[CODEC-341] Fix Base16 custom alphabet decode table#434
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Derive Base16 decode tables from custom encode tables so a configured codec can decode its own output. Reject encode tables that do not contain exactly 16 unique byte values. Reviewed-by: OpenAI Codex Reviewed-by: Anthropic Claude Code
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JIRA: https://issues.apache.org/jira/browse/CODEC-341
Problem
Base16.Builder#setEncodeTable(...)honors a custom alphabet for encoding, but only ever pairs it with the built-in upper/lower decode table. ABase16built with any other alphabet, therefore, cannot decode its own output.Fix
Derive the decode table from the configured encode table (
toDecodeTable), so a custom alphabet round-trips. Encode tables that are not 16 unique bytes are rejected withIllegalArgumentException.Notes (behavior changes)
setEncodeTable(...)now throwsIllegalArgumentExceptionfor tables that are not 16 unique bytes (previously accepted, producing undecodable output).Builder#setLowerCase(true)now also sets the matching decode table; before,builder().setLowerCase(true)could not decode its own lower-casea–foutput.Tests
Added to
Base16Test: custom-alphabet round-trip, rejection of duplicate and wrong-length tables, and abuilder().setLowerCase(true)round-trip that fails without this change.Verification
mvnpasses locally (tests, Checkstyle, PMD, Javadoc).