add(ldap): speed up student search when exact

ldap/rhul-student-info.py

@@ -62,12 +62,25 @@ ATTRS = [
     'cn', 'department', 'description', 'memberOf', 'mail',
     'extensionAttribute3'
 ]
-search_disjuncts = [
-    f"({field}=*{term}*)"
-    for field, term in product(ATTRS, search_terms)
-]
+
+# detect exact student searches for faster LDAP lookup
+# first full email, then student ID
+one_arg = (len(search_terms) == 1)
+if one_arg and re.match(r"^[\w.-]+@(live.)?rhul.ac.uk", search_terms[0]):
+    print("Searching by exact email..")
+    ldap_filter = f"(mail={search_terms[0]})"
+elif one_arg and re.match(r"\d{9}", search_terms[0]):
+    print("Searching by exact student ID..")
+    ldap_filter = f"(extensionAttribute3={search_terms[0]})"
+else:
+    search_disjuncts = [
+        f"({field}=*{term}*)"
+        for field, term in product(ATTRS, search_terms)
+    ]
+    ldap_filter = "(|" + "".join(search_disjuncts) + ")"
+
+# added late because can't be used for a search term when building ldap_filter
 ATTRS.append("whenCreated")
-ldap_filter = "(|" + "".join(search_disjuncts) + ")"
 
 password = subprocess.check_output(PASS_CMD, stderr=subprocess.DEVNULL) \
                      .decode("ascii") \