출처 : http://gamecode.tistory.com/13

http://www.tistory.com/Account/Test.asp 에서 ID와 PW를 받아 로그인 인증을 처리한다고 가정

이 포스팅에서는 GET 방식과 POST 방식의 장단점 자세한 설명보다는
C++ 코드로 작성하는 방법의 차이에 대해서 설명 합니다.

우선 HTTP 요청의 포맷은 다음과 같습니다.

<div class="container"><div class="line number1 index0 alt2"><code class="html plain"><</code><code class="html keyword">request-line</code><code class="html plain">></code></div><div class="line number2 index1 alt1"><code class="html plain"><</code><code class="html keyword">headers</code><code class="html plain">></code></div><div class="line number3 index2 alt2"><code class="html plain"><</code><code class="html keyword">blank-line</code><code class="html plain">></code></div><div class="line number4 index3 alt1"><code class="html plain">[<</code><code class="html keyword">request-body</code><code class="html plain">>]</code></div><div class="line number5 index4 alt2"><code class="html plain"></</code><code class="html keyword">request-body</code><code class="html plain">></</code><code class="html keyword">blank-line</code><code class="html plain">></</code><code class="html keyword">headers</code><code class="html plain">></</code><code class="html keyword">request-line</code><code class="html plain">>

1. GET 방식

<div class="container"><div class="line number1 index0 alt2"><code class="cpp comments">// Auth: Lewis. Kim</code></div><div class="line number2 index1 alt1"><code class="cpp comments">// Date: 2010.10.12</code></div><div class="line number3 index2 alt2"><code class="cpp comments">// www.gamecode.tistory.com</code></div><div class="line number4 index3 alt1"><code class="cpp plain">std::string strData = </code><code class="cpp string">"?ID=Test&PW=1234"</code><code class="cpp plain">; </code><code class="cpp comments">// GET 방식은 ? 구분자로 URL과 파라미터를 구분한다.</code></div><div class="line number5 index4 alt2"><code class="cpp plain">std::string strMsg = </code><code class="cpp string">"GET /Account/Test.asp"</code><code class="cpp plain">;</code></div><div class="line number6 index5 alt1"><code class="cpp plain">strMsg += strData;</code></div><div class="line number7 index6 alt2"><code class="cpp plain">strMsg += </code><code class="cpp string">" HTTP/1.1\r\n"</code><code class="cpp plain">;</code></div><div class="line number8 index7 alt1"><code class="cpp plain">strMsg += </code><code class="cpp string">"Host: www.tistory.com\r\n"</code><code class="cpp plain">;</code></div><div class="line number9 index8 alt2"><code class="cpp plain">strMsg += </code><code class="cpp string">"Accept: */*\r\n"</code><code class="cpp plain">;</code></div><div class="line number10 index9 alt1"><code class="cpp plain">strMsg += </code><code class="cpp string">"User-Agent: Mozilla/4.0 (compatible; MSIE 6.0;* Windows NT)\r\n"</code><code class="cpp plain">;</code></div><div class="line number11 index10 alt2"><code class="cpp plain">strMsg += </code><code class="cpp string">"\r\nConnection: close\r\n\r\n"</code><code class="cpp plain">;</code></div></div><code class="html plain">

GET 방식은 URL 주소 뒤에 파라미터를 붙여서 전송하는 방식 입니다.
URL과 파라미터를 구분하기 위해 ? 를 구분자로 쓰며, 파라미터가 여러개 일 경우 & 를 각 파라미터의 구분자로 사용합니다.
마지막 헤더 Connection 다음에 공백 라인이 한 줄 더 있는데,
요청 본문이 없다고 하더라도 이는 꼭 필요 합니다.(HTTP 요청 포맷 참조)

<div class="line number1 index0 alt2"><code class="text plain">GET /Account/Test.asp?ID=Test&PW=1234 HTTP/1.1</code></div><div class="line number2 index1 alt1"><code class="text plain">Host: www.tistory.com</code></div><div class="line number3 index2 alt2"><code class="text plain">Accept: */*</code></div><div class="line number4 index3 alt1"><code class="text plain">User-Agent: Mozilla/4.0 (compatible; MSIE 6.0;* Windows NT)</code></div><div class="line number5 index4 alt2"><code class="text plain">nConnection: close</code> </div><code class="html plain">


2. POST 방식

<div class="container"><div class="line number1 index0 alt2"><code class="php comments">// Auth: Lewis. Kim </code></div><div class="line number2 index1 alt1"><code class="php comments">// Date: 2010.10.12</code></div><div class="line number3 index2 alt2"><code class="php comments">// www.gamecode.tistory.com </code></div><div class="line number4 index3 alt1"><code class="php plain">std::string strData = </code><code class="php string">"ID=Test&PW=1234"</code><code class="php plain">; </code></div><div class="line number5 index4 alt2"><code class="php plain">std::string strMsg = </code><code class="php string">"POST /Account/Test.asp"</code><code class="php plain">; </code></div><div class="line number6 index5 alt1"><code class="php plain">strMsg += </code><code class="php string">" HTTP/1.1\r\n"</code><code class="php plain">; </code></div><div class="line number7 index6 alt2"><code class="php plain">strMsg += </code><code class="php string">"Host: www.tistory.com\r\n"</code><code class="php plain">; </code></div><div class="line number8 index7 alt1"><code class="php plain">strMsg += </code><code class="php string">"Accept: */*\r\n"</code><code class="php plain">; </code></div><div class="line number9 index8 alt2"><code class="php plain">strMsg += </code><code class="php string">"User-Agent: Mozilla/4.0 (compatible; MSIE 6.0;* Windows NT)\r\n"</code><code class="php plain">; </code></div><div class="line number10 index9 alt1"><code class="php plain">strMsg += </code><code class="php string">"Content-type: application/x-www-form-urlencoded\r\n"</code><code class="php plain">; </code></div><div class="line number11 index10 alt2"><code class="php plain">strMsg += </code><code class="php string">"Content-Length: "</code><code class="php plain">; </code></div><div class="line number12 index11 alt1"><code class="php plain">strMsg += strData.length(); </code></div><div class="line number13 index12 alt2"><code class="php plain">strMsg += </code><code class="php string">"\r\nConnection: close\r\n\r\n"</code><code class="php plain">; </code></div><div class="line number14 index13 alt1"><code class="php plain">strMsg += strData;</code> </div></div><code class="html plain">

POST 방식은 URL 주소 뒤에 파라미터를 붙이는 방식이 아닌, 요청헤더에 포함시켜서 전송하는 방식 입니다.
위의 GET 방식에서는 strData를 request-line 에 포함하였는데, POST 방식에서는 마지막 헤더와 공백라인 뒤에
요청본문을 포함합니다.
<div class="container"><div class="line number1 index0 alt2"><code class="text plain">POST /Account/Test.asp HTTP/1.1</code></div><div class="line number2 index1 alt1"><code class="text plain">Host: www.tistory.com</code></div><div class="line number3 index2 alt2"><code class="text plain">Accept: */*</code></div><div class="line number4 index3 alt1"><code class="text plain">User-Agent: Mozilla/4.0 (compatible; MSIE 6.0;* Windows NT)</code></div><div class="line number5 index4 alt2"><code class="text plain">Content-type: application/x-www-form-urlencoded</code></div><div class="line number6 index5 alt1"><code class="text plain">Content-Length: </code></div><div class="line number7 index6 alt2"><code class="text plain">nConnection: close</code></div><div class="line number8 index7 alt1"> </div><div class="line number9 index8 alt2"><code class="text plain">ID=Test&PW=1234</code> </div></div><code class="html plain">

위에 코드에서는 문제가 없지만 만약 ID가 Test가 아닌 Test& 라면 어떻게 될까요?
gamecode.tistory.com/Account/Test.asp?ID=Test&&PW=1234

이러한 문제를 해결 하기 위해 URL Encoding이 필요 합니다.
다음 포스팅에는 URL Encoding에 대하여 쓰도록 하겠습니다.