gitweb: Incremental blame (using JavaScript)

Add 'blame_incremental' view, which uses "git blame --incremental"
and JavaScript (Ajax), where 'blame' use "git blame --porcelain".

 * gitweb generates initial info by putting file contents (from
   "git cat-file") together with line numbers in blame table
 * then gitweb makes web browser JavaScript engine call startBlame()
   function from gitweb.js
 * startBlame() opens XMLHttpRequest connection to 'blame_data' view,
   which in turn calls "git blame --incremental" for a file, and
   streams output of git-blame to JavaScript (gitweb.js)
 * XMLHttpRequest event handler updates line info in blame view as soon
   as it gets data from 'blame_data' (from server), and it also updates
   progress info
 * when 'blame_data' ends, and gitweb.js finishes updating line info,
   it fixes colors to match (as far as possible) ordinary 'blame' view,
   and updates information about how long it took to generate page.

Gitweb deals with streamed 'blame_data' server errors by displaying
them in the progress info area (just in case).

The 'blame_incremental' view tries to be equivalent to 'blame' action;
there are however a few differences in output between 'blame' and
'blame_incremental' view:

 * 'blame_incremental' always used query form for this part of link(s)
   which is generated by JavaScript code.  The difference is visible
   if we use path_info link (pass some or all arguments in path_info).
   Changing this would require implementing something akin to href()
   subroutine from gitweb.perl in JavaScript (in gitweb.js).
 * 'blame_incremental' always uses "rowspan" attribute, even if
   rowspan="1".  This simplifies code, and is not visible to user.
 * The progress bar and progress info are still there even after
   JavaScript part of 'blame_incremental' finishes work.

Note that currently no link generated by gitweb leads to this new view.

This code is based on patch by Petr Baudis <pasky@suse.cz> patch, which
in turn was tweaked up version of Fredrik Kuivinen <frekui@gmail.com>'s
proof of concept patch.

This patch adds GITWEB_JS compile configuration option, and modifies
git-instaweb.sh to take gitweb.js into account.  The code for
git-instaweb.sh was taken from Pasky's patch.

Signed-off-by: Fredrik Kuivinen <frekui@gmail.com>
Signed-off-by: Petr Baudis <pasky@suse.cz>
Signed-off-by: Jakub Narebski <jnareb@gmail.com>
Signed-off-by: Junio C Hamano <gitster@pobox.com>

4 files changed, 928 insertions, 87 deletions

diff --git a/gitweb/README b/gitweb/README
index 9056d1e090..cbcd993ecb 100644
--- a/gitweb/README
+++ b/gitweb/README
@@ -92,6 +92,10 @@ You can specify the following configuration variables when building GIT:
    web browsers that support favicons (website icons) may display them
    in the browser's URL bar and next to site name in bookmarks).  Relative
    to base URI of gitweb.  [Default: git-favicon.png]
+ * GITWEB_JS
+   Points to the localtion where you put gitweb.js on your web server
+   (or to be more generic URI of JavaScript code used by gitweb).
+   Relative to base URI of gitweb.  [Default: gitweb.js]
  * GITWEB_CONFIG
    This Perl file will be loaded using 'do' and can be used to override any
    of the options above as well as some other options -- see the "Runtime
diff --git a/gitweb/gitweb.css b/gitweb/gitweb.css
index 9893443edc..4a2e496568 100644
--- a/gitweb/gitweb.css
+++ b/gitweb/gitweb.css
@@ -348,6 +348,17 @@ td.mode {
 	font-family: monospace;
 }
 
+/* progress of blame_interactive */
+div#progress_bar {
+	height: 2px;
+	margin-bottom: -2px;
+	background-color: #d8d9d0;
+}
+div#progress_info {
+	float: right;
+	text-align: right;
+}
+
 /* styling of diffs (patchsets): commitdiff and blobdiff views */
 div.diff.header,
 div.diff.extended_header {
diff --git a/gitweb/gitweb.js b/gitweb/gitweb.js
new file mode 100644
index 0000000000..b15e2a7944
--- /dev/null
+++ b/gitweb/gitweb.js
@@ -0,0 +1,726 @@
+// Copyright (C) 2007, Fredrik Kuivinen <frekui@gmail.com>
+//               2007, Petr Baudis <pasky@suse.cz>
+//          2008-2009, Jakub Narebski <jnareb@gmail.com>
+
+/**
+ * @fileOverview JavaScript code for gitweb (git web interface).
+ * @license GPLv2 or later
+ */
+
+/*
+ * This code uses DOM methods instead of (nonstandard) innerHTML
+ * to modify page.
+ *
+ * innerHTML is non-standard IE extension, though supported by most
+ * browsers; however Firefox up to version 1.5 didn't implement it in
+ * a strict mode (application/xml+xhtml mimetype).
+ *
+ * Also my simple benchmarks show that using elem.firstChild.data =
+ * 'content' is slightly faster than elem.innerHTML = 'content'.  It
+ * is however more fragile (text element fragment must exists), and
+ * less feature-rich (we cannot add HTML).
+ *
+ * Note that DOM 2 HTML is preferred over generic DOM 2 Core; the
+ * equivalent using DOM 2 Core is usually shown in comments.
+ */
+
+
+/* ============================================================ */
+/* generic utility functions */
+
+
+/**
+ * pad number N with nonbreakable spaces on the left, to WIDTH characters
+ * example: padLeftStr(12, 3, '&nbsp;') == '&nbsp;12'
+ *          ('&nbsp;' is nonbreakable space)
+ *
+ * @param {Number|String} input: number to pad
+ * @param {Number} width: visible width of output
+ * @param {String} str: string to prefix to string, e.g. '&nbsp;'
+ * @returns {String} INPUT prefixed with (WIDTH - INPUT.length) x STR
+ */
+function padLeftStr(input, width, str) {
+	var prefix = '';
+
+	width -= input.toString().length;
+	while (width > 1) {
+		prefix += str;
+		width--;
+	}
+	return prefix + input;
+}
+
+/**
+ * Pad INPUT on the left to SIZE width, using given padding character CH,
+ * for example padLeft('a', 3, '_') is '__a'.
+ *
+ * @param {String} input: input value converted to string.
+ * @param {Number} width: desired length of output.
+ * @param {String} ch: single character to prefix to string.
+ *
+ * @returns {String} Modified string, at least SIZE length.
+ */
+function padLeft(input, width, ch) {
+	var s = input + "";
+	while (s.length < width) {
+		s = ch + s;
+	}
+	return s;
+}
+
+/**
+ * Create XMLHttpRequest object in cross-browser way
+ * @returns XMLHttpRequest object, or null
+ */
+function createRequestObject() {
+	try {
+		return new XMLHttpRequest();
+	} catch (e) {}
+	try {
+		return window.createRequest();
+	} catch (e) {}
+	try {
+		return new ActiveXObject("Msxml2.XMLHTTP");
+	} catch (e) {}
+	try {
+		return new ActiveXObject("Microsoft.XMLHTTP");
+	} catch (e) {}
+
+	return null;
+}
+
+/* ============================================================ */
+/* utility/helper functions (and variables) */
+
+var xhr;        // XMLHttpRequest object
+var projectUrl; // partial query + separator ('?' or ';')
+
+// 'commits' is an associative map. It maps SHA1s to Commit objects.
+var commits = {};
+
+/**
+ * constructor for Commit objects, used in 'blame'
+ * @class Represents a blamed commit
+ * @param {String} sha1: SHA-1 identifier of a commit
+ */
+function Commit(sha1) {
+	if (this instanceof Commit) {
+		this.sha1 = sha1;
+		this.nprevious = 0; /* number of 'previous', effective parents */
+	} else {
+		return new Commit(sha1);
+	}
+}
+
+/* ............................................................ */
+/* progress info, timing, error reporting */
+
+var blamedLines = 0;
+var totalLines  = '???';
+var div_progress_bar;
+var div_progress_info;
+
+/**
+ * Detects how many lines does a blamed file have,
+ * This information is used in progress info
+ *
+ * @returns {Number|String} Number of lines in file, or string '...'
+ */
+function countLines() {
+	var table =
+		document.getElementById('blame_table') ||
+		document.getElementsByTagName('table')[0];
+
+	if (table) {
+		return table.getElementsByTagName('tr').length - 1; // for header
+	} else {
+		return '...';
+	}
+}
+
+/**
+ * update progress info and length (width) of progress bar
+ *
+ * @globals div_progress_info, div_progress_bar, blamedLines, totalLines
+ */
+function updateProgressInfo() {
+	if (!div_progress_info) {
+		div_progress_info = document.getElementById('progress_info');
+	}
+	if (!div_progress_bar) {
+		div_progress_bar = document.getElementById('progress_bar');
+	}
+	if (!div_progress_info && !div_progress_bar) {
+		return;
+	}
+
+	var percentage = Math.floor(100.0*blamedLines/totalLines);
+
+	if (div_progress_info) {
+		div_progress_info.firstChild.data  = blamedLines + ' / ' + totalLines +
+			' (' + padLeftStr(percentage, 3, '&nbsp;') + '%)';
+	}
+
+	if (div_progress_bar) {
+		//div_progress_bar.setAttribute('style', 'width: '+percentage+'%;');
+		div_progress_bar.style.width = percentage + '%';
+	}
+}
+
+
+var t_interval_server = '';
+var cmds_server = '';
+var t0 = new Date();
+
+/**
+ * write how much it took to generate data, and to run script
+ *
+ * @globals t0, t_interval_server, cmds_server
+ */
+function writeTimeInterval() {
+	var info_time = document.getElementById('generating_time');
+	if (!info_time || !t_interval_server) {
+		return;
+	}
+	var t1 = new Date();
+	info_time.firstChild.data += ' + (' +
+		t_interval_server + ' sec server blame_data / ' +
+		(t1.getTime() - t0.getTime())/1000 + ' sec client JavaScript)';
+
+	var info_cmds = document.getElementById('generating_cmd');
+	if (!info_time || !cmds_server) {
+		return;
+	}
+	info_cmds.firstChild.data += ' + ' + cmds_server;
+}
+
+/**
+ * show an error message alert to user within page (in prohress info area)
+ * @param {String} str: plain text error message (no HTML)
+ *
+ * @globals div_progress_info
+ */
+function errorInfo(str) {
+	if (!div_progress_info) {
+		div_progress_info = document.getElementById('progress_info');
+	}
+	if (div_progress_info) {
+		div_progress_info.className = 'error';
+		div_progress_info.firstChild.data = str;
+	}
+}
+
+/* ............................................................ */
+/* coloring rows like 'blame' after 'blame_data' finishes */
+
+/**
+ * returns true if given row element (tr) is first in commit group
+ * to be used only after 'blame_data' finishes (after processing)
+ *
+ * @param {HTMLElement} tr: table row
+ * @returns {Boolean} true if TR is first in commit group
+ */
+function isStartOfGroup(tr) {
+	return tr.firstChild.className === 'sha1';
+}
+
+var colorRe = /(?:light|dark)/;
+
+/**
+ * change colors to use zebra coloring (2 colors) instead of 3 colors
+ * concatenate neighbour commit groups belonging to the same commit
+ *
+ * @globals colorRe
+ */
+function fixColorsAndGroups() {
+	var colorClasses = ['light', 'dark'];
+	var linenum = 1;
+	var tr, prev_group;
+	var colorClass = 0;
+	var table =
+		document.getElementById('blame_table') ||
+		document.getElementsByTagName('table')[0];
+
+	while ((tr = document.getElementById('l'+linenum))) {
+	// index origin is 0, which is table header; start from 1
+	//while ((tr = table.rows[linenum])) { // <- it is slower
+		if (isStartOfGroup(tr, linenum, document)) {
+			if (prev_group &&
+			    prev_group.firstChild.firstChild.href ===
+			            tr.firstChild.firstChild.href) {
+				// we have to concatenate groups
+				var prev_rows = prev_group.firstChild.rowSpan || 1;
+				var curr_rows =         tr.firstChild.rowSpan || 1;
+				prev_group.firstChild.rowSpan = prev_rows + curr_rows;
+				//tr.removeChild(tr.firstChild);
+				tr.deleteCell(0); // DOM2 HTML way
+			} else {
+				colorClass = (colorClass + 1) % 2;
+				prev_group = tr;
+			}
+		}
+		var tr_class = tr.className;
+		tr.className = tr_class.replace(colorRe, colorClasses[colorClass]);
+		linenum++;
+	}
+}
+
+/* ............................................................ */
+/* time and data */
+
+/**
+ * used to extract hours and minutes from timezone info, e.g '-0900'
+ * @constant
+ */
+var tzRe = /^([+-][0-9][0-9])([0-9][0-9])$/;
+
+/**
+ * return date in local time formatted in iso-8601 like format
+ * 'yyyy-mm-dd HH:MM:SS +/-ZZZZ' e.g. '2005-08-07 21:49:46 +0200'
+ *
+ * @param {Number} epoch: seconds since '00:00:00 1970-01-01 UTC'
+ * @param {String} timezoneInfo: numeric timezone '(+|-)HHMM'
+ * @returns {String} date in local time in iso-8601 like format
+ *
+ * @globals tzRe
+ */
+function formatDateISOLocal(epoch, timezoneInfo) {
+	var match = tzRe.exec(timezoneInfo);
+	// date corrected by timezone
+	var localDate = new Date(1000 * (epoch +
+		(parseInt(match[1],10)*3600 + parseInt(match[2],10)*60)));
+	var localDateStr = // e.g. '2005-08-07'
+		localDate.getUTCFullYear()                 + '-' +
+		padLeft(localDate.getUTCMonth()+1, 2, '0') + '-' +
+		padLeft(localDate.getUTCDate(),    2, '0');
+	var localTimeStr = // e.g. '21:49:46'
+		padLeft(localDate.getUTCHours(),   2, '0') + ':' +
+		padLeft(localDate.getUTCMinutes(), 2, '0') + ':' +
+		padLeft(localDate.getUTCSeconds(), 2, '0');
+
+	return localDateStr + ' ' + localTimeStr + ' ' + timezoneInfo;
+}
+
+/* ............................................................ */
+/* unquoting/unescaping filenames */
+
+/**#@+
+ * @constant
+ */
+var escCodeRe = /\\([^0-7]|[0-7]{1,3})/g;
+var octEscRe = /^[0-7]{1,3}$/;
+var maybeQuotedRe = /^\"(.*)\"$/;
+/**#@-*/
+
+/**
+ * unquote maybe git-quoted filename
+ * e.g. 'aa' -> 'aa', '"a\ta"' -> 'a	a'
+ *
+ * @param {String} str: git-quoted string
+ * @returns {String} Unquoted and unescaped string
+ *
+ * @globals escCodeRe, octEscRe, maybeQuotedRe
+ */
+function unquote(str) {
+	function unq(seq) {
+		var es = {
+			// character escape codes, aka escape sequences (from C)
+			// replacements are to some extent JavaScript specific
+			t: "\t",   // tab            (HT, TAB)
+			n: "\n",   // newline        (NL)
+			r: "\r",   // return         (CR)
+			f: "\f",   // form feed      (FF)
+			b: "\b",   // backspace      (BS)
+			a: "\x07", // alarm (bell)   (BEL)
+			e: "\x1B", // escape         (ESC)
+			v: "\v"    // vertical tab   (VT)
+		};
+
+		if (seq.search(octEscRe) !== -1) {
+			// octal char sequence
+			return String.fromCharCode(parseInt(seq, 8));
+		} else if (seq in es) {
+			// C escape sequence, aka character escape code
+			return es[seq];
+		}
+		// quoted ordinary character
+		return seq;
+	}
+
+	var match = str.match(maybeQuotedRe);
+	if (match) {
+		str = match[1];
+		// perhaps str = eval('"'+str+'"'); would be enough?
+		str = str.replace(escCodeRe,
+			function (substr, p1, offset, s) { return unq(p1); });
+	}
+	return str;
+}
+
+/* ============================================================ */
+/* main part: parsing response */
+
+/**
+ * Function called for each blame entry, as soon as it finishes.
+ * It updates page via DOM manipulation, adding sha1 info, etc.
+ *
+ * @param {Commit} commit: blamed commit
+ * @param {Object} group: object representing group of lines,
+ *                        which blame the same commit (blame entry)
+ *
+ * @globals blamedLines
+ */
+function handleLine(commit, group) {
+	/*
+	   This is the structure of the HTML fragment we are working
+	   with:
+
+	   <tr id="l123" class="">
+	     <td class="sha1" title=""><a href=""> </a></td>
+	     <td class="linenr"><a class="linenr" href="">123</a></td>
+	     <td class="pre"># times (my ext3 doesn&#39;t).</td>
+	   </tr>
+	*/
+
+	var resline = group.resline;
+
+	// format date and time string only once per commit
+	if (!commit.info) {
+		/* e.g. 'Kay Sievers, 2005-08-07 21:49:46 +0200' */
+		commit.info = commit.author + ', ' +
+			formatDateISOLocal(commit.authorTime, commit.authorTimezone);
+	}
+
+	// loop over lines in commit group
+	for (var i = 0; i < group.numlines; i++, resline++) {
+		var tr = document.getElementById('l'+resline);
+		if (!tr) {
+			break;
+		}
+		/*
+			<tr id="l123" class="">
+			  <td class="sha1" title=""><a href=""> </a></td>
+			  <td class="linenr"><a class="linenr" href="">123</a></td>
+			  <td class="pre"># times (my ext3 doesn&#39;t).</td>
+			</tr>
+		*/
+		var td_sha1  = tr.firstChild;
+		var a_sha1   = td_sha1.firstChild;
+		var a_linenr = td_sha1.nextSibling.firstChild;
+
+		/* <tr id="l123" class=""> */
+		var tr_class = 'light'; // or tr.className
+		if (commit.boundary) {
+			tr_class += ' boundary';
+		}
+		if (commit.nprevious === 0) {
+			tr_class += ' no-previous';
+		} else if (commit.nprevious > 1) {
+			tr_class += ' multiple-previous';
+		}
+		tr.className = tr_class;
+
+		/* <td class="sha1" title="?" rowspan="?"><a href="?">?</a></td> */
+		if (i === 0) {
+			td_sha1.title = commit.info;
+			td_sha1.rowSpan = group.numlines;
+
+			a_sha1.href = projectUrl + 'a=commit;h=' + commit.sha1;
+			a_sha1.firstChild.data = commit.sha1.substr(0, 8);
+			if (group.numlines >= 2) {
+				var fragment = document.createDocumentFragment();
+				var br   = document.createElement("br");
+				var text = document.createTextNode(
+					commit.author.match(/\b([A-Z])\B/g).join(''));
+				if (br && text) {
+					var elem = fragment || td_sha1;
+					elem.appendChild(br);
+					elem.appendChild(text);
+					if (fragment) {
+						td_sha1.appendChild(fragment);
+					}
+				}
+			}
+		} else {
+			//tr.removeChild(td_sha1); // DOM2 Core way
+			tr.deleteCell(0); // DOM2 HTML way
+		}
+
+		/* <td class="linenr"><a class="linenr" href="?">123</a></td> */
+		var linenr_commit =
+			('previous' in commit ? commit.previous : commit.sha1);
+		var linenr_filename =
+			('file_parent' in commit ? commit.file_parent : commit.filename);
+		a_linenr.href = projectUrl + 'a=blame_incremental' +
+			';hb=' + linenr_commit +
+			';f='  + encodeURIComponent(linenr_filename) +
+			'#l' + (group.srcline + i);
+
+		blamedLines++;
+
+		//updateProgressInfo();
+	}
+}
+
+// ----------------------------------------------------------------------
+
+var inProgress = false;   // are we processing response
+
+/**#@+
+ * @constant
+ */
+var sha1Re = /^([0-9a-f]{40}) ([0-9]+) ([0-9]+) ([0-9]+)/;
+var infoRe = /^([a-z-]+) ?(.*)/;
+var endRe  = /^END ?([^ ]*) ?(.*)/;
+/**@-*/
+
+var curCommit = new Commit();
+var curGroup  = {};
+
+var pollTimer = null;
+
+/**
+ * Parse output from 'git blame --incremental [...]', received via
+ * XMLHttpRequest from server (blamedataUrl), and call handleLine
+ * (which updates page) as soon as blame entry is completed.
+ *
+ * @param {String[]} lines: new complete lines from blamedata server
+ *
+ * @globals commits, curCommit, curGroup, t_interval_server, cmds_server
+ * @globals sha1Re, infoRe, endRe
+ */
+function processBlameLines(lines) {
+	var match;
+
+	for (var i = 0, len = lines.length; i < len; i++) {
+
+		if ((match = sha1Re.exec(lines[i]))) {
+			var sha1 = match[1];
+			var srcline  = parseInt(match[2], 10);
+			var resline  = parseInt(match[3], 10);
+			var numlines = parseInt(match[4], 10);
+
+			var c = commits[sha1];
+			if (!c) {
+				c = new Commit(sha1);
+				commits[sha1] = c;
+			}
+			curCommit = c;
+
+			curGroup.srcline = srcline;
+			curGroup.resline = resline;
+			curGroup.numlines = numlines;
+
+		} else if ((match = infoRe.exec(lines[i]))) {
+			var info = match[1];
+			var data = match[2];
+			switch (info) {
+			case 'filename':
+				curCommit.filename = unquote(data);
+				// 'filename' information terminates the entry
+				handleLine(curCommit, curGroup);
+				updateProgressInfo();
+				break;
+			case 'author':
+				curCommit.author = data;
+				break;
+			case 'author-time':
+				curCommit.authorTime = parseInt(data, 10);
+				break;
+			case 'author-tz':
+				curCommit.authorTimezone = data;
+				break;
+			case 'previous':
+				curCommit.nprevious++;
+				// store only first 'previous' header
+				if (!'previous' in curCommit) {
+					var parts = data.split(' ', 2);
+					curCommit.previous    = parts[0];
+					curCommit.file_parent = unquote(parts[1]);
+				}
+				break;
+			case 'boundary':
+				curCommit.boundary = true;
+				break;
+			} // end switch
+
+		} else if ((match = endRe.exec(lines[i]))) {
+			t_interval_server = match[1];
+			cmds_server = match[2];
+
+		} else if (lines[i] !== '') {
+			// malformed line
+
+		} // end if (match)
+
+	} // end for (lines)
+}
+
+/**
+ * Process new data and return pointer to end of processed part
+ *
+ * @param {String} unprocessed: new data (from nextReadPos)
+ * @param {Number} nextReadPos: end of last processed data
+ * @return {Number} end of processed data (new value for nextReadPos)
+ */
+function processData(unprocessed, nextReadPos) {
+	var lastLineEnd = unprocessed.lastIndexOf('\n');
+	if (lastLineEnd !== -1) {
+		var lines = unprocessed.substring(0, lastLineEnd).split('\n');
+		nextReadPos += lastLineEnd + 1 /* 1 == '\n'.length */;
+
+		processBlameLines(lines);
+	} // end if
+
+	return nextReadPos;
+}
+
+/**
+ * Handle XMLHttpRequest errors
+ *
+ * @param {XMLHttpRequest} xhr: XMLHttpRequest object
+ *
+ * @globals pollTimer, commits, inProgress
+ */
+function handleError(xhr) {
+	errorInfo('Server error: ' +
+		xhr.status + ' - ' + (xhr.statusText || 'Error contacting server'));
+
+	clearInterval(pollTimer);
+	commits = {}; // free memory
+
+	inProgress = false;
+}
+
+/**
+ * Called after XMLHttpRequest finishes (loads)
+ *
+ * @param {XMLHttpRequest} xhr: XMLHttpRequest object (unused)
+ *
+ * @globals pollTimer, commits, inProgress
+ */
+function responseLoaded(xhr) {
+	clearInterval(pollTimer);
+
+	fixColorsAndGroups();
+	writeTimeInterval();
+	commits = {}; // free memory
+
+	inProgress = false;
+}
+
+/**
+ * handler for XMLHttpRequest onreadystatechange event
+ * @see startBlame
+ *
+ * @globals xhr, inProgress
+ */
+function handleResponse() {
+
+	/*
+	 * xhr.readyState
+	 *
+	 *  Value  Constant (W3C)    Description
+	 *  -------------------------------------------------------------------
+	 *  0      UNSENT            open() has not been called yet.
+	 *  1      OPENED            send() has not been called yet.
+	 *  2      HEADERS_RECEIVED  send() has been called, and headers
+	 *                           and status are available.
+	 *  3      LOADING           Downloading; responseText holds partial data.
+	 *  4      DONE              The operation is complete.
+	 */
+
+	if (xhr.readyState !== 4 && xhr.readyState !== 3) {
+		return;
+	}
+
+	// the server returned error
+	if (xhr.readyState === 3 && xhr.status !== 200) {
+		return;
+	}
+	if (xhr.readyState === 4 && xhr.status !== 200) {
+		handleError(xhr);
+		return;
+	}
+
+	// In konqueror xhr.responseText is sometimes null here...
+	if (xhr.responseText === null) {
+		return;
+	}
+
+	// in case we were called before finished processing
+	if (inProgress) {
+		return;
+	} else {
+		inProgress = true;
+	}
+
+	// extract new whole (complete) lines, and process them
+	while (xhr.prevDataLength !== xhr.responseText.length) {
+		if (xhr.readyState === 4 &&
+		    xhr.prevDataLength === xhr.responseText.length) {
+			break;
+		}
+
+		xhr.prevDataLength = xhr.responseText.length;
+		var unprocessed = xhr.responseText.substring(xhr.nextReadPos);
+		xhr.nextReadPos = processData(unprocessed, xhr.nextReadPos);
+	} // end while
+
+	// did we finish work?
+	if (xhr.readyState === 4 &&
+	    xhr.prevDataLength === xhr.responseText.length) {
+		responseLoaded(xhr);
+	}
+
+	inProgress = false;
+}
+
+// ============================================================
+// ------------------------------------------------------------
+
+/**
+ * Incrementally update line data in blame_incremental view in gitweb.
+ *
+ * @param {String} blamedataUrl: URL to server script generating blame data.
+ * @param {String} bUrl: partial URL to project, used to generate links.
+ *
+ * Called from 'blame_incremental' view after loading table with
+ * file contents, a base for blame view.
+ *
+ * @globals xhr, t0, projectUrl, div_progress_bar, totalLines, pollTimer
+*/
+function startBlame(blamedataUrl, bUrl) {
+
+	xhr = createRequestObject();
+	if (!xhr) {
+		errorInfo('ERROR: XMLHttpRequest not supported');
+		return;
+	}
+
+	t0 = new Date();
+	projectUrl = bUrl + (bUrl.indexOf('?') === -1 ? '?' : ';');
+	if ((div_progress_bar = document.getElementById('progress_bar'))) {
+		//div_progress_bar.setAttribute('style', 'width: 100%;');
+		div_progress_bar.style.cssText = 'width: 100%;';
+	}
+	totalLines = countLines();
+	updateProgressInfo();
+
+	/* add extra properties to xhr object to help processing response */
+	xhr.prevDataLength = -1;  // used to detect if we have new data
+	xhr.nextReadPos = 0;      // where unread part of response starts
+
+	xhr.onreadystatechange = handleResponse;
+	//xhr.onreadystatechange = function () { handleResponse(xhr); };
+
+	xhr.open('GET', blamedataUrl);
+	xhr.setRequestHeader('Accept', 'text/plain');
+	xhr.send(null);
+
+	// not all browsers call onreadystatechange event on each server flush
+	// poll response using timer every second to handle this issue
+	pollTimer = setInterval(xhr.onreadystatechange, 1000);
+}
+
+// end of gitweb.js
diff --git a/gitweb/gitweb.perl b/gitweb/gitweb.perl
index 18cbf35391..6cdd8c39b4 100755
--- a/gitweb/gitweb.perl
+++ b/gitweb/gitweb.perl
@@ -96,6 +96,8 @@ our $stylesheet = undef;
 our $logo = "++GITWEB_LOGO++";
 # URI of GIT favicon, assumed to be image/png type
 our $favicon = "++GITWEB_FAVICON++";
+# URI of gitweb.js (JavaScript code for gitweb)
+our $javascript = "++GITWEB_JS++";
 
 # URI and label (title) of GIT logo link
 #our $logo_url = "http://www.kernel.org/pub/software/scm/git/docs/";
@@ -564,6 +566,8 @@ our %cgi_param_mapping = @cgi_param_mapping;
 # we will also need to know the possible actions, for validation
 our %actions = (
 	"blame" => \&git_blame,
+	"blame_incremental" => \&git_blame_incremental,
+	"blame_data" => \&git_blame_data,
 	"blobdiff" => \&git_blobdiff,
 	"blobdiff_plain" => \&git_blobdiff_plain,
 	"blob" => \&git_blob,
@@ -4787,7 +4791,9 @@ sub git_tag {
 	git_footer_html();
 }
 
-sub git_blame {
+sub git_blame_common {
+	my $format = shift || 'porcelain';
+
 	# permissions
 	gitweb_check_feature('blame')
 		or die_error(403, "Blame view not allowed");
@@ -4809,10 +4815,43 @@ sub git_blame {
 		}
 	}
 
-	# run git-blame --porcelain
-	open my $fd, "-|", git_cmd(), "blame", '-p',
-		$hash_base, '--', $file_name
-		or die_error(500, "Open git-blame failed");
+	my $fd;
+	if ($format eq 'incremental') {
+		# get file contents (as base)
+		open $fd, "-|", git_cmd(), 'cat-file', 'blob', $hash
+			or die_error(500, "Open git-cat-file failed");
+	} elsif ($format eq 'data') {
+		# run git-blame --incremental
+		open $fd, "-|", git_cmd(), "blame", "--incremental",
+			$hash_base, "--", $file_name
+			or die_error(500, "Open git-blame --incremental failed");
+	} else {
+		# run git-blame --porcelain
+		open $fd, "-|", git_cmd(), "blame", '-p',
+			$hash_base, '--', $file_name
+			or die_error(500, "Open git-blame --porcelain failed");
+	}
+
+	# incremental blame data returns early
+	if ($format eq 'data') {
+		print $cgi->header(
+			-type=>"text/plain", -charset => "utf-8",
+			-status=> "200 OK");
+		local $| = 1; # output autoflush
+		print while <$fd>;
+		close $fd
+			or print "ERROR $!\n";
+
+		print 'END';
+		if (defined $t0 && gitweb_check_feature('timed')) {
+			print ' '.
+			      Time::HiRes::tv_interval($t0, [Time::HiRes::gettimeofday()]).
+			      ' '.$number_of_git_cmds;
+		}
+		print "\n";
+
+		return;
+	}
 
 	# page header
 	git_header_html();
@@ -4823,109 +4862,170 @@ sub git_blame {
 		$cgi->a({-href => href(action=>"history", -replay=>1)},
 		        "history") .
 		" | " .
-		$cgi->a({-href => href(action=>"blame", file_name=>$file_name)},
+		$cgi->a({-href => href(action=>$action, file_name=>$file_name)},
 		        "HEAD");
 	git_print_page_nav('','', $hash_base,$co{'tree'},$hash_base, $formats_nav);
 	git_print_header_div('commit', esc_html($co{'title'}), $hash_base);
 	git_print_page_path($file_name, $ftype, $hash_base);
 
 	# page body
+	if ($format eq 'incremental') {
+		print "<noscript>\n<div class=\"error\"><center><b>\n".
+		      "This page requires JavaScript to run.\n Use ".
+		      $cgi->a({-href => href(action=>'blame',-replay=>1)},
+		              'this page').
+		      " instead.\n".
+		      "</b></center></div>\n</noscript>\n";
+
+		print qq!<div id="progress_bar" style="width: 100%; background-color: yellow"></div>\n!;
+	}
+
+	print qq!<div class="page_body">\n!;
+	print qq!<div id="progress_info">... / ...</div>\n!
+		if ($format eq 'incremental');
+	print qq!<table id="blame_table" class="blame" width="100%">\n!.
+	      #qq!<col width="5.5em" /><col width="2.5em" /><col width="*" />\n!.
+	      qq!<thead>\n!.
+	      qq!<tr><th>Commit</th><th>Line</th><th>Data</th></tr>\n!.
+	      qq!</thead>\n!.
+	      qq!<tbody>\n!;
+
 	my @rev_color = qw(light dark);
 	my $num_colors = scalar(@rev_color);
 	my $current_color = 0;
-	my %metainfo = ();
 
-	print <<HTML;
-<div class="page_body">
-<table class="blame">
-<tr><th>Commit</th><th>Line</th><th>Data</th></tr>
-HTML
- LINE:
-	while (my $line = <$fd>) {
-		chomp $line;
-		# the header: <SHA-1> <src lineno> <dst lineno> [<lines in group>]
-		# no <lines in group> for subsequent lines in group of lines
-		my ($full_rev, $orig_lineno, $lineno, $group_size) =
-		   ($line =~ /^([0-9a-f]{40}) (\d+) (\d+)(?: (\d+))?$/);
-		if (!exists $metainfo{$full_rev}) {
-			$metainfo{$full_rev} = { 'nprevious' => 0 };
-		}
-		my $meta = $metainfo{$full_rev};
-		my $data;
-		while ($data = <$fd>) {
-			chomp $data;
-			last if ($data =~ s/^\t//); # contents of line
-			if ($data =~ /^(\S+)(?: (.*))?$/) {
-				$meta->{$1} = $2 unless exists $meta->{$1};
+	if ($format eq 'incremental') {
+		my $color_class = $rev_color[$current_color];
+
+		#contents of a file
+		my $linenr = 0;
+	LINE:
+		while (my $line = <$fd>) {
+			chomp $line;
+			$linenr++;
+
+			print qq!<tr id="l$linenr" class="$color_class">!.
+			      qq!<td class="sha1"><a href=""> </a></td>!.
+			      qq!<td class="linenr">!.
+			      qq!<a class="linenr" href="">$linenr</a></td>!;
+			print qq!<td class="pre">! . esc_html($line) . "</td>\n";
+			print qq!</tr>\n!;
+		}
+
+	} else { # porcelain, i.e. ordinary blame
+		my %metainfo = (); # saves information about commits
+
+		# blame data
+	LINE:
+		while (my $line = <$fd>) {
+			chomp $line;
+			# the header: <SHA-1> <src lineno> <dst lineno> [<lines in group>]
+			# no <lines in group> for subsequent lines in group of lines
+			my ($full_rev, $orig_lineno, $lineno, $group_size) =
+			   ($line =~ /^([0-9a-f]{40}) (\d+) (\d+)(?: (\d+))?$/);
+			if (!exists $metainfo{$full_rev}) {
+				$metainfo{$full_rev} = { 'nprevious' => 0 };
 			}
-			if ($data =~ /^previous /) {
-				$meta->{'nprevious'}++;
+			my $meta = $metainfo{$full_rev};
+			my $data;
+			while ($data = <$fd>) {
+				chomp $data;
+				last if ($data =~ s/^\t//); # contents of line
+				if ($data =~ /^(\S+)(?: (.*))?$/) {
+					$meta->{$1} = $2 unless exists $meta->{$1};
+				}
+				if ($data =~ /^previous /) {
+					$meta->{'nprevious'}++;
+				}
 			}
-		}
-		my $short_rev = substr($full_rev, 0, 8);
-		my $author = $meta->{'author'};
-		my %date =
-			parse_date($meta->{'author-time'}, $meta->{'author-tz'});
-		my $date = $date{'iso-tz'};
-		if ($group_size) {
-			$current_color = ($current_color + 1) % $num_colors;
-		}
-		my $tr_class = $rev_color[$current_color];
-		$tr_class .= ' boundary' if (exists $meta->{'boundary'});
-		$tr_class .= ' no-previous' if ($meta->{'nprevious'} == 0);
-		$tr_class .= ' multiple-previous' if ($meta->{'nprevious'} > 1);
-		print "<tr id=\"l$lineno\" class=\"$tr_class\">\n";
-		if ($group_size) {
-			print "<td class=\"sha1\"";
-			print " title=\"". esc_html($author) . ", $date\"";
-			print " rowspan=\"$group_size\"" if ($group_size > 1);
-			print ">";
-			print $cgi->a({-href => href(action=>"commit",
-			                             hash=>$full_rev,
-			                             file_name=>$file_name)},
-			              esc_html($short_rev));
-			if ($group_size >= 2) {
-				my @author_initials = ($author =~ /\b([[:upper:]])\B/g);
-				if (@author_initials) {
-					print "<br />" .
-					      esc_html(join('', @author_initials));
-					#           or join('.', ...)
+			my $short_rev = substr($full_rev, 0, 8);
+			my $author = $meta->{'author'};
+			my %date =
+				parse_date($meta->{'author-time'}, $meta->{'author-tz'});
+			my $date = $date{'iso-tz'};
+			if ($group_size) {
+				$current_color = ($current_color + 1) % $num_colors;
+			}
+			my $tr_class = $rev_color[$current_color];
+			$tr_class .= ' boundary' if (exists $meta->{'boundary'});
+			$tr_class .= ' no-previous' if ($meta->{'nprevious'} == 0);
+			$tr_class .= ' multiple-previous' if ($meta->{'nprevious'} > 1);
+			print "<tr id=\"l$lineno\" class=\"$tr_class\">\n";
+			if ($group_size) {
+				print "<td class=\"sha1\"";
+				print " title=\"". esc_html($author) . ", $date\"";
+				print " rowspan=\"$group_size\"" if ($group_size > 1);
+				print ">";
+				print $cgi->a({-href => href(action=>"commit",
+				                             hash=>$full_rev,
+				                             file_name=>$file_name)},
+				              esc_html($short_rev));
+				if ($group_size >= 2) {
+					my @author_initials = ($author =~ /\b([[:upper:]])\B/g);
+					if (@author_initials) {
+						print "<br />" .
+						      esc_html(join('', @author_initials));
+						#           or join('.', ...)
+					}
 				}
+				print "</td>\n";
 			}
-			print "</td>\n";
-		}
-		# 'previous' <sha1 of parent commit> <filename at commit>
-		if (exists $meta->{'previous'} &&
-		    $meta->{'previous'} =~ /^([a-fA-F0-9]{40}) (.*)$/) {
-			$meta->{'parent'} = $1;
-			$meta->{'file_parent'} = unquote($2);
-		}
-		my $linenr_commit =
-			exists($meta->{'parent'}) ?
-			$meta->{'parent'} : $full_rev;
-		my $linenr_filename =
-			exists($meta->{'file_parent'}) ?
-			$meta->{'file_parent'} : unquote($meta->{'filename'});
-		my $blamed = href(action => 'blame',
-		                  file_name => $linenr_filename,
-		                  hash_base => $linenr_commit);
-		print "<td class=\"linenr\">";
-		print $cgi->a({ -href => "$blamed#l$orig_lineno",
-		                -class => "linenr" },
-		              esc_html($lineno));
-		print "</td>";
-		print "<td class=\"pre\">" . esc_html($data) . "</td>\n";
-		print "</tr>\n";
+			# 'previous' <sha1 of parent commit> <filename at commit>
+			if (exists $meta->{'previous'} &&
+			    $meta->{'previous'} =~ /^([a-fA-F0-9]{40}) (.*)$/) {
+				$meta->{'parent'} = $1;
+				$meta->{'file_parent'} = unquote($2);
+			}
+			my $linenr_commit =
+				exists($meta->{'parent'}) ?
+				$meta->{'parent'} : $full_rev;
+			my $linenr_filename =
+				exists($meta->{'file_parent'}) ?
+				$meta->{'file_parent'} : unquote($meta->{'filename'});
+			my $blamed = href(action => 'blame',
+			                  file_name => $linenr_filename,
+			                  hash_base => $linenr_commit);
+			print "<td class=\"linenr\">";
+			print $cgi->a({ -href => "$blamed#l$orig_lineno",
+			                -class => "linenr" },
+			              esc_html($lineno));
+			print "</td>";
+			print "<td class=\"pre\">" . esc_html($data) . "</td>\n";
+			print "</tr>\n";
+		} # end while
+
 	}
-	print "</table>\n";
-	print "</div>";
+
+	# footer
+	print "</tbody>\n".
+	      "</table>\n"; # class="blame"
+	print "</div>\n";   # class="blame_body"
 	close $fd
 		or print "Reading blob failed\n";
 
-	# page footer
+	if ($format eq 'incremental') {
+		print qq!<script type="text/javascript" src="$javascript"></script>\n!.
+		      qq!<script type="text/javascript">\n!.
+		      qq!startBlame("!. href(action=>"blame_data", -replay=>1) .qq!",\n!.
+		      qq!           "!. href() .qq!");\n!.
+		      qq!</script>\n!;
+	}
+
 	git_footer_html();
 }
 
+sub git_blame {
+	git_blame_common();
+}
+
+sub git_blame_incremental {
+	git_blame_common('incremental');
+}
+
+sub git_blame_data {
+	git_blame_common('data');
+}
+
 sub git_tags {
 	my $head = git_get_head_hash($project);
 	git_header_html();