Support file uploading without multipart/form-data

src/RestSharp/Request/RequestContent.cs

@@ -36,38 +36,60 @@ class RequestContent : IDisposable {
         _parameters = new RequestParameters(_request.Parameters.Union(_client.DefaultParameters));
     }
 
-    public HttpContent BuildContent() {
-        AddFiles();
+    public HttpContent BuildContent() 
+    {
         var postParameters = _parameters.GetContentParameters(_request.Method).ToArray();
-        AddBody(postParameters.Length > 0);
-        AddPostParameters(postParameters);
-        AddHeaders();
-
-        return Content!;
-    }
-
-    void AddFiles() {
-        if (!_request.HasFiles() && !_request.AlwaysMultipartFormData) return;
-
-        var mpContent = CreateMultipartFormDataContent();
+        var postParametersExists = postParameters.Length > 0;
+        var bodyParametersExists = _request.TryGetBodyParameter(out var bodyParameter);
+        var filesExists = _request.Files.Any();
 
-        foreach (var file in _request.Files) {
-            var stream = file.GetFile();
-            _streams.Add(stream);
-            var fileContent = new StreamContent(stream);
+        if (filesExists)
+            AddFiles();
 
-            fileContent.Headers.ContentType = file.ContentType.AsMediaTypeHeaderValue;
+        if (bodyParametersExists)
+            AddBody(postParametersExists, bodyParameter!);
 
-            var dispositionHeader = file.Options.DisableFilenameEncoding
-                ? ContentDispositionHeaderValue.Parse($"form-data; name=\"{file.Name}\"; filename=\"{file.FileName}\"")
-                : new ContentDispositionHeaderValue("form-data") { Name = $"\"{file.Name}\"", FileName = $"\"{file.FileName}\"" };
-            if (!file.Options.DisableFileNameStar) dispositionHeader.FileNameStar = file.FileName;
-            fileContent.Headers.ContentDisposition = dispositionHeader;
+        if (postParametersExists)
+            AddPostParameters(postParameters);
 
-            mpContent.Add(fileContent);
-        }
+        AddHeaders();
 
-        Content = mpContent;
+        return Content!;
+    }
+
+     void AddFiles() 
+     {
+         // File uploading without multipart/form-data
+         if (_request.AlwaysSingleFileAsContent && _request.Files.Count == 1)
+         {
+             var fileParameter = _request.Files.First();
+             Content = ToStreamContent(fileParameter);
+             return;
+         }
+
+         var mpContent = new MultipartFormDataContent(GetOrSetFormBoundary());
+
+         foreach (var fileParameter in _request.Files) 
+             mpContent.Add(ToStreamContent(fileParameter));
+
+         Content = mpContent; 
+     }
+
+    StreamContent ToStreamContent(FileParameter fileParameter)
+    {
+        var stream = fileParameter.GetFile();
+        _streams.Add(stream);
+        var streamContent = new StreamContent(stream);
+
+        streamContent.Headers.ContentType = fileParameter.ContentType.AsMediaTypeHeaderValue;
+
+        var dispositionHeader = fileParameter.Options.DisableFilenameEncoding
+            ? ContentDispositionHeaderValue.Parse($"form-data; name=\"{fileParameter.Name}\"; filename=\"{fileParameter.FileName}\"")
+            : new ContentDispositionHeaderValue("form-data") { Name = $"\"{fileParameter.Name}\"", FileName = $"\"{fileParameter.FileName}\"" };
+        if (!fileParameter.Options.DisableFileNameStar) dispositionHeader.FileNameStar = fileParameter.FileName;
+        streamContent.Headers.ContentDisposition = dispositionHeader;
+
+        return streamContent;
     }
 
     HttpContent Serialize(BodyParameter body) {
@@ -117,9 +139,8 @@ class RequestContent : IDisposable {
         return mpContent;
     }
 
-    void AddBody(bool hasPostParameters) {
-        if (!_request.TryGetBodyParameter(out var bodyParameter)) return;
-
+    void AddBody(bool hasPostParameters, BodyParameter bodyParameter) 
+    {
         var bodyContent = Serialize(bodyParameter);
 
         // we need to send the body

src/RestSharp/Request/RestRequest.cs

@@ -81,7 +81,12 @@ public RestRequest(Uri resource, Method method = Method.Get)
     /// Always send a multipart/form-data request - even when no Files are present.
     /// </summary>
     public bool AlwaysMultipartFormData { get; set; }
-
+
+    /// <summary>
+    /// Always send a file as request content without multipart/form-data request - even when the request contains only one file parameter
+    /// </summary>
+    public bool AlwaysSingleFileAsContent { get; set; }
+
     /// <summary>
     /// When set to true, parameter values in a multipart form data requests will be enclosed in
     /// quotation marks. Default is false. Enable it if the remote endpoint requires parameters

src/RestSharp/Request/RestRequestExtensions.cs

@@ -501,4 +501,21 @@ public static RestRequest AddXmlBody<T>(this RestRequest request, T obj, Content
 
         if (duplicateKeys.Any()) throw new ArgumentException($"Duplicate header names exist: {string.Join(", ", duplicateKeys)}");
     }
+
+    public static void ValidateParameters(this RestRequest request) {
+
+        if (request.AlwaysSingleFileAsContent) {
+            var postParametersExists = request.Parameters.GetContentParameters(request.Method).Any();
+            var bodyParametersExists = request.Parameters.Any(p => p.Type == ParameterType.RequestBody);
+
+            if (request.AlwaysMultipartFormData) 
+                throw new ArgumentException("Failed to put file as content because flag AlwaysMultipartFormData enabled");
+
+            if (postParametersExists) 
+                throw new ArgumentException("Failed to put file as content because added post parameters");
+
+            if (bodyParametersExists) 
+                throw new ArgumentException("Failed to put file as content because added body parameters"); 
+        }
+    }
 }

src/RestSharp/RestClient.Async.cs

@@ -77,6 +77,7 @@ public partial class RestClient {
             throw new ObjectDisposedException(nameof(RestClient));
         }
 
+        request.ValidateParameters();
         var authenticator = request.Authenticator ?? Options.Authenticator;
         if (authenticator != null) await authenticator.Authenticate(this, request).ConfigureAwait(false);
 

test/RestSharp.Tests/RestRequestParametersTests.cs

@@ -0,0 +1,75 @@
+//  Copyright (c) .NET Foundation and Contributors
+// 
+// Licensed under the Apache License, Version 2.0 (the "License");
+// you may not use this file except in compliance with the License.
+// You may obtain a copy of the License at
+// 
+// http://www.apache.org/licenses/LICENSE-2.0
+// 
+// Unless required by applicable law or agreed to in writing, software
+// distributed under the License is distributed on an "AS IS" BASIS,
+// WITHOUT WARRANTIES OR CONDITIONS OF ANY KIND, either express or implied.
+// See the License for the specific language governing permissions and
+// limitations under the License.
+// 
+
+namespace RestSharp.Tests;
+
+public class RestRequestValidateParametersTests {
+    [Fact]
+    public void RestRequest_AlwaysMultipartFormData_IsAllowed() {
+        var request = new RestRequest {
+            AlwaysMultipartFormData = true
+        };
+
+        request.ValidateParameters();
+    }
+
+    [Fact]
+    public void RestRequest_AlwaysSingleFileAsContent_IsAllowed() {
+        var request = new RestRequest {
+            AlwaysSingleFileAsContent = true
+        };
+
+        request.ValidateParameters();
+    }
+
+    [Fact]
+    public void RestRequest_AlwaysSingleFileAsContent_And_AlwaysMultipartFormData_IsNotAllowed() {
+        var request = new RestRequest {
+            AlwaysSingleFileAsContent = true,
+            AlwaysMultipartFormData   = true
+        };
+
+        Assert.Throws<ArgumentException>(
+            () => { request.ValidateParameters(); }
+        );
+    }
+
+    [Fact]
+    public void RestRequest_AlwaysSingleFileAsContent_And_PostParameters_IsNotAllowed() {
+        var request = new RestRequest {
+            Method = Method.Post,
+            AlwaysSingleFileAsContent = true,
+        };
+
+        request.AddParameter("name", "value", ParameterType.GetOrPost);
+
+        Assert.Throws<ArgumentException>(
+            () => { request.ValidateParameters(); }
+        );
+    }
+
+    [Fact]
+    public void RestRequest_AlwaysSingleFileAsContent_And_BodyParameters_IsNotAllowed() {
+        var request = new RestRequest {
+            AlwaysSingleFileAsContent = true,
+        };
+
+        request.AddParameter("name", "value", ParameterType.RequestBody);
+
+        Assert.Throws<ArgumentException>(
+            () => { request.ValidateParameters(); }
+        );
+    }
+}