From a6301e40a9e7dd5b9e7d9c6987ff71950c1579e2 Mon Sep 17 00:00:00 2001
From: Daniel Kukula <daniel.kuku@gmail.com>
Date: Sun, 27 Sep 2026 08:42:18 +0200
Subject: [PATCH] Avoid intermediate lists in URI query decoding

Instead of calling :binary.split/2 twice per key-value pair
(once on "&" and once on "="), decode query parameters directly
using binary pattern matching and binary_part/3.

This eliminates 2 intermediate list allocations per query pair
in URI.query_decoder/2 and URI.decode_query/1,2,3.

Assisted-by: Antigravity:Gemini 3.8 Flash
---
 lib/elixir/lib/uri.ex | 52 +++++++++++++++++++++++++++++--------------
 1 file changed, 35 insertions(+), 17 deletions(-)

diff --git a/lib/elixir/lib/uri.ex b/lib/elixir/lib/uri.ex
index 3a32da98ff..9e9420bba7 100644
--- a/lib/elixir/lib/uri.ex
+++ b/lib/elixir/lib/uri.ex
@@ -292,27 +292,45 @@ defmodule URI do
     Stream.unfold(query, &decode_next_query_pair(&1, encoding))
   end
 
-  defp decode_next_query_pair("", _encoding) do
+  defp decode_next_query_pair(<<>>, _encoding) do
     nil
   end
 
   defp decode_next_query_pair(query, encoding) do
-    {undecoded_next_pair, rest} =
-      case :binary.split(query, "&") do
-        [next_pair, rest] -> {next_pair, rest}
-        [next_pair] -> {next_pair, ""}
-      end
-
-    next_pair =
-      case :binary.split(undecoded_next_pair, "=") do
-        [key, value] ->
-          {decode_with_encoding(key, encoding), decode_with_encoding(value, encoding)}
-
-        [key] ->
-          {decode_with_encoding(key, encoding), ""}
-      end
-
-    {next_pair, rest}
+    parse_next_key(query, query, 0, encoding)
+  end
+
+  defp parse_next_key(<<?=, rest::binary>>, original, skip, encoding) do
+    key = binary_part(original, 0, skip) |> decode_with_encoding(encoding)
+    parse_next_val(rest, rest, 0, key, encoding)
+  end
+
+  defp parse_next_key(<<?&, rest::binary>>, original, skip, encoding) do
+    key = binary_part(original, 0, skip) |> decode_with_encoding(encoding)
+    {{key, ""}, rest}
+  end
+
+  defp parse_next_key(<<_char, rest::binary>>, original, skip, encoding) do
+    parse_next_key(rest, original, skip + 1, encoding)
+  end
+
+  defp parse_next_key(<<>>, original, skip, encoding) do
+    key = binary_part(original, 0, skip) |> decode_with_encoding(encoding)
+    {{key, ""}, ""}
+  end
+
+  defp parse_next_val(<<?&, rest::binary>>, original, skip, key, encoding) do
+    val = binary_part(original, 0, skip) |> decode_with_encoding(encoding)
+    {{key, val}, rest}
+  end
+
+  defp parse_next_val(<<_char, rest::binary>>, original, skip, key, encoding) do
+    parse_next_val(rest, original, skip + 1, key, encoding)
+  end
+
+  defp parse_next_val(<<>>, original, skip, key, encoding) do
+    val = binary_part(original, 0, skip) |> decode_with_encoding(encoding)
+    {{key, val}, ""}
   end
 
   defp decode_with_encoding(string, :www_form) do