Fix metrics broken by comma and equal in labels

The logic for turning a key back into the labelles that defined it would
not account for the labels values possibly including a comma or equal
sign, which in turn broke the logic for handling these metrics.

Fix by properly parsing the keys.

packages/lib/src/prometheus.ts

@@ -272,18 +272,27 @@ function labelsToKey(labels: LabelValues, metricLabels: string[]) {
 function keyToLabels(key: string) {
 	let labels = new Map<string, string>();
 
-	if (key !== "") {
-		for (let pair of key.split(",")) {
-			let [name, value] = pair.split("=", 2);
-			if (!name || value === undefined) {
-				continue;
+	let pos = 0;
+	let matchLabel = /([^=]+)="(([^\\"]|\\["n\\])+)"/y;
+	while (pos < key.length) {
+		if (pos !== 0) {
+			if (key[pos] !== ",") {
+				throw Error(`Expected , at pos ${pos} in "${key}"`);
 			}
+			pos += 1;
+		}
+		matchLabel.lastIndex = pos;
+		const match = matchLabel.exec(key);
+		if (match) {
+			let [, name, value] = match;
 			labels.set(name, value
-				.slice(1, -1)
 				.replace(/\\"/g, "\"")
 				.replace(/\\n/g, "\n")
 				.replace(/\\\\/g, "\\")
 			);
+			pos += match[0].length;
+		} else {
+			throw new Error(`Failed to parse label at pos ${pos} in "${key}"`);
 		}
 	}
 

test/lib/prometheus.js

@@ -651,8 +651,21 @@ describe("lib/prometheus", function() {
 				let gauge = new prometheus.Gauge(
 					"test", "Help", { register: false, labels: ["a", "b"] }
 				);
-				gauge.labels('x\\\\\n\"\"\n\\', "2");
-				gauge.removeAll({ a: 'x\\\\\n\"\"\n\\' });
+
+				let labelValue = "";
+				for (let i = 0; i < 128; i++) {
+					const char = String.fromCodePoint(i);
+					if (!/[1-9B-Zb-z]/.test(char)) { // exclude boring characters
+						labelValue += char;
+					}
+				}
+				labelValue += "©💣";
+
+				gauge.labels(labelValue, "2");
+				gauge.removeAll({ a: labelValue });
+				assert(gauge._values.size === 0, "Matching labels remained");
+				gauge.labels("1", labelValue);
+				gauge.removeAll({ a: "1" });
 				assert(gauge._values.size === 0, "Matching labels remained");
 			});
 		});