source: vendor/current/lib/util/iov_buf.c

/*
 * Unix SMB/CIFS implementation.
 * Samba system utilities
 * Copyright (C) Volker Lendecke 2014
 *
 * This program is free software; you can redistribute it and/or modify
 * it under the terms of the GNU General Public License as published by
 * the Free Software Foundation; either version 3 of the License, or
 * (at your option) any later version.
 *
 * This program is distributed in the hope that it will be useful,
 * but WITHOUT ANY WARRANTY; without even the implied warranty of
 * MERCHANTABILITY or FITNESS FOR A PARTICULAR PURPOSE.  See the
 * GNU General Public License for more details.
 *
 * You should have received a copy of the GNU General Public License
 * along with this program.  If not, see <http://www.gnu.org/licenses/>.
 */

#include "replace.h"
#include "system/filesys.h"
#include "iov_buf.h"

ssize_t iov_buflen(const struct iovec *iov, int iovcnt)
{
        return iov_buf(iov, iovcnt, NULL, 0);
}

ssize_t iov_buf(const struct iovec *iov, int iovcnt,
                uint8_t *buf, size_t buflen)
{
        size_t needed = 0;
        uint8_t *p = buf;
        int i;

        for (i=0; i<iovcnt; i++) {
                size_t thislen = iov[i].iov_len;
                size_t tmp;

                tmp = needed + thislen;

                if (tmp < needed) {
                        /* wrap */
                        return -1;
                }
                needed = tmp;

                if (needed <= buflen) {
                        memcpy(p, iov[i].iov_base, thislen);
                        p += thislen;
                }
        }

        return needed;
}

bool iov_advance(struct iovec **iov, int *iovcnt, size_t n)
{
        struct iovec *v = *iov;
        int cnt = *iovcnt;

        while (n > 0) {
                if (cnt == 0) {
                        return false;
                }
                if (n < v->iov_len) {
                        v->iov_base = (char *)v->iov_base + n;
                        v->iov_len -= n;
                        break;
                }
                n -= v->iov_len;
                v += 1;
                cnt -= 1;
        }

        /*
         * Skip 0-length iovec's
         *
         * There might be empty buffers at the end of iov. Next time we do a
         * readv/writev based on this iov would give 0 transferred bytes, also
         * known as EPIPE. So we need to be careful discarding them.
         */

        while ((cnt > 0) && (v->iov_len == 0)) {
                v += 1;
                cnt -= 1;
        }

        *iov = v;
        *iovcnt = cnt;
        return true;
}