.

wcfs/internal/_wcfs.pyx

@@ -70,6 +70,8 @@ cdef extern from "wcfs_watchlink.h" nogil:
         Tid     at
         string  msg
 
+    error _twlinkwrite(WatchLink wlink, const string& pkt)
+
 
 cdef extern from "wcfs.h" nogil:
     cppclass WCFS:
@@ -175,6 +177,13 @@ cdef class PyPinReq:
             return pypin.pinreq.msg
 
 
+def _tpywlinkwrite(PyWatchLink pywlink, bytes pypkt):
+    cdef string pkt = pypkt
+    with nogil:
+        err = _twlinkwrite_pyexc(pywlink.wlink, pkt)
+    if err != nil:
+        raise RuntimeError(err.Error())     # XXX exc class?
+
 # ---- misc ----
 
 from golang cimport topyexc
@@ -195,3 +204,6 @@ cdef nogil:
 
     pair[string, error] wlink_sendReq_pyexc(WatchLink wlink, context.Context ctx, const string &req)   except +topyexc:
         return wlink.sendReq(ctx, req)
+
+    error _twlinkwrite_pyexc(WatchLink wlink, const string& pkt)    except +topyexc:
+        return _twlinkwrite(wlink, pkt)

wcfs/internal/wcfs_watchlink.cpp

@@ -224,6 +224,9 @@ error _WatchLink::_send(StreamID stream, const string &msg) {
     return wlink->_write(pkt);
 }
 
+error _twlinkwrite(WatchLink wlink, const string &pkt) {
+    return wlink->_write(pkt);
+}
 error _WatchLink::_write(const string &pkt) {
     _WatchLink *wlink = this;
 

wcfs/internal/wcfs_watchlink.h

@@ -113,6 +113,8 @@ private:
     error _send(StreamID stream, const string &msg);
     error _write(const string &pkt);
     tuple<chan<rxPkt>, error> _sendReq(context::Context ctx, const string &req);
+
+    friend error _twlinkwrite(WatchLink wlink, const string &pkt);
 };
 
 // PinReq represents 1 server-initiated wcfs pin request received over /head/watch link.
@@ -126,4 +128,7 @@ struct PinReq {
 };
 
 
+// for testing
+error _twlinkwrite(WatchLink wlink, const string &pkt);
+
 #endif

wcfs/wcfs_test.py

@@ -52,6 +52,7 @@ import pytest; xfail = pytest.mark.xfail
 from pytest import raises, fail
 from six import reraise
 from .internal import io, mm
+from .internal._wcfs import _tpywlinkwrite as _twlinkwrite
 from .internal.wcfs_test import _tDB, read_nogil, install_sigbus_trap, fadvise_dontneed
 
 # XXX `py.test -v` -> WENDELIN_CORE_WCFS_OPTIONS += -v=1?
@@ -1240,7 +1241,7 @@ def test_wcfs_watch_robust():
 
     # invalid request not following frame structure -> fatal + wcfs must close watch link
     assert wl.fatalv == []
-    wl._write(b'zzz hello\n')
+    _twlinkwrite(wl, b'zzz hello\n')
     _, _rx = select(
         timeout().done().recv,
         wl.rx_eof.recv,