Introduce reqContext for cli

License: MIT
Signed-off-by: Jakub Sztandera <kubuxu@protonmail.ch>

cli/cmd.go

@@ -1,17 +1,47 @@
 package cli
 
 import (
+	"context"
+	"os"
+	"os/signal"
+	"syscall"
+
 	"github.com/filecoin-project/go-lotus/api"
 	"gopkg.in/urfave/cli.v2"
 )
 
+const (
+	metadataContext = "context"
+	metadataAPI     = "api"
+)
+
+// ApiConnector returns API instance
 type ApiConnector func() api.API
 
 func getApi(ctx *cli.Context) api.API {
-	return ctx.App.Metadata["api"].(ApiConnector)()
+	return ctx.App.Metadata[metadataAPI].(ApiConnector)()
+}
+
+// reqContext returns context for cli execution. Calling it for the first time
+// installs SIGTERM handler that will close returned context.
+// Not safe for concurrent execution.
+func reqContext(cctx *cli.Context) context.Context {
+	if uctx, ok := cctx.App.Metadata[metadataContext]; ok {
+		// unchecked cast as if somethign else is in there
+		// it is crash worthy either way
+		return uctx.(context.Context)
+	}
+	ctx, done := context.WithCancel(context.Background())
+	sigChan := make(chan os.Signal, 2)
+	go func() {
+		<-sigChan
+		done()
+	}()
+	signal.Notify(sigChan, syscall.SIGTERM, syscall.SIGINT)
+
+	return ctx
 }
 
-// Commands is the root group of CLI commands
 var Commands = []*cli.Command{
 	netCmd,
 	versionCmd,