From 66500ac6e4f002a673e95e9788a4992178bf989a Mon Sep 17 00:00:00 2001
From: Gabriel Schneider <gbrls@0x4200.cafe>
Date: Tue, 29 Sep 2026 18:16:13 -0300
Subject: The 9P monkey counts the lines a write runs as the tree does: a short
 write's unended tail is a line of its own

Since round 24 (uwzuqzxp), a write to a lines file shorter than a Twrite holds is whole, as acme takes each write, so a look line written a byte a Twrite is as many looks as bytes, each missing with its own err. one_failure_rule still split the data on newlines whole, allowed one err, and failed the fixed smoke seed (20260929 step 607, size 20 6 written in bytes to look: 7 errs). served_lines models the tree's write (tree.zig) and has a self-check run at start.

Co-Authored-By: Claude Opus 5.5 <noreply@anthropic.com>
---
 test/monkey9p.py | 41 ++++++++++++++++++++++++++++++++++++-----
 1 file changed, 36 insertions(+), 5 deletions(-)

(limited to 'test/monkey9p.py')

diff --git a/test/monkey9p.py b/test/monkey9p.py
index 4c1732e5..6a8f27c1 100644
--- a/test/monkey9p.py
+++ b/test/monkey9p.py
@@ -640,12 +640,13 @@ def op_write(sess, op):
     timeout = SLOW_TIMEOUT if slow(data) else TIMEOUT
     ok, body = w.call(TOPEN, struct.pack('<IB', fid, mode), timeout)
     res.add(open_kind(path, mode), path, ok, None if ok else body)
-    allowances(res, path, data)
+    sizes = chunking(op.get('chunks', 'whole'), len(data), w.msize - 23)
+    allowances(res, path, data, sizes, w.msize - 24)
     opened = ok
     sent = data
     if ok:
         offset = 0
-        for size in chunking(op.get('chunks', 'whole'), len(data), w.msize - 23):
+        for size in sizes:
             piece = data[offset:offset + size]
             ok, body = w.call(TWRITE, struct.pack('<IQI', fid, op.get('offset', offset), len(piece)) + piece, timeout)
             # A write on a fid opened for reading is 9P misuse, not a write
@@ -663,13 +664,35 @@ def op_write(sess, op):
     return res
 
 
-def allowances(res, path, data):
+def served_lines(data, sizes, room):
+    """The lines a lines file runs for `data` written in pieces of `sizes`
+    (fs.md, tree.zig write): each ended line, and the unended tail of a piece
+    shorter than a Twrite holds (`room`, msize less 24), which is whole in
+    itself, as acme takes each write; a piece that fills its Twrite may go
+    on, and its tail waits for the next. A line written a byte a Twrite is
+    so as many lines as bytes."""
+    lines, pending, at = [], b'', 0
+    for size in sizes:
+        piece = data[at:at + size]
+        at += size
+        pending += piece
+        *done, pending = pending.split(b'\n')
+        lines += done
+        if pending and len(piece) < room:
+            lines.append(pending)
+            pending = b''
+    if pending:
+        lines.append(pending)
+    return lines
+
+
+def allowances(res, path, data, sizes, room):
     """Errs a successful write may log (fs.md): a look that finds nothing logs
     one, per line, whether written to look, written back as an event record
     (acme's xfid.c:842) or run as the Look builtin; an Edit block whose text
     never ended runs, and fails, at the close."""
     base = path.rsplit('/', 1)[-1]
-    lines = [line for line in data.split(b'\n') if line.strip()]
+    lines = [line for line in served_lines(data, sizes, room) if line.strip()]
     if base in ('look', 'event'):
         n = len(lines)
     elif base in ('exec', 'ctl', 'tagexec'):
@@ -692,6 +715,13 @@ def open_kind(path, mode):
     return 'open'
 
 
+def check_served_lines():
+    assert served_lines(b'a\nb\n', [4], 8000) == [b'a', b'b']
+    assert served_lines(b'ab\n', [1, 1, 1], 8000) == [b'a', b'b', b'']
+    assert served_lines(b'abcd', [2, 2], 2) == [b'abcd']
+    assert served_lines(b'ab\ncd', [3, 2], 8000) == [b'ab', b'cd']
+
+
 def chunking(spec, n, cap):
     if n == 0:
         return [0]
@@ -820,7 +850,7 @@ def op_hwrite(sess, op):
     fid, path, mode, off, _ = h
     data = dec(op['data'])[:sess.wire.msize - 23]  # one Twrite
     h[4] = data
-    allowances(res, path, data)
+    allowances(res, path, data, [len(data)], sess.wire.msize - 24)
     ok, body = sess.wire.call(TWRITE, struct.pack('<IQI', fid, off[0], len(data)) + data,
                               SLOW_TIMEOUT if slow(data) else TIMEOUT)
     res.add('write' if mode & 3 else 'write-badfid', path, ok, None if ok else body)
@@ -1919,6 +1949,7 @@ def main():
     ap.add_argument('--verbose', '-v', action='store_true', help='replay: print each request and log record')
     ap.add_argument('--out', default=DEFAULT_OUT)
     args = ap.parse_args()
+    check_served_lines()
     args.binary = os.path.abspath(args.binary)
     for key in [k for k in os.environ if k.startswith('PARDES_') or k in ('NINE_MOUNT', 'NAMESPACE')]:
         del os.environ[key]
-- 
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