Swagger UI failed to fetch on simple server

[rcorre]

Problem statement

Even the simplest server I could come up with fails on swagger UI with TypeError: Failed to fetch

Swagger specification

{
  "consumes": [
    "application/json"
  ],
  "produces": [
    "application/json"
  ],
  "schemes": [
    "http",
    "https"
  ],
  "swagger": "2.0",
  "info": {
    "description": "Title: example",
    "title": "is an example REST app",
    "version": "0.0.1"
  },
  "host": "localhost:3000",
  "basePath": "/v1",
  "paths": {
    "/foo": {
      "get": {
        "description": "Get a foo",
        "operationId": "getFoo",
        "responses": {
          "200": {
            "$ref": "#/responses/getFooResponse"
          }
        }
      }
    }
  },
  "responses": {
    "getFooResponse": {
      "description": "GetFooResponse is returned by GET /foo",
      "schema": {
        "type": "object",
        "properties": {
          "Name": {
            "description": "Name of the foo",
            "type": "string"
          }
        }
      }
    }
  },
  "securityDefinitions": {
    "bearer": {
      "type": "apiKey",
      "name": "Authorization",
      "in": "header"
    }
  },
  "security": [
    {
      "bearer": []
    }
  ]
}

Steps to reproduce

main.go:

// Package main is an example REST app
//
//     Title: example
//     Schemes: http, https
//     Host: localhost:3000
//     BasePath: /v1
//     Version: 0.0.1
//
//     Consumes:
//     - application/json
//
//     Produces:
//     - application/json
//
//	   Security:
//     - bearer:
//
//     SecurityDefinitions:
//       bearer:
//         type: apiKey
//         name: Authorization
//         in: header
// swagger:meta
package main

import (
	"encoding/json"
	"log"
	"net/http"
	"time"
)

func main() {
	s := &http.Server{
		Addr:           ":3000",
		Handler:        &myHandler{},
		ReadTimeout:    10 * time.Second,
		WriteTimeout:   10 * time.Second,
		MaxHeaderBytes: 1 << 20,
	}
	log.Fatal(s.ListenAndServe())
}

type myHandler struct{}

// GetFoo handles a GET to /foo
//
// swagger:route GET /foo getFoo
//
// Get a foo
//
//     Responses:
//       200: getFooResponse
func (myHandler) ServeHTTP(w http.ResponseWriter, r *http.Request) {
	log.Printf("Got request %+v", r)
	defer r.Body.Close()

	var resp GetFooResponse
	resp.Body.Name = "foo"

	jsonBody, err := json.Marshal(&resp.Body)
	if err != nil {
		http.Error(w, "failed to marshal", 500)
		return
	}

	w.Write(jsonBody)
}

// GetFooArgs are the parameters to GET /foo
//
// swagger:parameters getFoo
type GetFooArgs struct {
}

// GetFooResponse is returned by GET /foo
//
// swagger:response getFooResponse
type GetFooResponse struct {
	// in:body
	Body struct {
		// Name of the foo
		Name string
	}
}

go build && swagger generate spec -o swagger.json
./example & swagger serve swagger.json -F swagger

Through the swagger UI, try to make a GET request to /foo. It will fail.

Environment

swagger version: dev
go version: go1.8.3
OS: linux/amd64

[casualjim]

your server needs to add a cors middleware, that's the cause of the failure.
#481