HTTP 协议

HTTP（Hypertext Transfer Protocol）是万维网通信的基石。

initiated by Tim Berners-Lee in 1989.
HTTP/1.0：RFC 1945；
May 1996；
HTTP/1.1：RFC 2068 -> 2616 -> 7230-7235；
January 1997 -> June 1999 -> June 2014
HTTP/2：RFC 7540；
May 2015
List of HTTP status codes（标准 HTTP 状态码）；
NGINX HTTP Return Codes；
List of HTTP header fields；
HTTP 标准 Header；
online URL Parser / Query String Splitter @ freeformatter.com；
base64，base64 在线编码、解码；
Nginx：HTTP and reverse proxy server, a mail proxy server, and a generic TCP/UDP proxy server.

http status code

URL 可以多长？
What is the maximum length of a URL in different browsers？
最长保持在 2000 字节以内没问题；
451
Unavailable For Legal Reasons (RFC 7725)；
Nginx 499 Client Closed Request（了解 LXR）

Used when the client has closed the request before the server could send a response.
Used in Nginx logs to indicate when the connection has been closed by client while the server is still processing its request, making server unable to send a status code back.
Client Error
The 4XX class of codes indicate you did something wrong. Specifically, there's an error on the client side.

http server @ github

a simple zero-configuration command-line http server.
使用非常简单；

Transfer-Encoding Header

Transfer-Encoding: chunked
开发 PHP 服务时，如果确切地知道返回的内容长度，一定要指定 Content-Length头，否则 Nginx 默认使用 chunked，因为它不知道何时结束，导致即使0字节的返回，网络上也有5个字节的内容传送（不包括 http header 的长度）。
mdn上的例子很好地诠释了这个原因，如下图：

mozilla.org上的 chunked 编码示例

Meta refresh

How to Use the Meta Refresh Tag？
示例

drawbacks：impairs the web browser's "back" button；user dissatisfaction；
legitimate uses：Many large websites use it to refresh news or status updates, especially when dependencies on JavaScript and redirect headers are unwanted.
You should mention that automatic refresh can be disabled in some browsers.

Refresh Header

不是 HTTP 标准 Header；
Netscape 创建的；
被 W3C 通过 Meta refresh 方式所接纳；

3 ways of redirection

Via 3xx response (in the Location HTTP response header)
Via Javascript (or any other client side code) in the response page (e.g. document.location=...)
Via "META REFRESH" ()
Refresh Header was invented by Netscape ；

URL Redirection

URL 跳转
The simplest way of JavaScript redirect using the onload property of the body tag:

HTTP 1.0 vs 1.1

Major differences between versions HTTP/1.0 and HTTP/1.1；