Add OpenFaaS function pattern examples in Go, Python, and Node.js

.gitignore

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+template/
+build/
+context/
+.secrets/
+*.tar.gz
+__pycache__/
+.pytest_cache/
+.tox/
+*.py[cod]
+node_modules/

README.md

@@ -1,2 +1,38 @@
 # function-patterns
 Patterns for OpenFaaS Functions
+
+Examples for the OpenFaaS documentation. Each example is
+self-contained: it has its own `stack.yaml` and function directories, so it
+can be built and deployed on its own.
+
+## Examples
+
+- [**Director**](https://docs.openfaas.com/languages/patterns/director/) — [Go](go/director/) · [Python](python/director/) · [Node.js](node/director/)
+- [**Fan-out**](https://docs.openfaas.com/languages/patterns/fan-out/) — [Go](go/fan-out/) · [Python](python/fan-out/) · [Node.js](node/fan-out/)
+- [**Singleton**](https://docs.openfaas.com/languages/patterns/singleton/) — [Go](go/singleton/) · [Python](python/singleton/)
+
+## Prerequisites
+
+- [faas-cli](https://docs.openfaas.com/cli/install/)
+- Docker, for building images
+- A running OpenFaaS cluster, for e2e testing — set `OPENFAAS_URL` and
+  provide credentials, or point the `gateway` in each `stack.yaml` at a
+  local gateway
+
+## Build and test an example
+
+```bash
+cd go/director
+faas-cli up --tag=digest
+```
+
+`faas-cli up` builds each function image, pushes it to the registry, and
+deploys it to the gateway.
+
+The examples default to the public [ttl.sh](https://ttl.sh) registry so they
+can be pushed without credentials. The registry and owner are overridable
+through environment variables:
+
+```bash
+REGISTRY=ghcr.io OWNER=welteki faas-cli up
+```

go/director/.gitignore

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+template
+build
+.secrets

go/director/README.md

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+# Director pattern — telemetry triage
+
+The director function `telemetry-workflow` validates a sensor reading, invokes
+temperature and battery checks in parallel, and combines their results into an
+`ok` or `alert` response:
+
+```
+telemetry-workflow ◄── director: owns the workflow and handles errors
+    ├── 1. invoke ──► validate-reading
+    ├── 2. invoke in parallel
+    │       ├──► temperature-check ──┐
+    │       └──► battery-check ──────┤
+    │◄──── check results ────────────┘
+    └── 3. combine results and return ok or alert
+```
+
+Documentation: [Director pattern](https://docs.openfaas.com/languages/patterns/director/)
+
+## Build and deploy
+
+```bash
+faas-cli up --tag=digest
+```
+
+The stage functions are invoked through the gateway. The `stage_timeout`
+environment variable limits each downstream call, while the watchdog timeout
+variables limit the complete director invocation.
+
+## Invoke
+
+```bash
+curl -s http://127.0.0.1:8080/function/telemetry-workflow \
+  -H "Content-Type: application/json" \
+  -d '{"device_id":"pump-17","temperature_c":82.4,"battery_percent":12}' | \
+  jq
+```
+
+Example output:
+
+```json
+{
+  "device_id": "pump-17",
+  "status": "alert",
+  "temperature": {
+    "value_c": 82.4,
+    "threshold_c": 75,
+    "alert": true
+  },
+  "battery": {
+    "value_percent": 12,
+    "threshold_percent": 20,
+    "alert": true
+  },
+  "duration_ms": 4
+}
+```

go/director/battery-check/go.mod

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+module handler/function
+
+go 1.25.0

go/director/battery-check/handler.go

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+package function
+
+import (
+	"encoding/json"
+	"net/http"
+)
+
+const thresholdPercent = 20
+
+type Reading struct {
+	BatteryPercent int `json:"battery_percent"`
+}
+
+type Response struct {
+	ValuePercent     int  `json:"value_percent"`
+	ThresholdPercent int  `json:"threshold_percent"`
+	Alert            bool `json:"alert"`
+}
+
+func Handle(w http.ResponseWriter, r *http.Request) {
+	defer r.Body.Close()
+
+	var reading Reading
+	if err := json.NewDecoder(r.Body).Decode(&reading); err != nil {
+		http.Error(w, "expected a JSON sensor reading", http.StatusBadRequest)
+		return
+	}
+
+	w.Header().Set("Content-Type", "application/json")
+	json.NewEncoder(w).Encode(Response{
+		ValuePercent:     reading.BatteryPercent,
+		ThresholdPercent: thresholdPercent,
+		Alert:            reading.BatteryPercent < thresholdPercent,
+	})
+}

go/director/battery-check/handler_test.go

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+package function
+
+import (
+	"encoding/json"
+	"net/http"
+	"net/http/httptest"
+	"strings"
+	"testing"
+)
+
+func TestHandleBatteryThreshold(t *testing.T) {
+	tests := []struct {
+		name  string
+		value int
+		alert bool
+	}{
+		{name: "below", value: 19, alert: true},
+		{name: "at threshold", value: 20, alert: false},
+		{name: "above", value: 21, alert: false},
+	}
+
+	for _, test := range tests {
+		t.Run(test.name, func(t *testing.T) {
+			req := httptest.NewRequest(http.MethodPost, "/", strings.NewReader(
+				`{"battery_percent":`+jsonNumber(test.value)+`}`,
+			))
+			recorder := httptest.NewRecorder()
+			Handle(recorder, req)
+
+			var response Response
+			if err := json.Unmarshal(recorder.Body.Bytes(), &response); err != nil {
+				t.Fatal(err)
+			}
+			if response.Alert != test.alert {
+				t.Fatalf("want alert %t, got %t", test.alert, response.Alert)
+			}
+		})
+	}
+}
+
+func jsonNumber(value int) string {
+	data, _ := json.Marshal(value)
+	return string(data)
+}

go/director/stack.yaml

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+version: 1.0
+provider:
+  name: openfaas
+  gateway: http://127.0.0.1:8080
+functions:
+  telemetry-workflow:
+    lang: golang-middleware
+    handler: ./telemetry-workflow
+    image: ${REGISTRY:-ttl.sh}/${OWNER:-openfaas-examples}/telemetry-workflow:latest
+    environment:
+      stage_timeout: 5s
+      exec_timeout: 15s
+      read_timeout: 16s
+      write_timeout: 16s
+
+  validate-reading:
+    lang: golang-middleware
+    handler: ./validate-reading
+    image: ${REGISTRY:-ttl.sh}/${OWNER:-openfaas-examples}/validate-reading:latest
+
+  temperature-check:
+    lang: golang-middleware
+    handler: ./temperature-check
+    image: ${REGISTRY:-ttl.sh}/${OWNER:-openfaas-examples}/temperature-check:latest
+
+  battery-check:
+    lang: golang-middleware
+    handler: ./battery-check
+    image: ${REGISTRY:-ttl.sh}/${OWNER:-openfaas-examples}/battery-check:latest

go/director/telemetry-workflow/go.mod

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+module handler/function
+
+go 1.25.0