[SOLVED] Store an HTTP Request

Store an HTTP Request

I am trying to store an HTTP request as a global variable. My software is about connecting WiFi, and the WiFi library I'm using is event-based, which means I must store the HTTP request somewhere and wait for a callback on events. Problem: the program crashes after I try to access it again. Log:

> Guru Meditation Error: Core  0 panic'ed (StoreProhibited). Exception
> was unhandled.
> 
> Core  0 register dump: PC      : 0x400ff5e5  PS      : 0x00060430  A0 
> : 0x800d79a1  A1      : 0x3ffbdf90
> --- 0x400ff5e5: httpd_resp_send at F:/Espressif/frameworks/esp-idf-v5.2.5/components/esp_http_server/src/httpd_txrx.c:248
> 
> A2      : 0x3ffc93c8  A3      : 0x3f4038ec  A4      : 0x00000003  A5  
> : 0x00000000 A6      : 0x00000000  A7      : 0x3ffc93c8  A8      :
> 0x00000000  A9      : 0x3ffbdf30 A10     : 0x000001f4  A11     :
> 0x3ffbdf30  A12     : 0x3ffbde44  A13     : 0x3ffbde0c A14     :
> 0x3ffbde20  A15     : 0x3ffbdff0  SAR     : 0x00000004  EXCCAUSE:
> 0x0000001d EXCVADDR: 0x00000218  LBEG    : 0x400014fd  LEND    :
> 0x4000150d  LCOUNT  : 0xffffffff
> --- 0x400014fd: strlen in ROM
> --- 0x4000150d: strlen in ROM
> 
> 
> 
> Backtrace: 0x400ff5e2:0x3ffbdf90 0x400d799e:0x3ffbdfd0
> 0x400d773b:0x3ffbdff0 0x400d7ad1:0x3ffbe020 0x4016387d:0x3ffbe050
> 0x401633c6:0x3ffbe080 0x401634a1:0x3ffbe0c0 0x4008a129:0x3ffbe0e0
> --- 0x400ff5e2: httpd_resp_send at F:/Espressif/frameworks/esp-idf-v5.2.5/components/esp_http_server/src/httpd_txrx.c:248
> --- 0x400d799e: wifi_setup_handle_response at F:/Documents/dashboardfordevice/device-software/main/wifi_setup_webpage.c:44
> --- 0x400d773b: disconnect_handler at F:/Documents/dashboardfordevice/device-software/main/wifi_manager.c:20
> --- 0x400d7ad1: run_on_event at F:/Documents/dashboardfordevice/device-software/main/wifi.c:32
> --- 0x4016387d: handler_execute at F:/Espressif/frameworks/esp-idf-v5.2.5/components/esp_event/esp_event.c:137
> --- 0x401633c6: esp_event_loop_run at F:/Espressif/frameworks/esp-idf-v5.2.5/components/esp_event/esp_event.c:593
> --- 0x401634a1: esp_event_loop_run_task at F:/Espressif/frameworks/esp-idf-v5.2.5/components/esp_event/esp_event.c:107
> --- 0x4008a129: vPortTaskWrapper at F:/Espressif/frameworks/esp-idf-v5.2.5/components/freertos/FreeRTOS-Kernel/portable/xtensa/port.c:13

from my understanding, this is caused by a null string at first, but this is line 44 inwifi_setup_webpage.c httpd_resp_send(request, "200", 3); which from my knowledge, can't be the issue considering that my other handlers doing the same thing doesn't crash, only difference is that their pointer to the request is "fresh."

I store the request by using a global variable: httpd_req_t* request; and then assigning it using request = req; full code for that method:

esp_err_t connect_post_handler(httpd_req_t *req) 
{
    size_t size = req->content_len;
    if (size > 1024) {
        // too big
        const char* response = "Content too massive, but you know what else is massive?";
        httpd_resp_send_err(req, HTTPD_400_BAD_REQUEST, response);

        return ESP_OK;
    }

    char content[1024];

    int bytes_read = httpd_req_recv(req, content, size);
    if (bytes_read == 0) {
        // connection closed
        return ESP_ERR_HTTPD_INVALID_REQ;
    }

    cJSON* jsonData = cJSON_ParseWithLength(content, size);
    if (jsonData == NULL) {
        // json parsing failed, bad request
        const char* response = "Bad JSON format";
        httpd_resp_send_err(req, HTTPD_400_BAD_REQUEST, response);
        return ESP_OK;
    }
    char* ssid = cJSON_GetObjectItem(jsonData, "ssid")->valuestring;
    char* password = cJSON_GetObjectItem(jsonData, "password")->valuestring;

    cJSON_Delete(jsonData);

    request = req;

    reconnect_callback(ssid, password);

    return ESP_OK;
}

and the full code for the method that sends the request:

void wifi_setup_handle_response(bool boolean, const char * response) 
{
    // cJSON* response_data = cJSON_CreateObject();
    // cJSON_AddBoolToObject(response_data, "success", boolean);
    // cJSON_AddStringToObject(response_data, "message", response);
    

    // char* response_string = cJSON_Print(response_data);

    // ESP_LOGI(LOG_TAG, "Raw Response: %s", response_string);

    // if (response_string == NULL) {
    //     // failed
    //     ESP_LOGE(LOG_TAG, "Could not write wifi connect response to string");
    //     httpd_resp_send_500(request);
    //     cJSON_Delete(response_data);
    //     return;
    // }

    if (request == NULL) {
        ESP_LOGE(LOG_TAG, "request is null, aha!");
        return;
    }

    httpd_resp_send(request, "200", 3);
    

    // free(response_string);
    // cJSON_Delete(response_data);
}

FYI: there is a ~3 second gap between those two functions. order: connect_post_handler THEN void wifi_setup_handle_response. I think it is because something related to the stack memory getting destroyed then the pointer to it is no longer valid, but I don't know how to handle it since the request typedef has a lot of fancy pointers to other stuff.

Solution

An HTTP request instance is only valid until the request handler callback returns.

If you want to use a request instance outside of the handler callback, you should use httpd_req_async_handler_begin() to make a copy of the request which you can subsequently use elsewhere. Call httpd_req_async_handler_complete() to delete the copy when no longer needed.