Preflight 未通过控制检查 Access-Control-Allow-Origin Not Present

Question

我有一个在 React 中运行的简单客户端。我正在尝试使用 Axios 向本地运行的 Go 服务器发出 GET 请求。 React 代码在 3000 端口上运行，Go 服务器在 4000 上运行。

如果我将 GET 请求本身粘贴到浏览器窗口中，它可以正常工作：http://localhost:4000/numberconverter?number=10&oldBase=10&newBase=2

我做了一些研究并找到了this post，但插件和 Chrome 选项没有帮助。这不是我做过的唯一研究，但这似乎是最有希望的。我发现的大多数东西都不涉及 Go 服务器。

我也找到了this post，但这也没有解决我的问题。如果我取消注释服务器中的代码，它仍然会失败。

如果我将允许的方法更改为：

writer.Header().Set("Access-Control-Allow-Methods", "GET, POST, PATCH, PUT, DELETE, OPTIONS")

失败并出现 405 错误。服务器打印出这个：

&{0xc4200f4000 0xc42000a500 {} 0x10ec430 true false false false 0xc4200143c0 {0xc420100000 map[Access-Control-Allow-Origin:[*] Access-Control-Allow-Methods:[GET, POST, PATCH, PUT, DELETE, OPTIONS] Content-Type:[text/plain; charset=utf-8] X-Content-Type-Options:[nosniff]] false false} map[Access-Control-Allow-Origin:[*] Access-Control-Allow-Methods:[GET, POST, PATCH, PUT, DELETE, OPTIONS] Content-Type:[text/plain; charset=utf-8] X-Content-Type-Options:[nosniff]] true 19 -1 405 false false [] 0 [0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0] [0 0 0 0 0 0 0 0 0 0] 0xc4200620e0 0}

我想我的问题是这是服务器端还是客户端的问题，以及我该如何解决这个问题？

客户：

import React, {Component} from 'react';
import axios from 'axios';

class Converter extends Component {
    constructor(props) {
        super(props);
        this.state = {
            // number: 0,
            // base: 10,
            // newBase: 10
        };
        this.convertButtonPressed = this.convertButtonPressed.bind(this);
        this.handleChange = this.handleChange.bind(this);
    }

    handleChange(event) {
        const target = event.target;
        const value = target.value;
        const name = target.name;

        this.setState({
        [name]: value
        });
    }

    convertButtonPressed(event) {
        axios({
            method: 'GET',
            baseURL: 'http://localhost:4000/',
            url: '/numberconverter',
            headers: {
                'Access-Control-Allow-Origin': '*',
                'Access-Control-Allow-Methods': 'GET, POST, PATCH, PUT, DELETE, OPTIONS',
                'Access-Control-Allow-Headers': 'Origin, Content-Type, X-Auth-Token'
            },
            params: {
            number: this.state.number,
            oldBase: this.state.base,
            newBase: this.state.newBase
            }
        });
    }

    render() {
        return (
        <div className="App">
            <p>Number Converter</p>
            <div>
            Number:
            <input name="number" onChange={this.handleChange} type="text" placeholder="Number"></input><br />
            Base:
            <input name="base" onChange={this.handleChange} type="text" placeholder="Base"></input><br />
            New Base:
            <input name="newBase" onChange={this.handleChange} type="text" placeholder="New Base"></input><br />
            </div>
            <button onClick={this.convertButtonPressed}>Convert</button>
        </div>
        );
    }
}

export default Converter;

服务器：

package rest

// Example:
// http://localhost:3000/numberconverter?number=500000&oldBase=10&newBase=16

import (
    "fmt"
    "log"
    "net/http"

    "../converter"
)

// Start starts the server
func Start() {
    //muxRouter := http.NewServeMux()
    //muxRouter.HandleFunc("/numberconverter", numberconverter)
    //http.Handle("/", muxRouter)
    http.HandleFunc("/numberconverter", numberconverter)
    log.Fatal(http.ListenAndServe(":4000", nil))
}

func numberconverter(writer http.ResponseWriter, response *http.Request) {
    //writer.Header().Set("Access-Control-Allow-Origin", "*")
    //writer.Header().Set("Access-Control-Allow-Methods", "*")
    //writer.Header().Set("Content-Type", "text/html; charset=utf-8")

    // Check if the method is a get
    if response.Method != http.MethodGet {
        http.Error(writer, http.StatusText(405), 405)
        fmt.Println(writer)
        return
    }

    number := response.FormValue("number")
    oldBase := response.FormValue("oldBase")
    newBase := response.FormValue("newBase")
    result := converter.ConvertStringNumberToNewBase(number, oldBase, newBase)
    fmt.Fprintf(writer, "%s base %s is %s in base %s", number, oldBase, result, newBase)
}

Answer 1

一旦我注释掉 React 代码中的标头，GET 请求就会起作用。我要感谢sideshowbarker 的回答。我真的很感激。

convertButtonPressed(event) {
    axios({
        method: 'GET',
        baseURL: 'http://localhost:4000/',
        url: '/numberconverter',
        // headers: {
        //     'Access-Control-Allow-Origin': '*',
        //     'Access-Control-Allow-Methods': 'GET, POST, PATCH, PUT, DELETE, OPTIONS',
        //     'Access-Control-Allow-Headers': 'Origin, Content-Type, X-Auth-Token'
        // },
        params: {
          number: this.state.number,
          oldBase: this.state.base,
          newBase: this.state.newBase
        }
      });
}