git » prometheus-expvar-exporter » commit c1785e5

Auto-replace ASCII metric characters with `_` when needed

author Alberto Bertogli
2024-04-19 12:24:17 UTC
committer Alberto Bertogli
2024-04-19 12:34:25 UTC
parent 083a3ee84d0b47f31c002d1268d3fadbbfca1d17
Auto-replace ASCII metric characters with `_` when needed

Prometheus metric names must match the regex `[a-zA-Z_:][a-zA-Z0-9_:]*`.
Today, we only automatically replace `/` with `_`, and any other
non-compliant character will trigger a panic in the Prometheus
libraries.

Some characters like `-` are also common in metric names, and this
limitation adds unnecessary configuration overhead.

This patch makes the code auto-replace all ASCII characters that aren't
compatible with Prometheus' limits with `_`.

Note that non-ASCII characters will still trigger a panic. There is no
good way to handle all of them automatically, as they can't be all reasonably
mapped to ascii. In the future, we may handle _some_ of them automatically when
possible. But for now, forcing the users to be explicit is the safest option,
and also ensures forwards compatibility.

Thanks to mschirrmeister@github for reporting this issue in
https://github.com/albertito/prometheus-expvar-exporter/issues/1.
main.go +42 -1 
diff --git a/main.go b/main.go
index 8ecfbc8..4a1db22 100644
--- a/main.go
+++ b/main.go
@@ -11,6 +11,7 @@ import (
 	"net/http"
 	"regexp"
 	"strings"
+	"unicode"
 
 	"github.com/pelletier/go-toml"
 	"github.com/prometheus/client_golang/prometheus"
@@ -122,7 +123,7 @@ func (c *Collector) Collect(ch chan<- prometheus.Metric) {
 	}
 
 	for k, v := range vs {
-		name := strings.ReplaceAll(k, "/", "_")
+		name := sanitizeMetricName(k)
 		if n, ok := c.names[k]; ok {
 			name = n
 		}
@@ -181,6 +182,46 @@ func valToFloat(v interface{}) float64 {
 	panic(fmt.Sprintf("unexpected value type: %#v", v))
 }
 
+func sanitizeMetricName(n string) string {
+	// Prometheus metric names must match the regex
+	// `[a-zA-Z_:][a-zA-Z0-9_:]*`.
+	// https://prometheus.io/docs/concepts/data_model/#metric-names-and-labels
+	//
+	// This function replaces all non-matching ASCII characters with
+	// underscores.
+	//
+	// In particular, it is common that expvar names contain `/` or `-`, which
+	// we replace with `_` so they end up resembling more Prometheus-ideomatic
+	// names.
+	//
+	// Non-ascii characters are not supported, and will panic as so to force
+	// users to handle them explicitly.  There is no good way to handle all of
+	// them automatically, as they can't be all reasonably mapped to ascii. In
+	// the future, we may handle _some_ of them automatically when possible.
+	// But for now, forcing the users to be explicit is the safest option, and
+	// also ensures forwards compatibility.
+	return strings.Map(func(r rune) rune {
+		if r >= 'a' && r <= 'z' {
+			return r
+		}
+		if r >= 'A' && r <= 'Z' {
+			return r
+		}
+		if r >= '0' && r <= '9' {
+			return r
+		}
+		if r == '_' || r == ':' {
+			return r
+		}
+		if r > unicode.MaxASCII {
+			panic(fmt.Sprintf(
+				"non-ascii character %q is unsupported, please configure the metric %q explicitly",
+				r, n))
+		}
+		return '_'
+	}, n)
+}
+
 const indexHTML = `<!DOCTYPE html>
 <html lang="en">
   <head>