fix: support non-standard MIME type in response header

src/Microsoft.OpenApi.Hidi/OpenApiService.cs

@@ -254,7 +254,7 @@ private static async Task<OpenApiDocument> GetOpenApiAsync(HidiOptions options,
             else if (!string.IsNullOrEmpty(options.OpenApi))
             {
                 stream = await GetStreamAsync(options.OpenApi, logger, cancellationToken).ConfigureAwait(false);
-                var result = await ParseOpenApiAsync(options.OpenApi, format, options.InlineExternal, logger, stream, cancellationToken).ConfigureAwait(false);
+                var result = await ParseOpenApiAsync(options.OpenApi, options.InlineExternal, logger, stream, cancellationToken).ConfigureAwait(false);
                 document = result.Document;
             }
             else throw new InvalidOperationException("No input file path or URL provided");
@@ -351,8 +351,7 @@ private static MemoryStream ApplyFilterToCsdl(Stream csdlStream, string entitySe
             try
             {
                 using var stream = await GetStreamAsync(openApi, logger, cancellationToken).ConfigureAwait(false);
-                var openApiFormat = !string.IsNullOrEmpty(openApi) ? GetOpenApiFormat(openApi, logger) : OpenApiFormat.Yaml;
-                result = await ParseOpenApiAsync(openApi, openApiFormat.GetDisplayName(),false, logger, stream, cancellationToken).ConfigureAwait(false);
+                result = await ParseOpenApiAsync(openApi, false, logger, stream, cancellationToken).ConfigureAwait(false);
 
                 using (logger.BeginScope("Calculating statistics"))
                 {
@@ -380,7 +379,7 @@ private static MemoryStream ApplyFilterToCsdl(Stream csdlStream, string entitySe
             return result.Diagnostic.Errors.Count == 0;
         }
 
-        private static async Task<ReadResult> ParseOpenApiAsync(string openApiFile, string format, bool inlineExternal, ILogger logger, Stream stream, CancellationToken cancellationToken = default)
+        private static async Task<ReadResult> ParseOpenApiAsync(string openApiFile, bool inlineExternal, ILogger logger, Stream stream, CancellationToken cancellationToken = default)
         {
             ReadResult result;
             var stopwatch = Stopwatch.StartNew();
@@ -396,7 +395,7 @@ private static async Task<ReadResult> ParseOpenApiAsync(string openApiFile, stri
                         new Uri("file://" + new FileInfo(openApiFile).DirectoryName + Path.DirectorySeparatorChar)
                 };
 
-                result = await OpenApiDocument.LoadAsync(stream, format, settings, cancellationToken).ConfigureAwait(false);
+                result = await OpenApiDocument.LoadAsync(stream, settings: settings, cancellationToken: cancellationToken).ConfigureAwait(false);
 
                 logger.LogTrace("{Timestamp}ms: Completed parsing.", stopwatch.ElapsedMilliseconds);
 

src/Microsoft.OpenApi/Models/OpenApiOperation.cs

@@ -160,7 +160,7 @@ public void SerializeAsV3(IOpenApiWriter writer)
         /// </summary>
         private void SerializeInternal(IOpenApiWriter writer, OpenApiSpecVersion version, Action<IOpenApiWriter, IOpenApiSerializable> callback)
         {
-            Utils.CheckArgumentNull(writer);;
+            Utils.CheckArgumentNull(writer);
 
             writer.WriteStartObject();
 

src/Microsoft.OpenApi/Reader/OpenApiModelFactory.cs

@@ -39,7 +39,11 @@ public static ReadResult Load(MemoryStream stream,
                                       string format = null,
                                       OpenApiReaderSettings settings = null)
         {
+#if NET6_0_OR_GREATER
+            ArgumentNullException.ThrowIfNull(stream);
+#else
             if (stream is null) throw new ArgumentNullException(nameof(stream));
+#endif
             settings ??= new OpenApiReaderSettings();
 
             // Get the format of the stream if not provided
@@ -112,7 +116,11 @@ public static async Task<T> LoadAsync<T>(string url, OpenApiSpecVersion version,
         /// <returns></returns>
         public static async Task<ReadResult> LoadAsync(Stream input, string format = null, OpenApiReaderSettings settings = null, CancellationToken cancellationToken = default)
         {
+#if NET6_0_OR_GREATER
+            ArgumentNullException.ThrowIfNull(input);
+#else
             if (input is null) throw new ArgumentNullException(nameof(input));
+#endif
             settings ??= new OpenApiReaderSettings();
 
             Stream preparedStream;
@@ -160,7 +168,11 @@ public static async Task<T> LoadAsync<T>(Stream input,
                                                  CancellationToken token = default) where T : IOpenApiElement
         {
             Utils.CheckArgumentNull(openApiDocument);
+#if NET6_0_OR_GREATER
+            ArgumentNullException.ThrowIfNull(input);
+#else
             if (input is null) throw new ArgumentNullException(nameof(input));
+#endif
             if (input is MemoryStream memoryStream)
             {
                 return Load<T>(memoryStream, version, format, openApiDocument, out var _, settings);
@@ -185,7 +197,11 @@ public static ReadResult Parse(string input,
                                        string format = null,
                                        OpenApiReaderSettings settings = null)
         {
-            if (input is null) throw new ArgumentNullException(nameof(input));
+#if NET6_0_OR_GREATER
+            ArgumentException.ThrowIfNullOrEmpty(input);
+#else
+            if (string.IsNullOrEmpty(input)) throw new ArgumentNullException(nameof(input));
+#endif
             format ??= InspectInputFormat(input);
             settings ??= new OpenApiReaderSettings();
 
@@ -212,7 +228,11 @@ public static T Parse<T>(string input,
                                  string format = null,
                                  OpenApiReaderSettings settings = null) where T : IOpenApiElement
         {
-            if (input is null) throw new ArgumentNullException(nameof(input));
+#if NET6_0_OR_GREATER
+            ArgumentException.ThrowIfNullOrEmpty(input);
+#else
+            if (string.IsNullOrEmpty(input)) throw new ArgumentNullException(nameof(input));
+#endif
             format ??= InspectInputFormat(input);
             settings ??= new OpenApiReaderSettings();
             using var stream = new MemoryStream(Encoding.UTF8.GetBytes(input));
@@ -278,11 +298,12 @@ private static ReadResult InternalLoad(MemoryStream input, string format, OpenAp
                     var response = await _httpClient.GetAsync(url, token).ConfigureAwait(false);
                     var mediaType = response.Content.Headers.ContentType.MediaType;
                     var contentType = mediaType.Split(";".ToCharArray(), StringSplitOptions.RemoveEmptyEntries)[0];
-                    format = contentType.Split('/').LastOrDefault();
+                    format = contentType.Split('/').Last().Split('+').Last().Split('-').Last();
+                    // 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);
                 }
@@ -321,8 +342,12 @@ private static string InspectInputFormat(string input)
 
         private static string InspectStreamFormat(Stream stream)
         {
-            if (stream == null) throw new ArgumentNullException(nameof(stream));            
-
+#if NET6_0_OR_GREATER
+            ArgumentNullException.ThrowIfNull(stream);
+#else
+            if (stream is null) throw new ArgumentNullException(nameof(stream));
+#endif
+
             long initialPosition = stream.Position;
             int firstByte = stream.ReadByte();
 

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); 
+        }
     }
 }