Fix Postgres JSON literal escaping (#740)

Author: lukaszsamson

lib/ecto/adapters/postgres/connection.ex

@@ -2023,12 +2023,10 @@ if Code.ensure_loaded?(Postgrex) do
     end
 
     defp escape_json(value) when is_binary(value) do
-      escaped =
-        value
-        |> escape_string()
-        |> :binary.replace("\"", "\\\"", [:global])
-
-      [?", escaped, ?"]
+      value
+      |> json_library().encode_to_iodata!()
+      |> IO.iodata_to_binary()
+      |> escape_string()
     end
 
     defp escape_json(value) when is_integer(value) do
@@ -2038,6 +2036,10 @@ if Code.ensure_loaded?(Postgrex) do
     defp escape_json(true), do: ["true"]
     defp escape_json(false), do: ["false"]
 
+    defp json_library do
+      Application.get_env(:postgrex, :json_library, Jason)
+    end
+
     # To allow columns in json paths, we use the array[...] syntax
     # which requires special handling for strings and column references.
     # We still keep the escape_json/1 variant for strings because it is

test/ecto/adapters/postgres_test.exs

@@ -1011,6 +1011,22 @@ defmodule Ecto.Adapters.PostgresTest do
     query = Schema |> where([s], s.meta["id"] == "123") |> select(true) |> plan()
     assert all(query) == ~s|SELECT TRUE FROM "schema" AS s0 WHERE ((s0."meta"@>'{"id": "123"}'))|
 
+    query = Schema |> where([s], s.meta["k"] == "a\\b") |> select(true) |> plan()
+    assert all(query) == ~S|SELECT TRUE FROM "schema" AS s0 WHERE ((s0."meta"@>'{"k": "a\\b"}'))|
+
+    query = Schema |> where([s], s.meta["k"] == "l1\nl2") |> select(true) |> plan()
+
+    assert all(query) ==
+             ~S|SELECT TRUE FROM "schema" AS s0 WHERE ((s0."meta"@>'{"k": "l1\nl2"}'))|
+
+    query = Schema |> where([s], s.meta["k"] == "a\\q") |> select(true) |> plan()
+    assert all(query) == ~S|SELECT TRUE FROM "schema" AS s0 WHERE ((s0."meta"@>'{"k": "a\\q"}'))|
+
+    query = Schema |> where([s], s.meta["a\\b"] == "value") |> select(true) |> plan()
+
+    assert all(query) ==
+             ~S|SELECT TRUE FROM "schema" AS s0 WHERE ((s0."meta"@>'{"a\\b": "value"}'))|
+
     query = Schema |> where([s], s.meta["tags"][0]["name"] == "123") |> select(true) |> plan()
 
     assert all(query) ==