75 lines
1.9 KiB
C
75 lines
1.9 KiB
C
/* SPDX-License-Identifier: GPL-2.0+ */
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#include <errno.h>
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#include <sys/socket.h>
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#include <netax25/ax25.h>
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#include "utils.h"
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/*
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* AX.25 addresses are based on Amateur radio callsigns followed by an SSID
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* like XXXXXX-SS where the callsign is up to 6 characters which are either
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* letters or digits and the SSID is a decimal number in the range 0..15.
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* Amateur radio callsigns are assigned by a country's relevant authorities
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* and are 3..6 characters though a few countries have assigned callsigns
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* longer than that. AX.25 is not able to handle such longer callsigns.
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*
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* Being based on HDLC AX.25 encodes addresses by shifting them one bit left
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* thus zeroing bit 0, the HDLC extension bit for all but the last bit of
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* a packet's address field but for our purposes here we're not considering
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* the HDLC extension bit that is it will always be zero.
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*
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* Linux' internal representation of AX.25 addresses in Linux is very similar
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* to this on the on-air or on-the-wire format. The callsign is padded to
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* 6 octets by adding spaces, followed by the SSID octet then all 7 octets
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* are left-shifted by one byte.
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*
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* This for example turns "LINUX-1" where the callsign is LINUX and SSID is 1
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* into 98:92:9c:aa:b0:40:02.
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*/
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static const char *ax25_ntop1(const ax25_address *src, char *dst,
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socklen_t size)
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{
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char c, *s;
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int n;
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for (n = 0, s = dst; n < 6; n++) {
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c = (src->ax25_call[n] >> 1) & 0x7f;
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if (c != ' ')
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*s++ = c;
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}
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*s++ = '-';
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n = ((src->ax25_call[6] >> 1) & 0x0f);
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if (n > 9) {
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*s++ = '1';
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n -= 10;
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}
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*s++ = n + '0';
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*s++ = '\0';
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if (*dst == '\0' || *dst == '-') {
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dst[0] = '*';
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dst[1] = '\0';
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}
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return dst;
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}
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const char *ax25_ntop(int af, const void *addr, char *buf, socklen_t buflen)
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{
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switch (af) {
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case AF_AX25:
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errno = 0;
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return ax25_ntop1((ax25_address *)addr, buf, buflen);
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default:
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errno = EAFNOSUPPORT;
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}
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return NULL;
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}
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