[5.7] Fix database cache on PostgreSQL

[staudenmeir]

Storing serialized objects in the database cache doesn't work on PostgreSQL:

Schema::create('cache', function ($table) {
    $table->string('key')->unique();
    $table->text('value');
    $table->integer('expiration');
});

Cache::put('user', new User(), 1);
Cache::get('user');

Retrieving the value throws an exception:

unserialize(): Error at offset 21 of 25 bytes

The database cache uses serialize() to serialize the value. For objects, the serialization contains null bytes. PostgreSQL can't store null bytes in a text column, truncates the string (O:8:"App\User":27:{s:11:") and thereby breaks the unserialization.

The proposed solution is using Base64 encoding if the serialized value contains a null byte. When the value is retrieved, we can detect the Base64 encoding by looking for : or ;. A Base64-encoded string can't contain this characters; a serialized string always contains at least one of them.

I used this to find the possible data type serializations:

dd(
    serialize(null),
    serialize(true),
    serialize(1),
    serialize(1.0),
    serialize('a'),
    serialize([]),
    serialize((object) [])
);

This would only be a breaking change if someone was actually using the corrupted serialization – which makes no sense.

An alternative approach is storing the value in a binary column (bytea). This would also require changes to the DatabaseStore and the user would have to adjust the migration. With the Base64 encoding, the user doesn't have to worry about the used database. The only downside is the increased payload size.

Fixes #25466.

[tillkruss]

@staudenmeir: How do you feel about encoding all cache values for Postgres, instead of checking for characters?

[staudenmeir]

@tillkruss In order to simplify the code? I don't think it's worth the increased payload size. And we would still require Str::contains($value, [':', ';']) to make it a non-breaking change.

[MyBestPro-Stephane]

I think I have the same issue with SQLserver...

[staudenmeir]

@MyBestPro-Stephane Please submit a new issue.