jw/pkg/lib/util.run_cmd(): Chunked read_stream()

jw-pkg distro dup got hung in a chroot environment. strace shows that
write(2) into a pipe is the hanging syscall, with the write buffer
hinting at zypper dup output.

I strongly suspect that run_cmd() tries to write stdout into the pipe
which read_stream() fails to empty. So, make read_stream() more
resilient by using read(4096) instead of readline(), which I suspect
to be prone to hang on overlong lines.

Signed-off-by: Jan Lindemann <jan@janware.com>

src/python/jw/pkg/lib/util.py

@@ -172,13 +172,20 @@ async def run_cmd(
             stderr_log_enc = output_encoding
 
         async def read_stream(stream, prio, collector: list[bytes], log_enc: str):
+            buf = b""
             while True:
-                line = await stream.readline()
+                chunk = await stream.read(4096)
-                if not line:
+                if not chunk:
                     break
-                collector.append(line)
+                collector.append(chunk)
                 if verbose:
-                    __log(prio, line.decode(log_enc, errors="replace").rstrip("\n"))
+                    buf += chunk
+                    while b"\n" in buf:
+                        line, buf = buf.split(b"\n", 1)
+                        __log(prio, line.decode(log_enc, errors="replace"))
+            if verbose and buf:
+                # flush trailing partial line (no newline)
+                __log(prio, buf.decode(log_enc, errors="replace"))
 
         tasks = [
             asyncio.create_task(