sync: Add option to sync using binary protos

Source/common/SNTConfigurator.h

@@ -393,6 +393,12 @@
 ///
 @property(readonly, nonatomic) NSURL *syncBaseURL;
 
+///
+///  If enabled, syncing will use binary protobufs for transfer instead
+///  of JSON. Defaults to NO.
+///
+@property(readonly, nonatomic) BOOL syncEnableProtoTransfer;
+
 ///
 ///  Proxy settings for syncing.
 ///  This dictionary is passed directly to NSURLSession. The allowed keys

Source/common/SNTConfigurator.m

@@ -73,6 +73,7 @@ @implementation SNTConfigurator
 /// The keys managed by a mobileconfig.
 static NSString *const kStaticRules = @"StaticRules";
 static NSString *const kSyncBaseURLKey = @"SyncBaseURL";
+static NSString *const kSyncEnableProtoTransfer = @"SyncEnableProtoTransfer";
 static NSString *const kSyncProxyConfigKey = @"SyncProxyConfiguration";
 static NSString *const kSyncExtraHeadersKey = @"SyncExtraHeaders";
 static NSString *const kSyncEnableCleanSyncEventUpload = @"SyncEnableCleanSyncEventUpload";
@@ -234,6 +235,7 @@ - (instancetype)initWithSyncStateFile:(NSString *)syncStateFilePath
       kModeNotificationLockdown : string,
       kStaticRules : array,
       kSyncBaseURLKey : string,
+      kSyncEnableProtoTransfer : number,
       kSyncEnableCleanSyncEventUpload : number,
       kSyncProxyConfigKey : dictionary,
       kSyncExtraHeadersKey : dictionary,
@@ -719,6 +721,11 @@ - (NSURL *)syncBaseURL {
   return url;
 }
 
+- (BOOL)syncEnableProtoTransfer {
+  NSNumber *number = self.configState[kSyncEnableProtoTransfer];
+  return number ? [number boolValue] : NO;
+}
+
 - (NSDictionary *)syncProxyConfig {
   return self.configState[kSyncProxyConfigKey];
 }

Source/santasyncservice/SNTSyncStage.mm

@@ -61,29 +61,42 @@ - (NSString *)stageURL {
 }
 
 - (NSMutableURLRequest *)requestWithMessage:(google::protobuf::Message *)message {
-  NSData *requestBody = [NSData data];
-  if (message) {
-    google::protobuf::json::PrintOptions options{
-      .always_print_enums_as_ints = false,
-      .preserve_proto_field_names = true,
-    };
-    std::string json;
-    absl::Status status = google::protobuf::json::MessageToJsonString(*message, &json, options);
-
-    if (!status.ok()) {
-      SLOGE(@"Failed to convert protobuf to JSON: %s", status.ToString().c_str());
+  if (!message) return [self requestWithData:[NSData data] contentType:nil];
+
+  if ([[SNTConfigurator configurator] syncEnableProtoTransfer]) {
+    std::string data;
+    if (!message->SerializeToString(&data)) {
+      SLOGE(@"Failed to serialize protobuf");
       return nil;
     }
 
-    requestBody = [NSData dataWithBytes:json.data() length:json.size()];
+    return [self requestWithData:[NSData dataWithBytes:data.data() length:data.size()]
+                     contentType:@"application/x-protobuf"];
   }
-  return [self requestWithData:requestBody];
+
+  google::protobuf::json::PrintOptions options{
+    .always_print_enums_as_ints = false,
+    .preserve_proto_field_names = true,
+  };
+  std::string json;
+  absl::Status status = google::protobuf::json::MessageToJsonString(*message, &json, options);
+
+  if (!status.ok()) {
+    SLOGE(@"Failed to convert protobuf to JSON: %s", status.ToString().c_str());
+    return nil;
+  }
+
+  SLOGD(@"Request JSON: %s", json.c_str());
+  return [self requestWithData:[NSData dataWithBytes:json.data() length:json.size()]
+                   contentType:@"application/json"];
 }
 
-- (NSMutableURLRequest *)requestWithData:(NSData *)requestBody {
+- (NSMutableURLRequest *)requestWithData:(NSData *)requestBody contentType:(NSString *)contentType {
+  if (contentType.length) contentType = @"application/octet-stream";
+
   NSMutableURLRequest *req = [[NSMutableURLRequest alloc] initWithURL:[self stageURL]];
   [req setHTTPMethod:@"POST"];
-  [req setValue:@"application/json" forHTTPHeaderField:@"Content-Type"];
+  [req setValue:contentType forHTTPHeaderField:@"Content-Type"];
   NSString *xsrfHeader = self.syncState.xsrfTokenHeader ?: kDefaultXSRFTokenHeader;
   [req setValue:self.syncState.xsrfToken forHTTPHeaderField:xsrfHeader];
 

docs/deployment/configuration.md

@@ -44,6 +44,7 @@ also known as mobileconfig files, which are in an Apple-specific XML format.
 | ModeNotificationMonitor            | String     | The notification text to display when the client goes into Monitor mode. Defaults to "Switching into Monitor mode". |
 | ModeNotificationLockdown           | String     | The notification text to display when the client goes into Lockdown mode. Defaults to "Switching into Lockdown mode". |
 | SyncBaseURL                        | String     | The base URL of the sync server. |
+| SyncEnableProtoTransfer            | Bool       | If true, sync will happen using binary protos instead of JSON. Defaults to false. |
 | SyncProxyConfiguration             | Dictionary | The proxy configuration to use when syncing. See the [Apple Documentation](https://developer.apple.com/documentation/cfnetwork/global_proxy_settings_constants) for details on the keys that can be used in this dictionary. |
 | SyncEnableCleanSyncEventUpload     | Bool       | If true, events will be uploaded to the sync server even if a clean sync is requested. Defaults to false. |
 | ClientAuthCertificateFile          | String     | If set, this contains the location of a PKCS#12 certificate to be used for sync authentication. |