internal/db: add set_once_columns function (#3117)

* internal/db: add set_once_columns function

Also replace existing before_soft_delete_credential_vault_store
function and trigger with the new function.

* internal/db/schema: add note to replaced definitions

internal/db/schema/migrations/oss/postgres/10/04_vault_credential.up.sql

@@ -67,6 +67,8 @@ begin;
   -- and an update contains a value for delete_time different from the current
   -- value, this trigger will raise an error with error code 23602 which is a
   -- class 23 integrity constraint violation: set_once_violation.
+  --
+  -- Deleted in 66/02_use_set_once_columns.up.sql
   create function before_soft_delete_credential_vault_store() returns trigger
   as $$
   begin
@@ -83,6 +85,7 @@ begin;
   end;
   $$ language plpgsql;
 
+  -- Replaced in 66/02_use_set_once_columns.up.sql
   create trigger before_soft_delete_credential_vault_store before update on credential_vault_store
     for each row execute procedure before_soft_delete_credential_vault_store();
 

internal/db/schema/migrations/oss/postgres/66/01_add_set_once_columns.up.sql

@@ -0,0 +1,30 @@
+-- Copyright (c) HashiCorp, Inc.
+-- SPDX-License-Identifier: MPL-2.0
+
+begin;
+
+  create function set_once_columns() returns trigger
+  as $$
+  declare 
+    col_name text; 
+    new_value text;
+    old_value text;
+  begin
+    foreach col_name in array tg_argv loop
+      execute format('SELECT $1.%I', col_name) into new_value using new;
+      execute format('SELECT $1.%I', col_name) into old_value using old;
+      if old_value is not null and new_value is distinct from old_value then
+        raise exception 'set_once_violation: %.%', tg_table_name, col_name using
+          errcode = '23602', 
+          schema = tg_table_schema,
+          table = tg_table_name,
+          column = col_name;
+      end if;
+    end loop;
+    return new;
+  end;
+  $$ language plpgsql;
+  comment on function set_once_columns() is
+    'set_once_columns asserts that a column cannot be updated after being set to a non-null value';
+
+commit;

internal/db/schema/migrations/oss/postgres/66/02_use_set_once_columns.up.sql

@@ -0,0 +1,12 @@
+-- Copyright (c) HashiCorp, Inc.
+-- SPDX-License-Identifier: MPL-2.0
+
+begin;
+
+  drop trigger before_soft_delete_credential_vault_store on credential_vault_store;
+  drop function before_soft_delete_credential_vault_store;
+
+  create trigger set_once_columns before update on credential_vault_store
+    for each row execute procedure set_once_columns('delete_time');
+
+commit;

internal/db/sqltest/tests/credential/vault/credential_vault_store.sql

@@ -0,0 +1,26 @@
+-- Copyright (c) HashiCorp, Inc.
+-- SPDX-License-Identifier: MPL-2.0
+
+-- credential_vault_store tests the credential_vault_store table
+
+begin;
+
+  select plan(3);
+  select wtt_load('widgets', 'iam', 'kms', 'auth', 'hosts', 'targets', 'credentials');
+
+  -- validate the setup data
+  select is(count(*), 1::bigint) from credential_vault_store where public_id = 'vs_______cvs1';
+
+  prepare soft_delete_credential_vault_store as
+    update credential_vault_store
+      set delete_time = clock_timestamp() -- Can't use now() or current_timestamp since constant within transaction
+    where public_id = 'vs_______cvs1';
+
+  -- First delete succeeds
+  select lives_ok('soft_delete_credential_vault_store');
+  -- Second delete fails because we can only set delete_time once
+  select throws_ok('soft_delete_credential_vault_store', 'set_once_violation: credential_vault_store.delete_time', '23602');
+
+  select * from finish();
+
+rollback;