AG_DATASOURCE(3)

NAME
AG_DataSource - agar data source access

SYNOPSIS

    #include <agar/core.h>

DESCRIPTION
The AG_DataSource structure provides a generic interface to different data sources. Built-in sources include AG_FileSource for files, AG_CoreSource for fixed-size memory, AG_AutoCoreSource for automatically-allocated memory and AG_ConstCoreSource for read-only memory. AG_NetSocketSource for AG_Net(3) sockets.

New data sources can be implemented by overloading the AG_DataSource structure.

INTERFACE
AG_DataSource * AG_OpenFile(const char *path, const char *mode)

AG_DataSource * AG_OpenFileHandle(FILE *f)

AG_DataSource * AG_OpenCore(void *p, size_t size)

AG_DataSource * AG_OpenConstCore(const void *p, size_t size)

AG_DataSource * AG_OpenAutoCore(void)

AG_DataSource * AG_OpenNetSocket(AG_NetSocket *ns)

void AG_CloseDataSource(AG_DataSource *ds)

int AG_Read(AG_DataSource *ds, void *buf, size_t size)

int AG_ReadAt(AG_DataSource *ds, void *buf, size_t size, off_t pos)

int AG_Write(AG_DataSource *ds, const void *buf, size_t size)

int AG_WriteAt(AG_DataSource *ds, const void *buf, size_t size, off_t pos)

int AG_ReadP(AG_DataSource *ds, void *buf, size_t size, size_t *nRead)

int AG_ReadAtP(AG_DataSource *ds, void *buf, size_t size, off_t pos, size_t *nRead)

int AG_WriteP(AG_DataSource *ds, const void *buf, size_t size, size_t *nWrote)

int AG_WriteAtP(AG_DataSource *ds, const void *buf, size_t size, off_t pos, size_t *nWrote)

off_t AG_Tell(AG_DataSource *ds)

int AG_Seek(AG_DataSource *ds, off_t offs, enum ag_seek_mode mode)

void AG_LockDataSource(AG_DataSource *ds)

void AG_UnlockDataSource(AG_DataSource *ds)

void AG_SetByteOrder(AG_DataSource *ds, enum ag_byte_order order)

void AG_SetSourceDebug(AG_DataSource *ds, int enable)

void AG_DataSourceInit(AG_DataSource *ds)

void AG_DataSourceDestroy(AG_DataSource *ds)

void AG_DataSourceSetErrorFn(AG_DataSource *ds, void (*fn)(AG_Event *), const char *fmt, ...)

void AG_DataSourceError(AG_DataSource *ds, const char *fmt, ...)

int AG_DataSourceRealloc(AG_CoreSource *dsCore, size_t size)

The AG_OpenFile() function opens the file at path, where mode is a fopen(3) style mode string. AG_OpenFileHandle() creates a new data source for a previously opened file.

The AG_OpenCore() and AG_OpenConstCore() functions create new data sources referencing the region of memory p of size bytes.

AG_OpenAutoCore() creates a new data source using dynamically-allocated memory (accessible as the data member of the structure).

AG_OpenNetSocket() creates a new data source using a network socket (see AG_Net(3)).

The AG_CloseDataSource() function closes the data source, freeing any data allocated by the AG_DataSource layer (such as the data buffer allocated by AG_OpenAutoCore()). For network sockets opened with AG_OpenNetSocket(), the underlying socket is left open.

AG_Read() reads size bytes from the data source into the destination buffer buf. AG_Write() writes size bytes from the source buffer buf to the destination data source. AG_ReadAt() and AG_WriteAt() allow a source/target position (byte offset) to be specified. These functions all return 0 on success or -1 if an error has occured. Partial transfers are treated as errors.

The AG_ReadP(), AG_WriteP(), AG_ReadAtP() and AG_WriteAtP() variants do not treat partial reads or writes as errors, returning the total number of bytes transferred into the nRead or nWrote argument (if not NULL). Depending on the underlying data source, a byte count of 0 may indicate either an end-of-file condition or a closed socket.

AG_Tell() returns the current position in the data source. If the underlying data source does not support this operation, a value of 0 is returned.

AG_Seek() seeks to the given position in the data source. Acceptable values for mode include AG_SEEK_SET (relative to data start), AG_SEEK_CUR (relative to current position), AG_SEEK_END (relative to data end).

The AG_LockDataSource() and AG_UnlockDataSource() functions acquire and release the exclusive lock protecting this data source, and are no-ops if thread support is disabled.

AG_SetByteOrder() configures the byte order to be used by integer read/write operations. Accepted parameters are AG_BYTEORDER_BE for big-endian and AG_BYTEORDER_LE for little-endian. To determine the byte order of the current architecture, you can use the standard AG_BYTEORDER define (which evaluates to AG_BIG_ENDIAN or AG_LITTLE_ENDIAN).

AG_SetSourceDebug() enables or disables the inclusion of debugging information in the archive. Debugging information allows type-safety checking at the primitive data level, at the cost of an increased archive size due to the additional metadata that must be encoded.

The AG_DataSourceInit() and AG_DataSourceDestroy() functions are used when implementing new data source types. They are used internally by the AG_Open*() and AG_Close*() functions.

AG_DataSourceSetErrorFn() configures an alternate handler routine for data source exceptions (which can occur when using routines such as AG_ReadUint32(), for example on I/O error). From the handler routine, a pointer to the AG_DataSource can be retrieved using AG_SELF, and the error message is retrieved using AG_STRING(1). The default exception handler simply calls AG_FatalError(3).

The AG_DataSourceError() function raises a data source error, with the optional error message string. It is intended for use in custom I/O routines which do not return an error status. If fmt is NULL, the error is obtained from AG_GetError(3).

The AG_DataSourceRealloc() routine explicitely resizes the buffer of a data source previously created with AG_OpenAutoCore(). While the buffer is already resized automatically as data is written to the source, setting an explicit buffer size may be desirable in some situations.

INTEGER OPERATIONS
The following functions read and write integer values using the byte order specified for the data source.

Uint8 AG_ReadUint8(AG_DataSource *ds)

int AG_ReadUint8v(AG_DataSource *ds, Uint8 *v)

Sint8 AG_ReadSint8(AG_DataSource *ds)

int AG_ReadSint8v(AG_DataSource *ds, Sint8 *v)

Uint16 AG_ReadUint16(AG_DataSource *ds)

int AG_ReadUint16v(AG_DataSource *ds, Uint16 *v)

Sint16 AG_ReadSint16(AG_DataSource *ds)

int AG_ReadSint16v(AG_DataSource *ds, Sint16 *v)

Uint32 AG_ReadUint32(AG_DataSource *ds)

int AG_ReadUint32v(AG_DataSource *ds, Uint32 *v)

Sint32 AG_ReadSint32(AG_DataSource *ds)

int AG_ReadSint32(AG_DataSource *ds, Sint32 *v)

Uint64 AG_ReadUint64(AG_DataSource *ds)

int AG_ReadUint64v(AG_DataSource *ds, Uint64 *v)

Sint64 AG_ReadSint64(AG_DataSource *ds)

int AG_ReadSint64v(AG_DataSource *ds, Sint64 *v)

void AG_WriteUint8(AG_DataSource *ds, Uint8 value)

int AG_WriteUint8v(AG_DataSource *ds, const Uint8 *value)

void AG_WriteSint8(AG_DataSource *ds, Sint8 value)

int AG_WriteSint8v(AG_DataSource *ds, const Sint8 *value)

void AG_WriteUint16(AG_DataSource *ds, Uint16 value)

int AG_WriteUint16v(AG_DataSource *ds, const Uint16 *value)

void AG_WriteSint16(AG_DataSource *ds, Sint16 value)

int AG_WriteSint16v(AG_DataSource *ds, const Sint16 *value)

void AG_WriteUint32(AG_DataSource *ds, Uint32 value)

int AG_WriteUint32v(AG_DataSource *ds, const Uint32 *value)

void AG_WriteSint32(AG_DataSource *ds, Sint32 value)

int AG_WriteSint32v(AG_DataSource *ds, const Sint32 *value)

void AG_WriteUint64(AG_DataSource *ds, Uint64 value)

int AG_WriteUint64v(AG_DataSource *ds, const Uint64 *value)

void AG_WriteSint64(AG_DataSource *ds, Sint64 value)

int AG_WriteSint64v(AG_DataSource *ds, const Sint64 *value)

void AG_WriteUint8At(AG_DataSource *ds, Uint8 value, off_t offs)

void AG_WriteSint8At(AG_DataSource *ds, Sint8 value, off_t offs)

void AG_WriteUint16At(AG_DataSource *ds, Uint16 value, off_t offs)

void AG_WriteSint16At(AG_DataSource *ds, Sint16 value, off_t offs)

void AG_WriteUint32At(AG_DataSource *ds, Uint32 value, off_t offs)

void AG_WriteSint32At(AG_DataSource *ds, Sint32 value, off_t offs)

void AG_WriteUint64At(AG_DataSource *ds, Uint64 value, off_t offs)

void AG_WriteSint64At(AG_DataSource *ds, Sint64 value, off_t offs)

The AG_Read[SU]intN() functions read and return an integer value of N bits from the data source. The AG_Read[SU]intNv() variants write the value to the specified pointer.

The AG_Write[SU]intN() functions write an integer value of N bits to the data source. The AG_Write[SU]intNv() variants accept a pointer argument.

The AG_Write[SU]intNAt() variants write the integer to the specified position in the data source.

All AG_Read*v() functions return 0 on success and -1 on failure, without raising any exceptions. The other functions will raise a data source exception if an failuer (e.g., an I/O error) occured.

The 64-bit types are only available if HAVE_64BIT is defined.

FLOATING POINT OPERATIONS
The following routines read and write floating-point numbers in IEEE.754 representation.

float AG_ReadFloat(AG_DataSource *ds)

int AG_ReadFloatv(AG_DataSource *ds, float *f)

double AG_ReadDouble(AG_DataSource *ds)

int AG_ReadDoublev(AG_DataSource *ds, double *f)

long double AG_ReadLongDouble(AG_DataSource *ds)

int AG_ReadLongDouble(AG_DataSource *ds, long double *f)

void AG_WriteFloat(AG_DataSource *ds, float f)

int AG_WriteFloatv(AG_DataSource *ds, float *f)

void AG_WriteFloatAt(AG_DataSource *ds, float f, off_t pos)

void AG_WriteDouble(AG_DataSource *ds, double f)

int AG_WriteDoublev(AG_DataSource *ds, double *f)

void AG_WriteDoubleAt(AG_DataSource *ds, double f, off_t pos)

void AG_WriteLongDouble(AG_DataSource *ds, long double f)

int AG_WriteLongDoublev(AG_DataSource *ds, long double *f)

void AG_WriteLongDoubleAt(AG_DataSource *ds, long double f, off_t pos)

AG_ReadFloat(), AG_ReadDouble() and AG_ReadLongDouble() read a floating-point value from the data source.

AG_WriteFloat(), AG_WriteDouble() and AG_WriteLongDouble() write a floating-point value to the data source. The AG_Write*At() variants write the value at a given position.

All AG_Read*v() functions return 0 on success and -1 on failure, without raising any exceptions. The other functions will raise a data source exception if an failuer (e.g., an I/O error) occured.

The long double functions are available only if HAVE_LONG_DOUBLE is defined.

STRING OPERATIONS
The following functions read and write arbitrary strings, and are commonly used for text. The encoding of the strings is simply an unsigned 32-bit integer byte count, followed by the string. The encoding may or may not include a terminating NUL.

char * AG_ReadStringLen(AG_DataSource *ds, size_t maxsize)

int AG_ReadStringLenv(AG_DataSource *ds, size_t maxsize, char **s)

char * AG_ReadString(AG_DataSource *ds)

int AG_ReadStringv(AG_DataSource *ds, char **s)

char * AG_ReadNulStringLen(AG_DataSource *ds, size_t maxsize)

char * AG_ReadNulString(AG_DataSource *ds)

size_t AG_CopyString(char *buf, AG_DataSource *ds, size buf_size)

size_t AG_CopyNulString(char *buf, AG_DataSource *ds, size buf_size)

void AG_SkipString(AG_DataSource *ds)

void AG_WriteString(AG_DataSource *ds, const char *s)

int AG_WriteStringv(AG_DataSource *ds, const char *s)

The AG_ReadStringLen() function reads a string of up to maxsize bytes and returns a dynamically allocated, NUL-terminated copy of the string. AG_ReadString() implicitely limits the string to AG_LOAD_STRING_MAX bytes. Both functions will raise a data source exception on error.

The AG_ReadStringLenv() and AG_ReadStringv() variants accept a pointer s to an existing, valid string buffer which will be reallocated to fit the new string. Both functions will return -1 (without raising a data source exception) on failure. If a low-level I/O error occurs after the buffer is reallocated, the string at s will be truncated to zero-length.

AG_CopyString() copies the string directly into a fixed-size buffer buf of buf_size bytes and NUL-terminates it. AG_CopyString() returns the number of bytes that would have been copied were buf_size unlimited. If an error occurs, a data source exception is raised.

The AG_ReadNulString(), AG_ReadNulStringLen() and AG_CopyNulString() variants handle strings where the encoding includes the NUL-termination. These functions do not perform type checking are mostly useful when reading non-Agar generated data files.

The AG_SkipString() routine skips over the string at the current position in the buffer.

The AG_WriteString() function writes a string to a data source, where the encoding is not NUL-terminated. If an error occurs, a data source exception is raised. The AG_WriteStringv() variant returns 0 on success and -1 on failure, without raising exceptions.

INTERNAL DATA SOURCE API
New sources can be implementing by defining a new structure inheriting from AG_DataSource.

Public members of the AG_DataSource structure include:

    typedef struct ag_data_source {
    	AG_Mutex lock;			/* Lock on all operations */
    	enum ag_byte_order byte_order;	/* Byte order of source */
    	size_t wrLast;			/* Last write count (bytes) */
    	size_t rdLast;			/* Last read count (bytes) */
    	size_t wrTotal;			/* Total write count (bytes) */
    	size_t rdTotal;			/* Total read count (bytes) */
    	AG_IOStatus (*read)(struct ag_data_source *, void *buf,
    	                    size_t size, size_t *rv);
    	AG_IOStatus (*read_at)(struct ag_data_source *, void *buf,
    	                       size_t size, off_t pos, size_t *rv);
    	AG_IOStatus (*write)(struct ag_data_source *, const void *buf,
    	                     size_t size, size_t *rv);
    	AG_IOStatus (*write_at)(struct ag_data_source *, const void *buf,
    	                        size_t size, off_t pos, size_t *rv);
    	off_t       (*tell)(struct ag_data_source *);
    	int         (*seek)(struct ag_data_source *, off_t offs,
    	                    enum ag_seek_mode mode);
    	void        (*close)(struct ag_data_source *);
    } AG_DataSource;

The byte_order setting affects integer read operations.

The wrLast, rdLast, wrTotal and rdTotal fields keep count of the read/written bytes, and are automatically incremented by the generic AG_DataSource calls.

The read operation reads size bytes from the data source and into buf, returning the total number of bytes read into rv. The read_at variant reads data at a specified offset.

The write operation writes size bytes from buf to the data source, returning the total number of bytes written into rv. The write_at variant writes the data at a specified offset.

tell returns the current offset.

seek moves to the specified offset and returns 0 on success and -1 on failure.

close closes the data source.

SEE ALSO
AG_ByteSwap(3), AG_Intro(3), AG_Net(3), AG_Version(3)

HISTORY
A similar interface called ‘AG_Netbuf’ first appeared in Agar 1.0. The current AG_DataSource interface appeared in Agar 1.3. Exception handling and error-checking variants of the primitive I/O routines appeared in Agar 1.3.3. The interface to network sockets appeared in Agar 1.5.0.