[PATCH 07/14] hval: use File::Spec to make relative paths for href

[Eric Wong <e@80x24.org>]

File::Spec->abs2rel doesn't touch the filesystem at all when
given an absolute base arg ($env->{PATH_INFO}), so we can rely
on it to generate relative links that work with the `mount'
from Plack::Builder and also people running `wget -r' mirrors.
---
 lib/PublicInbox/Hval.pm | 12 +++++++++++-
 1 file changed, 11 insertions(+), 1 deletion(-)

diff --git a/lib/PublicInbox/Hval.pm b/lib/PublicInbox/Hval.pm
index e9b9ae64..b804254a 100644
--- a/lib/PublicInbox/Hval.pm
+++ b/lib/PublicInbox/Hval.pm
@@ -13,6 +13,7 @@ our @EXPORT_OK = qw/ascii_html obfuscate_addrs to_filename src_escape
 		to_attr prurl mid_href fmt_ts ts2str utf8_maybe/;
 use POSIX qw(strftime);
 my $enc_ascii = find_encoding('us-ascii');
+use File::Spec;
 
 # safe-ish acceptable filename pattern for portability
 our $FN = '[a-zA-Z0-9][a-zA-Z0-9_\-\.]+[a-zA-Z0-9]'; # needs \z anchor
@@ -69,7 +70,16 @@ sub prurl ($$) {
 		$u = $host_match[0] // $u->[0];
 		# fall through to below:
 	}
-	index($u, '//') == 0 ? "$env->{'psgi.url_scheme'}:$u" : $u;
+	my $dslash = index($u, '//');
+	if ($dslash == 0) {
+		"$env->{'psgi.url_scheme'}:$u"
+	} elsif ($dslash < 0 && substr($u, 0, 1) ne '/' &&
+			substr(my $path = $env->{PATH_INFO}, 0, 1) eq '/') {
+		# this won't touch the FS at all:
+		File::Spec->abs2rel("/$u", $path);
+	} else {
+		$u;
+	}
 }
 
 # for misguided people who believe in this stuff, give them a