使用 Python、Flask 和 Angular 的 Google Cloud Platform 上的 CORS 问题

Question

我正在 GCP（谷歌云平台）上使用 Python、Flask 和 Angular 开发单页 Web 应用程序，并且遇到了与 CORS 相关的顽固问题。 当我构建和服务前端时，我收到以下错误：

CORS 策略阻止了在“ https://jsonData-devshell.appspot.com/org ”上从源“ https://mySPA-devshell.appspot.com ”访问 XMLHttpRequest：无“Access-Control-Allow-Origin” ' 请求的资源上存在标头。

后端

为了配置 CORS，我导入了 flask_cors 模块，并通过在我的服务器文件 main.py 中添加CORS(app)将其添加到服务器文件中。

main.py

from .entities.entity import Session, eco_env_engine, Base
from .entities.org import Org, OrgSchema
from flask import Flask, jsonify
from flask_cors import CORS


app = Flask(__name__)
# enable cross origin resource sharing
CORS(app)

Base.metadata.create_all(eco_env_engine)

@app.route('/org', methods=['GET'])
def get_org():
    session = Session()
    org_objects = session.query(Org).all()
    # transform into JSON-serializable objects
    schema = OrgSchema(many=True)
    org = schema.dump(org_objects)
    # serialize as json
    session.close()
    response = jsonify(org)
    return response

我有一个 shell 脚本 server.sh，它创建了一个我可以在http://0.0.0.0:5000访问的接口。

server.sh

# set ../src/main.py as the value of the FLASK_APP environment variable
export FLASK_APP=../src/main.py
# FLASK_ENV=development
# FLASK_DEBUG=1

#activate the virtual environment
source $(pipenv --venv)/bin/activate

#run flask listening on all interfaces
#-h binds to interface
flask run -h 0.0.0.0

当我使用curl -I http://0.0.0.0:5000/org我回来了

HTTP/1.0 200 OK
Content-Type: application/json
Content-Length: 4766
Access-Control-Allow-Origin: *
Server: Werkzeug/1.0.0 Python/3.7.3
Date: Wed, 01 Apr 2020 01:27:11 GMT

注意Access-Control-Allow-Origin:*标头，在我的理解中它应该解决这个问题，但它没有。

我正在 GCP Cloud Shell 编辑器中编写代码并从 GCP Cloud Shell 终端中进行部署。 为了让事情运行，我使用./server.sh &部署后端，使用ng serve部署前端

我尝试过的 CORS 变体：

CORS(app, resource={r'*/*': {'origins': '*/*'}})
CORS(app, resources={r"*": {"origins": ['https://mySPA-devshell.appspot.com', 'https://jsonData-devshell.appspot.com']}})
CORS(app, resources={r'*': {"origins": "*"}})
CORS(app, resources={r"*": {"origins": ['http://localhost:4200', 'http://localhost:5000']}})

前端

org-api.service.ts

import {Injectable} from '@angular/core';
import {HttpClient, HttpErrorResponse} from '@angular/common/http';
import {HttpHeaders, HttpClientModule} from '@angular/common/http';
import {Observable} from 'rxjs/Observable';
import {API_URL} from '../env';
import {Org} from './org.model';
import { catchError } from 'rxjs/operators';
import { throwError } from 'rxjs';

@Injectable()
export class OrgApiService {

  //create private variable 'http' of type HttpClient
  constructor(private http: HttpClient) {
  }

  private static _handleError(err: HttpErrorResponse | any) {
    // return Observable.throw(err.message || 'Error: Unable to complete request.');
    return throwError(err.message || 'Error: Unable to complete request.');
  }

  getOrg(): Observable<Org[]> {
    return this.http    
      .get<Org[]>(`${API_URL}/org`)
      .pipe(catchError(OrgApiService._handleError));
  }

}

org.component.ts

import {Component, OnDestroy, OnInit} from '@angular/core';
import {Subscription} from 'rxjs/Subscription';
import {Org} from './org.model';
import {OrgApiService} from './org-api.service';

@Component({
  selector: 'org',
   template: `
     <div>
       <ul>
         <li *ngFor="let org of orgList">
           {{org.name}}
         </li>
       </ul>
     </div>
   `,
  styleUrls: ['org.component.css'],
})

export class OrgComponent implements OnInit, OnDestroy {
  orgListSubs: Subscription;
  orgList: Org[];
  authenticated = false;

  constructor(private orgApi: OrgApiService) { }

  ngOnInit() {
    this.orgListSubs = this.orgApi
      .getOrg()
      .subscribe(res => {
          this.orgList = res;
        },
        console.error
      );
    const self = this;
  }

  ngOnDestroy() {
    this.orgListSubs.unsubscribe();
  }
}

此外，我遇到了以下解决方案并决定采用它，因为为什么不......无济于事：在我的前端目录中创建一个proxy.conf.json ，其中包含以下内容

{
    "/": {
        "target": "http://0.0.0.0:5000",
        "secure": false,
        "logLevel": "debug"
    }
}

然后向serve目标添加了一个proxyConfig选项。

更新

@sideshowbarker 指出在某些情况下 302 响应没有“Access-Control-Allow-Origin”标头，这在我的情况下是正确的。 在进一步挖掘后，我发现这篇文章提到 chrome 在收到状态代码 302 时取消请求。它还让我进入 chrome://net-export/，在那里我发现我的请求也被取消了。

我还没有对此提出明显/公认的解决方案。 如果您正在阅读本文并有建议……请分享。

t=131761 [st=  4]      QUIC_CONNECTION_MIGRATION_MODE
                       --> connection_migration_mode = 0
t=131761 [st=  4]     +HTTP_TRANSACTION_SEND_REQUEST  [dt=0]
t=131761 [st=  4]        HTTP_TRANSACTION_QUIC_SEND_REQUEST_HEADERS
                         --> :method: GET
                             :authority: 5000-dot-XXXXXXX-dot-devshell.appspot.com
                             :scheme: https
                             :path: /
                             accept: application/json, text/plain, */*
                             sec-fetch-dest: empty
                             user-agent: Mozilla/5.0 (Macintosh; Intel Mac OS X 10_15_3) AppleWebKit/537.36 (KHTML, like Gecko) Chrome/80.0.3987.149 Safari/537.36
                             origin: https://4200-dot-XXXXXXX-dot-devshell.appspot.com
                             sec-fetch-site: cross-site
                             sec-fetch-mode: cors
                             referer: https://4200-dot-XXXXXXX-dot-devshell.appspot.com/?authuser=0&environment_name=default
                             accept-encoding: gzip, deflate, br
                             accept-language: en-US,en;q=0.9
                         --> quic_priority = 4
                         --> quic_stream_id = 5
t=131761 [st=  4]     -HTTP_TRANSACTION_SEND_REQUEST
t=131761 [st=  4]     +HTTP_TRANSACTION_READ_HEADERS  [dt=168]
t=131928 [st=171]        HTTP_TRANSACTION_READ_RESPONSE_HEADERS
                         --> HTTP/1.1 302
                             status: 302
                             date: Wed, 01 Apr 2020 06:33:46 GMT
                             content-type: text/html; charset=utf-8
                             content-length: 498
                             location: https://some.url.com
                             via: 1.1 google
                             alt-svc: quic=":443"; ma=2592000; v="46,43",h3-Q050=":443"; ma=2592000,h3-Q049=":443"; ma=2592000,h3-Q048=":443"; ma=2592000,h3-Q046=":443"; ma=2592000,h3-Q043=":443"; ma=2592000,h3-T050=":443"; ma=2592000
t=131929 [st=172]     -HTTP_TRANSACTION_READ_HEADERS
t=131929 [st=172]      HTTP_CACHE_WRITE_INFO  [dt=0]
t=131929 [st=172]      HTTP_CACHE_WRITE_DATA  [dt=0]
t=131929 [st=172]      HTTP_CACHE_WRITE_INFO  [dt=0]
t=131929 [st=172]      NETWORK_DELEGATE_HEADERS_RECEIVED  [dt=1]
t=131930 [st=173]      URL_REQUEST_DELEGATE_RECEIVED_REDIRECT  [dt=0]
t=131930 [st=173]      CANCELLED
t=131930 [st=173] -REQUEST_ALIVE

我花了几天时间试图解决这个问题，但是我基本上没有成功。 我觉得好像有一个比我尝试过的所有方法都更简单的解决方案。 预先感谢您的帮助！

Answer 1

解决了！

将前端/应用程序中的env.ts编辑为

export const API_URL = 'http://localhost:4200'

而不是localhost:5000

API_URL 对应ng serve开发部署