Add the link-trailers extension

1 file changed, 109 insertions, 0 deletions

diff --git a/custom/extensions/link-trailers.lua b/custom/extensions/link-trailers.lua
new file mode 100644
index 0000000..645c517
--- /dev/null
+++ b/custom/extensions/link-trailers.lua
@@ -0,0 +1,109 @@
+-- cgit trailer-filter that turns the value of a commit trailer into a link,
+-- named by the trailer-filter or repo.trailer-filter setting in cgitrc. cgit
+-- opens it once per trailer with the trailer key and the page name as its
+-- arguments and hands over the value already HTML-escaped, so all this does
+-- is wrap the value, or the part of it a rule captures, in an anchor. Runs on
+-- Lua 5.1 through 5.4 and LuaJIT with nothing outside the standard library.
+--
+--     trailer-filter=lua:/path/to/link-trailers.lua
+--
+-- Trailers whose value is a person, such as Signed-off-by, never reach this
+-- filter. cgit writes those through the email filter instead.
+
+
+-- Rules are tried in order and the first whose key matches the trailer, case
+-- insensitively, and whose pattern matches the value wins. Each pattern is a
+-- Lua pattern with a single capture and a URL where %s is replaced by that
+-- capture, percent-encoded. The matched run is what gets wrapped and the
+-- capture is only what goes into the URL. A rule without a key applies to
+-- every trailer.
+--
+-- Lua patterns are not regular expressions. The reference is
+-- https://www.lua.org/manual/5.1/manual.html#5.4.1
+--
+-- Patterns run against the escaped value, so match the entity spellings
+-- '&', '<' and '>' rather than the bare characters, and keep a
+-- pattern from ending part way through one.
+local rules = {
+	-- Fixes: 1234567 ("subject") and Reverts: 1234567 link the object name
+	-- to its commit page. The relative form is resolved against the
+	-- current page and works for the common virtual-root layout.
+	{ key = "Fixes", pattern = "^(%x%x%x%x%x%x%x+)", url = "./?id=%s" },
+	{ key = "Reverts", pattern = "^(%x%x%x%x%x%x%x+)", url = "./?id=%s" },
+	-- Closes: #123 and Bug: 123 point at the tracker.
+	{ key = "Closes", pattern = "^#?(%d+)$", url = "https://bugs.example.com/?bug=%s" },
+	{ key = "Bug", pattern = "^#?(%d+)$", url = "https://bugs.example.com/?bug=%s" },
+	-- { key = "CVE", pattern = "^CVE%-(%d%d%d%d%-%d+)$",
+	--   url = "https://www.cve.org/CVERecord?id=CVE-%s" },
+}
+
+-- A value that is nothing but one http or https URL, under any key, links to
+-- itself. Set false to leave such values as text.
+local link_urls = true
+
+
+local key = ""
+local chunks = {}
+
+-- Percent-encode everything but the URL unreserved characters, so a captured
+-- value cannot break out of the href attribute or out of the URL itself.
+local function url_encode(s)
+	return (string.gsub(s, "[^%w._~-]", function(c)
+		return string.format("%%%02X", string.byte(c))
+	end))
+end
+
+-- Build one anchor from a URL template holding %s and the text to show. The
+-- replacement is a function so that a '%' in the encoded value is not taken
+-- for a gsub reference.
+local function make_link(url_template, capture, display)
+	local encoded = url_encode(capture)
+	local href = string.gsub(url_template, "%%s", function()
+		return encoded
+	end)
+	return "<a href='" .. href .. "'>" .. display .. "</a>"
+end
+
+-- The value is already escaped, which is also what an attribute wants, so a
+-- URL only has to be kept away from the quote that closes the attribute.
+local function link_url(text)
+	if not link_urls or not string.find(text, "^https?://[^%s'\"]+$") then
+		return nil
+	end
+	return "<a href='" .. text .. "'>" .. text .. "</a>"
+end
+
+local function link_rule(text)
+	local wanted = string.lower(key)
+	for _, rule in ipairs(rules) do
+		if rule.key == nil or string.lower(rule.key) == wanted then
+			-- A malformed pattern is an operator error, so skip
+			-- that rule rather than fail the whole page.
+			local ok, start, stop, capture = pcall(string.find, text, rule.pattern)
+			if ok and start then
+				if capture == nil then
+					capture = string.sub(text, start, stop)
+				end
+				return string.sub(text, 1, start - 1) ..
+					make_link(rule.url, capture, string.sub(text, start, stop)) ..
+					string.sub(text, stop + 1)
+			end
+		end
+	end
+	return nil
+end
+
+function filter_open(trailer_key, page)
+	key = trailer_key or ""
+	chunks = {}
+end
+
+function filter_write(str)
+	chunks[#chunks + 1] = str
+end
+
+function filter_close()
+	local text = table.concat(chunks)
+	html(link_url(text) or link_rule(text) or text)
+	return 0
+end