How to write a smart contract

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Goals
Build a sample Java SCORE.
Deploy the Java SCORE to Lisbon.
Verify the transactions
Requirements
You need to install OpenJDK 11 version. Visit OpenJDK.net for prebuilt binaries. Or you can install a proper OpenJDK package from your OS vendors.
In macOS:
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$ brew tap AdoptOpenJDK/openjdk
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$ brew install --cask adoptopenjdk11
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In Linux (Ubuntu 20.04):
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$ sudo apt install openjdk-11-jdk
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Download and Install Go
In macOS:
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$ brew install go
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In Linux (Ubuntu 20.04):
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$ wget -c https://go.dev/dl/go1.16.15.linux-amd64.tar.gz -O - | sudo tar -xz -C /usr/local
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$ export PATH=$PATH:/usr/local/go/bin
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Verify installation
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$ go version
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Step 1. Build goloop CLI
You need to checkout the "goloop" repository for building the goloop CLI.
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$ git clone [email protected]:icon-project/goloop.git
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$ GOLOOP_ROOT=/path/to/goloop
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Then build the goloop CLI binary.
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$ cd ${GOLOOP_ROOT}
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$ GOBUILD_TAGS= make goloop
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Make sure the binary builds successfully.
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$ ./bin/goloop version
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goloop version v1.2.3-7-g78f7f438 linux/amd64 tags()-2022-03-21-14:09:46
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Step 2. Build sample Java SCORE
You need to checkout the "java-score-examples" repository for sample java SCORE.
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$ git clone [email protected]:icon-project/java-score-examples.git
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$ cd java-score-examples
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Build the SCORE
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$ ./gradlew build
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The compiled jar bundle will be generated at ./hello-world/build/libs/hello-world-0.1.0.jar.
Optimize the jar
You need to optimize your jar bundle before you deploy it to local or ICON networks. This involves some pre-processing to ensure the actual deployment successful.
gradle-javaee-plugin is a Gradle plugin to automate the process of generating the optimized jar bundle. Run the optimizedJar task to generate the optimized jar bundle.
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$ ./gradlew optimizedJar
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The output jar will be located at ./hello-world/build/libs/hello-world-0.1.0-optimized.jar.
Step 3. Generate a keystore and get test ICX
Generate a keystore.
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$ ${GOLOOP_ROOT}/bin/goloop ks gen --out keystore.json --password gochain
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hxd8fefc57e0d358e0cf338d684c3e438190d64145 ==> keystore.json
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Then get test ICX in Lisbon using the faucets.
Step 4. Deploy the optimized jar
Using goloop CLI command
You can deploy the optimized jar by using goloop CLI binary.
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$ ${GOLOOP_ROOT}/bin/goloop rpc sendtx deploy ./hello-world/build/libs/hello-world-0.1.0-optimized.jar \
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    --uri https://lisbon.net.solidwallet.io/api/v3 \
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    --key_store keystore.json --key_password gochain \
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    --nid 2 --step_limit 10000000000 \
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    --content_type application/java \
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    --param name=Alice
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"0xfee1e31e3ecb88106e785a6cb8b0b957e42f5f908a7c2c66a0c19aebd659f7ef"
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Using deployJar extension
Alternatively, you can use deployToLisbon task as follows.
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$ ./gradlew hello-world:deployToLisbon -PkeystoreName=keystore.json -PkeystorePass=gochain
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​
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> Task :hello-world:deployToLisbon
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>>> deploy to https://lisbon.net.solidwallet.io/api/v3
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>>> optimizedJar = ./hello-world/build/libs/hello-world-0.1.0-optimized.jar
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>>> keystore = keystore.json
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Succeeded to deploy: 0xfee1e31e3ecb88106e785a6cb8b0b957e42f5f908a7c2c66a0c19aebd659f7ef
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SCORE address: cxd1f5d12e92459a4fcdf2678a14b572687471a70e
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Step 5. Verify the execution
Check the deployed SCORE address first using the txresult command.
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$ ${GOLOOP_ROOT}/bin/goloop rpc txresult 0xfee1e31e3ecb88106e785a6cb8b0b957e42f5f908a7c2c66a0c19aebd659f7ef \
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    --uri https://lisbon.net.solidwallet.io/api/v3
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{
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  "to": "cx0000000000000000000000000000000000000000",
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  "cumulativeStepUsed": "0x3d70a5c3",
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  "stepUsed": "0x3d70a5c3",
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  "stepPrice": "0x2e90edd00",
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  "eventLogs": [],
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  "logsBloom": "0x0000000000000000000000000000000000000000000000000000000000000000000000000000000000000...",
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  "status": "0x1",
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  "scoreAddress": "cxd1f5d12e92459a4fcdf2678a14b572687471a70e",
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  "blockHash": "0xe678a4a19d43c54c709c16b4d794e59a3214af64d9efd860eb8f97fc6bdece7d",
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  "blockHeight": "0x1b6",
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  "txIndex": "0x0",
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  "txHash": "0xfee1e31e3ecb88106e785a6cb8b0b957e42f5f908a7c2c66a0c19aebd659f7ef"
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}
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Note that scoreAddress field above represents the newly created SCORE address (you need to use this address for RPC calls hereafter).
Then you can query getGreeting method via the following call command.
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$ ${GOLOOP_ROOT}/bin/goloop rpc call --to cxd1f5d12e92459a4fcdf2678a14b572687471a70e \
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    --uri https://lisbon.net.solidwallet.io/api/v3 \
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    --method getGreeting
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"Hello Alice!"
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And you can invoke setName method via the following sendtx command.
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$ ${GOLOOP_ROOT}/bin/goloop rpc sendtx call --to cxd1f5d12e92459a4fcdf2678a14b572687471a70e \
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    --uri https://lisbon.net.solidwallet.io/api/v3 \
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    --key_store keystore.json --key_password gochain \
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    --nid 2 --step_limit 10000000000 \
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    --method setName \
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    --param name=Bob
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"0x07868af25c42e0d201073eae9d490d895e0922a431918199aa3bd461d6d9e65f"
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Check the transaction result using the txresult command.
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$ ${GOLOOP_ROOT}/bin/goloop rpc txresult 0x07868af25c42e0d201073eae9d490d895e0922a431918199aa3bd461d6d9e65f \
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    --uri https://lisbon.net.solidwallet.io/api/v3
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{
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  "to": "cxd1f5d12e92459a4fcdf2678a14b572687471a70e",
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  "cumulativeStepUsed": "0x1fe85",
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  "stepUsed": "0x1fe85",
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  "stepPrice": "0x2e90edd00",
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  "eventLogs": [],
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  "logsBloom": "0x0000000000000000000000000000000000000000000000000000000000000000000000000000000000000...",
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  "status": "0x1",
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  "blockHash": "0xae2be6e87b715f786c2ba599f5f570f9a4f018a20338cfb1d055ae3463d65571",
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  "blockHeight": "0x2bc",
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  "txIndex": "0x0",
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  "txHash": "0x07868af25c42e0d201073eae9d490d895e0922a431918199aa3bd461d6d9e65f"
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}
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Query getGreeting method again to confirm the name change.
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$ ${GOLOOP_ROOT}/bin/goloop rpc call --to cxd1f5d12e92459a4fcdf2678a14b572687471a70e \
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    --uri https://lisbon.net.solidwallet.io/api/v3 \
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    --method getGreeting
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"Hello Bob!"
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Further Resources
​ICON Smart contract examples​