Update to return HttpResponseMessage for file downloads

src/Refitter.Core/RefitInterfaceGenerator.cs

@@ -116,6 +116,12 @@ protected string GetTypeName(OpenApiOperation operation)
             return type is null or "void" ? GetAsyncOperationType(true) : $"{GetAsyncOperationType(false)}<{WellKnownNamespaces.TrimImportedNamespaces(type)}>";
         }
 
+        // Check if response is a file stream
+        if (IsFileStreamResponse(operation))
+        {
+            return $"{GetAsyncOperationType(false)}<HttpResponseMessage>";
+        }
+
         // First check for explicit success status codes
         var successCodes = new[] { "200", "201", "203", "206" };
         var returnTypeParameter = successCodes
@@ -138,6 +144,54 @@ protected string GetTypeName(OpenApiOperation operation)
         return GetReturnType(returnTypeParameter);
     }
 
+    /// <summary>
+    /// Determines if the operation response is a file stream (binary content).
+    /// </summary>
+    /// <param name="operation">The OpenAPI operation to check.</param>
+    /// <returns>True if the response is a file stream, false otherwise.</returns>
+    private static bool IsFileStreamResponse(OpenApiOperation operation)
+    {
+        var successCodes = new[] { "200", "201", "203", "206", "2XX" };
+
+        foreach (var code in successCodes)
+        {
+            if (!operation.Responses.TryGetValue(code, out var apiResponse))
+                continue;
+
+            var response = apiResponse.ActualResponse;
+
+            if (response.Content?.Any() != true)
+                continue;
+
+            foreach (var contentEntry in response.Content)
+            {
+                if (IsFileContentType(contentEntry.Key))
+                {
+                    var schema = contentEntry.Value?.Schema;
+                    if (schema?.Format == "binary" || schema?.Type == NJsonSchema.JsonObjectType.File)
+                        return true;
+                }
+            }
+        }
+
+        return false;
+    }
+
+    private static bool IsFileContentType(string contentType)
+    {
+        return
+            contentType.StartsWith("application/octet-stream", StringComparison.OrdinalIgnoreCase) ||
+            contentType.StartsWith("application/pdf", StringComparison.OrdinalIgnoreCase) ||
+            contentType.StartsWith("application/vnd", StringComparison.OrdinalIgnoreCase) ||
+            contentType.StartsWith("image/", StringComparison.OrdinalIgnoreCase) ||
+            contentType.StartsWith("video/", StringComparison.OrdinalIgnoreCase) ||
+            contentType.StartsWith("audio/", StringComparison.OrdinalIgnoreCase) ||
+            contentType.StartsWith("application/zip", StringComparison.OrdinalIgnoreCase) ||
+            contentType.StartsWith("application/gzip", StringComparison.OrdinalIgnoreCase) ||
+            (contentType.StartsWith("application/x-", StringComparison.OrdinalIgnoreCase) &&
+             !contentType.StartsWith("application/x-www-form-urlencoded", StringComparison.OrdinalIgnoreCase));
+    }
+
     private string GetTypeName(string code, OpenApiOperation operation)
     {
         var schema = operation.Responses[code].ActualResponse.Schema;
@@ -254,6 +308,16 @@ 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<>]+>)?>",

src/Refitter.Tests/Examples/FileStreamResponseTests.cs

@@ -0,0 +1,163 @@
+using FluentAssertions;
+using Refitter.Core;
+using Refitter.Tests.Build;
+using Refitter.Tests.TestUtilities;
+using TUnit.Core;
+
+namespace Refitter.Tests.Examples;
+
+public class FileStreamResponseTests
+{
+    private const string OpenApiSpec = @"
+openapi: '3.0.0'
+info:
+  title: File Download API
+  version: 1.0.0
+paths:
+  '/files/{fileId}/download':
+    get:
+      operationId: downloadFile
+      summary: Download a file
+      parameters:
+        - name: fileId
+          in: path
+          required: true
+          schema:
+            type: string
+      responses:
+        '200':
+          description: File downloaded successfully
+          content:
+            application/octet-stream:
+              schema:
+                type: string
+                format: binary
+  '/images/{imageId}':
+    get:
+      operationId: getImage
+      summary: Get an image
+      parameters:
+        - name: imageId
+          in: path
+          required: true
+          schema:
+            type: string
+      responses:
+        '200':
+          description: Image retrieved successfully
+          content:
+            image/jpeg:
+              schema:
+                type: string
+                format: binary
+            image/png:
+              schema:
+                type: string
+                format: binary
+  '/documents/{docId}':
+    get:
+      operationId: getDocument
+      summary: Get a PDF document
+      parameters:
+        - name: docId
+          in: path
+          required: true
+          schema:
+            type: string
+      responses:
+        '200':
+          description: Document retrieved successfully
+          content:
+            application/pdf:
+              schema:
+                type: string
+                format: binary
+  '/forms/{formId}/submit':
+    get:
+      operationId: submitForm
+      summary: Submit form data
+      parameters:
+        - name: formId
+          in: path
+          required: true
+          schema:
+            type: string
+      responses:
+        '200':
+          description: Form submission result
+          content:
+            application/x-www-form-urlencoded:
+              schema:
+                type: object
+                properties:
+                  result:
+                    type: string
+";
+
+    [Test]
+    public async Task Can_Generate_Code()
+    {
+        string generatedCode = await GenerateCode();
+        generatedCode.Should().NotBeNullOrWhiteSpace();
+    }
+
+    [Test]
+    public async Task Generates_HttpResponseMessage_For_OctetStream()
+    {
+        string generatedCode = await GenerateCode();
+        generatedCode.Should().Contain("Task<HttpResponseMessage> DownloadFile(string fileId");
+    }
+
+    [Test]
+    public async Task Generates_HttpResponseMessage_For_ImageJpeg()
+    {
+        string generatedCode = await GenerateCode();
+        generatedCode.Should().Contain("Task<HttpResponseMessage> GetImage(string imageId");
+    }
+
+    [Test]
+    public async Task Generates_HttpResponseMessage_For_ApplicationPdf()
+    {
+        string generatedCode = await GenerateCode();
+        generatedCode.Should().Contain("Task<HttpResponseMessage> GetDocument(string docId");
+    }
+
+    [Test]
+    public async Task Does_Not_Generate_HttpResponseMessage_For_FormUrlEncoded()
+    {
+        string generatedCode = await GenerateCode();
+        generatedCode.Should().Contain("submitForm");
+        generatedCode.Should().NotContain("Task<HttpResponseMessage> SubmitForm(");
+    }
+
+    [Test]
+    public async Task Can_Build_Generated_Code()
+    {
+        string generatedCode = await GenerateCode();
+        BuildHelper
+            .BuildCSharp(generatedCode)
+            .Should()
+            .BeTrue();
+    }
+
+    [Test]
+    public async Task Generates_HttpResponseMessage_With_IApiResponse_Setting()
+    {
+        string generatedCode = await GenerateCode(returnIApiResponse: true);
+        generatedCode.Should().Contain("Task<HttpResponseMessage> DownloadFile(string fileId");
+    }
+
+    private static async Task<string> GenerateCode(bool returnIApiResponse = false)
+    {
+        var swaggerFile = await SwaggerFileHelper.CreateSwaggerFile(OpenApiSpec);
+        var settings = new RefitGeneratorSettings
+        {
+            OpenApiPath = swaggerFile,
+            ReturnIApiResponse = returnIApiResponse
+        };
+
+        var sut = await RefitGenerator.CreateAsync(settings);
+        var generatedCode = sut.Generate();
+        return generatedCode;
+    }
+}