“通过XHR访问Reddit托管视频的HLS / DASH URL时，CORS标头'Access-Control-Allow-Origin'丢失”错误

Question

我正在尝试使用hls.js库显示来自HLS / DASH播放列表的Reddit托管视频。但是，由于错误提示是违反同源策略，所以通过XHR访问任何Reddit HLS / DASH url（例如this one）将失败，因为该错误表明是违反了同源策略：

Cross-Origin Request Blocked: The Same Origin Policy disallows reading the remote resource at https://v.redd.it/5r0nz8sywgl41/DASHPlaylist.mpd. (Reason: CORS header ‘Access-Control-Allow-Origin’ missing).

奇怪的是，请求之前的GET是OPTIONS，它确实返回带有正确原始URL的Access-Control-Allow-Origin标头。我可以在开发人员控制台中看到响应，但是请求仍然“失败”。如果我使用“允许CORS：Access-Control-Allow-Origin”扩展名，则一切正常。 我做错了什么？

OPTIONS请求标头：

Host: v.redd.it
User-Agent: Mozilla/5.0 (Windows NT 10.0; Win64; x64; rv:73.0) Gecko/20100101 Firefox/73.0
Accept: */*
Accept-Language: lt,en-US;q=0.7,en;q=0.3
Accept-Encoding: gzip, deflate, br
Access-Control-Request-Method: GET
Access-Control-Request-Headers: authorization
Referer: http://localhost:3000/
Origin: http://localhost:3000
DNT: 1
Connection: keep-alive
Save-Data: on
Pragma: no-cache
Cache-Control: no-cache
TE: Trailers

OPTIONS响应标头：

HTTP/2 200 OK
retry-after: 0
access-control-allow-origin: http://localhost:3000
access-control-allow-headers: authorization
access-control-allow-methods: GET
access-control-max-age: 3000
date: Sun, 08 Mar 2020 18:40:29 GMT
via: 1.1 varnish
x-served-by: cache-hhn4029-HHN
x-cache: HIT
x-cache-hits: 0
x-timer: S1583692829.044409,VS0,VE0
server: snooserv
accept-ranges: bytes
x-cdn-server-region: EU-East
x-cdn-client-region: EU
x-cdn-name: fastly
access-control-expose-headers: x-cdn-server-region, x-cdn-client-region, x-cdn-name
cache-control: public, max-age=604800, s-maxage=86400, must-revalidate
vary: Access-Control-Request-Headers, Access-Control-Request-Method,Origin
content-length: 0
X-Firefox-Spdy: h2

获取请求标头：

Host: v.redd.it
User-Agent: Mozilla/5.0 (Windows NT 10.0; Win64; x64; rv:73.0) Gecko/20100101 Firefox/73.0
Accept: */*
Accept-Language: lt,en-US;q=0.7,en;q=0.3
Accept-Encoding: gzip, deflate, br
Referer: http://localhost:3000/
Authorization: Bearer --------------------------- (actual token here)
Origin: http://localhost:3000
DNT: 1
Connection: keep-alive
Save-Data: on
Pragma: no-cache
Cache-Control: no-cache
TE: Trailers

获取响应标题：

HTTP/2 200 OK
last-modified: Sun, 08 Mar 2020 15:34:11 GMT
etag: "0abfb243cb8d03188bf34ff29d6d4af8"
content-type: application/dash+xml
via: 1.1 varnish
date: Sun, 08 Mar 2020 18:40:29 GMT
via: 1.1 varnish
x-served-by: cache-bwi5138-BWI, cache-hhn4029-HHN
x-cache: HIT, HIT
x-cache-hits: 2, 34
x-timer: S1583692829.127808,VS0,VE0
server: snooserv
accept-ranges: bytes
x-cdn-server-region: EU-East
x-cdn-client-region: EU
x-cdn-name: fastly
access-control-expose-headers: x-cdn-server-region, x-cdn-client-region, x-cdn-name
cache-control: public, max-age=604800, s-maxage=86400, must-revalidate
vary: Origin
content-length: 1976
X-Firefox-Spdy: h2

获取回复：

<?xml version="1.0" encoding="UTF-8" standalone="yes"?>
<MPD mediaPresentationDuration="PT15.034S" minBufferTime="PT1.500S" profiles="urn:mpeg:dash:profile:isoff-on-demand:2011" type="static" xmlns="urn:mpeg:dash:schema:mpd:2011">
    <Period duration="PT15.034S">
        <AdaptationSet segmentAlignment="true" subsegmentAlignment="true" subsegmentStartsWithSAP="1">
            <Representation bandwidth="1172841" codecs="avc1.4d401f" frameRate="30" height="480" id="VIDEO-1" mimeType="video/mp4" startWithSAP="1" width="720">
                <BaseURL>DASH_480</BaseURL>
                <SegmentBase indexRange="913-992" indexRangeExact="true">
                    <Initialization range="0-912"/>
                </SegmentBase>
            </Representation>
            <Representation bandwidth="784684" codecs="avc1.4d401e" frameRate="30" height="360" id="VIDEO-2" mimeType="video/mp4" startWithSAP="1" width="540">
                <BaseURL>DASH_360</BaseURL>
                <SegmentBase indexRange="915-994" indexRangeExact="true">
                    <Initialization range="0-914"/>
                </SegmentBase>
            </Representation>
            <Representation bandwidth="592784" codecs="avc1.4d401e" frameRate="30" height="240" id="VIDEO-3" mimeType="video/mp4" startWithSAP="1" width="360">
                <BaseURL>DASH_240</BaseURL>
                <SegmentBase indexRange="915-994" indexRangeExact="true">
                    <Initialization range="0-914"/>
                </SegmentBase>
            </Representation>
            <Representation bandwidth="91690" codecs="avc1.4d400a" frameRate="30" height="96" id="VIDEO-4" mimeType="video/mp4" startWithSAP="1" width="144">
                <BaseURL>DASH_96</BaseURL>
                <SegmentBase indexRange="912-991" indexRangeExact="true">
                    <Initialization range="0-911"/>
                </SegmentBase>
            </Representation>
        </AdaptationSet>
    </Period>
</MPD>

非常感谢您的帮助。

Answer 1

...]，将无法通过XHR访问任何Reddit HLS / DASH url，例如通过XHR进行访问。

问题就是：代码中从https://v.redd.it/5r0nz8sywgl41/DASHPlaylist.mpd到GET请求的响应不包含Access-Control-Allow-Origin响应标头。奇怪的是，它确实包含Access-Control-Expose-Headers响应标头。因此，原因仅在于服务器配置错误。实际上并没有正确启用CORS。