From b6ae9ffaeb0e18e9fa3d5be62faa8d3c9f340a58 Mon Sep 17 00:00:00 2001
From: Vladislav Grishenko <themiron@mail.ru>
Date: Fri, 26 Jul 2024 00:51:09 +0500
Subject: [PATCH] odhcp6c: allow to request specific ipv6 prefix

Expand -P option with optional exact ipv6 prefix format.
This allows to keep the IPv6 prefix in some cases, for example
if the prefix is issued dynamically on upstream.

Examples:
    -P <length>
    -P <prefix/length>

Based on https://github.com/openwrt/odhcp6c/pull/86
---
 src/dhcpv6.c  |  3 ++-
 src/odhcp6c.c | 20 ++++++++++++++++----
 src/odhcp6c.h |  3 ++-
 3 files changed, 20 insertions(+), 6 deletions(-)

diff --git a/src/dhcpv6.c b/src/dhcpv6.c
index ca5957e..c1603f5 100644
--- a/src/dhcpv6.c
+++ b/src/dhcpv6.c
@@ -384,7 +384,8 @@ static void dhcpv6_send(enum dhcpv6_msg type, uint8_t trid[3], uint32_t ecs)
 			struct dhcpv6_ia_prefix pref = {
 				.type = htons(DHCPV6_OPT_IA_PREFIX),
 				.len = htons(sizeof(pref) - 4),
-				.prefix = request_prefixes[i].length
+				.prefix = request_prefixes[i].length,
+				.addr = request_prefixes[i].addr
 			};
 			memcpy(ia_pd + ia_pd_len, &hdr_ia_pd, sizeof(hdr_ia_pd));
 			ia_pd_len += sizeof(hdr_ia_pd);
diff --git a/src/odhcp6c.c b/src/odhcp6c.c
index 4a6d7bd..20b4040 100644
--- a/src/odhcp6c.c
+++ b/src/odhcp6c.c
@@ -241,17 +241,29 @@ int main(_unused int argc, char* const argv[])
 			if (allow_slaac_only >= 0 && allow_slaac_only < 10)
 				allow_slaac_only = 10;
 
+			struct odhcp6c_request_prefix prefix = { 0 };
+
+			optpos = strchr(optarg, '/');
+			if (optpos) {
+				strncpy((char *)buf, optarg, optpos - optarg);
+				buf[optpos - optarg] = '\0';
+				if (inet_pton(AF_INET6, (char *)buf, &prefix.addr) <= 0) {
+					syslog(LOG_ERR, "invalid argument: '%s'", optarg);
+					return 1;
+				}
+				optpos++;
+			} else
+				optpos = optarg;
+
 			char *iaid_begin;
 			int iaid_len = 0;
-			int prefix_length = strtoul(optarg, &iaid_begin, 10);
+			prefix.length = strtoul(optpos, &iaid_begin, 10);
 
 			if (*iaid_begin != '\0' && *iaid_begin != ',' && *iaid_begin != ':') {
 				syslog(LOG_ERR, "invalid argument: '%s'", optarg);
 				return 1;
 			}
 
-			struct odhcp6c_request_prefix prefix = { 0, prefix_length };
-
 			if (*iaid_begin == ',' && (iaid_len = strlen(iaid_begin)) > 1)
 				memcpy(&prefix.iaid, iaid_begin + 1, iaid_len > 4 ? 4 : iaid_len);
 			else if (*iaid_begin == ':')
@@ -614,7 +626,7 @@ static int usage(void)
 	"	-S <time>	Wait at least <time> sec for a DHCP-server (0)\n"
 	"	-D		Discard advertisements without any address or prefix proposed\n"
 	"	-N <mode>	Mode for requesting addresses [try|force|none]\n"
-	"	-P <length>	Request IPv6-Prefix (0 = auto)\n"
+	"	-P <[pfx/]len>	Request IPv6-Prefix (0 = auto)\n"
 	"	-F		Force IPv6-Prefix\n"
 	"	-V <class>	Set vendor-class option (base-16 encoded)\n"
 	"	-u <user-class> Set user-class option string\n"
diff --git a/src/odhcp6c.h b/src/odhcp6c.h
index 5d9d5e3..7904946 100644
--- a/src/odhcp6c.h
+++ b/src/odhcp6c.h
@@ -367,7 +367,8 @@ struct odhcp6c_entry {
 
 struct odhcp6c_request_prefix {
 	uint32_t iaid;
-	uint16_t length;
+	uint8_t length;
+	struct in6_addr addr;
 };
 
 enum odhcp6c_opt_flags {
-- 
2.30.2