dhcp: Enable custom config for timeouts, thresholds, backoff time

Enables to configure:
* DHCP_COARSE_TIMER_SECS
* if DHCP_DEFINE_CUSTOM_TIMEOUTS defined these addtional options are
available:
  - DHCP_CALC_TIMEOUT_FROM_OFFERED_T0_LEASE to adjust the t0 lease timeout from the offered value
  - DHCP_CALC_TIMEOUT_FROM_OFFERED_T1_RENEW same for t1 renew
  - DHCP_CALC_TIMEOUT_FROM_OFFERED_T2_REBIND same for t2 rebind
  - DHCP_NEXT_TIMEOUT_THRESHOLD to adjust the period of the next timeout
  - DHCP_REQUEST_BACKOFF_SEQUENCE to adjust back-off times based on DHCP
request attempts
Also updates timeout type from u16 to u32 - eps useful when DHCP_COARSE_TIMER_SECS is a smaller number

src/core/ipv4/dhcp.c

@@ -93,8 +93,14 @@
 #define LWIP_HOOK_DHCP_PARSE_OPTION(netif, dhcp, state, msg, msg_type, option, len, pbuf, offset) do { LWIP_UNUSED_ARG(msg); } while(0)
 #endif
 
-/** Calculating and setting DHCP timeouts, thresholds and backoff sequences
+/** DHCP_DEFINE_CUSTOM_TIMEOUTS: if this is defined then you can customize various DHCP timeouts using these macros:
+      - DHCP_SET_TIMEOUT_FROM_OFFERED_T0_LEASE() to adjust the t0 lease timeout from the offered value
+      - DHCP_SET_TIMEOUT_FROM_OFFERED_T1_RENEW() same for t1 renew
+      - DHCP_SET_TIMEOUT_FROM_OFFERED_T2_REBIND() same for t2 rebind
+      - DHCP_NEXT_TIMEOUT_THRESHOLD to adjust the period of the next timeout
+      - DHCP_REQUEST_BACKOFF_SEQUENCE to adjust back-off times based on DHCP request attempts
  */
+#ifndef DHCP_DEFINE_CUSTOM_TIMEOUTS
 #define SET_TIMEOUT_FROM_OFFERED(result, offered, min, max) do { \
   u32_t timeout = (offered + DHCP_COARSE_TIMER_SECS / 2) / DHCP_COARSE_TIMER_SECS;  \
   if (timeout > max) {    \
@@ -103,7 +109,7 @@
   if (timeout == min) {   \
     timeout = 1;          \
   } \
-  result = (u16_t)timeout; \
+  result = (dhcp_timeout_t)timeout; \
 } while(0)
 
 #define DHCP_SET_TIMEOUT_FROM_OFFERED_T0_LEASE(res, dhcp)  SET_TIMEOUT_FROM_OFFERED(res, (dhcp)->offered_t0_lease, 0, 0xffff)
@@ -113,6 +119,8 @@
 #define DHCP_NEXT_TIMEOUT_THRESHOLD ((60 + DHCP_COARSE_TIMER_SECS / 2) / DHCP_COARSE_TIMER_SECS)
 #define DHCP_REQUEST_BACKOFF_SEQUENCE(tries)   (u16_t)(( (tries) < 6 ? 1 << (tries) : 60) * 1000)
 
+#endif /* DHCP_DEFINE_CUSTOM_TIMEOUTS */
+
 /** DHCP_CREATE_RAND_XID: if this is set to 1, the xid is created using
  * LWIP_RAND() (this overrides DHCP_GLOBAL_XID)
  */
@@ -605,7 +613,7 @@ dhcp_t1_timeout(struct netif *netif)
     dhcp_renew(netif);
     /* Calculate next timeout */
     if (((dhcp->t2_timeout - dhcp->lease_used) / 2) >= DHCP_NEXT_TIMEOUT_THRESHOLD) {
-      dhcp->t1_renew_time = (u16_t)((dhcp->t2_timeout - dhcp->lease_used) / 2);
+      dhcp->t1_renew_time = (dhcp_timeout_t)((dhcp->t2_timeout - dhcp->lease_used) / 2);
     }
   }
 }
@@ -631,7 +639,7 @@ dhcp_t2_timeout(struct netif *netif)
     dhcp_rebind(netif);
     /* Calculate next timeout */
     if (((dhcp->t0_timeout - dhcp->lease_used) / 2) >= DHCP_NEXT_TIMEOUT_THRESHOLD) {
-      dhcp->t2_rebind_time = (u16_t)((dhcp->t0_timeout - dhcp->lease_used) / 2);
+      dhcp->t2_rebind_time = (dhcp_timeout_t)((dhcp->t0_timeout - dhcp->lease_used) / 2);
     }
   }
 }

src/include/lwip/dhcp.h

@@ -53,8 +53,17 @@
 extern "C" {
 #endif
 
+/** Define DHCP_TIMEOUT_SIZE_T in opt.h if you want use a different integer than u16_t.
+ *  Especially useful if DHCP_COARSE_TIMER_SECS is in smaller units, so timeouts easily reach UINT16_MAX and more */
+#ifdef DHCP_TIMEOUT_SIZE_T
+typedef DHCP_TIMEOUT_SIZE_T dhcp_timeout_t;
+#else /* DHCP_TIMEOUT_SIZE_T */
+typedef u16_t dhcp_timeout_t;
+#endif /* DHCP_TIMEOUT_SIZE_T*/
 /** period (in seconds) of the application calling dhcp_coarse_tmr() */
+#ifndef DHCP_COARSE_TIMER_SECS
 #define DHCP_COARSE_TIMER_SECS  60
+#endif /* DHCP_COARSE_TIMER_SECS */
 /** period (in milliseconds) of the application calling dhcp_coarse_tmr() */
 #define DHCP_COARSE_TIMER_MSECS (DHCP_COARSE_TIMER_SECS * 1000UL)
 /** period (in milliseconds) of the application calling dhcp_fine_tmr() */
@@ -84,13 +93,13 @@ struct dhcp
   /** see DHCP_FLAG_* */
   u8_t flags;
 
-  u16_t request_timeout; /* #ticks with period DHCP_FINE_TIMER_SECS for request timeout */
-  u16_t t1_timeout;  /* #ticks with period DHCP_COARSE_TIMER_SECS for renewal time */
-  u16_t t2_timeout;  /* #ticks with period DHCP_COARSE_TIMER_SECS for rebind time */
-  u16_t t1_renew_time;  /* #ticks with period DHCP_COARSE_TIMER_SECS until next renew try */
-  u16_t t2_rebind_time; /* #ticks with period DHCP_COARSE_TIMER_SECS until next rebind try */
-  u16_t lease_used; /* #ticks with period DHCP_COARSE_TIMER_SECS since last received DHCP ack */
-  u16_t t0_timeout; /* #ticks with period DHCP_COARSE_TIMER_SECS for lease time */
+  dhcp_timeout_t request_timeout; /* #ticks with period DHCP_FINE_TIMER_SECS for request timeout */
+  dhcp_timeout_t t1_timeout;  /* #ticks with period DHCP_COARSE_TIMER_SECS for renewal time */
+  dhcp_timeout_t t2_timeout;  /* #ticks with period DHCP_COARSE_TIMER_SECS for rebind time */
+  dhcp_timeout_t t1_renew_time;  /* #ticks with period DHCP_COARSE_TIMER_SECS until next renew try */
+  dhcp_timeout_t t2_rebind_time; /* #ticks with period DHCP_COARSE_TIMER_SECS until next rebind try */
+  dhcp_timeout_t lease_used; /* #ticks with period DHCP_COARSE_TIMER_SECS since last received DHCP ack */
+  dhcp_timeout_t t0_timeout; /* #ticks with period DHCP_COARSE_TIMER_SECS for lease time */
   ip_addr_t server_ip_addr; /* dhcp server address that offered this lease (ip_addr_t because passed to UDP) */
   ip4_addr_t offered_ip_addr;
   ip4_addr_t offered_sn_mask;