OVMS3-idf/examples/protocols/http_server/restful_server/README.md

HTTP Restful API Server Example

(See the README.md file in the upper level 'examples' directory for more information about examples.)

Overview

This example mainly introduces how to implement a RESTful API server and HTTP server on ESP32, with a frontend browser UI.

This example designs several APIs to fetch resources as follows:

API	Method	Resource Example	Description	Page URL
/api/v1/system/info	GET	{ version:"v4.0-dev", cores:2 }	Used for clients to get system information like IDF version, ESP32 cores, etc	/
/api/v1/temp/raw	GET	{ raw:22 }	Used for clients to get raw temperature data read from sensor	/chart
/api/v1/light/brightness	POST	{ red:160, green:160, blue:160 }	Used for clients to upload control values to ESP32 in order to control LED’s brightness	/light

Page URL is the URL of the webpage which will send a request to the API.

About mDNS

The IP address of an IoT device may vary from time to time, so it’s impracticable to hard code the IP address in the webpage. In this example, we use the mDNS to parse the domain name esp-home.local, so that we can alway get access to the web server by this URL no matter what the real IP address behind it. See here for more information about mDNS.

Notes: mDNS is installed by default on most operating systems or is available as separate package.

About deploy mode

In development mode, it would be awful to flash the whole webpages every time we update the html, js or css files. So it is highly recommended to deploy the webpage to host PC via semihost technology. Whenever the browser fetch the webpage, ESP32 can forward the required files located on host PC. By this mean, it will save a lot of time when designing new pages.

After developing, the pages should be deployed to one of the following destinations:

• SPI Flash - which is recommended when the website after built is small (e.g. less than 2MB).
• SD Card - which would be an option when the website after built is very large that the SPI Flash have not enough space to hold (e.g. larger than 2MB).

About frontend framework

Many famous frontend frameworks (e.g. Vue, React, Angular) can be used in this example. Here we just take Vue as example and adopt the vuetify as the UI library.

How to use example

Hardware Required

To run this example, you need an ESP32 dev board (e.g. ESP32-WROVER Kit, ESP32-Ethernet-Kit) or ESP32 core board (e.g. ESP32-DevKitC). An extra JTAG adapter might also needed if you choose to deploy the website by semihosting. For more information about supported JTAG adapter, please refer to select JTAG adapter. Or if you choose to deploy the website to SD card, an extra SD slot board is needed.

Pin Assignment:

Only if you deploy the website to SD card, then the following pin connection is used in this example.

ESP32	SD Card
GPIO2	D0
GPIO4	D1
GPIO12	D2
GPIO13	D3
GPIO14	CLK
GPIO15	CMD

Configure the project

Enter make menuconfig if you are using GNU Make based build system or enter idf.py menuconfig if you are using CMake based build system.

In the Example Connection Configuration menu:

• Choose the network interface in Connect using option based on your board. Currently we support both Wi-Fi and Ethernet.
• If you select the Wi-Fi interface, you also have to set:
  • Wi-Fi SSID and Wi-Fi password that your esp32 will connect to.
• If you select the Ethernet interface, you also have to set:
  • PHY model in Ethernet PHY option, e.g. IP101.
  • PHY address in PHY Address option, which should be determined by your board schematic.
  • EMAC Clock mode, GPIO used by SMI.

In the Example Configuration menu:

• Set the domain name in mDNS Host Name option.
• Choose the deploy mode in Website deploy mode, currently we support deploy website to host PC, SD card and SPI Nor flash.
  • If we choose to Deploy website to host (JTAG is needed), then we also need to specify the full path of the website in Host path to mount (e.g. absolute path to web dist directory).
• Set the mount point of the website in Website mount point in VFS option, the default value is /www.

Build and Flash

After the webpage design work has been finished, you should compile them by running following commands:

cd path_to_this_example/front/web-demo
npm install
npm run build

After a while, you will see a dist directory which contains all the website files (e.g. html, js, css, images).

Enter make -j4 flash monitor if you are using GNU Make based build system or enter idf.py build flash monitor if you are using CMake based build system.

(To exit the serial monitor, type Ctrl-].)

See the Getting Started Guide for full steps to configure and use ESP-IDF to build projects.

Extra steps to do for deploying website by semihost

We need to run the latest version of OpenOCD which should support semihost feature when we test this deploy mode:

openocd-esp32/bin/openocd -s openocd-esp32/share/openocd/scripts -f interface/ftdi/esp32_devkitj_v1.cfg -f board/esp-wroom-32.cfg

Example Output

Render webpage in browser

In your browser, enter the URL where the website located (e.g. http://esp-home.local). You can also enter the IP address that ESP32 obtained if your operating system currently don't have support for mDNS service.

ESP monitor output

In the Light page, after we set up the light color and click on the check button, the browser will send a post request to ESP32, and in the console, we just print the color value.

I (6115) example_connect: Connected to Ethernet
I (6115) example_connect: IPv4 address: 192.168.2.151
I (6325) esp-home: Partition size: total: 1920401, used: 1587575
I (6325) esp-rest: Starting HTTP Server
I (128305) esp-rest: File sending complete
I (128565) esp-rest: File sending complete
I (128855) esp-rest: File sending complete
I (129525) esp-rest: File sending complete
I (129855) esp-rest: File sending complete
I (137485) esp-rest: Light control: red = 50, green = 85, blue = 28

Troubleshooting

1. Error occurred when building example: ...front/web-demo/dist doesn't exit. Please run 'npm run build' in ...front/web-demo.
   • When you choose to deploy website to SPI flash, make sure the dist directory has been generated before you building this example.

(For any technical queries, please open an issue on GitHub. We will get back to you as soon as possible.)