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gd_cbopen(3) GETDATA gd_cbopen(3)

NAME

gd_cbopen, gd_open — open or create a dirfile

SYNOPSIS

#include <getdata.h>

DIRFILE* gd_cbopen(const char *dirfilename, unsigned long flags, gd_parser_callback_t sehandler, void *extra);

DIRFILE* gd_open(const char *dirfilename, unsigned long flags);

DESCRIPTION

The gd_cbopen() function opens or creates the dirfile specified by dirfilename, returning a DIRFILE object associated with it. Opening a dirfile will cause the library to read and parse the dirfile's format specification (see dirfile-format(5)).

If not NULL, sehandler should be a pointer to a function which will be called whenever a syntax error is encountered during parsing the format specification. Specify NULL for this parameter if no callback function is to be used. The caller may use this function to correct the error or modify the error handling of the format specification parser. See The Callback Function section below for details on this function. The extra argument allows the caller to pass data to the callback function. The pointer will be passed to the callback function verbatim.

The gd_open() function is equivalent to gd_cbopen(), with sehandler and extra set to NULL.

The flags argument should include one of the access modes: GD_RDONLY (read-only) or GD_RDWR (read-write), and may also contain zero or more of the following flags, bitwise-or'd together:

GD_ARM_ENDIAN

GD_NOT_ARM_ENDIAN
Specifies that double precision floating point raw data on disk are, or are not, stored in the middle-endian format used by older ARM processors.

These flag only set the default endianness, and will be overridden when an /ENDIAN directive specifies the byte sex of RAW fields, unless GD_FORCE_ENDIAN is also specified.

On every platform, one of these flags (GD_NOT_ARM_ENDIAN on all but middle-ended ARM systems) indicates the native behaviour of the platform. That symbol will equal zero, and may be omitted.

GD_BIG_ENDIAN

GD_LITTLE_ENDIAN
Specifies the default byte sex of raw data stored on disk to be either big-endian (most significant byte first) or little-endian (least significant byte first). Omitting both flags indicates the default should be the native endianness of the platform.

Unlike the ARM endianness flags above, neither of these symbols is ever zero. Specifying both these flags together will cause the library to assume that the endianness of the data is opposite to that of the native architecture, whatever that might be.

These flag only set the default endianness, and will be overridden when an /ENDIAN directive specifies the byte sex of RAW fields, unless GD_FORCE_ENDIAN is also specified.

An empty dirfile will be created, if one does not already exist. This will create both the dirfile directory and an empty format specification file called format. If the call creates a dirfile, then the specified access mode is ignored: a newly-created DIRFILE is always opened with access mode GD_RDWR, even if GD_RDONLY had been specified.

The directory will have have mode S_IRWXU | S_IRWXG | S_IRWXO (0777), modified by the caller's umask value (see umask(2)). The format file will have mode S_IRUSR | S_IWUSR | S_IRGRP | S_IWGRP | S_IROTH | S_IWOTH (0666), also modified by the caller's umask. The owner of the dirfile directory and format file will be the effective user ID of the caller. Group ownership follows the rules outlined in mkdir(2).

Ensure that this call creates a dirfile: when specified along with GD_CREAT, the call will fail if the dirfile specified by dirfilename already exists. If GD_CREAT is not specified, this flag is ignored. This flag suffers from all the limitations of the O_EXCL flag as indicated in open(2).
Specifies that /ENCODING directives (see dirfile-format(5)) found in the dirfile format specification should be ignored. The encoding scheme specified in flags will be used instead (see below).
Specifies that /ENDIAN directives (see dirfile-format(5)) found in the dirfile format specification should be ignored. All raw data will be assumed to have the byte sex indicated through the presence or absence of the GD_ARM_ENDIAN, GD_BIG_ENDIAN, GD_LITTLE_ENDIAN, and GD_NOT_ARM_ENDIAN flags.
If the dirfile format metadata specifies more than one field with the same name, all but one of them will be ignored by the parser. Without this flag, parsing would fail with the GD_E_FORMAT error, possibly resulting in invocation of the registered callback function. Which of the duplicate fields is kept is not specified. As a result, this flag is typically only useful in the case where identical copies of a field specification line are present.

No indication is provided to indicate whether a duplicate field has been discarded. If finer grained control is required, the caller should handle GD_E_FORMAT_DUPLICATE suberrors itself with an appropriate callback function.

Reject dirfiles which don't conform to the Dirfile Standards. See the Standards Compliance section below for full details.
Allow non-compliant format specification syntax, even when given along with a conflicting /VERSION directive. See the Standards Compliance section below for full details.
When dirfile metadata are flushed to disk (either explicitly via gd_metaflush(3), gd_rewrite_fragment(3), or gd_flush(3) or implicitly by closing the dirfile), an attempt will be made to create a nicer looking format specification (from a human-readable standpoint). What this explicitly means is not part of the API, and any particular behaviour should not be relied on. If the dirfile is opened read-only, this flag is ignored.
If dirfilename specifies an already existing dirfile, it will be truncated before opening. Since gd_cbopen() decides whether dirfilename specifies an existing dirfile before attempting to parse the dirfile, dirfilename is considered to specify an existing dirfile if it refers to a directory containing a regular file called format, regardless of the content or form of that file.

Truncation occurs by deleting every regular file and symlink in the specified directory, whether the files were referred to by the dirfile before truncation or not. Accordingly, this flag should be used with caution. Unless GD_TRUNCSUB is also specified, subdirectories are left untouched. Notably, this operation does not consider directories used in /INCLUDE directives. If the dirfile does not exist, this flag is ignored.

If specified along with GD_TRUNC, truncation will descend into subdirectories, deleting all regular files and symlinks recursively. It does not descend into directories pointed to by symbolic links: in these cases, just the symlink itself is deleted. If specified without an accompanying GD_TRUNC, this flag is ignored.
Specifies that whenever an error is triggered by the library when working on this dirfile, the corresponding error string, which can be retrieved by calling gd_error_string(3), should be written on the caller's standard error stream (stderr(3)) by GetData. The error string may be prefixed by a string specified by the caller; see gd_verbose_prefix(3). Without this flag, GetData writes nothing to standard error. (GetData never writes to standard output.)

Those flags which affect the operation of the library beyond this call itself may be modified later using the gd_flags(3) function.

The flags argument may also be bitwise or'd with one of the following symbols indicating the default encoding scheme of the dirfile. Like the endianness flags, the choice of encoding here is ignored if the encoding is specified in the dirfile itself, unless GD_FORCE_ENCODED is also specified. If none of these symbols is present, GD_AUTO_ENCODED is assumed, unless the gd_cbopen() call results in creation or truncation of the dirfile. In that case, GD_UNENCODED is assumed. See dirfile-encoding(5) for details on dirfile encoding schemes.

Specifies that the encoding type is not known in advance, but should be detected by the GetData library. Detection is accomplished by searching for raw data files with extensions appropriate to the encoding scheme. This method will notably fail if the the library is called via putdata(3) to create a previously non-existent raw field unless a read is first successfully performed on the dirfile. Once the library has determined the encoding scheme for the first time, it remembers it for subsequent calls.
Specifies that raw data files are compressed using the Burrows-Wheeler block sorting text compression algorithm and Huffman coding, as implemented in the bzip2 format.
Specifies that raw data files are compressed using Lempel-Ziv coding (LZ77) as implemented in the gzip format.
Specifies that raw data files are compressed using the Lempel-Ziv Markov Chain Algorithm (LZMA) as implemented in the xz container format.
Specifies that raw data files are compressed using the slimlib library.
Specified that raw data files are sample-index encoded, similar to run-length encoding, suitable for data that change rarely.
Specifies that raw data files are encoded as text files containing one data sample per line.
Specifies that raw data files are not encoded, but written as simply binary data to disk.
Specifies that raw data files are compressed using the DEFLATE algorithm. All raw data files for a given fragment are collected together and stored in a PKZIP archive called raw.zip.
Specifies that raw data files are compressed using a combinations of compression schemes: first files are slim-compressed, as with the GD_SLIM_ENCODED scheme, and then they are collected together and compressed (again) into a PKZIP archive called raw.zip, as in the GD_ZZIP_ENCODED scheme.

Standards Compliance

The latest Dirfile Standards Version which this release of GetData understands is provided in the preprocessor macro GD_DIRFILE_STANDARDS_VERSION defined in getdata.h. GetData is able to open and parse any dirfile which conforms to this Standards Version, or to any earlier Version. The dirfile-format(5) manual page lists the changes between Standards Versions.

The GetData parser can operate in two modes: a permissive mode, in which much non-Standards-compliant syntax is allowed, and a pedantic mode, in which the parser adheres strictly to the Standards. The mode made change during the parsing of a dirfile. If GD_PEDANTIC is passed to gd_cbopen(), the parser will start parsing the format specification in pedantic mode, otherwise it will start in permissive mode.

Permissive mode is provided primarily to allow GetData to be used on dirfiles which conform to no single Standard, but which were accepted by the GetData parser in previous versions. It is notably lax regarding reserved field names, and field name characters, the mixing of old and new data type specifiers, and generally ignores the presence of /VERSION directives. In read-write mode, permissive mode should be used with caution, as it can cause unintentional corruption of dirfile metadata on write, if the heuristics in the parser incorrectly guessed the intention of non-compliant syntax. In permissive mode, actual syntax errors are still reported as such.

In pedantic mode, the parser conforms to one specific Standards Version. This target version may change any number of times in the course of scanning a single format specification. If invoked using the GD_PEDANTIC flag, the parser will start in pedantic mode with a target version equal to GD_DIRFILE_STANDARDS_VERSION. Whenever a /VERSION directive is encountered in the format specification, the target version is changed to the Standards Version specified. When encountering a /VERSION directive in permissive mode, the parser will switch to pedantic mode, unless the GD_PERMISSIVE flag was passed to gd_cbopen(), in which case no mode switch will take place.

Independent of the mode of the parser when parsing the format specification, GetData will calculate a list of Standards Versions to which the parsed metadata conform to. The gd_dirfile_standards(3) function can provide this information, and also specify the desired Standards Version for writing format metadata back to disk.

The Callback Function

The caller-supplied sehandler function is called whenever the format specification parser encounters a syntax error (i.e. whenever it would return the GD_E_FORMAT error). This callback may be used to correct the error, or to tell the parser how to recover from it.

This function should take two pointers as arguments, and return an int:

int sehandler(gd_parser_data_t *pdata, void *extra);

The extra parameter is the pointer supplied to gd_cbopen(), passed verbatim to this function. It can be used to pass caller data to the callback. GetData does not inspect this pointer, not even to check its validity. If the caller needs to pass no data to the callback, it may be NULL.

The gd_parser_data_t type is a structure with at least the following members:


typedef struct {


  const DIRFILE* dirfile;


  int suberror;


  int linenum;


  const char* filename;


  char* line;


  size_t buflen;


  ...
} gd_parser_data_t;

The pdata->dirfile member will be a pointer to a DIRFILE object suitable only for passing to gd_error_string(). Notably, the caller should not assume this pointer will be the same as the pointer eventually returned by gd_cbopen(), nor that it will be valid after the callback function returns.

The pdata->suberror parameter will be one of the following symbols indicating the type of syntax error encountered:

The parent specified for a meta field was an alias.
The line was indecipherable. Typically this means that the line contained neither a reserved word, nor a field type.
The specified field name was invalid.
The samples-per-frame of a RAW field was out-of-range.
The data type of a RAW field was unrecognised.
The first bit of a BIT field was out-of-range.
The last bit of a BIT field was out-of-range.
An invalid character was found in the line, or a character escape sequence was malformed.
The specified field name already exists.
The byte sex specified by an /ENDIAN directive was unrecognised.
An unexpected character was encountered in a complex literal.
The parent of a metafield was defined in another fragment.
An attempt was made to use a metafield as the parent to a new metafield.
An attempt was made to add a RAW metafield.
A MPLEX specification has a negative period.
The number of fields of a LINCOM field was out-of-range.
An insufficient number of tokens was found on the line.
The parent of a metafield was not found.
The number of bits of a BIT field was out-of-range.
The protection level specified by a /PROTECT directive was unrecognised.
A field was specified with the reserved name INDEX (or with the reserved name FILEFRAM in a dirfile conforming to Standards Version 5 or earlier).
The last token of the line was unterminated.
The operation in a WINDOW field was not recognised.

pdata->filename and pdata->linenum members contains the pathname of the fragment and line number where the syntax error was encountered. The first line in a fragment is line one.

The pdata->line member contains a copy of the line containing the syntax error. This line may be freely modified by the callback function. It will then be reparsed if the callback function returns the symbol GD_SYNTAX_RESCAN (see below). The size of the memory buffer (which may be greater than the length of the actual string) is provided in pdata->buflen, and space is available for at least GD_MAX_LINE_LENGTH bytes. A larger buffer may be used if desired, by assigning a pointer to the new buffer of the desired length to pdata->line. The new buffer should be allocated with malloc(3). It will be freed by the parser. Do not call free(3) or realloc(3) on the original pointer passed to the callback as pdata->line: it, too, will be freed by the parser.

The callback function should return one of the following symbols, which tells the parser how to subsequently handle the error:

The parser should immediately abort parsing the format specification and fail with the error GD_E_FORMAT. This is the default behaviour, if no callback function is provided (or if the parser is invoked by calling gd_open()).
The parser should continue parsing the format specification. However, once parsing has finished, the parser will fail with the error GD_E_FORMAT, even if no further syntax errors are encountered. This behaviour may be used by the caller to identify all lines containing syntax errors in the format specification, instead of just the first one.
The parser should ignore the line containing the syntax error completely, and carry on parsing the format specification. If no further errors are encountered, the dirfile will be successfully opened.
The parser should rescan the line argument, which replaces the line which originally contained the syntax error. The line is assumed to have been corrected by the callback function. If the line still contains a syntax error, the callback function will be called again.

Note: the line is not corrected on disk; however, the caller may subsequently correct the fragment on disk by calling gd_rewrite_fragment(3).

The callback function handles only syntax errors. The parser may still abort early, if a different kind of library error is encountered. Furthermore, although a line may contain more than one syntax error, the parser will only ever report one syntax error per line, even if the callback function returns GD_SYNTAX_CONTINUE.

RETURN VALUE

A call to gd_cbopen() or gd_open() always returns a pointer to a newly allocated DIRFILE object, except in instances when it is unable to allocate memory for the DIRFILE object itself, in which case it will return NULL. The DIRFILE object is an opaque structure containing the parsed dirfile metadata. If an error occurred, the dirfile error will be set to a non-zero error value. The DIRFILE object will also be internally flagged as invalid. Possible error values are:

The library was asked to truncate a dirfile opened read-only (i.e. GD_TRUNC was specified in flags along with GD_RDONLY).
The library was unable to allocate memory.
The reference field specified by a /REFERENCE directive in the format specification (see dirfile-format(5)) was not found, or was not a RAW field.
The registered callback function, sehandler, returned an unrecognised response.
The library was unable to create the dirfile.
The dirfile already exists and both GD_CREAT and GD_EXCL were specified.
A syntax error occurred in the format specification. See also The Callback Function section above.
The dirfile format file, or another file that it includes, could not be opened, or dirfilename does not specify a valid dirfile.
The parser encountered a line in the format specification longer than it was able to deal with. Lines are limited by the storage size of ssize_t. On 32-bit systems, this limits format specification lines to 2**31 bytes. The limit is larger on 64-bit systems.

The dirfile error may be retrieved by calling gd_error(3). A descriptive error string for the last error encountered can be obtained from a call to gd_error_string(3). When finished with it, a caller should de-allocate the DIRFILE object by calling gd_close(3), or gd_discard(3), even if the open failed.

BUGS

When working with dirfiles conforming to Standards Versions 4 and earlier (before the introduction of the /ENDIAN directive), GetData assumes the dirfile has native byte sex, even though, officially, these early Standards stipulated data to be little-endian. This is necessary since, in the absence of an explicit /VERSION directive, it is often impossible to determine the intended Standards Version of a dirfile, and the current behaviour is to assume native byte sex for modern dirfiles lacking /ENDIAN. To read an old, little-ended dirfile on a big-ended platform, an /ENDIAN directive should be added to the format specification, or else GD_LITTLE_ENDIAN should be specified by the caller.

GetData's parser assumes it is running on an ASCII-compatible platform. Format specification parsing will fail gloriously on an EBCDIC platform.

SEE ALSO

dirfile(5), dirfile-encoding(5), dirfile-format(5), gd_close(3), gd_dirfile_standards(3), gd_discard(3), gd_error(3), gd_error_string(3), gd_flags(3), gd_getdata(3), gd_include(3), gd_parser_callback(3), gd_verbose_prefix(3)

16 October 2014 Version 0.9.0