Relax response status code policy

The remote-write specification doesn't define the expected status code.
It extends the policy to all the successful status codes because it can't
make assumptions. There are so many implementations and the protocol
doesn't limit them to return any code.
e.g. Mimir uses a 200 OK as response status code.

Author: codebien

pkg/remote/client.go

@@ -92,10 +92,7 @@ func (c *WriteClient) Store(ctx context.Context, series []*prompb.TimeSeries) er
 	defer resp.Body.Close()
 	io.Copy(io.Discard, resp.Body) //nolint:errcheck
 
-	if resp.StatusCode != http.StatusNoContent {
-		return fmt.Errorf("got status code: %s instead expected: 204 No Content", resp.Status)
-	}
-	return nil
+	return validateResponseStatus(resp.StatusCode)
 }
 
 func newWriteRequestBody(series []*prompb.TimeSeries) ([]byte, error) {
@@ -111,3 +108,11 @@ func newWriteRequestBody(series []*prompb.TimeSeries) ([]byte, error) {
 	}
 	return snappy.Encode(nil, b), nil
 }
+
+func validateResponseStatus(code int) error {
+	if code >= http.StatusOK && code < 300 {
+		return nil
+	}
+
+	return fmt.Errorf("got status code: %d instead expected a 2xx successful status code", code)
+}

pkg/remote/client_test.go

@@ -128,7 +128,7 @@ func TestClientStoreHTTPBasic(t *testing.T) {
 			},
 		},
 	}
-	assert.Error(t, c.Store(context.Background(), nil))
+	assert.NoError(t, c.Store(context.Background(), nil))
 }
 
 func TestClientStoreHeaders(t *testing.T) {
@@ -155,7 +155,7 @@ func TestClientStoreHeaders(t *testing.T) {
 			}),
 		},
 	}
-	assert.Error(t, c.Store(context.Background(), nil))
+	assert.NoError(t, c.Store(context.Background(), nil))
 }
 
 func TestNewWriteRequestBody(t *testing.T) {
@@ -170,3 +170,23 @@ func TestNewWriteRequestBody(t *testing.T) {
 	require.NotEmpty(t, string(b))
 	assert.Contains(t, string(b), `label1`)
 }
+
+func TestValidateStatusCode(t *testing.T) {
+	t.Parallel()
+	tests := []struct {
+		status int
+		expErr bool
+	}{
+		{status: http.StatusOK, expErr: false},        // Mimir
+		{status: http.StatusNoContent, expErr: false}, // Prometheus
+		{status: http.StatusBadRequest, expErr: true},
+	}
+	for _, tt := range tests {
+		err := validateResponseStatus(tt.status)
+		if tt.expErr {
+			assert.Error(t, err)
+			continue
+		}
+		assert.NoError(t, err)
+	}
+}