Maintain log buffer and flush errors at the end

cmd/helpers/extractorBuilder.go

@@ -33,49 +33,49 @@ func BuildExtractorFromArguments(c *cli.Context) *extractor.Extractor {
 	if ignoreSlice != nil && len(ignoreSlice) > 0 {
 		ignoreExp, err := extractor.NewIgnoreExpressions(ignoreSlice...)
 		if err != nil {
-			stderrLog.Panicln(err)
+			ErrLog.Panicln(err)
 		}
 		config.Ignore = ignoreExp
 	}
 
 	if batchSize < 1 {
-		stderrLog.Fatalf("Batch size must be >= 1, is %d\n", batchSize)
+		ErrLog.Fatalf("Batch size must be >= 1, is %d\n", batchSize)
 	}
 
 	fileglobs := c.Args()
 
 	if len(fileglobs) == 0 || fileglobs[0] == "-" { // Read from stdin
 		ret, err := extractor.New(extractor.ConvertReaderToStringChan(os.Stdin, batchSize), &config)
 		if err != nil {
-			stderrLog.Panicln(err)
+			ErrLog.Panicln(err)
 		}
 		StartFileReading("<stdin>")
 		return ret
 	} else if follow { // Read from source file
 		if gunzip {
-			stderrLog.Println("Cannot combine -f and -z")
+			ErrLog.Println("Cannot combine -f and -z")
 		}
 
 		tailChannels := make([]<-chan []extractor.BString, 0)
 		for _, filename := range globExpand(fileglobs, recursive) {
 			tail, err := tail.TailFile(filename, tail.Config{Follow: true, ReOpen: followReopen, Poll: followPoll})
 
 			if err != nil {
-				stderrLog.Fatal("Unable to open file: ", err)
+				ErrLog.Fatal("Unable to open file: ", err)
 			}
 			tailChannels = append(tailChannels, tailLineToChan(tail.Lines, batchSize))
 			StartFileReading(filename)
 		}
 
 		ret, err := extractor.New(extractor.CombineChannels(tailChannels...), &config)
 		if err != nil {
-			stderrLog.Panicln(err)
+			ErrLog.Panicln(err)
 		}
 		return ret
 	} else { // Read (no-follow) source file(s)
 		ret, err := extractor.New(openFilesToChan(globExpand(fileglobs, recursive), gunzip, concurrentReaders, batchSize), &config)
 		if err != nil {
-			stderrLog.Panicln(err)
+			ErrLog.Panicln(err)
 		}
 		return ret
 	}
@@ -144,6 +144,18 @@ func AdaptCommandForExtractor(command cli.Command) *cli.Command {
 	if command.ArgsUsage == "" {
 		command.ArgsUsage = DefaultArgumentDescriptor
 	}
+
+	// While this doesn't own the log, this is the last place
+	// that has the option to flush the log buffer to sderr
+	originalAfter := command.After
+	command.After = func(c *cli.Context) error {
+		DisableAndFlushLogBuffer()
+		if originalAfter != nil {
+			return originalAfter(c)
+		}
+		return nil
+	}
+
 	return &command
 }
 

cmd/helpers/log.go

@@ -1,8 +1,36 @@
 package helpers
 
 import (
+	"bytes"
 	"log"
 	"os"
 )
 
-var stderrLog = log.New(os.Stderr, "[Log] ", 0)
+var ErrLog *log.Logger
+
+const logPrefix = "[Log] "
+
+var logBuffer *bytes.Buffer
+
+func resetLog() {
+	ErrLog = log.New(os.Stderr, "[Log] ", 0)
+}
+
+func init() {
+	resetLog()
+}
+
+func EnableLogBuffer() {
+	if logBuffer == nil {
+		logBuffer = new(bytes.Buffer)
+		ErrLog = log.New(logBuffer, logPrefix, 0)
+	}
+}
+
+func DisableAndFlushLogBuffer() {
+	if logBuffer != nil {
+		os.Stderr.Write(logBuffer.Bytes())
+		logBuffer = nil
+		resetLog()
+	}
+}

cmd/helpers/readChannels.go

@@ -54,7 +54,7 @@ func openFileToReader(filename string, gunzip bool) (io.ReadCloser, error) {
 	if gunzip {
 		zfile, err := gzip.NewReader(file)
 		if err != nil {
-			stderrLog.Printf("Gunzip error for file %s: %v\n", filename, err)
+			ErrLog.Printf("Gunzip error for file %s: %v\n", filename, err)
 		} else {
 			file = zfile
 		}
@@ -79,7 +79,7 @@ func openFilesToChan(filenames []string, gunzip bool, concurrency int, batchSize
 				var file io.ReadCloser
 				file, err := openFileToReader(goFilename, gunzip)
 				if err != nil {
-					stderrLog.Printf("Error opening file %s: %v\n", goFilename, err)
+					ErrLog.Printf("Error opening file %s: %v\n", goFilename, err)
 					return
 				}
 				defer file.Close()
@@ -127,7 +127,7 @@ func globExpand(paths []string, recursive bool) []string {
 		} else {
 			expanded, err := filepath.Glob(p)
 			if err != nil {
-				stderrLog.Printf("Path error: %v\n", err)
+				ErrLog.Printf("Path error: %v\n", err)
 			} else {
 				out = append(out, expanded...)
 			}

cmd/helpers/updatingAggregator.go

@@ -22,6 +22,7 @@ import (
 func RunAggregationLoop(ext *extractor.Extractor, aggregator aggregation.Aggregator, writeOutput func()) {
 
 	defer multiterm.ResetCursor()
+	EnableLogBuffer()
 
 	// Updater sync variables
 	outputDone := make(chan bool)