fix: Replace string with stringBuffer in verb builders

packages/at_commons/lib/src/verb/config_verb_builder.dart

@@ -11,27 +11,25 @@ class ConfigVerbBuilder implements VerbBuilder {
   String? configType;
   String? operation;
   List<String>? atSigns;
+
   @override
   String buildCommand() {
-    var command = 'config:';
-    command += '$configType:';
+    StringBuffer serverCommandBuffer = StringBuffer('config:$configType:');
     if (operation == 'show') {
-      command += operation!;
+      serverCommandBuffer.write(operation!);
     } else {
-      command += '$operation:';
+      serverCommandBuffer.write('$operation:');
     }
     if (atSigns != null && atSigns!.isNotEmpty) {
       for (var atSign in atSigns!) {
-        command += '${VerbUtil.formatAtSign(atSign)}';
+        serverCommandBuffer.write('${VerbUtil.formatAtSign(atSign)}');
       }
     }
-
-    return '${command.trim()}\n';
+    return '${serverCommandBuffer.toString().trim()}\n';
   }
 
   @override
   bool checkParams() {
-    // TODO: implement checkParams
-    return true;
+    return (configType != null && operation != null);
   }
 }

packages/at_commons/lib/src/verb/delete_verb_builder.dart

@@ -1,5 +1,9 @@
-import 'package:at_commons/at_commons.dart';
+import 'package:at_commons/src/at_constants.dart';
+import 'package:at_commons/src/exception/at_client_exceptions.dart';
+import 'package:at_commons/src/utils/string_utils.dart';
 import 'package:at_commons/src/verb/abstract_verb_builder.dart';
+import 'package:at_commons/src/verb/syntax.dart';
+import 'package:at_commons/src/verb/verb_util.dart';
 
 /// Delete verb builder generates a command to delete a [atKey] from the secondary server.
 /// ```
@@ -11,9 +15,8 @@ import 'package:at_commons/src/verb/abstract_verb_builder.dart';
 class DeleteVerbBuilder extends AbstractVerbBuilder {
   @override
   String buildCommand() {
-    var command = 'delete:';
-    command += '${buildKey()}\n';
-    return command;
+    StringBuffer serverCommandBuffer = StringBuffer('delete:${buildKey()}\n');
+    return serverCommandBuffer.toString();
   }
 
   /// Returns a builder instance from a delete command

packages/at_commons/lib/src/verb/from_verb_builder.dart

@@ -1,7 +1,7 @@
 import 'dart:convert';
 
 import 'package:at_commons/at_builders.dart';
-import 'package:at_commons/at_commons.dart';
+import 'package:at_commons/src/at_constants.dart';
 
 class FromVerbBuilder implements VerbBuilder {
   late String atSign;
@@ -11,13 +11,13 @@ class FromVerbBuilder implements VerbBuilder {
 
   @override
   String buildCommand() {
-    var command = 'from:$atSign';
+    StringBuffer serverCommandBuffer = StringBuffer('from:$atSign');
     if (clientConfig.isNotEmpty) {
       var clientConfigStr = jsonEncode(clientConfig);
-      command += ':${AtConstants.clientConfig}:$clientConfigStr';
+      serverCommandBuffer.write(':${AtConstants.clientConfig}:$clientConfigStr');
     }
-    command += '\n';
-    return command;
+    serverCommandBuffer.write('\n');
+    return serverCommandBuffer.toString();
   }
 
   @override

packages/at_commons/lib/src/verb/llookup_verb_builder.dart

@@ -1,4 +1,3 @@
-import 'package:at_commons/at_commons.dart';
 import 'package:at_commons/src/verb/abstract_verb_builder.dart';
 
 /// Local lookup verb builder generates a command to lookup value of [atKey] stored in the secondary server.
@@ -62,11 +61,12 @@ class LLookupVerbBuilder extends AbstractVerbBuilder {
 
   @override
   String buildCommand() {
-    var command = 'llookup:';
+    StringBuffer serverCommandBuffer = StringBuffer('llookup:');
     if (operation != null) {
-      command += '$operation:';
+      serverCommandBuffer.write('$operation:');
     }
-    return command += '${buildKey()}\n';
+    serverCommandBuffer.write('${buildKey()}\n');
+    return serverCommandBuffer.toString();
   }
 
   @override

packages/at_commons/lib/src/verb/lookup_verb_builder.dart

@@ -24,15 +24,15 @@ class LookupVerbBuilder extends AbstractVerbBuilder {
 
   @override
   String buildCommand() {
-    String command = 'lookup:';
+    StringBuffer serverCommandBuffer = StringBuffer('lookup:');
     if (bypassCache == true) {
-      command += 'bypassCache:$bypassCache:';
+      serverCommandBuffer.write('bypassCache:$bypassCache:');
     }
     if (operation != null) {
-      command += '$operation:';
+      serverCommandBuffer.write('$operation:');
     }
-    command += atKey.toString();
-    return '$command\n';
+    serverCommandBuffer.write('${atKey.toString()}\n');
+    return serverCommandBuffer.toString();
   }
 
   @override

packages/at_commons/lib/src/verb/notify_all_verb_builder.dart

@@ -1,5 +1,6 @@
-import 'package:at_commons/at_commons.dart';
 import 'package:at_commons/src/verb/abstract_verb_builder.dart';
+import 'package:at_commons/src/verb/operation_enum.dart';
+import 'package:at_commons/src/verb/verb_util.dart';
 
 class NotifyAllVerbBuilder extends AbstractVerbBuilder {
   /// Value of the key typically in string format. Images, files, etc.,
@@ -13,36 +14,37 @@ class NotifyAllVerbBuilder extends AbstractVerbBuilder {
 
   @override
   String buildCommand() {
-    var command = 'notify:';
+    StringBuffer serverCommandBuffer = StringBuffer('notify:');
 
     if (operation != null) {
-      command += '${getOperationName(operation)}:';
+      serverCommandBuffer.write('${getOperationName(operation)}:');
     }
     if (atKey.metadata.ttl != null) {
-      command += 'ttl:${atKey.metadata.ttl}:';
+      serverCommandBuffer.write('ttl:${atKey.metadata.ttl}:');
     }
     if (atKey.metadata.ttb != null) {
-      command += 'ttb:${atKey.metadata.ttb}:';
+      serverCommandBuffer.write('ttb:${atKey.metadata.ttb}:');
     }
     if (atKey.metadata.ttr != null) {
       atKey.metadata.ccd ??= false;
-      command += 'ttr:${atKey.metadata.ttr}:ccd:${atKey.metadata.ccd}:';
+      serverCommandBuffer
+          .write('ttr:${atKey.metadata.ttr}:ccd:${atKey.metadata.ccd}:');
     }
     if (sharedWithList != null && sharedWithList!.isNotEmpty) {
       var sharedWith = sharedWithList!.join(',');
-      command += '${VerbUtil.formatAtSign(sharedWith)}:';
+      serverCommandBuffer.write('${VerbUtil.formatAtSign(sharedWith)}:');
     }
     if (atKey.metadata.isPublic == true) {
-      command += 'public:';
+      serverCommandBuffer.write('public:');
     }
-    command += atKey.toString();
+    serverCommandBuffer.write(atKey.toString());
     if (atKey.sharedBy != null) {
-      command += '${VerbUtil.formatAtSign(atKey.sharedBy)}';
+      serverCommandBuffer.write('${VerbUtil.formatAtSign(atKey.sharedBy)}');
     }
     if (value != null) {
-      command += ':$value';
+      serverCommandBuffer.write(':$value');
     }
-    return '$command\n';
+    return (serverCommandBuffer..write('\n')).toString();
   }
 
   @override

packages/at_commons/lib/src/verb/notify_fetch_verb_builder.dart

@@ -1,4 +1,4 @@
-import 'package:at_commons/at_commons.dart';
+import 'package:at_commons/src/exception/at_exceptions.dart';
 import 'package:at_commons/src/verb/verb_builder.dart';
 
 /// NotifyFetchVerbBuilder generated the command to fetches the notification
@@ -18,7 +18,7 @@ class NotifyFetchVerbBuilder implements VerbBuilder {
 
   @override
   String buildCommand() {
-    var command = 'notify:fetch:';
+    StringBuffer serverCommandBuffer = StringBuffer('notify:fetch:');
     try {
       if (notificationId.isEmpty) {
         throw InvalidSyntaxException(
@@ -28,8 +28,8 @@ class NotifyFetchVerbBuilder implements VerbBuilder {
       throw InvalidSyntaxException(
           'Notification-id is not set. Notification-id is mandatory');
     }
-    command += '$notificationId\n';
-    return command;
+    serverCommandBuffer.write('$notificationId\n');
+    return serverCommandBuffer.toString();
   }
 
   @override

packages/at_commons/lib/src/verb/notify_list_verb_builder.dart

@@ -7,17 +7,18 @@ class NotifyListVerbBuilder implements VerbBuilder {
 
   @override
   String buildCommand() {
-    var command = 'notify:list';
+    StringBuffer serverCommandBuffer = StringBuffer('notify:list');
+
     if (fromDate != null) {
-      command += ':$fromDate';
+      serverCommandBuffer.write(':$fromDate');
     }
     if (toDate != null) {
-      command += ':$toDate';
+      serverCommandBuffer.write(':$toDate');
     }
     if (regex != null) {
-      command += ':$regex';
+      serverCommandBuffer.write(':$regex');
     }
-    return command += '\n';
+    return (serverCommandBuffer..write('\n')).toString();
   }
 
   @override

packages/at_commons/lib/src/verb/notify_status_verb_builder.dart

@@ -1,3 +1,5 @@
+import 'package:at_commons/src/exception/at_exceptions.dart';
+import 'package:at_commons/src/utils/string_utils.dart';
 import 'package:at_commons/src/verb/verb_builder.dart';
 
 class NotifyStatusVerbBuilder implements VerbBuilder {
@@ -6,19 +8,16 @@ class NotifyStatusVerbBuilder implements VerbBuilder {
 
   @override
   String buildCommand() {
-    var command = 'notify:status:';
-    if (notificationId != null) {
-      command += '$notificationId\n';
+    StringBuffer serverCommandBuffer = StringBuffer('notify:status:');
+    if (notificationId.isNullOrEmpty) {
+      throw InvalidAtKeyException('NotificationId cannot be null or empty');
     }
-    return command;
+    serverCommandBuffer.write('$notificationId\n');
+    return serverCommandBuffer.toString();
   }
 
   @override
   bool checkParams() {
-    var isValid = true;
-    if (notificationId == null) {
-      isValid = false;
-    }
-    return isValid;
+    return notificationId.isNotNullOrEmpty;
   }
 }

packages/at_commons/lib/src/verb/pkam_verb_builder.dart

@@ -13,19 +13,17 @@ class PkamVerbBuilder implements VerbBuilder {
 
   @override
   String buildCommand() {
-    var command = 'pkam';
+    StringBuffer serverCommandBuffer = StringBuffer('pkam');
     if (signingAlgo != null && signingAlgo!.isNotEmpty) {
-      command += ':signingAlgo:$signingAlgo';
+      serverCommandBuffer.write(':signingAlgo:$signingAlgo');
     }
     if (hashingAlgo != null && hashingAlgo!.isNotEmpty) {
-      command += ':hashingAlgo:$hashingAlgo';
+      serverCommandBuffer.write(':hashingAlgo:$hashingAlgo');
     }
     if (enrollmentlId != null && enrollmentlId!.isNotEmpty) {
-      command += ':enrollmentId:$enrollmentlId';
+      serverCommandBuffer.write(':enrollmentId:$enrollmentlId');
     }
-    command += ':$signature';
-    command += '\n';
-    return command;
+    return (serverCommandBuffer..write(':$signature\n')).toString();
   }
 
   @override

packages/at_commons/lib/src/verb/plookup_verb_builder.dart

@@ -1,4 +1,3 @@
-import 'package:at_commons/at_commons.dart';
 import 'package:at_commons/src/verb/abstract_verb_builder.dart';
 import 'package:at_commons/src/verb/verb_util.dart';
 
@@ -16,15 +15,17 @@ class PLookupVerbBuilder extends AbstractVerbBuilder {
 
   @override
   String buildCommand() {
-    String command = 'plookup:';
+    StringBuffer serverCommandBuffer = StringBuffer('plookup:');
     if (bypassCache == true) {
-      command += 'bypassCache:$bypassCache:';
+      serverCommandBuffer.write('bypassCache:$bypassCache:');
     }
     if (operation != null) {
-      command += '$operation:';
+      serverCommandBuffer.write('$operation:');
     }
-    command += atKey.key;
-    return '$command${VerbUtil.formatAtSign(atKey.sharedBy)}\n';
+    serverCommandBuffer.write(atKey.key);
+    return (serverCommandBuffer
+          ..write('${VerbUtil.formatAtSign(atKey.sharedBy)}\n'))
+        .toString();
   }
 
   @override

packages/at_commons/lib/src/verb/scan_verb_builder.dart

@@ -1,5 +1,6 @@
-import 'package:at_commons/at_commons.dart';
+import 'package:at_commons/src/at_constants.dart';
 import 'package:at_commons/src/verb/verb_builder.dart';
+import 'package:at_commons/src/verb/verb_util.dart';
 
 /// Scan verb builder generates a command to scan keys of current atSign(with ot without auth).
 /// If a [regex] is set, keys matching the regex are returned.
@@ -40,18 +41,18 @@ class ScanVerbBuilder implements VerbBuilder {
 
   @override
   String buildCommand() {
-    var scanCommand = 'scan';
+    StringBuffer serverCommandBuffer = StringBuffer('scan');
+
     if (showHiddenKeys) {
-      scanCommand += ':${AtConstants.showHidden}:true';
+      serverCommandBuffer.write(':${AtConstants.showHidden}:true');
     }
     if (sharedBy != null) {
-      scanCommand += ':${VerbUtil.formatAtSign(sharedBy)}';
+      serverCommandBuffer.write(':${VerbUtil.formatAtSign(sharedBy)}');
     }
     if (regex != null) {
-      scanCommand += ' $regex';
+      serverCommandBuffer.write(' $regex');
     }
-    scanCommand += '\n';
-    return scanCommand;
+    return (serverCommandBuffer..write('\n')).toString();
   }
 
   @override

packages/at_commons/lib/src/verb/stats_verb_builder.dart

@@ -23,15 +23,14 @@ class StatsVerbBuilder implements VerbBuilder {
 
   @override
   String buildCommand() {
-    var statsCommand = 'stats';
+    StringBuffer serverCommandBuffer = StringBuffer('stats');
     if (statIds != null) {
-      statsCommand += ':$statIds';
+      serverCommandBuffer.write(':$statIds');
       if (regex != null) {
-        statsCommand += ':$regex';
+        serverCommandBuffer.write(':$regex');
       }
     }
-    statsCommand += '\n';
-    return statsCommand;
+    return (serverCommandBuffer..write('\n')).toString();
   }
 
   @override

packages/at_commons/lib/src/verb/sync_verb_builder.dart

@@ -11,19 +11,18 @@ class SyncVerbBuilder implements VerbBuilder {
 
   @override
   String buildCommand() {
-    var command = 'sync:';
+    StringBuffer serverCommandBuffer = StringBuffer('sync:');
     if (isPaginated) {
-      command += 'from:';
+      serverCommandBuffer.write('from:');
     }
-    command += '$commitId';
+    serverCommandBuffer.write('$commitId');
     if (isPaginated) {
-      command += ':limit:$limit';
+      serverCommandBuffer.write(':limit:$limit');
     }
     if (regex != null && regex!.isNotEmpty) {
-      command += ':$regex';
+      serverCommandBuffer.write(':$regex');
     }
-    command += '\n';
-    return command;
+    return (serverCommandBuffer..write('\n')).toString();
   }
 
   @override