test-resolved-packet: skip most of the loop

We want to test the edge cases, but testing all the values in between
is mostly pointless and slow on slow architectures (>1s on rpi).

src/resolve/resolved-dns-packet.c

@@ -28,7 +28,6 @@
 
 #define EDNS0_OPT_DO (1<<15)
 
-#define DNS_PACKET_SIZE_START 512u
 assert_cc(DNS_PACKET_SIZE_START > DNS_PACKET_HEADER_SIZE)
 
 typedef struct DnsPacketRewinder {

src/resolve/resolved-dns-packet.h

@@ -56,10 +56,14 @@ struct DnsPacketHeader {
 #define UDP_PACKET_HEADER_SIZE (sizeof(struct iphdr) + sizeof(struct udphdr))
 
 /* The various DNS protocols deviate in how large a packet can grow,
-   but the TCP transport has a 16bit size field, hence that appears to
-   be the absolute maximum. */
+ * but the TCP transport has a 16bit size field, hence that appears to
+ * be the absolute maximum. */
 #define DNS_PACKET_SIZE_MAX 0xFFFFu
 
+/* The default size to use for allocation when we don't know how large
+ * the packet will turn out to be. */
+#define DNS_PACKET_SIZE_START 512u
+
 /* RFC 1035 say 512 is the maximum, for classic unicast DNS */
 #define DNS_PACKET_UNICAST_SIZE_MAX 512u
 

src/resolve/test-resolved-packet.c

@@ -31,6 +31,9 @@ static void test_dns_packet_new(void) {
 
                 log_debug("dns_packet_new: %zu → %zu", i, p->allocated);
                 assert_se(p->allocated >= MIN(DNS_PACKET_SIZE_MAX, i));
+
+                if (i > DNS_PACKET_SIZE_START + 10 && i < DNS_PACKET_SIZE_MAX - 10)
+                        i = MIN(i * 2, DNS_PACKET_SIZE_MAX - 10);
         }
 
         assert_se(dns_packet_new(&p2, DNS_PROTOCOL_DNS, DNS_PACKET_SIZE_MAX + 1) == -EFBIG);