Http1.1最初定义在Hypertext Transfer Protocol -- HTTP/1.1中，后面被Hypertext Transfer Protocol (HTTP/1.1): Message Syntax and Routing废除，因此当前HTTP1.1协议实际上包括：

RFC7230:Hypertext Transfer Protocol (HTTP/1.1): Message Syntax and Routing
RFC7231:Hypertext Transfer Protocol (HTTP/1.1): Semantics and Content
RFC7232:Hypertext Transfer Protocol (HTTP/1.1): Conditional Requests
RFC7233:Hypertext Transfer Protocol (HTTP/1.1): Range Requests
RFC7234:Hypertext Transfer Protocol (HTTP/1.1): Caching
RFC7235:Hypertext Transfer Protocol (HTTP/1.1): Authentication

概要

GET /hello.txt HTTP/1.1
User-Agent: curl/7.16.3 libcurl/7.16.3 OpenSSL/0.9.7l zlib/1.2.3
Host: www.example.com
Accept-Language: en, mi

HTTP/1.1 200 OK
Date: Mon, 27 Jul 2009 12:28:53 GMT
Server: Apache
Last-Modified: Wed, 22 Jul 2009 19:15:56 GMT
ETag: "34aa387-d-1568eb00"
Accept-Ranges: bytes
Content-Length: 51
Vary: Accept-Encoding
Content-Type: text/plain

Hello World! My payload includes a trailing CRLF.

HTTP消息格式

HTTP-message   = start-line
                 *( header-field CRLF )
                 CRLF
                 [ message-body ]

程序首先读取start-line以及header，然后根据header里面的内容决定是否含有body。body则按照长度读取定长字节。

start-line

start-line     = request-line / status-line
request-line   = method SP request-target SP HTTP-version CRLF
status-line    = HTTP-version SP status-code SP reason-phrase CRLF

其中：

HTTP中并未直接定义request-line的长度限制，倘若超过服务端实现所支持的长度，则建议返回501(Not implemented)
HTTP建议request-line支持至少8000字符长
若request-target超过服务器预期则必须返回414 (URI Too Long)

header-field

header-field   = field-name ":" OWS field-value OWS

field-name     = token
field-value    = *( field-content / obs-fold )
field-content  = field-vchar [ 1*( SP / HTAB ) field-vchar ]
field-vchar    = VCHAR / obs-text

obs-fold       = CRLF 1*( SP / HTAB )

通常header-field是不应该重复，但有一些例外：

若该header有多个值，则可以定义为多个field-name: field-value或是按照逗号分隔值
Set-Cookie通常会出现多次，但因无法合并到一起，是一个例外

field-value通常只包含US-ASCII 字符集。

对于header的长度HTTP并未直接限制，实际通常根据header的含义在实现上有对应的限制。对于超出预期的请求，规定必须返回4xx错误而不是忽略，以防止 HTTP请求夹带技术攻击。