mirror of
https://github.com/restoreddev/phpapprentice.git
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76 lines
3.2 KiB
Markdown
76 lines
3.2 KiB
Markdown
+++
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title = "HTTP"
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description = "Understanding the format of the web"
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tags = ["web", "http"]
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slug = "http"
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previous = "exceptions.html"
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next = "web/http-post.html"
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+++
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HTTP stands for Hypertext Transfer Protocol. It is a standard for how requests and responses should be formatted for
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a server and a web browser. When you open a link in your web browser, you are sending a HTTP request to a server and it
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is responding with a HTTP response. The browser then takes the response, parses it and displays it to the user.
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Let us look at a HTTP request for PHP Apprentice. This is the request sent to the server from Firefox:
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```http
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GET /basics.html HTTP/2.0
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Host: phpapprentice.com
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User-Agent: Mozilla/5.0 (Macintosh; Intel Mac OS X 10.14; rv:65.0) Gecko/20100101 Firefox/65.0
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Accept: text/html,application/xhtml+xml,application/xml;q=0.9,image/webp,*/*;q=0.8
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Accept-Language: en-US,en;q=0.5
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Accept-Encoding: gzip, deflate, br
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Connection: keep-alive
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Upgrade-Insecure-Requests: 1
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Pragma: no-cache
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Cache-Control: no-cache
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```
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The first line of the request tells us three things. First, the method of the request. A `GET` request tells the server
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that the browser just wants to download whatever is stored at the link. The second value `/basics.html` determines
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what should be loaded from `phpapprentice.com`. Finally, the third value tells the server what type of HTTP request it is.
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All of the lines below the top line are key/value pairs called headers. They give the server different pieces of information
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about the client and the request to the server. For example, `Host` tells the server what website the browser is
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trying to access.
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In response to the client's HTTP request, the server will respond with a HTTP response. Here is the response for the above request:
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```http
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HTTP/2.0 200 OK
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server: GitHub.com
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content-type: text/html; charset=utf-8
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last-modified: Sun, 13 Jan 2019 22:57:50 GMT
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etag: W/"5c3bc26e-15a0"
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access-control-allow-origin: *
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expires: Mon, 18 Feb 2019 02:38:31 GMT
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cache-control: max-age=600
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content-encoding: gzip
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x-github-request-id: 8596:461C:46C99E:5BB366:5C6A184F
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accept-ranges: bytes
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date: Mon, 18 Feb 2019 03:06:02 GMT
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via: 1.1 varnish
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age: 52
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x-served-by: cache-fty21342-FTY
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x-cache: HIT
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x-cache-hits: 2
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x-timer: S1550459163.720652,VS0,VE0
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vary: Accept-Encoding
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x-fastly-request-id: 00f0eec6f3037e428b8fc86742fe0f9965501a51
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content-length: 2084
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```
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The top line of the response is in two parts, similar to a request.
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The first part `HTTP/2.0` indicates the connection type, like the client.
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The second part `200 OK` is the response code. `200` indicates a successful response.
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There are many different response codes, the most famous being `404 Not Found`.
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A response will have headers as well, but they are to give the client information about the response. As you can see,
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the `Content-Type` is set to `text/html`, which tells the client how to render the content of the response.
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Notice that below the list of response headers, there is also the content of the response. In this case, it is just HTML
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which the browser can you use to display the page.
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HTTP requests and responses are the core of web communication. Next, we will look at a request type other than `GET`.
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