fix/multi whitespace

src/Microsoft.OpenApi/Reader/OpenApiModelFactory.cs

@@ -360,7 +360,9 @@ SecurityException or
 
         private static string InspectInputFormat(string input)
         {
-            return input.StartsWith("{", StringComparison.OrdinalIgnoreCase) || input.StartsWith("[", StringComparison.OrdinalIgnoreCase) ? OpenApiConstants.Json : OpenApiConstants.Yaml;
+            var trimmedInput = input.TrimStart();
+            return trimmedInput.StartsWith("{", StringComparison.OrdinalIgnoreCase) || trimmedInput.StartsWith("[", StringComparison.OrdinalIgnoreCase) ?
+                    OpenApiConstants.Json : OpenApiConstants.Yaml;
         }
 
         /// <summary>
@@ -393,7 +395,7 @@ private static bool TryInspectStreamFormat(Stream stream, out string? format)
                 var firstByte = (char)stream.ReadByte();
 
                 // Skip whitespace if present and read the next non-whitespace byte
-                if (char.IsWhiteSpace(firstByte))
+                while (char.IsWhiteSpace(firstByte))
                 {
                     firstByte = (char)stream.ReadByte();
                 }

test/Microsoft.OpenApi.Tests/Reader/OpenApiModelFactoryTests.cs

@@ -203,6 +203,32 @@ public async Task CanLoadAnAsyncOnlyStreamInYamlAndDetectFormat()
         Assert.Equal("Sample API", document.Info.Title);
     }
 
+    [Fact]
+    public async Task CanLoadANonSeekableStreamInJsonAndDetectFormatWhenPrecededBySpaces()
+    {
+        // Given
+        using var memoryStream = new MemoryStream(System.Text.Encoding.UTF8.GetBytes("     " + documentJson));
+        using var nonSeekableStream = new NonSeekableStream(memoryStream);
+
+        // When
+        var (document, _) = await OpenApiDocument.LoadAsync(nonSeekableStream);
+
+        // Then
+        Assert.NotNull(document);
+        Assert.Equal("Sample API", document.Info.Title);
+    }
+
+    [Fact]
+    public void CanLoadAStringJsonAndDetectFormatWhenPrecededBySpaces()
+    {
+        // When
+        var (document, _) = OpenApiDocument.Parse("     " + documentJson);
+
+        // Then
+        Assert.NotNull(document);
+        Assert.Equal("Sample API", document.Info.Title);
+    }
+
     public sealed class AsyncOnlyStream : Stream
     {
         private readonly Stream _innerStream;