Trim avatar addresses in linear time

The trim pattern backtracked over a run of spaces inside an address,
which a commit can carry, and a log page runs the filter for every row.
Forty thousand spaces took two seconds per row.

1 file changed, 15 insertions, 1 deletion

diff --git a/custom/extensions/email-gravatar.lua b/custom/extensions/email-gravatar.luaindex 6eb5376..01db3f9 100644--- a/custom/extensions/email-gravatar.lua+++ b/custom/extensions/email-gravatar.lua@@ -58,6 +58,20 @@ local function hash_hex(input) 	return hex end +-- Lua patterns backtrack, so "^%s*(.-)%s*$" would cost the square of a long+-- run of spaces inside the address. Finding each end directly stays linear.+local function trim(text)+	local first = text:find("%S")+	if first == nil then+		return ""+	end+	local last = #text+	while text:find("^%s", last) do+		last = last - 1+	end+	return text:sub(first, last)+end+ -- cgit can hand over the address still wrapped in angle brackets, and the -- service hashes the trimmed lowercase form, so an address that skipped this -- would hash to something the service has never heard of. A missing or empty@@ -70,7 +84,7 @@ local function normalize_email(email) 	if inner ~= nil then 		email = inner 	end-	email = (email:gsub("^%s*(.-)%s*$", "%1")):lower()+	email = trim(email):lower() 	if email == "" then 		return nil 	end
diff --git a/custom/extensions/email-gravatar.lua b/custom/extensions/email-gravatar.lua
index 6eb5376..01db3f9 100644
--- a/custom/extensions/email-gravatar.lua
+++ b/custom/extensions/email-gravatar.lua
@@ -58,6 +58,20 @@ local function hash_hex(input)
 	return hex
 end
 
+-- Lua patterns backtrack, so "^%s*(.-)%s*$" would cost the square of a long
+-- run of spaces inside the address. Finding each end directly stays linear.
+local function trim(text)
+	local first = text:find("%S")
+	if first == nil then
+		return ""
+	end
+	local last = #text
+	while text:find("^%s", last) do
+		last = last - 1
+	end
+	return text:sub(first, last)
+end
+
 -- cgit can hand over the address still wrapped in angle brackets, and the
 -- service hashes the trimmed lowercase form, so an address that skipped this
 -- would hash to something the service has never heard of. A missing or empty
@@ -70,7 +84,7 @@ local function normalize_email(email)
 	if inner ~= nil then
 		email = inner
 	end
-	email = (email:gsub("^%s*(.-)%s*$", "%1")):lower()
+	email = trim(email):lower()
 	if email == "" then
 		return nil
 	end