Packet, packetalloc, packetappend, packetasize, packetcmp, packetconcat, packetconsume, packetcopy, packetdup, packetforeign, packetfragments, packetfree, packetheader, packetpeek, packetprefix, packetsha1, packetsize, packetsplit, packetstats, packettrailer, packettrim – zero–copy network buffers

#include <u.h>
#include <libc.h>
#include <venti.h>

Packet* packetalloc(void);

void      packetappend(Packet *p, uchar *buf, int n)

uint      packetasize(Packet *p)

int       packetcmp(Packet *p, Packet *q)

void      packetconcat(Packet *p, Packet *q)

int       packetconsume(Packet *p, uchar *buf, int n)

int       packetcopy(Packet *p, uchar *buf, int offset, int n)

Packet* packetdup(Packet *p, int offset, int n)

Packet* packetforeign(uchar *buf, int n,
void (*free)(void *a), void *a)

int       packetfragments(Packet *p, IOchunk *io, int nio,
int offset)

void      packetfree(Packet *p)

uchar*    packetheader(Packet *p, int n)

uchar*    packetpeek(Packet *p, uchar *buf, int offset, int n)

void      packetprefix(Packet *p, uchar *buf, int n)

void      packetsha1(Packet *p, uchar sha1[20])

uint      packetsize(Packet *p)

Packet* packetsplit(Packet *p, int n)

void      packetstats(void)

uchar*    packettrailer(Packet *p, int n)

int       packettrim(Packet *p, int offset, int n)

A Packet is a chain of blocks of data. Each block, called a fragment, is contiguous in memory, but the entire packet may not be. This representation helps avoid unnecessary memory copies.

Packetalloc allocates an empty packet.

Packetappend appends the n bytes at buf to the end of p.

Packetasize returns the number of data bytes allocated to p. This may be larger than the number of bytes stored in p because fragments may not be filled completely.

Packetcmp compares the data sections of two packets as memcmp (see memory(2)) would.

Packetconcat removes all data from q, appending it to p.

Packetconsume removes n bytes from the beginning of p, storing them into buf.

Packetcopy copies n bytes at offset in p to buf.

Packetdup creates a new packet initialized with n bytes from offset in p.

Packetforeign allocates a packet containing `foreign' data: the n bytes pointed to by buf. Once the bytes are no longer needed, they are freed by calling free(a).

Packetfragments initializes up to nio of the io structures with pointers to the data in p, starting at offset. It returns the total number of bytes represented by the returned structures. Packetfragments initializes any unused io structures with nil pointer and zero length.

Packetfree frees the packet p.

Packetheader returns a pointer to the first n bytes of p, making them contiguous in memory if necessary.

Packetpeek returns a pointer to the n bytes at offset in p. If the requested bytes are already stored contiguously in memory, the returned pointer points at the internal data storage for p. Otherwise, the bytes are copied into buf, and packetpeek returns buf.

Packetprefix inserts a copy of the n bytes at buf at the beginning of p.

Packetsha1 computes the SHA1 hash of the data contained in p.

Packetsize returns the length, in bytes, of the data contained in p.

Packetsplit returns a new packet initialized with n bytes removed from the beginning of p.

Packetstats prints run–time statistics to standard output.

Packettrailer returns a pointer to the last n bytes of p, making them contiguous in memory if necessary.

Packettrim deletes all bytes from the packet p except the n bytes at offset offset.



These functions return errors only when passed invalid inputs, e.g., requests for data at negative offsets or beyond the end of a packet.

Functions returning pointers return nil on error; functions returning integers return –1 on error. Most functions returning integers return 0 on success. The exceptions are packetfragments and packetcmp, whose return values are described above.

When these functions run out of memory, they print error messages and call sysfatal.

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