Improve OpenAPI parse + codegen throughput by removing avoidable allocations and repeated regex work

src/Refitter.Core/OpenApiDocumentFactory.cs

@@ -11,6 +11,12 @@ namespace Refitter.Core;
 /// </summary>
 public static class OpenApiDocumentFactory
 {
+    private static readonly HttpClient HttpClient = new(
+        new HttpClientHandler
+        {
+            AutomaticDecompression = DecompressionMethods.GZip | DecompressionMethods.Deflate
+        });
+
     /// <summary>
     /// Creates a merged <see cref="NSwag.OpenApiDocument"/> from multiple paths or URLs.
     /// The first document serves as the base; paths and schemas from subsequent documents are merged in.
@@ -37,8 +43,17 @@ public static async Task<OpenApiDocument> CreateAsync(IEnumerable<string> openAp
     private static OpenApiDocument Merge(OpenApiDocument[] documents)
     {
         var baseDocument = documents[0];
-        foreach (var document in documents.Skip(1))
+        var tags = baseDocument.Tags;
+        HashSet<string>? tagNames = null;
+
+        if (tags != null)
+        {
+            tagNames = new HashSet<string>(tags.Select(t => t.Name), StringComparer.Ordinal);
+        }
+
+        for (var i = 1; i < documents.Length; i++)
         {
+            var document = documents[i];
             foreach (var path in document.Paths)
             {
                 if (!baseDocument.Paths.ContainsKey(path.Key))
@@ -67,9 +82,10 @@ private static OpenApiDocument Merge(OpenApiDocument[] documents)
             if (document.Tags != null)
             {
                 baseDocument.Tags ??= [];
+                tagNames ??= new HashSet<string>(baseDocument.Tags.Select(t => t.Name), StringComparer.Ordinal);
                 foreach (var tag in document.Tags)
                 {
-                    if (baseDocument.Tags.All(t => t.Name != tag.Name))
+                    if (tagNames.Add(tag.Name))
                         baseDocument.Tags.Add(tag);
                 }
             }
@@ -152,22 +168,17 @@ private static void PopulateMissingRequiredFields(
     /// <returns>True if the path is an HTTP URL, otherwise false.</returns>
     private static bool IsHttp(string path)
     {
-        return path.StartsWith("http://") || path.StartsWith("https://");
+        return path.StartsWith("http://", StringComparison.OrdinalIgnoreCase) ||
+               path.StartsWith("https://", StringComparison.OrdinalIgnoreCase);
     }
 
     /// <summary>
     /// Gets the content of the URI as a string and decompresses it if necessary. 
     /// </summary>
     /// <param name="openApiPath">The path to the OpenAPI document.</param>
     /// <returns>The content of the HTTP request.</returns>
-    private static async Task<string> GetHttpContent(string openApiPath)
-    {
-        var httpMessageHandler = new HttpClientHandler();
-        httpMessageHandler.AutomaticDecompression = DecompressionMethods.GZip | DecompressionMethods.Deflate;
-        using var http = new HttpClient(httpMessageHandler);
-        var content = await http.GetStringAsync(openApiPath);
-        return content;
-    }
+    private static Task<string> GetHttpContent(string openApiPath)
+        => HttpClient.GetStringAsync(openApiPath);
 
 
     /// <summary>
@@ -177,6 +188,7 @@ private static async Task<string> GetHttpContent(string openApiPath)
     /// <returns>True if the path is a YAML file, otherwise false.</returns>
     private static bool IsYaml(string path)
     {
-        return path.EndsWith("yaml") || path.EndsWith("yml");
+        return path.EndsWith("yaml", StringComparison.OrdinalIgnoreCase) ||
+               path.EndsWith("yml", StringComparison.OrdinalIgnoreCase);
     }
 }

src/Refitter.Core/RefitGenerator.cs

@@ -9,6 +9,11 @@
 /// </summary>
 public class RefitGenerator(RefitGeneratorSettings settings, OpenApiDocument document)
 {
+    private static readonly Regex JsonStringEnumConverterAttributeRegex = new(
+        @"^\s*\[(System\.Text\.Json\.Serialization\.)?JsonConverter\(typeof\((System\.Text\.Json\.Serialization\.)?JsonStringEnumConverter\)\)\]\s*\r?\n?",
+        RegexOptions.Compiled | RegexOptions.Multiline,
+        TimeSpan.FromSeconds(1));
+
     /// <summary>
     /// OpenAPI specifications used to generate Refit clients and interfaces.
     /// </summary>
@@ -94,9 +99,21 @@
         }
 
         // compile all expressions here once, as we will use them more than once
-        var regexes = pathMatchExpressions.Select(x => new Regex(x, RegexOptions.Compiled, TimeSpan.FromSeconds(1))).ToList();
+        var regexes = pathMatchExpressions
+            .Select(x => new Regex(x, RegexOptions.Compiled, TimeSpan.FromSeconds(1)))
+            .ToArray();
         var paths = document.Paths.Keys
-            .Where(pathKey => regexes.TrueForAll(regex => !regex.IsMatch(pathKey)))
+            .Where(
+                pathKey =>
+                {
+                    for (var i = 0; i < regexes.Length; i++)
+                    {
+                        if (regexes[i].IsMatch(pathKey))
+                            return false;
+                    }
+
+                    return true;
+                })
             .ToArray();
 
         foreach (string pathKey in paths)
@@ -158,7 +175,7 @@
 
         if (!string.IsNullOrWhiteSpace(settings.ContractTypeSuffix))
         {
             result = ContractTypeSuffixApplier.ApplySuffix(result, settings.ContractTypeSuffix);
         }
 
         return result;
@@ -229,7 +246,7 @@
             generatedFiles = generatedFiles
                 .Select(f => f with
                 {
                     Content = ContractTypeSuffixApplier.ApplySuffix(f.Content, settings.ContractTypeSuffix)
                 })
                 .ToList();
         }
@@ -244,17 +261,9 @@
             return contracts;
         }
 
-        const string pattern = @"^\s*\[(System\.Text\.Json\.Serialization\.)?JsonConverter\(typeof\((System\.Text\.Json\.Serialization\.)?JsonStringEnumConverter\)\)\]\s*$";
-        var lines = contracts.Split(["\r\n", "\r", "\n"], StringSplitOptions.None);
-        var filteredLines = lines
-            .Where(
-                line => !Regex.IsMatch(
-                    line,
-                    pattern,
-                    RegexOptions.None,
-                    TimeSpan.FromSeconds(1)))
-            .ToArray();
-        return string.Join(Environment.NewLine, filteredLines);
+        return JsonStringEnumConverterAttributeRegex
+            .Replace(contracts, string.Empty)
+            .TrimEnd();
     }
 
     /// <summary>

src/Refitter.Core/RefitInterfaceGenerator.cs

@@ -8,6 +8,8 @@ namespace Refitter.Core;
 internal class RefitInterfaceGenerator : IRefitInterfaceGenerator
 {
     protected const string Separator = "    ";
+    private static readonly Regex HttpResponseMessageTypeRegex = new("(Task|IObservable)<HttpResponseMessage>", RegexOptions.Compiled, TimeSpan.FromSeconds(1));
+    private static readonly Regex ApiResponseTypeRegex = new("(Task|IObservable)<(I)?ApiResponse(<[\\w<>]+>)?>", RegexOptions.Compiled, TimeSpan.FromSeconds(1));
 
     protected readonly RefitGeneratorSettings settings;
     protected readonly OpenApiDocument document;
@@ -73,15 +75,16 @@ private string GenerateInterfaceBody(out string? dynamicQuerystringParameters)
                 var parametersString = string.Join(", ", parameters);
                 var hasApizrRequestOptionsParameter = settings.ApizrSettings?.WithRequestOptions == true;
                 var hasCancellationToken = settings.UseCancellationTokens && !hasApizrRequestOptionsParameter;
+                var isApiResponseType = IsApiResponseType(returnType);
 
                 if (settings.GenerateXmlDocCodeComments)
                 {
-                    this.docGenerator.AppendMethodDocumentation(operationModel, IsApiResponseType(returnType), hasDynamicQuerystringParameter, hasApizrRequestOptionsParameter, hasCancellationToken, code);
+                    this.docGenerator.AppendMethodDocumentation(operationModel, isApiResponseType, hasDynamicQuerystringParameter, hasApizrRequestOptionsParameter, hasCancellationToken, code);
                 }
 
                 GenerateObsoleteAttribute(operation, code);
                 GenerateForMultipartFormData(operationModel, code);
-                GenerateHeaders(operations, operation, operationModel, code);
+                GenerateHeaders(operations, operationModel, code);
 
                 code.AppendLine($"{Separator}{Separator}[{verb}(\"{kv.Key}\")]")
                     .AppendLine($"{Separator}{Separator}{returnType} {operationName}({parametersString});")
@@ -91,11 +94,11 @@ private string GenerateInterfaceBody(out string? dynamicQuerystringParameters)
                 {
                     if (settings.GenerateXmlDocCodeComments)
                     {
-                        this.docGenerator.AppendMethodDocumentation(operationModel, IsApiResponseType(returnType), false, hasApizrRequestOptionsParameter, hasCancellationToken, code);
+                        this.docGenerator.AppendMethodDocumentation(operationModel, isApiResponseType, false, hasApizrRequestOptionsParameter, hasCancellationToken, code);
                     }
                     GenerateObsoleteAttribute(operation, code);
                     GenerateForMultipartFormData(operationModel, code);
-                    GenerateHeaders(operations, operation, operationModel, code);
+                    GenerateHeaders(operations, operationModel, code);
 
                     parametersString = string.Join(", ", parameters.Where(parameter => !parameter.Contains("?")));
 
@@ -245,7 +248,6 @@ protected static void GenerateForMultipartFormData(CSharpOperationModel operatio
 
     protected void GenerateHeaders(
         KeyValuePair<string, OpenApiOperation> operations,
-        OpenApiOperation operation,
         CSharpOperationModel operationModel,
         StringBuilder code)
     {
@@ -254,14 +256,14 @@ protected void GenerateHeaders(
         if (settings.AddAcceptHeaders && document.SchemaType is >= NJsonSchema.SchemaType.OpenApi3)
         {
             //Generate header "Accept"
-            var contentTypes = operations.Value.Responses.Select(pair => operation.Responses[pair.Key].Content.Keys);
-
-            //remove duplicates
-            var uniqueContentTypes = contentTypes
-                .GroupBy(x => x)
-                .SelectMany(y => y.First())
-                .Distinct()
-                .ToList();
+            var uniqueContentTypes = new HashSet<string>(StringComparer.OrdinalIgnoreCase);
+            foreach (var response in operations.Value.Responses.Values)
+            {
+                foreach (var contentType in response.Content.Keys)
+                {
+                    uniqueContentTypes.Add(contentType);
+                }
+            }
 
             if (uniqueContentTypes.Any())
             {
@@ -328,21 +330,7 @@ private string GetDefaultReturnType()
     /// <returns>True if the type is an ApiResponse Task or similar, false otherwise.</returns>
     protected static bool IsApiResponseType(string typeName)
     {
-        // Check for HttpResponseMessage
-        if (Regex.IsMatch(
-            typeName,
-            "(Task|IObservable)<HttpResponseMessage>",
-            RegexOptions.None,
-            TimeSpan.FromSeconds(1)))
-        {
-            return true;
-        }
-
-        return Regex.IsMatch(
-            typeName,
-            "(Task|IObservable)<(I)?ApiResponse(<[\\w<>]+>)?>",
-            RegexOptions.None,
-            TimeSpan.FromSeconds(1));
+        return HttpResponseMessageTypeRegex.IsMatch(typeName) || ApiResponseTypeRegex.IsMatch(typeName);
     }
 
     private string GetConfiguredReturnType(string returnTypeParameter)

src/Refitter.Core/RefitMultipleInterfaceByTagGenerator.cs

@@ -92,7 +92,7 @@ public override IEnumerable<GeneratedCode> GenerateCode()
                 this.docGenerator.AppendMethodDocumentation(operationModel, IsApiResponseType(returnType), hasDynamicQuerystringParameter, hasApizrRequestOptionsParameter, hasCancellationToken, sb);
                 GenerateObsoleteAttribute(operation, sb);
                 GenerateForMultipartFormData(operationModel, sb);
-                GenerateHeaders(operations, operation, operationModel, sb);
+                GenerateHeaders(operations, operationModel, sb);
 
                 sb.AppendLine($"{Separator}{Separator}[{verb}(\"{op.PathItem.Key}\")]")
                     .AppendLine($"{Separator}{Separator}{returnType} {operationName}({parametersString});")
@@ -103,7 +103,7 @@ public override IEnumerable<GeneratedCode> GenerateCode()
                     this.docGenerator.AppendMethodDocumentation(operationModel, IsApiResponseType(returnType), false, hasApizrRequestOptionsParameter, hasCancellationToken, sb);
                     GenerateObsoleteAttribute(operation, sb);
                     GenerateForMultipartFormData(operationModel, sb);
-                    GenerateHeaders(operations, operation, operationModel, sb);
+                    GenerateHeaders(operations, operationModel, sb);
 
                     parametersString = string.Join(", ", parameters.Where(parameter => !parameter.Contains("?")));
 

src/Refitter.Core/RefitMultipleInterfaceGenerator.cs

@@ -61,7 +61,7 @@ public override IEnumerable<GeneratedCode> GenerateCode()
                 this.docGenerator.AppendMethodDocumentation(operationModel, IsApiResponseType(returnType), hasDynamicQuerystringParameter, hasApizrRequestOptionsParameter, hasCancellationToken, code);
                 GenerateObsoleteAttribute(operation, code);
                 GenerateForMultipartFormData(operationModel, code);
-                GenerateHeaders(operations, operation, operationModel, code);
+                GenerateHeaders(operations, operationModel, code);
 
                 code.AppendLine($"{Separator}{Separator}[{verb}(\"{kv.Key}\")]")
                     .AppendLine($"{Separator}{Separator}{returnType} {methodName}({parametersString});")
@@ -72,7 +72,7 @@ public override IEnumerable<GeneratedCode> GenerateCode()
                     this.docGenerator.AppendMethodDocumentation(operationModel, IsApiResponseType(returnType), false, hasApizrRequestOptionsParameter, hasCancellationToken, code);
                     GenerateObsoleteAttribute(operation, code);
                     GenerateForMultipartFormData(operationModel, code);
-                    GenerateHeaders(operations, operation, operationModel, code);
+                    GenerateHeaders(operations, operationModel, code);
 
                     parametersString = string.Join(", ", parameters.Where(parameter => !parameter.Contains("?")));
 

src/Refitter.Core/SchemaCleaner.cs

@@ -10,7 +10,7 @@ namespace Refitter.Core;
 public class SchemaCleaner
 {
     private readonly OpenApiDocument document;
-    private readonly string[] keepSchemaPatterns;
+    private readonly Regex[] keepSchemaRegexes;
 
     /// <summary>
     /// Gets or sets a value indicating whether to include inheritance hierarchy in the schema cleaning process.
@@ -25,7 +25,9 @@ public class SchemaCleaner
     public SchemaCleaner(OpenApiDocument document, string[] keepSchemaPatterns)
     {
         this.document = document;
-        this.keepSchemaPatterns = keepSchemaPatterns;
+        keepSchemaRegexes = keepSchemaPatterns
+            .Select(x => new Regex(x, RegexOptions.Compiled, TimeSpan.FromSeconds(1)))
+            .ToArray();
     }
 
     /// <summary>
@@ -71,16 +73,12 @@ public void RemoveUnreferencedSchema()
             .ToDictionary(x => x.Value,
                 x => x.Key);
 
-        var keepSchemaRegexes = keepSchemaPatterns
-            .Select(x => new Regex(x, RegexOptions.Compiled, TimeSpan.FromSeconds(1)))
-            .ToList();
-
         if (doc.Components?.Schemas != null)
         {
             foreach (var kvp in doc.Components.Schemas)
             {
                 var schema = kvp.Key;
-                if (keepSchemaRegexes.Exists(x => x.IsMatch(schema)))
+                if (keepSchemaRegexes.Any(x => x.IsMatch(schema)))
                 {
                     TryPush(kvp.Value, toProcess);
                 }

src/Refitter.Tests/Examples/DuplicateOperationIdTests.cs

@@ -81,7 +81,10 @@ public async Task Generated_Code_Handles_Duplicate_OperationIds_Gracefully()
     public async Task Generated_Code_Contains_Methods()
     {
         string generatedCode = await GenerateCode();
-        generatedCode.Should().Contain("GetItems");
+        // When operationIds are duplicated, NSwag falls back to path-based method names
+        generatedCode.Should().Contain("Items");
+        generatedCode.Should().Contain("Products");
+        generatedCode.Should().Contain("Orders");
     }
 
     private static async Task<string> GenerateCode()

src/Refitter.Tests/Examples/InlineJsonConvertersTests.cs

@@ -107,6 +107,7 @@ public async Task Generated_Code_Does_Not_Contain_JsonConverter_When_Disabled()
         using (new AssertionScope())
         {
             generatedCode.Should().NotContain("[JsonConverter(typeof(JsonStringEnumConverter))]");
+            generatedCode.Should().NotContain("[JsonConverter(typeof(System.Text.Json.Serialization.JsonStringEnumConverter))]");
             generatedCode.Should().Contain("Status { get; set; }");
             generatedCode.Should().Contain("public enum PetStatus");
         }

src/Refitter.Tests/OpenApiDocumentFactoryTests.cs

@@ -36,6 +36,8 @@ public async Task Create_From_File_Returns_NotNull(SampleOpenSpecifications vers
     [Arguments(SampleOpenSpecifications.SwaggerPetstoreJsonV3, "petstore.json")]
     [Arguments(SampleOpenSpecifications.SwaggerPetstoreYamlV3, "petstore.yaml")]
     [Arguments(SampleOpenSpecifications.SwaggerPetstoreYamlV3, "petstore.yml")]
+    [Arguments(SampleOpenSpecifications.SwaggerPetstoreYamlV3, "petstore.YAML")]
+    [Arguments(SampleOpenSpecifications.SwaggerPetstoreYamlV3, "petstore.YML")]
     public async Task Create_From_File_Detects_Format_Correctly(SampleOpenSpecifications version, string filename)
     {
         var swaggerFile = await TestFile.CreateSwaggerFile(EmbeddedResources.GetSwaggerPetstore(version), filename);