fix: resolve GELF hostname at adapter creation, not package init

adapters/gelf/gelf.go

@@ -15,27 +15,28 @@ import (
 	"github.com/gliderlabs/logspout/router"
 )
 
-var hostname string
-
+// getHostname resolves the GELF source hostname. It must be called when an
+// adapter is created (NewGelfAdapter) rather than at package init: the Home
+// Assistant launcher sets SYSLOG_HOSTNAME inside main(), which runs after all
+// package init() functions, so reading it at init time would always miss the
+// configured value and fall back to the default below.
 func getHostname() string {
 	content, err := os.ReadFile("/etc/host_hostname")
 	if err == nil && len(content) > 0 {
-		hostname = strings.TrimRight(string(content), "\r\n")
-	} else {
-		hostname = cfg.GetEnvDefault("SYSLOG_HOSTNAME", "{{.Container.Config.Hostname}}")
+		return strings.TrimRight(string(content), "\r\n")
 	}
-	return hostname
+	return cfg.GetEnvDefault("SYSLOG_HOSTNAME", "{{.Container.Config.Hostname}}")
 }
 
 func init() {
-	hostname = getHostname()
 	router.AdapterFactories.Register(NewGelfAdapter, "gelf")
 }
 
 // Adapter is an adapter that streams UDP JSON to Graylog
 type Adapter struct {
-	writer gelf.Writer
-	route  *router.Route
+	writer   gelf.Writer
+	route    *router.Route
+	hostname string
 }
 
 // NewGelfAdapter creates an Adapter with UDP as the default transport.
@@ -46,8 +47,9 @@ func NewGelfAdapter(route *router.Route) (router.LogAdapter, error) {
 	}
 
 	return &Adapter{
-		route:  route,
-		writer: gelfWriter,
+		route:    route,
+		writer:   gelfWriter,
+		hostname: getHostname(),
 	}, nil
 }
 
@@ -84,7 +86,7 @@ func (a *Adapter) Stream(logstream chan *router.Message) {
 
 		msg := gelf.Message{
 			Version:  "1.1",
-			Host:     hostname,
+			Host:     a.hostname,
 			Short:    m.Data,
 			TimeUnix: float64(m.Time.UnixNano()/int64(time.Millisecond)) / 1000.0,
 			Level:    int32(level),

adapters/gelf/gelf_test.go

@@ -188,3 +188,46 @@ func TestGelfNewAdapterUnknownTransport(t *testing.T) {
 		t.Error("expected error for unknown transport, got nil")
 	}
 }
+
+// TestGelfAdapterResolvesHostnameAtCreation is the regression test for the
+// init-order bug. The Home Assistant launcher sets SYSLOG_HOSTNAME inside
+// main(), which Go runs AFTER every package init(). Resolving the hostname in
+// init() (the old behavior) froze it to the "{{.Container.Config.Hostname}}"
+// default before the launcher could set the configured value, so that literal
+// template string was shipped as the GELF source. The adapter must read
+// SYSLOG_HOSTNAME when it is created instead.
+func TestGelfAdapterResolvesHostnameAtCreation(t *testing.T) {
+	t.Setenv("SYSLOG_HOSTNAME", "myhost.example.com")
+
+	route := &router.Route{Address: "127.0.0.1:12201"} // default udp transport
+	adapter, err := NewGelfAdapter(route)
+	if err != nil {
+		t.Fatalf("unexpected error: %v", err)
+	}
+
+	got := adapter.(*Adapter).hostname
+	if got != "myhost.example.com" {
+		t.Fatalf("expected hostname resolved from SYSLOG_HOSTNAME at creation, got %q", got)
+	}
+}
+
+// TestGelfStreamUsesAdapterHostname verifies the per-adapter hostname is stamped
+// on every emitted message's Host (the GELF source) field.
+func TestGelfStreamUsesAdapterHostname(t *testing.T) {
+	mock := &mockGelfWriter{}
+	adapter := &Adapter{writer: mock, hostname: "myhost.example.com"}
+
+	streamAndWait(adapter, &router.Message{
+		Container: newTestContainer(),
+		Data:      "hello world",
+		Source:    "stdout",
+		Time:      time.Now(),
+	})
+
+	if len(mock.messages) != 1 {
+		t.Fatalf("expected 1 message, got %d", len(mock.messages))
+	}
+	if mock.messages[0].Host != "myhost.example.com" {
+		t.Errorf("expected Host='myhost.example.com', got '%s'", mock.messages[0].Host)
+	}
+}