Support non-standard MIME type during format inference

Author: MaggieKimani1

src/Microsoft.OpenApi/Reader/OpenApiModelFactory.cs

@@ -279,10 +279,14 @@ private static ReadResult InternalLoad(MemoryStream input, string format, OpenAp
                     var mediaType = response.Content.Headers.ContentType.MediaType;
                     var contentType = mediaType.Split(";".ToCharArray(), StringSplitOptions.RemoveEmptyEntries)[0];
                     format = contentType.Split('/').LastOrDefault();
+                    if (!string.IsNullOrEmpty(format) && format.Contains('-'))
+                    {
+                        format = format.Split('-').LastOrDefault(); // for non-standard MIME types e.g. text/x-yaml used in older libs or apps
+                    }
 #if NETSTANDARD2_0
                     stream = await response.Content.ReadAsStreamAsync();
 #else
-                    stream = await response.Content.ReadAsStreamAsync(token).ConfigureAwait(false);;
+                    stream = await response.Content.ReadAsStreamAsync(token).ConfigureAwait(false);
 #endif
                     return (stream, format);
                 }

test/Microsoft.OpenApi.Readers.Tests/V3Tests/OpenApiDocumentTests.cs

@@ -26,6 +26,7 @@ namespace Microsoft.OpenApi.Readers.Tests.V3Tests
     public class OpenApiDocumentTests
     {
         private const string SampleFolderPath = "V3Tests/Samples/OpenApiDocument/";
+        private const string codacyApi = "https://api.codacy.com/api/api-docs/swagger.yaml";
 
         public OpenApiDocumentTests()
         {
@@ -1362,5 +1363,13 @@ public async Task ParseDocumentWithExampleReferencesPasses()
             var result = await OpenApiDocument.LoadAsync(Path.Combine(SampleFolderPath, "docWithExampleReferences.yaml"));
             Assert.Empty(result.Diagnostic.Errors);
         }
+
+        [Fact]
+        public async Task ParseDocumentWithNonStandardMIMETypePasses()
+        {
+            // Act & Assert: Ensure NotSupportedException is not thrown for non-standard MIME type: text/x-yaml
+            var result = await OpenApiDocument.LoadAsync(codacyApi);
+            Assert.NotNull(result.Document); 
+        }
     }
 }