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Add COAP example
Adds a COAP client and server example. Requires libcoap and tinydtls.
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‎README.md‎

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[picow_http_client](pico_w/wifi/http_client) | Demonstrates how to make http and https requests
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[picow_http_client_verify](pico_w/wifi/http_client) | Demonstrates how to make a https request with server authentication
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[picow_mqtt_client](pico_w/wifi/mqtt) | Demonstrates how to implement a MQTT client application
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[picow_coap](pico_w/wifi/mqtt) | Demonstrates how to implment a COAP client
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#### FreeRTOS examples
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‎pico_w/wifi/CMakeLists.txt‎

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add_subdirectory_exclude_platforms(udp_beacon)
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add_subdirectory_exclude_platforms(http_client)
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add_subdirectory_exclude_platforms(mqtt)
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add_subdirectory_exclude_platforms(coap)
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if (NOT PICO_MBEDTLS_PATH)
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message("Skipping tls examples as PICO_MBEDTLS_PATH is not defined")

‎pico_w/wifi/coap/CMakeLists.txt‎

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if (DEFINED ENV{COAP_SERVER} AND NOT COAP_SERVER)
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set(COAP_SERVER $ENV{COAP_SERVER})
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message("Using COAP_SERVER from environment ('${COAP_SERVER}')")
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endif()
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if (NOT COAP_SERVER)
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message("Skipping COAP example as COAP_SERVER is not defined")
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return()
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endif()
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set(COAP_SERVER "${COAP_SERVER}" CACHE INTERNAL "COAP server for examples")
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if (DEFINED ENV{LIB_COAP_DIR} AND NOT LIB_COAP_DIR)
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set(LIB_COAP_DIR $ENV{LIB_COAP_DIR})
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endif()
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if (NOT LIB_COAP_DIR)
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message("Skipping COAP example as LIB_COAP_DIR is not defined")
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return()
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endif()
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set(LIB_COAP_DIR "${LIB_COAP_DIR}" CACHE INTERNAL "LIB_COAP_DIR for examples")
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if (DEFINED ENV{LIB_TINYDTLS_DIR} AND NOT LIB_TINYDTLS_DIR)
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set(LIB_TINYDTLS_DIR $ENV{LIB_TINYDTLS_DIR})
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endif()
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if (NOT LIB_TINYDTLS_DIR)
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message("Skipping COAP example as LIB_TINYDTLS_DIR is not defined")
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return()
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endif()
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set(LIB_TINYDTLS_DIR "${LIB_TINYDTLS_DIR}" CACHE INTERNAL "LIB_TINYDTLS_DIR for examples")
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include(libcoap.cmake)
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include(libtinydtls.cmake)
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set(TARGET_NAME coap_server)
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add_executable(${TARGET_NAME}
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coap_server.c
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)
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target_include_directories(${TARGET_NAME} PRIVATE
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${CMAKE_CURRENT_LIST_DIR}
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${CMAKE_CURRENT_LIST_DIR}/.. # for our common headers
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)
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target_link_libraries(${TARGET_NAME} PRIVATE
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pico_cyw43_arch_lwip_threadsafe_background
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pico_async_context_threadsafe_background
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pico_lwip_nosys
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pico_stdlib
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pico_coap
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hardware_adc
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pico_tinydtls
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)
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target_compile_definitions(${TARGET_NAME} PRIVATE
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CYW43_HOST_NAME=\"pico_coap_example\"
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)
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if (EXISTS "${CMAKE_CURRENT_LIST_DIR}/certs/${COAP_SERVER}")
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target_compile_definitions(${TARGET_NAME} PRIVATE
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COAP_CERT_INC=\"certs/${COAP_SERVER}/coap_server.inc\"
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)
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endif()
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target_compile_definitions(${TARGET_NAME} PRIVATE
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WIFI_SSID=\"${WIFI_SSID}\"
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WIFI_PASSWORD=\"${WIFI_PASSWORD}\"
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)
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pico_add_extra_outputs(${TARGET_NAME})
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set(TARGET_NAME coap_client)
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add_executable(${TARGET_NAME}
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coap_client.c
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)
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target_include_directories(${TARGET_NAME} PRIVATE
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${CMAKE_CURRENT_LIST_DIR}
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${CMAKE_CURRENT_LIST_DIR}/.. # for our common lwipopts
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)
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target_link_libraries(${TARGET_NAME} PRIVATE
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pico_cyw43_arch_lwip_threadsafe_background
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pico_lwip_nosys
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pico_stdlib
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pico_coap
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pico_tinydtls
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)
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target_compile_definitions(${TARGET_NAME} PRIVATE
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COAP_SERVER=\"${COAP_SERVER}\"
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)
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if (EXISTS "${CMAKE_CURRENT_LIST_DIR}/certs/${COAP_SERVER}")
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target_compile_definitions(${TARGET_NAME} PRIVATE
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COAP_CERT_INC=\"certs/${COAP_SERVER}/coap_client.inc\"
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)
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endif()
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target_compile_definitions(${TARGET_NAME} PRIVATE
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WIFI_SSID=\"${WIFI_SSID}\"
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WIFI_PASSWORD=\"${WIFI_PASSWORD}\"
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)
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pico_add_extra_outputs(${TARGET_NAME})

‎pico_w/wifi/coap/README.md‎

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# Setup
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These examples require libcoap and tinydtls to work. Clone these repos somewhere,,,
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```
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git clone https://github.com/obgm/libcoap.git
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git submodule update --init
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```
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You can define these paths in environment variables or pass the names to cmake
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```
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export LIB_COAP_DIR=/home/pi/libcoap
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export LIB_TINYDTLS_DIR=/home/pi/tinydtls
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```
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You also need to define the coap server in another environment variable...
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```
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export COAP_SERVER=myhost
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```
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The examples use keys generated by a script in the certs folder...
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```
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cd certs
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./makecerts.sh
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```
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The code should now build.
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tinydtls and this example currently only supports raw public keys.
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```
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cd libcoap
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mkdir build
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cd build
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cmake .. -DDTLS_BACKEND=tinydtls
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make -j8
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```
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# Coap Client
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To test the client you need a server to talk to. The libcoap library comes with the coap-server example that should work.
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server.key is generated by the makecerts.sh script above.
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```
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coap-server -M server.key -v 7
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```
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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
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# Coap Server
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The coap server example supports the following...
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* Find out what requests it supports: coap-client -M client.key -m get coaps://$COAP_SERVER/.well-known/core
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* Get the current temperature: coap-client -M client.key -m get coaps://$COAP_SERVER/temp
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* Get the current led state: coap-client -M client.key -m get coaps://$COAP_SERVER/led
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* Turn the led on: coap-client -M client.key -m put coaps://$COAP_SERVER/led -e 1
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* Subscribe to temperature changes: coap-client -M client.key -m get coaps://$COAP_SERVER/temp -s 60 -w
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* Get time: coap-client -M client.key -m get coaps://$COAP_SERVER/time
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$COAP_SERVER is the name of the coap server.
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client.key is generated by the makecerts.sh script above.

‎pico_w/wifi/coap/certs/.gitignore‎

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*/

‎pico_w/wifi/coap/certs/makecerts.sh‎

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#!/usr/bin/bash
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if [ "${PWD##*/}" != "certs" ]; then
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echo Run this in the certs folder
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exit 1
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fi
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if [ -z "$COAP_SERVER" ]; then
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echo Define COAP_SERVER
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exit 1
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fi
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SERVER_NAME=$COAP_SERVER
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if [ -d "$SERVER_NAME" ]; then
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echo Run \"rm -fr $SERVER_NAME\" to regenerate these keys
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exit 1
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fi
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mkdir $SERVER_NAME
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echo Generating keys in $PWD/$SERVER_NAME
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openssl ecparam -name prime256v1 -genkey -noout -out $SERVER_NAME/client.key
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openssl ec -in $SERVER_NAME/client.key -pubout -out $SERVER_NAME/client.pub
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echo -n \#define COAP_KEY \" > $SERVER_NAME/coap_client.inc
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cat $SERVER_NAME/client.key | awk '{printf "%s\\n\\\n", $0}' >> $SERVER_NAME/coap_client.inc
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echo "\"" >> $SERVER_NAME/coap_client.inc
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echo >> $SERVER_NAME/coap_client.inc
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echo -n \#define COAP_PUB_KEY \" >> $SERVER_NAME/coap_client.inc
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cat $SERVER_NAME/client.pub | awk '{printf "%s\\n\\\n", $0}' >> $SERVER_NAME/coap_client.inc
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echo "\"" >> $SERVER_NAME/coap_client.inc
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openssl ecparam -name prime256v1 -genkey -noout -out $SERVER_NAME/server.key
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openssl ec -in $SERVER_NAME/server.key -pubout -out $SERVER_NAME/server.pub
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echo -n \#define COAP_KEY \" > $SERVER_NAME/coap_server.inc
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cat $SERVER_NAME/server.key | awk '{printf "%s\\n\\\n", $0}' >> $SERVER_NAME/coap_server.inc
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echo "\"" >> $SERVER_NAME/coap_server.inc
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echo >> $SERVER_NAME/coap_server.inc
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echo -n \#define COAP_PUB_KEY \" >> $SERVER_NAME/coap_server.inc
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cat $SERVER_NAME/server.pub | awk '{printf "%s\\n\\\n", $0}' >> $SERVER_NAME/coap_server.inc
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echo "\"" >> $SERVER_NAME/coap_server.inc

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