🎨 HTTP 協議的前世今生

{"type":"doc","content":[{"type":"heading","attrs":{"align":null,"level":2},"content":[{"type":"text","text":"0. 前言","attrs":{}}]},{"type":"paragraph","attrs":{"indent":0,"number":0,"align":null,"origin":null},"content":[{"type":"text","text":"你知道當我們在網頁瀏覽器的地址欄中輸入 URL 時，Web 頁面是如何呈現的嗎？","attrs":{}}]},{"type":"image","attrs":{"src":"https://static001.geekbang.org/infoq/ad/ad1e5dfe5e8a66941cbf2b312a085cc8.png","alt":"","title":null,"style":[{"key":"width","value":"75%"},{"key":"bordertype","value":"none"}],"href":null,"fromPaste":true,"pastePass":true}},{"type":"paragraph","attrs":{"indent":0,"number":0,"align":null,"origin":null},"content":[{"type":"text","text":"Web 界面當然不會憑空出來，根據 Web 瀏覽器地址欄中指定的 URL，Web 使用一種名爲 HTTP 的協議作爲規範，完成從客戶端到服務端的一些流程。","attrs":{}},{"type":"text","marks":[{"type":"strong","attrs":{}}],"text":"「可以說，Web 是建立在 HTTP 協議上進行通信的」","attrs":{}},{"type":"text","text":"。","attrs":{}}]},{"type":"heading","attrs":{"align":null,"level":2},"content":[{"type":"text","text":"1. HTTP 的誕生","attrs":{}}]},{"type":"paragraph","attrs":{"indent":0,"number":0,"align":null,"origin":null},"content":[{"type":"text","text":"其實，在 1983 年 3 月之前，互聯網還只屬於少數人，全世界的網民之間的信息是無法共享的。在這一互聯網的黎明時期，HTTP 應運而生。","attrs":{}}]},{"type":"paragraph","attrs":{"indent":0,"number":0,"align":null,"origin":null},"content":[{"type":"text","text":"歐洲核子研究組織的 Tim Berners-Lee 博士提出了一種能夠讓遠隔兩地的網民共享知識的設想，最初的理念是：藉助多文檔之間相互關聯的超文本（HyperTest），連成可相互參閱的 WWW（World Wide Web，萬維網）。","attrs":{}}]},{"type":"paragraph","attrs":{"indent":0,"number":0,"align":null,"origin":null},"content":[{"type":"text","text":"現在已提出了 3 項 WWW 構建技術，分別是：","attrs":{}}]},{"type":"bulletedlist","content":[{"type":"listitem","content":[{"type":"paragraph","attrs":{"indent":0,"number":0,"align":null,"origin":null},"content":[{"type":"text","marks":[{"type":"strong","attrs":{}}],"text":"把 SGML（標準通用標記語言）作爲頁面的文本標記語言 HTML","attrs":{}}]}],"attrs":{}},{"type":"listitem","content":[{"type":"paragraph","attrs":{"indent":0,"number":0,"align":null,"origin":null},"content":[{"type":"text","marks":[{"type":"strong","attrs":{}}],"text":"作爲文檔傳遞協議的 HTTP","attrs":{}}]}],"attrs":{}},{"type":"listitem","content":[{"type":"paragraph","attrs":{"indent":0,"number":0,"align":null,"origin":null},"content":[{"type":"text","marks":[{"type":"strong","attrs":{}}],"text":"指定文檔所在地址的 URL","attrs":{}}]}],"attrs":{}}],"attrs":{}},{"type":"paragraph","attrs":{"indent":0,"number":0,"align":null,"origin":null},"content":[{"type":"text","text":"WWW 這一名稱，是 Web 瀏覽器當年用來瀏覽超文本的客戶端應用程序的名稱，現在用來表示這一系列的集合，也可簡稱爲 Web。","attrs":{}}]},{"type":"heading","attrs":{"align":null,"level":2},"content":[{"type":"text","text":"2. 什麼是 HTTP","attrs":{}}]},{"type":"paragraph","attrs":{"indent":0,"number":0,"align":null,"origin":null},"content":[{"type":"text","text":"說了這麼多，大家只知道 HTTP 很牛逼，對 HTTP 是什麼仍然沒有很直觀的概念。別急，在瞭解什麼是 HTTP 之前，我們有必要知道超文本是什麼。","attrs":{}}]},{"type":"paragraph","attrs":{"indent":0,"number":0,"align":null,"origin":null},"content":[{"type":"text","text":"HTTP 傳輸的內容就是","attrs":{}},{"type":"text","marks":[{"type":"strong","attrs":{}}],"text":"「超文本」","attrs":{}},{"type":"text","text":"：","attrs":{}}]},{"type":"bulletedlist","content":[{"type":"listitem","content":[{"type":"paragraph","attrs":{"indent":0,"number":0,"align":null,"origin":null},"content":[{"type":"text","marks":[{"type":"strong","attrs":{}}],"text":"我們先來理解「文本」：在互聯網早期的時候只是簡單的字符文字，但隨着技術的發展，現在「文本」的涵義已經可以擴展爲圖片、視頻、壓縮包等，在 HTTP 眼裏這些都算做「文本」。","attrs":{}}]}],"attrs":{}},{"type":"listitem","content":[{"type":"paragraph","attrs":{"indent":0,"number":0,"align":null,"origin":null},"content":[{"type":"text","marks":[{"type":"strong","attrs":{}}],"text":"再來理解「超文本」：它就是超越了普通文本的文本，它是文字、圖片、視頻等的混合體。最關鍵有「超鏈接」","attrs":{}},{"type":"text","text":"，能從一個超文本跳轉到另外一個超文本。","attrs":{}}]}],"attrs":{}}],"attrs":{}},{"type":"paragraph","attrs":{"indent":0,"number":0,"align":null,"origin":null},"content":[{"type":"text","text":"OK，下面我們正式介紹什麼是 HTTP？","attrs":{}}]},{"type":"paragraph","attrs":{"indent":0,"number":0,"align":null,"origin":null},"content":[{"type":"text","marks":[{"type":"strong","attrs":{}}],"text":"「HTTP：超文本傳輸協議」","attrs":{}},{"type":"text","text":"（HyperText Transfer Protocol）是當今互聯網上應用最爲廣泛的一種網絡協議。所有的 WWW（萬維網） 文件都必須遵守這個標準。","attrs":{}},{"type":"text","marks":[{"type":"underline","attrs":{}}],"text":"HTTP 和 TCP/IP 協議簇中的衆多協議一樣，用於客戶端和服務器端之間的通信","attrs":{}},{"type":"text","text":"。","attrs":{}}]},{"type":"image","attrs":{"src":"https://static001.geekbang.org/infoq/45/45afee5358d809b3e001241989e5c44b.png","alt":"","title":null,"style":[{"key":"width","value":"75%"},{"key":"bordertype","value":"none"}],"href":null,"fromPaste":true,"pastePass":true}},{"type":"heading","attrs":{"align":null,"level":2},"content":[{"type":"text","text":"3. 駐足不前的 HTTP","attrs":{}}]},{"type":"paragraph","attrs":{"indent":0,"number":0,"align":null,"origin":null},"content":[{"type":"text","text":"至今被世人廣泛使用的 HTTP 協議，仍然是 20 多年前的版本。也就是說，作爲 Web 文檔傳輸協議的 HTTP，它的版本幾乎沒有更新，從另一方面來說，前人的智慧真的牛逼 👍","attrs":{}}]},{"type":"paragraph","attrs":{"indent":0,"number":0,"align":null,"origin":null},"content":[{"type":"text","marks":[{"type":"strong","attrs":{}}],"text":"「HTTP/0.9」","attrs":{}},{"type":"text","text":"：HTTP 於 1990 年問世，","attrs":{}},{"type":"text","marks":[{"type":"underline","attrs":{}}],"text":"功能簡陋，僅支持 GET 請求方式，並且僅能訪問 HTML 格式的資源","attrs":{}},{"type":"text","text":"。那時的 HTTP 並沒有作爲正式的標準被建立，因此被被稱爲 HTTP 0.9。","attrs":{}}]},{"type":"paragraph","attrs":{"indent":0,"number":0,"align":null,"origin":null},"content":[{"type":"text","marks":[{"type":"strong","attrs":{}}],"text":"「HTTP/1.0」","attrs":{}},{"type":"text","text":"：1996 年 5 月 HTTP 正式作爲標準被公佈，版本號爲 HTTP 1.0。","attrs":{}},{"type":"text","marks":[{"type":"underline","attrs":{}}],"text":"在 0.9 版本上做了進步，增加了請求方式 POST 和 HEAD；不再侷限於 0.9 版本的 HTML 格式，根據 Content-Type 可以支持多種數據格式...... 需要注意的是：1.0 版本的工作方式是短連接","attrs":{}},{"type":"text","text":"。雖說 HTTP/1.0 是初期標準，但該協議標準至今仍然在被廣泛使用。","attrs":{}}]},{"type":"paragraph","attrs":{"indent":0,"number":0,"align":null,"origin":null},"content":[{"type":"text","marks":[{"type":"strong","attrs":{}}],"text":"「HTTP/1.1」","attrs":{}},{"type":"text","text":"：1997 年公佈的 HTTP 1.1 是目前主流的 HTTP 協議版本。當年的 HTTP 協議的出現主要是爲了解決文本傳輸的難題，現在的 HTTP 早已超出了 Web 這個框架的侷限，被運用到了各種場景裏。當然，","attrs":{}},{"type":"text","marks":[{"type":"underline","attrs":{}}],"text":"1.1 版本的最大變化，就是引入了長連接以及流水線機制（管道機制）","attrs":{}},{"type":"text","text":"。","attrs":{}}]},{"type":"paragraph","attrs":{"indent":0,"number":0,"align":null,"origin":null},"content":[{"type":"text","text":"這裏面出現的各種專有名詞大家留個印象就行，下文會逐漸講解。","attrs":{}}]},{"type":"heading","attrs":{"align":null,"level":2},"content":[{"type":"text","text":"4. 區分 URL 和 URI","attrs":{}}]},{"type":"paragraph","attrs":{"indent":0,"number":0,"align":null,"origin":null},"content":[{"type":"text","text":"與 URI（","attrs":{}},{"type":"text","marks":[{"type":"strong","attrs":{}}],"text":"「統一資源標識符」","attrs":{}},{"type":"text","text":"） 相比，大家應該更熟悉 URL（Uniform Resource Location，","attrs":{}},{"type":"text","marks":[{"type":"strong","attrs":{}}],"text":"「統一資源定位符」","attrs":{}},{"type":"text","text":"），URL 就是我們使用 Web 瀏覽器訪問 Web 頁面時需要輸入的網頁地址。比如 ","attrs":{}},{"type":"codeinline","content":[{"type":"text","text":"http://baidu.com","attrs":{}}],"attrs":{}},{"type":"text","text":"。","attrs":{}}]},{"type":"paragraph","attrs":{"indent":0,"number":0,"align":null,"origin":null},"content":[{"type":"text","text":"URI 是 Uniform Resource Identifier 的縮寫，RFC 2386 分別對這三個單詞進行如下定義：","attrs":{}}]},{"type":"bulletedlist","content":[{"type":"listitem","content":[{"type":"paragraph","attrs":{"indent":0,"number":0,"align":null,"origin":null},"content":[{"type":"text","marks":[{"type":"strong","attrs":{}}],"text":"Uniform：統一規定的格式可方便處理多種不同類型的資源","attrs":{}}]}],"attrs":{}},{"type":"listitem","content":[{"type":"paragraph","attrs":{"indent":0,"number":0,"align":null,"origin":null},"content":[{"type":"text","marks":[{"type":"strong","attrs":{}}],"text":"Resource：資源的定義是可標識的任何東西。不僅可以是單一的，也可以是一個集合","attrs":{}}]}],"attrs":{}},{"type":"listitem","content":[{"type":"paragraph","attrs":{"indent":0,"number":0,"align":null,"origin":null},"content":[{"type":"text","marks":[{"type":"strong","attrs":{}}],"text":"Identifier：標識可標識的對象。也稱爲標識符","attrs":{}}]}],"attrs":{}}],"attrs":{}},{"type":"paragraph","attrs":{"indent":0,"number":0,"align":null,"origin":null},"content":[{"type":"text","text":"綜上，URI 就是由某個協議方法表示的資源的定位標識符。比如說，採用 HTTP 協議時，協議方案就是 ","attrs":{}},{"type":"codeinline","content":[{"type":"text","text":"http","attrs":{}}],"attrs":{}},{"type":"text","text":"，除此之外，還有 ","attrs":{}},{"type":"codeinline","content":[{"type":"text","text":"ftp","attrs":{}}],"attrs":{}},{"type":"text","text":"、","attrs":{}},{"type":"codeinline","content":[{"type":"text","text":"telnet","attrs":{}}],"attrs":{}},{"type":"text","text":" 等，標準的 URI 協議方法有 30 種左右。","attrs":{}}]},{"type":"paragraph","attrs":{"indent":0,"number":0,"align":null,"origin":null},"content":[{"type":"text","text":"URI 有兩種格式，相對 URI 和絕對 URI。","attrs":{}}]},{"type":"bulletedlist","content":[{"type":"listitem","content":[{"type":"paragraph","attrs":{"indent":0,"number":0,"align":null,"origin":null},"content":[{"type":"text","marks":[{"type":"strong","attrs":{}}],"text":"「相對 URI」","attrs":{}},{"type":"text","text":"：指從瀏覽器中基本 URI 處指定的 URL，形如 ","attrs":{}},{"type":"codeinline","content":[{"type":"text","text":"/user/logo.png","attrs":{}}],"attrs":{}}]}],"attrs":{}},{"type":"listitem","content":[{"type":"paragraph","attrs":{"indent":0,"number":0,"align":null,"origin":null},"content":[{"type":"text","marks":[{"type":"strong","attrs":{}}],"text":"「絕對 URI」","attrs":{}},{"type":"text","text":"：使用涵蓋全部必要信息","attrs":{}}]}],"attrs":{}}],"attrs":{}},{"type":"image","attrs":{"src":"https://static001.geekbang.org/infoq/6e/6e23a399114ef9efc63e74810c0d844a.png","alt":"","title":null,"style":[{"key":"width","value":"75%"},{"key":"bordertype","value":"none"}],"href":null,"fromPaste":true,"pastePass":true}},{"type":"bulletedlist","content":[{"type":"listitem","content":[{"type":"paragraph","attrs":{"indent":0,"number":0,"align":null,"origin":null}}],"attrs":{}}],"attrs":{}},{"type":"paragraph","attrs":{"indent":0,"number":0,"align":null,"origin":null},"content":[{"type":"text","text":"總結來說：","attrs":{}},{"type":"text","marks":[{"type":"strong","attrs":{}}],"text":"「URI 用字符串標識某一處互聯網資源，而 URL 標識資源的地點（互聯網上所處的位置），可見 URL 是 URI 的子集」","attrs":{}},{"type":"text","text":"。","attrs":{}}]},{"type":"heading","attrs":{"align":null,"level":2},"content":[{"type":"text","text":"5. HTTP 請求和響應","attrs":{}}]},{"type":"paragraph","attrs":{"indent":0,"number":0,"align":null,"origin":null},"content":[{"type":"text","text":"HTTP 協議規定，在兩臺計算機之間使用 HTTP 協議進行通信時，在一條通信線路上必定有一端是客戶端，另一端則是服務端。","attrs":{}},{"type":"text","marks":[{"type":"underline","attrs":{}}],"text":"當在瀏覽器中輸入網址訪問某個網站時， 你的瀏覽器（客戶端）會將你的請求封裝成一個 HTTP 請求發送給服務器站點，服務器接收到請求後會組織響應數據封裝成一個 HTTP 響應返回給瀏覽器","attrs":{}},{"type":"text","text":"。換句話說，肯定是先從客戶端開始建立通信的，服務器端在沒有接收到請求之前不會發送響應。","attrs":{}}]},{"type":"image","attrs":{"src":"https://static001.geekbang.org/infoq/1c/1c3c3fffc19832c08d1293add63571d1.png","alt":"","title":null,"style":[{"key":"width","value":"75%"},{"key":"bordertype","value":"none"}],"href":null,"fromPaste":true,"pastePass":true}},{"type":"paragraph","attrs":{"indent":0,"number":0,"align":null,"origin":null},"content":[{"type":"text","text":"下面我們詳細分析一下 HTTP 的請求報文和響應報文","attrs":{}}]},{"type":"heading","attrs":{"align":null,"level":3},"content":[{"type":"text","text":"① HTTP 請求報文","attrs":{}}]},{"type":"paragraph","attrs":{"indent":0,"number":0,"align":null,"origin":null},"content":[{"type":"text","text":"HTTP 請求報文由 3 大部分組成：","attrs":{}}]},{"type":"paragraph","attrs":{"indent":0,"number":0,"align":null,"origin":null},"content":[{"type":"text","text":"1）請求行（必須在 HTTP 請求報文的第一行）","attrs":{}}]},{"type":"paragraph","attrs":{"indent":0,"number":0,"align":null,"origin":null},"content":[{"type":"text","text":"2）請求頭（從第二行開始，到第一個空行結束。請求頭和請求體之間存在一個空行）","attrs":{}}]},{"type":"paragraph","attrs":{"indent":0,"number":0,"align":null,"origin":null},"content":[{"type":"text","text":"3）請求體（通常以鍵值對 ","attrs":{}},{"type":"codeinline","content":[{"type":"text","text":"{key:value}","attrs":{}}],"attrs":{}},{"type":"text","text":"方式傳遞數據）","attrs":{}}]},{"type":"paragraph","attrs":{"indent":0,"number":0,"align":null,"origin":null},"content":[{"type":"text","text":"舉個請求報文的例子：","attrs":{}}]},{"type":"image","attrs":{"src":"https://static001.geekbang.org/infoq/42/426f7549c7316f11592de05dbaa4fd25.png","alt":"","title":null,"style":[{"key":"width","value":"75%"},{"key":"bordertype","value":"none"}],"href":null,"fromPaste":true,"pastePass":true}},{"type":"paragraph","attrs":{"indent":0,"number":0,"align":null,"origin":null},"content":[{"type":"text","text":"請求行開頭的 ","attrs":{}},{"type":"codeinline","content":[{"type":"text","text":"POST","attrs":{}}],"attrs":{}},{"type":"text","text":" 表示請求訪問服務器的類型，稱爲方法（method）。隨後的字符串 ","attrs":{}},{"type":"codeinline","content":[{"type":"text","text":"/form/login","attrs":{}}],"attrs":{}},{"type":"text","text":" 指明瞭請求訪問的資源對象，也叫做請求 URI（request-URI）。最後的 ","attrs":{}},{"type":"codeinline","content":[{"type":"text","text":"HTTP/1.1","attrs":{}}],"attrs":{}},{"type":"text","text":" 即 HTTP 的版本號，用來提示客戶端使用的 HTTP 協議功能。","attrs":{}}]},{"type":"paragraph","attrs":{"indent":0,"number":0,"align":null,"origin":null},"content":[{"type":"text","text":"綜上來看，這段請求的意思就是：請求訪問某臺 HTTP 服務器上的 ","attrs":{}},{"type":"codeinline","content":[{"type":"text","text":"/form/login","attrs":{}}],"attrs":{}},{"type":"text","text":" 頁面資源，並附帶參數 name = veal、age = 37。","attrs":{}}]},{"type":"blockquote","content":[{"type":"paragraph","attrs":{"indent":0,"number":0,"align":null,"origin":null},"content":[{"type":"text","marks":[{"type":"color","attrs":{"color":"#6a737d","name":"user"}},{"type":"strong","attrs":{}}],"text":"❝","attrs":{}}]},{"type":"paragraph","attrs":{"indent":0,"number":0,"align":null,"origin":null},"content":[{"type":"text","marks":[{"type":"color","attrs":{"color":"#6a737d","name":"user"}}],"text":"注意，無論是 HTTP 請求報文還是 HTTP 響應報文，請求頭/響應頭和請求體/響應體之間都會有一個","attrs":{}},{"type":"text","marks":[{"type":"color","attrs":{"color":"#6a737d","name":"user"}},{"type":"strong","attrs":{}}],"text":"「空行」","attrs":{}},{"type":"text","marks":[{"type":"color","attrs":{"color":"#6a737d","name":"user"}}],"text":"，且請求體/響應體並不是必須的。","attrs":{}}]},{"type":"paragraph","attrs":{"indent":0,"number":0,"align":null,"origin":null},"content":[{"type":"text","marks":[{"type":"color","attrs":{"color":"#6a737d","name":"user"}}],"text":"❞","attrs":{}}]}],"attrs":{}},{"type":"heading","attrs":{"align":null,"level":4},"content":[{"type":"text","text":"HTTP 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down.zip。","attrs":{}}]},{"type":"paragraph","attrs":{"indent":0,"number":0,"align":null,"origin":null},"content":[{"type":"codeinline","content":[{"type":"text","text":"GET /down.zip HTTP/1.1 ","attrs":{}}],"marks":[{"type":"color","attrs":{"color":"#abb2bf","name":"user"}},{"type":"bgcolor","attrs":{"color":"#282c34","name":"user"}}],"attrs":{}},{"type":"codeinline","content":[{"type":"text","text":"Accept: image/gif, image/x-xbitmap, image/jpeg, image/pjpeg, application/vnd.ms- ","attrs":{}}],"attrs":{}},{"type":"codeinline","content":[{"type":"text","text":"excel, application/msword, application/vnd.ms-powerpoint, */* ","attrs":{}}],"attrs":{}},{"type":"codeinline","content":[{"type":"text","text":"Accept-Language: zh-cn ","attrs":{}}],"attrs":{}},{"type":"codeinline","content":[{"type":"text","text":"Accept-Encoding: gzip, deflate ","attrs":{}}],"attrs":{}},{"type":"codeinline","content":[{"type":"text","text":"User-Agent: Mozilla/4.0 (compatible; MSIE 5.01; Windows NT 5.0) ","attrs":{}}],"attrs":{}},{"type":"codeinline","content":[{"type":"text","text":"Connection: Keep-Alive ","attrs":{}}],"attrs":{}}]},{"type":"paragraph","attrs":{"indent":0,"number":0,"align":null,"origin":null},"content":[{"type":"text","text":"服務器收到請求後，按要求尋找請求的文件，提取文件的信息，然後返回給瀏覽器，返回信息如下：","attrs":{}}]},{"type":"paragraph","attrs":{"indent":0,"number":0,"align":null,"origin":null},"content":[{"type":"codeinline","content":[{"type":"text","text":"200 ","attrs":{}}],"marks":[{"type":"color","attrs":{"color":"#abb2bf","name":"user"}},{"type":"bgcolor","attrs":{"color":"#282c34","name":"user"}}],"attrs":{}},{"type":"codeinline","content":[{"type":"text","text":"Content-Length=106786028 ","attrs":{}}],"attrs":{}},{"type":"codeinline","content":[{"type":"text","text":"Accept-Ranges=bytes ","attrs":{}}],"attrs":{}},{"type":"codeinline","content":[{"type":"text","text":"Date=Mon, 30 Apr 2001 12:56:11 GMT ","attrs":{}}],"attrs":{}},{"type":"codeinline","content":[{"type":"text","text":"ETag=W/","attrs":{}},{"type":"text","marks":[{"type":"color","attrs":{"color":"#98c379","name":"user"}}],"text":"\"02ca57e173c11:95b\"","attrs":{}},{"type":"text","text":" ","attrs":{}}],"attrs":{}},{"type":"codeinline","content":[{"type":"text","text":"Content-Type=application/octet-stream ","attrs":{}}],"attrs":{}},{"type":"codeinline","content":[{"type":"text","text":"Server=Microsoft-IIS/5.0 ","attrs":{}}],"attrs":{}},{"type":"codeinline","content":[{"type":"text","text":"Last-Modified=Mon, 30 Apr 2001 12:56:11 GMT ","attrs":{}}],"attrs":{}}]},{"type":"paragraph","attrs":{"indent":0,"number":0,"align":null,"origin":null},"content":[{"type":"text","text":"OK，那麼既然要斷點續傳，客戶端瀏覽器請求服務器的時候要多加一條信息 — 從哪裏開始請求數據。 比如要求從 2000070 字節開始：","attrs":{}}]},{"type":"paragraph","attrs":{"indent":0,"number":0,"align":null,"origin":null},"content":[{"type":"codeinline","content":[{"type":"text","text":"GET /down.zip HTTP/1.0 ","attrs":{}}],"marks":[{"type":"color","attrs":{"color":"#abb2bf","name":"user"}},{"type":"bgcolor","attrs":{"color":"#282c34","name":"user"}}],"attrs":{}},{"type":"codeinline","content":[{"type":"text","text":"User-Agent: NetFox ","attrs":{}}],"attrs":{}},{"type":"codeinline","content":[{"type":"text","text":"RANGE: bytes=2000070- ","attrs":{}}],"attrs":{}},{"type":"codeinline","content":[{"type":"text","text":"Accept: text/html, image/gif, image/jpeg, *; q=.2, */*; q=.2 ","attrs":{}}],"attrs":{}}]},{"type":"paragraph","attrs":{"indent":0,"number":0,"align":null,"origin":null},"content":[{"type":"text","text":"仔細看一下就會發現多了一行 ","attrs":{}},{"type":"codeinline","content":[{"type":"text","text":"RANGE: bytes=2000070-","attrs":{}}],"attrs":{}},{"type":"text","text":"。這一行的意思就是告訴服務器 down.zip 這個文件從 2000070 字節開始傳，前面的字節不用傳了。","attrs":{}}]},{"type":"paragraph","attrs":{"indent":0,"number":0,"align":null,"origin":null},"content":[{"type":"text","text":"服務器收到這個請求以後，返回的信息如下：","attrs":{}}]},{"type":"paragraph","attrs":{"indent":0,"number":0,"align":null,"origin":null},"content":[{"type":"codeinline","content":[{"type":"text","text":"206","attrs":{}}],"marks":[{"type":"color","attrs":{"color":"#abb2bf","name":"user"}},{"type":"bgcolor","attrs":{"color":"#282c34","name":"user"}}],"attrs":{}},{"type":"codeinline","content":[{"type":"text","text":"Content-Length=106786028","attrs":{}}],"attrs":{}},{"type":"codeinline","content":[{"type":"text","text":"Content-Range=bytes 2000070-106786027/106786028","attrs":{}}],"attrs":{}},{"type":"codeinline","content":[{"type":"text","text":"Date=Mon, 30 Apr 2001 12:55:20 GMT","attrs":{}}],"attrs":{}},{"type":"codeinline","content":[{"type":"text","text":"ETag=W/","attrs":{}},{"type":"text","marks":[{"type":"color","attrs":{"color":"#98c379","name":"user"}}],"text":"\"02ca57e173c11:95b\"","attrs":{}}],"attrs":{}},{"type":"codeinline","content":[{"type":"text","text":"Content-Type=application/octet-stream","attrs":{}}],"attrs":{}},{"type":"codeinline","content":[{"type":"text","text":"Server=Microsoft-IIS/5.0","attrs":{}}],"attrs":{}},{"type":"codeinline","content":[{"type":"text","text":"Last-Modified=Mon, 30 Apr 2001 12:55:20 GMT","attrs":{}}],"attrs":{}}]},{"type":"paragraph","attrs":{"indent":0,"number":0,"align":null,"origin":null},"content":[{"type":"text","text":"和前面服務器返回的信息比較一下，就會發現增加了一行： ","attrs":{}},{"type":"codeinline","content":[{"type":"text","text":"Content-Range=bytes 2000070-106786027/106786028","attrs":{}}],"attrs":{}},{"type":"text","text":"。返回的代碼也改爲 206 了，而不再是 200 了。","attrs":{}}]},{"type":"heading","attrs":{"align":null,"level":2},"content":[{"type":"text","text":"9. HTTP 的缺點","attrs":{}}]},{"type":"paragraph","attrs":{"indent":0,"number":0,"align":null,"origin":null},"content":[{"type":"text","text":"到現在爲止，我們已經瞭解到了 HTTP 具有相當優秀和方便的一面，然後，事務皆有兩面性，他也是有不足之處的：","attrs":{}}]},{"type":"bulletedlist","content":[{"type":"listitem","content":[{"type":"paragraph","attrs":{"indent":0,"number":0,"align":null,"origin":null},"content":[{"type":"text","marks":[{"type":"strong","attrs":{}}],"text":"通信使用明文（不加密），內容可能被「竊聽」","attrs":{}}]}],"attrs":{}},{"type":"listitem","content":[{"type":"paragraph","attrs":{"indent":0,"number":0,"align":null,"origin":null},"content":[{"type":"text","marks":[{"type":"strong","attrs":{}}],"text":"不驗證通信對方的身份，因此有可能遭遇「僞裝」","attrs":{}}]}],"attrs":{}},{"type":"listitem","content":[{"type":"paragraph","attrs":{"indent":0,"number":0,"align":null,"origin":null},"content":[{"type":"text","marks":[{"type":"strong","attrs":{}}],"text":"無法證明報文的完整性，所以有可能被「篡改」","attrs":{}}]}],"attrs":{}}],"attrs":{}},{"type":"paragraph","attrs":{"indent":0,"number":0,"align":null,"origin":null},"content":[{"type":"text","text":"這些問題不僅在 HTTP 上出現，其他未加密的協議中也存在類似問題，爲了解決 HTTP 的痛點，HTTPS 應用而生，說白了 ","attrs":{}},{"type":"text","marks":[{"type":"strong","attrs":{}}],"text":"「HTTP + 加密 + 認證 + 完整性保護就是 HTTPS 協議」","attrs":{}},{"type":"text","text":"，關於 HTTPS 協議的內容也非常之多且重要，後續會單開一篇文章進行講解。","attrs":{}}]},{"type":"paragraph","attrs":{"indent":0,"number":0,"align":null,"origin":null}},{"type":"heading","attrs":{"align":null,"level":2},"content":[{"type":"text","text":"🎉 關注公衆號 | 飛天小牛肉，即時獲取更新","attrs":{}}]},{"type":"bulletedlist","content":[{"type":"listitem","content":[{"type":"paragraph","attrs":{"indent":0,"number":0,"align":null,"origin":null},"content":[{"type":"text","text":"博主東南大學研一在讀，利用課餘時間運營一個","attrs":{}},{"type":"text","marks":[{"type":"strong","attrs":{}}],"text":"公衆號『 飛天小牛肉 』","attrs":{}},{"type":"text","text":"，專注分享計算機基礎（數據結構 + 算法 + 計算機網絡 + 數據庫 + 操作系統 + Linux）、Java 基礎和麪試指南的相關原創技術好文。本公衆號的目的就是","attrs":{}},{"type":"text","marks":[{"type":"strong","attrs":{}}],"text":"讓大家可以快速掌握重點知識，有的放矢","attrs":{}},{"type":"text","text":"。關注公衆號，第一時間獲取文章更新，與小牛肉一起成長吧！","attrs":{}}]}],"attrs":{}}],"attrs":{}},{"type":"image","attrs":{"src":"https://static001.geekbang.org/infoq/0d/0d993720bb1afd13bdbbe959ed8a55d0.png","alt":null,"title":"","style":[{"key":"width","value":"25%"},{"key":"bordertype","value":"none"}],"href":"","fromPaste":false,"pastePass":false}},{"type":"paragraph","attrs":{"indent":0,"number":0,"align":null,"origin":null}},{"type":"bulletedlist","content":[{"type":"listitem","content":[{"type":"paragraph","attrs":{"indent":0,"number":0,"align":null,"origin":null},"content":[{"type":"text","text":"並推薦個人維護的開源教程類項目： ","attrs":{}},{"type":"link","attrs":{"href":"https://gitee.com/veal98/CS-Wiki","title":null},"content":[{"type":"text","text":"CS-Wiki（Gitee 推薦項目，現已 0.9k star）","attrs":{}}],"marks":[{"type":"strong"}]},{"type":"text","text":", 面向全棧，致力於構建完善的知識體系（數據結構、計算機網絡、操作系統、算法、數據庫、設計模式、Java 技術棧、機器學習、深度學習、強化學習等）。相比公衆號，本倉庫擁有更加健全的知識體系，歡迎各位小夥伴前來 star ~ 😊","attrs":{}}]}],"attrs":{}}],"attrs":{}},{"type":"paragraph","attrs":{"indent":0,"number":0,"align":null,"origin":null}}]}