From 1a4c672ac32330718797183ec4ef9f1bb2a75fa2 Mon Sep 17 00:00:00 2001
From: Alberto Bertogli <albertito@blitiri.com.ar>
Date: Mon, 2 Feb 2026 19:21:41 +0000
Subject: [PATCH] expvarom: Remove empty newlines and comments to conform to
 stricter parsing
MIME-Version: 1.0
Content-Type: text/plain; charset=UTF-8
Content-Transfer-Encoding: 8bit

The openmetrics format doesn't support empty newlines or miscellaneous
comments, and the Prometheus parser has become more strict over time,
which is now causing scraping errors.

This patch fixes those issues by adjusting to the stricter openmetrics
format.

Thanks to Jakub Ječmínek for reporting this issue!
---
 internal/expvarom/expvarom.go      | 12 ++++--------
 internal/expvarom/expvarom_test.go | 17 ++---------------
 2 files changed, 6 insertions(+), 23 deletions(-)

diff --git a/internal/expvarom/expvarom.go b/internal/expvarom/expvarom.go
index 12f9ce2..6197cc7 100644
--- a/internal/expvarom/expvarom.go
+++ b/internal/expvarom/expvarom.go
@@ -98,9 +98,8 @@ func MetricsHandler(w http.ResponseWriter, r *http.Request) {
 		writeVar(w, &v)
 	}
 
-	fmt.Fprintf(w, "# Generated by expvarom\n")
-	fmt.Fprintf(w, "# EXPERIMENTAL - Format is not fully standard yet\n")
-	fmt.Fprintf(w, "# Ignored variables: %q\n", ignored)
+	fmt.Fprintf(w, "# HELP generated_by expvarom\n")
+	fmt.Fprintf(w, "# HELP ignored_variables %q\n", ignored)
 	fmt.Fprintf(w, "# EOF\n") // Mandated by the standard.
 }
 
@@ -110,12 +109,12 @@ func writeVar(w io.Writer, v *exportedVar) {
 	}
 
 	if v.I != nil {
-		fmt.Fprintf(w, "%s %d\n\n", v.Name, v.I.Value())
+		fmt.Fprintf(w, "%s %d\n", v.Name, v.I.Value())
 		return
 	}
 
 	if v.F != nil {
-		fmt.Fprintf(w, "%s %g\n\n", v.Name, v.F.Value())
+		fmt.Fprintf(w, "%s %g\n", v.Name, v.F.Value())
 		return
 	}
 
@@ -139,9 +138,6 @@ func writeVar(w io.Writer, v *exportedVar) {
 				v.Name, v.LabelName, labelValue, vs)
 			count++
 		})
-		if count > 0 {
-			fmt.Fprintf(w, "\n")
-		}
 	}
 }
 
diff --git a/internal/expvarom/expvarom_test.go b/internal/expvarom/expvarom_test.go
index b375ed9..b4be539 100644
--- a/internal/expvarom/expvarom_test.go
+++ b/internal/expvarom/expvarom_test.go
@@ -36,24 +36,16 @@ var (
 )
 
 const expected string = `_ame_5 5
-
 i3name 3
-
 nAme_4Z 4
-
 name_1z 1
-
 # HELP name_2 name with $
 name_2 2
-
 # HELP testF float test var
 testF 3.43434
-
 # HELP testI1 int test var
 testI1 1
-
 testI2 2
-
 # HELP testMF float map test var
 testMF{label="key2.0"} 6.6
 testMF{label="key2.1"} 6.61
@@ -63,17 +55,12 @@ testMF{label="key2.4-	"} 6.64
 testMF{label="key2.5-a\nb"} 6.65
 testMF{label="key2.6-a\"b"} 6.66
 testMF{label="key2.7-\\u00f1aca-A\\t\\xff\\xfe\\xfdB"} 6.67
-
 # HELP testMI int map test var
 testMI{label="key1"} 5
-
 testMXF{key="key4"} 8e-08
-
 testMXI{key="key3"} 7
-
-# Generated by expvarom
-# EXPERIMENTAL - Format is not fully standard yet
-# Ignored variables: ["cmdline" "memstats" "testS"]
+# HELP generated_by expvarom
+# HELP ignored_variables ["cmdline" "memstats" "testS"]
 # EOF
 `