Add user agent customization

src/OpenTelemetry.Exporter.OpenTelemetryProtocol/OtlpExporterOptions.cs

@@ -32,17 +32,16 @@ public class OtlpExporterOptions : IOtlpExporterOptions
     internal const OtlpExportProtocol DefaultOtlpExportProtocol = OtlpExportProtocol.Grpc;
 #endif
 
-    internal static readonly KeyValuePair<string, string>[] StandardHeaders = new KeyValuePair<string, string>[]
-    {
-        new("User-Agent", GetUserAgentString()),
-    };
+    internal static KeyValuePair<string, string>[] StandardHeaders => standardHeaders;
 
     internal readonly Func<HttpClient> DefaultHttpClientFactory;
 
+    private static KeyValuePair<string, string>[]? standardHeaders;
     private OtlpExportProtocol? protocol;
     private Uri? endpoint;
     private int? timeoutMilliseconds;
     private Func<HttpClient>? httpClientFactory;
+    private string? userAgentProductIdentifier;
 
     /// <summary>
     /// Initializes a new instance of the <see cref="OtlpExporterOptions"/> class.
@@ -78,6 +77,11 @@ internal OtlpExporterOptions(
             };
         };
 
+        standardHeaders =
+        [
+            new("User-Agent", this.GetUserAgentString())
+        ];
+
         this.BatchExportProcessorOptions = defaultBatchOptions!;
     }
 
@@ -124,6 +128,23 @@ public OtlpExportProtocol Protocol
         set => this.protocol = value;
     }
 
+    /// <summary>
+    /// Gets or sets the user agent identifier.
+    /// </summary>
+    public string UserAgentProductIdentifier
+    {
+        get => this.userAgentProductIdentifier ?? string.Empty;
+        set
+        {
+            this.userAgentProductIdentifier = string.IsNullOrWhiteSpace(value) ? string.Empty : value;
+
+            standardHeaders =
+            [
+                new("User-Agent", this.GetUserAgentString())
+            ];
+        }
+    }
+
     /// <summary>
     /// Gets or sets the export processor type to be used with the OpenTelemetry Protocol Exporter. The default value is <see cref="ExportProcessorType.Batch"/>.
     /// </summary>
@@ -226,10 +247,17 @@ internal OtlpExporterOptions ApplyDefaults(OtlpExporterOptions defaultExporterOp
         return this;
     }
 
-    private static string GetUserAgentString()
+    private string GetUserAgentString()
     {
         var assembly = typeof(OtlpExporterOptions).Assembly;
-        return $"OTel-OTLP-Exporter-Dotnet/{assembly.GetPackageVersion()}";
+        var baseUserAgent = $"OTel-OTLP-Exporter-Dotnet/{assembly.GetPackageVersion()}";
+
+        if (!string.IsNullOrEmpty(this.userAgentProductIdentifier))
+        {
+            return $"{this.userAgentProductIdentifier} {baseUserAgent}";
+        }
+
+        return baseUserAgent;
     }
 
     private void ApplyConfiguration(

test/OpenTelemetry.Exporter.OpenTelemetryProtocol.Tests/OtlpExporterOptionsTests.cs

@@ -262,4 +262,102 @@ public void OtlpExporterOptions_ApplyDefaultsTest()
         Assert.NotEqual(defaultOptionsWithData.TimeoutMilliseconds, targetOptionsWithData.TimeoutMilliseconds);
         Assert.NotEqual(defaultOptionsWithData.HttpClientFactory, targetOptionsWithData.HttpClientFactory);
     }
+
+    [Fact]
+    public void UserAgentProductIdentifier_Default_IsEmpty()
+    {
+        var options = new OtlpExporterOptions();
+
+        Assert.Equal(string.Empty, options.UserAgentProductIdentifier);
+    }
+
+    [Fact]
+    public void UserAgentProductIdentifier_DefaultUserAgent_ContainsExporterInfo()
+    {
+        var options = new OtlpExporterOptions();
+
+        var userAgentHeader = OtlpExporterOptions.StandardHeaders.FirstOrDefault(h => h.Key == "User-Agent");
+
+        Assert.NotNull(userAgentHeader.Key);
+        Assert.StartsWith("OTel-OTLP-Exporter-Dotnet/", userAgentHeader.Value, StringComparison.OrdinalIgnoreCase);
+    }
+
+    [Fact]
+    public void UserAgentProductIdentifier_WithProductIdentifier_IsPrepended()
+    {
+        var options = new OtlpExporterOptions
+        {
+            UserAgentProductIdentifier = "MyDistribution/1.2.3",
+        };
+
+        Assert.Equal("MyDistribution/1.2.3", options.UserAgentProductIdentifier);
+
+        var userAgentHeader = OtlpExporterOptions.StandardHeaders.FirstOrDefault(h => h.Key == "User-Agent");
+
+        Assert.NotNull(userAgentHeader.Key);
+        Assert.StartsWith("MyDistribution/1.2.3 OTel-OTLP-Exporter-Dotnet/", userAgentHeader.Value, StringComparison.OrdinalIgnoreCase);
+    }
+
+    [Fact]
+    public void UserAgentProductIdentifier_UpdatesStandardHeaders()
+    {
+        var options = new OtlpExporterOptions();
+
+        var initialUserAgent = OtlpExporterOptions.StandardHeaders.FirstOrDefault(h => h.Key == "User-Agent").Value;
+        Assert.StartsWith("OTel-OTLP-Exporter-Dotnet/", initialUserAgent, StringComparison.OrdinalIgnoreCase);
+
+        options.UserAgentProductIdentifier = "MyProduct/1.0.0";
+
+        var updatedUserAgent = OtlpExporterOptions.StandardHeaders.FirstOrDefault(h => h.Key == "User-Agent").Value;
+        Assert.StartsWith("MyProduct/1.0.0 OTel-OTLP-Exporter-Dotnet/", updatedUserAgent, StringComparison.OrdinalIgnoreCase);
+        Assert.NotEqual(initialUserAgent, updatedUserAgent);
+    }
+
+    [Fact]
+    public void UserAgentProductIdentifier_Rfc7231Compliance_SpaceSeparatedTokens()
+    {
+        var options = new OtlpExporterOptions
+        {
+            UserAgentProductIdentifier = "MyProduct/1.0.0",
+        };
+
+        var userAgentHeader = OtlpExporterOptions.StandardHeaders.FirstOrDefault(h => h.Key == "User-Agent").Value;
+
+        // Should have two product tokens separated by a space
+        var tokens = userAgentHeader.Split(' ');
+        Assert.Equal(2, tokens.Length);
+        Assert.Equal("MyProduct/1.0.0", tokens[0]);
+        Assert.StartsWith("OTel-OTLP-Exporter-Dotnet/", tokens[1],StringComparison.OrdinalIgnoreCase);
+    }
+
+    [Theory]
+    [InlineData("")]
+    [InlineData(" ")]
+    [InlineData("  ")]
+    public void UserAgentProductIdentifier_EmptyOrWhitespace_UsesDefaultUserAgent(string identifier)
+    {
+        var options = new OtlpExporterOptions
+        {
+            UserAgentProductIdentifier = identifier,
+        };
+
+        var userAgentHeader = OtlpExporterOptions.StandardHeaders.FirstOrDefault(h => h.Key == "User-Agent").Value;
+
+        // Should only contain the default exporter identifier, no leading space
+        Assert.StartsWith("OTel-OTLP-Exporter-Dotnet/", userAgentHeader, StringComparison.OrdinalIgnoreCase);
+        Assert.DoesNotContain("  ", userAgentHeader, StringComparison.OrdinalIgnoreCase); // No double spaces
+    }
+
+    [Fact]
+    public void UserAgentProductIdentifier_MultipleProducts_CorrectFormat()
+    {
+        var options = new OtlpExporterOptions
+        {
+            UserAgentProductIdentifier = "MySDK/2.0.0 MyDistribution/1.0.0",
+        };
+
+        var userAgentHeader = OtlpExporterOptions.StandardHeaders.FirstOrDefault(h => h.Key == "User-Agent").Value;
+
+        Assert.StartsWith("MySDK/2.0.0 MyDistribution/1.0.0 OTel-OTLP-Exporter-Dotnet/", userAgentHeader, StringComparison.OrdinalIgnoreCase);
+    }
 }