init commit

components/dns_server/CMakeLists.txt

@@ -0,0 +1,3 @@
+idf_component_register(SRCS dns_server.c
+                       INCLUDE_DIRS include
+                       PRIV_REQUIRES esp_netif)

components/dns_server/dns_server.c

@@ -0,0 +1,290 @@
+/*
+ * SPDX-FileCopyrightText: 2021-2023 Espressif Systems (Shanghai) CO LTD
+ *
+ * SPDX-License-Identifier: Unlicense OR CC0-1.0
+ */
+
+#include <sys/param.h>
+#include <inttypes.h>
+
+#include "esp_log.h"
+#include "esp_system.h"
+#include "esp_check.h"
+#include "esp_netif.h"
+
+#include "lwip/err.h"
+#include "lwip/sockets.h"
+#include "lwip/sys.h"
+#include "lwip/netdb.h"
+#include "dns_server.h"
+
+#define DNS_PORT (53)
+#define DNS_MAX_LEN (256)
+
+#define OPCODE_MASK (0x7800)
+#define QR_FLAG (1 << 7)
+#define QD_TYPE_A (0x0001)
+#define ANS_TTL_SEC (300)
+
+static const char *TAG = "example_dns_redirect_server";
+
+// DNS Header Packet
+typedef struct __attribute__((__packed__))
+{
+    uint16_t id;
+    uint16_t flags;
+    uint16_t qd_count;
+    uint16_t an_count;
+    uint16_t ns_count;
+    uint16_t ar_count;
+} dns_header_t;
+
+// DNS Question Packet
+typedef struct {
+    uint16_t type;
+    uint16_t class;
+} dns_question_t;
+
+// DNS Answer Packet
+typedef struct __attribute__((__packed__))
+{
+    uint16_t ptr_offset;
+    uint16_t type;
+    uint16_t class;
+    uint32_t ttl;
+    uint16_t addr_len;
+    uint32_t ip_addr;
+} dns_answer_t;
+
+// DNS server handle
+struct dns_server_handle {
+    bool started;
+    TaskHandle_t task;
+    int num_of_entries;
+    dns_entry_pair_t entry[];
+};
+
+/*
+    Parse the name from the packet from the DNS name format to a regular .-seperated name
+    returns the pointer to the next part of the packet
+*/
+static char *parse_dns_name(char *raw_name, char *parsed_name, size_t parsed_name_max_len)
+{
+
+    char *label = raw_name;
+    char *name_itr = parsed_name;
+    int name_len = 0;
+
+    do {
+        int sub_name_len = *label;
+        // (len + 1) since we are adding  a '.'
+        name_len += (sub_name_len + 1);
+        if (name_len > parsed_name_max_len) {
+            return NULL;
+        }
+
+        // Copy the sub name that follows the the label
+        memcpy(name_itr, label + 1, sub_name_len);
+        name_itr[sub_name_len] = '.';
+        name_itr += (sub_name_len + 1);
+        label += sub_name_len + 1;
+    } while (*label != 0);
+
+    // Terminate the final string, replacing the last '.'
+    parsed_name[name_len - 1] = '\0';
+    // Return pointer to first char after the name
+    return label + 1;
+}
+
+// Parses the DNS request and prepares a DNS response with the IP of the softAP
+static int parse_dns_request(char *req, size_t req_len, char *dns_reply, size_t dns_reply_max_len, dns_server_handle_t h)
+{
+    if (req_len > dns_reply_max_len) {
+        return -1;
+    }
+
+    // Prepare the reply
+    memset(dns_reply, 0, dns_reply_max_len);
+    memcpy(dns_reply, req, req_len);
+
+    // Endianess of NW packet different from chip
+    dns_header_t *header = (dns_header_t *)dns_reply;
+    ESP_LOGD(TAG, "DNS query with header id: 0x%X, flags: 0x%X, qd_count: %d",
+             ntohs(header->id), ntohs(header->flags), ntohs(header->qd_count));
+
+    // Not a standard query
+    if ((header->flags & OPCODE_MASK) != 0) {
+        return 0;
+    }
+
+    // Set question response flag
+    header->flags |= QR_FLAG;
+
+    uint16_t qd_count = ntohs(header->qd_count);
+    header->an_count = htons(qd_count);
+
+    int reply_len = qd_count * sizeof(dns_answer_t) + req_len;
+    if (reply_len > dns_reply_max_len) {
+        return -1;
+    }
+
+    // Pointer to current answer and question
+    char *cur_ans_ptr = dns_reply + req_len;
+    char *cur_qd_ptr = dns_reply + sizeof(dns_header_t);
+    char name[128];
+
+    // Respond to all questions based on configured rules
+    for (int qd_i = 0; qd_i < qd_count; qd_i++) {
+        char *name_end_ptr = parse_dns_name(cur_qd_ptr, name, sizeof(name));
+        if (name_end_ptr == NULL) {
+            ESP_LOGE(TAG, "Failed to parse DNS question: %s", cur_qd_ptr);
+            return -1;
+        }
+
+        dns_question_t *question = (dns_question_t *)(name_end_ptr);
+        uint16_t qd_type = ntohs(question->type);
+        uint16_t qd_class = ntohs(question->class);
+
+        ESP_LOGD(TAG, "Received type: %d | Class: %d | Question for: %s", qd_type, qd_class, name);
+
+        if (qd_type == QD_TYPE_A) {
+            esp_ip4_addr_t ip = { .addr = IPADDR_ANY };
+            // Check the configured rules to decide whether to answer this question or not
+            for (int i = 0; i < h->num_of_entries; ++i) {
+                // check if the name either corresponds to the entry, or if we should answer to all queries ("*")
+                if (strcmp(h->entry[i].name, "*") == 0 || strcmp(h->entry[i].name, name) == 0) {
+                    if (h->entry[i].if_key) {
+                        esp_netif_ip_info_t ip_info;
+                        esp_netif_get_ip_info(esp_netif_get_handle_from_ifkey(h->entry[i].if_key), &ip_info);
+                        ip.addr = ip_info.ip.addr;
+                        break;
+                    } else if (h->entry->ip.addr != IPADDR_ANY) {
+                        ip.addr = h->entry[i].ip.addr;
+                        break;
+                    }
+                }
+            }
+            if (ip.addr == IPADDR_ANY) {    // no rule applies, continue with another question
+                continue;
+            }
+            dns_answer_t *answer = (dns_answer_t *)cur_ans_ptr;
+
+            answer->ptr_offset = htons(0xC000 | (cur_qd_ptr - dns_reply));
+            answer->type = htons(qd_type);
+            answer->class = htons(qd_class);
+            answer->ttl = htonl(ANS_TTL_SEC);
+
+            ESP_LOGD(TAG, "Answer with PTR offset: 0x%" PRIX16 " and IP 0x%" PRIX32, ntohs(answer->ptr_offset), ip.addr);
+
+            answer->addr_len = htons(sizeof(ip.addr));
+            answer->ip_addr = ip.addr;
+        }
+    }
+    return reply_len;
+}
+
+/*
+    Sets up a socket and listen for DNS queries,
+    replies to all type A queries with the IP of the softAP
+*/
+void dns_server_task(void *pvParameters)
+{
+    char rx_buffer[128];
+    char addr_str[128];
+    int addr_family;
+    int ip_protocol;
+    dns_server_handle_t handle = pvParameters;
+
+    while (handle->started) {
+
+        struct sockaddr_in dest_addr;
+        dest_addr.sin_addr.s_addr = htonl(INADDR_ANY);
+        dest_addr.sin_family = AF_INET;
+        dest_addr.sin_port = htons(DNS_PORT);
+        addr_family = AF_INET;
+        ip_protocol = IPPROTO_IP;
+        inet_ntoa_r(dest_addr.sin_addr, addr_str, sizeof(addr_str) - 1);
+
+        int sock = socket(addr_family, SOCK_DGRAM, ip_protocol);
+        if (sock < 0) {
+            ESP_LOGE(TAG, "Unable to create socket: errno %d", errno);
+            break;
+        }
+        ESP_LOGI(TAG, "Socket created");
+
+        int err = bind(sock, (struct sockaddr *)&dest_addr, sizeof(dest_addr));
+        if (err < 0) {
+            ESP_LOGE(TAG, "Socket unable to bind: errno %d", errno);
+        }
+        ESP_LOGI(TAG, "Socket bound, port %d", DNS_PORT);
+
+        while (handle->started) {
+            ESP_LOGI(TAG, "Waiting for data");
+            struct sockaddr_in6 source_addr; // Large enough for both IPv4 or IPv6
+            socklen_t socklen = sizeof(source_addr);
+            int len = recvfrom(sock, rx_buffer, sizeof(rx_buffer) - 1, 0, (struct sockaddr *)&source_addr, &socklen);
+
+            // Error occurred during receiving
+            if (len < 0) {
+                ESP_LOGE(TAG, "recvfrom failed: errno %d", errno);
+                close(sock);
+                break;
+            }
+            // Data received
+            else {
+                // Get the sender's ip address as string
+                if (source_addr.sin6_family == PF_INET) {
+                    inet_ntoa_r(((struct sockaddr_in *)&source_addr)->sin_addr.s_addr, addr_str, sizeof(addr_str) - 1);
+                } else if (source_addr.sin6_family == PF_INET6) {
+                    inet6_ntoa_r(source_addr.sin6_addr, addr_str, sizeof(addr_str) - 1);
+                }
+
+                // Null-terminate whatever we received and treat like a string...
+                rx_buffer[len] = 0;
+
+                char reply[DNS_MAX_LEN];
+                int reply_len = parse_dns_request(rx_buffer, len, reply, DNS_MAX_LEN, handle);
+
+                ESP_LOGI(TAG, "Received %d bytes from %s | DNS reply with len: %d", len, addr_str, reply_len);
+                if (reply_len <= 0) {
+                    ESP_LOGE(TAG, "Failed to prepare a DNS reply");
+                } else {
+                    int err = sendto(sock, reply, reply_len, 0, (struct sockaddr *)&source_addr, sizeof(source_addr));
+                    if (err < 0) {
+                        ESP_LOGE(TAG, "Error occurred during sending: errno %d", errno);
+                        break;
+                    }
+                }
+            }
+        }
+
+        if (sock != -1) {
+            ESP_LOGE(TAG, "Shutting down socket");
+            shutdown(sock, 0);
+            close(sock);
+        }
+    }
+    vTaskDelete(NULL);
+}
+
+dns_server_handle_t start_dns_server(dns_server_config_t *config)
+{
+    dns_server_handle_t handle = calloc(1, sizeof(struct dns_server_handle) + config->num_of_entries * sizeof(dns_entry_pair_t));
+    ESP_RETURN_ON_FALSE(handle, NULL, TAG, "Failed to allocate dns server handle");
+
+    handle->started = true;
+    handle->num_of_entries = config->num_of_entries;
+    memcpy(handle->entry, config->item, config->num_of_entries * sizeof(dns_entry_pair_t));
+
+    xTaskCreate(dns_server_task, "dns_server", 4096, handle, 5, &handle->task);
+    return handle;
+}
+
+void stop_dns_server(dns_server_handle_t handle)
+{
+    if (handle) {
+        handle->started = false;
+        vTaskDelete(handle->task);
+        free(handle);
+    }
+}

components/dns_server/include/dns_server.h

@@ -0,0 +1,78 @@
+/*
+ * SPDX-FileCopyrightText: 2021-2023 Espressif Systems (Shanghai) CO LTD
+ *
+ * SPDX-License-Identifier: Unlicense OR CC0-1.0
+ */
+
+#pragma once
+
+#ifdef __cplusplus
+extern "C" {
+#endif
+
+#ifndef DNS_SERVER_MAX_ITEMS
+#define DNS_SERVER_MAX_ITEMS 1
+#endif
+
+#define DNS_SERVER_CONFIG_SINGLE(queried_name, netif_key)  {        \
+        .num_of_entries = 1,                                        \
+        .item = { { .name = queried_name, .if_key = netif_key } }   \
+        }
+
+/**
+ * @brief Definition of one DNS entry: NAME - IP (or the netif whose IP to answer)
+ *
+ * @note Please use string literals (or ensure they are valid during dns_server lifetime) as names, since
+ * we don't take copies of the config values `name` and `if_key`
+ */
+typedef struct dns_entry_pair {
+    const char* name;       /**<! Exact match of the name field of the DNS query to answer */
+    const char* if_key;     /**<! Use this network interface IP to answer, only if NULL, use the static IP below */
+    esp_ip4_addr_t ip;      /**<! Constant IP address to answer this query, if "if_key==NULL" */
+} dns_entry_pair_t;
+
+/**
+ * @brief DNS server config struct defining the rules for answering DNS (A type) queries
+ *
+ * @note If you want to define more rules, you can set `DNS_SERVER_MAX_ITEMS` before including this header
+ * Example of using 2 entries with constant IP addresses
+ * \code{.c}
+ * #define DNS_SERVER_MAX_ITEMS 2
+ * #include "dns_server.h"
+ *
+ * dns_server_config_t config = {
+ *   .num_of_entries = 2,
+ *   .item = { {.name = "my-esp32.com", .ip = { .addr = ESP_IP4TOADDR( 192, 168, 4, 1) } } ,
+ *             {.name = "my-utils.com", .ip = { .addr = ESP_IP4TOADDR( 192, 168, 4, 100) } } } };
+ * start_dns_server(&config);
+ * \endcode
+ */
+typedef struct dns_server_config {
+    int num_of_entries;                             /**<! Number of rules specified in the config struct */
+    dns_entry_pair_t item[DNS_SERVER_MAX_ITEMS];    /**<! Array of pairs */
+} dns_server_config_t;
+
+/**
+ * @brief DNS server handle
+ */
+typedef struct dns_server_handle *dns_server_handle_t;
+
+/**
+ * @brief Set ups and starts a simple DNS server that will respond to all A queries (IPv4)
+ * based on configured rules, pairs of name and either IPv4 address or a netif ID (to respond by it's IPv4 add)
+ *
+ * @param config Configuration structure listing the pairs of (name, IP/netif-id)
+ * @return dns_server's handle on success, NULL on failure
+ */
+dns_server_handle_t start_dns_server(dns_server_config_t *config);
+
+/**
+ * @brief Stops and destroys DNS server's task and structs
+ * @param handle DNS server's handle to destroy
+ */
+void stop_dns_server(dns_server_handle_t handle);
+
+
+#ifdef __cplusplus
+}
+#endif