SSLRead挂起然后返回零字节读取

Question

我正在使用SecureTransport通过HTTPS与Google Places API进行通信。但是，当我在其中间的某处读取响应时，SSLRead例程首先挂起几分钟，然后返回零字节读取，从而使我的响应不完整。它可能是什么？

do {
    if (httpResponseBodyContentLength > -1 && offset_recv >= httpResponseBodyContentLength) {
        break;
    }

    size_t bytes_available;
    for (int try = 0; try < 30; try++) {
        if ((ssl_status = SSLGetBufferedReadSize(ssl_context, &bytes_available)) != 0) {
            NetDebugLog(@"%@", [NSError errorWithDomain:NSOSStatusErrorDomain code:ssl_status userInfo:nil]);
            bytes_available = 0;
            @try {
                usleep(30000);
            }
            @catch (NSException *exception) {
                NetDebugLog(@"%@", exception);
            }
        }
        else if (bytes_available == 0) {
            @try {
                usleep(30000);
            }
            @catch (NSException *exception) {
                NetDebugLog(@"%@", exception);
            }
        }
        else {
            break;
        }
    }
    ssl_status = SSLRead(ssl_context, responseBodyBuffer + offset_recv, MIN(responseBodyBufferLength - offset_recv, bytes_available), &bytes_recv_size_t);
    bytes_recv_int = bytes_recv_size_t;
    NetDebugLog(@"SSLRead() body: %zd bytes of %zd length (%ld offset)", bytes_recv_size_t, MIN(responseBodyBufferLength - offset_recv, bytes_available), offset_recv);

    if (ssl_status != 0) {
        NSError *ssl_error = [NSError errorWithDomain:NSOSStatusErrorDomain code:ssl_status userInfo:nil];
        NetDebugLog(@"%@", ssl_error);
    }

    [responseBufferNSMutableData appendBytes:responseBodyBuffer + offset_recv length:bytes_recv_int];

    responseBodyTotalLength += bytes_recv_int;
    offset_recv += bytes_recv_int;

    if (ssl_status == -36) {
        @throw [NSException exceptionWithName:@"NAExtensions"
                                       reason:[[NSString alloc]initWithFormat:@"SSLRead() failed: %ld", bytes_recv_size_t]
                                     userInfo:nil];
    }
    else if (offset_recv == responseBodyBufferLength) {
        offset_recv = 0;
    }
}
while (bytes_recv_int > 0);