如何从HTTP CORS获取文件信息？

Question

我正在客户端使用OkHttp库获取文件信息。我正在尝试使用以下代码从Google云端硬盘中获取它：

val url = "https://doc-0g-0c-docs.googleusercontent.com/docs/securesc/ha0ro937gcuc7l7deffksulhg5h7mbp1/uqi0f95jaa3cp9t78aqcmfg352flft7d/1554019200000/16042636045718966916/*/1vjNTRlUeMXFx9_H3IE7jw5yBKV0F3bIO?e=download"
val request = Request.Builder().url(url)
        .header("User-Agent", "Mozilla/5.0 (Linux; Android 7.0) AppleWebKit/537.36 (KHTML, like Gecko) Version/4.0 Focus/2.2 Chrome/61.0.3163.98 Mobile Safari/537.36")
        .header("Origin", "*")
        .header("Access-Control-Request-Method", "POST")
        .header("Access-Control-Request-Headers", "Accept, Content-Length")
        .build()
OkHttpClient().newCall(request).execute().use { response ->
    println(response.headers()) // print all headers
    println("------------------------------")
    println("File size: " + response.header("Content-Length"))
    println("Response code: " + response.code())
}

但是在标题列表中找不到Content-Length：

X-GUploader-UploadID: AEnB2UriGmFlC7rQhj22k_7ABtzFKZzRsU4WMlIvPXmfIzaHnfrdnk6sENez7kMsE
Access-Control-Allow-Origin: *
Access-Control-Allow-Credentials: false
Access-Control-Allow-Headers: Accept, Accept-Language, Authorization, Cache-Control, Content-Disposition, Content-Encoding, Content-Language, Content-Length, Content-MD5, Content-Range, Content-Type, Date, GData-Version, google-cloud-resource-prefix, Host, If-Match, If-Modified-Since, If-None-Match, If-Unmodified-Since, Origin, OriginToken, Pragma, Range, Slug, Transfer-Encoding, Want-Digest, x-chrome-connected, X-ClientDetails, X-Client-Version, X-Firebase-Locale, X-GData-Client, X-GData-Key, X-Goog-AdX-Buyer-Impersonation, X-Goog-Api-Client, X-Goog-AuthUser, X-Goog-PageId, X-Goog-Encode-Response-If-Executable, X-Goog-Correlation-Id, X-Goog-Request-Info, X-Goog-Request-Reason, X-Goog-Experiments, x-goog-iam-authority-selector, x-goog-iam-authorization-token, X-Goog-Spatula, X-Goog-Upload-Command, X-Goog-Upload-Content-Disposition, X-Goog-Upload-Content-Length, X-Goog-Upload-Content-Type, X-Goog-Upload-File-Name, X-Goog-Upload-Header-Content-Length, X-Goog-Upload-Offset, X-Goog-Upload-Protocol, X-Goog-Visitor-Id, X-Goog-FieldMask, X-HTTP-Method-Override, X-JavaScript-User-Agent, X-Pan-Versionid, X-Proxied-User-IP, X-Origin, X-Referer, X-Requested-With, X-Upload-Content-Length, X-Upload-Content-Type, X-Use-HTTP-Status-Code-Override, X-Ios-Bundle-Identifier, X-Android-Package, X-Ariane-Xsrf-Token, X-YouTube-VVT, X-YouTube-Page-CL, X-YouTube-Page-Timestamp, X-Goog-Meeting-Botguardid, X-Goog-Meeting-Debugid, X-Goog-Meeting-Token, X-Client-Data, X-Sfdc-Authorization, MIME-Version, Content-Transfer-Encoding
Access-Control-Allow-Methods: GET,OPTIONS
Content-Type: video/mp4
Content-Disposition: attachment;filename="some-name.mp4"
Date: Sun, 31 Mar 2019 14:54:53 GMT
Expires: Sun, 31 Mar 2019 14:54:53 GMT
Cache-Control: private, max-age=0
X-Goog-Hash: crc32c=6SCARA==
Transfer-Encoding: chunked
Server: UploadServer
Alt-Svc: quic=":443"; ma=2592000; v="46,44,43,39"
------------------------------
File size: null
Response code: 200

我读过很多关于CORS的帖子，但我只找到了服务器到服务器的代码。我试图从客户端获取文件信息，即Android。所以，你知道要取它吗？

提前致谢。

Answer 1

见RFC 2616 Section 4.4

2.如果存在Transfer-Encoding标头字段（第14.41节）并且具有“identity”以外的任何值，则使用“chunked”传输编码（第3.6节）定义传输长度，除非消息通过关闭连接终止。

当你有Content-Length时，你不会得到Transfer-Encoding: chunked标题。

我想如果你需要的话，你必须使用another Google Drive API来获取文件大小。

Answer 2

我建议使用Google Drive API。您需要在文件API集合中使用get API。这是演示link。您可以尝试查看响应标头。这是，fetch文件API的示例Response头。你可以在这里看到内容长度。

HTTP/1.1 200 
date: Sun, 31 Mar 2019 17:11:23 GMT
content-encoding: gzip
server: GSE
content-type: application/json; charset=UTF-8
vary: Origin, X-Origin
cache-control: private, max-age=0, must-revalidate, no-transform
content-length: 162
expires: Sun, 31 Mar 2019 17:11:23 GMT

这些步骤可帮助您执行所需操作：

1. 在Google API控制台中注册您的应用程序。你可以参考这个link。
2. 使用您的Access令牌，您可以调用download API来流式传输内容或下载内容。

请查看此link以获取示例项目