PHP发送HEADER头消息
PHP中我们经常需要通过HEADER发送HTTP标头消息，以便告诉浏览器一些处理状态(Status)或显示参量，最典型的就是发送页面处理HEADER和发送状态HEADER。
无论是发送哪种HEADER消息，都必须保证在发送HEADER之前没有输出任何信息到终端浏览器。
一、使用HEADER发送文本类型头信息
例1：
<?php
header("Content-Type: text/html; charset=UTF-8");//告知各位观众下面将要输出的文本类型
?>
例
1输出HEADER告诉浏览器将要输出的文本编码格式为UTF-8。这在全页面PHP处理上是必须的，否则可能会引起终端浏览器显示乱码或空白页显示现
象。由于PHP指定在HEADER输出前不能有任何输出信息，包括空格，所以当页面运行出现HEADER信息已经发送的提示时候，需要首先检查在
HEADER之前是否输出了某些信息，包括本PHP页面的包含头文件是否输出信息。
如果需要输出文件提示下载可使用如下方法：
<?php
header("Content-type: application/octet-stream");//FILE流
header("Accept-Ranges: bytes");
header("Accept-Length: $filesize");//提示将要接收的文件大小
header("Content-Disposition: attachment; filename=".$fname); //提示终端浏览器下载操作
?>
如
果是PDF格式也可用header("Content-type:
application/pdf");其它格式类似处理，不过上面的例子是个下载文件流通例，但是指定详细的文本格式似乎对浏览器的默认处理似乎更好，比
如让播放器自动播放下载音乐、或PDF编辑器自动打开远程PDF文档等。
附Content-type的MIME类型说明：
<?php
$mimetypes = array(
\'ez\' => \'application/andrew-inset\',
\'hqx\' => \'application/mac-binhex40\',
\'cpt\' => \'application/mac-compactpro\',
\'doc\' => \'application/msword\',
\'bin\' => \'application/octet-stream\',
\'dms\' => \'application/octet-stream\',
\'lha\' => \'application/octet-stream\',
\'lzh\' => \'application/octet-stream\',
\'exe\' => \'application/octet-stream\',
\'class\' => \'application/octet-stream\',
\'so\' => \'application/octet-stream\',
\'dll\' => \'application/octet-stream\',
\'oda\' => \'application/oda\',
\'pdf\' => \'application/pdf\',
\'ai\' => \'application/postscript\',
\'eps\' => \'application/postscript\',
\'ps\' => \'application/postscript\',
\'smi\' => \'application/smil\',
\'smil\' => \'application/smil\',
\'mif\' => \'application/vnd.mif\',
\'xls\' => \'application/vnd.ms-excel\',
\'ppt\' => \'application/vnd.ms-powerpoint\',
\'wbxml\' => \'application/vnd.wap.wbxml\',
\'wmlc\' => \'application/vnd.wap.wmlc\',
\'wmlsc\' => \'application/vnd.wap.wmlscriptc\',
\'bcpio\' => \'application/x-bcpio\',
\'vcd\' => \'application/x-cdlink\',
\'pgn\' => \'application/x-chess-pgn\',
\'cpio\' => \'application/x-cpio\',
\'csh\' => \'application/x-csh\',
\'dcr\' => \'application/x-director\',
\'dir\' => \'application/x-director\',
\'dxr\' => \'application/x-director\',
\'dvi\' => \'application/x-dvi\',
\'spl\' => \'application/x-futuresplash\',
\'gtar\' => \'application/x-gtar\',
\'hdf\' => \'application/x-hdf\',
\'js\' => \'application/x-javascript\',
\'skp\' => \'application/x-koan\',
\'skd\' => \'application/x-koan\',
\'skt\' => \'application/x-koan\',
\'skm\' => \'application/x-koan\',
\'latex\' => \'application/x-latex\',
\'nc\' => \'application/x-netcdf\',
\'cdf\' => \'application/x-netcdf\',
\'sh\' => \'application/x-sh\',
\'shar\' => \'application/x-shar\',
\'swf\' => \'application/x-shockwave-flash\',
\'sit\' => \'application/x-stuffit\',
\'sv4cpio\' => \'application/x-sv4cpio\',
\'sv4crc\' => \'application/x-sv4crc\',
\'tar\' => \'application/x-tar\',
\'tcl\' => \'application/x-tcl\',
\'tex\' => \'application/x-tex\',
\'texinfo\' => \'application/x-texinfo\',
\'texi\' => \'application/x-texinfo\',
\'t\' => \'application/x-troff\',
\'tr\' => \'application/x-troff\',
\'roff\' => \'application/x-troff\',
\'man\' => \'application/x-troff-man\',
\'me\' => \'application/x-troff-me\',
\'ms\' => \'application/x-troff-ms\',
\'ustar\' => \'application/x-ustar\',
\'src\' => \'application/x-wais-source\',
\'xhtml\' => \'application/xhtml+xml\',
\'xht\' => \'application/xhtml+xml\',
\'zip\' => \'application/zip\',
\'au\' => \'audio/basic\',
\'snd\' => \'audio/basic\',
\'mid\' => \'audio/midi\',
\'midi\' => \'audio/midi\',
\'kar\' => \'audio/midi\',
\'mpga\' => \'audio/mpeg\',
\'mp2′ => \'audio/mpeg\',
\'mp3′ => \'audio/mpeg\',
\'aif\' => \'audio/x-aiff\',
\'aiff\' => \'audio/x-aiff\',
\'aifc\' => \'audio/x-aiff\',
\'m3u\' => \'audio/x-mpegurl\',
\'ram\' => \'audio/x-pn-realaudio\',
\'rm\' => \'audio/x-pn-realaudio\',
\'rpm\' => \'audio/x-pn-realaudio-plugin\',
\'ra\' => \'audio/x-realaudio\',
\'wav\' => \'audio/x-wav\',
\'pdb\' => \'chemical/x-pdb\',
\'xyz\' => \'chemical/x-xyz\',
\'bmp\' => \'image/bmp\',
\'gif\' => \'image/gif\',
\'ief\' => \'image/ief\',
\'jpeg\' => \'image/jpeg\',
\'jpg\' => \'image/jpeg\',
\'jpe\' => \'image/jpeg\',
\'png\' => \'image/png\',
\'tiff\' => \'image/tiff\',
\'tif\' => \'image/tiff\',
\'djvu\' => \'image/vnd.djvu\',
\'djv\' => \'image/vnd.djvu\',
\'wbmp\' => \'image/vnd.wap.wbmp\',
\'ras\' => \'image/x-cmu-raster\',
\'pnm\' => \'image/x-portable-anymap\',
\'pbm\' => \'image/x-portable-bitmap\',
\'pgm\' => \'image/x-portable-graymap\',
\'ppm\' => \'image/x-portable-pixmap\',
\'rgb\' => \'image/x-rgb\',
\'xbm\' => \'image/x-xbitmap\',
\'xpm\' => \'image/x-xpixmap\',
\'xwd\' => \'image/x-xwindowdump\',
\'igs\' => \'model/iges\',
\'iges\' => \'model/iges\',
\'msh\' => \'model/mesh\',
\'mesh\' => \'model/mesh\',
\'silo\' => \'model/mesh\',
\'wrl\' => \'model/vrml\',
\'vrml\' => \'model/vrml\',
\'css\' => \'text/css\',
\'html\' => \'text/html\',
\'htm\' => \'text/html\',
\'asc\' => \'text/plain\',
\'txt\' => \'text/plain\',
\'rtx\' => \'text/richtext\',
\'rtf\' => \'text/rtf\',
\'sgml\' => \'text/sgml\',
\'sgm\' => \'text/sgml\',
\'tsv\' => \'text/tab-separated-values\',
\'wml\' => \'text/vnd.wap.wml\',
\'wmls\' => \'text/vnd.wap.wmlscript\',
\'etx\' => \'text/x-setext\',
\'xsl\' => \'text/xml\',
\'xml\' => \'text/xml\',
\'mpeg\' => \'video/mpeg\',
\'mpg\' => \'video/mpeg\',
\'mpe\' => \'video/mpeg\',
\'qt\' => \'video/quicktime\',
\'mov\' => \'video/quicktime\',
\'mxu\' => \'video/vnd.mpegurl\',
\'avi\' => \'video/x-msvideo\',
\'movie\' => \'video/x-sgi-movie\',
\'ice\' => \'x-conference/x-cooltalk\',
);
?>
二、使用HEADER发送状态(Status)信息
当
我们在响应浏览器操作时候，可能需要输出一些提示状态信息，比如访问的文件不存（404状态）在或者文件被转移（301状态）等，告诉用户（包括搜索引
擎）所访问页面的当前状态，这在实际使用中对站长非常重要，因为这直接影响到搜索引擎对当前页面的判定。当前对于301固定转移（HTTP/1.1
301 Moved
Permanently）我们也可以采用其它方式（.htaccess或IIS重定向），但是了解PHP自编程解决这些页面状态提示会加深自己对浏览器状
态的认知。
HEADER状态消息头格式如下：
header("第一部分 第二部分 第三部分");
其中第一部分为HTTP协议的
版本号(HTTP-Version)，第二部分为将要发送的状态代码(Status)，第三部分为状态原因(Reason-Phrase)
，三部分中间用一个空格分割，第一部分和第二部分都是必需，第三部分的状态原因为可选项，一般推荐按照标准写出（参下文）。
例2：
<?php
header("HTTP/1.1 404 Not Found");
?>
例2实际在使用中很少用到的，感觉有点忽悠终端浏览者的意思。
最经常遇到是下面的例3：
<?php
header("HTTP/1.1 301 Moved Permanently");//301永久迁移
header("Location: 跳转新URL地址，默认Location可能会发送302头，笔者暂不确定。
?>
此语句告诉搜索引擎或浏览者，本页面已经被“蚂蚁搬家”了，走，我带你看看新家去（新网页）。更多关于301重定向的内容请参考完美解决IIS和APACHE的301重定向一文。
下面专门把W3上Header状态代码(Status)罗列一下供各位使用参考：
1、状态码类(Status)定义
1xx类：Informational - Request received, continuing process（信息状态码类：请求已收到，继续处理）
2xx类：Success - The action was successfully received, understood,and accepted（成功状态码类：本次操作已收到并处理OK）
3xx类：Redirection - Further action must be taken in order to complete the request （重定向状态码类：完成请求前必须进一步执行操作）
4xx类：Client Error - The request contains bad syntax or cannot be fulfilled（发往客户端的错误状态码类：请求包含语法错误或请求不能完成）
5xx类：Server Error - The server failed to fulfill an apparently valid request （服务器端的错误状态码类：服务器执行合法请求失败）
2、常用状态码(Status)列表（部分）：
| "100" ; Continue
| "101" ; Switching Protocols
| "200" ; OK
| "201" ; Created
| "202" ; Accepted
| "203" ; Non-Authoritative Information
| "204" ; No Content
| "205" ; Reset Content
| "206" ; Partial Content
| "300" ; Multiple Choices
| "301" ; Moved Permanently
| "302" ; Moved Temporarily
| "303" ; See Other
| "304" ; Not Modified
| "305" ; Use Proxy
| "400" ; Bad Request
| "401" ; Unauthorized
| "402" ; Payment Required
| "403" ; Forbidden
| "404" ; Not Found
| "405" ; Method Not Allowed
| "406" ; Not Acceptable
| "407" ; Proxy Authentication Required
| "408" ; Request Time-out
| "409" ; Conflict
| "410" ; Gone
| "411" ; Length Required
| "412" ; Precondition Failed
| "413" ; Request Entity Too Large
| "414" ; Request-URI Too Large
| "415" ; Unsupported Media Type
| "500" ; Internal Server Error
| "501" ; Not Implemented
| "502" ; Bad Gateway
| "503" ; Service Unavailable
| "504" ; Gateway Time-out
| "505" ; HTTP Version not supported
另外我们还可以使用PHP 的HEADER发送一些缓存参数命令、超期命令等，例如：
<?php
header("Cache-Control: no-cache, must-revalidate"); //不要缓存
header("Expires: Fri, 1 Dec 2099 08:00:00 GMT"); // 页面过期时间
?>