下载时的头部信息
$filename = "test.jpg";
header('Content-Type:image/gif'); //下载文件类型
header('Content-Disposition: attachment; filename="'.$filename.'"'); //下载文件的描述
header('Content-Length:'.filesize($filename)); //下载文件的大小常用的下载文件类型：
gif image/gif
jpg image/jpeg
png image/png
bmp image/bmp
pdf application/pdf
psd application/octet-stream
ico image/x-icon
rar application/octet-stream
doc application/msword
xls application/vnd.ms-excel
ppt application/vnd.ms-powerpoint
chm application/octet-stream
sql application/octet-stream
log text/plain
dat application/octet-stream
ini application/octet-stream
php application/octet-stream
zip application/zip
7z application/octet-stream
mp3 audio/mpeg
wav audio/wav
lrc application/octet-stream
txt text/plain
html text/html
htm text/html
exe application/octet-stream
avi video/avi
rmvb application/vnd.rn-realmedia-vbr
3gp application/octet-stream
flv application/octet-stream
ttf application/octet-stream
js application/x-javascript
xml text/xml
