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Version: 0.1.0-alpha.4 (alpha)

C compiler and runtime profile

For application development, use Creating a capsule. That shared tutorial has all six language choices and uses dev init, build, deploy and test. You do not need the source-build commands below for it.

This reference is for compiler integration, custom package signing and direct node admission. The complete source recipe is retained here for developers who need to work below the packaged workflow.

Create an independent C project, edit its typed contract, and run its signed package on a local node. Your application lives outside the LSF checkout and uses a pinned copy of the maintained guest SDK.

Use Linux, Python 3.13.5, Zig 0.16.0, Rust 1.97.1 for the host tools, wasm-tools 1.254.0 and wit-bindgen-cli 0.62.0. Follow the toolchain setup, install tools/requirements.lock in your Python environment, and run these commands from the LSF repository root. The build tools are compiled once:

python3 tools/install_guest_bindgen.py "$PWD/target/guest-tools"
export PATH="$PWD/target/guest-tools:$PATH"
cargo build --locked -p latent -p latentd --bins \
  -p latent-packaging --example package --example capsule_contracts \
  -p latent-policy --example capsule_authoring

The binding installer needs a fresh output path. If it is already installed, keep that directory on PATH. Run the following Bash blocks in one terminal.

1. Create a project​

set -euo pipefail
umask 077
LSF_CHECKOUT=$PWD
BIN="${CARGO_TARGET_DIR:-$PWD/target}/debug"
export LSF_C_PROJECTS="${LSF_C_PROJECTS:-$(mktemp -d "${TMPDIR:-/tmp}/lsf-c-projects.XXXXXXXX")}"
python3 tools/c_capsule.py new "$LSF_C_PROJECTS/my-greeting" --template greeting

Open my-greeting/src/main.c and my-greeting/wit/world.wit. They contain the complete greeting example, including its normal C function and generated component export. The C template preserves the same contract and behavior. Its contract is:

greet: func(name: string) -> result<string, string>;

The generated project includes the authoritative WIT, generated-at-build bindings, a pinned SDK under vendor/lsf, and capsule-project.json. Edit your src and wit files and update the selected world in capsule-project.json when renaming the contract. Keep the SDK files unchanged. The build rejects SDK drift, path escapes and unsupported contract shapes. Put additional C sources and headers in src; the build compiles the captured .c files with no external library search paths. Includes relative to an application's source file work normally. Absolute includes are outside this supported captured-source recipe.

The word-count and shipping templates provide equivalent C implementations of Creating a capsule. Choose another project directory and replace greeting in the creation command with either template name. http-status adds a typed, asynchronous HTTP call; its import still needs an installed provider and an explicit deployment grant. Creating a project grants no network access.

2. Build and package the project​

python3 tools/c_capsule.py build "$LSF_C_PROJECTS/my-greeting" \
  --output "$LSF_C_PROJECTS/greeting-build" \
  --contracts-tool "$BIN/examples/capsule_contracts" \
  --packager "$BIN/examples/package" \
  --repository https://github.com/KirilsTurkins/latent-service-fabric

Use your own public repository URL for an application you maintain. That label does not authenticate its source. The builder captures the actual project files, checks generated SDK bindings, builds the component, derives contracts from WIT, and inspects the package. BUILD-COMPLETE.json appears only after all steps succeed. Use a fresh output directory for each new attempt.

The output includes component.wasm, capsule.json, contracts.json, wit-lock.json, deployment.json, package/ and build-observation.json. Full-width WIT integers retain their original types; application errors remain result values. Unsupported WIT types fail explicitly during contract derivation.

3. Sign for this local experiment​

The following signer creates short-lived publisher and builder keys in memory, signs this exact build, and writes a policy for a new isolated node. It also adds an inventory of the package's component and WIT inputs. It does not assert a complete transitive dependency inventory. The keys never enter the compiler.

"$BIN/examples/capsule_authoring" demo-sign "$LSF_C_PROJECTS/releases" \
  "$LSF_C_PROJECTS/greeting-build"

This policy lasts for this experiment and accepts only the captured source and builder recipe. For a maintained deployment, use your organization's publisher, builder and revocation policies through the package workflow. Finish the steps below within 30 minutes of signing; otherwise sign into a new directory and start a new experiment.

4. Start a node with enforced admission​

This node listens on an automatically selected loopback port. Its random client credential stays in private files. It verifies both package signatures and the builder policy before admitting a release.

Download this step's script, then run it in the same terminal. You can expand the script to inspect the commands first.

View the setup script
mkdir "$LSF_C_PROJECTS/node" "$LSF_C_PROJECTS/results"
python3 - <<'PY'
import json, os, secrets, shutil
from pathlib import Path
root = Path(os.environ["LSF_C_PROJECTS"])
shutil.copyfile(root / "releases/policy.json", root / "node/policy.json")
token = secrets.token_urlsafe(32)
node = {
    "formatVersion": 1, "nodeId": "c-learning-node", "dataDirectory": "data",
    "bind": "127.0.0.1:0", "securityProfile": "local-experimental-v1",
    "supplyChain": {"mode": "enforced", "policyFile": "policy.json", "clockLeaseSeconds": 5},
    "execution": {"maximumWallTimeMillis": 5000},
    "credentials": [{"token": token, "subject": "c-learner", "tenant": "examples", "role": "operator"}],
}
with (root / "node/node.json").open("x") as output:
    json.dump(node, output)
PY
"$BIN/latentd" check-config --config "$LSF_C_PROJECTS/node/node.json"
"$BIN/latentd" serve --config "$LSF_C_PROJECTS/node/node.json" \
  >"$LSF_C_PROJECTS/node/status.jsonl" 2>"$LSF_C_PROJECTS/node/diagnostics.jsonl" &
C_NODE_PID=$!
stop_c_node() {
    if [[ -n "$C_NODE_PID" ]]; then
        local pid=$C_NODE_PID result=0
        C_NODE_PID=
        kill -TERM "$pid" 2>/dev/null || true
        for ((attempt=0; attempt<100; attempt++)); do
            if ! kill -0 "$pid" 2>/dev/null; then break; fi
            sleep 0.05
        done
        if kill -0 "$pid" 2>/dev/null; then kill -KILL "$pid" 2>/dev/null || true; result=1; fi
        wait "$pid" || result=1
        return "$result"
    fi
}
trap 'stop_c_node >/dev/null 2>&1 || true' EXIT
trap 'exit 130' INT
trap 'exit 143' TERM
python3 - <<'PY'
import json, os, time
from pathlib import Path
root = Path(os.environ["LSF_C_PROJECTS"])
deadline = time.monotonic() + 30
while True:
    lines = (root / "node/status.jsonl").read_text().splitlines()
    if lines:
        endpoint = json.loads(lines[0])["endpoint"]
        break
    if time.monotonic() >= deadline:
        raise SystemExit("Node did not start; inspect node/diagnostics.jsonl")
    time.sleep(0.05)
token = json.loads((root / "node/node.json").read_text())["credentials"][0]["token"]
client = {"formatVersion": 1, "defaultProfile": "local", "profiles": [{
    "name": "local", "endpoint": "http://" + endpoint, "tenant": "examples", "token": token,
    "connectTimeoutMillis": 1000, "rpcTimeoutMillis": 5000,
}]}
with (root / "client.json").open("x") as output:
    json.dump(client, output)
PY
c_cli() { "$BIN/latent" --config "$LSF_C_PROJECTS/client.json" --output json "$@"; }
c_cli node get c-learning-node >"$LSF_C_PROJECTS/results/node.json"

Run source "$HOME/Downloads/c-authoring-1.sh".

5. Publish, deploy and invoke​

Publishing returns an exact publication identity. Put that identity into the generated deployment before applying it:

Download this step's script, then run it in the same terminal. You can expand the script to inspect the commands first.

View the setup script
c_cli release publish-package "$LSF_C_PROJECTS/releases/my-greeting/package" \
  --evidence "$LSF_C_PROJECTS/releases/my-greeting/evidence/index.json" \
  --operation-id publish-my-greeting --expected-generation 0 \
  >"$LSF_C_PROJECTS/results/published.json"
python3 - <<'PY'
import json, os
from pathlib import Path
root = Path(os.environ["LSF_C_PROJECTS"])
deployment = json.loads((root / "releases/my-greeting/deployment.json").read_text())
published = json.loads((root / "results/published.json").read_text())
deployment["spec"]["publication"] = published["data"]["operation"]["publication"]["id"]
with (root / "results/deployment.json").open("x") as output:
    json.dump(deployment, output)
PY
c_cli deployment apply "$LSF_C_PROJECTS/results/deployment.json" --expected-generation 0 \
  >"$LSF_C_PROJECTS/results/deployed.json"
printf '["Ada"]\n' >"$LSF_C_PROJECTS/results/input.json"
c_cli invoke --service examples/my-greeting --route my-greeting \
  --contract examples:greeting/api@1.0.0 --function greet --activation-id my-greeting-valid \
  --input "$LSF_C_PROJECTS/results/input.json" >"$LSF_C_PROJECTS/results/answer.json"
c_answer() {
    python3 - "$1" <<'PY'
import base64, json, sys
data = json.load(open(sys.argv[1]))["data"]
payload = data.get("payload") or data["declaredError"]["payload"]
print(base64.b64decode(payload["data"]).decode())
PY
}
c_answer "$LSF_C_PROJECTS/results/answer.json"
printf '[""]\n' >"$LSF_C_PROJECTS/results/empty.json"
c_cli invoke --service examples/my-greeting --route my-greeting \
  --contract examples:greeting/api@1.0.0 --function greet --activation-id my-greeting-invalid \
  --input "$LSF_C_PROJECTS/results/empty.json" >"$LSF_C_PROJECTS/results/error.json" || test "$?" -eq 3
c_answer "$LSF_C_PROJECTS/results/error.json"

Run source "$HOME/Downloads/c-authoring-2.sh".

Expected answers are [{"ok":"Hello, Ada!"}] and [{"err":"Please enter a name."}]. Exit code 3 is a declared application error. Connection failures, exhausted budgets and guest traps have different outcomes. Use a new activation ID for a new request; an uncertain mutation must be inspected before any retry.

6. Clean up and continue​

GENERATION=$(python3 -c 'import json,os; print(json.load(open(os.environ["LSF_C_PROJECTS"]+"/results/deployed.json"))["data"]["deployment"]["generation"])')
c_cli deployment delete my-greeting --expected-generation "$GENERATION"
stop_c_node
printf 'Saved project and results: %s\n' "$LSF_C_PROJECTS"

Your source and results remain at that path. Edit the greeting, create a new build directory, and repeat signing and delivery to try a change. The delivery and recovery guide explains update and recovery principles using a separate Rust tutorial project and node. Follow that tutorial's prerequisites and variables when using its commands; for this project, retain the build, signing and admission path above.

For capabilities, use the guest SDK reference. It covers buffered and streaming HTTP, blobs, secrets, events, local calls, randomness and metrics, including each wrapper's close/drop rules. The C headers in vendor/lsf/sdk/c-guest/include/lsf provide explicit scopes, buffer owners and canonical async task frames. An imported effect is allowed only by host policy. Pending calls retain their budget until the host releases them; cancelling a subtask never proves an external effect did not occur.

If a build fails, inspect BUILD-FAILED.json and logs/ in that attempt's output. SDK binding drift means the SDK and generator pins disagree; do not edit the lock to bypass it. A denied publication commonly means the policy expired, the exact source approval differs, or an evidence file is missing. A denied HTTP call requires checking the deployment grant, provider binding and allowed destination.