Ruby: Limiting a UTF-8 string by byte-length

Question

This RabbitMQ page states:

Queue names may be up to 255 bytes of UTF-8 characters.

In ruby (1.9.3), how would I truncate a UTF-8 string by byte-count without breaking in the middle of a character? The resulting string should be the longest possible valid UTF-8 string that fits in the byte limit.

Answer 1

For Rails >= 3.0 you have ActiveSupport::Multibyte::Chars limit method.

From API docs:

- (Object) limit(limit) 

Limit the byte size of the string to a number of bytes without breaking characters. Usable when the storage for a string is limited for some reason.

Example:

'こんにちは'.mb_chars.limit(7).to_s # => "こん"