fix: Root table validation should return 400 (#1975)

When root table is missing it should return 400 with the correct
message. Currently it is returning 500 which would lead to clients
retrying even through the request is malformed.

.changeset/dirty-wolves-wash.md

@@ -0,0 +1,5 @@
+---
+"@core/sync-service": patch
+---
+
+Fix root table parameter validation to return 400 when missing

packages/sync-service/lib/electric/plug/serve_shape_plug.ex

@@ -153,6 +153,8 @@ defmodule Electric.Plug.ServeShapePlug do
       end
     end
 
+    def cast_root_table(%Ecto.Changeset{valid?: false} = changeset, _), do: changeset
+
     def cast_root_table(%Ecto.Changeset{} = changeset, opts) do
       table = fetch_change!(changeset, :table)
       where = fetch_field!(changeset, :where)

packages/sync-service/test/electric/plug/serve_shape_plug_test.exs

@@ -152,22 +152,43 @@ defmodule Electric.Plug.ServeShapePlugTest do
       :with_tenant_id
     ]
 
-    test "returns 400 for invalid params", ctx do
+    test "returns 400 for invalid table", ctx do
       conn =
         ctx
-        |> conn(:get, %{"table" => ".invalid_shape"}, "?offset=invalid")
+        |> conn(:get, %{"table" => ".invalid_shape"}, "?offset=-1")
         |> ServeShapePlug.call([])
 
       assert conn.status == 400
 
       assert Jason.decode!(conn.resp_body) == %{
-               "offset" => ["has invalid format"],
                "table" => [
                  "Invalid zero-length delimited identifier"
                ]
              }
     end
 
+    test "returns 400 for invalid offset", ctx do
+      conn =
+        ctx
+        |> conn(:get, %{"table" => "foo"}, "?offset=invalid")
+        |> ServeShapePlug.call([])
+
+      assert conn.status == 400
+
+      assert Jason.decode!(conn.resp_body) == %{"offset" => ["has invalid format"]}
+    end
+
+    test "returns 400 when table param is missing", ctx do
+      conn =
+        ctx
+        |> conn(:get, %{}, "?offset=-1")
+        |> ServeShapePlug.call([])
+
+      assert conn.status == 400
+
+      assert %{"table" => ["can't be blank"]} = Jason.decode!(conn.resp_body)
+    end
+
     test "returns 400 when table does not exist", ctx do
       # this will pass table name validation
       # but will fail to find the table