Why Does My Symfony 3 Application Get a 'PDO::__construct(): Server sent charset (255) unknown to the client' Error When Connecting to MySQL?

PDOs Unknown MySQL Character Set Dilemma

When attempting to connect to a MySQL database via a Symfony 3 application, you may encounter the enigmatic error message "PDO::__construct(): Server sent charset (255) unknown to the client. Please, report to the developers." This issue stems from a mismatch between the server's default character set and the client's understanding of it.

Background

MySQL version 8.0.1 altered its default character set to utf8mb4. However, certain clients remain unaware of this change. Consequently, when the server communicates its default character set to the client, an unrecognized response triggers the aforementioned error.

Resolution

The optimal solution entails upgrading the client to a version that acknowledges utf8mb4. However, as an interim measure, you can modify the server's character set to utf8 to accommodate non-upgraded clients. This is achieved by adding the following lines to /etc/my.cnf:

[client]
default-character-set=utf8

[mysql]
default-character-set=utf8


[mysqld]
collation-server = utf8_unicode_ci
character-set-server = utf8

Alternative Solution

Another potential solution is to forcibly set the MySQL connection charset to a specific value. In your PDO connection string, you can use the charset parameter, such as:

$dsn = "mysql:host=mysql;dbname=database;charset=utf8mb4;";

By explicitly defining the charset in the PDO connection string, you can bypass the server's default character set and ensure compatibility with both upgraded and non-upgraded clients.

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