An event record is delivered in pieces to reads shorter than it, so a bash read loop on event works

A read shorter than the record waiting was refused EINVAL, and bash's
read, a byte at a time on a file it cannot seek in, failed on the
first record. A short read now takes the record's front and the next
read the rest, as log and pty/data already did and acme allows. A
unit test reads two records a byte at a time; selfmount runs a bash
read on event through the mount.

Co-Authored-By: Claude Opus 5.5 <[email protected]>

1 files changed, 10 insertions, 0 deletions

diff --git a/test/selfmount.py b/test/selfmount.py
index dd59083c..503ce1e0 100644
--- a/test/selfmount.py
+++ b/test/selfmount.py
@@ -186,6 +186,16 @@ def run(binary):
             followed = recipe.read_text() if recipe.exists() else ''
             recipe.unlink(missing_ok=True)
             check(ran == '0' and 'recipe-heard' in followed, f'the log follow recipe with cat hears a new record ({followed[-120:]!r})')
+            # A bash read loop on a pane's event: bash reads it a piece at a
+            # time, and each record still arrives whole, in pieces.
+            looped = Path(f'/tmp/{name}.events')
+            ran = run((f"bash -c 'exec 3<{mount}/pane/{first}/event; "
+                       f"(sleep 1; echo Msg ev-loop > {mount}/pane/{first}/exec) & "
+                       f"read -r line <&3; echo \"$line\" > {looped}'\n").encode())
+            got_line = looped.read_text() if looped.exists() else ''
+            looped.unlink(missing_ok=True)
+            check(ran == '0' and got_line.startswith('FX') and got_line.rstrip().endswith('Msg ev-loop'),
+                  f'a bash read loop on event reads a whole record ({got_line!r})')
             client.write('/exec', b'Msg still here\n')
             text = ''.join(cell[0] for cell in client.screen()['cells'])
             check('still here' in text, 'the editor answers after all of that')