From a852e2a55fee8963073fb49e417f3b68a8b6427f Mon Sep 17 00:00:00 2001
From: Louis <me@louiscb.com>
Date: Thu, 8 May 2025 13:18:55 +0200
Subject: [PATCH 1/7] Add fallback to previous version

---
 lib/remote_persistent_term.ex                 | 46 ++++++++++++--
 lib/remote_persistent_term/fetcher.ex         |  6 ++
 lib/remote_persistent_term/fetcher/http.ex    |  3 +
 lib/remote_persistent_term/fetcher/s3.ex      | 63 ++++++++++++++++---
 lib/remote_persistent_term/fetcher/static.ex  |  5 +-
 mix.exs                                       |  2 +-
 .../fetcher/s3_test.exs                       | 54 ++++++++++++++++
 7 files changed, 163 insertions(+), 16 deletions(-)

diff --git a/lib/remote_persistent_term.ex b/lib/remote_persistent_term.ex
index 55e4534..fbca472 100644
--- a/lib/remote_persistent_term.ex
+++ b/lib/remote_persistent_term.ex
@@ -69,6 +69,15 @@ defmodule RemotePersistentTerm do
 
       Currently only supports gzip (0x1F, 0x8B).
       """
+    ],
+    version_fallback?: [
+      type: :boolean,
+      required: false,
+      default: false,
+      doc: """
+      If true, when deserialization fails, the system will attempt to use previous versions \
+      of the term until a valid version is found or all versions are exhausted.
+      """
     ]
   ]
 
@@ -77,7 +86,8 @@ defmodule RemotePersistentTerm do
           fetcher_state: term(),
           refresh_interval: pos_integer(),
           current_version: String.t(),
-          auto_decompress?: boolean()
+          auto_decompress?: boolean(),
+          version_fallback?: boolean()
         }
   defstruct [
     :fetcher_mod,
@@ -85,7 +95,8 @@ defmodule RemotePersistentTerm do
     :refresh_interval,
     :current_version,
     :name,
-    :auto_decompress?
+    :auto_decompress?,
+    :version_fallback?
   ]
 
   @doc """
@@ -138,7 +149,8 @@ defmodule RemotePersistentTerm do
             fetcher_state: fetcher_state,
             refresh_interval: opts[:refresh_interval],
             name: name(opts),
-            auto_decompress?: opts[:auto_decompress?]
+            auto_decompress?: opts[:auto_decompress?],
+            version_fallback?: opts[:version_fallback?]
           }
 
           if opts[:lazy_init?] do
@@ -307,9 +319,31 @@ defmodule RemotePersistentTerm do
 
   defp download_and_store_term(state, deserialize_fun, put_fun) do
     with {:ok, term} <- state.fetcher_mod.download(state.fetcher_state),
-         {:ok, decompressed} <- maybe_decompress(state, term),
-         {:ok, deserialized} <- deserialize_fun.(decompressed) do
-      put_fun.(deserialized)
+         {:ok, decompressed} <- maybe_decompress(state, term) do
+      try_deserialize_and_store(state, decompressed, deserialize_fun, put_fun)
+    end
+  end
+
+  defp try_deserialize_and_store(state, term, deserialize_fun, put_fun) do
+    case deserialize_fun.(term) do
+      {:ok, deserialized} ->
+        put_fun.(deserialized)
+
+      {:error, _reason} = error when state.version_fallback? ->
+        case state.fetcher_mod.previous_version(state.fetcher_state) do
+          {:ok, previous_state} ->
+            download_and_store_term(
+              %{state | fetcher_state: previous_state},
+              deserialize_fun,
+              put_fun
+            )
+
+          {:error, _} ->
+            error
+        end
+
+      error ->
+        error
     end
   end
 
diff --git a/lib/remote_persistent_term/fetcher.ex b/lib/remote_persistent_term/fetcher.ex
index 30933a5..676e13a 100644
--- a/lib/remote_persistent_term/fetcher.ex
+++ b/lib/remote_persistent_term/fetcher.ex
@@ -26,4 +26,10 @@ defmodule RemotePersistentTerm.Fetcher do
   Download the term from the remote source.
   """
   @callback download(state()) :: {:ok, term()} | {:error, term()}
+
+  @doc """
+  Get the previous version of the remote term.
+  Returns a new state that can be used to fetch the previous version.
+  """
+  @callback previous_version(state()) :: {:ok, state()} | {:error, term()}
 end
diff --git a/lib/remote_persistent_term/fetcher/http.ex b/lib/remote_persistent_term/fetcher/http.ex
index 1facdc9..e94d6ac 100644
--- a/lib/remote_persistent_term/fetcher/http.ex
+++ b/lib/remote_persistent_term/fetcher/http.ex
@@ -81,6 +81,9 @@ defmodule RemotePersistentTerm.Fetcher.Http do
     end
   end
 
+  @impl true
+  def previous_version(_state), do: {:error, :no_previous_version}
+
   defp response_status(url, status) do
     if status < 300 do
       Logger.info("successfully downloaded remote term from #{url} with status #{status}")
diff --git a/lib/remote_persistent_term/fetcher/s3.ex b/lib/remote_persistent_term/fetcher/s3.ex
index f2d16f2..7d126cc 100644
--- a/lib/remote_persistent_term/fetcher/s3.ex
+++ b/lib/remote_persistent_term/fetcher/s3.ex
@@ -14,9 +14,10 @@ defmodule RemotePersistentTerm.Fetcher.S3 do
           bucket: bucket,
           key: String.t(),
           region: region,
-          failover_buckets: [failover_bucket] | nil
+          failover_buckets: [failover_bucket] | nil,
+          version_id: String.t() | nil
         }
-  defstruct [:bucket, :key, :region, :failover_buckets]
+  defstruct [:bucket, :key, :region, :failover_buckets, :version_id]
 
   @failover_bucket_schema [
     bucket: [
@@ -136,9 +137,9 @@ defmodule RemotePersistentTerm.Fetcher.S3 do
   defp list_object_versions(state) do
     res =
       aws_client_request(
-        &ExAws.S3.get_bucket_object_versions/2,
+        :get_bucket_object_versions,
         state,
-        prefix: state.key
+        [[prefix: state.key]]
       )
 
     with {:ok, %{body: %{versions: versions}}} <- res do
@@ -147,7 +148,8 @@ defmodule RemotePersistentTerm.Fetcher.S3 do
   end
 
   defp get_object(state) do
-    aws_client_request(&ExAws.S3.get_object/2, state, state.key)
+    # aws_client_request(&ExAws.S3.get_object/2, state, state.key)
+    aws_client_request(:get_object, state, [state.key, [version_id: state.version_id]])
   end
 
   defp find_latest([_ | _] = contents) do
@@ -166,6 +168,51 @@ defmodule RemotePersistentTerm.Fetcher.S3 do
 
   defp find_latest(_), do: {:error, :not_found}
 
+  @impl true
+  def previous_version(state) do
+    Logger.info(
+      bucket: state.bucket,
+      key: state.key,
+      message: "About to fetch previous version of object",
+      version_id: state.version_id
+    )
+
+    with {:ok, versions} <- list_object_versions(state),
+         {:ok, previous_version} <- find_previous_version(versions, state.version_id) do
+      {:ok, %{state | version_id: previous_version.version_id}}
+    else
+      {:error, reason} ->
+        Logger.error(%{
+          bucket: state.bucket,
+          key: state.key,
+          reason: inspect(reason),
+          message: "Failed to get previous version of object"
+        })
+
+        {:error, reason}
+    end
+  end
+
+  defp find_previous_version(versions, current_version_id) do
+    versions
+    |> Enum.sort_by(
+      fn version ->
+        {:ok, datetime, _} = DateTime.from_iso8601(version.last_modified)
+        datetime
+      end,
+      {:desc, DateTime}
+    )
+    |> Enum.find(fn version ->
+      version.version_id != current_version_id
+    end)
+    |> case do
+      nil -> {:error, :no_previous_version}
+      version -> {:ok, version}
+    end
+  end
+
+  defp aws_client_request(op, state, opts \\ [])
+
   defp aws_client_request(op, %{failover_buckets: nil} = state, opts) do
     perform_request(op, state.bucket, state.region, opts)
   end
@@ -173,7 +220,7 @@ defmodule RemotePersistentTerm.Fetcher.S3 do
   defp aws_client_request(
          op,
          %{
-           failover_buckets: [_|_] = failover_buckets
+           failover_buckets: [_ | _] = failover_buckets
          } = state,
          opts
        ) do
@@ -222,8 +269,8 @@ defmodule RemotePersistentTerm.Fetcher.S3 do
     end
   end
 
-  defp perform_request(op, bucket, region, opts) do
-    op.(bucket, opts)
+  defp perform_request(func, bucket, region, opts) do
+    apply(ExAws.S3, func, [bucket | opts])
     |> client().request(region: region)
   end
 
diff --git a/lib/remote_persistent_term/fetcher/static.ex b/lib/remote_persistent_term/fetcher/static.ex
index 1b8f4fc..3b2531f 100644
--- a/lib/remote_persistent_term/fetcher/static.ex
+++ b/lib/remote_persistent_term/fetcher/static.ex
@@ -1,6 +1,6 @@
 defmodule RemotePersistentTerm.Fetcher.Static do
   @moduledoc """
-  A macro to help define a valid `RemotePersistentTerm.Fetcher` which 
+  A macro to help define a valid `RemotePersistentTerm.Fetcher` which
   always returns some hardcoded static data.
 
   Mostly intended for testing purposes.
@@ -26,6 +26,9 @@ defmodule RemotePersistentTerm.Fetcher.Static do
 
       @impl true
       def download(_), do: {:ok, unquote(Macro.escape(Keyword.fetch!(opts, :data)))}
+
+      @impl true
+      def previous_version(_), do: {:error, :no_previous_version}
     end
   end
 end
diff --git a/mix.exs b/mix.exs
index e6cbd69..bbab609 100644
--- a/mix.exs
+++ b/mix.exs
@@ -2,7 +2,7 @@ defmodule RemotePersistentTerm.MixProject do
   use Mix.Project
 
   @name "RemotePersistentTerm"
-  @version "0.12.0"
+  @version "0.13.0"
   @repo_url "https://github.com/AppMonet/remote_persistent_term"
 
   def project do
diff --git a/test/remote_persistent_term/fetcher/s3_test.exs b/test/remote_persistent_term/fetcher/s3_test.exs
index 9e7d34d..b914007 100644
--- a/test/remote_persistent_term/fetcher/s3_test.exs
+++ b/test/remote_persistent_term/fetcher/s3_test.exs
@@ -253,4 +253,58 @@ defmodule RemotePersistentTerm.Fetcher.S3Test do
       assert log =~ "Downloaded object from S3"
     end
   end
+
+  describe "previous_version/1" do
+    test "finds the correct previous version when given a current version ID" do
+      versions = [
+        %{
+          version_id: "v3",
+          last_modified: "2025-05-08T09:58:38.000Z",
+          is_latest: "true"
+        },
+        %{
+          version_id: "v2",
+          last_modified: "2025-04-02T10:21:18.000Z",
+          is_latest: "false"
+        },
+        %{
+          version_id: "v1",
+          last_modified: "2025-04-02T09:10:37.000Z",
+          is_latest: "false"
+        }
+      ]
+
+      expect(AwsClientMock, :request, fn operation, opts ->
+        assert operation.bucket == @bucket
+        assert operation.resource == "versions"
+        assert operation.params == [prefix: @key]
+        assert opts == [region: @region]
+        {:ok, %{body: %{versions: versions}}}
+      end)
+
+      state = %S3{bucket: @bucket, key: @key, region: @region, version_id: "v3"}
+      assert {:ok, %{version_id: "v2"}} = S3.previous_version(state)
+    end
+
+    test "returns error when there are no previous versions" do
+      versions = [
+        %{
+          version_id: "v1",
+          last_modified: "2025-04-02T09:10:37.000Z",
+          is_latest: "true"
+        }
+      ]
+
+      expect(AwsClientMock, :request, fn operation, opts ->
+        assert operation.bucket == @bucket
+        assert operation.resource == "versions"
+        assert operation.params == [prefix: @key]
+        assert opts == [region: @region]
+        {:ok, %{body: %{versions: versions}}}
+      end)
+
+      state = %S3{bucket: @bucket, key: @key, region: @region, version_id: "v1"}
+      assert {:error, :no_previous_version} = S3.previous_version(state)
+    end
+  end
 end

From 7a4bd976bb36a98cd01384d1cb105763b22b582d Mon Sep 17 00:00:00 2001
From: Louis <me@louiscb.com>
Date: Thu, 8 May 2025 13:26:36 +0200
Subject: [PATCH 2/7] Delete comment

---
 lib/remote_persistent_term/fetcher/s3.ex | 1 -
 1 file changed, 1 deletion(-)

diff --git a/lib/remote_persistent_term/fetcher/s3.ex b/lib/remote_persistent_term/fetcher/s3.ex
index 7d126cc..3e6ff58 100644
--- a/lib/remote_persistent_term/fetcher/s3.ex
+++ b/lib/remote_persistent_term/fetcher/s3.ex
@@ -148,7 +148,6 @@ defmodule RemotePersistentTerm.Fetcher.S3 do
   end
 
   defp get_object(state) do
-    # aws_client_request(&ExAws.S3.get_object/2, state, state.key)
     aws_client_request(:get_object, state, [state.key, [version_id: state.version_id]])
   end
 

From a73a5552b3276a69a4b20942f21f78d682b5115c Mon Sep 17 00:00:00 2001
From: Louis <me@louiscb.com>
Date: Thu, 8 May 2025 13:31:58 +0200
Subject: [PATCH 3/7] Remove function uneccessary

---
 lib/remote_persistent_term/fetcher/s3.ex | 2 --
 1 file changed, 2 deletions(-)

diff --git a/lib/remote_persistent_term/fetcher/s3.ex b/lib/remote_persistent_term/fetcher/s3.ex
index 3e6ff58..e8d0080 100644
--- a/lib/remote_persistent_term/fetcher/s3.ex
+++ b/lib/remote_persistent_term/fetcher/s3.ex
@@ -210,8 +210,6 @@ defmodule RemotePersistentTerm.Fetcher.S3 do
     end
   end
 
-  defp aws_client_request(op, state, opts \\ [])
-
   defp aws_client_request(op, %{failover_buckets: nil} = state, opts) do
     perform_request(op, state.bucket, state.region, opts)
   end

From de5797066322c345865b49b5c8097837b56e8c69 Mon Sep 17 00:00:00 2001
From: Louis <me@louiscb.com>
Date: Thu, 8 May 2025 14:57:36 +0200
Subject: [PATCH 4/7] Small changes from pr comment

---
 lib/remote_persistent_term.ex | 4 +++-
 1 file changed, 3 insertions(+), 1 deletion(-)

diff --git a/lib/remote_persistent_term.ex b/lib/remote_persistent_term.ex
index fbca472..71b5467 100644
--- a/lib/remote_persistent_term.ex
+++ b/lib/remote_persistent_term.ex
@@ -76,7 +76,8 @@ defmodule RemotePersistentTerm do
       default: false,
       doc: """
       If true, when deserialization fails, the system will attempt to use previous versions \
-      of the term until a valid version is found or all versions are exhausted.
+      of the term until a valid version is found or all versions are exhausted. \
+      Only currently supported by the S3 fetcher.
       """
     ]
   ]
@@ -330,6 +331,7 @@ defmodule RemotePersistentTerm do
         put_fun.(deserialized)
 
       {:error, _reason} = error when state.version_fallback? ->
+        Logger.error("#{state.name} - failed to deserialize remote term, falling back to previous version")
         case state.fetcher_mod.previous_version(state.fetcher_state) do
           {:ok, previous_state} ->
             download_and_store_term(

From 55bfd44026836bd49d0e120961f7e8d2e55d1b7a Mon Sep 17 00:00:00 2001
From: Louis <me@louiscb.com>
Date: Thu, 8 May 2025 14:57:56 +0200
Subject: [PATCH 5/7] Mix format

---
 lib/remote_persistent_term.ex | 5 ++++-
 1 file changed, 4 insertions(+), 1 deletion(-)

diff --git a/lib/remote_persistent_term.ex b/lib/remote_persistent_term.ex
index 71b5467..81022e5 100644
--- a/lib/remote_persistent_term.ex
+++ b/lib/remote_persistent_term.ex
@@ -331,7 +331,10 @@ defmodule RemotePersistentTerm do
         put_fun.(deserialized)
 
       {:error, _reason} = error when state.version_fallback? ->
-        Logger.error("#{state.name} - failed to deserialize remote term, falling back to previous version")
+        Logger.error(
+          "#{state.name} - failed to deserialize remote term, falling back to previous version"
+        )
+
         case state.fetcher_mod.previous_version(state.fetcher_state) do
           {:ok, previous_state} ->
             download_and_store_term(

From 412070c3a0262e843811ee245b8e61b00e5487ec Mon Sep 17 00:00:00 2001
From: Louis <me@louiscb.com>
Date: Thu, 8 May 2025 18:50:51 +0200
Subject: [PATCH 6/7] Cache the versions and sort date chronologically

---
 lib/remote_persistent_term.ex                 |  4 ++--
 lib/remote_persistent_term/fetcher.ex         |  2 +-
 lib/remote_persistent_term/fetcher/http.ex    |  4 ++--
 lib/remote_persistent_term/fetcher/s3.ex      | 21 ++++++++-----------
 lib/remote_persistent_term/fetcher/static.ex  |  4 ++--
 .../fetcher/s3_test.exs                       |  2 +-
 6 files changed, 17 insertions(+), 20 deletions(-)

diff --git a/lib/remote_persistent_term.ex b/lib/remote_persistent_term.ex
index 81022e5..f7bb58c 100644
--- a/lib/remote_persistent_term.ex
+++ b/lib/remote_persistent_term.ex
@@ -281,9 +281,9 @@ defmodule RemotePersistentTerm do
       start_meta,
       fn ->
         {status, version} =
-          with {:ok, current_version} <- state.fetcher_mod.current_version(state.fetcher_state),
+          with {:ok, current_version, updated_fetcher_state} <- state.fetcher_mod.current_version(state.fetcher_state),
                true <- state.current_version != current_version,
-               :ok <- download_and_store_term(state, deserialize_fun, put_fun) do
+               :ok <- download_and_store_term(%{state | fetcher_state: updated_fetcher_state}, deserialize_fun, put_fun) do
             {:updated, current_version}
           else
             false ->
diff --git a/lib/remote_persistent_term/fetcher.ex b/lib/remote_persistent_term/fetcher.ex
index 676e13a..29b7d3b 100644
--- a/lib/remote_persistent_term/fetcher.ex
+++ b/lib/remote_persistent_term/fetcher.ex
@@ -20,7 +20,7 @@ defmodule RemotePersistentTerm.Fetcher do
   Check the current version of the remote term. Used to avoid downloading the
   same term multiple times.
   """
-  @callback current_version(state()) :: {:ok, version()} | {:error, term()}
+  @callback current_version(state()) :: {:ok, version(), state()} | {:error, term()}
 
   @doc """
   Download the term from the remote source.
diff --git a/lib/remote_persistent_term/fetcher/http.ex b/lib/remote_persistent_term/fetcher/http.ex
index e94d6ac..a5fe2d5 100644
--- a/lib/remote_persistent_term/fetcher/http.ex
+++ b/lib/remote_persistent_term/fetcher/http.ex
@@ -66,8 +66,8 @@ defmodule RemotePersistentTerm.Fetcher.Http do
   end
 
   @impl true
-  def current_version(_state) do
-    {:ok, DateTime.utc_now() |> DateTime.to_string()}
+  def current_version(state) do
+    {:ok, DateTime.utc_now() |> DateTime.to_string(), state}
   end
 
   @impl true
diff --git a/lib/remote_persistent_term/fetcher/s3.ex b/lib/remote_persistent_term/fetcher/s3.ex
index e8d0080..5661e80 100644
--- a/lib/remote_persistent_term/fetcher/s3.ex
+++ b/lib/remote_persistent_term/fetcher/s3.ex
@@ -15,9 +15,10 @@ defmodule RemotePersistentTerm.Fetcher.S3 do
           key: String.t(),
           region: region,
           failover_buckets: [failover_bucket] | nil,
-          version_id: String.t() | nil
+          version_id: String.t() | nil,
+          versions: [map()] | nil
         }
-  defstruct [:bucket, :key, :region, :failover_buckets, :version_id]
+  defstruct [:bucket, :key, :region, :failover_buckets, :version_id, :versions]
 
   @failover_bucket_schema [
     bucket: [
@@ -92,7 +93,7 @@ defmodule RemotePersistentTerm.Fetcher.S3 do
         message: "Found latest version of object"
       )
 
-      {:ok, etag}
+      {:ok, etag, %{state | versions: versions}}
     else
       {:error, {:unexpected_response, %{body: reason}}} ->
         {:error, reason}
@@ -176,9 +177,11 @@ defmodule RemotePersistentTerm.Fetcher.S3 do
       version_id: state.version_id
     )
 
-    with {:ok, versions} <- list_object_versions(state),
+    versions = if state.versions, do: {:ok, state.versions}, else: list_object_versions(state)
+
+    with {:ok, versions} <- versions,
          {:ok, previous_version} <- find_previous_version(versions, state.version_id) do
-      {:ok, %{state | version_id: previous_version.version_id}}
+      {:ok, %{state | version_id: previous_version.version_id, versions: versions}}
     else
       {:error, reason} ->
         Logger.error(%{
@@ -194,13 +197,7 @@ defmodule RemotePersistentTerm.Fetcher.S3 do
 
   defp find_previous_version(versions, current_version_id) do
     versions
-    |> Enum.sort_by(
-      fn version ->
-        {:ok, datetime, _} = DateTime.from_iso8601(version.last_modified)
-        datetime
-      end,
-      {:desc, DateTime}
-    )
+    |> Enum.sort_by(& &1.last_modified, :desc)
     |> Enum.find(fn version ->
       version.version_id != current_version_id
     end)
diff --git a/lib/remote_persistent_term/fetcher/static.ex b/lib/remote_persistent_term/fetcher/static.ex
index 3b2531f..0a8ce9a 100644
--- a/lib/remote_persistent_term/fetcher/static.ex
+++ b/lib/remote_persistent_term/fetcher/static.ex
@@ -22,10 +22,10 @@ defmodule RemotePersistentTerm.Fetcher.Static do
       def init(_), do: {:ok, []}
 
       @impl true
-      def current_version(_), do: {:ok, unquote(Keyword.get(opts, :version, "1"))}
+      def current_version(state), do: {:ok, unquote(Keyword.get(opts, :version, "1")), state}
 
       @impl true
-      def download(_), do: {:ok, unquote(Macro.escape(Keyword.fetch!(opts, :data)))}
+      def download(state), do: {:ok, unquote(Macro.escape(Keyword.fetch!(opts, :data)))}
 
       @impl true
       def previous_version(_), do: {:error, :no_previous_version}
diff --git a/test/remote_persistent_term/fetcher/s3_test.exs b/test/remote_persistent_term/fetcher/s3_test.exs
index b914007..a3fee3f 100644
--- a/test/remote_persistent_term/fetcher/s3_test.exs
+++ b/test/remote_persistent_term/fetcher/s3_test.exs
@@ -99,7 +99,7 @@ defmodule RemotePersistentTerm.Fetcher.S3Test do
       log =
         capture_log(fn ->
           result = S3.current_version(state)
-          assert {:ok, "current-etag"} = result
+          assert {:ok, "current-etag", _updated_state} = result
         end)
 
       assert log =~ "bucket: \"#{@bucket}\""

From 0977c2b773efffa1809bf0dde4c3a0e25faaf34b Mon Sep 17 00:00:00 2001
From: Louis <me@louiscb.com>
Date: Tue, 13 May 2025 16:13:07 +0200
Subject: [PATCH 7/7] Improve readability based on pr comments

---
 lib/remote_persistent_term.ex                | 38 ++++++++++++--------
 lib/remote_persistent_term/fetcher/http.ex   |  2 +-
 lib/remote_persistent_term/fetcher/static.ex |  2 +-
 3 files changed, 26 insertions(+), 16 deletions(-)

diff --git a/lib/remote_persistent_term.ex b/lib/remote_persistent_term.ex
index f7bb58c..c028be5 100644
--- a/lib/remote_persistent_term.ex
+++ b/lib/remote_persistent_term.ex
@@ -281,9 +281,15 @@ defmodule RemotePersistentTerm do
       start_meta,
       fn ->
         {status, version} =
-          with {:ok, current_version, updated_fetcher_state} <- state.fetcher_mod.current_version(state.fetcher_state),
+          with {:ok, current_version, updated_fetcher_state} <-
+                 state.fetcher_mod.current_version(state.fetcher_state),
                true <- state.current_version != current_version,
-               :ok <- download_and_store_term(%{state | fetcher_state: updated_fetcher_state}, deserialize_fun, put_fun) do
+               :ok <-
+                 download_and_store_term(
+                   %{state | fetcher_state: updated_fetcher_state},
+                   deserialize_fun,
+                   put_fun
+                 ) do
             {:updated, current_version}
           else
             false ->
@@ -330,28 +336,32 @@ defmodule RemotePersistentTerm do
       {:ok, deserialized} ->
         put_fun.(deserialized)
 
-      {:error, _reason} = error when state.version_fallback? ->
+      {:error, _reason} when state.version_fallback? ->
         Logger.error(
           "#{state.name} - failed to deserialize remote term, falling back to previous version"
         )
 
-        case state.fetcher_mod.previous_version(state.fetcher_state) do
-          {:ok, previous_state} ->
-            download_and_store_term(
-              %{state | fetcher_state: previous_state},
-              deserialize_fun,
-              put_fun
-            )
-
-          {:error, _} ->
-            error
-        end
+        try_previous_version(state, deserialize_fun, put_fun)
 
       error ->
         error
     end
   end
 
+  defp try_previous_version(state, deserialize_fun, put_fun) do
+    case state.fetcher_mod.previous_version(state.fetcher_state) do
+      {:ok, previous_state} ->
+        download_and_store_term(
+          %{state | fetcher_state: previous_state},
+          deserialize_fun,
+          put_fun
+        )
+
+      {:error, _} = error ->
+        error
+    end
+  end
+
   defp maybe_decompress(%__MODULE__{auto_decompress?: true}, body) do
     case body do
       <<0x1F, 0x8B, _rest::binary>> = gzipped ->
diff --git a/lib/remote_persistent_term/fetcher/http.ex b/lib/remote_persistent_term/fetcher/http.ex
index a5fe2d5..986ed64 100644
--- a/lib/remote_persistent_term/fetcher/http.ex
+++ b/lib/remote_persistent_term/fetcher/http.ex
@@ -82,7 +82,7 @@ defmodule RemotePersistentTerm.Fetcher.Http do
   end
 
   @impl true
-  def previous_version(_state), do: {:error, :no_previous_version}
+  def previous_version(_state), do: {:error, :not_supported}
 
   defp response_status(url, status) do
     if status < 300 do
diff --git a/lib/remote_persistent_term/fetcher/static.ex b/lib/remote_persistent_term/fetcher/static.ex
index 0a8ce9a..09743e1 100644
--- a/lib/remote_persistent_term/fetcher/static.ex
+++ b/lib/remote_persistent_term/fetcher/static.ex
@@ -28,7 +28,7 @@ defmodule RemotePersistentTerm.Fetcher.Static do
       def download(state), do: {:ok, unquote(Macro.escape(Keyword.fetch!(opts, :data)))}
 
       @impl true
-      def previous_version(_), do: {:error, :no_previous_version}
+      def previous_version(_), do: {:error, :not_supported}
     end
   end
 end