Failed to load api definition swagger python

Swagger not loading — Failed to load API definition: Fetch error undefined

So after a lot of troubleshooting it came down to basically two things, but I feel that in general this could be helpful to someone else in the future so I’m posting an answer.

First- if ever your stuck with the aforementioned error the best way to actually see whats going on is by adding the following line to your Configure() method

app.UseDeveloperExceptionPage(); 

Now if you navigate to the ‘swagger/v1/swagger.json’ page you should see some more information which will point you in useful direction.

Second- now for me the error was something along the lines of

‘Multiple operations with path ‘some_path’ and method ‘GET’ ‘

However these API were located inside of dependency libraries so I was unable to apply a solution at the point of definition. As a workaround I found that adding the following line to your ConfigureServices() method resolved the issue

services.AddSwaggerGen(c => < c.SwaggerDoc("v1", new Info < Title = "API WSVAP (WebSmartView)", Version = "v1" >); c.ResolveConflictingActions(apiDescriptions => apiDescriptions.First()); //This line >); 

Finally- After all that I was able to generate a JSON file but still I wasn’t able to pull up the UI. In order to get this working I had to alter the end point in Configure()

I’m not sure why this was necessary, although it may be worth noting the web application’s virtual directory is hosted on IIS which might be having an effect.

NOTE: Navigating to swagger/v1/swagger.json will give you more details, for me it was causing issue due to undecorated action. This information is mentioned in comment by @MarkD

Hope this helps someone in the future.

Solution 2

I’ve been working with .Net Core 3.1 and I spent some time to find out and understanding what was going on.

The issue can arise from many different reasons:

1. Swagger configuration errors
2. Classes with the same name but in different namespaces
3. Public methods without the rest attribute (Get, Post, etc.)

First, take a look the link below just to check if your setup is ok:

A good tip to find out the problem is to run the application without to use IISExpress and check the console log. Any error found to generate the documentation will be displayed there.

In my case, the problems was that I had a public method (that should be private) without any rest attribute:

After change the method from public to private I solve the issue.

Solution 3

I was able to find the error by opening the network tab and looking at the response for swagger.json

Solution 4

Simply navigate to https://localhost:/swagger/v1/swagger.json and get much more details about the error message.

Solution 5

I’ve come across the same error before, after struggling to find the reason, I discovered that one of my API in one of my controllers have no HTTP verb as an attribute, So I fixed it by putting [HttpGet] on my API. So here is my advice, check your API controllers, maybe you forget the same thing as me!

Take a look at my code, I realized that I should change this :

 public async Task ProductDetail(int id)

 [Route("ProductDetail")] [HttpPost] public async Task ProductDetail(int id)

Jeremy S.

Full stack developer dabbling in everything from PostgreSQL to C# and react.

Updated on February 13, 2022

Comments

Trying to setup swagger in conjunction with a web application hosted on IIS express. API is built using ASP Net Core. I have followed the instructions prescribed on the relevant microsoft help page regarding Swashbuckle and ASP.NET Core. Thus far I have got the swagger page to load up and can see that the SwaggerDoc that I have defined is loading, however no API’s are present. Currently am getting the following error:

public class Startup < // This method gets called by the runtime. Use this method to add services to the container. public void ConfigureServices(IServiceCollection services) < // services.AddDbContext(opt => // opt.UseInMemoryDatabase("TodoList")); services.AddMvc() .SetCompatibilityVersion(CompatibilityVersion.Version_2_1); // Register the Swagger generator, defining 1 or more Swagger documents services.AddSwaggerGen(c => < c.SwaggerDoc("v1", new Info < Title = "API WSVAP (WebSmartView)", Version = "v1" >); >); > // This method gets called by the runtime. Use this method to configure the HTTP request pipeline. public void Configure(IApplicationBuilder app, IHostingEnvironment env) < // Enable middleware to serve generated Swagger as a JSON endpoint. app.UseSwagger(); // Enable middleware to serve swagger-ui (HTML, JS, CSS, etc.), // specifying the Swagger JSON endpoint. app.UseSwaggerUI(c =>< c.SwaggerEndpoint("./swagger/v1/swagger.json", "My API V1"); c.RoutePrefix = string.Empty; >); app.UseMvc(); > > 

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How to solve failed to load API definition in Svient flask-swagger-ui

The issue is related to the configuration of swagger.json, which is giving an error when accessed.

The error message is “Fetch error Failed to fetch C:\Project\test\swagger.json” followed by “Fetch error Possible cross-origin (CORS) issue? The URL origin (file://) does not match the page (http://127.0.0.1:5000). Check the server returns the correct ‘Access-Control-Allow-*’ headers.” When the “Invalid” button is clicked, an additional error message is displayed “<“schemaValidationMessages”:[<“level”:”error”,”message”:”Can’t read from file c:/Project\test\swagger.json”>]>”.

Code Snippet The following code snippet represents the URL and blueprint configuration for the swagger.json file:

SWAGGER_URL = '/swagger' API_URL = 'C:\Project\test\swagger.json' SWAGGERUI_BLUEPRINT = get_swaggerui_blueprint( SWAGGER_URL, API_URL, config= < 'app_name': "Seans-Python-Flask-REST-Boilerplate" >) app.register_blueprint(SWAGGERUI_BLUEPRINT, url_prefix=SWAGGER_URL) 

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Problem solution for How to solve failed to load API definition

The first step in solving the “failed to load API definition” error is to identify the root cause of the issue. This error can be caused by a variety of reasons, including incorrect API definition file paths, invalid API definition file formats, or problems with the API server.

Once the root cause of the issue has been identified, it is important to take the necessary steps to resolve it. For example, if the issue is caused by an incorrect file path, the API definition file should be moved to the correct location and the API server should be restarted. If the issue is caused by an invalid file format, the API definition file should be reviewed and corrected as necessary.

If the issue persists, it may be necessary to perform further debugging to identify the source of the problem. This may involve reviewing API server logs, checking for any configuration issues, or working with the API development team to identify any bugs or compatibility issues. Additionally, it may be useful to try updating the API server or the API definition file to the latest version to see if this resolves the issue.

Other popular problems with Svient flask-swagger-ui

Problem: JSON validation issue in flask-swagger-ui

One of the most common issues is the JSON validation error that occurs when there is a mismatch between the expected data format and the actual data format. This can be due to missing fields or incorrect data types.

Solution:

This issue can be solved by properly defining the schema in the API definition file. This will ensure that the API documentation is in sync with the actual implementation.

from flasgger import Swagger app = Flask(__name__) swagger = Swagger(app) @app.route("/api/", methods=["GET"]) def hello(name): """Example endpoint --- parameters: - name: name in: path type: string required: true description: Name of the person responses: 200: description: A single user item schema: id: User properties: name: type: string description: Name of the user default: Steve """ return jsonify() 

Problem: Parameter parsing issue in flask-swagger-ui

Another common issue is related to parameter parsing. This occurs when the API documentation is not in sync with the actual implementation, leading to incorrect parameter parsing.

Solution:

This issue can be solved by properly defining the parameters in the API definition file. This will ensure that the API documentation is in sync with the actual implementation.

from flasgger import Swagger app = Flask(__name__) swagger = Swagger(app) @app.route("/api/", methods=["POST"]) def hello(): """Example endpoint --- parameters: - name: body in: body required: true schema: id: User properties: name: type: string description: Name of the user default: Steve responses: 200: description: A single user item schema: id: User properties: name: type: string description: Name of the user default: Steve """ return jsonify() 

Problem: UI Customization issues in flask-swagger-ui

Another common issue is related to customizing the UI of the Swagger UI. This can include issues with branding, layout, or other design elements.

Solution:

This issue can be solved by using the template parameter in the Swagger object to specify the path to a custom UI template. This will allow you to use a custom UI template to change the look and feel of the Swagger UI.

from flasgger import Swagger app = Flask(__name__) swagger = Swagger(app, template_file="custom.html") @app.route("/api/", methods=["GET"]) def hello(name): """Example endpoint --- parameters: - name: name in: path type: string required: true description: Name of the person responses: 200: description: A single user item schema: id:User properties: name: type: string description: Name of the user default: Steve """ return jsonify()

A brief introduction to Svient flask-swagger-ui

Svient flask-swagger-ui is a tool that provides a user interface for generating and visualizing Swagger documentation for APIs built using the Flask framework. The UI allows developers to easily interact with the API documentation, test endpoints, and view the expected responses without having to write any additional code. It integrates seamlessly with Flask, making it easy to add documentation to existing Flask applications.

The tool is built on top of the Swagger specification, which provides a standardized way of describing RESTful APIs. The Swagger UI provides an interactive interface for exploring the API documentation, including the ability to view and test endpoints, as well as view the expected responses. Additionally, the tool can be easily customized to match the branding and design of an application, making it an ideal choice for teams that want to provide a polished, professional-looking API documentation experience for their users.

Most popular use cases for Svient flask-swagger-ui

1. Generating API documentation: Svient flask-swagger-ui can be used to generate human-readable documentation for APIs built using the Flask framework. The tool integrates with Flask applications and provides an easy way to document endpoints, request and response payloads, and other relevant information. The generated documentation is stored in a Swagger definition file, which can be used to visualize the API documentation in the Swagger UI.
2. Testing APIs: Svient flask-swagger-ui can be used to test APIs during the development process. The Swagger UI provides an interactive interface for exploring the API documentation and testing endpoints, making it easy to quickly verify that the API is functioning as expected.

from flasgger import Swagger app = Flask(__name__) swagger = Swagger(app) @app.route("/api/", methods=["GET"]) def hello(name): """Example endpoint --- parameters: - name: name in: path type: string required: true description: Name of the person responses: 200: description: A single user item schema: id: User properties: name: type: string description: Name of the user default: Steve """ return jsonify() 

In this example, the Swagger UI can be used to test the /api/ endpoint by specifying a name parameter and verifying the response payload.

1. Customizing the API documentation experience: Svient flask-swagger-ui can be used to customize the API documentation experience to match the branding and design of an application. The tool provides the ability to use custom UI templates to change the look and feel of the Swagger UI, making it easy to provide a polished, professional-looking API documentation experience for users.

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