dhcp: Add test for discover DHCP packet creation

Set a fake MAC address and emulate raw packet sending. When the buffer
containing the Discover message is received, check selected IP and
UDP headers and compute IP header and UDP message checksums. Also
send the DHCP message for option parsing and expect a successful
outcome.

Makefile.am

@@ -3880,6 +3880,8 @@ test_dhcp_client_SOURCES = \
 	src/libsystemd-dhcp/dhcp-protocol.h \
 	src/systemd/sd-dhcp-client.h \
 	src/libsystemd-dhcp/dhcp-client.c \
+	src/libsystemd-dhcp/dhcp-internal.h \
+	src/libsystemd-dhcp/dhcp-option.c \
 	src/libsystemd-dhcp/test-dhcp-client.c
 
 test_dhcp_client_LDADD = \

src/libsystemd-dhcp/test-dhcp-client.c

@@ -24,9 +24,16 @@
 #include <errno.h>
 #include <stdio.h>
 
+#include "util.h"
+
 #include "dhcp-protocol.h"
+#include "dhcp-internal.h"
 #include "sd-dhcp-client.h"
 
+static struct ether_addr mac_addr = {
+        .ether_addr_octet = {'A', 'B', 'C', '1', '2', '3'}
+};
+
 static void test_request_basic(void)
 {
         sd_dhcp_client *client;
@@ -112,10 +119,83 @@ static void test_checksum(void)
         assert(client_checksum(&buf, 20) == *val);
 }
 
+static int check_options(uint8_t code, uint8_t len, const uint8_t *option,
+                void *user_data)
+{
+        return 0;
+}
+
+int dhcp_network_send_raw_packet(int index, const void *packet, size_t len)
+{
+        size_t size;
+        _cleanup_free_ DHCPPacket *discover;
+        uint16_t ip_check, udp_check;
+        int res;
+
+        assert(index == 42);
+        assert(packet);
+
+        size = sizeof(DHCPPacket) + 4;
+        assert(len > size);
+
+        discover = memdup(packet, len);
+
+        assert(memcmp(discover->dhcp.chaddr,
+                      &mac_addr.ether_addr_octet, 6) == 0);
+        assert(discover->ip.ttl == IPDEFTTL);
+        assert(discover->ip.protocol == IPPROTO_UDP);
+        assert(discover->ip.saddr == INADDR_ANY);
+        assert(discover->ip.daddr == INADDR_BROADCAST);
+        assert(discover->udp.source == ntohs(DHCP_PORT_CLIENT));
+        assert(discover->udp.dest == ntohs(DHCP_PORT_SERVER));
+
+        ip_check = discover->ip.check;
+
+        discover->ip.ttl = 0;
+        discover->ip.check = discover->udp.len;
+
+        udp_check = ~client_checksum(&discover->ip.ttl, len - 8);
+        assert(udp_check == 0xffff);
+
+        discover->ip.ttl = IPDEFTTL;
+        discover->ip.check = ip_check;
+
+        ip_check = ~client_checksum(&discover->ip, sizeof(discover->ip));
+        assert(ip_check == 0xffff);
+
+        size = len - sizeof(struct iphdr) - sizeof(struct udphdr);
+
+        res = dhcp_option_parse(&discover->dhcp, size, check_options, NULL);
+        if (res < 0)
+                return res;
+
+        return 575;
+}
+
+static void test_discover_message(void)
+{
+        sd_dhcp_client *client;
+        int res;
+
+        client = sd_dhcp_client_new();
+        assert(client);
+
+        assert(sd_dhcp_client_set_index(client, 42) >= 0);
+        assert(sd_dhcp_client_set_mac(client, &mac_addr) >= 0);
+
+        assert(sd_dhcp_client_set_request_option(client, 248) >= 0);
+
+        res = sd_dhcp_client_start(client);
+
+        assert(res == 0 || res == -EINPROGRESS);
+}
+
 int main(int argc, char *argv[])
 {
         test_request_basic();
         test_checksum();
 
+        test_discover_message();
+
         return 0;
 }