Refactored out detectFileMIMEType, matchesMIMEType logic for reuse. Added standalone isMIMEType validator for flexibility

[dapzthelegend]

Summary

Adds a new built-in mimetype validator for file paths.

It supports both exact MIME matches and wildcard subtype matches:

validate.Var("photo.png", "mimetype=image/png")
validate.Var("photo.png", "mimetype=image/*")

Changes

• add mimetype as a built-in validation tag
• extract shared file MIME detection logic
• refactor isImage to reuse the shared MIME detection helper
• keep isImage's existing explicit image MIME allowlist unchanged
• add docs and tests for mimetype
• add default translations and translation tests for mimetype

Notes

mimetype accepts:

• type/subtype
• type/*

Validation fails if the field is not a string, the file does not exist, the path is a directory, the MIME type cannot be detected, or the validator param is invalid.

Make sure that you've checked the boxes below before you submit PR:

• Tests exist or have been written that cover this particular change.

@go-playground/validator-maintainers

[dapzthelegend]

@the-fanan @zemzale

PR #1 to refactor out the mime detection logic and create a flexible standalone isMIMEType Validator

To keep existing behavior I've retained the type dict for isImage

[zemzale]

One small tests thing, but the code looks good.

Would like someone else opinion about the validator itself, before merging.

[dapzthelegend]

Hi @zemzale — I've rebased this branch on the latest master (7 commits ahead, including bcp47_strict_language_tag, NoneOf, and the UUID fix). The translations/it/it.go conflict was the only one and it's resolved.

Branch is now conflict-free and CI should run cleanly. The APPROVED review from @zemzale is still on record. If a second reviewer sign-off is the remaining gate, happy to ping or wait — just let me know if there's anything else needed on my end to unblock merge.

[deankarn]

LGTM

Still look good to you @zemzale?