请求中的 response - header 中的content-type项是指�0�2�0�2服务器发送给客户端内容的MIME类型，如果 设置不对 那么浏览器怕是不能正常解析；

const path = require(“path”);

// 多用途Internet邮件扩展（MIME）类型
const mimeType= {
“.323”:“text/h323” ,
“.3gp”:“video/3gpp” ,
“.aab”:“application/x-authoware-bin” ,
“.aam”:“application/x-authoware-map” ,
“.aas”:“application/x-authoware-seg” ,
“.acx”:“application/internet-property-stream” ,
“.ai”:“application/postscript” ,
“.aif”:“audio/x-aiff” ,
“.aifc”:“audio/x-aiff” ,
“.aiff”:“audio/x-aiff” ,
“.als”:“audio/X-Alpha5” ,
“.amc”:“application/x-mpeg” ,
“.ani”:“application/octet-stream” ,
“.apk”:“application/vnd.android.package-archive” ,
“.asc”:“text/plain” ,
“.asd”:“application/astound” ,
“.asf”:“video/x-ms-asf” ,
“.asn”:“application/astound” ,
“.asp”:“application/x-asap” ,
“.asr”:“video/x-ms-asf” ,
“.asx”:“video/x-ms-asf” ,
“.au”:“audio/basic” ,
“.avb”:“application/octet-stream” ,
“.avi”:“video/x-msvideo” ,
“.awb”:“audio/amr-wb” ,
“.axs”:“application/olescript” ,
“.bas”:“text/plain” ,
“.bcpio”:“application/x-bcpio” ,
".bin ":“application/octet-stream” ,
“.bld”:“application/bld” ,
“.bld2”:“application/bld2” ,
“.bmp”:“image/bmp” ,
“.bpk”:“application/octet-stream” ,
“.bz2”:“application/x-bzip2” ,
“.c”:“text/plain” ,
“.cal”:“image/x-cals” ,
“.cat”:“application/vnd.ms-pkiseccat” ,
“.ccn”:“application/x-cnc” ,
“.cco”:“application/x-cocoa” ,
“.cdf”:“application/x-cdf” ,
“.cer”:“application/x-x509-ca-cert” ,
“.cgi”:“magnus-internal/cgi” ,
“.chat”:“application/x-chat” ,
“.class”:“application/octet-stream” ,
“.clp”:“application/x-msclip” ,
“.cmx”:“image/x-cmx” ,
“.co”:“application/x-cult3d-object” ,
“.cod”:“image/cis-cod” ,
“.conf”:“text/plain” ,
“.cpio”:“application/x-cpio” ,
“.cpp”:“text/plain” ,
“.cpt”:“application/mac-compactpro” ,
“.crd”:“application/x-mscardfile” ,
“.crl”:“application/pkix-crl” ,
“.crt”:“application/x-x509-ca-cert” ,
“.csh”:“application/x-csh” ,
“.csm”:“chemical/x-csml” ,
“.csml”:“chemical/x-csml” ,
“.css”:“text/css” ,
“.cur”:“application/octet-stream” ,
“.dcm”:“x-lml/x-evm” ,
“.dcr”:“application/x-director” ,
“.dcx”:“image/x-dcx” ,
“.der”:“application/x-x509-ca-cert” ,
“.dhtml”:“text/html” ,
“.dir”:“application/x-director” ,
“.dll”:“application/x-msdownload” ,
“.dmg”:“application/octet-stream” ,
“.dms”:“application/octet-stream” ,
“.doc”:“application/msword” ,
“.docx”:“application/vnd.openxmlformats-officedocument.wordprocessingml.document” ,
“.dot”:“application/msword” ,
“.dvi”:“application/x-dvi” ,
“.dwf”:“drawing/x-dwf” ,
“.dwg”:“application/x-autocad” ,
“.dxf”:“application/x-autocad” ,
“.dxr”:“application/x-director” ,
“.ebk”:“application/x-expandedbook” ,
“.emb”:“chemical/x-embl-dl-nucleotide” ,
“.embl”:“chemical/x-embl-dl-nucleotide” ,
“.eps”:“application/postscript” ,
“.epub”:“application/epub+zip” ,
“.eri”:“image/x-eri” ,
“.es”:“audio/echospeech” ,
“.esl”:“audio/echospeech” ,
“.etc”:“application/x-earthtime” ,
“.etx”:“text/x-setext” ,
“.evm”:“x-lml/x-evm” ,
“.evy”:“application/envoy” ,
“.exe”:“application/octet-stream” ,
“.fh4”:“image/x-freehand” ,
“.fh5”:“image/x-freehand” ,
“.fhc”:“image/x-freehand” ,
“.fif”:“application/fractals” ,
“.flr”:“x-world/x-vrml” ,
“.flv”:“flv-application/octet-stream” ,
“.fm”:“application/x-maker” ,
“.fpx”:“image/x-fpx” ,
“.fvi”:“video/isivideo” ,
“.gau”:“chemical/x-gaussian-input” ,
“.gca”:“application/x-gca-compressed” ,
“.gdb”:“x-lml/x-gdb” ,
“.gif”:“image/gif” ,
“.gps”:“application/x-gps” ,
“.gtar”:“application/x-gtar” ,
“.gz”:“application/x-gzip” ,
“.h”:“text/plain” ,
“.hdf”:“application/x-hdf” ,
“.hdm”:“text/x-hdml” ,
“.hdml”:“text/x-hdml” ,
“.hlp”:“application/winhlp” ,
“.hqx”:“application/mac-binhex40” ,
“.hta”:“application/hta” ,
“.htc”:“text/x-component” ,
“.htm”:“text/html” ,
“.html”:“text/html” ,
“.hts”:“text/html” ,
“.htt”:“text/webviewhtml” ,
“.ice”:“x-conference/x-cooltalk” ,
“.ico”:“image/x-icon” ,
“.ief”:“image/ief” ,
“.ifm”:“image/gif” ,
“.ifs”:“image/ifs” ,
“.iii”:“application/x-iphone” ,
“.imy”:“audio/melody” ,
“.ins”:“application/x-internet-signup” ,
“.ips”:“application/x-ipscript” ,
“.ipx”:“application/x-ipix” ,
“.isp”:“application/x-internet-signup” ,
“.it”:“audio/x-mod” ,
“.itz”:“audio/x-mod” ,
“.ivr”:“i-world/i-vrml” ,
“.j2k”:“image/j2k” ,
“.jad”:“text/vnd.sun.j2me.app-descriptor” ,
“.jam”:“application/x-jam” ,
“.jar”:“application/java-archive” ,
“.java”:“text/plain” ,
“.jfif”:“image/pipeg” ,
“.jnlp”:“application/x-java-jnlp-file” ,
“.jpe”:“image/jpeg” ,
“.jpeg”:“image/jpeg” ,
“.jpg”:“image/jpeg” ,
“.jpz”:“image/jpeg” ,
“.js”:“application/x-javascript” ,
“.jwc”:“application/jwc” ,
“.kjx”:“application/x-kjx” ,
“.lak”:“x-lml/x-lak” ,
“.latex”:“application/x-latex” ,
“.lcc”:“application/fastman” ,
“.lcl”:“application/x-digitalloca” ,
“.lcr”:“application/x-digitalloca” ,
“.lgh”:“application/lgh” ,
“.lha”:“application/octet-stream” ,
“.lml”:“x-lml/x-lml” ,
“.lmlpack”:“x-lml/x-lmlpack” ,
“.log”:“text/plain” ,
“.lsf”:“video/x-la-asf” ,
“.lsx”:“video/x-la-asf” ,
“.lzh”:“application/octet-stream” ,
“.m13”:“application/x-msmediaview” ,
“.m14”:“application/x-msmediaview” ,
“.m15”:“audio/x-mod” ,
“.m3u”:“audio/x-mpegurl” ,
“.m3url”:“audio/x-mpegurl” ,
“.m4a”:“audio/mp4a-latm” ,
“.m4b”:“audio/mp4a-latm” ,
“.m4p”:“audio/mp4a-latm” ,
“.m4u”:“video/vnd.mpegurl” ,
“.m4v”:“video/x-m4v” ,
“.ma1”:“audio/ma1” ,
“.ma2”:“audio/ma2” ,
“.ma3”:“audio/ma3” ,
“.ma5”:“audio/ma5” ,
“.man”:“application/x-troff-man” ,
“.map”:“magnus-internal/imagemap” ,
“.mbd”:“application/mbedlet” ,
“.mct”:“application/x-mascot” ,
“.mdb”:“application/x-msaccess” ,
“.mdz”:“audio/x-mod” ,
“.me”:“application/x-troff-me” ,
“.mel”:“text/x-vmel” ,
“.mht”:“message/rfc822” ,
“.mhtml”:“message/rfc822” ,
“.mi”:“application/x-mif” ,
“.mid”:“audio/mid” ,
“.midi”:“audio/midi” ,
“.mif”:“application/x-mif” ,
“.mil”:“image/x-cals” ,
“.mio”:“audio/x-mio” ,
“.mmf”:“application/x-skt-lbs” ,
“.mng”:“video/x-mng” ,
“.mny”:“application/x-msmoney” ,
“.moc”:“application/x-mocha” ,
“.mocha”:“application/x-mocha” ,
“.mod”:“audio/x-mod” ,
“.mof”:“application/x-yumekara” ,
“.mol”:“chemical/x-mdl-molfile” ,
“.mop”:“chemical/x-mopac-input” ,
“.mov”:“video/quicktime” ,
“.movie”:“video/x-sgi-movie” ,
“.mp2”:“video/mpeg” ,
“.mp3”:“audio/mpeg” ,
“.mp4”:“video/mp4” ,
“.mpa”:“video/mpeg” ,
“.mpc”:“application/vnd.mpohun.certificate” ,
“.mpe”:“video/mpeg” ,
“.mpeg”:“video/mpeg” ,
“.mpg”:“video/mpeg” ,
“.mpg4”:“video/mp4” ,
“.mpga”:“audio/mpeg” ,
“.mpn”:“application/vnd.mophun.application” ,
“.mpp”:“application/vnd.ms-project” ,
“.mps”:“application/x-mapserver” ,
“.mpv2”:“video/mpeg” ,
“.mrl”:“text/x-mrml” ,
“.mrm”:“application/x-mrm” ,
“.ms”:“application/x-troff-ms” ,
“.msg”:“application/vnd.ms-outlook” ,
“.mts”:“application/metastream” ,
“.mtx”:“application/metastream” ,
“.mtz”:“application/metastream” ,
“.mvb”:“application/x-msmediaview” ,
“.mzv”:“application/metastream” ,
“.nar”:“application/zip” ,
“.nbmp”:“image/nbmp” ,
“.nc”:“application/x-netcdf” ,
“.ndb”:“x-lml/x-ndb” ,
“.ndwn”:“application/ndwn” ,
“.nif”:“application/x-nif” ,
“.nmz”:“application/x-scream” ,
“.nokia-op-logo”:“image/vnd.nok-oplogo-color” ,
“.npx”:“application/x-netfpx” ,
“.nsnd”:“audio/nsnd” ,
“.nva”:“application/x-neva1” ,
“.nws”:“message/rfc822” ,
“.oda”:“application/oda” ,
“.ogg”:“audio/ogg” ,
“.oom”:“application/x-AtlasMate-Plugin” ,
“.p10”:“application/pkcs10” ,
“.p12”:“application/x-pkcs12” ,
“.p7b”:“application/x-pkcs7-certificates” ,
“.p7c”:“application/x-pkcs7-mime” ,
“.p7m”:“application/x-pkcs7-mime” ,
“.p7r”:“application/x-pkcs7-certreqresp” ,
“.p7s”:“application/x-pkcs7-signature” ,
“.pac”:“audio/x-pac” ,
“.pae”:“audio/x-epac” ,
“.pan”:“application/x-pan” ,
“.pbm”:“image/x-portable-bitmap” ,
“.pcx”:“image/x-pcx” ,
“.pda”:“image/x-pda” ,
“.pdb”:“chemical/x-pdb” ,
“.pdf”:“application/pdf” ,
“.pfr”:“application/font-tdpfr” ,
“.pfx”:“application/x-pkcs12” ,
“.pgm”:“image/x-portable-graymap” ,
“.pict”:“image/x-pict” ,
“.pko”:“application/ynd.ms-pkipko” ,
“.pm”:“application/x-perl” ,
“.pma”:“application/x-perfmon” ,
“.pmc”:“application/x-perfmon” ,
“.pmd”:“application/x-pmd” ,
“.pml”:“application/x-perfmon” ,
“.pmr”:“application/x-perfmon” ,
“.pmw”:“application/x-perfmon” ,
“.png”:“image/png” ,
“.pnm”:“image/x-portable-anymap” ,
“.pnz”:“image/png” ,
“.pot,”:“application/vnd.ms-powerpoint” ,
“.ppm”:“image/x-portable-pixmap” ,
“.pps”:“application/vnd.ms-powerpoint” ,
“.ppt”:“application/vnd.ms-powerpoint” ,
“.pptx”:“application/vnd.openxmlformats-officedocument.presentationml.presentation” ,
“.pqf”:“application/x-cprplayer” ,
“.pqi”:“application/cprplayer” ,
“.prc”:“application/x-prc” ,
“.prf”:“application/pics-rules” ,
“.prop”:“text/plain” ,
“.proxy”:“application/x-ns-proxy-autoconfig” ,
“.ps”:“application/postscript” ,
“.ptlk”:“application/listenup” ,
“.pub”:“application/x-mspublisher” ,
“.pvx”:“video/x-pv-pvx” ,
“.qcp”:“audio/vnd.qcelp” ,
“.qt”:“video/quicktime” ,
“.qti”:“image/x-quicktime” ,
“.qtif”:“image/x-quicktime” ,
“.r3t”:“text/vnd.rn-realtext3d” ,
“.ra”:“audio/x-pn-realaudio” ,
“.ram”:“audio/x-pn-realaudio” ,
“.rar”:“application/octet-stream” ,
“.ras”:“image/x-cmu-raster” ,
“.rc”:“text/plain” ,
“.rdf”:“application/rdf+xml” ,
“.rf”:“image/vnd.rn-realflash” ,
“.rgb”:“image/x-rgb” ,
“.rlf”:“application/x-richlink” ,
“.rm”:“audio/x-pn-realaudio” ,
“.rmf”:“audio/x-rmf” ,
“.rmi”:“audio/mid” ,
“.rmm”:“audio/x-pn-realaudio” ,
“.rmvb”:“audio/x-pn-realaudio” ,
“.rnx”:“application/vnd.rn-realplayer” ,
“.roff”:“application/x-troff” ,
“.rp”:“image/vnd.rn-realpix” ,
“.rpm”:“audio/x-pn-realaudio-plugin” ,
“.rt”:“text/vnd.rn-realtext” ,
“.rte”:“x-lml/x-gps” ,
“.rtf”:“application/rtf” ,
“.rtg”:“application/metastream” ,
“.rtx”:“text/richtext” ,
“.rv”:“video/vnd.rn-realvideo” ,
“.rwc”:“application/x-rogerwilco” ,
“.s3m”:“audio/x-mod” ,
“.s3z”:“audio/x-mod” ,
“.sca”:“application/x-supercard” ,
“.scd”:“application/x-msschedule” ,
“.sct”:“text/scriptlet” ,
“.sdf”:“application/e-score” ,
“.sea”:“application/x-stuffit” ,
“.setpay”:“application/set-payment-initiation” ,
“.setreg”:“application/set-registration-initiation” ,
“.sgm”:“text/x-sgml” ,
“.sgml”:“text/x-sgml” ,
“.sh”:“application/x-sh” ,
“.shar”:“application/x-shar” ,
“.shtml”:“magnus-internal/parsed-html” ,
“.shw”:“application/presentations” ,
“.si6”:“image/si6” ,
“.si7”:“image/vnd.stiwap.sis” ,
“.si9”:“image/vnd.lgtwap.sis” ,
“.sis”:“application/vnd.symbian.install” ,
“.sit”:“application/x-stuffit” ,
“.skd”:“application/x-Koan” ,
“.skm”:“application/x-Koan” ,
“.skp”:“application/x-Koan” ,
“.skt”:“application/x-Koan” ,
“.slc”:“application/x-salsa” ,
“.smd”:“audio/x-smd” ,
“.smi”:“application/smil” ,
“.smil”:“application/smil” ,
“.smp”:“application/studiom” ,
“.smz”:“audio/x-smd” ,
“.snd”:“audio/basic” ,
“.spc”:“application/x-pkcs7-certificates” ,
“.spl”:“application/futuresplash” ,
“.spr”:“application/x-sprite” ,
“.sprite”:“application/x-sprite” ,
“.sdp”:“application/sdp” ,
“.spt”:“application/x-spt” ,
“.src”:“application/x-wais-source” ,
“.sst”:“application/vnd.ms-pkicertstore” ,
“.stk”:“application/hyperstudio” ,
“.stl”:“application/vnd.ms-pkistl” ,
“.stm”:“text/html” ,
“.svg”:“image/svg+xml” ,
“.sv4cpio”:“application/x-sv4cpio” ,
“.sv4crc”:“application/x-sv4crc” ,
“.svf”:“image/vnd” ,
“.svg”:“image/svg+xml” ,
“.svh”:“image/svh” ,
“.svr”:“x-world/x-svr” ,
“.swf”:“application/x-shockwave-flash” ,
“.swfl”:“application/x-shockwave-flash” ,
“.t”:“application/x-troff” ,
“.tad”:“application/octet-stream” ,
“.talk”:“text/x-speech” ,
“.tar”:“application/x-tar” ,
“.taz”:“application/x-tar” ,
“.tbp”:“application/x-timbuktu” ,
“.tbt”:“application/x-timbuktu” ,
“.tcl”:“application/x-tcl” ,
“.tex”:“application/x-tex” ,
“.texi”:“application/x-texinfo” ,
“.texinfo”:“application/x-texinfo” ,
“.tgz”:“application/x-compressed” ,
“.thm”:“application/vnd.eri.thm” ,
“.tif”:“image/tiff” ,
“.tiff”:“image/tiff” ,
“.tki”:“application/x-tkined” ,
“.tkined”:“application/x-tkined” ,
“.toc”:“application/toc” ,
“.toy”:“image/toy” ,
“.tr”:“application/x-troff” ,
“.trk”:“x-lml/x-gps” ,
“.trm”:“application/x-msterminal” ,
“.tsi”:“audio/tsplayer” ,
“.tsp”:“application/dsptype” ,
“.tsv”:“text/tab-separated-values” ,
“.ttf”:“application/octet-stream” ,
“.ttz”:“application/t-time” ,
“.txt”:“text/plain” ,
“.uls”:“text/iuls” ,
“.ult”:“audio/x-mod” ,
“.ustar”:“application/x-ustar” ,
“.uu”:“application/x-uuencode” ,
“.uue”:“application/x-uuencode” ,
“.vcd”:“application/x-cdlink” ,
“.vcf”:“text/x-vcard” ,
“.vdo”:“video/vdo” ,
“.vib”:“audio/vib” ,
“.viv”:“video/vivo” ,
“.vivo”:“video/vivo” ,
“.vmd”:“application/vocaltec-media-desc” ,
“.vmf”:“application/vocaltec-media-file” ,
“.vmi”:“application/x-dreamcast-vms-info” ,
“.vms”:“application/x-dreamcast-vms” ,
“.vox”:“audio/voxware” ,
“.vqe”:“audio/x-twinvq-plugin” ,
“.vqf”:“audio/x-twinvq” ,
“.vql”:“audio/x-twinvq” ,
“.vre”:“x-world/x-vream” ,
“.vrml”:“x-world/x-vrml” ,
“.vrt”:“x-world/x-vrt” ,
“.vrw”:“x-world/x-vream” ,
“.vts”:“workbook/formulaone” ,
“.wav”:“audio/x-wav” ,
“.wax”:“audio/x-ms-wax” ,
“.wbmp”:“image/vnd.wap.wbmp” ,
“.wcm”:“application/vnd.ms-works” ,
“.wdb”:“application/vnd.ms-works” ,
“.web”:“application/vnd.xara” ,
“.wi”:“image/wavelet” ,
“.wis”:“application/x-InstallShield” ,
“.wks”:“application/vnd.ms-works” ,
“.wm”:“video/x-ms-wm” ,
“.wma”:“audio/x-ms-wma” ,
“.wmd”:“application/x-ms-wmd” ,
“.wmf”:“application/x-msmetafile” ,
“.wml”:“text/vnd.wap.wml” ,
“.wmlc”:“application/vnd.wap.wmlc” ,
“.wmls”:“text/vnd.wap.wmlscript” ,
“.wmlsc”:“application/vnd.wap.wmlscriptc” ,
“.wmlscript”:“text/vnd.wap.wmlscript” ,
“.wmv”:“audio/x-ms-wmv” ,
“.wmx”:“video/x-ms-wmx” ,
“.wmz”:“application/x-ms-wmz” ,
“.wpng”:“image/x-up-wpng” ,
“.wps”:“application/vnd.ms-works” ,
“.wpt”:“x-lml/x-gps” ,
“.wri”:“application/x-mswrite” ,
“.wrl”:“x-world/x-vrml” ,
“.wrz”:“x-world/x-vrml” ,
“.ws”:“text/vnd.wap.wmlscript” ,
“.wsc”:“application/vnd.wap.wmlscriptc” ,
“.wv”:“video/wavelet” ,
“.wvx”:“video/x-ms-wvx” ,
“.wxl”:“application/x-wxl” ,
“.x-gzip”:“application/x-gzip” ,
“.xaf”:“x-world/x-vrml” ,
“.xar”:“application/vnd.xara” ,
“.xbm”:“image/x-xbitmap” ,
“.xdm”:“application/x-xdma” ,
“.xdma”:“application/x-xdma” ,
“.xdw”:“application/vnd.fujixerox.docuworks” ,
“.xht”:“application/xhtml+xml” ,
“.xhtm”:“application/xhtml+xml” ,
“.xhtml”:“application/xhtml+xml” ,
“.xla”:“application/vnd.ms-excel” ,
“.xlc”:“application/vnd.ms-excel” ,
“.xll”:“application/x-excel” ,
“.xlm”:“application/vnd.ms-excel” ,
“.xls”:“application/vnd.ms-excel” ,
“.xlsx”:“application/vnd.openxmlformats-officedocument.spreadsheetml.sheet” ,
“.xlt”:“application/vnd.ms-excel” ,
“.xlw”:“application/vnd.ms-excel” ,
“.xm”:“audio/x-mod” ,
“.xml”:“text/plain”,
“.xml”:“application/xml”,
“.xmz”:“audio/x-mod” ,
“.xof”:“x-world/x-vrml” ,
“.xpi”:“application/x-xpinstall” ,
“.xpm”:“image/x-xpixmap” ,
“.xsit”:“text/xml” ,
“.xsl”:“text/xml” ,
“.xul”:“text/xul” ,
“.xwd”:“image/x-xwindowdump” ,
“.xyz”:“chemical/x-pdb” ,
“.yz1”:“application/x-yz1” ,
“.z”:“application/x-compress” ,
“.zac”:“application/x-zaurus-zac” ,
“.zip”:“application/zip” ,
“.json”:“application/json”
};

module.exports = function (filePath) {

let ext = path.extname(filePath) //extname 取得文件 后缀名（以. 啥文件结束的那一坨）
.split(".") //以 . 切割
.pop() //拿到最后一个
.toLowerCase(); //转成小写
if(!ext){
//如果path没有取到ext,返回txt 文本类型的；
return mimeType[".txt"]

}
// 返回 匹配的类型 在我们已有的表里没有的 类型返回txt 文本类型的
return mimeType["."+ext] || mimeType[".txt"] ;

};