Why is there "no response from server" in Swagger UI? - swagger-ui

Question

My API calls work correctly in Postman. But when I send requests from Swagger UI, it shows "no response from server" for all requests:
Response Body
no content
Response Code
0
Response Headers
{
"error": "no response from server"
}
What can the problem be and how to fix it?
The browser console shows these errors:
Failed to load resource: net::ERR_CONNECTION_REFUSED
Uncaught TypeError: Cannot read property 'length' of undefined
at showStatus (index.js:24)
at showErrorStatus (index.js:24)
at error (index.js:607) at spec-converter.js:533
at Request.callback (index.js:24)
at Request.crossDomainError (index.js:24)
at XMLHttpRequest.xhr.onreadystatechange (index.js:24)

Answer 1

net::ERR_CONNECTION_REFUSED sounds like you need to enable CORS on your localhost, so that it sends the Access-Control-Allow-Origin: * header in responses. How you do this depends on the server you use. More info here:
https://enable-cors.org/server.html
https://github.com/swagger-api/swagger-ui/#cors-support
You may also need to allow OPTIONS pre-flight requests.

Answer 2

Swagger returns 0 response code due to the Reference Looping in your serializer response.
Ignore the reference looping while getting the serializer response back.
If you are using Web API, use the following code
services.AddMvc()
.AddJsonOptions(opt =>
{
opt.SerializerSettings.ReferenceLoopHandling = Newtonsoft.Json.ReferenceLoopHandling.Ignore;
});

Answer 3

remove schemes from swagger config json file(in my case tsoa.json) and restart the server. It worked for me.
{
"readme": "https://github.com/lukeautry/tsoa/blob/HEAD/tsoa.json",
"swagger": {
"outputDirectory": "./dist/src",
"entryFile": "./src/server.ts",
"basePath": "/",
"schemes": [
"http",
"https"
],
"securityDefinitions": {
"basic": {
"type": "basic"
}
}
},
"routes": {
"basePath": "/",
"entryFile": "./src/server.ts",
"routesDir": "./src",
"authenticationModule": "./src/security/Authentication"
}
}

Answer 4

In my case there was a problem with https. In swagger config the http scheme was "disabled" (not available). I had it like this:
GlobalConfiguration.Configuration.EnableSwagger(c => { c.Schemes(new[] { "https" }); });
And I had to change it to make it work in debug on localhost:
GlobalConfiguration.Configuration.EnableSwagger(c => { c.Schemes(new[] { "https", "http" }); });
The first snippet worked on production with enabled https but id didn't work while debugging in Visual Studio in default config.

Answer 5

In my case I was sending very simple text response e.g. "Resource not found" in the body and set Content-Type to "application/json". Depends on version Swagger has a hard time deserializing simple text to json, so im my case changing Content-Type to "text/plain" did the trick.