让 ESP32 请求 JSON：把超时、状态码和旧数据分清

python3 test_server.py --bind 127.0.0.1 --port 8080
curl -i http://127.0.0.1:8080/ok
curl -i http://127.0.0.1:8080/404
curl -i http://127.0.0.1:8080/bad
curl --max-time 2 http://127.0.0.1:8080/slow

idf.py --version
idf.py set-target esp32s3
idf.py menuconfig
idf.py build
idf.py -p PORT flash monitor

// SPDX-License-Identifier: MIT
#include <string.h>
#include <math.h>
#include <inttypes.h>
#include "freertos/FreeRTOS.h"
#include "freertos/task.h"
#include "esp_log.h"
#include "esp_system.h"
#include "esp_timer.h"
#include "esp_http_client.h"
#include "cJSON.h"
#include "sdkconfig.h"
#include "net.h"
#define BODY_LIMIT 1024
static const char *TAG = "N03";
typedef struct { char bytes[BODY_LIMIT + 1]; size_t length; bool overflow; } body_t;
typedef struct { bool available; double temperature; uint32_t sequence; int64_t at_us; } sample_t;
static sample_t last = {0};
static esp_err_t http_event(esp_http_client_event_t *event) {
    if (event->event_id == HTTP_EVENT_ON_DATA && event->data_len > 0) {
        body_t *body = event->user_data;
        if ((size_t)event->data_len > BODY_LIMIT - body->length) body->overflow = true;
        else if (!body->overflow) {
            memcpy(body->bytes + body->length, event->data, (size_t)event->data_len);
            body->length += (size_t)event->data_len;
            body->bytes[body->length] = '\0';
        }
    }
    return ESP_OK;
}
static bool parse_sample(const body_t *body, sample_t *out) {
    const char *end = NULL;
    cJSON *root = cJSON_ParseWithLengthOpts(body->bytes, body->length + 1, &end, true);
    if (!cJSON_IsObject(root) || end != body->bytes + body->length) { cJSON_Delete(root); return false; }
    cJSON *temp = cJSON_GetObjectItemCaseSensitive(root, "temperature_c");
    cJSON *seq = cJSON_GetObjectItemCaseSensitive(root, "sequence");
    bool valid = cJSON_IsNumber(temp) && isfinite(temp->valuedouble) && temp->valuedouble >= -40 && temp->valuedouble <= 125 &&
                 cJSON_IsNumber(seq) && isfinite(seq->valuedouble) && seq->valuedouble >= 0 && seq->valuedouble <= UINT32_MAX && floor(seq->valuedouble) == seq->valuedouble;
    if (valid) *out = (sample_t){.available = true, .temperature = temp->valuedouble, .sequence = (uint32_t)seq->valuedouble, .at_us = esp_timer_get_time()};
    cJSON_Delete(root); return valid;
}
static void report_last(const char *state) {
    if (!last.available) ESP_LOGW(TAG, "state=%s current=NA last_valid=NONE", state);
    else ESP_LOGW(TAG, "state=%s current=NA last_valid_T_C=%.2f last_sequence=%" PRIu32 " age_ms=%" PRIi64, state, last.temperature, last.sequence, (esp_timer_get_time() - last.at_us) / 1000);
}
void app_main(void) {
    net_start();
    ESP_LOGI(TAG, "IDF=%s HTTP timeout=3000ms max_body=%u; no real network result recorded by this source", esp_get_idf_version(), BODY_LIMIT);
    for (;;) {
        if (!net_online()) { report_last("OFFLINE"); vTaskDelay(pdMS_TO_TICKS(5000)); continue; }
        body_t body = {0};
        esp_http_client_config_t config = {.url = CONFIG_DEMO_HTTP_URL, .timeout_ms = 3000, .event_handler = http_event, .user_data = &body, .disable_auto_redirect = true, .keep_alive_enable = false};
        esp_http_client_handle_t client = esp_http_client_init(&config);
        if (!client) { report_last("CLIENT_ALLOC_FAILED"); vTaskDelay(pdMS_TO_TICKS(5000)); continue; }
        esp_http_client_set_header(client, "Accept", "application/json");
        esp_err_t result = esp_http_client_perform(client);
        int status = esp_http_client_get_status_code(client);
        sample_t candidate = {0};
        if (result != ESP_OK) { ESP_LOGW(TAG, "transport=%s status=%d", esp_err_to_name(result), status); report_last("TRANSPORT_ERROR"); }
        else if (status != 200) { ESP_LOGW(TAG, "HTTP status=%d; body is not a sample", status); report_last("HTTP_ERROR"); }
        else if (body.overflow) report_last("BODY_TOO_LARGE");
        else if (!parse_sample(&body, &candidate)) report_last("INVALID_JSON_OR_FIELDS");
        else {
            last = candidate;
            ESP_LOGI(TAG, "state=VALID T_C=%.2f sequence=%" PRIu32 " received_ms=%" PRIi64, last.temperature, last.sequence, last.at_us / 1000);
        }
        esp_http_client_cleanup(client);
        vTaskDelay(pdMS_TO_TICKS(5000));
    }
}