er EINVAL if an unsupported value for flags was given. The Fn magic_list , Fn magic_load , Fn magic_compile , and Fn magic_check functions return 0 on success and -1 on failure. The Fn magic_buffer , Fn magic_getpath , and Fn magic_file , functions return a string on success and NULL on failure. The Fn magic_error function returns a textual description of the errors of the above functions, or NULL if there was no error. The Fn magic_version always returns the version number of the library. Finally, Fn magic_setflags returns -1 on systems that don't support utime(3), or utimes(2) when MAGIC_PRESERVE_ATIME is set.

FILES

/usr/share/misc/magic: The non-compiled default magic database.
/usr/share/misc/magic.mgc: The compiled default magic database.

BUGS

The results from Fn magic_buffer and Fn magic_file where the buffer and the file contain the same data can produce different results, because in the Fn magic_file case, the program can lseek(2) and stat(2) the file descriptor.

AUTHORS

An Måns Rullgård Initial libmagic implementation, and configuration. An Christos Zoulas API cleanup, error code and allocation handling.