feat(agent): add updater-agent binary and ship it in the image

internal/agent/config/config.go

@@ -0,0 +1,51 @@
+// Package config loads the agent's configuration from environment variables.
+package config
+
+import (
+	"errors"
+	"os"
+	"regexp"
+	"strings"
+)
+
+var masterKeyPattern = regexp.MustCompile(`^sha256:[0-9a-f]{64}$`)
+
+// Config holds the agent's runtime configuration.
+type Config struct {
+	MasterURL string // MASTER_URL, wss://host:port/agent
+	MasterKey string // MASTER_KEY, fingerprint shown in the master UI
+	Token     string // AGENT_TOKEN, shown once when the agent was added
+	SelfID    string // SELF_ID, defaults to the hostname (= container ID prefix)
+	LogLevel  string // LOG_LEVEL, default info
+}
+
+// Load reads and validates the agent configuration. It fails fast so a
+// misconfigured agent never starts dialling.
+func Load() (*Config, error) {
+	cfg := &Config{
+		MasterURL: os.Getenv("MASTER_URL"),
+		MasterKey: os.Getenv("MASTER_KEY"),
+		Token:     os.Getenv("AGENT_TOKEN"),
+		SelfID:    os.Getenv("SELF_ID"),
+		LogLevel:  os.Getenv("LOG_LEVEL"),
+	}
+	switch {
+	case cfg.MasterURL == "":
+		return nil, errors.New("MASTER_URL is required")
+	case !strings.HasPrefix(cfg.MasterURL, "wss://"):
+		return nil, errors.New("MASTER_URL must start with wss://")
+	case cfg.MasterKey == "":
+		return nil, errors.New("MASTER_KEY is required")
+	case !masterKeyPattern.MatchString(cfg.MasterKey):
+		return nil, errors.New("MASTER_KEY must look like sha256:<64 hex>")
+	case cfg.Token == "":
+		return nil, errors.New("AGENT_TOKEN is required")
+	}
+	if cfg.SelfID == "" {
+		cfg.SelfID, _ = os.Hostname()
+	}
+	if cfg.LogLevel == "" {
+		cfg.LogLevel = "info"
+	}
+	return cfg, nil
+}

internal/agent/config/config_test.go

@@ -0,0 +1,50 @@
+package config
+
+import (
+	"os"
+	"testing"
+
+	"github.com/stretchr/testify/assert"
+	"github.com/stretchr/testify/require"
+)
+
+const validKey = "sha256:0000000000000000000000000000000000000000000000000000000000000000"
+
+func setValid(t *testing.T) {
+	t.Setenv("MASTER_URL", "wss://10.0.0.5:8090/agent")
+	t.Setenv("MASTER_KEY", validKey)
+	t.Setenv("AGENT_TOKEN", "pua_abc")
+	t.Setenv("SELF_ID", "")
+	t.Setenv("LOG_LEVEL", "")
+}
+
+func TestLoad_Valid(t *testing.T) {
+	setValid(t)
+	cfg, err := Load()
+	require.NoError(t, err)
+	host, _ := os.Hostname()
+	assert.Equal(t, &Config{
+		MasterURL: "wss://10.0.0.5:8090/agent", MasterKey: validKey, Token: "pua_abc",
+		SelfID: host, LogLevel: "info",
+	}, cfg)
+}
+
+func TestLoad_Invalid(t *testing.T) {
+	cases := []struct {
+		name, key, value, wantErr string
+	}{
+		{"missing url", "MASTER_URL", "", "MASTER_URL is required"},
+		{"plain ws", "MASTER_URL", "ws://10.0.0.5:8090/agent", "MASTER_URL must start with wss://"},
+		{"missing key", "MASTER_KEY", "", "MASTER_KEY is required"},
+		{"malformed key", "MASTER_KEY", "abc", "MASTER_KEY must look like sha256:<64 hex>"},
+		{"missing token", "AGENT_TOKEN", "", "AGENT_TOKEN is required"},
+	}
+	for _, c := range cases {
+		t.Run(c.name, func(t *testing.T) {
+			setValid(t)
+			t.Setenv(c.key, c.value)
+			_, err := Load()
+			assert.ErrorContains(t, err, c.wantErr)
+		})
+	}
+}