PDOException when saving a node on non-English languages

Problem/Motivation

I got the following error as I try to save a node when non-English language (Chinese in my case) is enabled. The problem does not exist when English is the default language.
PDOException: 在 dblog_watchdog() (行 157 在 D:\xampp\htdocs\modules\dblog\dblog.module).

When I catch the exception, I found the following issue:
Incorrect string value: '\xE6\x9F' for column 'link' at row 1

The problematic code is:

  Database::getConnection('default', 'default')->insert('watchdog')
    ->fields(array('uid' => $user_uid,'type' => substr($log_entry['type'], 0, 64),'message' => $log_entry['message'],'variables' => serialize($log_entry['variables']),'severity' => $log_entry['severity'],'link' => substr($log_entry['link'], 0, 255), // <----- problematic'location' => $log_entry['request_uri'],'referer' => $log_entry['referer'],'hostname' => substr($log_entry['ip'], 0, 128),'timestamp' => $log_entry['timestamp'],
    ))
    ->execute();

In my case, the link is: 查看

So, substr($log_entry['link'], 0, 255) truncates in the middle of the Chinese characters: 查看.

I tried to reduce the substr length to 200: substr($log_entry['link'], 0, 200), then I don't see the problem.

I don't care about such logs, I'd be happy if it is just caught. But I'm sure there is a nice way to fix it.

To reproduce the issue one can for example store a node with a long URL alias including non-standard characters. You can use some of the Chinese characters above or just this exact URL alias:

åååååååååååååååååååååååååååååååååååååååååååååååååååååååååååååååååååååååååååååååååååååååååååååååååååååååååååååååååååååååååååååååååååååååååååååååååååååååååååååååååååååååååååååååååååååååååååååååååååååååååååååååååååååååååååå

Proposed resolution

See patch.

Remaining tasks

User interface changes

API changes

Beta phase evaluation