Fixing culture in PrometheusMetricBuilder (#839)

Co-authored-by: Cijo Thomas <cithomas@microsoft.com>

src/OpenTelemetry.Exporter.Prometheus/AssemblyInfo.cs

@@ -13,3 +13,10 @@
 // See the License for the specific language governing permissions and
 // limitations under the License.
 // </copyright>
+using System.Runtime.CompilerServices;
+
+#if SIGNED
+[assembly: InternalsVisibleTo("OpenTelemetry.Exporter.Prometheus.Tests, PublicKey=002400000480000094000000060200000024000052534131000400000100010051c1562a090fb0c9f391012a32198b5e5d9a60e9b80fa2d7b434c9e5ccb7259bd606e66f9660676afc6692b8cdc6793d190904551d2103b7b22fa636dcbb8208839785ba402ea08fc00c8f1500ccef28bbf599aa64ffb1e1d5dc1bf3420a3777badfe697856e9d52070a50c3ea5821c80bef17ca3acffa28f89dd413f096f898")]
+#else
+[assembly: InternalsVisibleTo("OpenTelemetry.Exporter.Prometheus.Tests")]
+#endif

src/OpenTelemetry.Exporter.Prometheus/Implementation/PrometheusMetricBuilder.cs

@@ -15,6 +15,7 @@
 // </copyright>
 using System;
 using System.Collections.Generic;
+using System.Globalization;
 using System.IO;
 using System.Linq;
 using System.Text;
@@ -163,7 +164,7 @@ namespace OpenTelemetry.Exporter.Prometheus.Implementation
                 // standard numerical values, Nan, +Inf, and -Inf are valid values representing not a number,
                 // positive infinity, and negative infinity, respectively.
                 writer.Write(" ");
-                writer.Write(m.Value);
+                writer.Write(m.Value.ToString(CultureInfo.InvariantCulture));
                 writer.Write(" ");
 
                 // The timestamp is an int64 (milliseconds since epoch, i.e. 1970-01-01 00:00:00 UTC, excluding

test/OpenTelemetry.Exporter.Prometheus.Tests/Implementation/PrometheusMetricBuilderTests.cs

@@ -0,0 +1,62 @@
+// <copyright file="PrometheusMetricBuilderTests.cs" company="OpenTelemetry Authors">
+// Copyright The OpenTelemetry Authors
+//
+// Licensed under the Apache License, Version 2.0 (the "License");
+// you may not use this file except in compliance with the License.
+// You may obtain a copy of the License at
+//
+//     http://www.apache.org/licenses/LICENSE-2.0
+//
+// Unless required by applicable law or agreed to in writing, software
+// distributed under the License is distributed on an "AS IS" BASIS,
+// WITHOUT WARRANTIES OR CONDITIONS OF ANY KIND, either express or implied.
+// See the License for the specific language governing permissions and
+// limitations under the License.
+// </copyright>
+
+using System.Globalization;
+using System.IO;
+using System.Text;
+using System.Threading;
+
+using OpenTelemetry.Exporter.Prometheus.Implementation;
+
+using Xunit;
+
+namespace OpenTelemetry.Exporter.Prometheus.Tests.Implementation
+{
+    public class PrometheusMetricBuilderTests
+    {
+        [Theory]
+        [InlineData(null)]
+        [InlineData("pt-BR")]
+        public void Test(string cultureInfo)
+        {
+            if (!string.IsNullOrEmpty(cultureInfo))
+            {
+                Thread.CurrentThread.CurrentCulture = new CultureInfo(cultureInfo);
+            }
+
+            using var stream = new MemoryStream();
+            using var writer = new StreamWriter(stream);
+            var builder = new PrometheusMetricBuilder();
+            builder.WithName("test-builder");
+            builder.WithDescription("test-description");
+            builder.WithType("test-type");
+
+            var metricValueBuilder = builder.AddValue();
+            metricValueBuilder = metricValueBuilder.WithValue(10.0123);
+            metricValueBuilder.WithLabel("test-double", "double");
+            builder.Write(writer);
+
+            writer.Flush();
+
+            // assert
+            string actual = Encoding.UTF8.GetString(stream.ToArray());
+            string[] lines = actual.Split('\n');
+            Assert.Equal("# HELP test_buildertest-description", lines[0]);
+            Assert.Equal("# TYPE test_builder test-type", lines[1]);
+            Assert.StartsWith("test_builder{test_double=\"double\"} 10.01", lines[2]);
+        }
+    }
+}