Stdlib: stream_bucket_make_writeable() / stream_bucket_append() — filter brigades (streamsfuncs.c)

[PurHur]

Category

stdlib · php-src-strict

Problem

Filtered stream pipelines in php-src use stream_bucket_make_writeable(), stream_bucket_append(), and stream_bucket_new() to move buckets between brigades. User-defined php://filter chains and custom filters call these after #3494 / stream filters land.

This compiler implements core fopen/fread/fwrite but not the bucket API — function_exists('stream_bucket_make_writeable') is false on VM.

php-src reference

• php/php-src ext/standard/streamsfuncs.c — PHP_FUNCTION(stream_bucket_make_writeable), stream_bucket_append, stream_bucket_new
• php/php-src main/streams/php_stream_filter.c — brigade/bucket lifecycle
• Tests: ext/standard/tests/streams/stream_bucket_*.phpt

Repro A — existence

<?php
var_export(function_exists('stream_bucket_make_writeable'));
var_export(function_exists('stream_bucket_append'));
var_export(function_exists('stream_bucket_new'));
echo "\n";

./script/docker-exec.sh -- bash -lc 'source script/php-env.sh
php repro_stream_bucket_exists.php      # true,true,true
php bin/vm.php repro_stream_bucket_exists.php  # false,false,false
'

Repro B — brigade mutation (after filters exist)

Port minimal php-src test: read via php://filter/read=string.toupper and inspect bucket objects when filter callbacks invoke bucket helpers (depends on #9047 stream_filter_* — can stub VM-only first).

Scope (this repo)

Layer	Path
VM stream layer	lib/VM/ stream wrappers + brigade objects
Builtins	ext/standard/stream_bucket_make_writeable.php, stream_bucket_append.php, stream_bucket_new.php, Module.php
PHP-in-PHP	bucket structs as PHP classes, not runtime/*.c tables
JIT	defer (VM-first); file follow-up if LLVM stream path needs buckets
Tests	test/compliance/cases/stdlib/stream_bucket_*.phpt

Done when

• Repro A: all three function_exists true on VM
• stream_bucket_make_writeable($brigade) returns bucket object or false like Zend
• stream_bucket_append($brigade, $bucket) mutates brigade; refcount semantics per php-src
• At least one filter pipeline script runs without undefined-function fatal
• script/capability-matrix.php regenerated

Links

• Stdlib: stream_context_set_option / get_options / get_params / set_default (ext/standard/streams.c parity) #3448 stream_context · Stdlib: stream_wrapper_register() — custom stream protocol handlers (ext/standard/streams.c parity) #3383 user wrappers · Stdlib/JIT: stream_filter_* builtins unsupported (and user filters rejected) #9047 stream_filter_* · Epic: Self-host critical path — compiler compiles itself (M3→M5) #1492

[PurHur]

claim: cursor-agent-lane-c — starting this run

[PurHur]

claim released: repro A green on master — function_exists(stream_bucket_make_writeable/append/new) all true on VM. Issue stale; pivoting.

[PurHur]

claim: cursor-agent-lane-c — starting this run (close stale issue: repro A/B green on master; add compliance guard)

[PurHur]

Merged via #18518

Verification (2026-07-13, Docker):

• Repro A: function_exists(stream_bucket_make_writeable/append/new/prepend) all true on VM
• Repro B: stream_user_filter_append.phpt + new stream_bucket_api.phpt (uppercase filter brigade) — PASS
• vendor/bin/phpunit test/compliance/VMTest.php --filter stream_bucket — PASS
• vendor/bin/phpunit test/unit/ext/standard/VmStreamBucketTest.php — PASS

Issue was stale on master; this PR adds the missing #4688 compliance guard and closes the ticket.