raspberrypi · peterharperuk · Feb 20, 2025
diff --git a/README.md b/README.md
@@ -196,6 +196,7 @@ App|Description
 [picow_http_client](pico_w/wifi/http_client) | Demonstrates how to make http and https requests
 [picow_http_client_verify](pico_w/wifi/http_client) | Demonstrates how to make a https request with server authentication
 [picow_mqtt_client](pico_w/wifi/mqtt) | Demonstrates how to implement a MQTT client application
+[picow_coap](pico_w/wifi/mqtt) | Demonstrates how to implment a COAP client
 
 #### FreeRTOS examples
 

diff --git a/pico_w/wifi/CMakeLists.txt b/pico_w/wifi/CMakeLists.txt
@@ -19,6 +19,7 @@ else()
     add_subdirectory_exclude_platforms(udp_beacon)
     add_subdirectory_exclude_platforms(http_client)
     add_subdirectory_exclude_platforms(mqtt)
+    add_subdirectory_exclude_platforms(coap)
 
     if (NOT PICO_MBEDTLS_PATH)
         message("Skipping tls examples as PICO_MBEDTLS_PATH is not defined")

diff --git a/pico_w/wifi/coap/CMakeLists.txt b/pico_w/wifi/coap/CMakeLists.txt
@@ -0,0 +1,87 @@
+if (DEFINED ENV{COAP_SERVER} AND NOT COAP_SERVER)
+    set(COAP_SERVER $ENV{COAP_SERVER})
+    message("Using COAP_SERVER from environment ('${COAP_SERVER}')")
+endif()
+if (NOT COAP_SERVER)
+    message("Skipping COAP example as COAP_SERVER is not defined")
+    return()
+endif()
+set(COAP_SERVER "${COAP_SERVER}" CACHE INTERNAL "COAP server for examples")
+if (DEFINED ENV{LIB_COAP_DIR} AND NOT LIB_COAP_DIR)
+    set(LIB_COAP_DIR $ENV{LIB_COAP_DIR})
+endif()
+if (NOT LIB_COAP_DIR)
+    message("Skipping COAP example as LIB_COAP_DIR is not defined")
+    return()
+endif()
+set(LIB_COAP_DIR "${LIB_COAP_DIR}" CACHE INTERNAL "LIB_COAP_DIR for examples")
+if (DEFINED ENV{LIB_TINYDTLS_DIR} AND NOT LIB_TINYDTLS_DIR)
+    set(LIB_TINYDTLS_DIR $ENV{LIB_TINYDTLS_DIR})
+endif()
+if (NOT LIB_TINYDTLS_DIR)
+    message("Skipping COAP example as LIB_TINYDTLS_DIR is not defined")
+    return()
+endif()
+set(LIB_TINYDTLS_DIR "${LIB_TINYDTLS_DIR}" CACHE INTERNAL "LIB_TINYDTLS_DIR for examples")
+include(libcoap.cmake)
+include(libtinydtls.cmake)
+
+set(TARGET_NAME coap_server)
+add_executable(${TARGET_NAME}
+    coap_server.c
+    )
+target_include_directories(${TARGET_NAME} PRIVATE
+    ${CMAKE_CURRENT_LIST_DIR}
+    ${CMAKE_CURRENT_LIST_DIR}/.. # for our common headers
+    )
+target_link_libraries(${TARGET_NAME} PRIVATE
+    pico_cyw43_arch_lwip_threadsafe_background
+    pico_async_context_threadsafe_background
+    pico_lwip_nosys
+    pico_stdlib
+    pico_coap
+    hardware_adc
+    pico_tinydtls
+    )
+target_compile_definitions(${TARGET_NAME} PRIVATE
+    CYW43_HOST_NAME=\"pico_coap_example\"
+    )
+if (EXISTS "${CMAKE_CURRENT_LIST_DIR}/certs/${COAP_SERVER}")
+    target_compile_definitions(${TARGET_NAME} PRIVATE
+        COAP_CERT_INC=\"certs/${COAP_SERVER}/coap_server.inc\"
+        )
+endif()
+target_compile_definitions(${TARGET_NAME} PRIVATE
+    WIFI_SSID=\"${WIFI_SSID}\"
+    WIFI_PASSWORD=\"${WIFI_PASSWORD}\"
+    )
+pico_add_extra_outputs(${TARGET_NAME})
+
+set(TARGET_NAME coap_client)
+add_executable(${TARGET_NAME}
+    coap_client.c
+    )
+target_include_directories(${TARGET_NAME} PRIVATE
+    ${CMAKE_CURRENT_LIST_DIR}
+    ${CMAKE_CURRENT_LIST_DIR}/.. # for our common lwipopts
+    )
+target_link_libraries(${TARGET_NAME} PRIVATE
+    pico_cyw43_arch_lwip_threadsafe_background
+    pico_lwip_nosys
+    pico_stdlib
+    pico_coap
+    pico_tinydtls
+    )
+target_compile_definitions(${TARGET_NAME} PRIVATE
+    COAP_SERVER=\"${COAP_SERVER}\"
+    )
+if (EXISTS "${CMAKE_CURRENT_LIST_DIR}/certs/${COAP_SERVER}")
+    target_compile_definitions(${TARGET_NAME} PRIVATE
+        COAP_CERT_INC=\"certs/${COAP_SERVER}/coap_client.inc\"
+        )
+endif()
+target_compile_definitions(${TARGET_NAME} PRIVATE
+    WIFI_SSID=\"${WIFI_SSID}\"
+    WIFI_PASSWORD=\"${WIFI_PASSWORD}\"
+    )
+pico_add_extra_outputs(${TARGET_NAME})
diff --git a/pico_w/wifi/coap/README.md b/pico_w/wifi/coap/README.md
@@ -0,0 +1,64 @@
+# Setup
+
+These examples require libcoap and tinydtls to work. Clone these repos somewhere,,,
+
+```
+git clone https://github.com/obgm/libcoap.git
+git submodule update --init
+```
+
+You can define these paths in environment variables or pass the names to cmake
+
+```
+export LIB_COAP_DIR=/home/pi/libcoap
+export LIB_TINYDTLS_DIR=/home/pi/tinydtls
+```
+
+You also need to define the coap server in another environment variable...
+
+```
+export COAP_SERVER=myhost
+```
+
+The examples use keys generated by a script in the certs folder...
+
+```
+cd certs
+./makecerts.sh
+```
+
+The code should now build.
+tinydtls and this example currently only supports raw public keys.
+
+```
+cd libcoap
+mkdir build
+cd build
+cmake .. -DDTLS_BACKEND=tinydtls
+make -j8
+```
+
+# Coap Client
+
+To test the client you need a server to talk to. The libcoap library comes with the coap-server example that should work.
+server.key is generated by the makecerts.sh script above.
+
+```
+coap-server -M server.key -v 7
+```
+
+The coap client example requests "coap://<COAP_SERVER>/.well-known/core" and subscribes to "coap://<COAP_SERVER>/time" and coap://<COAP_SERVER>/subscribe?123/led
+
+# Coap Server
+
+The coap server example supports the following...
+
+* Find out what requests it supports: coap-client -M client.key -m get coaps://$COAP_SERVER/.well-known/core
+* Get the current temperature: coap-client -M client.key -m get coaps://$COAP_SERVER/temp
+* Get the current led state: coap-client -M client.key -m get coaps://$COAP_SERVER/led
+* Turn the led on: coap-client -M client.key -m put coaps://$COAP_SERVER/led -e 1
+* Subscribe to temperature changes: coap-client -M client.key -m get coaps://$COAP_SERVER/temp -s 60 -w
+* Get time: coap-client -M client.key -m get coaps://$COAP_SERVER/time
+
+$COAP_SERVER is the name of the coap server.
+client.key is generated by the makecerts.sh script above.
diff --git a/pico_w/wifi/coap/certs/.gitignore b/pico_w/wifi/coap/certs/.gitignore
@@ -0,0 +1 @@
+*/
diff --git a/pico_w/wifi/coap/certs/makecerts.sh b/pico_w/wifi/coap/certs/makecerts.sh
@@ -0,0 +1,42 @@
+#!/usr/bin/bash
+
+if [ "${PWD##*/}" != "certs" ]; then
+    echo Run this in the certs folder
+    exit 1
+fi
+if [ -z "$COAP_SERVER" ]; then
+    echo Define COAP_SERVER
+    exit 1
+fi
+SERVER_NAME=$COAP_SERVER
+
+if [ -d "$SERVER_NAME" ]; then
+    echo Run \"rm -fr $SERVER_NAME\" to regenerate these keys
+    exit 1
+fi
+mkdir $SERVER_NAME
+echo Generating keys in $PWD/$SERVER_NAME
+
+openssl ecparam -name prime256v1 -genkey -noout -out $SERVER_NAME/client.key
+openssl ec -in $SERVER_NAME/client.key -pubout -out $SERVER_NAME/client.pub
+
+echo -n \#define COAP_KEY \" > $SERVER_NAME/coap_client.inc
+cat $SERVER_NAME/client.key | awk '{printf "%s\\n\\\n", $0}' >> $SERVER_NAME/coap_client.inc
+echo "\"" >> $SERVER_NAME/coap_client.inc
+echo >> $SERVER_NAME/coap_client.inc
+
+echo -n \#define COAP_PUB_KEY \" >> $SERVER_NAME/coap_client.inc
+cat $SERVER_NAME/client.pub | awk '{printf "%s\\n\\\n", $0}' >> $SERVER_NAME/coap_client.inc
+echo "\"" >> $SERVER_NAME/coap_client.inc
+
+openssl ecparam -name prime256v1 -genkey -noout -out $SERVER_NAME/server.key
+openssl ec -in $SERVER_NAME/server.key -pubout -out $SERVER_NAME/server.pub
+
+echo -n \#define COAP_KEY \" > $SERVER_NAME/coap_server.inc
+cat $SERVER_NAME/server.key | awk '{printf "%s\\n\\\n", $0}' >> $SERVER_NAME/coap_server.inc
+echo "\"" >> $SERVER_NAME/coap_server.inc
+echo >> $SERVER_NAME/coap_server.inc
+
+echo -n \#define COAP_PUB_KEY \" >> $SERVER_NAME/coap_server.inc
+cat $SERVER_NAME/server.pub | awk '{printf "%s\\n\\\n", $0}' >> $SERVER_NAME/coap_server.inc
+echo "\"" >> $SERVER_NAME/coap_server.inc