implement context cancellation on db error

pkg/lines/lines.go

@@ -1,6 +1,7 @@
 package lines
 
 import (
+	"context"
 	"log"
 	"sync"
 
@@ -23,7 +24,7 @@ type (
 )
 
 // assumes all lines are from same file
-func (unparsed RawC) Process(bufferLimitBytes int, parsed chan<- m.Record) {
+func (unparsed RawC) Process(ctx context.Context, bufferLimitBytes int, parsed chan<- m.Record) {
 	lines := make(chan singleLine)
 	go unparsed.parse(lines)
 
@@ -32,34 +33,42 @@ func (unparsed RawC) Process(bufferLimitBytes int, parsed chan<- m.Record) {
 
 	stdOut, stdErr := make(chan singleLine), make(chan singleLine)
 	go func() {
-		singleLines(stdOut).process(bufferLimitBytes, parsed)
+		singleLines(stdOut).process(ctx, bufferLimitBytes, parsed)
 		wg.Done()
 	}()
 	go func() {
-		singleLines(stdErr).process(bufferLimitBytes, parsed)
+		singleLines(stdErr).process(ctx, bufferLimitBytes, parsed)
 		wg.Done()
 	}()
 
+	defer func() {
+		close(stdOut)
+		close(stdErr)
+		wg.Wait()
+		close(parsed)
+	}()
+
 	// split stdout and stderr
 	for {
-		line, ok := <-lines
-		if !ok {
-			close(stdOut)
-			close(stdErr)
-			wg.Wait()
-			close(parsed)
+		select {
+		case <-ctx.Done():
 			return
-		}
 
-		if line.StdErr {
-			stdErr <- line
-		} else {
-			stdOut <- line
+		case line, ok := <-lines:
+			if !ok {
+				return
+			}
+
+			if line.StdErr {
+				stdErr <- line
+			} else {
+				stdOut <- line
+			}
 		}
 	}
 }
 
-func (lines singleLines) process(bufferLimitBytes int, parsed chan<- m.Record) {
+func (lines singleLines) process(ctx context.Context, bufferLimitBytes int, parsed chan<- m.Record) {
 	var firstMetadata *m.ParsedMetadata
 	var buffer []byte
 
@@ -86,12 +95,17 @@ func (lines singleLines) process(bufferLimitBytes int, parsed chan<- m.Record) {
 		}
 
 		if !line.partial {
-			parsed <- m.Record{
+			select {
+			case <-ctx.Done():
+				return
+
+			case parsed <- m.Record{
 				File:   line.File.File,
 				Offset: line.Offset,
 
 				String:         string(buffer),
 				ParsedMetadata: *firstMetadata,
+			}:
 			}
 
 			buffer = nil