server: Add basic support for Paged Results Control (RFC 2696)

This implements rudimentary support for the Paged
Results Control.

No actual pagination is performed, and we ignore
any requests for specific window sizes for paginated
results.

Instead, the full list of search results is returned
for any searches, and a control is added to the
SearchResultsDone message, informing the client that
there is no further results available.

server/src/infra/ldap_server.rs

@@ -13,7 +13,7 @@ use actix_rt::net::TcpStream;
 use actix_server::ServerBuilder;
 use actix_service::{fn_service, ServiceFactoryExt};
 use anyhow::{anyhow, Context, Result};
-use ldap3_proto::{proto::LdapMsg, LdapCodec};
+use ldap3_proto::{proto::LdapControl, proto::LdapMsg, proto::LdapOp, LdapCodec};
 use rustls::PrivateKey;
 use tokio_rustls::TlsAcceptor as RustlsTlsAcceptor;
 use tokio_util::codec::{FramedRead, FramedWrite};
@@ -39,12 +39,21 @@ where
             if result.is_empty() {
                 debug!("No response");
             }
+            let results: i64 = result.len().try_into().unwrap();
             for response in result.into_iter() {
                 debug!(?response);
+                let controls = if matches!(response, LdapOp::SearchResultDone(_)) {
+                    vec![LdapControl::SimplePagedResults {
+                        size: results - 1, // Avoid counting SearchResultDone as a result
+                        cookie: vec![],
+                    }]
+                } else {
+                    vec![]
+                };
                 resp.send(LdapMsg {
                     msgid: msg.msgid,
                     op: response,
-                    ctrl: vec![],
+                    ctrl: controls,
                 })
                 .await
                 .context("while sending a response: {:#}")?