From fd801d003bfcdfc83c2313dd3b951254f0db77ef Mon Sep 17 00:00:00 2001
From: single-right-quote
 <34298117+single-right-quote@users.noreply.github.com>
Date: Thu, 9 Sep 2021 03:58:09 +0000
Subject: [PATCH] allow headers to refer to requested hostname, resource

also document this fact
---
 README.md                                       |  5 +++++
 .../binaries/http-get-extra-headers.execline    | 17 ++++++++++++++---
 2 files changed, 19 insertions(+), 3 deletions(-)

diff --git a/README.md b/README.md
index cb149d1..cd7b815 100644
--- a/README.md
+++ b/README.md
@@ -119,6 +119,11 @@ a `Strict-Transport-Security` file is a good idea; if you find it
 prudent to allow access as an onion service, an `Onion-Location` file
 is a good idea. and so on.
 
+the hostname and requested resource for the current request will be
+substituted for all instances of `${hostname}` and `${resource}` in
+the header contents, which might prove useful for the `Location` and
+`Onion-Location` headers.
+
 `\r` and newlines will be stripped from filenames and file contents to
 prevent trivial mischevious configurations from breaking HTTP
 responses; other than this, **these HTTP header folders are not
diff --git a/visible-to-httpd/binaries/http-get-extra-headers.execline b/visible-to-httpd/binaries/http-get-extra-headers.execline
index 35185fa..03432b6 100755
--- a/visible-to-httpd/binaries/http-get-extra-headers.execline
+++ b/visible-to-httpd/binaries/http-get-extra-headers.execline
@@ -17,9 +17,16 @@
 # TODO: write a GUI?? with like, `yad(1)` or something??? idk
 
 multisubstitute {
-	importas -D -fallback hostname http_header_parse_Host
+	importas -D -no_hostname_parsed hostname http_header_parse_Host
+	importas -i requested_resource http_start_line_parse_resource
 	importas -i resource resource
 }
+define header_substitution_script
+"multisubstitute {
+	define hostname "${hostname}"
+	define resource "${requested_resource}"
+}
+s6-echo -n -- "
 
 backtick -x -n header-directory {
 	# for status code pages specifically
@@ -82,9 +89,13 @@ if -t { s6-test -v header-directory }
 			tr -d "\r\n"
 		}
 		if {
-			pipeline { cat ${header_name} }
-			tr -d "\r\n"
+			backtick -E -n unparsed_header_contents {
+				pipeline { cat ${header_name} }
+				tr -d "\r\n"
+			}
+			execlineb -WPc ${header_substitution_script}${unparsed_header_contents}
 		}
+
 		s6-echo -n -- "\r\n"
 	# do remember to add the terminating `\r\n`!
 
-- 
2.47.3