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How to fix ESPAsyncWebserver undefined reference to `SHA1Init'

Problem:

When using ESPAsyncWebserver with websockets, you see the following error messages while linking:

espasync_link_errors.txt
Linking .pio/build/esp32dev/firmware.elf
/home/uli/.platformio/packages/toolchain-xtensa-esp32@8.4.0+2021r2-patch3/bin/../lib/gcc/xtensa-esp32-elf/8.4.0/../../../../xtensa-esp32-elf/bin/ld: .pio/build/esp32dev/lib67a/libESP Async WebServer.a(AsyncWebSocket.cpp.o):(.literal._ZN22AsyncWebSocketResponseC2ERK6StringP14AsyncWebSocket+0x10): undefined reference to `SHA1Init'
/home/uli/.platformio/packages/toolchain-xtensa-esp32@8.4.0+2021r2-patch3/bin/../lib/gcc/xtensa-esp32-elf/8.4.0/../../../../xtensa-esp32-elf/bin/ld: .pio/build/esp32dev/lib67a/libESP Async WebServer.a(AsyncWebSocket.cpp.o):(.literal._ZN22AsyncWebSocketResponseC2ERK6StringP14AsyncWebSocket+0x18): undefined reference to `SHA1Update'
/home/uli/.platformio/packages/toolchain-xtensa-esp32@8.4.0+2021r2-patch3/bin/../lib/gcc/xtensa-esp32-elf/8.4.0/../../../../xtensa-esp32-elf/bin/ld: .pio/build/esp32dev/lib67a/libESP Async WebServer.a(AsyncWebSocket.cpp.o):(.literal._ZN22AsyncWebSocketResponseC2ERK6StringP14AsyncWebSocket+0x1c): undefined reference to `SHA1Final'
/home/uli/.platformio/packages/toolchain-xtensa-esp32@8.4.0+2021r2-patch3/bin/../lib/gcc/xtensa-esp32-elf/8.4.0/../../../../xtensa-esp32-elf/bin/ld: .pio/build/esp32dev/lib67a/libESP Async WebServer.a(AsyncWebSocket.cpp.o): in function `AsyncWebSocketResponse::AsyncWebSocketResponse(String const&, AsyncWebSocket*)':
/home/uli/dev/My-Firmware/.pio/libdeps/esp32dev/ESP Async WebServer/src/AsyncWebSocket.cpp:1269: undefined reference to `SHA1Init'
/home/uli/.platformio/packages/toolchain-xtensa-esp32@8.4.0+2021r2-patch3/bin/../lib/gcc/xtensa-esp32-elf/8.4.0/../../../../xtensa-esp32-elf/bin/ld: /home/uli/dev/My-Firmware/.pio/libdeps/esp32dev/ESP Async WebServer/src/AsyncWebSocket.cpp:1270: undefined reference to `SHA1Update'
/home/uli/.platformio/packages/toolchain-xtensa-esp32@8.4.0+2021r2-patch3/bin/../lib/gcc/xtensa-esp32-elf/8.4.0/../../../../xtensa-esp32-elf/bin/ld: /home/uli/dev/My-Firmware/.pio/libdeps/esp32dev/ESP Async WebServer/src/AsyncWebSocket.cpp:1271: undefined reference to `SHA1Final'
/home/uli/.platformio/packages/toolchain-xtensa-esp32@8.4.0+2021r2-patch3/bin/../lib/gcc/xtensa-esp32-elf/8.4.0/../../../../xtensa-esp32-elf/bin/ld: .pio/build/esp32dev/lib67a/libESP Async WebServer.a(WebAuthentication.cpp.o):(.literal._ZL6getMD5PhtPc+0x4): undefined reference to `mbedtls_md5_starts'
/home/uli/.platformio/packages/toolchain-xtensa-esp32@8.4.0+2021r2-patch3/bin/../lib/gcc/xtensa-esp32-elf/8.4.0/../../../../xtensa-esp32-elf/bin/ld: .pio/build/esp32dev/lib67a/libESP Async WebServer.a(WebAuthentication.cpp.o): in function `getMD5(unsigned char*, unsigned short, char*)':
/home/uli/dev/My-Firmware/.pio/libdeps/esp32dev/ESP Async WebServer/src/WebAuthentication.cpp:73: undefined reference to `mbedtls_md5_starts'

Solution

This is a bug in the ESPAsyncWebserver official library, which is not regularly maintained. But you can use use the esphome fork of ESPAsyncWebserver and their fork of AsyncTCP instead.

In platformio.ini, instead of

platformio_lib_deps_example.ini
lib_deps =
    ESP Async Webserver@1.2.3

use the esphome fork and AsyncTCP:

example.ini
lib_deps =
    esphome/AsyncTCP-esphome@^1.2.2
    esphome/ESPAsyncWebServer-esphome@^2.1.0

After that, try to build / upload, the linking errors should be gone.

Full platformio.ini example

platformio.ini
[env:esp32dev]
platform = espressif32
platform_packages = framework-arduinoespressif32 @ https://github.com/espressif/arduino-esp32.git#2.0.3
board = esp32dev
framework = arduino
lib_deps =
    esphome/AsyncTCP-esphome@^1.2.2
    esphome/ESPAsyncWebServer-esphome@^2.1.0
    ArduinoJSON@6.19.1
upload_speed = 460800
monitor_speed = 115200
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