Multipart processing @Body annotation decodes to string using incorrect charset

[tfield]

Expected Behavior

When using the @Body annotation to extract multipart parameters into a Map<String,List>, the list of parameter values should be decoded to strings as UTF-8

Actual Behaviour

The list of parameter values is decoded to strings using latin1. The strings need to be decoded to bytes then re-converted to strings using utf-8.

Steps To Reproduce

See repository linked below. But to roll your own:

• create a form that posts strings to a controller using multipart/form-data
• add non-latin1 characters to the string (e.g. smart quotes)
• decode values using @Body Map<String,List>
• observe incorrect decoding
• convert to bytes using latin1
• convert back to string using utf8
• observe correct decoding

Environment Information

• Micronaut 4.4.2
• Micronaut Servlet (Tomcat)
• Multipart enabled
• MacOS 15.1

Example Application

https://github.com/tfield/micronaut-servlet-multipart

Version

4.4.2