3c6db4ed9b
Api for saving heap when Client class is used by a Server (WiFiServer class): Client = Server.available(). Suppose the local end is the server and the remote end is the client, we will deal with heap memory at the local end. When the local application (server) decides to close an active connection with a remote end it issues an Client.stop. The stop() function calls the close() function of ClientContext class which in turn calls tcp_close. The connexion is closed by tcp_close and the protocol control block (pcb) can be put in the following states depending on the requests sent by the remote: CLOSING, FIN_WAIT_1 and FIN_WAIT_2. In theses states pcbs are not freed, then consume some memory heap. If an acknowledgment from the remote end is received, the pcb enter in TIME_WAIT state for some minutes but pcbs in TIME_WAIT state are not freed. Then consume some heap memory. TIME_WAIT pcbs are automatically freed after some minutes or can be freed for instance issuing an tcp_kill_timewait() in the local application which will free the oldest pcb in TIME_WAIT state. If the connection is first closed from the remote end (the client), the local end (server) receive a connection termination request. It then acknowledge it and enter in CLOSE_WAIT state waiting for a connection termination request from the local application. It then send a termination request and enter in LAST_ACK state until it receive an acknowledgment from the remote end. After receiving the acknowledgment it enter in ClOSED state and the local pcb is freed leaving some room in the heap memory. To summarize, when a connexion termination request is send by one end (remote or local), the local pcb is not freed immediatly. This pcb can be in the following states: FIN_WAIT_1, FIN_WAIT_2, CLOSING, TIME_WAIT, CLOSE_WAIT, LAST_ACK. As a consequence, some old pcbs from old closed connections are still consuming heap memory. The local application can call tcp_kill_timewait hoping it will free some TIME_WAIT state pcbs. But if the server receive frequent connections requests and close them after sending whatever it has to send, there may be zero pcbs in TIME_WAIT state among all previously closed connections. In case of insufficient memory to accept a new connection, lwip has developped a strategy: it successively tries to kill the oldest pcb in TIME_WAIT state, or in LAST_ACK state or in CLOSING state or the oldest active connection with lower priority than the new one. As a matter of fact this "urgent" strategy is deployed only when very few heap memory remain available (less than some kb). In case of success, Client.available returns a valid Client but the local application will crash when sending or receiving data from the client (Client.read ou readuntil or available) because this need more heap memory and just some kb were freed in lwip to allocate the new pcb structure ans start the new connection. The propose API is intended to avoid this drawback by calling the abort function of ClientContext which in turn calls tcp_abort which calls tcp_abandon. The connection is aborted and notified to the client with a RESET and the pcb and ressources associated are immediately released increasing the available heap memory.
Arduino core for ESP8266 WiFi chip
Quick links
Arduino on ESP8266
This project brings support for the ESP8266 chip to the Arduino environment. It lets you write sketches, using familiar Arduino functions and libraries, and run them directly on ESP8266, with no external microcontroller required.
ESP8266 Arduino core comes with libraries to communicate over WiFi using TCP and UDP, set up HTTP, mDNS, SSDP, and DNS servers, do OTA updates, use a file system in flash memory, and work with SD cards, servos, SPI and I2C peripherals.
Contents
- Installing options:
- Documentation
- Issues and support
- Contributing
- License and credits
Installing with Boards Manager
Starting with 1.6.4, Arduino allows installation of third-party platform packages using Boards Manager. We have packages available for Windows, Mac OS, and Linux (32 and 64 bit).
- Install the current upstream Arduino IDE at the 1.8.9 level or later. The current version is on the Arduino website.
- Start Arduino and open the Preferences window.
- Enter
https://arduino.esp8266.com/stable/package_esp8266com_index.jsoninto the File>Preferences>Additional Boards Manager URLs field of the Arduino IDE. You can add multiple URLs, separating them with commas. - Open Boards Manager from Tools > Board menu and install esp8266 platform (and don't forget to select your ESP8266 board from Tools > Board menu after installation).
Latest release 
Boards manager link: https://arduino.esp8266.com/stable/package_esp8266com_index.json
Documentation: https://arduino-esp8266.readthedocs.io/en/3.0.2/
Using git version
Also known as latest git or master branch.
- When using Arduino IDE, follow our instructions here.
- When using PlatformIO, refer to platformio/espressif8266 platform documentation.
Using PlatformIO
PlatformIO is an open source ecosystem for IoT development with a cross-platform build system, a library manager, and full support for Espressif (ESP8266) development. It works on the following popular host operating systems: macOS, Windows, Linux 32/64, and Linux ARM (like Raspberry Pi, BeagleBone, CubieBoard).
- What is PlatformIO?
- PlatformIO IDE
- PlatformIO Core (command line tool)
- Advanced usage - custom settings, uploading to SPIFFS, Over-the-Air (OTA), staging version
- Integration with Cloud and Standalone IDEs - Cloud9, Codeanywhere, Eclipse Che (Codenvy), Atom, CLion, Eclipse, Emacs, NetBeans, Qt Creator, Sublime Text, VIM, Visual Studio, and VSCode
- Project Examples
Building with make
makeEspArduino is a generic makefile for any ESP8266 Arduino project. Using make instead of the Arduino IDE makes it easier to do automated and production builds.
Documentation
Documentation for latest development version: https://arduino-esp8266.readthedocs.io/en/latest/
Issues and support
ESP8266 Community Forum is a well-established community for questions and answers about Arduino for ESP8266. Stackoverflow is also an alternative. If you need help, have a "How do I..." type question, have a problem with a 3rd party library not hosted in this repo, or just want to discuss how to approach a problem, please ask there.
If you find the forum useful, please consider supporting it with a donation.
If you encounter an issue which you think is a bug in the ESP8266 Arduino Core or the associated libraries, or if you want to propose an enhancement, you are welcome to submit it here on Github: https://github.com/esp8266/Arduino/issues.
Please provide as much context as possible, as well as the information requested in the issue template:
- ESP8266 Arduino core version which you are using (you can check it in Boards Manager)
- your sketch code; please wrap it into a code block, see Github markdown manual
- when encountering an issue that happens at run time, attach the serial output. Wrap it into a code block, just like the code.
- for issues that happen at compile time, enable verbose compiler output in the IDE preferences, and attach that output (also inside a code block)
- ESP8266 development board model
- IDE settings (board choice, flash size)
- etc
Contributing
For minor fixes of code and documentation, please go ahead and submit a pull request. A gentle introduction to the process can be found here.
Check out the list of issues that are easy to fix — easy issues pending. Working on them is a great way to move the project forward.
Larger changes (rewriting parts of existing code from scratch, adding new functions to the core, adding new libraries) should generally be discussed by opening an issue first. PRs with such changes require testing and approval.
Feature branches with lots of small commits (especially titled "oops", "fix typo", "forgot to add file", etc.) should be squashed before opening a pull request. At the same time, please refrain from putting multiple unrelated changes into a single pull request.
License and credits
Arduino IDE is developed and maintained by the Arduino team. The IDE is licensed under GPL.
ESP8266 core includes an xtensa gcc toolchain, which is also under GPL.
Esptool.py was initially created by Fredrik Ahlberg (@themadinventor, @kongo), and is currently maintained by Angus Gratton (@projectgus) under GPL 2.0 license.
Espressif's NONOS SDK included in this build is under Espressif MIT License.
ESP8266 core files are licensed under LGPL.
SPI Flash File System (SPIFFS) written by Peter Andersson is used in this project. It is distributed under the MIT license.
umm_malloc memory management library written by Ralph Hempel is used in this project. It is distributed under the MIT license.
SoftwareSerial library and examples written by Peter Lerup. Distributed under LGPL 2.1.
BearSSL library written by Thomas Pornin, built from https://github.com/earlephilhower/bearssl-esp8266, is used in this project. It is distributed under the MIT License.
LittleFS library written by ARM Limited and released under the BSD 3-clause license.
uzlib library written and (c) 2014-2018 Paul Sokolovsky, licensed under the ZLib license (https://www.zlib.net/zlib_license.html). uzlib is based on: tinf library by Joergen Ibsen (Deflate decompression); Deflate Static Huffman tree routines by Simon Tatham; LZ77 compressor by Paul Sokolovsky; with library integrated and maintained by Paul Sokolovsky.
Other useful links
Serial Monitor Arduino IDE plugin Original discussion here, quick download there.