Fix race condition when writing JSON output

1 files changed, 8 insertions, 1 deletions

diff --git a/modules/output/ndjson/ndjson.go b/modules/output/ndjson/ndjson.go
index 956b2ed..a24aaa6 100644
--- a/modules/output/ndjson/ndjson.go
+++ b/modules/output/ndjson/ndjson.go
@@ -9,6 +9,7 @@ import (
 	"io"
 	"log"
 	"os"
+	"sync"
 	"time"
 
 	"github.com/philippta/flyscrape"
@@ -24,7 +25,8 @@ type Module struct {
 		File   string `json:"file"`
 	} `json:"output"`
 
-	w io.WriteCloser
+	w  io.WriteCloser
+	mu *sync.Mutex
 }
 
 func (Module) ModuleInfo() flyscrape.ModuleInfo {
@@ -39,6 +41,8 @@ func (m *Module) Provision(ctx flyscrape.Context) {
 		return
 	}
 
+	m.mu = &sync.Mutex{}
+
 	if m.Output.File == "" {
 		m.w = nopCloser{os.Stdout}
 		return
@@ -70,6 +74,9 @@ func (m *Module) ReceiveResponse(resp *flyscrape.Response) {
 		o.Error = resp.Error.Error()
 	}
 
+	m.mu.Lock()
+	defer m.mu.Unlock()
+
 	enc := json.NewEncoder(m.w)
 	enc.SetEscapeHTML(false)
 	enc.Encode(o)