https://blog.****.net/xh870189248/article/details/80095139
https://www.wandianshenme.com/play/arduino-ota-arduino-ide-ota-upgrade-esp8266-application/
我这里详细地说下这里包含了啥信息！
由下面可得，不同的8266模块，其外部falsh大小决定了编译时候的user.bin路径，所以大家在此OTA升级，必须要摸清楚你买的模块是哪个falsh大小的，注意1M = 8Mbit！！！安信可的 32Mbit 其实就是 4M的falsh，类似 25Q32这样的存储芯片。
server.on("/", HTTP_GET, []() {
server.sendHeader("Connection", "close");
server.send(200, "text/html", serverIndex);
});
server.on("/update", HTTP_POST, []() {
server.sendHeader("Connection", "close");
server.send(200, "text/plain", (Update.hasError()) ? "FAIL" : "OK");
ESP.restart();
}, []() {
HTTPUpload& upload = server.upload();
if (upload.status == UPLOAD_FILE_START) {
Serial.setDebugOutput(true);
WiFiUDP::stopAll();
Serial.printf("Update: %s\n", upload.filename.c_str());
uint32_t maxSketchSpace = (ESP.getFreeSketchSpace() - 0x1000) & 0xFFFFF000;
if (!Update.begin(maxSketchSpace)) { //start with max available size
Update.printError(Serial);
}
} else if (upload.status == UPLOAD_FILE_WRITE) {
if (Update.write(upload.buf, upload.currentSize) != upload.currentSize) {
Update.printError(Serial);
}
} else if (upload.status == UPLOAD_FILE_END) {
if (Update.end(true)) { //true to set the size to the current progress
Serial.printf("Update Success: %u\nRebooting...\n", upload.totalSize);
} else {
Update.printError(Serial);
}
Serial.setDebugOutput(false);
}
yield();
});