用不同语言的套接字编码谜题

我用PHP编写了以下代码，负责服务器套接字，特别是通过向某些套接字写入消息：

header('Content-Type: text/html; charset=utf-8');
const PAYLOAD_LENGTH_16 = 126;
const PAYLOAD_LENGTH_63 = 127;
const OPCODE_CONTINUATION  = 0;
for ($i = 0; $i < $frameCount; $i++) {
    // fetch fin, opcode and buffer length for frame
    $fin = $i != $maxFrame ? 0 : self::FIN;
    $opcode = $i != 0 ? self::OPCODE_CONTINUATION : $opcode;
    $bufferLength = $i != $maxFrame ? $bufferSize : $lastFrameBufferLength;
    // set payload length variables for frame
    if ($bufferLength <= 125) {
        $payloadLength = $bufferLength;
        $payloadLengthExtended = '';
        $payloadLengthExtendedLength = 0;
    }
    elseif($bufferLength <= 65535) {
        $payloadLength = self::PAYLOAD_LENGTH_16;
        $payloadLengthExtended = pack('n', $bufferLength);
        $payloadLengthExtendedLength = 2;
    } else {
        $payloadLength = self::PAYLOAD_LENGTH_63;
        $payloadLengthExtended = pack('xxxxN', $bufferLength); // pack 32 bit int, should really be 64 bit int
        $payloadLengthExtendedLength = 8;
    }
    // set frame bytes
    $buffer = pack('n', (($fin | $opcode) << 8) | $payloadLength).$payloadLengthExtended.substr($message, $i * $bufferSize, $bufferLength);

下面是Objective-C中负责从套接字服务器接收这些消息的代码：

NSInteger len = 0;
        uint8_t buffer[4096];
        while ([inputStream hasBytesAvailable]) {
            len = [inputStream read:buffer maxLength:sizeof(buffer)];
            if (len > 0) {
                [self.data appendBytes:buffer length:len];
                [self.log insertText:[NSString stringWithFormat:@"Log: Received a message from server:'n'n"]];
                NSLog(@"Received a message from server...");
            }
        }

当接收到所有字节时，我运行以下命令将数据转换为文件：

[self.data writeToFile:@"dataComes.txt" options:NSDataWritingAtomic error:nil]

问题

我们将为objective-c发送一个JSON格式的大文件，他将收到该信息，并生成一个名为dataComes.txt的文件，我可以正常看到JSON文件，但除了一些奇怪的字符，如：

~ or ~Â or â-Û

这些奇怪的字符总是出现在Objective-C接收到的每个消息块的开头（是的，套接字服务器和TCP将大型消息划分为消息块）。

这个问题的原因是什么？它如何解决这个问题？