Add RFC 7710 support in the dhcp stack (IDFGH-973)

[plasger-ebv]

These commits add support for rfc 7710 (captive portal) to the dhcp-stack.

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[cgiles]

Hello, can you provide an example of how to use it ?

And would it be possible to adapt it for the arduino mode ? It's not a request just a question if it is feasible or not :)

Thanks for your work !

[freakyxue]

hi @cgiles
We could potentially expand the example to have an option for using this. Although from my research it seems like the support for this feature among Android/iOS

[freakyxue]

hi @cgiles @plasger-ebv
from my research it seems like the support for this feature among Android/iOS is not there, so it probably won't be very useful (yet).

[joecjdi]

Looks like Android 11 supports RFC 7710... would be great to see support added to ESP-IDF!

[david-cermak]

Hi @plasger-ebv et all,

Thanks again for the contribution and the idea of adding additional options to DHCP server messages! Will address this in a more generic way (as provided in other LWIP modules), enabling users to define their own options and append it to various DHCP messages.
The update in IDF is very simple:

diff --git a/components/lwip/apps/dhcpserver/dhcpserver.c b/components/lwip/apps/dhcpserver/dhcpserver.c
@@ -19,6 +19,14 @@
 
 #if ESP_DHCPS
 
+#ifdef LWIP_HOOK_FILENAME
+#include LWIP_HOOK_FILENAME
+#endif
+
+#ifndef LWIP_HOOK_DHCPS_POST_APPEND_OPTS
+#define LWIP_HOOK_DHCPS_POST_APPEND_OPTS(netif, dhcps, state, pp_opts)
+#endif
+
 #define BOOTP_BROADCAST 0x8000
 
 #define DHCP_REQUEST        1
@@ -538,6 +546,7 @@ static void send_offer(dhcps_t *dhcps, struct dhcps_msg *m, u16_t len)
 
     end = add_msg_type(&m->options[4], DHCPOFFER);
     end = add_offer_options(dhcps, end);
+    LWIP_HOOK_DHCPS_POST_APPEND_OPTS(dhcps->netif, dhcps, DHCPOFFER, &end)
     end = add_end(end);
 
     p = dhcps_pbuf_alloc(len);
@@ -615,6 +624,7 @@ static void send_nak(dhcps_t *dhcps, struct dhcps_msg *m, u16_t len)
     create_msg(dhcps, m);
 
     end = add_msg_type(&m->options[4], DHCPNAK);
+    LWIP_HOOK_DHCPS_POST_APPEND_OPTS(dhcps->netif, dhcps, DHCPNAK, &end)
     end = add_end(end);
 
     p = dhcps_pbuf_alloc(len);
@@ -691,6 +701,7 @@ static void send_ack(dhcps_t *dhcps, struct dhcps_msg *m, u16_t len)
 
     end = add_msg_type(&m->options[4], DHCPACK);
     end = add_offer_options(dhcps, end);
+    LWIP_HOOK_DHCPS_POST_APPEND_OPTS(dhcps->netif, dhcps, DHCPACK, &end)
     end = add_end(end);
 
     p = dhcps_pbuf_alloc(len);

Then, if we'd like to add the captive portal option, we'd just provide the macro definition

  #define LWIP_HOOK_DHCPS_POST_APPEND_OPTS(netif, dhcp, state, pp_opts) \
      if ((state)==DHCPOFFER) { *(pp_opts) = append_captive_portal_uri(*(pp_opts)); }

  static inline uint8_t *append_captive_portal_uri(uint8_t *optptr)
  {
    const static uint8_t DHCP_OPTION_CAPTIVE_PORTAL=160;
    const static char CAPTIVE_PORTAL_URI[]="my_uri";
    int size = sizeof(CAPTIVE_PORTAL_URI) - 1;
    *optptr++ = DHCP_OPTION_CAPTIVE_PORTAL;
    *optptr++ = size;
    for(int i = 0; i < size; ++i) {
        *optptr++ = CAPTIVE_PORTAL_URI[i];
    }
    return optptr;
  }

This needs to be added to the build process of lwip component, so includes an adjustment of our project makefile (assuming that the definitions above are provided in a file add_captive_portal.h located directly in our main component):

  idf_component_get_property(lwip lwip COMPONENT_LIB)
  target_compile_options(${lwip} PRIVATE "-I${PROJECT_DIR}/main")
  target_compile_definitions(${lwip} PRIVATE "-DESP_IDF_LWIP_HOOK_FILENAME=\"add_captive_portal.h\"")

[Alvin1Zhang]

Changes merged with b5d13b9, thanks for your contribution again.

[Alson-tang]

DHCP option 160 seems an outdated option. The latest option is 114, please refer to https://datatracker.ietf.org/doc/html/draft-ietf-capport-rfc7710bis