Stdlib: mb_encode_mimeheader()/mb_decode_mimeheader() — MIME header encoding missing (ext/mbstring/mbstring.c)

[PurHur]

Category

stdlib

Problem

ext/mbstring provides mb_encode_mimeheader() and mb_decode_mimeheader() for RFC 2047 encoded-word headers (mail subjects, HTTP headers with non-ASCII). This compiler has partial mbstring (mb_strlen yes) but function_exists('mb_encode_mimeheader') / mb_decode_mimeheader() → false on VM.

Mail and i18n code targeting PHP 8.x expects these alongside mb_convert_encoding() (tracked #3075).

php-src reference

• php/php-src ext/mbstring/mbstring.c — PHP_FUNCTION(mb_encode_mimeheader), PHP_FUNCTION(mb_decode_mimeheader)
• php/php-src ext/mbstring/libmbfl — MIME header encoding helpers

Repro

./script/docker-exec.sh -- php bin/vm.php -r '
echo function_exists("mb_encode_mimeheader") ? "yes" : "no", PHP_EOL;
echo function_exists("mb_decode_mimeheader") ? "yes" : "no", PHP_EOL;
'

Observed (VM):

mb_encode_mimeheader: no
mb_decode_mimeheader: no

Zend PHP expected: both exist; round-trip non-ASCII subject lines per php-src tests.

Scope (this repo)

• ext/mbstring/mb_encode_mimeheader.php, mb_decode_mimeheader.php
• Register in ext/mbstring/Module.php (Bootstrap: ext/mbstring/ module skeleton — register mbstring builtins for self-host (M4) #5695 skeleton)
• Port RFC 2047 Q/B encoding in PHP (or reuse tables from Stdlib: mb_convert_encoding / mb_detect_encoding (ext/mbstring parity) #3075)
• Enum operands → TypeError (php-src-strict, Stdlib: mb_strlen() — enum case operand must TypeError (ext/mbstring/mbstring.c) #5873 pattern)
• Avoid growing runtime/; thin ABI only if profiling proves hot-path need

Done when

• Both functions registered; function_exists → true
• Round-trip: mb_decode_mimeheader(mb_encode_mimeheader("日本語", "UTF-8")) matches Zend for UTF-8 fixtures
• Enum case string operands throw catchable TypeError, not silent coerce / VM fatal
• test/compliance/cases/stdlib/mb_encode_mimeheader.phpt green on VM
• ./script/docker-exec.sh -- vendor/bin/phpunit --filter MbEncodeMimeheader

Implementation hints (PHP-in-PHP)

• Add PHP MIME encoding; reuse charset tables from future mb_convert_encoding work (Stdlib: mb_convert_encoding / mb_detect_encoding (ext/mbstring parity) #3075).

Verification

• test/compliance/cases/stdlib/mb_encode_mimeheader.phpt

Links

• Stdlib: mb_convert_encoding / mb_detect_encoding (ext/mbstring parity) #3075 mb_convert_encoding · Stdlib: mb_substr / mb_strpos / mb_strtolower — mbstring beyond mb_strlen (ext/mbstring parity) #3239 mb_substr family · Stdlib: mb_strlen() — enum case operand must TypeError (ext/mbstring/mbstring.c) #5873 mb_strlen enum TypeError · Stdlib: mb_scrub() — PHP 8.4 invalid-byte scrubbing missing (ext/mbstring/mbstring.c) #6050 mb_scrub · Epic: Self-host critical path — compiler compiles itself (M3→M5) #1492

[PurHur]

claim: PHP Compiler STD Lib — starting this run

[PurHur]

Merged via #8679.

Verification

• VM: mb_encode_mimeheader("日本語","UTF-8") → =?UTF-8?B?5pel5pys6Kqe?=; round-trip + mixed Hello 世界 match Zend
• PHPUnit: vendor/bin/phpunit --filter mb_encode_mimeheader → OK (6/6 VM+JIT+AOT+enum TypeError)
• php-src ref: ext/mbstring/mbstring.c — PHP_FUNCTION(mb_encode_mimeheader), PHP_FUNCTION(mb_decode_mimeheader)
• Implementation: ext/mbstring/VmMbstring.php, mb_encode_mimeheader.php, mb_decode_mimeheader.php, JitMbMimeheader.php