server, ldap: add support for Subschema requests (#1071)

Add a subschema entry to the rootDSE, which shows all attributes and
objectclasses present on the LLDAP server, which is needed for some
applications that need to index the LDAP server. The current
implementation's goal is to have a bare minimum working subschema which
follows the LDAP RFC. It also updates the GraphQL interface to follow
the changes that have been made in actually separating out
objectclasses, instead of having them as an attribute.

Co-authored-by: nitnelave <valentin@tolmer.fr>

crates/ldap/src/handler.rs

@@ -7,8 +7,8 @@ use crate::{
     create, delete, modify,
     password::{self, do_password_modification},
     search::{
-        self, is_root_dse_request, make_search_error, make_search_request, make_search_success,
-        root_dse_response,
+        self, is_root_dse_request, is_subschema_entry_request, make_ldap_subschema_entry,
+        make_search_error, make_search_request, make_search_success, root_dse_response,
     },
 };
 use ldap3_proto::proto::{
@@ -18,8 +18,8 @@ use ldap3_proto::proto::{
 };
 use lldap_access_control::AccessControlledBackendHandler;
 use lldap_auth::access_control::ValidationResults;
-use lldap_domain::types::AttributeName;
-use lldap_domain_handlers::handler::{BackendHandler, LoginHandler};
+use lldap_domain::{public_schema::PublicSchema, types::AttributeName};
+use lldap_domain_handlers::handler::{BackendHandler, LoginHandler, ReadSchemaBackendHandler};
 use lldap_opaque_handler::OpaqueHandler;
 use tracing::{debug, instrument};
 
@@ -141,6 +141,26 @@ impl<Backend: BackendHandler + LoginHandler + OpaqueHandler> LdapHandler<Backend
                 root_dse_response(&self.ldap_info.base_dn_str),
                 make_search_success(),
             ]);
+        } else if is_subschema_entry_request(request) {
+            // See RFC4512 section 4.4 "Subschema discovery"
+            debug!("Schema request");
+            let backend_handler = self
+                .user_info
+                .as_ref()
+                .and_then(|u| self.backend_handler.get_schema_only_handler(u))
+                .ok_or_else(|| LdapError {
+                    code: LdapResultCode::InsufficentAccessRights,
+                    message: "No user currently bound".to_string(),
+                })?;
+
+            let schema = backend_handler.get_schema().await.map_err(|e| LdapError {
+                code: LdapResultCode::OperationsError,
+                message: format!("Unable to get schema: {:#}", e),
+            })?;
+            return Ok(vec![
+                make_ldap_subschema_entry(PublicSchema::from(schema)),
+                make_search_success(),
+            ]);
         }
         self.do_search(request).await
     }