tcpgetdata.c

来自「TCP-IP红宝书源代码」· C语言 代码 · 共 50 行

/* tcpgetdata.c - tcpgetdata */

#include <conf.h>
#include <kernel.h>
#include <network.h>

/*------------------------------------------------------------------------
 *  tcpgetdata  -  copy data from a TCP receive buffer to a user buffer
 *------------------------------------------------------------------------
 */
int
tcpgetdata(struct tcb *ptcb, u_char *pch, unsigned len)
{
	tcpseq		seq;
	unsigned	cc;

	seq = ptcb->tcb_rnext - ptcb->tcb_rbcount; /* start sequence	*/
	if (ptcb->tcb_flags & TCBF_RUPOK) {
		int nbc, ubc;	/* normal & urgent byte counts	*/

		nbc = ptcb->tcb_rnext - ptcb->tcb_rupseq - 1;
		if (nbc >= 0) {		/* urgent boundary in buffer	*/
			ubc = ptcb->tcb_rbcount - nbc;
			if ((int)len >= ubc) {
				len = ubc;
				ptcb->tcb_flags &= ~TCBF_RUPOK;
			}
		}
	}
	for (cc=0; ptcb->tcb_rbcount && cc < len;) {
		*pch++ = ptcb->tcb_rcvbuf[ptcb->tcb_rbstart];
		--ptcb->tcb_rbcount;
		if (++ptcb->tcb_rbstart >= ptcb->tcb_rbsize)
			ptcb->tcb_rbstart = 0;
		++cc;
	}
	if (ptcb->tcb_rbcount == 0)
		ptcb->tcb_flags &= ~TCBF_PUSH;
	/*
	 * open the receive window, if it's closed and we've made
	 * enough space to fit a segment.
	 */
	if (SEQCMP(ptcb->tcb_cwin, ptcb->tcb_rnext) <= 0 &&
			tcprwindow(ptcb)) {
		ptcb->tcb_flags |= TCBF_NEEDOUT;
		tcpkick(ptcb);
	}
	return cc;
}