ESP32 HTTP POST with JSON body using ArduinoJson

This example parses a HTTP POST request body using ArduinoJson. I recommend using my HumanESPHTTP library as simple server library based on the ESP-IDF HTTP server.

constexpr size_t JsonParseBufferSize = 2048;
typedef ArduinoJson::StaticJsonDocument JsonParseBuffer;

 * This buffer is used to parse /api/configure events
static JsonParseBuffer document;

static const httpd_uri_t configureHandler = {
    .uri       = "/api/configure",
    .method    = HTTP_POST,
    .handler   = [](httpd_req_t *req) {
        // Receive POST body data into a new buffer
        char* jsonBody = (char*)malloc(req->content_len + 1);
        jsonBody[req->content_len] = '\0'; // NUL terminate [just in case]
        if(jsonBody == nullptr) {
            return SendStatusError(req, "Failed to allocate memory for JSON body");
        int err = httpd_req_recv(req, jsonBody, req->content_len);
        if(err != req->content_len) {
            return SendStatusError(req, "Failed to read request body");
        // Parse the body as JSON
        deserializeJson(document, jsonBody, req->content_len);
        // TODO: Do something with [document]
        // Cleanup
        return SendStatusOK(req);

which uses the following utility functions:

esp_err_t SendStatusError(httpd_req_t *request, const char* description) {
    httpd_resp_set_type(request, "application/json");
    httpd_resp_send_chunk(request, "{\"status\":\"error\", \"error\": \"", HTTPD_RESP_USE_STRLEN);
    // NOTE: We silently assume that description does not have any special characters
    httpd_resp_send_chunk(request, description, HTTPD_RESP_USE_STRLEN);
    httpd_resp_send_chunk(request, "\"}", HTTPD_RESP_USE_STRLEN);
    httpd_resp_send_chunk(request, nullptr, 0); // Finished
    return ESP_OK;

esp_err_t SendStatusOK(httpd_req_t *request) {
    httpd_resp_set_type(request, "application/json");
    httpd_resp_sendstr(request, "{\"status\":\"ok\"}");
    return ESP_OK;