Add RBE metrics dump in Soong UI.

From aosp/1329396, the RBE metrics protobuf file is part of the
metrics uploading process. The RBE metrics protobuf file is
generated by running the bootstrap shutdown command. A new function
named DumpRBEMetrics was written in order to generate the RBE metrics
protobuf file before sending to the uploading process.

Bug: b/140638454
Test: * Unit test cases
      * Ran RBE build on my local host and verified the
        metrics protobuf file is created.
      * Ran non-RBE build after RBE build and verified that
        the previous metrics protobuf file was deleted.

Change-Id: I4b8068905cb67c4b8c2d94793917b98974fed707
diff --git a/ui/build/rbe.go b/ui/build/rbe.go
index ceea4bf..fcdab3b 100644
--- a/ui/build/rbe.go
+++ b/ui/build/rbe.go
@@ -15,14 +15,39 @@
 package build
 
 import (
+	"os"
 	"path/filepath"
 
 	"android/soong/ui/metrics"
 )
 
-const bootstrapCmd = "bootstrap"
-const rbeLeastNProcs = 2500
-const rbeLeastNFiles = 16000
+const (
+	rbeLeastNProcs = 2500
+	rbeLeastNFiles = 16000
+
+	// prebuilt RBE binaries
+	bootstrapCmd = "bootstrap"
+
+	// RBE metrics proto buffer file
+	rbeMetricsPBFilename = "rbe_metrics.pb"
+)
+
+func rbeCommand(ctx Context, config Config, rbeCmd string) string {
+	var cmdPath string
+	if rbeDir, ok := config.Environment().Get("RBE_DIR"); ok {
+		cmdPath = filepath.Join(rbeDir, rbeCmd)
+	} else if home, ok := config.Environment().Get("HOME"); ok {
+		cmdPath = filepath.Join(home, "rbe", rbeCmd)
+	} else {
+		ctx.Fatalf("rbe command path not found")
+	}
+
+	if _, err := os.Stat(cmdPath); err != nil && os.IsNotExist(err) {
+		ctx.Fatalf("rbe command %q not found", rbeCmd)
+	}
+
+	return cmdPath
+}
 
 func startRBE(ctx Context, config Config) {
 	ctx.BeginTrace(metrics.RunSetupTool, "rbe_bootstrap")
@@ -35,18 +60,50 @@
 		ctx.Fatalf("max open files is insufficient: %d; want >= %d.\n", n, rbeLeastNFiles)
 	}
 
-	var rbeBootstrap string
-	if rbeDir, ok := config.Environment().Get("RBE_DIR"); ok {
-		rbeBootstrap = filepath.Join(rbeDir, bootstrapCmd)
-	} else if home, ok := config.Environment().Get("HOME"); ok {
-		rbeBootstrap = filepath.Join(home, "rbe", bootstrapCmd)
-	} else {
-		ctx.Fatalln("rbe bootstrap not found")
-	}
-
-	cmd := Command(ctx, config, "boostrap", rbeBootstrap)
+	cmd := Command(ctx, config, "startRBE bootstrap", rbeCommand(ctx, config, bootstrapCmd))
 
 	if output, err := cmd.CombinedOutput(); err != nil {
 		ctx.Fatalf("rbe bootstrap failed with: %v\n%s\n", err, output)
 	}
 }
+
+func stopRBE(ctx Context, config Config) {
+	cmd := Command(ctx, config, "stopRBE bootstrap", rbeCommand(ctx, config, bootstrapCmd), "-shutdown")
+	if output, err := cmd.CombinedOutput(); err != nil {
+		ctx.Fatalf("rbe bootstrap with shutdown failed with: %v\n%s\n", err, output)
+	}
+}
+
+// DumpRBEMetrics creates a metrics protobuf file containing RBE related metrics.
+// The protobuf file is created if RBE is enabled and the proxy service has
+// started. The proxy service is shutdown in order to dump the RBE metrics to the
+// protobuf file.
+func DumpRBEMetrics(ctx Context, config Config, filename string) {
+	ctx.BeginTrace(metrics.RunShutdownTool, "dump_rbe_metrics")
+	defer ctx.EndTrace()
+
+	// Remove the previous metrics file in case there is a failure or RBE has been
+	// disable for this run.
+	os.Remove(filename)
+
+	// If RBE is not enabled then there are no metrics to generate.
+	// If RBE does not require to start, the RBE proxy maybe started
+	// manually for debugging purpose and can generate the metrics
+	// afterwards.
+	if !config.StartRBE() {
+		return
+	}
+
+	outputDir := config.RBEStatsOutputDir()
+	if outputDir == "" {
+		ctx.Fatal("RBE output dir variable not defined. Aborting metrics dumping.")
+	}
+	metricsFile := filepath.Join(outputDir, rbeMetricsPBFilename)
+
+	// Stop the proxy first in order to generate the RBE metrics protobuf file.
+	stopRBE(ctx, config)
+
+	if _, err := copyFile(metricsFile, filename); err != nil {
+		ctx.Fatalf("failed to copy %q to %q: %v\n", metricsFile, filename, err)
+	}
+}