core: io/sparse_file + io/write_buffer (stage 4)

sami/vdm

io/sparse_file — the single O_WRONLY output file (docs/04 §4). open()
posix_fallocate's the full size (falls back to ftruncate on
EOPNOTSUPP/ENOSYS, reported via preallocated()); write_at() pwrites at an
absolute offset, looping short writes and retrying EINTR; sync() is
fdatasync (timer/pause only); advise_dontneed() is
posix_fadvise(DONTNEED); resize() trims a preallocated tail or sizes a
chunked download. errno -> vdm::Error (ENOSPC->disk_full,
EACCES->permission_denied, ENOENT/ENOTDIR/...->path_rejected). No lock on
write_at — POSIX makes each pwrite atomic for a regular file, so N
segment threads writing disjoint ranges is safe (tested, TSan-clean).

io/write_buffer — per-segment accumulate-and-flush buffer, preallocated
at construction; append() only memcpys (no allocation on the write-
callback hot path, docs/04 §8 — asserted by a global-new counter in the
test). Flushes on fill via a caller-supplied FlushFn; a chunk >= capacity
arriving on an empty buffer writes straight through. On a flush error
next_offset() stays at the last durable position. Single-threaded; the
disk-writer-thread handoff is stage 8.

Also: vtest.hpp VT_CHECK_EQ/NE now copy operands (auto, not auto&&) — an
assertion must not outlive a temporary the expression returned a
reference into (ASan caught this on Result<void>{}.error().code).

Co-Authored-By: Claude Sonnet 5 <[email protected]>
Claude-Session: https://claude.ai/code/session_01HPPSGhiArbvQgwC2DNiURS

This commit is contained in:

sami

2026-09-10 00:41:31 +04:00

co-authored by

Claude Sonnet 5

parent e8a6b64c2f

commit bd0a24c87a

9 changed files with 781 additions and 4 deletions

									
										core/CMakeLists.txt
									
		+2
		
												View File
												
				@@ -17,6 +17,8 @@ add_library(veloxcore STATIC

				    src/net/content_disposition.cpp

				    src/net/url.cpp

				    src/net/probe.cpp

				    src/io/sparse_file.cpp

				    src/io/write_buffer.cpp

				)

				add_library(velox::core ALIAS veloxcore)