fix(anonymizer): truncate output files on open to prevent stale JSON

When running the anonymizer tool multiple times pointing to the same
output paths, the files were opened with O_CREATE|O_WRONLY but without
O_TRUNC. This means any previous content is kept in place and new data
is written on top. If the new output happens to be shorter than the old
one, the leftover bytes at the end produce malformed JSON that cannot
be parsed.

Added os.O_TRUNC to all three os.OpenFile calls across writer.go and
extractor.go so the file is always zeroed out before writing begins.

Fixes: #8231

Signed-off-by: Sakthi Harish <sakthi.harish@edgeverve.com>

Author: Retr0-XD

cmd/anonymizer/app/uiconv/extractor.go

@@ -24,7 +24,7 @@ type extractor struct {
 
 // newExtractor creates extractor.
 func newExtractor(uiFile string, traceID string, reader *spanReader, logger *zap.Logger) (*extractor, error) {
-	f, err := os.OpenFile(uiFile, os.O_CREATE|os.O_WRONLY, os.ModePerm)
+	f, err := os.OpenFile(uiFile, os.O_CREATE|os.O_WRONLY|os.O_TRUNC, os.ModePerm)
 	if err != nil {
 		return nil, fmt.Errorf("cannot create output file: %w", err)
 	}

cmd/anonymizer/app/writer/writer.go

@@ -48,13 +48,13 @@ func New(config Config, logger *zap.Logger) (*Writer, error) {
 	}
 	logger.Sugar().Infof("Current working dir is %s", wd)
 
-	cf, err := os.OpenFile(config.CapturedFile, os.O_CREATE|os.O_WRONLY, os.ModePerm)
+	cf, err := os.OpenFile(config.CapturedFile, os.O_CREATE|os.O_WRONLY|os.O_TRUNC, os.ModePerm)
 	if err != nil {
 		return nil, fmt.Errorf("cannot create output file: %w", err)
 	}
 	logger.Sugar().Infof("Writing captured spans to file %s", config.CapturedFile)
 
-	af, err := os.OpenFile(config.AnonymizedFile, os.O_CREATE|os.O_WRONLY, os.ModePerm)
+	af, err := os.OpenFile(config.AnonymizedFile, os.O_CREATE|os.O_WRONLY|os.O_TRUNC, os.ModePerm)
 	if err != nil {
 		return nil, fmt.Errorf("cannot create output file: %w", err)
 	}