MtProtoKit: bound decoded-object log lines, honour MTLogSetEnabled

A tester's log came back 44 MB across 21 rotated files covering only 6.6
hours — the previous log covered 21 hours in the same budget. 31.3 MB of it,
71% of everything collected, was two lines:

  [MTRequestMessageService#... response for <id> is <whole decoded object>]
  [MTProto#...@... [N] received <whole decoded object> (...)]

`%@` on a parsed rpc result prints the object in full. Sticker-set responses
alone accounted for 14.6 MB across 113 lines — 129 KB per line, one of them
458,653 characters. Rotation is by file count against a fixed per-file size,
so the payloads were evicting the diagnostics they were meant to sit beside.

MTLogTruncatedDescription caps a description at 1024 characters and appends
the true length, expanding the cut to whole character sequences so it cannot
land inside a surrogate pair. Replaying the same log through the cap leaves
13.1 MB of 42 MB — the same rotation budget now holds roughly 3.2x the span.

Separately, MTLog/MTLogWithPrefix/MTShortLog tested only whether a logging
function was installed. NetworkRegisterLoggingFunction installs those once
and never removes them; MTLogSetEnabled only flips MTLogEnabledValue, which
MTLogEnabled() consults but the log functions themselves did not. Turning
logging off therefore silenced only the call sites wrapped in an explicit
MTLogEnabled() check, and MTProto's outgoing short-message line was building
its description and logging unconditionally. Both are fixed.

Co-authored-by: D3C0Y <decoder-dev@users.noreply.github.com>

Author: decoder-dev

submodules/MtProtoKit/PublicHeaders/MtProtoKit/MTLogging.h

@@ -10,6 +10,14 @@ extern "C" {
 #endif
 
 bool MTLogEnabled();
+
+/// A decoded MTProto object, cut down to something a log line can hold.
+///
+/// `%@` on a parsed rpc result or update prints the entire object. A sticker set or a forum
+/// topic list runs to hundreds of kilobytes on a single line, and in one tester's log the
+/// responses alone came to 31.3 MB of 44 MB — 71% of everything collected, against a fixed
+/// rotation budget. The head of the description identifies the message; the rest is payload.
+NSString *MTLogTruncatedDescription(id value);
 void MTLog(NSString *format, ...);
 void MTLogWithPrefix(NSString *(^getLogPrefix)(), NSString *format, ...);
 void MTShortLog(NSString *format, ...);

submodules/MtProtoKit/Sources/MTLogging.m

@@ -8,10 +8,21 @@ bool MTLogEnabled() {
     return loggingFunction != NULL && MTLogEnabledValue;
 }
 
+NSString *MTLogTruncatedDescription(id value) {
+    NSString *description = [NSString stringWithFormat:@"%@", value];
+    static const NSUInteger limit = 1024;
+    if (description.length <= limit) {
+        return description;
+    }
+    // Expanded to whole character sequences, so the cut cannot land inside a surrogate pair.
+    NSRange range = [description rangeOfComposedCharacterSequencesForRange:NSMakeRange(0, limit)];
+    return [NSString stringWithFormat:@"%@… (truncated, %lu characters total)", [description substringWithRange:range], (unsigned long)description.length];
+}
+
 void MTLog(NSString *format, ...) {
     va_list L;
     va_start(L, format);
-    if (loggingFunction != NULL) {
+    if (loggingFunction != NULL && MTLogEnabledValue) {
         NSString *string = [[NSString alloc] initWithFormat:format arguments:L];
         loggingFunction(string);
     }
@@ -21,7 +32,7 @@ void MTLog(NSString *format, ...) {
 void MTLogWithPrefix(NSString *(^getLogPrefix)(), NSString *format, ...) {
     va_list L;
     va_start(L, format);
-    if (loggingFunction != NULL) {
+    if (loggingFunction != NULL && MTLogEnabledValue) {
         NSString *string = [[NSString alloc] initWithFormat:format arguments:L];
         if (getLogPrefix) {
             NSString *prefix = getLogPrefix();
@@ -37,7 +48,7 @@ void MTLogWithPrefix(NSString *(^getLogPrefix)(), NSString *format, ...) {
 void MTShortLog(NSString *format, ...) {
     va_list L;
     va_start(L, format);
-    if (shortLoggingFunction != NULL) {
+    if (shortLoggingFunction != NULL && MTLogEnabledValue) {
         NSString *string = [[NSString alloc] initWithFormat:format arguments:L];
         shortLoggingFunction(string);
     }

submodules/MtProtoKit/Sources/MTProto.m

@@ -880,7 +880,7 @@ - (NSString *)outgoingShortMessageDescription:(MTOutgoingMessage *)message messa
 
 - (NSString *)incomingMessageDescription:(MTIncomingMessage *)message
 {
-    return [[NSString alloc] initWithFormat:@"%@ (%" PRId64", %" PRId64"/%" PRId64")", message.body, message.messageId, message.authKeyId, message.sessionId];
+    return [[NSString alloc] initWithFormat:@"%@ (%" PRId64", %" PRId64"/%" PRId64")", MTLogTruncatedDescription(message.body), message.messageId, message.authKeyId, message.sessionId];
 }
 
 - (MTDatacenterAuthKey *)getAuthKeyForCurrentScheme:(MTTransportScheme *)scheme createIfNeeded:(bool)createIfNeeded authInfoSelector:(MTDatacenterAuthInfoSelector *)authInfoSelector {
@@ -1106,8 +1106,10 @@ - (void)transportReadyForTransaction:(MTTransport *)transport scheme:(MTTranspor
                         NSString *messageDescription = [self outgoingMessageDescription:outgoingMessage messageId:messageId messageSeqNo:messageSeqNo authKeyId:authKey.authKeyId];
                         MTLogWithPrefix(_getLogPrefix, @"[MTProto#%p@%p preparing %@]", self, _context, messageDescription);
                     }
-                    NSString *shortMessageDescription = [self outgoingShortMessageDescription:outgoingMessage messageId:messageId messageSeqNo:messageSeqNo];
-                    MTShortLog(@"[MTProto#%p@%p preparing %@]", self, _context, shortMessageDescription);
+                    if (MTLogEnabled()) {
+                        NSString *shortMessageDescription = [self outgoingShortMessageDescription:outgoingMessage messageId:messageId messageSeqNo:messageSeqNo];
+                        MTShortLog(@"[MTProto#%p@%p preparing %@]", self, _context, shortMessageDescription);
+                    }
 
                     if (!monotonityViolated || _useUnauthorizedMode)
                     {

submodules/MtProtoKit/Sources/MTRequestMessageService.m

@@ -822,7 +822,7 @@ - (void)mtProto:(MTProto *)__unused mtProto receivedMessage:(MTIncomingMessage *
 
                     if (rpcResult != nil) {
                         if (MTLogEnabled()) {
-                            MTLog(@"[MTRequestMessageService#%p response for %" PRId64 " is %@]", self, request.requestContext.messageId, rpcResult);
+                            MTLog(@"[MTRequestMessageService#%p response for %" PRId64 " is %@]", self, request.requestContext.messageId, MTLogTruncatedDescription(rpcResult));
                         }
                     } else {
                         if (MTLogEnabled()) {