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$Id: lwres_buffer.3,v 1.3 2000/08/01 01:20:26 tale Exp $
.Dd Jun 30, 2000 .Dt LWRES_BUFFER 3 .Os BIND9 9 .Sh NAME .Nm lwres_buffer_init , .Nm lwres_buffer_invalidate , .Nm lwres_buffer_add , .Nm lwres_buffer_subtract , .Nm lwres_buffer_clear , .Nm lwres_buffer_first , .Nm lwres_buffer_forward , .Nm lwres_buffer_back , .Nm lwres_buffer_getuint8 , .Nm lwres_buffer_putuint8 , .Nm lwres_buffer_getuint16 , .Nm lwres_buffer_putuint16 , .Nm lwres_buffer_getuint32 , .Nm lwres_buffer_putuint32 , .Nm lwres_buffer_putmem , .Nm lwres_buffer_getmem .Nd lightweight resolver buffer management .Sh SYNOPSIS .Fd #include <lwres/lwbuffer.h> .Fd .Ft void .Fo lwres_buffer_init .Fa "lwres_buffer_t *b" .Fa "void *base" .Fa "unsigned int length" .Fc .Ft void .Fo lwres_buffer_invalidate .Fa "lwres_buffer_t *b" .Fc .Ft void .Fo lwres_buffer_add .Fa "lwres_buffer_t *b" .Fa "unsigned int n" .Fc .Ft void .Fo lwres_buffer_subtract .Fa "lwres_buffer_t *b" .Fa "unsigned int n" .Fc .Ft void .Fo lwres_buffer_clear .Fa "lwres_buffer_t *b" .Fc .Ft void .Fo lwres_buffer_first .Fa "lwres_buffer_t *b" .Fc .Ft void .Fo lwres_buffer_forward .Fa "lwres_buffer_t *b" .Fa "unsigned int n" .Fc .Ft void .Fo lwres_buffer_back .Fa "lwres_buffer_t *b" .Fa "unsigned int n" .Fc .Ft lwres_uint8_t .Fo lwres_buffer_getuint8 .Fa "lwres_buffer_t *b" .Fc .Ft void .Fo lwres_buffer_putuint8 .Fa "lwres_buffer_t *b" .Fa "lwres_uint8_t val" .Fc .Ft lwres_uint16_t .Fo lwres_buffer_getuint16 .Fa "lwres_buffer_t *b" .Fc .Ft void .Fo lwres_buffer_putuint16 .Fa "lwres_buffer_t *b" .Fa "lwres_uint16_t val" .Fc .Ft lwres_uint32_t .Fo lwres_buffer_getuint32 .Fa "lwres_buffer_t *b" .Fc .Ft void .Fo lwres_buffer_putuint32 .Fa "lwres_buffer_t *b" .Fa "lwres_uint32_t val" .Fc .Ft void .Fo lwres_buffer_putmem .Fa "lwres_buffer_t *b" .Fa "const unsigned char *base" .Fa "unsigned int length" .Fc .Ft void .Fo lwres_buffer_getmem .Fa "lwres_buffer_t *b" .Fa "unsigned char *base" .Fa "unsigned int length" .Fc .Sh DESCRIPTION These functions use the following structure as a buffer descriptor to manage the actual storage: d -literal -offset indent typedef struct lwres_buffer lwres_buffer_t; struct lwres_buffer { unsigned int magic; unsigned char *base; /* The following integers are byte offsets from 'base'. */ unsigned int length; unsigned int used; unsigned int current; unsigned int active; }; .Ed The main reason for making the buffer structure public is so that buffer operations can be implemented using macros. Applications should not manipulate this structure directly. They should use the functions listed below.
p A buffer is a region of memory, together with a set of related subregions. The \*qused region\*q and the \*qavailable\*q region are disjoint, and their union is the buffer's region. The used region extends from the beginning of the buffer region to the last used byte. The available region extends from one byte greater than the last used byte to the end of the buffer's region. The size of the used region can be changed using various buffer commands. Initially, the used region is empty.
p The used region is further subdivided into two disjoint regions: the \*qconsumed region\*q and the \*qremaining region\*q. The union of these two regions is the used region. The consumed region extends from the beginning of the used region to the byte before the \*qcurrent\*q offset (if any). The \*qremaining\*q region the current pointer to the end of the used region. The size of the consumed region can be changed using various buffer commands. Initially, the consumed region is empty.
p The \*qactive region\*q is an (optional) subregion of the remaining region. It extends from the current offset to an offset in the remaining region. Initially, the active region is empty. If the current offset advances beyond the chosen offset, the active region will also be empty.
p Except for .Fn lwres_buffer_init , all of the buffer managements functions contain an assertion check that .Fa b is a pointer to a valid lightweight resolver buffer.
p .Fn lwres_buffer_init makes the .Dv "struct lwres_buffer" referenced by .Fa *b to be associated with a memory region of size .Fa length bytes starting at location .Fa base. The function checks that .Fa *b is not .Dv NULL .
p The .Dv lwres_buffer_t .Fa *b is invalidated by .Fn lwres_buffer_invalidate . .Fa *b must be a valid lightweight resolver buffer.
p The functions .Fn lwres_buffer_add and .Fn lwres_buffer_subtract respectively increase and decrease the used space in buffer .Fa *b by .Fa n bytes. .Fa *b .Fn lwres_buffer_add checks for buffer overflow and .Fn lwres_buffer_subtract checks for underflow. These functions do not allocate or deallocate memory. They just change the value of .Li b->used .
p A lightweight resolver buffer is re-initialised by .Fn lwres_buffer_clear . The function sets .Li b->used , .Li b->current and .Li b->active to zero.
p .Fn lwres_buffer_first makes the consumed region of buffer .Fa *p empty by setting .Li b->current to zero: the start of the buffer.
p The consumed region of buffer .Fa *b is increased by .Fa n bytes using .Fn lwres_buffer_forward . The function checks for buffer overflow. Similarly, .Fn lwres_buffer_back decreases buffer .Fa b 's consumed region by .Fa n bytes and checks for buffer underflow.
p .Fn lwres_buffer_getuint8 reads an unsigned 8-bit integer from .Fa *b and returns it. The function checks that it does not read past the end of the buffer's consumed region. .Fn lwres_buffer_putuint8 writes the unsigned 8-bit integer .Fa val to buffer .Fa *b . It checks that the buffer has available space for .Fa val .
p .Fn lwres_buffer_getuint16 and .Fn lwres_buffer_getuint32 are identical to .Fn lwres_buffer_putuint8 except that they respectively read an unsigned 16-bit or 32-bit integer from .Fa b converting it from network byte order to host byte order before returning its value. Similarly, .Fn lwres_buffer_putuint16 and .Fn lwres_buffer_putuint32 writes the unsigned 16-bit or 32-bit integer .Fa val to buffer .Fa b , converting it from host byte order to network byte order.
p Arbitrary amounts of data are read or written from a lightweight resolver buffer with .Fn lwres_buffer_getmem and .Fn lwres_buffer_putmem respectively. .Fn lwres_buffer_putmem copies .Fa length bytes of memory at .Fa base to .Fa b. Conversely, .Fn lwres_buffer_getmem copies .Fa length bytes of memory from .Fa b to .Fa base . For both functions, .Fa base should point to at least .Fa length bytes of valid memory. .Fa base .Sh RETURN VALUES .Fn lwres_buffer_getuint8 , .Fn lwres_buffer_getuint16 and .Fn lwres_buffer_getuint32 return an 8-, 16- or 32-bit unsigned integer respectively from the current offset in buffer .Fa b . The 16- and 32-bit quantities are presented in host byte order even though they are stored in network byte order inside the buffer. .Sh SEE ALSO .Sh BUGS Buffers have no synchronization. Clients must ensure exclusive access for thread-safe operations.