feat: i guess we're undoing agent work

cmd/hp_agent/hp_agent.go

@@ -1,15 +1,27 @@
 package main
 
 import (
+	"bufio"
 	"context"
 	"encoding/json"
 	"os"
+	"os/signal"
+	"syscall"
 
 	"github.com/tale/headplane/internal/config"
 	"github.com/tale/headplane/internal/tsnet"
 	"github.com/tale/headplane/internal/util"
 )
 
+type output struct {
+	Self  string                     `json:"self"`
+	Hosts map[string]json.RawMessage `json:"hosts"`
+}
+
+type errorOutput struct {
+	Error string `json:"error"`
+}
+
 func main() {
 	log := util.GetLogger()
 	cfg, err := config.Load()
@@ -23,21 +35,30 @@ func main() {
 
 	agent.Connect()
 
-	hosts, err := agent.FetchAllHostInfo(context.Background())
-	if err != nil {
-		log.Fatal("Failed to fetch host info: %s", err)
-	}
-
-	output := struct {
-		Self  string                     `json:"self"`
-		Hosts map[string]json.RawMessage `json:"hosts"`
-	}{
-		Self:  agent.ID,
-		Hosts: hosts,
-	}
-
 	enc := json.NewEncoder(os.Stdout)
-	if err := enc.Encode(output); err != nil {
-		log.Fatal("Failed to encode result: %s", err)
+	scanner := bufio.NewScanner(os.Stdin)
+
+	// Shut down cleanly on signal or stdin close
+	sigCh := make(chan os.Signal, 1)
+	signal.Notify(sigCh, syscall.SIGTERM, syscall.SIGINT)
+
+	go func() {
+		<-sigCh
+		agent.Shutdown()
+		os.Exit(0)
+	}()
+
+	// Each line on stdin triggers a sync. The line content is ignored.
+	for scanner.Scan() {
+		hosts, err := agent.FetchAllHostInfo(context.Background())
+		if err != nil {
+			enc.Encode(errorOutput{Error: err.Error()})
+			continue
+		}
+
+		enc.Encode(output{
+			Self:  agent.ID,
+			Hosts: hosts,
+		})
 	}
 }