[PATCH 2/2] gitweb: Use character or octal escape codes (and add span.cntrl) in esc_path

[Jakub Narebski <jnareb@gmail.com>]

Instead of simply hiding control characters in esc_path by replacing
them with '?', use Character Escape Codes (CEC) i.e. alphabetic
backslash sequences like those found in C programming language and
many other languages influenced by it, such as Java and Perl.  If
control characted doesn't have corresponding character escape code,
use octal char sequence to escape it.

Additionally use 'span' element with 'cntrl' attribute to mark escaped
control characters. Add style for span.cntrl in the CSS.

Below there is alternative quoting using Unicode Printable
Representation (PR), i.e. replace control characters with appropriate
Unicode Control Pictures U+2400 - U+243F (9216 - 9279), the Unicode
characters reserved for representing control characters when it is
necessary to print or display them:

sub esc_path {
	my $str = shift;
	$str = esc_html($str);
	$str =~ s!([[:cntrl:]])!sprintf('<span class="cntrl">&#%04d;</span>', 0x2400+ord($1))!eg;
	return $str;
}

Signed-off-by: Jakub Narebski <jnareb@gmail.com>
---
The styling (span.cntrl style) isn't best, I agree.

 gitweb/gitweb.css  |    7 +++++++
 gitweb/gitweb.perl |   25 ++++++++++++++++++++++++-
 2 files changed, 31 insertions(+), 1 deletions(-)

diff --git a/gitweb/gitweb.css b/gitweb/gitweb.css
index 0eda982..e19e6bc 100644
--- a/gitweb/gitweb.css
+++ b/gitweb/gitweb.css
@@ -16,6 +16,13 @@ a:hover, a:visited, a:active {
 	color: #880000;
 }
 
+span.cntrl {
+	border: dashed #aaaaaa;
+	border-width: 1px;
+	padding: 0px 2px 0px 2px;
+	margin:  0px 2px 0px 2px;
+}
+
 img.logo {
 	float: right;
 	border-width: 0px;
diff --git a/gitweb/gitweb.perl b/gitweb/gitweb.perl
index 32926f9..c9b16b5 100755
--- a/gitweb/gitweb.perl
+++ b/gitweb/gitweb.perl
@@ -587,8 +587,31 @@ sub esc_html ($;%) {
 # quote control characters and escape filename to HTML
 sub esc_path {
 	my $str = shift;
+
+	sub quot {
+		my $seq = shift;
+		my %es = ( # character escape codes, aka escape sequences
+			"\t" => '\t',   # tab            (HT, TAB)
+			"\n" => '\n',   # newline        (NL)
+			"\r" => '\r',   # return         (CR)
+			"\f" => '\f',   # form feed      (FF)
+			"\b" => '\b',   # backspace      (BS)
+			"\a" => '\a',   # alarm (bell)   (BEL)
+			"\e" => '\e',   # escape         (ESC)
+			"\013" => '\v', # vertical tab   (VT)
+			"\000" => '\0', # null character (NUL)
+		);
+
+		if (exists $es{$seq}) {
+			# C escape sequence, aka character escape code
+			return $es{$seq};
+		}
+		# octal char sequence
+		return sprintf('\%03o', ord($seq));
+	}
+
 	$str = esc_html($str);
-	$str =~ s/[[:cntrl:]]/?/g; # like --hide-control-chars in ls
+	$str =~ s!([[:cntrl:]])!'<span class="cntrl">' . quot($1) . '</span>'!eg;
 	return $str;
 }
 
-- 
1.4.3.4