From 20c99e7aa07352b599bd0517cd5ca945f4af0407 Mon Sep 17 00:00:00 2001
From: Jarod Watkins <jwatkins@jarodw.com>
Date: Mon, 9 Nov 2020 12:08:19 -0500
Subject: [PATCH] Add unique label validation (#263)

* Add unique label validation

Originally created as a PR in the
[client_golang](https://github.com/prometheus/client_golang/pull/812)
repo however was suggested to move it here.

Signed-off-by: Jarod Watkins <jarod@42lines.net>
---
 expfmt/text_parse.go      | 11 +++++++++++
 expfmt/text_parse_test.go |  5 +++++
 2 files changed, 16 insertions(+)

diff --git a/expfmt/text_parse.go b/expfmt/text_parse.go
index 342e5940..b6079b31 100644
--- a/expfmt/text_parse.go
+++ b/expfmt/text_parse.go
@@ -299,6 +299,17 @@ func (p *TextParser) startLabelName() stateFn {
 		p.parseError(fmt.Sprintf("expected '=' after label name, found %q", p.currentByte))
 		return nil
 	}
+	// Check for duplicate label names.
+	labels := make(map[string]struct{})
+	for _, l := range p.currentMetric.Label {
+		lName := l.GetName()
+		if _, exists := labels[lName]; !exists {
+			labels[lName] = struct{}{}
+		} else {
+			p.parseError(fmt.Sprintf("duplicate label names for metric %q", p.currentMF.GetName()))
+			return nil
+		}
+	}
 	return p.startLabelValue
 }
 
diff --git a/expfmt/text_parse_test.go b/expfmt/text_parse_test.go
index ba23c55d..949bbd64 100644
--- a/expfmt/text_parse_test.go
+++ b/expfmt/text_parse_test.go
@@ -635,6 +635,11 @@ metric{quantile="0x1p-3"} 3.14
 `,
 			err: "text format parsing error in line 3: expected float as value for 'quantile' label",
 		},
+		// 33: Check duplicate label.
+		{
+			in:  `metric{label="bla",label="bla"} 3.14`,
+			err: "text format parsing error in line 1: duplicate label names for metric",
+		},
 	}
 
 	for i, scenario := range scenarios {