Adding logging + logic to migrating seq num (#200)

* adding logging

* addressing comments

* cleanup tests

* nit change

* remove install failed logic

* nit error msg change

* fix unit tests

main/cmds.go

@@ -72,7 +72,7 @@ func install(ctx *log.Context, h HandlerEnvironment, seqNum int) (string, error)
 	// If it is (2) attempt to migrate to mrseq.  Find the latest settings
 	// file, and set the sequence to it.
 	if _, err := os.Stat(mostRecentSequence); os.IsNotExist(err) {
-		migrateToMostRecentSequence(ctx, h, seqNum)
+		migrateToMostRecentSequence(ctx, seqNum)
 	}
 
 	ctx.Log("event", "created data dir", "path", dataDir)
@@ -80,36 +80,28 @@ func install(ctx *log.Context, h HandlerEnvironment, seqNum int) (string, error)
 	return "", nil
 }
 
-func migrateToMostRecentSequence(ctx *log.Context, h HandlerEnvironment, seqNum int) {
-	// The status folder is used instead of the settings because the settings file is written
-	// by the agent before install is called.  As a result, the extension cannot determine if this
-	// is a new install or an upgrade.
-	//
-	// If this is an upgrade there will be a status file. The agent will re-write the last status
-	// file to indicate that the upgrade happened successfully. The extension uses the last status
-	// sequence number to determine the last settings file that was executed.
-	//
-	// The agent helpfully copies mrseq every time an extension is upgraded thereby preserving the
-	// most recent executed sequence. If extensions use mrseq they benefit from this mechanism, and
-	// do not have invent another method.  The CustomScript extension should have been using this
-	// from the beginning, but it was not.
-	//
-	computedSeqNum, err := FindSeqNumStatus(h.HandlerEnvironment.StatusFolder)
-	if err != nil {
-		// If there was an error, the sequence number is zero.
-		ctx.Log("event", "migrate to mrseq", "error", err)
-		return
-	}
-
+func migrateToMostRecentSequence(ctx *log.Context, seqNum int) {
+	// The configSequenceNumber (seqNum) env variable is used for mrseq if mrseq not found
+	// based on logic in main.go the seqNum should always be populated
+	ctx.Log("event", "recreate mrseq", "message", fmt.Sprintf("cannot find %v", mostRecentSequence))
 	fout, err := os.Create(mostRecentSequence)
 	if err != nil {
-		ctx.Log("event", "migrate to mrseq", "error", err)
+		ctx.Log("event", "error creating sequence file", "error", err)
 		return
 	}
 	defer fout.Close()
 
-	ctx.Log("event", "migrate to mrseq", "message", fmt.Sprintf("migrated mrseq to %v", computedSeqNum))
-	fout.WriteString(fmt.Sprintf("%v", computedSeqNum))
+	if seqNum != 0 {
+		_, err := fout.WriteString(fmt.Sprintf("%v", seqNum))
+		if err != nil {
+			ctx.Log("event", "error writing to sequence file", "error", err)
+			return
+		}
+		ctx.Log("event", "recreate mrseq", "message", fmt.Sprintf("recreating mrseq with configSeqNum %v", seqNum))
+		return
+	}
+
+	ctx.Log("event", "recreate mrseq", "message", "seq number is 0")
 }
 
 func uninstall(ctx *log.Context, h HandlerEnvironment, seqNum int) (string, error) {
@@ -203,6 +195,7 @@ func checkAndSaveSeqNum(ctx log.Logger, seq int, mrseqPath string) (shouldExit b
 		// sequence number.
 		return true, nil
 	}
+	ctx.Log("event", "mrseq not found", "message", "attempting to save config seqnum")
 	if err := seqnum.Set(mrseqPath, seq); err != nil {
 		return false, errors.Wrap(err, "failed to save sequence number")
 	}

main/cmds_test.go

@@ -151,3 +151,19 @@ func Test_decodeScriptGzip(t *testing.T) {
 	require.Equal(t, info, "32;3;gzip=1")
 	require.Equal(t, s, "ls\n")
 }
+
+func Test_migrateToMostRecentSequence(t *testing.T) {
+	ctx := log.NewContext(log.NewSyncLogger(log.NewLogfmtLogger(
+		os.Stdout))).With("time", log.DefaultTimestamp).With("version", VersionString())
+
+	seqNum := 1
+
+	migrateToMostRecentSequence(ctx, seqNum)
+
+	content, err := ioutil.ReadFile("mrseq")
+	require.Nil(t, err)
+	require.Equal(t, "1", string(content))
+
+	//cleanup
+	_ = os.Remove("mrseq")
+}