rhai/doc/src/safety/max-string-size.md

Maximum Length of Strings

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Limiting How Long Strings Can Grow

Rhai by default does not limit how long a [string] can be.

This can be changed via the Engine::set_max_string_size method, with zero being unlimited (the default).

A script attempting to create a string literal longer than the maximum length will terminate with a parse error.

Any script operation that produces a string longer than the maximum also terminates the script with an error result.

This check can be disabled via the [unchecked] feature for higher performance (but higher risks as well).

let mut engine = Engine::new();

engine.set_max_string_size(500);    // allow strings only up to 500 bytes long (in UTF-8 format)

engine.set_max_string_size(0);      // allow unlimited string length

Setting Maximum Length

Be conservative when setting a maximum limit and always consider the fact that a registered function may grow a string's length without Rhai noticing until the very end.

For instance, the built-in '+' operator for strings concatenates two strings together to form one longer string; if both strings are slightly below the maximum length limit, the resultant string may be almost twice the maximum length.