defmodule Plug.Conn.Query do
@moduledoc """
Conveniences for decoding and encoding url encoded queries.
Plug allows a developer to build query strings
that map to Elixir structures in order to make
manipulation of such structures easier on the server
side. Here are some examples:
iex> decode("foo=bar")["foo"]
"bar"
If a value is given more than once, the last value takes precedence:
iex> decode("foo=bar&foo=baz")["foo"]
"baz"
Nested structures can be created via `[key]`:
iex> decode("foo[bar]=baz")["foo"]["bar"]
"baz"
Lists are created with `[]`:
iex> decode("foo[]=bar&foo[]=baz")["foo"]
["bar", "baz"]
Dicts can be encoded:
iex> encode(%{foo: "bar", baz: "bat"})
"baz=bat&foo=bar"
Encoding keyword lists preserves the order of the fields:
iex> encode([foo: "bar", baz: "bat"])
"foo=bar&baz=bat"
When encoding keyword lists with duplicate keys, the key that comes first
takes precedence:
iex> encode([foo: "bar", foo: "bat"])
"foo=bar"
Encoding named lists:
iex> encode(%{foo: ["bar", "baz"]})
"foo[]=bar&foo[]=baz"
Encoding nested structures:
iex> encode(%{foo: %{bar: "baz"}})
"foo[bar]=baz"
"""
@doc """
Decodes the given binary.
"""
def decode(query, initial \\ %{})
def decode("", initial) do
initial
end
def decode(query, initial) do
parts = :binary.split(query, "&", [:global])
Enum.reduce(Enum.reverse(parts), initial, &decode_string_pair(&1, &2))
end
defp decode_string_pair(binary, acc) do
current =
case :binary.split(binary, "=") do
[key, value] ->
{URI.decode_www_form(key), URI.decode_www_form(value)}
[key] ->
{URI.decode_www_form(key), nil}
end
decode_pair(current, acc)
end
@doc """
Decodes the given tuple and stores it in the accumulator.
It parses the key and stores the value into the current
accumulator.
Parameter lists are added to the accumulator in reverse
order, so be sure to pass the parameters in reverse order.
"""
def decode_pair({key, value}, acc) do
parts =
if key != "" and :binary.last(key) == ?] do
# Remove trailing ]
subkey = :binary.part(key, 0, byte_size(key) - 1)
# Split the first [ then split remaining ][.
#
# users[address][street #=> [ "users", "address][street" ]
#
case :binary.split(subkey, "[") do
[key, subpart] ->
[key|:binary.split(subpart, "][", [:global])]
_ ->
[key]
end
else
[key]
end
assign_parts parts, value, acc
end
# We always assign the value in the last segment.
# `age=17` would match here.
defp assign_parts([key], value, acc) do
Map.put_new(acc, key, value)
end
# The current segment is a list. We simply prepend
# the item to the list or create a new one if it does
# not yet. This assumes that items are iterated in
# reverse order.
defp assign_parts([key,""|t], value, acc) do
case Map.fetch(acc, key) do
{:ok, current} when is_list(current) ->
Map.put(acc, key, assign_list(t, current, value))
:error ->
Map.put(acc, key, assign_list(t, [], value))
_ ->
acc
end
end
# The current segment is a parent segment of a
# map. We need to create a map and then
# continue looping.
defp assign_parts([key|t], value, acc) do
case Map.fetch(acc, key) do
{:ok, %{} = current} ->
Map.put(acc, key, assign_parts(t, value, current))
:error ->
Map.put(acc, key, assign_parts(t, value, %{}))
_ ->
acc
end
end
defp assign_list(t, current, value) do
if value = assign_list(t, value), do: [value|current], else: current
end
defp assign_list([], value), do: value
defp assign_list(t, value), do: assign_parts(t, value, %{})
@doc """
Encodes the given dict.
"""
def encode(dict, encoder \\ &to_string/1) do
IO.iodata_to_binary encode_pair("", dict, encoder)
end
# covers structs
defp encode_pair(field, %{__struct__: struct} = map, encoder) when is_atom(struct) do
[field, ?=|encode_value(map, encoder)]
end
# covers maps
defp encode_pair(parent_field, %{} = map, encoder) do
encode_dict(map, parent_field, encoder)
end
# covers keyword lists
defp encode_pair(parent_field, list, encoder) when is_list(list) and is_tuple(hd(list)) do
encode_dict(Enum.uniq(list, &elem(&1, 0)), parent_field, encoder)
end
# covers non-keyword lists
defp encode_pair(parent_field, list, encoder) when is_list(list) do
prune Enum.flat_map list, fn value ->
[?&, encode_pair(parent_field <> "[]", value, encoder)]
end
end
# covers nil
defp encode_pair(field, nil, _encoder) do
[field, ?=]
end
# encoder fallback
defp encode_pair(field, value, encoder) do
[field, ?=|encode_value(value, encoder)]
end
defp encode_dict(dict, parent_field, encoder) do
prune Enum.flat_map dict, fn
{_, value} when value in [%{}, []] ->
[]
{field, value} ->
field =
if parent_field == "" do
encode_key(field)
else
parent_field <> "[" <> encode_key(field) <> "]"
end
[?&, encode_pair(field, value, encoder)]
end
end
defp encode_key(item) do
item |> to_string |> URI.encode_www_form
end
defp encode_value(item, encoder) do
item |> encoder.() |> URI.encode_www_form
end
defp prune([?&|t]), do: t
defp prune([]), do: []
end