js-cfb/bits/84_mht.js

var ContentTypeMap = ({
	"htm": "text/html",
	"xml": "text/xml",

	"gif": "image/gif",
	"jpg": "image/jpeg",
	"png": "image/png",

	"mso": "application/x-mso",
	"thmx": "application/vnd.ms-officetheme",
	"sh33tj5": "application/octet-stream"
}/*:any*/);

function get_content_type(fi/*:CFBEntry*/, fp/*:string*/)/*:string*/ {
	if(fi.ctype) return fi.ctype;

	var ext = fi.name || "", m = ext.match(/\.([^\.]+)$/);
	if(m && ContentTypeMap[m[1]]) return ContentTypeMap[m[1]];

	if(fp) {
		m = (ext = fp).match(/[\.\\]([^\.\\])+$/);
		if(m && ContentTypeMap[m[1]]) return ContentTypeMap[m[1]];
	}

	return "application/octet-stream";
}

/* 76 character chunks TODO: intertwine encoding */
function write_base64_76(bstr/*:string*/)/*:string*/ {
	var data = Base64_encode(bstr);
	var o = [];
	for(var i = 0; i < data.length; i+= 76) o.push(data.slice(i, i+76));
	return o.join("\r\n") + "\r\n";
}

/*
Rules for QP:
	- escape =## applies for all non-display characters and literal "="
	- space or tab at end of line must be encoded
	- \r\n newlines can be preserved, but bare \r and \n must be escaped
	- lines must not exceed 76 characters, use soft breaks =\r\n

TODO: Some files from word appear to write line extensions with bare equals:

```
<table class=3DMsoTableGrid border=3D1 cellspacing=3D0 cellpadding=3D0 width=
="70%"
```
*/
function write_quoted_printable(text/*:string*/)/*:string*/ {
	var encoded = text.replace(/[\x00-\x08\x0B\x0C\x0E-\x1F\x7E-\xFF=]/g, function(c) {
		var w = c.charCodeAt(0).toString(16).toUpperCase();
		return "=" + (w.length == 1 ? "0" + w : w);
	});

	encoded = encoded.replace(/ $/mg, "=20").replace(/\t$/mg, "=09");

	if(encoded.charAt(0) == "\n") encoded = "=0D" + encoded.slice(1);
	encoded = encoded.replace(/\r(?!\n)/mg, "=0D").replace(/\n\n/mg, "\n=0A").replace(/([^\r\n])\n/mg, "$1=0A");

	var o/*:Array<string>*/ = [], split = encoded.split("\r\n");
	for(var si = 0; si < split.length; ++si) {
		var str = split[si];
		if(str.length == 0) { o.push(""); continue; }
		for(var i = 0; i < str.length;) {
			var end = 76;
			var tmp = str.slice(i, i + end);
			if(tmp.charAt(end - 1) == "=") end --;
			else if(tmp.charAt(end - 2) == "=") end -= 2;
			else if(tmp.charAt(end - 3) == "=") end -= 3;
			tmp = str.slice(i, i + end);
			i += end;
			if(i < str.length) tmp += "=";
			o.push(tmp);
		}
	}

	return o.join("\r\n");
}
function parse_quoted_printable(data/*:Array<string>*/)/*:RawBytes*/ {
	var o = [];

	/* unify long lines */
	for(var di = 0; di < data.length; ++di) {
		var line = data[di];
		while(di <= data.length && line.charAt(line.length - 1) == "=") line = line.slice(0, line.length - 1) + data[++di];
		o.push(line);
	}

	/* decode */
	for(var oi = 0; oi < o.length; ++oi) o[oi] = o[oi].replace(/[=][0-9A-Fa-f]{2}/g, function($$) { return String.fromCharCode(parseInt($$.slice(1), 16)); });
	return s2a(o.join("\r\n"));
}


function parse_mime(cfb/*:CFBContainer*/, data/*:Array<string>*/, root/*:string*/)/*:void*/ {
	var fname = "", cte = "", ctype = "", fdata;
	var di = 0;
	for(;di < 10; ++di) {
		var line = data[di];
		if(!line || line.match(/^\s*$/)) break;
		var m = line.match(/^(.*?):\s*([^\s].*)$/);
		if(m) switch(m[1].toLowerCase()) {
			case "content-location": fname = m[2].trim(); break;
			case "content-type": ctype = m[2].trim(); break;
			case "content-transfer-encoding": cte = m[2].trim(); break;
		}
	}
	++di;
	switch(cte.toLowerCase()) {
		case 'base64': fdata = s2a(Base64_decode(data.slice(di).join(""))); break;
		case 'quoted-printable': fdata = parse_quoted_printable(data.slice(di)); break;
		default: throw new Error("Unsupported Content-Transfer-Encoding " + cte);
	}
	var file = cfb_add(cfb, fname.slice(root.length), fdata, {unsafe: true});
	if(ctype) file.ctype = ctype;
}

function parse_mad(file/*:RawBytes*/, options/*:CFBReadOpts*/)/*:CFBContainer*/ {
	if(a2s(file.slice(0,13)).toLowerCase() != "mime-version:") throw new Error("Unsupported MAD header");
	var root = (options && options.root || "");
	// $FlowIgnore
	var data = (has_buf && Buffer.isBuffer(file) ? file.toString("binary") : a2s(file)).split("\r\n");
	var di = 0, row = "";

	/* if root is not specified, scan for the common prefix */
	for(di = 0; di < data.length; ++di) {
		row = data[di];
		if(!/^Content-Location:/i.test(row)) continue;
		row = row.slice(row.indexOf("file"));
		if(!root) root = row.slice(0, row.lastIndexOf("/") + 1);
		if(row.slice(0, root.length) == root) continue;
		while(root.length > 0) {
			root = root.slice(0, root.length - 1);
			root = root.slice(0, root.lastIndexOf("/") + 1);
			if(row.slice(0,root.length) == root) break;
		}
	}

	var mboundary = (data[1] || "").match(/boundary="(.*?)"/);
	if(!mboundary) throw new Error("MAD cannot find boundary");
	var boundary = "--" + (mboundary[1] || "");

	var FileIndex/*:CFBFileIndex*/ = [], FullPaths/*:Array<string>*/ = [];
	var o = {
		FileIndex: FileIndex,
		FullPaths: FullPaths
	};
	init_cfb(o);
	var start_di, fcnt = 0;
	for(di = 0; di < data.length; ++di) {
		var line = data[di];
		if(line !== boundary && line !== boundary + "--") continue;
		if(fcnt++) parse_mime(o, data.slice(start_di, di), root);
		start_di = di;
	}
	return o;
}

function write_mad(cfb/*:CFBContainer*/, options/*:CFBWriteOpts*/)/*:string*/ {
	var opts = options || {};
	var boundary = opts.boundary || "SheetJS";
	boundary = '------=' + boundary;

	var out = [
		'MIME-Version: 1.0',
		'Content-Type: multipart/related; boundary="' + boundary.slice(2) + '"',
		'',
		'',
		''
	];

	var root = cfb.FullPaths[0], fp = root, fi = cfb.FileIndex[0];
	for(var i = 1; i < cfb.FullPaths.length; ++i) {
		fp = cfb.FullPaths[i].slice(root.length);
		fi = cfb.FileIndex[i];
		if(!fi.size || !fi.content || fp == "\u0001Sh33tJ5") continue;

		/* Normalize filename */
		fp = fp.replace(/[\x00-\x08\x0B\x0C\x0E-\x1F\x7E-\xFF]/g, function(c) {
			return "_x" + c.charCodeAt(0).toString(16) + "_";
		}).replace(/[\u0080-\uFFFF]/g, function(u) {
			return "_u" + u.charCodeAt(0).toString(16) + "_";
		});

		/* Extract content as binary string */
		var ca = fi.content;
		// $FlowIgnore
		var cstr = has_buf && Buffer.isBuffer(ca) ? ca.toString("binary") : a2s(ca);

		/* 4/5 of first 1024 chars ascii -> quoted printable, else base64 */
		var dispcnt = 0, L = Math.min(1024, cstr.length), cc = 0;
		for(var csl = 0; csl <= L; ++csl) if((cc=cstr.charCodeAt(csl)) >= 0x20 && cc < 0x80) ++dispcnt;
		var qp = dispcnt >= L * 4 / 5;

		out.push(boundary);
		out.push('Content-Location: ' + (opts.root || 'file:///C:/SheetJS/') + fp);
		out.push('Content-Transfer-Encoding: ' + (qp ? 'quoted-printable' : 'base64'));
		out.push('Content-Type: ' + get_content_type(fi, fp));
		out.push('');

		out.push(qp ? write_quoted_printable(cstr) : write_base64_76(cstr));
	}
	out.push(boundary + '--\r\n');
	return out.join("\r\n");
}