Allow passing the slicer module in as an option to the Tesla middleware

lib/meta_logger/slicer.ex

@@ -5,42 +5,46 @@ defmodule MetaLogger.Slicer do
 
   @typedoc "Max length in bytes or `:infinity` if the entry should not be sliced."
   @type max_entry_length :: non_neg_integer() | :infinity
-
-  @doc """
-  Returns sliced log entries according to the given max entry length.
-
-  If the entry is smaller than given max length, or if `:infinity ` is given
-  as option, a list with one entry is returned. Otherwise a list with multiple
-  entries is returned.
-
-  ## Examples
-
-      iex> #{inspect(__MODULE__)}.slice("1234567890", 10)
-      ["1234567890"]
-
-      iex> #{inspect(__MODULE__)}.slice("1234567890", :infinity)
-      ["1234567890"]
-
-      iex> #{inspect(__MODULE__)}.slice("1234567890", 5)
-      ["12345", "67890"]
-
-  """
-  @spec slice(String.t(), max_entry_length()) :: [String.t()]
-  def slice(entry, max_entry_length)
-      when max_entry_length == :infinity
-      when byte_size(entry) <= max_entry_length,
-      do: [entry]
-
-  def slice(entry, max_entry_length) do
-    entry_length = byte_size(entry)
-    rem = rem(entry_length, max_entry_length)
-    sliced_entries = for <<slice::binary-size(max_entry_length) <- entry>>, do: slice
-
-    if rem > 0 do
-      remainder_entry = binary_part(entry, entry_length, rem * -1)
-      sliced_entries ++ [remainder_entry]
-    else
-      sliced_entries
+  @callback slice(String.t(), max_entry_length()) :: [String.t()]
+
+  defmodule Default do
+    @behaviour MetaLogger.Slicer
+    @doc """
+    Returns sliced log entries according to the given max entry length.
+
+    If the entry is smaller than given max length, or if `:infinity ` is given
+    as option, a list with one entry is returned. Otherwise a list with multiple
+    entries is returned.
+
+    ## Examples
+
+        iex> #{inspect(__MODULE__)}.slice("1234567890", 10)
+        ["1234567890"]
+
+        iex> #{inspect(__MODULE__)}.slice("1234567890", :infinity)
+        ["1234567890"]
+
+        iex> #{inspect(__MODULE__)}.slice("1234567890", 5)
+        ["12345", "67890"]
+
+    """
+    @impl MetaLogger.Slicer
+    def slice(entry, max_entry_length)
+        when max_entry_length == :infinity
+        when byte_size(entry) <= max_entry_length,
+        do: [entry]
+
+    def slice(entry, max_entry_length) do
+      entry_length = byte_size(entry)
+      rem = rem(entry_length, max_entry_length)
+      sliced_entries = for <<slice::binary-size(max_entry_length) <- entry>>, do: slice
+
+      if rem > 0 do
+        remainder_entry = binary_part(entry, entry_length, rem * -1)
+        sliced_entries ++ [remainder_entry]
+      else
+        sliced_entries
+      end
     end
   end
 end

lib/tesla/middleware/meta_logger.ex

@@ -71,6 +71,7 @@ if Code.ensure_loaded?(Tesla) do
       |> maybe_put_default_value(:log_level, :info)
       |> maybe_put_default_value(:log_tag, __MODULE__)
       |> maybe_put_default_value(:max_entry_length, :infinity)
+      |> maybe_put_default_value(:slicer, MetaLogger.Slicer.Default)
     end
 
     @spec maybe_put_default_values(Env.opts(), [atom()], any()) :: Env.opts()
@@ -182,9 +183,10 @@ if Code.ensure_loaded?(Tesla) do
 
     defp log(message, level, options) when is_binary(message) do
       max_entry_length = Keyword.get(options, :max_entry_length)
+      slicer = Keyword.get(options, :slicer)
 
       message
-      |> Slicer.slice(max_entry_length)
+      |> slicer.slice(max_entry_length)
       |> Enum.map(&prepend_tag(&1, options))
       |> Enum.each(&MetaLogger.log(level, &1))
     end

test/meta_logger/slicer_test.exs

@@ -1,7 +1,7 @@
 defmodule MetaLogger.SlicerTest do
   use ExUnit.Case, async: true
 
-  alias MetaLogger.Slicer, as: Subject
+  alias MetaLogger.Slicer.Default, as: Subject
 
   doctest Subject
 

test/tesla/middleware/meta_logger_test.exs

@@ -5,6 +5,15 @@ defmodule Tesla.Middleware.MetaLoggerTest do
 
   alias Tesla.Middleware.MetaLogger, as: Subject
 
+  defmodule AlternativeSlicer do
+    @behaviour MetaLogger.Slicer
+
+    @impl MetaLogger.Slicer
+    def slice(entry, _max_entry_length) do
+      ["slice1", "slice2"]
+    end
+  end
+
   defmodule FakeClient do
     use Tesla
 
@@ -251,6 +260,18 @@ defmodule Tesla.Middleware.MetaLoggerTest do
       assert logs =~ "[warning] [#{inspect(Subject)}] response body moved"
     end
 
+    test "when a slicer module is given, uses it to slice the message" do
+      logs =
+        capture_log(fn ->
+          FakeClient.post("/huge-response", "1234567890",
+            opts: [slicer: __MODULE__.AlternativeSlicer]
+          )
+        end)
+
+      assert logs =~ "[debug] [Tesla.Middleware.MetaLogger] slice1"
+      assert logs =~ "[debug] [Tesla.Middleware.MetaLogger] slice2"
+    end
+
     test "when the request fails to connect, logs the error" do
       logs = capture_log(fn -> FakeClient.get("/connection-error") end)