Reject JAR Files with Non-UTF-8 Manifests

[mizdebsk]

As a Java package maintainer,
I want javapackages-validator to detect and reject JAR files that contain manifests not encoded in UTF-8,
so that I can ensure all JAR metadata is reliably parsed and safely handled by Java tools that expect UTF-8, preventing encoding-related errors or unexpected behavior during build or runtime.

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Acceptance Criteria

• The validator inspects all .jar files included in the SRPM or built artifacts.
• It attempts to read the META-INF/MANIFEST.MF file using UTF-8 encoding.
• If the manifest cannot be parsed as UTF-8 (e.g., contains invalid byte sequences), validation fails.
• The error output must include:
  • The name of the JAR file
  • A note that the manifest is not UTF-8 encoded

Test Cases

• ✅ Valid Case: JAR contains a META-INF/MANIFEST.MF file encoded in valid UTF-8
  → Validation passes

• ❌ Invalid Case: JAR contains a manifest with non-UTF-8 bytes (e.g., Latin-1 or Windows-1252)
  → Validation fails, error message displayed

• ❌ Corrupted Case: JAR manifest contains invalid UTF-8 sequences (e.g., truncated multibyte character)
  → Validation fails, manifest identified in output