Improve ap example (#233)

peterharperuk · web-flow · commit 566ce86a6e75 · 2023-01-23T08:35:33.000-06:00
* Add dns server The access point example is a bit complicated to use as you have to open a browser and enter a url with the IP address of the device Add a simple dns server that can be used to make the access point behave like a captive portal. All DNS requests point back to the gateway IP. * Improve AP example The web page /ledtest gives you a web page with an option to turn the led on and off Start the DNS server and redirect all HTTP requests to this page. Improve the code so it can handle more than one request at a time. Fixes: #232
diff --git a/pico_w/access_point/CMakeLists.txt b/pico_w/access_point/CMakeLists.txt
@@ -1,12 +1,14 @@
 add_executable(picow_access_point_background
         picow_access_point.c
         dhcpserver/dhcpserver.c
+        dnsserver/dnsserver.c
         )
 
 target_include_directories(picow_access_point_background PRIVATE
         ${CMAKE_CURRENT_LIST_DIR}
         ${CMAKE_CURRENT_LIST_DIR}/.. # for our common lwipopts
         ${CMAKE_CURRENT_LIST_DIR}/dhcpserver
+        ${CMAKE_CURRENT_LIST_DIR}/dnsserver
         )
 
 target_link_libraries(picow_access_point_background
@@ -19,15 +21,16 @@ pico_add_extra_outputs(picow_access_point_background)
 add_executable(picow_access_point_poll
         picow_access_point.c
         dhcpserver/dhcpserver.c
+        dnsserver/dnsserver.c
         )
 target_include_directories(picow_access_point_poll PRIVATE
         ${CMAKE_CURRENT_LIST_DIR}
         ${CMAKE_CURRENT_LIST_DIR}/.. # for our common lwipopts
         ${CMAKE_CURRENT_LIST_DIR}/dhcpserver
+        ${CMAKE_CURRENT_LIST_DIR}/dnsserver
         )
 target_link_libraries(picow_access_point_poll
         pico_cyw43_arch_lwip_poll
         pico_stdlib
         )
 pico_add_extra_outputs(picow_access_point_poll)
-
diff --git a/pico_w/access_point/dhcpserver/dhcpserver.c b/pico_w/access_point/dhcpserver/dhcpserver.c
@@ -63,7 +63,6 @@
 #define PORT_DHCP_SERVER (67)
 #define PORT_DHCP_CLIENT (68)
 
-#define DEFAULT_DNS MAKE_IP4(8, 8, 8, 8)
 #define DEFAULT_LEASE_TIME_S (24 * 60 * 60) // in seconds
 
 #define MAC_LEN (6)
@@ -274,7 +273,7 @@ static void dhcp_server_process(void *arg, struct udp_pcb *upcb, struct pbuf *p,
     opt_write_n(&opt, DHCP_OPT_SERVER_ID, 4, &ip4_addr_get_u32(ip_2_ip4(&d->ip)));
     opt_write_n(&opt, DHCP_OPT_SUBNET_MASK, 4, &ip4_addr_get_u32(ip_2_ip4(&d->nm)));
     opt_write_n(&opt, DHCP_OPT_ROUTER, 4, &ip4_addr_get_u32(ip_2_ip4(&d->ip))); // aka gateway; can have mulitple addresses
-    opt_write_u32(&opt, DHCP_OPT_DNS, DEFAULT_DNS); // can have mulitple addresses
+    opt_write_n(&opt, DHCP_OPT_DNS, 4, &ip4_addr_get_u32(ip_2_ip4(&d->ip))); // this server is the dns
     opt_write_u32(&opt, DHCP_OPT_IP_LEASE_TIME, DEFAULT_LEASE_TIME_S);
     *opt++ = DHCP_OPT_END;
     dhcp_socket_sendto(&d->udp, &dhcp_msg, opt - (uint8_t *)&dhcp_msg, 0xffffffff, PORT_DHCP_CLIENT);
diff --git a/pico_w/access_point/dnsserver/dnsserver.c b/pico_w/access_point/dnsserver/dnsserver.c
@@ -0,0 +1,235 @@
+/**
+ * Copyright (c) 2022 Raspberry Pi (Trading) Ltd.
+ *
+ * SPDX-License-Identifier: BSD-3-Clause
+ */
+
+#include <stdio.h>
+#include <string.h>
+#include <errno.h>
+#include <assert.h>
+#include <stdbool.h>
+
+#include "dnsserver.h"
+#include "lwip/udp.h"
+
+#define PORT_DNS_SERVER 53
+#define DUMP_DATA 0
+
+#define DEBUG_printf(...)
+#define ERROR_printf printf
+
+typedef struct dns_header_t_ {
+    uint16_t id;
+    uint16_t flags;
+    uint16_t question_count;
+    uint16_t answer_record_count;
+    uint16_t authority_record_count;
+    uint16_t additional_record_count;
+} dns_header_t;
+
+#define MAX_DNS_MSG_SIZE 300
+
+static int dns_socket_new_dgram(struct udp_pcb **udp, void *cb_data, udp_recv_fn cb_udp_recv) {
+    *udp = udp_new();
+    if (*udp == NULL) {
+        return -ENOMEM;
+    }
+    udp_recv(*udp, cb_udp_recv, (void *)cb_data);
+    return ERR_OK;
+}
+
+static void dns_socket_free(struct udp_pcb **udp) {
+    if (*udp != NULL) {
+        udp_remove(*udp);
+        *udp = NULL;
+    }
+}
+
+static int dns_socket_bind(struct udp_pcb **udp, uint32_t ip, uint16_t port) {
+    ip_addr_t addr;
+    IP4_ADDR(&addr, ip >> 24 & 0xff, ip >> 16 & 0xff, ip >> 8 & 0xff, ip & 0xff);
+    err_t err = udp_bind(*udp, &addr, port);
+    if (err != ERR_OK) {
+        ERROR_printf("dns failed to bind to port %u: %d", port, err);
+        assert(false);
+    }
+    return err;
+}
+
+#if DUMP_DATA
+static void dump_bytes(const uint8_t *bptr, uint32_t len) {
+    unsigned int i = 0;
+
+    for (i = 0; i < len;) {
+        if ((i & 0x0f) == 0) {
+            printf("\n");
+        } else if ((i & 0x07) == 0) {
+            printf(" ");
+        }
+        printf("%02x ", bptr[i++]);
+    }
+    printf("\n");
+}
+#endif
+
+static int dns_socket_sendto(struct udp_pcb **udp, const void *buf, size_t len, const ip_addr_t *dest, uint16_t port) {
+    if (len > 0xffff) {
+        len = 0xffff;
+    }
+
+    struct pbuf *p = pbuf_alloc(PBUF_TRANSPORT, len, PBUF_RAM);
+    if (p == NULL) {
+        ERROR_printf("DNS: Failed to send message out of memory\n");
+        return -ENOMEM;
+    }
+
+    memcpy(p->payload, buf, len);
+    err_t err = udp_sendto(*udp, p, dest, port);
+
+    pbuf_free(p);
+
+    if (err != ERR_OK) {
+        ERROR_printf("DNS: Failed to send message %d\n", err);
+        return err;
+    }
+
+#if DUMP_DATA
+    dump_bytes(buf, len);
+#endif
+    return len;
+}
+
+static void dns_server_process(void *arg, struct udp_pcb *upcb, struct pbuf *p, const ip_addr_t *src_addr, u16_t src_port) {
+    dns_server_t *d = arg;
+    DEBUG_printf("dns_server_process %u\n", p->tot_len);
+
+    uint8_t dns_msg[MAX_DNS_MSG_SIZE];
+    dns_header_t *dns_hdr = (dns_header_t*)dns_msg;
+
+    size_t msg_len = pbuf_copy_partial(p, dns_msg, sizeof(dns_msg), 0);
+    if (msg_len < sizeof(dns_header_t)) {
+        goto ignore_request;
+    }
+
+#if DUMP_DATA
+    dump_bytes(dns_msg, msg_len);
+#endif
+
+    uint16_t flags = lwip_ntohs(dns_hdr->flags);
+    uint16_t question_count = lwip_ntohs(dns_hdr->question_count);
+
+    DEBUG_printf("len %d\n", msg_len);
+    DEBUG_printf("dns flags 0x%x\n", flags);
+    DEBUG_printf("dns question count 0x%x\n", question_count);
+
+    // flags from rfc1035
+    // +--+--+--+--+--+--+--+--+--+--+--+--+--+--+--+--+
+    // |QR|   Opcode  |AA|TC|RD|RA|   Z    |   RCODE   |
+    // +--+--+--+--+--+--+--+--+--+--+--+--+--+--+--+--+
+
+    // Check QR indicates a query
+    if (((flags >> 15) & 0x1) != 0) {
+        DEBUG_printf("Ignoring non-query\n");
+        goto ignore_request;
+    }
+
+    // Check for standard query
+    if (((flags >> 11) & 0xf) != 0) {
+        DEBUG_printf("Ignoring non-standard query\n");
+        goto ignore_request;
+    }
+
+    // Check question count
+    if (question_count < 1) {
+        DEBUG_printf("Invalid question count\n");
+        goto ignore_request;
+    }
+
+    // Print the question
+    DEBUG_printf("question: ");
+    const uint8_t *question_ptr_start = dns_msg + sizeof(dns_header_t);
+    const uint8_t *question_ptr_end = dns_msg + msg_len;
+    const uint8_t *question_ptr = question_ptr_start;
+    while(question_ptr < question_ptr_end) {
+        if (*question_ptr == 0) {
+            question_ptr++;
+            break;
+        } else {
+            if (question_ptr > question_ptr_start) {
+                DEBUG_printf(".");
+            }
+            int label_len = *question_ptr++;
+            if (label_len > 63) {
+                DEBUG_printf("Invalid label\n");
+                goto ignore_request;
+            }
+            DEBUG_printf("%.*s", label_len, question_ptr);
+            question_ptr += label_len;
+        }
+    }
+    DEBUG_printf("\n");
+
+    // Check question length
+    if (question_ptr - question_ptr_start > 255) {
+        DEBUG_printf("Invalid question length\n");
+        goto ignore_request;
+    }
+
+    // Skip QNAME and QTYPE
+    question_ptr += 4;
+
+    // Generate answer
+    uint8_t *answer_ptr = dns_msg + (question_ptr - dns_msg);
+    *answer_ptr++ = 0xc0; // pointer
+    *answer_ptr++ = question_ptr_start - dns_msg; // pointer to question
+    
+    *answer_ptr++ = 0;
+    *answer_ptr++ = 1; // host address
+
+    *answer_ptr++ = 0;
+    *answer_ptr++ = 1; // Internet class
+
+    *answer_ptr++ = 0;
+    *answer_ptr++ = 0;
+    *answer_ptr++ = 0;
+    *answer_ptr++ = 60; // ttl 60s
+
+    *answer_ptr++ = 0;
+    *answer_ptr++ = 4; // length
+    memcpy(answer_ptr, &d->ip.addr, 4); // use our address
+    answer_ptr += 4;
+
+    dns_hdr->flags = lwip_htons(
+                0x1 << 15 | // QR = response
+                0x1 << 10 | // AA = authoritive
+                0x1 << 7);   // RA = authenticated
+    dns_hdr->question_count = lwip_htons(1);
+    dns_hdr->answer_record_count = lwip_htons(1);
+    dns_hdr->authority_record_count = 0;
+    dns_hdr->additional_record_count = 0;
+
+    // Send the reply
+    DEBUG_printf("Sending %d byte reply to %s:%d\n", answer_ptr - dns_msg, ipaddr_ntoa(src_addr), src_port);
+    dns_socket_sendto(&d->udp, &dns_msg, answer_ptr - dns_msg, src_addr, src_port);
+
+ignore_request:
+    pbuf_free(p);
+}
+
+void dns_server_init(dns_server_t *d, ip_addr_t *ip) {
+    if (dns_socket_new_dgram(&d->udp, d, dns_server_process) != ERR_OK) {
+        DEBUG_printf("dns server failed to start\n");
+        return;
+    }
+    if (dns_socket_bind(&d->udp, 0, PORT_DNS_SERVER) != ERR_OK) {
+        DEBUG_printf("dns server failed to bind\n");
+        return;
+    }
+    ip_addr_copy(d->ip, *ip);
+    DEBUG_printf("dns server listening on port %d\n", PORT_DNS_SERVER);
+}
+
+void dns_server_deinit(dns_server_t *d) {
+    dns_socket_free(&d->udp);
+}
diff --git a/pico_w/access_point/dnsserver/dnsserver.h b/pico_w/access_point/dnsserver/dnsserver.h
@@ -0,0 +1,20 @@
+/**
+ * Copyright (c) 2022 Raspberry Pi (Trading) Ltd.
+ *
+ * SPDX-License-Identifier: BSD-3-Clause
+ */
+
+#ifndef _DNSSERVER_H_
+#define _DNSSERVER_H_
+
+#include "lwip/ip_addr.h"
+
+typedef struct dns_server_t_ {
+    struct udp_pcb *udp;
+     ip_addr_t ip;
+} dns_server_t;
+
+void dns_server_init(dns_server_t *d, ip_addr_t *ip);
+void dns_server_deinit(dns_server_t *d);
+
+#endif
diff --git a/pico_w/access_point/picow_access_point.c b/pico_w/access_point/picow_access_point.c
