Cookies - Web DevelopmentYouTube↗  IA↗(long shot)
Education  38.4K views 315 likes 11 dislikes   23 Feb 2015
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Cookieは小さなデータで
Cookie is a small piece of data stored in
ブラウザに格納されています
the browser for a website. And by small, I
4キロバイト未満のデータで
mean less than four kilobytes. And in practice, we're
実際は100バイト程度の文字列です
only talking about 100 bytes, just a small you know,
概念的には次のような書式で記述されます
really just a string. It takes the format conceptually
名前=値という形です
is something like this, name equals value. And in practice
例えばuser.id=12345のように記述します
it may look something like this, user.id equals 12345.
CookieはユーザIDのようなものによく使用され
Cookies are really commonly used for things like user IDs
ブラウザに必要な一時的な情報を格納します
and, and you know, kind of temporary information that, that a
例えばWebサイトへのログイン状態などです
browser wants to store, you know, whether you're logged into a website.
このCookieは12345というユーザとして
You know, generally, you, you have a cookie that represents the, the
ログインしていることを表しています
fact that you're logged in as user, you know, 12345. So to
簡単な図で説明します
kind of draw you a little picture of how these things
ブラウザがリクエストを送信し
fit together, you know, we might have your browser, and it makes
そのリクエストをWebサーバが受信します
requests, you know, to some web servers. And a web server might
WebサーバはレスポンスのHTTPヘッダに
send back, in it's response, some cookie data, and this is in
Cookieデータを含めてブラウザに返します
the form of an HTTP header. And then your browser
CookieはWebサイトに関連づけられています
basically just stores this cookie, it's associated with this website.
詳細は後ほどお話ししますが ブラウザは
We'll talk more about that shortly. And then every time
Webサイトにリクエストする度に
your browser makes a request to this website in the
ブラウザ内のCookieを
future, now that it has this cookie, it will, it
サーバに送り返します
will send the cookie back to the server. So, you
例えばログインする場合は
know, if you are logging in, you might, you might
ブラウザがフォームを送ってサーバが
post some form here and the server might respond with okay,
12345というユーザのログインを承認します
welcome to our website you are user 12345. And then on
リクエストの度に12345だと名乗っているのです
every future request, you say, hey, I'm user 12345. And that's
これでサイト側はユーザのログインを把握できます
how the website knows that you're logged in. And a cookie,
Cookieはブラウザに格納されるファイルです
you know, is, is just basically a file that your browser stores.
1つのWebサイト当たり20個のCookieを格納できます
Generally, you can store about, about 20 cookies per website. Now,
これはブラウザ側の制限次第です
this is basically up to the browser. It's some sort of,
もう1つの制限がCookieの長さです
it, it, it's a browser limitation. Another limitation is probably the
4キロバイト未満と言いましたが
length of the cookie, which we said is less than four k,
実際にはこれは5バイトです
but in reality [LAUGH], you know, this is this is
格納されるCookieの多くは
five bytes. And we're probably, you know, most of the
恐らく数千バイトに満たないでしょう
cookies we're storing are not, you know, thousands of bytes.
またCookieは特定のドメインに
Another limitation is a cookie has to be associated with a
関連づけられている必要があります
particular domain. So, you know, a cook, a cookie for
udacity.com用のCookieは ユーザとudacity.comにのみ送られ
udacity.com is only sent to you to udacity.com and, and udacity.com
udacity.comが設定できるのは udacity.com用のCookieだけです
can only set cookies for udacity.com. So, it's, each website
各Webサイトが専用のCookieを
has you know, a few cookies that it can store that
プライベートに格納できます
are private for that website. A lot of this depends
この多くが適切に動作するかはブラウザ次第です
on the browser to behave properly. So, you know, this
20個までというのは 以前のInternet Explorerの制限です
20 cookies per website that's an old Internet Explorer limitation.
モダンブラウザの制限数は分かりませんが
Honestly I don't know what the limit is for modern browsers.
20個以上のCookieを格納する場合
But if you're storing more than 20 cookies on, on
少し再考が必要になるでしょう
a particular domain, you'll probably rethink things a little bit.
1つのCookieにもっと多くのデータを
You know, maybe store more data in, you know, in
格納するかもしれませんし 4キロバイトの制限に関しても
a, a single cookie. The four kilobytes, again, there, there's so
大きなCookieを送信し始めると
many things that can go wrong when you start sending big
いろいろうまくいかなくなるでしょう
cookies that are, you know, 4000 bytes long. You know, you can
ブラウザによっては
set, some, some browsers don't handle
複数行のCookieに対応していません
multi-line cookies properly. Some web servers
Webサーバが複数行に対応していないこともあるので
don't handle multi, multi-line cookies properly, so I would suggest keeping it
Cookieは簡潔で短いままがいいでしょう
short and simple. And, and most of our use cases are for
データベースが必要ないくらいの小さなデータは
storing small pieces of data that you don't want to store in a
Cookieに格納する方が簡単です
database. It's easier to just store them in a cookie. Or, you
小さくて一時的なデータで
know, small pieces of, you know, temporary data that is, that is
特定のブラウザで特定のユーザにのみ関連しています
only relevant to this particular user in this particular browser right
CookieはWebサイトに関連づけられますが
now. Now this, this constraint, you know, a cookie being associated
この制約は重要です
with pick your website is, is important. It prevents you know,
Cookieのおかげで多くのWebサイトに
me from, you know, the, the cookie is, is, is what makes
ログインできます　もし別のサイトが
me be logged in at a lot of websites, so. If
Cookieを偽造したり読んだりできたら
another website could forge this cookie or read this cookie, you know,
他人がなりすましたり
they could pretend to be me on another website. You know,
ログが盗まれたりする可能性があります
they could steal my log in information. So cookies, the, the domain
Cookieが属するドメインは重要ですが ブラウザ次第です
that cookie belongs to is, is really important. But it's up to the browser to
ブラウザにバグが見つかることがあります
enforce those rules. And sometimes browsers have bugs
モダンブラウザでは見かけませんが注意してください
you know, none of the modern ones do. I can't remember the last time that happened. But you know, it's just something to be aware of. These are, this is all kind
これらはすべてブラウザ側で規制されます
of browser side, you know, client side, enforced
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