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// SPDX-License-Identifier: LGPL-3.0-or-later
// Copyright 2016-2025 Hristo Gochkov, Mathieu Carbou, Emil Muratov
//
// Shows how to use request continuation to pause a request for a long processing task, and be able to resume it later.
//
#include <Arduino.h>
#ifdef ESP32
#include <AsyncTCP.h>
#include <WiFi.h>
#elif defined(ESP8266)
#include <ESP8266WiFi.h>
#include <ESPAsyncTCP.h>
#elif defined(TARGET_RP2040) || defined(TARGET_RP2350) || defined(PICO_RP2040) || defined(PICO_RP2350)
#include <RPAsyncTCP.h>
#include <WiFi.h>
#endif
#include <ESPAsyncWebServer.h>
#include <list>
#include <memory>
#include <mutex>
static AsyncWebServer server(80);
// ===============================================================
// The code below is used to simulate some long running operations
// ===============================================================
typedef struct {
size_t id;
AsyncWebServerRequestPtr requestPtr;
uint8_t data;
} LongRunningOperation;
static std::list<std::unique_ptr<LongRunningOperation>> longRunningOperations;
static size_t longRunningOperationsCount = 0;
#ifdef ESP32
static std::mutex longRunningOperationsMutex;
#endif
static void startLongRunningOperation(AsyncWebServerRequestPtr &&requestPtr) {
#ifdef ESP32
std::lock_guard<std::mutex> lock(longRunningOperationsMutex);
#endif
// LongRunningOperation *op = new LongRunningOperation();
std::unique_ptr<LongRunningOperation> op(new LongRunningOperation());
op->id = ++longRunningOperationsCount;
op->data = 10;
// you need to hold the AsyncWebServerRequestPtr returned by pause();
// This object is authorized to leave the scope of the request handler.
op->requestPtr = std::move(requestPtr);
Serial.printf("[%u] Start long running operation for %" PRIu8 " seconds...\n", op->id, op->data);
longRunningOperations.push_back(std::move(op));
}
static bool processLongRunningOperation(LongRunningOperation *op) {
// request was deleted ?
if (op->requestPtr.expired()) {
Serial.printf("[%u] Request was deleted - stopping long running operation\n", op->id);
return true; // operation finished
}
// processing the operation
Serial.printf("[%u] Long running operation processing... %" PRIu8 " seconds left\n", op->id, op->data);
// check if we have finished ?
op->data--;
if (op->data) {
// not finished yet
return false;
}
// Try to get access to the request pointer if it is still exist.
// If there has been a disconnection during that time, the pointer won't be valid anymore
if (auto request = op->requestPtr.lock()) {
Serial.printf("[%u] Long running operation finished! Sending back response...\n", op->id);
request->send(200, "text/plain", String(op->id) + " ");
} else {
Serial.printf("[%u] Long running operation finished, but request was deleted!\n", op->id);
}
return true; // operation finished
}
/// ==========================================================
void setup() {
Serial.begin(115200);
#ifndef CONFIG_IDF_TARGET_ESP32H2
WiFi.mode(WIFI_AP);
WiFi.softAP("esp-captive");
#endif
// Add a middleware to see how pausing a request affects the middleware chain
server.addMiddleware([](AsyncWebServerRequest *request, ArMiddlewareNext next) {
Serial.printf("Middleware chain start\n");
// continue to the next middleware, and at the end the request handler
next();
// we can check the request pause state after the handler was executed
if (request->isPaused()) {
Serial.printf("Request was paused!\n");
}
Serial.printf("Middleware chain ends\n");
});
// HOW TO RUN THIS EXAMPLE:
//
// 1. Open several terminals to trigger some requests concurrently that will be paused with:
// > time curl -v http://192.168.4.1/
//
// 2. Look at the output of the Serial console to see how the middleware chain is executed
// and to see the long running operations being processed and resume the requests.
//
// 3. You can try close your curl command to cancel the request and check that the request is deleted.
// Note: in case the network is disconnected, the request will be deleted.
//
server.on("/", HTTP_GET, [](AsyncWebServerRequest *request) {
// Print a message in case the request is disconnected (network disconnection, client close, etc.)
request->onDisconnect([]() {
Serial.printf("Request was disconnected!\n");
});
// Instruct ESPAsyncWebServer to pause the request and get a AsyncWebServerRequestPtr to be able to access the request later.
// The AsyncWebServerRequestPtr is the ONLY object authorized to leave the scope of the request handler.
// The Middleware chain will continue to run until the end after this handler exit, but the request will be paused and will not
// be sent to the client until send() is called later.
Serial.printf("Pausing request...\n");
AsyncWebServerRequestPtr requestPtr = request->pause();
// start our long operation...
startLongRunningOperation(std::move(requestPtr));
});
server.begin();
}
static uint32_t lastTime = 0;
void loop() {
if (millis() - lastTime >= 1000) {
#ifdef ESP32
Serial.printf("Free heap: %" PRIu32 "\n", ESP.getFreeHeap());
std::lock_guard<std::mutex> lock(longRunningOperationsMutex);
#endif
// process all long running operations
longRunningOperations.remove_if([](const std::unique_ptr<LongRunningOperation> &op) {
return processLongRunningOperation(op.get());
});
lastTime = millis();
}
}
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