Updated V2 writer to output relative server Urls

Author: darrelmiller

src/Microsoft.OpenApi/Models/OpenApiDocument.cs

@@ -232,17 +232,33 @@ private static void WriteHostInfoV2(IOpenApiWriter writer, IList<OpenApiServer>
 
             // Divide the URL in the Url property into host and basePath required in OpenAPI V2
             // The Url property cannotcontain path templating to be valid for V2 serialization.
-            var firstServerUrl = new Uri(firstServer.Url);
+            var firstServerUrl = new Uri(firstServer.Url, UriKind.RelativeOrAbsolute);
 
             // host
-            writer.WriteProperty(
-                OpenApiConstants.Host,
-                firstServerUrl.GetComponents(UriComponents.Host | UriComponents.Port, UriFormat.SafeUnescaped));
-
-            // basePath
-            if (firstServerUrl.AbsolutePath != "/")
+            if (firstServerUrl.IsAbsoluteUri)
+            {
+                writer.WriteProperty(
+                    OpenApiConstants.Host,
+                    firstServerUrl.GetComponents(UriComponents.Host | UriComponents.Port, UriFormat.SafeUnescaped));
+                
+                // basePath
+                if (firstServerUrl.AbsolutePath != "/")
+                {
+                    writer.WriteProperty(OpenApiConstants.BasePath, firstServerUrl.AbsolutePath);
+                }
+            } else
             {
-                writer.WriteProperty(OpenApiConstants.BasePath, firstServerUrl.AbsolutePath);
+                var relativeUrl = firstServerUrl.OriginalString;
+                if (relativeUrl.StartsWith("//"))
+                {
+                    var pathPosition = relativeUrl.IndexOf('/', 3);
+                    writer.WriteProperty(OpenApiConstants.Host, relativeUrl.Substring(0, pathPosition));
+                    relativeUrl = relativeUrl.Substring(pathPosition);
+                }
+                if (!String.IsNullOrEmpty(relativeUrl) && relativeUrl != "/")
+                {
+                    writer.WriteProperty(OpenApiConstants.BasePath, relativeUrl);
+                }
             }
 
             // Consider all schemes of the URLs in the server list that have the same
@@ -260,7 +276,7 @@ private static void WriteHostInfoV2(IOpenApiWriter writer, IList<OpenApiServer>
                             UriComponents.Host | UriComponents.Port | UriComponents.Path,
                             UriFormat.SafeUnescaped,
                             StringComparison.OrdinalIgnoreCase) ==
-                        0)
+                        0 && u.IsAbsoluteUri)
                 .Select(u => u.Scheme)
                 .Distinct()
                 .ToList();

test/Microsoft.OpenApi.Tests/Models/OpenApiDocumentTests.cs

@@ -2552,5 +2552,97 @@ public void SerializeDocumentWithReferenceButNoComponents()
             // Assert
             Assert.NotEmpty(actual);
         }
+
+        [Fact]
+        public void SerializeRelativePathAsV2JsonWorks()
+        {
+            // Arrange
+            var expected =
+                @"swagger: '2.0'
+info:
+  version: 1.0.0
+basePath: /server1
+paths: { }";
+            var doc = new OpenApiDocument()
+            {
+                Info = new OpenApiInfo() { Version = "1.0.0" },
+                Servers = new List<OpenApiServer>() {
+                    new OpenApiServer()
+                    {
+                        Url = "/server1"
+                    }
+                }
+            };
+
+            // Act
+            var actual = doc.SerializeAsYaml(OpenApiSpecVersion.OpenApi2_0);
+
+            // Assert
+            actual = actual.MakeLineBreaksEnvironmentNeutral();
+            expected = expected.MakeLineBreaksEnvironmentNeutral();
+            actual.Should().Be(expected);
+        }
+
+        [Fact]
+        public void SerializeRelativePathWithHostAsV2JsonWorks()
+        {
+            // Arrange
+            var expected =
+                @"swagger: '2.0'
+info:
+  version: 1.0.0
+host: //example.org
+basePath: /server1
+paths: { }";
+            var doc = new OpenApiDocument()
+            {
+                Info = new OpenApiInfo() { Version = "1.0.0" },
+                Servers = new List<OpenApiServer>() {
+                    new OpenApiServer()
+                    {
+                        Url = "//example.org/server1"
+                    }
+                }
+            };
+
+            // Act
+            var actual = doc.SerializeAsYaml(OpenApiSpecVersion.OpenApi2_0);
+
+            // Assert
+            actual = actual.MakeLineBreaksEnvironmentNeutral();
+            expected = expected.MakeLineBreaksEnvironmentNeutral();
+            actual.Should().Be(expected);
+        }
+
+        [Fact]
+        public void SerializeRelativeRootPathWithHostAsV2JsonWorks()
+        {
+            // Arrange
+            var expected =
+                @"swagger: '2.0'
+info:
+  version: 1.0.0
+host: //example.org
+paths: { }";
+            var doc = new OpenApiDocument()
+            {
+                Info = new OpenApiInfo() { Version = "1.0.0" },
+                Servers = new List<OpenApiServer>() {
+                    new OpenApiServer()
+                    {
+                        Url = "//example.org/"
+                    }
+                }
+            };
+
+            // Act
+            var actual = doc.SerializeAsYaml(OpenApiSpecVersion.OpenApi2_0);
+
+            // Assert
+            actual = actual.MakeLineBreaksEnvironmentNeutral();
+            expected = expected.MakeLineBreaksEnvironmentNeutral();
+            actual.Should().Be(expected);
+        }
+
     }
 }