img: Add back support for SVG images, bypassing ImageMagick and simply passing the SVG through to the browser

SVG scaling by img directives has subtly changed; where before size=wxh
would preserve aspect ratio, this cannot be done when passing them through
and so specifying both a width and height can change the SVG's aspect
ratio.

(This patch looks significantly more complex than it was, because a large
block of code had to be indented.)

[smcv: drop trailing whitespace, fix some spelling]

3 files changed, 106 insertions, 89 deletions

diff --git a/IkiWiki/Plugin/img.pm b/IkiWiki/Plugin/img.pm
index ed2e9354d..494fe2335 100644
--- a/IkiWiki/Plugin/img.pm
+++ b/IkiWiki/Plugin/img.pm
@@ -23,8 +23,8 @@ sub getsetup () {
 		},
 		img_allowed_formats => {
 			type => "string",
-			default => [qw(jpeg png gif)],
-			description => "Image formats to process (jpeg, png, gif, pdf, svg or 'everything' to accept all)",
+			default => [qw(jpeg png gif svg)],
+			description => "Image formats to process (jpeg, png, gif, svg, pdf or 'everything' to accept all)",
 			# ImageMagick has had arbitrary code execution flaws,
 			# and the whole delegates mechanism is scary from
 			# that perspective
@@ -36,7 +36,7 @@ sub getsetup () {
 sub allowed {
 	my $format = shift;
 	my $allowed = $config{img_allowed_formats};
-	$allowed = ['jpeg', 'png'] unless defined $allowed && @$allowed;
+	$allowed = ['jpeg', 'png', 'gif', 'svg'] unless defined $allowed && @$allowed;
 
 	foreach my $a (@$allowed) {
 		return 1 if $a eq $format || $a eq 'everything';
@@ -131,17 +131,7 @@ sub preprocess (@) {
 	error sprintf(gettext("%s image processing disabled in img_allowed_formats configuration"), $format ? $format : "\"$extension\"") unless allowed($format ? $format : "everything");
 
 	# Try harder to protect ImageMagick from itself
-	if ($format eq 'svg') {
-		my $content;
-		read($in, $content, 5) or error sprintf(gettext("failed to read %s: %s"), $file, $!);
-		# This is an over-simplification, but ?xml is the check that
-		# ImageMagick uses. We also accept <svg for the simplest
-		# possible SVGs.
-		if ($content !~ m/^(.\?xml|<svg)/is) {
-			error sprintf(gettext("\"%s\" does not seem to be a valid %s file"), $file, $format);
-		}
-	}
-	elsif ($magic) {
+	if (defined $magic) {
 		my $content;
 		read($in, $content, length $magic) or error sprintf(gettext("failed to read %s: %s"), $file, $!);
 		if ($magic ne $content) {
@@ -149,94 +139,112 @@ sub preprocess (@) {
 		}
 	}
 
-	my $issvg = $base=~s/\.svg$/.png/i;
 	my $ispdf = $base=~s/\.pdf$/.png/i;
 	my $pagenumber = exists($params{pagenumber}) ? int($params{pagenumber}) : 0;
 	if ($pagenumber != 0) {
 		$base = "p$pagenumber-$base";
 	}
 
-	eval q{use Image::Magick};
-	error gettext("Image::Magick is not installed") if $@;
-	my $im = Image::Magick->new();
 	my $imglink;
 	my $imgdatalink;
-	my $r = $im->Read("$format:$srcfile\[$pagenumber]");
-	error sprintf(gettext("failed to read %s: %s"), $file, $r) if $r;
+	my ($dwidth, $dheight);
 
-	if (! defined $im->Get("width") || ! defined $im->Get("height")) {
-		error sprintf(gettext("failed to get dimensions of %s"), $file);
+	my ($w, $h);
+	if ($params{size} ne 'full') {
+		($w, $h) = ($params{size} =~ /^(\d*)x(\d*)$/);
 	}
 
-	my ($dwidth, $dheight);
+	if ($format eq 'svg') {
+		# svg images are not scaled using ImageMagick because the
+		# pipeline is complex. Instead, the image size is simply
+		# set to the provided values.
+		#
+		# Aspect ratio will be preserved automatically when
+		# only a width or only a height is specified.
+		# When both are specified, aspect ratio will not be
+		# preserved.
+		$imglink = $file;
+		$dwidth = $w if length $w;
+		$dheight = $h if length $h;
+	}
+	else {
+		eval q{use Image::Magick};
+		error gettext("Image::Magick is not installed") if $@;
+		my $im = Image::Magick->new();
+		my $r = $im->Read("$format:$srcfile\[$pagenumber]");
+		error sprintf(gettext("failed to read %s: %s"), $file, $r) if $r;
+
+		if (! defined $im->Get("width") || ! defined $im->Get("height")) {
+			error sprintf(gettext("failed to get dimensions of %s"), $file);
+		}
 
-	if ($params{size} eq 'full') {
-		$dwidth = $im->Get("width");
-		$dheight = $im->Get("height");
-	} else {
-		my ($w, $h) = ($params{size} =~ /^(\d*)x(\d*)$/);
-		error sprintf(gettext('wrong size format "%s" (should be WxH)'), $params{size})
-			unless (defined $w && defined $h &&
-			        (length $w || length $h));
-
-		if ($im->Get("width") == 0 || $im->Get("height") == 0) {
-			($dwidth, $dheight)=(0, 0);
-		} elsif (! length $w || (length $h && $im->Get("height")*$w > $h * $im->Get("width"))) {
-			# using height because only height is given or ...
-			# because original image is more portrait than $w/$h
-			# ... slimness of $im > $h/w
-			# ... $im->Get("height")/$im->Get("width") > $h/$w
-			# ... $im->Get("height")*$w > $h * $im->Get("width")
-
-			$dheight=$h;
-			$dwidth=$h / $im->Get("height") * $im->Get("width");
-		} else { # (! length $h) or $w is what determines the resized size
-			$dwidth=$w;
-			$dheight=$w / $im->Get("width") * $im->Get("height");
+		if (! length $w && ! length $h) {
+			$dwidth = $im->Get("width");
+			$dheight = $im->Get("height");
+		} else {
+			error sprintf(gettext('wrong size format "%s" (should be WxH)'), $params{size})
+				unless (defined $w && defined $h &&
+				        (length $w || length $h));
+
+			if ($im->Get("width") == 0 || $im->Get("height") == 0) {
+				($dwidth, $dheight)=(0, 0);
+			} elsif (! length $w || (length $h && $im->Get("height")*$w > $h * $im->Get("width"))) {
+				# using height because only height is given or ...
+				# because original image is more portrait than $w/$h
+				# ... slimness of $im > $h/w
+				# ... $im->Get("height")/$im->Get("width") > $h/$w
+				# ... $im->Get("height")*$w > $h * $im->Get("width")
+
+				$dheight=$h;
+				$dwidth=$h / $im->Get("height") * $im->Get("width");
+			} else { # (! length $h) or $w is what determines the resized size
+				$dwidth=$w;
+				$dheight=$w / $im->Get("width") * $im->Get("height");
+			}
 		}
-	}
 
-	if ($dwidth < $im->Get("width") || $ispdf) {
-		# resize down, or resize to pixels at all
+		if ($dwidth < $im->Get("width") || $ispdf) {
+			# resize down, or resize to pixels at all
 
-		my $outfile = "$config{destdir}/$dir/$params{size}-$base";
-		$imglink = "$dir/$params{size}-$base";
+			my $outfile = "$config{destdir}/$dir/$params{size}-$base";
+			$imglink = "$dir/$params{size}-$base";
 
-		will_render($params{page}, $imglink);
+			will_render($params{page}, $imglink);
 
-		if (-e $outfile && (-M $srcfile >= -M $outfile)) {
-			$im = Image::Magick->new;
-			$r = $im->Read($outfile);
-			error sprintf(gettext("failed to read %s: %s"), $outfile, $r) if $r;
-		}
-		else {
-			$r = $im->Resize(geometry => "${dwidth}x${dheight}");
-			error sprintf(gettext("failed to resize: %s"), $r) if $r;
-
-			$im->set(($issvg || $ispdf) ? (magick => 'png') : ());
-			my @blob = $im->ImageToBlob();
-			# don't actually write resized file in preview mode;
-			# rely on width and height settings
-			if (! $params{preview}) {
-				writefile($imglink, $config{destdir}, $blob[0], 1);
+			if (-e $outfile && (-M $srcfile >= -M $outfile)) {
+				$im = Image::Magick->new;
+				$r = $im->Read($outfile);
+				error sprintf(gettext("failed to read %s: %s"), $outfile, $r) if $r;
 			}
 			else {
-				eval q{use MIME::Base64};
-				error($@) if $@;
-				$imgdatalink = "data:image/".$im->Get("magick").";base64,".encode_base64($blob[0]);
+				$r = $im->Resize(geometry => "${dwidth}x${dheight}");
+				error sprintf(gettext("failed to resize: %s"), $r) if $r;
+
+				$im->set($ispdf ? (magick => 'png') : ());
+				my @blob = $im->ImageToBlob();
+				# don't actually write resized file in preview mode;
+				# rely on width and height settings
+				if (! $params{preview}) {
+					writefile($imglink, $config{destdir}, $blob[0], 1);
+				}
+				else {
+					eval q{use MIME::Base64};
+					error($@) if $@;
+					$imgdatalink = "data:image/".$im->Get("magick").";base64,".encode_base64($blob[0]);
+				}
 			}
+
+			# always get the true size of the resized image (it could be
+			# that imagemagick did its calculations differently)
+			$dwidth  = $im->Get("width");
+			$dheight = $im->Get("height");
+		} else {
+			$imglink = $file;
 		}
 
-		# always get the true size of the resized image (it could be
-		# that imagemagick did its calculations differently)
-		$dwidth  = $im->Get("width");
-		$dheight = $im->Get("height");
-	} else {
-		$imglink = $file;
-	}
-	
-	if (! defined($dwidth) || ! defined($dheight)) {
-		error sprintf(gettext("failed to determine size of image %s"), $file)
+		if (! defined($dwidth) || ! defined($dheight)) {
+			error sprintf(gettext("failed to determine size of image %s"), $file)
+		}
 	}
 
 	my ($fileurl, $imgurl);
@@ -255,10 +263,10 @@ sub preprocess (@) {
 		}
 	}
 	
-	my $imgtag='<img src="'.$imgurl.
-		'" width="'.$dwidth.
-		'" height="'.$dheight.'"'.
-		$attrs.
+	my $imgtag='<img src="'.$imgurl.'"';
+	$imgtag.=' width="'.$dwidth.'"' if defined $dwidth;
+	$imgtag.=' height="'.$dheight.'"' if defined $dheight;
+	$imgtag.= $attrs.
 		(exists $params{align} && ! exists $params{caption} ? ' align="'.$params{align}.'"' : '').
 		' />';
 
diff --git a/debian/changelog b/debian/changelog
index d5f2eca25..02894877d 100644
--- a/debian/changelog
+++ b/debian/changelog
@@ -16,6 +16,13 @@ ikiwiki (3.20160122) UNRELEASED; urgency=medium
   * d/control: add Vcs-Browser
 
   [ Joey Hess ]
+  * img: Add back support for SVG images, bypassing ImageMagick and
+    simply passing the SVG through to the browser, which is supported by all
+    commonly used browsers these days.
+    SVG scaling by img directives has subtly changed; where before
+    size=wxh would preserve aspect ratio, this cannot be done when passing
+    them through and so specifying both a width and height can change
+    the SVG's aspect ratio.
   * loginselector: When only openid and emailauth are enabled, but
     passwordauth is not, avoid showing a "Other" box which opens an
     empty form.
diff --git a/doc/ikiwiki/directive/img.mdwn b/doc/ikiwiki/directive/img.mdwn
index 08d158987..fa3b40f50 100644
--- a/doc/ikiwiki/directive/img.mdwn
+++ b/doc/ikiwiki/directive/img.mdwn
@@ -12,11 +12,13 @@ providing a link to a full-size version.
 The image file will be searched for using the same rules as used to find
 the file pointed to by a [[ikiwiki/WikiLink]].
 
-The `size` parameter is optional, defaulting to full size. Note that the
-original image's aspect ratio is always preserved, even if this means
-making the image smaller than the specified size. You can also specify only
-the width or the height, and the other value will be calculated based on
-it: "200x", "x200"
+The `size` parameter is optional, defaulting to full size.
+You can specify only the width or the height, and the other value will
+be calculated based on it: "200x", "x200".
+
+If you specify both the width and height, the original image's aspect
+ratio will be preserved, even if this means making the image smaller
+than the specified size. (However, this is not done for svg images.)
 
 You can also pass `alt`, `title`, `class`, `align`, `id`, `hspace`, and
 `vspace` parameters.