fix: Unset Content-Encoding header when uncompressed

mrueg · mrueg · commit f7f8f3a1e2c0 · 2024-08-23T18:53:42.000+02:00
Fixes: #1595 Signed-off-by: Manuel Rüger <manuel@rueg.eu>
diff --git a/prometheus/promhttp/http.go b/prometheus/promhttp/http.go
@@ -203,8 +203,10 @@ func HandlerForTransactional(reg prometheus.TransactionalGatherer, opts HandlerO
 
 		defer closeWriter()
 
-		rsp.Header().Set(contentEncodingHeader, encodingHeader)
-
+		// Set Content-Encoding only when data is compressed
+		if encodingHeader != string(Identity) {
+			rsp.Header().Set(contentEncodingHeader, encodingHeader)
+		}
 		enc := expfmt.NewEncoder(w, contentType)
 
 		// handleError handles the error according to opts.ErrorHandling
diff --git a/prometheus/promhttp/http_test.go b/prometheus/promhttp/http_test.go
@@ -267,7 +267,7 @@ func TestInstrumentMetricHandler(t *testing.T) {
 		t.Errorf("got HTTP status code %d, want %d", got, want)
 	}
 
-	if got, want := writer.Header().Get(contentEncodingHeader), string(Identity); got != want {
+	if got, want := writer.Header().Get(contentEncodingHeader), ""; got != want {
 		t.Errorf("got HTTP content encoding header %s, want %s", got, want)
 	}
 

Original file line number	Diff line number	Diff line change
`@@ -267,7 +267,7 @@ func TestInstrumentMetricHandler(t *testing.T) {`
`267`	`267`	`t.Errorf("got HTTP status code %d, want %d", got, want)`
`268`	`268`	`}`
`269`	`269`
`270`		`- if got, want := writer.Header().Get(contentEncodingHeader), string(Identity); got != want {`
	`270`	`+ if got, want := writer.Header().Get(contentEncodingHeader), ""; got != want {`
`271`	`271`	`t.Errorf("got HTTP content encoding header %s, want %s", got, want)`
`272`	`272`	`}`
`273`	`273`