Added sanity check for the setter of PrometheusExporter's HTTP listeners. (#2771)

Author: Yun-Ting

src/OpenTelemetry.Exporter.Prometheus/PrometheusExporterOptions.cs

@@ -29,6 +29,7 @@ public class PrometheusExporterOptions
         internal Func<DateTimeOffset> GetUtcNowDateTimeOffset = () => DateTimeOffset.UtcNow;
 
         private int scrapeResponseCacheDurationMilliseconds = 10 * 1000;
+        private IReadOnlyCollection<string> httpListenerPrefixes = new string[] { "http://*:80/" };
 
 #if NETCOREAPP3_1_OR_GREATER
         /// <summary>
@@ -48,7 +49,27 @@ public class PrometheusExporterOptions
         /// Gets or sets the prefixes to use for the http listener. Default
         /// value: http://*:80/.
         /// </summary>
-        public IReadOnlyCollection<string> HttpListenerPrefixes { get; set; } = new string[] { "http://*:80/" };
+        public IReadOnlyCollection<string> HttpListenerPrefixes
+        {
+            get => this.httpListenerPrefixes;
+            set
+            {
+                _ = value ?? throw new ArgumentNullException(nameof(this.httpListenerPrefixes));
+
+                foreach (string inputUri in value)
+                {
+                    if (!(Uri.TryCreate(inputUri, UriKind.Absolute, out var uri) &&
+                        (uri.Scheme == Uri.UriSchemeHttp || uri.Scheme == Uri.UriSchemeHttps)))
+                    {
+                        throw new ArgumentException(
+                            "Prometheus server path should be a valid URI with http/https scheme.",
+                            nameof(this.httpListenerPrefixes));
+                    }
+                }
+
+                this.httpListenerPrefixes = value;
+            }
+        }
 
         /// <summary>
         /// Gets or sets the path to use for the scraping endpoint. Default value: /metrics.

test/OpenTelemetry.Exporter.Prometheus.Tests/PrometheusExporterHttpServerTests.cs

@@ -105,5 +105,50 @@ public async Task PrometheusExporterHttpServerIntegration()
                 "^# TYPE counter_double counter\ncounter_double{key1='value1',key2='value2'} 101.17 \\d+\n$".Replace('\'', '"'),
                 await response.Content.ReadAsStringAsync().ConfigureAwait(false));
         }
+
+        [Theory]
+        [InlineData("http://example.com")]
+        [InlineData("https://example.com")]
+        [InlineData("http://127.0.0.1")]
+        [InlineData("http://example.com", "https://example.com", "http://127.0.0.1")]
+        public void ServerEndpointSanityCheckPositiveTest(params string[] uris)
+        {
+            using MeterProvider meterProvider = Sdk.CreateMeterProviderBuilder()
+                .AddPrometheusExporter(opt =>
+                {
+                    opt.HttpListenerPrefixes = uris;
+                })
+                .Build();
+        }
+
+        [Theory]
+        [InlineData("")]
+        [InlineData(null)]
+        [InlineData("ftp://example.com")]
+        [InlineData("http://example.com", "https://example.com", "ftp://example.com")]
+        public void ServerEndpointSanityCheckNegativeTest(params string[] uris)
+        {
+            try
+            {
+                using MeterProvider meterProvider = Sdk.CreateMeterProviderBuilder()
+                    .AddPrometheusExporter(opt =>
+                    {
+                        opt.HttpListenerPrefixes = uris;
+                    })
+                    .Build();
+            }
+            catch (Exception ex)
+            {
+                if (ex is not ArgumentNullException)
+                {
+                    Assert.Equal("System.ArgumentException", ex.GetType().ToString());
+#if NET461
+                    Assert.Equal("Prometheus server path should be a valid URI with http/https scheme.\r\nParameter name: httpListenerPrefixes", ex.Message);
+#else
+                    Assert.Equal("Prometheus server path should be a valid URI with http/https scheme. (Parameter 'httpListenerPrefixes')", ex.Message);
+#endif
+                }
+            }
+        }
     }
 }