Generate strongly-typed C# client for ASP.Net Core Web API with OpenAPI (swagger) support running on localhost

Some time ago I wrote how to generate C# client for web api with OpenAPI support using online service https://generator3.swagger.io/api/generate. Limitation of this approach is that web api should be available online as well. But what to do if you develop web api and it is available only on localhost? One of the way is to use https://github.com/swagger-api/swagger-codegen but it is not very easy to use it on localhost.

Simpler solution is to use tool called NSwagStudio. At first we need to add support of OpenAPI to our web api - in my previous post I wrote how to do that: Add OpenAPI (Swagger) support to ASP.Net Core Web API. We will use the same code example here.

When we add OpenAPI support to our web api in addition to online documentation (which is available by url http://localhost:{port}/swagger/index.html) we also get endpoint with OpenAPI (swagger) JSON:

http://localhost:{port}/swagger/v1/swagger.json

which looks like this:

Having this endpoint it is very easy to generate strongly-typed C# client for our web api running on localhost using mentioned NSwagStudio. All we have to do is to choose runtime (we will use .NET6), paste url of swagger.json endpoint to the studio, check CSharp Client checkbox and click Generate Outputs:

Here is example of C# client generated for web api from our example with default settings:

//----------------------
// <auto-generated>
//     Generated using the NSwag toolchain v13.18.2.0 (NJsonSchema v10.8.0.0 (Newtonsoft.Json v13.0.0.0)) (http://NSwag.org)
// </auto-generated>
//----------------------

#pragma warning disable 108 // Disable "CS0108 '{derivedDto}.ToJson()' hides inherited member '{dtoBase}.ToJson()'. Use the new keyword if hiding was intended."
#pragma warning disable 114 // Disable "CS0114 '{derivedDto}.RaisePropertyChanged(String)' hides inherited member 'dtoBase.RaisePropertyChanged(String)'. To make the current member override that implementation, add the override keyword. Otherwise add the new keyword."
#pragma warning disable 472 // Disable "CS0472 The result of the expression is always 'false' since a value of type 'Int32' is never equal to 'null' of type 'Int32?'
#pragma warning disable 1573 // Disable "CS1573 Parameter '...' has no matching param tag in the XML comment for ...
#pragma warning disable 1591 // Disable "CS1591 Missing XML comment for publicly visible type or member ..."
#pragma warning disable 8073 // Disable "CS8073 The result of the expression is always 'false' since a value of type 'T' is never equal to 'null' of type 'T?'"
#pragma warning disable 3016 // Disable "CS3016 Arrays as attribute arguments is not CLS-compliant"
#pragma warning disable 8603 // Disable "CS8603 Possible null reference return"

namespace MyNamespace
{
    using System = global::System;

    [System.CodeDom.Compiler.GeneratedCode("NSwag", "13.18.2.0 (NJsonSchema v10.8.0.0 (Newtonsoft.Json v13.0.0.0))")]
    public partial class Client 
    {
        private string _baseUrl = "";
        private System.Net.Http.HttpClient _httpClient;
        private System.Lazy<Newtonsoft.Json.JsonSerializerSettings> _settings;

        public Client(string baseUrl, System.Net.Http.HttpClient httpClient)
        {
            BaseUrl = baseUrl;
            _httpClient = httpClient;
            _settings = new System.Lazy<Newtonsoft.Json.JsonSerializerSettings>(CreateSerializerSettings);
        }

        private Newtonsoft.Json.JsonSerializerSettings CreateSerializerSettings()
        {
            var settings = new Newtonsoft.Json.JsonSerializerSettings();
            UpdateJsonSerializerSettings(settings);
            return settings;
        }

        public string BaseUrl
        {
            get { return _baseUrl; }
            set { _baseUrl = value; }
        }

        protected Newtonsoft.Json.JsonSerializerSettings JsonSerializerSettings { get { return _settings.Value; } }

        partial void UpdateJsonSerializerSettings(Newtonsoft.Json.JsonSerializerSettings settings);

        partial void PrepareRequest(System.Net.Http.HttpClient client, System.Net.Http.HttpRequestMessage request, string url);
        partial void PrepareRequest(System.Net.Http.HttpClient client, System.Net.Http.HttpRequestMessage request, System.Text.StringBuilder urlBuilder);
        partial void ProcessResponse(System.Net.Http.HttpClient client, System.Net.Http.HttpResponseMessage response);

        /// <returns>Success</returns>
        /// <exception cref="ApiException">A server side error occurred.</exception>
        public virtual System.Threading.Tasks.Task<System.Collections.Generic.ICollection<User>> ListAsync()
        {
            return ListAsync(System.Threading.CancellationToken.None);
        }

        /// <param name="cancellationToken">A cancellation token that can be used by other objects or threads to receive notice of cancellation.</param>
        /// <returns>Success</returns>
        /// <exception cref="ApiException">A server side error occurred.</exception>
        public virtual async System.Threading.Tasks.Task<System.Collections.Generic.ICollection<User>> ListAsync(System.Threading.CancellationToken cancellationToken)
        {
            var urlBuilder_ = new System.Text.StringBuilder();
            urlBuilder_.Append(BaseUrl != null ? BaseUrl.TrimEnd('/') : "").Append("/User/List");

            var client_ = _httpClient;
            var disposeClient_ = false;
            try
            {
                using (var request_ = new System.Net.Http.HttpRequestMessage())
                {
                    request_.Method = new System.Net.Http.HttpMethod("GET");
                    request_.Headers.Accept.Add(System.Net.Http.Headers.MediaTypeWithQualityHeaderValue.Parse("text/plain"));

                    PrepareRequest(client_, request_, urlBuilder_);

                    var url_ = urlBuilder_.ToString();
                    request_.RequestUri = new System.Uri(url_, System.UriKind.RelativeOrAbsolute);

                    PrepareRequest(client_, request_, url_);

                    var response_ = await client_.SendAsync(request_, System.Net.Http.HttpCompletionOption.ResponseHeadersRead, cancellationToken).ConfigureAwait(false);
                    var disposeResponse_ = true;
                    try
                    {
                        var headers_ = System.Linq.Enumerable.ToDictionary(response_.Headers, h_ => h_.Key, h_ => h_.Value);
                        if (response_.Content != null && response_.Content.Headers != null)
                        {
                            foreach (var item_ in response_.Content.Headers)
                                headers_[item_.Key] = item_.Value;
                        }

                        ProcessResponse(client_, response_);

                        var status_ = (int)response_.StatusCode;
                        if (status_ == 200)
                        {
                            var objectResponse_ = await ReadObjectResponseAsync<System.Collections.Generic.ICollection<User>>(response_, headers_, cancellationToken).ConfigureAwait(false);
                            if (objectResponse_.Object == null)
                            {
                                throw new ApiException("Response was null which was not expected.", status_, objectResponse_.Text, headers_, null);
                            }
                            return objectResponse_.Object;
                        }
                        else
                        if (status_ == 500)
                        {
                            string responseText_ = ( response_.Content == null ) ? string.Empty : await response_.Content.ReadAsStringAsync().ConfigureAwait(false);
                            throw new ApiException("Server Error", status_, responseText_, headers_, null);
                        }
                        else
                        {
                            var objectResponse_ = await ReadObjectResponseAsync<ProblemDetails>(response_, headers_, cancellationToken).ConfigureAwait(false);
                            if (objectResponse_.Object == null)
                            {
                                throw new ApiException("Response was null which was not expected.", status_, objectResponse_.Text, headers_, null);
                            }
                            throw new ApiException<ProblemDetails>("Error", status_, objectResponse_.Text, headers_, objectResponse_.Object, null);
                        }
                    }
                    finally
                    {
                        if (disposeResponse_)
                            response_.Dispose();
                    }
                }
            }
            finally
            {
                if (disposeClient_)
                    client_.Dispose();
            }
        }

        /// <returns>Success</returns>
        /// <exception cref="ApiException">A server side error occurred.</exception>
        public virtual System.Threading.Tasks.Task<User> DetailsAsync(int? id)
        {
            return DetailsAsync(id, System.Threading.CancellationToken.None);
        }

        /// <param name="cancellationToken">A cancellation token that can be used by other objects or threads to receive notice of cancellation.</param>
        /// <returns>Success</returns>
        /// <exception cref="ApiException">A server side error occurred.</exception>
        public virtual async System.Threading.Tasks.Task<User> DetailsAsync(int? id, System.Threading.CancellationToken cancellationToken)
        {
            var urlBuilder_ = new System.Text.StringBuilder();
            urlBuilder_.Append(BaseUrl != null ? BaseUrl.TrimEnd('/') : "").Append("/User/Details?");
            if (id != null)
            {
                urlBuilder_.Append(System.Uri.EscapeDataString("id") + "=").Append(System.Uri.EscapeDataString(ConvertToString(id, System.Globalization.CultureInfo.InvariantCulture))).Append("&");
            }
            urlBuilder_.Length--;

            var client_ = _httpClient;
            var disposeClient_ = false;
            try
            {
                using (var request_ = new System.Net.Http.HttpRequestMessage())
                {
                    request_.Method = new System.Net.Http.HttpMethod("GET");
                    request_.Headers.Accept.Add(System.Net.Http.Headers.MediaTypeWithQualityHeaderValue.Parse("text/plain"));

                    PrepareRequest(client_, request_, urlBuilder_);

                    var url_ = urlBuilder_.ToString();
                    request_.RequestUri = new System.Uri(url_, System.UriKind.RelativeOrAbsolute);

                    PrepareRequest(client_, request_, url_);

                    var response_ = await client_.SendAsync(request_, System.Net.Http.HttpCompletionOption.ResponseHeadersRead, cancellationToken).ConfigureAwait(false);
                    var disposeResponse_ = true;
                    try
                    {
                        var headers_ = System.Linq.Enumerable.ToDictionary(response_.Headers, h_ => h_.Key, h_ => h_.Value);
                        if (response_.Content != null && response_.Content.Headers != null)
                        {
                            foreach (var item_ in response_.Content.Headers)
                                headers_[item_.Key] = item_.Value;
                        }

                        ProcessResponse(client_, response_);

                        var status_ = (int)response_.StatusCode;
                        if (status_ == 200)
                        {
                            var objectResponse_ = await ReadObjectResponseAsync<User>(response_, headers_, cancellationToken).ConfigureAwait(false);
                            if (objectResponse_.Object == null)
                            {
                                throw new ApiException("Response was null which was not expected.", status_, objectResponse_.Text, headers_, null);
                            }
                            return objectResponse_.Object;
                        }
                        else
                        if (status_ == 404)
                        {
                            var objectResponse_ = await ReadObjectResponseAsync<ProblemDetails>(response_, headers_, cancellationToken).ConfigureAwait(false);
                            if (objectResponse_.Object == null)
                            {
                                throw new ApiException("Response was null which was not expected.", status_, objectResponse_.Text, headers_, null);
                            }
                            throw new ApiException<ProblemDetails>("Not Found", status_, objectResponse_.Text, headers_, objectResponse_.Object, null);
                        }
                        else
                        if (status_ == 500)
                        {
                            string responseText_ = ( response_.Content == null ) ? string.Empty : await response_.Content.ReadAsStringAsync().ConfigureAwait(false);
                            throw new ApiException("Server Error", status_, responseText_, headers_, null);
                        }
                        else
                        {
                            var objectResponse_ = await ReadObjectResponseAsync<ProblemDetails>(response_, headers_, cancellationToken).ConfigureAwait(false);
                            if (objectResponse_.Object == null)
                            {
                                throw new ApiException("Response was null which was not expected.", status_, objectResponse_.Text, headers_, null);
                            }
                            throw new ApiException<ProblemDetails>("Error", status_, objectResponse_.Text, headers_, objectResponse_.Object, null);
                        }
                    }
                    finally
                    {
                        if (disposeResponse_)
                            response_.Dispose();
                    }
                }
            }
            finally
            {
                if (disposeClient_)
                    client_.Dispose();
            }
        }

        /// <returns>Success</returns>
        /// <exception cref="ApiException">A server side error occurred.</exception>
        public virtual System.Threading.Tasks.Task SaveAsync(User body)
        {
            return SaveAsync(body, System.Threading.CancellationToken.None);
        }

        /// <param name="cancellationToken">A cancellation token that can be used by other objects or threads to receive notice of cancellation.</param>
        /// <returns>Success</returns>
        /// <exception cref="ApiException">A server side error occurred.</exception>
        public virtual async System.Threading.Tasks.Task SaveAsync(User body, System.Threading.CancellationToken cancellationToken)
        {
            var urlBuilder_ = new System.Text.StringBuilder();
            urlBuilder_.Append(BaseUrl != null ? BaseUrl.TrimEnd('/') : "").Append("/User/Save");

            var client_ = _httpClient;
            var disposeClient_ = false;
            try
            {
                using (var request_ = new System.Net.Http.HttpRequestMessage())
                {
                    var json_ = Newtonsoft.Json.JsonConvert.SerializeObject(body, _settings.Value);
                    var content_ = new System.Net.Http.StringContent(json_);
                    content_.Headers.ContentType = System.Net.Http.Headers.MediaTypeHeaderValue.Parse("application/json");
                    request_.Content = content_;
                    request_.Method = new System.Net.Http.HttpMethod("POST");

                    PrepareRequest(client_, request_, urlBuilder_);

                    var url_ = urlBuilder_.ToString();
                    request_.RequestUri = new System.Uri(url_, System.UriKind.RelativeOrAbsolute);

                    PrepareRequest(client_, request_, url_);

                    var response_ = await client_.SendAsync(request_, System.Net.Http.HttpCompletionOption.ResponseHeadersRead, cancellationToken).ConfigureAwait(false);
                    var disposeResponse_ = true;
                    try
                    {
                        var headers_ = System.Linq.Enumerable.ToDictionary(response_.Headers, h_ => h_.Key, h_ => h_.Value);
                        if (response_.Content != null && response_.Content.Headers != null)
                        {
                            foreach (var item_ in response_.Content.Headers)
                                headers_[item_.Key] = item_.Value;
                        }

                        ProcessResponse(client_, response_);

                        var status_ = (int)response_.StatusCode;
                        if (status_ == 200)
                        {
                            return;
                        }
                        else
                        if (status_ == 500)
                        {
                            string responseText_ = ( response_.Content == null ) ? string.Empty : await response_.Content.ReadAsStringAsync().ConfigureAwait(false);
                            throw new ApiException("Server Error", status_, responseText_, headers_, null);
                        }
                        else
                        {
                            var objectResponse_ = await ReadObjectResponseAsync<ProblemDetails>(response_, headers_, cancellationToken).ConfigureAwait(false);
                            if (objectResponse_.Object == null)
                            {
                                throw new ApiException("Response was null which was not expected.", status_, objectResponse_.Text, headers_, null);
                            }
                            throw new ApiException<ProblemDetails>("Error", status_, objectResponse_.Text, headers_, objectResponse_.Object, null);
                        }
                    }
                    finally
                    {
                        if (disposeResponse_)
                            response_.Dispose();
                    }
                }
            }
            finally
            {
                if (disposeClient_)
                    client_.Dispose();
            }
        }

        /// <returns>Success</returns>
        /// <exception cref="ApiException">A server side error occurred.</exception>
        public virtual System.Threading.Tasks.Task DeleteAsync(int? id)
        {
            return DeleteAsync(id, System.Threading.CancellationToken.None);
        }

        /// <param name="cancellationToken">A cancellation token that can be used by other objects or threads to receive notice of cancellation.</param>
        /// <returns>Success</returns>
        /// <exception cref="ApiException">A server side error occurred.</exception>
        public virtual async System.Threading.Tasks.Task DeleteAsync(int? id, System.Threading.CancellationToken cancellationToken)
        {
            var urlBuilder_ = new System.Text.StringBuilder();
            urlBuilder_.Append(BaseUrl != null ? BaseUrl.TrimEnd('/') : "").Append("/User/Delete?");
            if (id != null)
            {
                urlBuilder_.Append(System.Uri.EscapeDataString("id") + "=").Append(System.Uri.EscapeDataString(ConvertToString(id, System.Globalization.CultureInfo.InvariantCulture))).Append("&");
            }
            urlBuilder_.Length--;

            var client_ = _httpClient;
            var disposeClient_ = false;
            try
            {
                using (var request_ = new System.Net.Http.HttpRequestMessage())
                {
                    request_.Method = new System.Net.Http.HttpMethod("DELETE");

                    PrepareRequest(client_, request_, urlBuilder_);

                    var url_ = urlBuilder_.ToString();
                    request_.RequestUri = new System.Uri(url_, System.UriKind.RelativeOrAbsolute);

                    PrepareRequest(client_, request_, url_);

                    var response_ = await client_.SendAsync(request_, System.Net.Http.HttpCompletionOption.ResponseHeadersRead, cancellationToken).ConfigureAwait(false);
                    var disposeResponse_ = true;
                    try
                    {
                        var headers_ = System.Linq.Enumerable.ToDictionary(response_.Headers, h_ => h_.Key, h_ => h_.Value);
                        if (response_.Content != null && response_.Content.Headers != null)
                        {
                            foreach (var item_ in response_.Content.Headers)
                                headers_[item_.Key] = item_.Value;
                        }

                        ProcessResponse(client_, response_);

                        var status_ = (int)response_.StatusCode;
                        if (status_ == 200)
                        {
                            return;
                        }
                        else
                        if (status_ == 404)
                        {
                            var objectResponse_ = await ReadObjectResponseAsync<ProblemDetails>(response_, headers_, cancellationToken).ConfigureAwait(false);
                            if (objectResponse_.Object == null)
                            {
                                throw new ApiException("Response was null which was not expected.", status_, objectResponse_.Text, headers_, null);
                            }
                            throw new ApiException<ProblemDetails>("Not Found", status_, objectResponse_.Text, headers_, objectResponse_.Object, null);
                        }
                        else
                        if (status_ == 500)
                        {
                            string responseText_ = ( response_.Content == null ) ? string.Empty : await response_.Content.ReadAsStringAsync().ConfigureAwait(false);
                            throw new ApiException("Server Error", status_, responseText_, headers_, null);
                        }
                        else
                        {
                            var objectResponse_ = await ReadObjectResponseAsync<ProblemDetails>(response_, headers_, cancellationToken).ConfigureAwait(false);
                            if (objectResponse_.Object == null)
                            {
                                throw new ApiException("Response was null which was not expected.", status_, objectResponse_.Text, headers_, null);
                            }
                            throw new ApiException<ProblemDetails>("Error", status_, objectResponse_.Text, headers_, objectResponse_.Object, null);
                        }
                    }
                    finally
                    {
                        if (disposeResponse_)
                            response_.Dispose();
                    }
                }
            }
            finally
            {
                if (disposeClient_)
                    client_.Dispose();
            }
        }

        protected struct ObjectResponseResult<T>
        {
            public ObjectResponseResult(T responseObject, string responseText)
            {
                this.Object = responseObject;
                this.Text = responseText;
            }

            public T Object { get; }

            public string Text { get; }
        }

        public bool ReadResponseAsString { get; set; }

        protected virtual async System.Threading.Tasks.Task<ObjectResponseResult<T>> ReadObjectResponseAsync<T>(System.Net.Http.HttpResponseMessage response, System.Collections.Generic.IReadOnlyDictionary<string, System.Collections.Generic.IEnumerable<string>> headers, System.Threading.CancellationToken cancellationToken)
        {
            if (response == null || response.Content == null)
            {
                return new ObjectResponseResult<T>(default(T), string.Empty);
            }

            if (ReadResponseAsString)
            {
                var responseText = await response.Content.ReadAsStringAsync().ConfigureAwait(false);
                try
                {
                    var typedBody = Newtonsoft.Json.JsonConvert.DeserializeObject<T>(responseText, JsonSerializerSettings);
                    return new ObjectResponseResult<T>(typedBody, responseText);
                }
                catch (Newtonsoft.Json.JsonException exception)
                {
                    var message = "Could not deserialize the response body string as " + typeof(T).FullName + ".";
                    throw new ApiException(message, (int)response.StatusCode, responseText, headers, exception);
                }
            }
            else
            {
                try
                {
                    using (var responseStream = await response.Content.ReadAsStreamAsync().ConfigureAwait(false))
                    using (var streamReader = new System.IO.StreamReader(responseStream))
                    using (var jsonTextReader = new Newtonsoft.Json.JsonTextReader(streamReader))
                    {
                        var serializer = Newtonsoft.Json.JsonSerializer.Create(JsonSerializerSettings);
                        var typedBody = serializer.Deserialize<T>(jsonTextReader);
                        return new ObjectResponseResult<T>(typedBody, string.Empty);
                    }
                }
                catch (Newtonsoft.Json.JsonException exception)
                {
                    var message = "Could not deserialize the response body stream as " + typeof(T).FullName + ".";
                    throw new ApiException(message, (int)response.StatusCode, string.Empty, headers, exception);
                }
            }
        }

        private string ConvertToString(object value, System.Globalization.CultureInfo cultureInfo)
        {
            if (value == null)
            {
                return "";
            }

            if (value is System.Enum)
            {
                var name = System.Enum.GetName(value.GetType(), value);
                if (name != null)
                {
                    var field = System.Reflection.IntrospectionExtensions.GetTypeInfo(value.GetType()).GetDeclaredField(name);
                    if (field != null)
                    {
                        var attribute = System.Reflection.CustomAttributeExtensions.GetCustomAttribute(field, typeof(System.Runtime.Serialization.EnumMemberAttribute)) 
                            as System.Runtime.Serialization.EnumMemberAttribute;
                        if (attribute != null)
                        {
                            return attribute.Value != null ? attribute.Value : name;
                        }
                    }

                    var converted = System.Convert.ToString(System.Convert.ChangeType(value, System.Enum.GetUnderlyingType(value.GetType()), cultureInfo));
                    return converted == null ? string.Empty : converted;
                }
            }
            else if (value is bool) 
            {
                return System.Convert.ToString((bool)value, cultureInfo).ToLowerInvariant();
            }
            else if (value is byte[])
            {
                return System.Convert.ToBase64String((byte[]) value);
            }
            else if (value.GetType().IsArray)
            {
                var array = System.Linq.Enumerable.OfType<object>((System.Array) value);
                return string.Join(",", System.Linq.Enumerable.Select(array, o => ConvertToString(o, cultureInfo)));
            }

            var result = System.Convert.ToString(value, cultureInfo);
            return result == null ? "" : result;
        }
    }

    [System.CodeDom.Compiler.GeneratedCode("NJsonSchema", "13.18.2.0 (NJsonSchema v10.8.0.0 (Newtonsoft.Json v13.0.0.0))")]
    public partial class ProblemDetails
    {
        [Newtonsoft.Json.JsonProperty("type", Required = Newtonsoft.Json.Required.Default, NullValueHandling = Newtonsoft.Json.NullValueHandling.Ignore)]
        public string Type { get; set; }

        [Newtonsoft.Json.JsonProperty("title", Required = Newtonsoft.Json.Required.Default, NullValueHandling = Newtonsoft.Json.NullValueHandling.Ignore)]
        public string Title { get; set; }

        [Newtonsoft.Json.JsonProperty("status", Required = Newtonsoft.Json.Required.Default, NullValueHandling = Newtonsoft.Json.NullValueHandling.Ignore)]
        public int? Status { get; set; }

        [Newtonsoft.Json.JsonProperty("detail", Required = Newtonsoft.Json.Required.Default, NullValueHandling = Newtonsoft.Json.NullValueHandling.Ignore)]
        public string Detail { get; set; }

        [Newtonsoft.Json.JsonProperty("instance", Required = Newtonsoft.Json.Required.Default, NullValueHandling = Newtonsoft.Json.NullValueHandling.Ignore)]
        public string Instance { get; set; }

        private System.Collections.Generic.IDictionary<string, object> _additionalProperties;

        [Newtonsoft.Json.JsonExtensionData]
        public System.Collections.Generic.IDictionary<string, object> AdditionalProperties
        {
            get { return _additionalProperties ?? (_additionalProperties = new System.Collections.Generic.Dictionary<string, object>()); }
            set { _additionalProperties = value; }
        }

    }

    [System.CodeDom.Compiler.GeneratedCode("NJsonSchema", "13.18.2.0 (NJsonSchema v10.8.0.0 (Newtonsoft.Json v13.0.0.0))")]
    public partial class User
    {
        [Newtonsoft.Json.JsonProperty("id", Required = Newtonsoft.Json.Required.DisallowNull, NullValueHandling = Newtonsoft.Json.NullValueHandling.Ignore)]
        public int Id { get; set; }

        [Newtonsoft.Json.JsonProperty("firstName", Required = Newtonsoft.Json.Required.Default, NullValueHandling = Newtonsoft.Json.NullValueHandling.Ignore)]
        public string FirstName { get; set; }

        [Newtonsoft.Json.JsonProperty("lastName", Required = Newtonsoft.Json.Required.Default, NullValueHandling = Newtonsoft.Json.NullValueHandling.Ignore)]
        public string LastName { get; set; }

        [Newtonsoft.Json.JsonProperty("email", Required = Newtonsoft.Json.Required.Default, NullValueHandling = Newtonsoft.Json.NullValueHandling.Ignore)]
        public string Email { get; set; }

    }



    [System.CodeDom.Compiler.GeneratedCode("NSwag", "13.18.2.0 (NJsonSchema v10.8.0.0 (Newtonsoft.Json v13.0.0.0))")]
    public partial class ApiException : System.Exception
    {
        public int StatusCode { get; private set; }

        public string Response { get; private set; }

        public System.Collections.Generic.IReadOnlyDictionary<string, System.Collections.Generic.IEnumerable<string>> Headers { get; private set; }

        public ApiException(string message, int statusCode, string response, System.Collections.Generic.IReadOnlyDictionary<string, System.Collections.Generic.IEnumerable<string>> headers, System.Exception innerException)
            : base(message + "\n\nStatus: " + statusCode + "\nResponse: \n" + ((response == null) ? "(null)" : response.Substring(0, response.Length >= 512 ? 512 : response.Length)), innerException)
        {
            StatusCode = statusCode;
            Response = response;
            Headers = headers;
        }

        public override string ToString()
        {
            return string.Format("HTTP Response: \n\n{0}\n\n{1}", Response, base.ToString());
        }
    }

    [System.CodeDom.Compiler.GeneratedCode("NSwag", "13.18.2.0 (NJsonSchema v10.8.0.0 (Newtonsoft.Json v13.0.0.0))")]
    public partial class ApiException<TResult> : ApiException
    {
        public TResult Result { get; private set; }

        public ApiException(string message, int statusCode, string response, System.Collections.Generic.IReadOnlyDictionary<string, System.Collections.Generic.IEnumerable<string>> headers, TResult result, System.Exception innerException)
            : base(message, statusCode, response, headers, innerException)
        {
            Result = result;
        }
    }

}

#pragma warning restore 1591
#pragma warning restore 1573
#pragma warning restore  472
#pragma warning restore  114
#pragma warning restore  108
#pragma warning restore 3016
#pragma warning restore 8603

Having this client makes it much easier to use our web api from client apps (comparing with developing api calls manually). In addition to that NSwagStudio allows to set many different settings which change generated C# code (e.g. include synchronous method in addition to asynchronous which are generated by default, generate interfaces for client classes for simplifying unit testing, default namespace, etc):

You may check other settings when will play with NSwagStudio which for sure worth to spend some time on it. Hope that this knowledge will help to reduce development time and simplify consumption of your web APIs.

Generate C# client for API with Swagger (OpenAPI) support

If you develop web API it worth to consider to add support for Swagger specification (or OpenAPI specification) to it. As documentation says:

OAS defines an API’s contract, allowing all the API’s stakeholders, be it your development team, or your end consumers, to understand what the API does and interact with its various resources, without having to integrate it into their own application.

One of the practical advantage is possibility to easily create documentation for web API which supports Swagger. Another big advantage is possibility to generate SDK (client) for web API using preferred language. There are Swagger Codegen tools for that. One of them is online web service https://generator3.swagger.io/api/generate which can be used for generating SDK online.

Let's see how to use that and generate C# client for sample web API https://petstore.swagger.io/v2/swagger.json with Swagger support. We need to send HTTP POST request tohttps://generator3.swagger.io/api/generate with the following body:

{
  "specURL" : "https://petstore.swagger.io/v2/swagger.json",
  "lang" : "csharp",
  "type" : "CLIENT",
  "codegenVersion" : "V3"
}

and add header "Content-Type": "application/json". In "lang" parameter we specified which language should be used for generating SDK. After that web service will generate C# client for us and will return generated .cs classes in zip archive. If you use Postman then instead of Send button need to use Send and Download:

Zip archive will contain Visual Studio solution with generated SDK for web API:

As you can see it contains generated model classes and API for working with them so no need to code it manually. It may save a lot of time when you work with external web API.

Update 2023-03-29: see also another blog post Generate strongly-typed C# client for ASP.Net Core Web API with OpenAPI (swagger) support running on localhost which describes how to generate C# client for web api running on localhost.