从原始图像‘ null’访问已被 CORS 策略阻止

我在 OpenLayers3中有 JavaScript 应用程序，我的基础层是由本地平铺创建的。我工作只在我的电脑，所以我不知道为什么我有 CORS 错误。

    var newLayer = new ol.layer.Tile({
source: new ol.source.OSM({
url: 'E:/Maperitive/Tiles/vychod/{z}/{x}/{y}.png'
})
});
var schladming = [21.6187, 48.7327]; // longitude first, then latitude
// since we are using OSM, we have to transform the coordinates...
var schladmingWebMercator = ol.proj.fromLonLat(schladming);


var map = new ol.Map({
layers: [
newLayer
],
controls: [],
target: 'mapid',
view: new ol.View({
center: schladmingWebMercator,
zoom: 10,
minZoom: 10,
maxZoom: 14
})
});

来自控制台的错误消息:

从原始 null访问 file:///E:/Maperitive/Tiles/vychod/10/573/352.png的图像已被 CORS 策略阻止: 无效响应。因此，不允许访问起源 null。

当我双击图片网址，图片是打开的。有什么想法是错误的吗? 我从来没有这样的错误之前。

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Under the covers there will be some form of URL loading request. You can't load images or any other content via this method from a local file system.

Your image needs to be loaded via a web server, so accessed via a proper http URL.

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You're running into a CORS error.

Trying to access your file using the local file system doesn't work in your case.

Origin is null because it's your local file system. Could you possibly host this png file?

Suggestion:

Host these files to an AWS S3 bucket instead. Then you can use the http protocol rather than the file protocol. OR setup some http server on your local system and use http to your localhost to serve the files from if you want to keep everything local.

More Reading:

How CORS Works

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Try to bypass CORS:

For Chrome: edit shortcut or with cmd: C:\Chrome.exe --disable-web-security

For Firefox: Open Firefox and type about:config into the URL bar. search for: security.fileuri.strict_origin_policy set to false

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The problem was actually solved by providing crossOrigin: null to OpenLayers OSM source:

var newLayer = new ol.layer.Tile({
source: new ol.source.OSM({
url: 'E:/Maperitive/Tiles/vychod/{z}/{x}/{y}.png',
crossOrigin: null
})
});
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A solution to this is to serve your code, and make it run on a server, you could use web server for chrome to easily serve your pages.

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In this case the CORS problem has been caused by using the wrong source constructor in OpenLayers. ol.source.OSM is intended for accessing the default OpenStreetMap tiles from the web and for that reason defaults to crossOrigin:'anonymous'. If you are using a local source URL you should use the generic ol.source.XYZ constructor which doesn't default the crossOrigin setting (which is why setting crossOrigin:null above happened to work). And it is perfectly legitimate want to use file protocol for maps, for example on an SD card of a mobile device.

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I was having the exact same problem. In my case none of the above solutions worked, what did it for me was to add the following:

app.UseCors(builder => builder
.AllowAnyOrigin()
.AllowAnyMethod()
.AllowAnyHeader()

So basically, allow everything.

Bear in mind that this is safe only if running locally.

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To solve your error I propose this solution: to work on Visual studio code editor and install live server extension in the editor, which allows you to connect to your local server, for me I put the picture in my workspace 127.0.0.1:5500/workspace/data/pict.png and it works!

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For local development you could serve the files with a simple web server.

With Python 2.7 installed, go into the folder where your project is served, like cd my-project/. And then use python -m SimpleHTTPServer which would make index.html and it's JavaScript files available at localhost:8000.

EDIT: For Python 3 use python -m http.server

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The browser is at the local file system where you're requesting the file. The request was made through XHR. So the origin is mentioned as null. if 'null' is added in the list of protocol schemes supported by CORS, you would access it. But sadly you cant.

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just install live server if using vs code in vs code and enable it , it solved the issue in my case.


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