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Part 3: Publishing on the DAL

Now that you can get information about the DAL, the next step is to publish data to it and verify that the kernel can access it.

Planning ahead

Before trying to run the code yourself, look at Explorus and choose a slot that is not currently being used.

The examples in this tutorial use slot 10.

Switching slots​

When you have selected a slot that does not appear to be in use, follow these steps to restart the Smart Rollup and DAL node:

  1. Stop the DAL node and restart it with a new --producer-profiles argument. For example, this command uses slot 10:

    octez-dal-node run --endpoint ${ENDPOINT} \
        --producer-profiles=10 --data-dir _dal_node

  2. Update the kernel to monitor that slot by updating this line:

    match run(host, &param, 0) {

    For example, to monitor slot 10, change the 0 to a 10, as in this code:

    match run(host, &param, 10) {

  3. Run the commands to build and deploy the Smart Rollup and start the node. You can use the script in Part 1: Getting the DAL parameters to simplify the process.

Publishing messages​

The DAL node provides an RPC endpoint for clients to send data to be added to a slot: POST /slot, whose body is the contents of the slot.

  1. Run this command to publish a message to the DAL:

    curl localhost:10732/slot --data '"Hello, world!"' -H 'Content-Type: application/json'

    This command assumes that you have not changed the default RPC server address.

    The command returns the certificate from the DAL node, which looks like this example:

    {
      "commitment": "sh1u3tr3YKPDYUp2wWKCfmV5KZb82FREhv8GtDeR3EJccsBerWGwJYKufsDNH8rk4XqGrXdooZ",
      "commitment_proof":"8229c63b8e858d9a96321c80a204756020dd13243621c11bec61f182a23714cf6e0985675fff45f1164657ad0c7b9418"
    }

    Note that the value of the message is in double quotes because it must be a valid JSON string, as hinted by the Content-Type header.

  2. Using the values of the commitment and proof from the previous command, post the certificate to layer 1 with this command:

    commitment="sh1u3tr3YKPDYUp2wWKCfmV5KZb82FREhv8GtDeR3EJccsBerWGwJYKufsDNH8rk4XqGrXdooZ"
    proof="8229c63b8e858d9a96321c80a204756020dd13243621c11bec61f182a23714cf6e0985675fff45f1164657ad0c7b9418"
    octez-client --endpoint ${ENDPOINT} \
        publish dal commitment "${commitment}" from ${MY_ACCOUNT} for slot 10 \
        with proof "${proof}"

    After 4 blocks, you should see a message in the kernel log that looks like this:

    RollupDalParameters { number_of_slots: 32, attestation_lag: 4, slot_size: 65536, page_size: 4096 }
    Attested slot at index 10 for level 57293: [72, 101, 108, 108, 111, 44, 32, 119, 111, 114]
    See you in the next level

    You can verify your message by converting the bytes in the message back to the first 10 characters of the string "Hello, World!"

    If you see a message that says "A slot header for this slot was already proposed," another transaction tried to write to that slot in the same block, so you must try again.

    If you don't see information about the attested slot, check the page at https://explorus.io/dal. If that page shows red (unattested) slots, it's possible that the attesters for the network are offline.

Publishing files​

You can also send raw bytes to the DAL node with the header Content-Type: application/octet-stream. In this case, you must prefix the data with its size due to limitations of the DAL.

  1. Install the jq and xxd programs.

  2. Create a file named upload_file.sh and add this code:

    #!/usr/bin/bash

    path="${1}"
    alias="${2}"
    index="${3}"

    target="$(mktemp)"
    echo "storing temporary file at ${target}"
    file_size="$(cat "${path}" | wc -c)"
    slot_size_bin="$(printf "%08x" "${file_size}")"
    slot_contents="$(cat ${path} | xxd -p)"

    echo -n "${slot_size_bin}${slot_contents}" | xxd -p -r > "${target}"

    certificate="$(curl localhost:10732/slot --data-binary "@${target}" -H 'Content-Type: application/octet-stream')"

    echo "${certificate}"

    commitment="$(echo -n ${certificate} | jq '.commitment' -r)"
    proof="$(echo -n ${certificate} | jq '.commitment_proof' -r)"

    octez-client --endpoint ${ENDPOINT} \
        publish dal commitment "${commitment}" from "${alias}" \
        for slot "${index}" with proof "${proof}"

    rm "${target}"

    The script accepts three arguments: the file to send, the account alias to use and the slot index to use. This script also assumes that the PATH and ENDPOINT environment variables are correctly set. For example:

    ./upload_file.sh myFile.txt $MY_ACCOUNT 10

    Again, by inspecting the kernel logs, you should be able to see that the file that you wanted to publish is indeed the one fetched by the Smart Rollup.

Now you can publish data to the DAL and use it in a Smart Rollup. In the next section, you write to and retrieve the entire slot. When you are ready, go to Part 4: Using the entire slot.

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