python tests: add msg() utility function (#562)

Most tests need to send a request, process it, then retrieve the reply.
Add a utility function to avoid lots of tedious boilerplate.

Signed-off-by: John Levon <john.levon@nutanix.com>
Reviewed-by: Thanos Makatos <thanos.makatos@nutanix.com>

9 files changed, 98 insertions, 271 deletions

diff --git a/test/py/libvfio_user.py b/test/py/libvfio_user.py
index 1105fb5..f0fc568 100644
--- a/test/py/libvfio_user.py
+++ b/test/py/libvfio_user.py
@@ -486,6 +486,19 @@ def get_reply(sock, expect=0):
     assert errno == expect
     return buf[16:]
 
+def msg(ctx, sock, cmd, payload, expect=0, fds=None):
+    """Round trip a request and reply to the server."""
+    hdr = vfio_user_header(cmd, size=len(payload))
+
+    if fds:
+        sock.sendmsg([hdr + payload], [(socket.SOL_SOCKET, socket.SCM_RIGHTS,
+                                        struct.pack("I" * len(fds), *fds))])
+    else:
+        sock.send(hdr + payload)
+
+    vfu_run_ctx(ctx)
+    return get_reply(sock, expect=expect)
+
 def get_pci_header(ctx):
     ptr = lib.vfu_pci_get_config_space(ctx)
     return c.cast(ptr, c.POINTER(vfu_pci_hdr_t)).contents
diff --git a/test/py/test_device_get_info.py b/test/py/test_device_get_info.py
index a778604..ea9251b 100644
--- a/test/py/test_device_get_info.py
+++ b/test/py/test_device_get_info.py
@@ -52,28 +52,19 @@ def test_device_get_info():
 
     payload = struct.pack("II", 0, 0)
 
-    hdr = vfio_user_header(VFIO_USER_DEVICE_GET_INFO, size=len(payload))
-    sock.send(hdr + payload)
-    vfu_run_ctx(ctx)
-    get_reply(sock, expect=errno.EINVAL)
+    msg(ctx, sock, VFIO_USER_DEVICE_GET_INFO, payload, expect=errno.EINVAL)
 
     # bad argsz
 
     payload = vfio_user_device_info(argsz=8, flags=0, num_regions=0, num_irqs=0)
 
-    hdr = vfio_user_header(VFIO_USER_DEVICE_GET_INFO, size=len(payload))
-    sock.send(hdr + payload)
-    vfu_run_ctx(ctx)
-    get_reply(sock, expect=errno.EINVAL)
+    msg(ctx, sock, VFIO_USER_DEVICE_GET_INFO, payload, expect=errno.EINVAL)
 
     # valid with larger argsz
 
     payload = vfio_user_device_info(argsz=32, flags=0, num_regions=0, num_irqs=0)
 
-    hdr = vfio_user_header(VFIO_USER_DEVICE_GET_INFO, size=len(payload))
-    sock.send(hdr + payload)
-    vfu_run_ctx(ctx)
-    result = get_reply(sock)
+    result = msg(ctx, sock, VFIO_USER_DEVICE_GET_INFO, payload)
 
     (argsz, flags, num_regions, num_irqs) = struct.unpack("IIII", result)
 
diff --git a/test/py/test_device_get_irq_info.py b/test/py/test_device_get_irq_info.py
index 8283083..4d6b3d7 100644
--- a/test/py/test_device_get_irq_info.py
+++ b/test/py/test_device_get_irq_info.py
@@ -59,28 +59,19 @@ def test_device_get_irq_info_setup():
 def test_device_get_irq_info_bad_in():
     payload = struct.pack("II", 0, 0)
 
-    hdr = vfio_user_header(VFIO_USER_DEVICE_GET_IRQ_INFO, size=len(payload))
-    sock.send(hdr + payload)
-    vfu_run_ctx(ctx)
-    get_reply(sock, expect=errno.EINVAL)
+    msg(ctx, sock, VFIO_USER_DEVICE_GET_IRQ_INFO, payload, expect=errno.EINVAL)
 
     # bad argsz
     payload = vfio_irq_info(argsz=8, flags=0, index=VFU_DEV_REQ_IRQ,
                             count=0)
 
-    hdr = vfio_user_header(VFIO_USER_DEVICE_GET_IRQ_INFO, size=len(payload))
-    sock.send(hdr + payload)
-    vfu_run_ctx(ctx)
-    get_reply(sock, expect=errno.EINVAL)
+    msg(ctx, sock, VFIO_USER_DEVICE_GET_IRQ_INFO, payload, expect=errno.EINVAL)
 
     # bad index
     payload = vfio_irq_info(argsz=argsz, flags=0, index=VFU_DEV_NUM_IRQS,
                             count=0)
 
-    hdr = vfio_user_header(VFIO_USER_DEVICE_GET_IRQ_INFO, size=len(payload))
-    sock.send(hdr + payload)
-    vfu_run_ctx(ctx)
-    get_reply(sock, expect=errno.EINVAL)
+    msg(ctx, sock, VFIO_USER_DEVICE_GET_IRQ_INFO, payload, expect=errno.EINVAL)
 
 def test_device_get_irq_info():
 
@@ -89,20 +80,12 @@ def test_device_get_irq_info():
     payload = vfio_irq_info(argsz=argsz + 16, flags=0, index=VFU_DEV_REQ_IRQ,
                             count=0)
 
-    hdr = vfio_user_header(VFIO_USER_DEVICE_GET_IRQ_INFO, size=len(payload))
-
-    sock.send(hdr + payload)
-    vfu_run_ctx(ctx)
-    get_reply(sock)
+    msg(ctx, sock, VFIO_USER_DEVICE_GET_IRQ_INFO, payload)
 
     payload = vfio_irq_info(argsz=argsz, flags=0, index=VFU_DEV_REQ_IRQ,
                             count=0)
 
-    hdr = vfio_user_header(VFIO_USER_DEVICE_GET_IRQ_INFO, size=len(payload))
-
-    sock.send(hdr + payload)
-    vfu_run_ctx(ctx)
-    result = get_reply(sock)
+    result = msg(ctx, sock, VFIO_USER_DEVICE_GET_IRQ_INFO, payload)
 
     info, _ = vfio_irq_info.pop_from_buffer(result)
 
@@ -114,11 +97,7 @@ def test_device_get_irq_info():
     payload = vfio_irq_info(argsz=argsz, flags=0, index=VFU_DEV_ERR_IRQ,
                             count=0)
 
-    hdr = vfio_user_header(VFIO_USER_DEVICE_GET_IRQ_INFO, size=len(payload))
-
-    sock.send(hdr + payload)
-    vfu_run_ctx(ctx)
-    result = get_reply(sock)
+    result = msg(ctx, sock, VFIO_USER_DEVICE_GET_IRQ_INFO, payload)
 
     info, _ = vfio_irq_info.pop_from_buffer(result)
 
@@ -130,11 +109,7 @@ def test_device_get_irq_info():
     payload = vfio_irq_info(argsz=argsz, flags=0, index=VFU_DEV_MSIX_IRQ,
                             count=0)
 
-    hdr = vfio_user_header(VFIO_USER_DEVICE_GET_IRQ_INFO, size=len(payload))
-
-    sock.send(hdr + payload)
-    vfu_run_ctx(ctx)
-    result = get_reply(sock)
+    result = msg(ctx, sock, VFIO_USER_DEVICE_GET_IRQ_INFO, payload)
 
     info, _ = vfio_irq_info.pop_from_buffer(result)
 
diff --git a/test/py/test_device_get_region_info.py b/test/py/test_device_get_region_info.py
index 4209cfb..710efd8 100644
--- a/test/py/test_device_get_region_info.py
+++ b/test/py/test_device_get_region_info.py
@@ -76,10 +76,8 @@ def test_device_get_region_info_short_write():
 
     payload = struct.pack("II", 0, 0)
 
-    hdr = vfio_user_header(VFIO_USER_DEVICE_GET_REGION_INFO, size=len(payload))
-    sock.send(hdr + payload)
-    vfu_run_ctx(ctx)
-    get_reply(sock, expect=errno.EINVAL)
+    msg(ctx, sock, VFIO_USER_DEVICE_GET_REGION_INFO, payload,
+        expect=errno.EINVAL)
 
 def test_device_get_region_info_bad_argsz():
 
@@ -87,10 +85,8 @@ def test_device_get_region_info_bad_argsz():
                                index=VFU_PCI_DEV_BAR1_REGION_IDX, cap_offset=0,
                                size=0, offset=0)
 
-    hdr = vfio_user_header(VFIO_USER_DEVICE_GET_REGION_INFO, size=len(payload))
-    sock.send(hdr + payload)
-    vfu_run_ctx(ctx)
-    get_reply(sock, expect=errno.EINVAL)
+    msg(ctx, sock, VFIO_USER_DEVICE_GET_REGION_INFO, payload,
+        expect=errno.EINVAL)
 
 def test_device_get_region_info_bad_index():
 
@@ -98,10 +94,8 @@ def test_device_get_region_info_bad_index():
                                index=VFU_PCI_DEV_NUM_REGIONS, cap_offset=0,
                                size=0, offset=0)
 
-    hdr = vfio_user_header(VFIO_USER_DEVICE_GET_REGION_INFO, size=len(payload))
-    sock.send(hdr + payload)
-    vfu_run_ctx(ctx)
-    get_reply(sock, expect=errno.EINVAL)
+    msg(ctx, sock, VFIO_USER_DEVICE_GET_REGION_INFO, payload,
+        expect=errno.EINVAL)
 
 def test_device_get_region_info_larger_argsz():
 
@@ -109,10 +103,7 @@ def test_device_get_region_info_larger_argsz():
                           index=VFU_PCI_DEV_BAR1_REGION_IDX, cap_offset=0,
                           size=0, offset=0)
 
-    hdr = vfio_user_header(VFIO_USER_DEVICE_GET_REGION_INFO, size=len(payload))
-    sock.send(hdr + payload)
-    vfu_run_ctx(ctx)
-    result = get_reply(sock)
+    result = msg(ctx, sock, VFIO_USER_DEVICE_GET_REGION_INFO, payload)
 
     assert(len(result) == argsz)
 
@@ -133,10 +124,7 @@ def test_device_get_region_info_small_argsz_caps():
                           index=VFU_PCI_DEV_BAR2_REGION_IDX, cap_offset=0,
                           size=0, offset=0)
 
-    hdr = vfio_user_header(VFIO_USER_DEVICE_GET_REGION_INFO, size=len(payload))
-    sock.send(hdr + payload)
-    vfu_run_ctx(ctx)
-    result = get_reply(sock)
+    result = msg(ctx, sock, VFIO_USER_DEVICE_GET_REGION_INFO, payload)
 
     info, _ = vfio_region_info.pop_from_buffer(result)
 
@@ -163,10 +151,7 @@ def test_device_get_region_info_caps():
                           size=0, offset=0)
     payload = bytes(payload) + b'\0' * (80 - 32)
 
-    hdr = vfio_user_header(VFIO_USER_DEVICE_GET_REGION_INFO, size=len(payload))
-    sock.send(hdr + payload)
-    vfu_run_ctx(ctx)
-    result = get_reply(sock)
+    result = msg(ctx, sock, VFIO_USER_DEVICE_GET_REGION_INFO, payload)
 
     info, result = vfio_region_info.pop_from_buffer(result)
     cap, result = vfio_region_info_cap_sparse_mmap.pop_from_buffer(result)
@@ -201,10 +186,7 @@ def test_device_get_region_info_migr():
                           size=0, offset=0)
     payload = bytes(payload) + b'\0' * (80 - 32)
 
-    hdr = vfio_user_header(VFIO_USER_DEVICE_GET_REGION_INFO, size=len(payload))
-    sock.send(hdr + payload)
-    vfu_run_ctx(ctx)
-    result = get_reply(sock)
+    result = msg(ctx, sock, VFIO_USER_DEVICE_GET_REGION_INFO, payload)
 
     info, result = vfio_region_info.pop_from_buffer(result)
     mcap, result = vfio_region_info_cap_type.pop_from_buffer(result)
diff --git a/test/py/test_device_set_irqs.py b/test/py/test_device_set_irqs.py
index ebc3768..a958db3 100644
--- a/test/py/test_device_set_irqs.py
+++ b/test/py/test_device_set_irqs.py
@@ -68,120 +68,84 @@ def test_device_set_irqs_no_irq_set():
 def test_device_set_irqs_short_write():
     payload = struct.pack("II", 0, 0)
 
-    hdr = vfio_user_header(VFIO_USER_DEVICE_SET_IRQS, size=len(payload))
-    sock.send(hdr + payload)
-    vfu_run_ctx(ctx)
-    get_reply(sock, expect=errno.EINVAL)
+    msg(ctx, sock, VFIO_USER_DEVICE_SET_IRQS, payload, expect=errno.EINVAL)
 
 def test_device_set_irqs_bad_argsz():
     payload = vfio_irq_set(argsz=3, flags=VFIO_IRQ_SET_ACTION_TRIGGER |
                            VFIO_IRQ_SET_DATA_NONE, index=VFU_DEV_REQ_IRQ,
                            start=0, count=0)
 
-    hdr = vfio_user_header(VFIO_USER_DEVICE_SET_IRQS, size=len(payload))
-    sock.send(hdr + payload)
-    vfu_run_ctx(ctx)
-    get_reply(sock, expect=errno.EINVAL)
+    msg(ctx, sock, VFIO_USER_DEVICE_SET_IRQS, payload, expect=errno.EINVAL)
 
 def test_device_set_irqs_bad_index():
     payload = vfio_irq_set(argsz=argsz, flags=VFIO_IRQ_SET_ACTION_TRIGGER |
                            VFIO_IRQ_SET_DATA_NONE, index=VFU_DEV_NUM_IRQS,
                            start=0, count=0)
 
-    hdr = vfio_user_header(VFIO_USER_DEVICE_SET_IRQS, size=len(payload))
-    sock.send(hdr + payload)
-    vfu_run_ctx(ctx)
-    get_reply(sock, expect=errno.EINVAL)
+    msg(ctx, sock, VFIO_USER_DEVICE_SET_IRQS, payload, expect=errno.EINVAL)
 
 def test_device_set_irqs_bad_flags_MASK_and_UNMASK():
     payload = vfio_irq_set(argsz=argsz, flags=VFIO_IRQ_SET_ACTION_MASK |
                            VFIO_IRQ_SET_ACTION_UNMASK, index=VFU_DEV_MSIX_IRQ,
                            start=0, count=0)
 
-    hdr = vfio_user_header(VFIO_USER_DEVICE_SET_IRQS, size=len(payload))
-    sock.send(hdr + payload)
-    vfu_run_ctx(ctx)
-    get_reply(sock, expect=errno.EINVAL)
+    msg(ctx, sock, VFIO_USER_DEVICE_SET_IRQS, payload, expect=errno.EINVAL)
 
 def test_device_set_irqs_bad_flags_DATA_NONE_and_DATA_BOOL():
     payload = vfio_irq_set(argsz=argsz, flags=VFIO_IRQ_SET_ACTION_MASK |
                            VFIO_IRQ_SET_DATA_NONE | VFIO_IRQ_SET_DATA_BOOL,
                            index=VFU_DEV_MSIX_IRQ, start=0, count=0)
 
-    hdr = vfio_user_header(VFIO_USER_DEVICE_SET_IRQS, size=len(payload))
-    sock.send(hdr + payload)
-    vfu_run_ctx(ctx)
-    get_reply(sock, expect=errno.EINVAL)
+    msg(ctx, sock, VFIO_USER_DEVICE_SET_IRQS, payload, expect=errno.EINVAL)
 
 def test_device_set_irqs_bad_start_count_range():
     payload = vfio_irq_set(argsz=argsz, flags=VFIO_IRQ_SET_ACTION_MASK |
                            VFIO_IRQ_SET_DATA_NONE, index=VFU_DEV_MSIX_IRQ,
                            start=2047, count=2)
 
-    hdr = vfio_user_header(VFIO_USER_DEVICE_SET_IRQS, size=len(payload))
-    sock.send(hdr + payload)
-    vfu_run_ctx(ctx)
-    get_reply(sock, expect=errno.EINVAL)
+    msg(ctx, sock, VFIO_USER_DEVICE_SET_IRQS, payload, expect=errno.EINVAL)
 
 def test_device_set_irqs_bad_start_count_range():
     payload = vfio_irq_set(argsz=argsz, flags=VFIO_IRQ_SET_ACTION_MASK |
                            VFIO_IRQ_SET_DATA_NONE, index=VFU_DEV_MSIX_IRQ,
                            start=2049, count=1)
 
-    hdr = vfio_user_header(VFIO_USER_DEVICE_SET_IRQS, size=len(payload))
-    sock.send(hdr + payload)
-    vfu_run_ctx(ctx)
-    get_reply(sock, expect=errno.EINVAL)
+    msg(ctx, sock, VFIO_USER_DEVICE_SET_IRQS, payload, expect=errno.EINVAL)
 
 def test_device_set_irqs_bad_action_for_err_irq():
     payload = vfio_irq_set(argsz=argsz, flags=VFIO_IRQ_SET_ACTION_MASK |
                            VFIO_IRQ_SET_DATA_NONE, index=VFU_DEV_ERR_IRQ,
                            start=0, count=1)
 
-    hdr = vfio_user_header(VFIO_USER_DEVICE_SET_IRQS, size=len(payload))
-    sock.send(hdr + payload)
-    vfu_run_ctx(ctx)
-    get_reply(sock, expect=errno.EINVAL)
+    msg(ctx, sock, VFIO_USER_DEVICE_SET_IRQS, payload, expect=errno.EINVAL)
 
 def test_device_set_irqs_bad_action_for_req_irq():
     payload = vfio_irq_set(argsz=argsz, flags=VFIO_IRQ_SET_ACTION_MASK |
                            VFIO_IRQ_SET_DATA_NONE, index=VFU_DEV_REQ_IRQ,
                            start=0, count=1)
 
-    hdr = vfio_user_header(VFIO_USER_DEVICE_SET_IRQS, size=len(payload))
-    sock.send(hdr + payload)
-    vfu_run_ctx(ctx)
-    get_reply(sock, expect=errno.EINVAL)
+    msg(ctx, sock, VFIO_USER_DEVICE_SET_IRQS, payload, expect=errno.EINVAL)
 
 def test_device_set_irqs_bad_start_for_count_0():
     payload = vfio_irq_set(argsz=argsz, flags=VFIO_IRQ_SET_ACTION_MASK |
                            VFIO_IRQ_SET_DATA_NONE, index=VFU_DEV_MSIX_IRQ,
                            start=1, count=0)
 
-    hdr = vfio_user_header(VFIO_USER_DEVICE_SET_IRQS, size=len(payload))
-    sock.send(hdr + payload)
-    vfu_run_ctx(ctx)
-    get_reply(sock, expect=errno.EINVAL)
+    msg(ctx, sock, VFIO_USER_DEVICE_SET_IRQS, payload, expect=errno.EINVAL)
 
 def test_device_set_irqs_bad_action_for_count_0():
     payload = vfio_irq_set(argsz=argsz, flags=VFIO_IRQ_SET_ACTION_MASK |
                            VFIO_IRQ_SET_DATA_NONE, index=VFU_DEV_MSIX_IRQ,
                            start=0, count=0)
 
-    hdr = vfio_user_header(VFIO_USER_DEVICE_SET_IRQS, size=len(payload))
-    sock.send(hdr + payload)
-    vfu_run_ctx(ctx)
-    get_reply(sock, expect=errno.EINVAL)
+    msg(ctx, sock, VFIO_USER_DEVICE_SET_IRQS, payload, expect=errno.EINVAL)
 
 def test_device_set_irqs_bad_action_and_data_type_for_count_0():
     payload = vfio_irq_set(argsz=argsz, flags=VFIO_IRQ_SET_ACTION_TRIGGER |
                            VFIO_IRQ_SET_DATA_BOOL, index=VFU_DEV_MSIX_IRQ,
                            start=0, count=0)
 
-    hdr = vfio_user_header(VFIO_USER_DEVICE_SET_IRQS, size=len(payload))
-    sock.send(hdr + payload)
-    vfu_run_ctx(ctx)
-    get_reply(sock, expect=errno.EINVAL)
+    msg(ctx, sock, VFIO_USER_DEVICE_SET_IRQS, payload, expect=errno.EINVAL)
 
 def test_device_set_irqs_bad_fds_for_DATA_BOOL():
     payload = vfio_irq_set(argsz=argsz, flags=VFIO_IRQ_SET_ACTION_TRIGGER |
@@ -192,11 +156,8 @@ def test_device_set_irqs_bad_fds_for_DATA_BOOL():
 
     fd = eventfd()
 
-    hdr = vfio_user_header(VFIO_USER_DEVICE_SET_IRQS, size=len(payload))
-    sock.sendmsg([hdr + payload], [(socket.SOL_SOCKET, socket.SCM_RIGHTS,
-                 struct.pack("I", fd))])
-    vfu_run_ctx(ctx)
-    get_reply(sock, expect=errno.EINVAL)
+    msg(ctx, sock, VFIO_USER_DEVICE_SET_IRQS, payload, expect=errno.EINVAL,
+        fds=[fd])
 
     os.close(fd)
 
@@ -207,11 +168,8 @@ def test_device_set_irqs_bad_fds_for_DATA_NONE():
 
     fd = eventfd()
 
-    hdr = vfio_user_header(VFIO_USER_DEVICE_SET_IRQS, size=len(payload))
-    sock.sendmsg([hdr + payload], [(socket.SOL_SOCKET, socket.SCM_RIGHTS,
-                 struct.pack("I", fd))])
-    vfu_run_ctx(ctx)
-    get_reply(sock, expect=errno.EINVAL)
+    msg(ctx, sock, VFIO_USER_DEVICE_SET_IRQS, payload, expect=errno.EINVAL,
+        fds=[fd])
 
     os.close(fd)
 
@@ -222,11 +180,8 @@ def test_device_set_irqs_bad_fds_for_count_2():
 
     fd = eventfd()
 
-    hdr = vfio_user_header(VFIO_USER_DEVICE_SET_IRQS, size=len(payload))
-    sock.sendmsg([hdr + payload], [(socket.SOL_SOCKET, socket.SCM_RIGHTS,
-                 struct.pack("I", fd))])
-    vfu_run_ctx(ctx)
-    get_reply(sock, expect=errno.EINVAL)
+    msg(ctx, sock, VFIO_USER_DEVICE_SET_IRQS, payload, expect=errno.EINVAL,
+        fds=[fd])
 
     os.close(fd)
 
@@ -235,19 +190,13 @@ def test_device_set_irqs_disable():
                            VFIO_IRQ_SET_DATA_NONE, index=VFU_DEV_REQ_IRQ,
                            start=0, count=0)
 
-    hdr = vfio_user_header(VFIO_USER_DEVICE_SET_IRQS, size=len(payload))
-    sock.send(hdr + payload)
-    vfu_run_ctx(ctx)
-    get_reply(sock)
+    msg(ctx, sock, VFIO_USER_DEVICE_SET_IRQS, payload)
 
     payload = vfio_irq_set(argsz=argsz, flags=VFIO_IRQ_SET_ACTION_TRIGGER |
                            VFIO_IRQ_SET_DATA_EVENTFD, index=VFU_DEV_REQ_IRQ,
                            start=0, count=1)
 
-    hdr = vfio_user_header(VFIO_USER_DEVICE_SET_IRQS, size=len(payload))
-    sock.send(hdr + payload)
-    vfu_run_ctx(ctx)
-    get_reply(sock)
+    msg(ctx, sock, VFIO_USER_DEVICE_SET_IRQS, payload)
 
 def test_device_set_irqs_enable():
     payload = vfio_irq_set(argsz=argsz, flags=VFIO_IRQ_SET_ACTION_TRIGGER |
@@ -256,11 +205,7 @@ def test_device_set_irqs_enable():
 
     fd = eventfd()
 
-    hdr = vfio_user_header(VFIO_USER_DEVICE_SET_IRQS, size=len(payload))
-    sock.sendmsg([hdr + payload], [(socket.SOL_SOCKET, socket.SCM_RIGHTS,
-                 struct.pack("I", fd))])
-    vfu_run_ctx(ctx)
-    get_reply(sock)
+    msg(ctx, sock, VFIO_USER_DEVICE_SET_IRQS, payload, fds=[fd])
 
 def test_device_set_irqs_trigger_bool_too_small():
     payload = vfio_irq_set(argsz=argsz + 1, flags=VFIO_IRQ_SET_ACTION_TRIGGER |
@@ -268,10 +213,7 @@ def test_device_set_irqs_trigger_bool_too_small():
                            start=0, count=2)
     payload = bytes(payload) + struct.pack("?", False)
 
-    hdr = vfio_user_header(VFIO_USER_DEVICE_SET_IRQS, size=len(payload))
-    sock.send(hdr + payload)
-    vfu_run_ctx(ctx)
-    get_reply(sock, expect=errno.EINVAL)
+    msg(ctx, sock, VFIO_USER_DEVICE_SET_IRQS, payload, expect=errno.EINVAL)
 
 def test_device_set_irqs_trigger_bool_too_large():
     payload = vfio_irq_set(argsz=argsz + 3, flags=VFIO_IRQ_SET_ACTION_TRIGGER |
@@ -279,10 +221,7 @@ def test_device_set_irqs_trigger_bool_too_large():
                            start=0, count=2)
     payload = bytes(payload) + struct.pack("???", False, False, False)
 
-    hdr = vfio_user_header(VFIO_USER_DEVICE_SET_IRQS, size=len(payload))
-    sock.send(hdr + payload)
-    vfu_run_ctx(ctx)
-    get_reply(sock, expect=errno.EINVAL)
+    msg(ctx, sock, VFIO_USER_DEVICE_SET_IRQS, payload, expect=errno.EINVAL)
 
 def test_device_set_irqs_enable_update():
     payload = vfio_irq_set(argsz=argsz, flags=VFIO_IRQ_SET_ACTION_TRIGGER |
@@ -291,11 +230,7 @@ def test_device_set_irqs_enable_update():
 
     fd = eventfd()
 
-    hdr = vfio_user_header(VFIO_USER_DEVICE_SET_IRQS, size=len(payload))
-    sock.sendmsg([hdr + payload], [(socket.SOL_SOCKET, socket.SCM_RIGHTS,
-                 struct.pack("I", fd))])
-    vfu_run_ctx(ctx)
-    get_reply(sock)
+    msg(ctx, sock, VFIO_USER_DEVICE_SET_IRQS, payload, fds=[fd])
 
 def test_device_set_irqs_enable_trigger_none():
     payload = vfio_irq_set(argsz=argsz, flags=VFIO_IRQ_SET_ACTION_TRIGGER |
@@ -305,20 +240,13 @@ def test_device_set_irqs_enable_trigger_none():
     fd1 = eventfd(initval=4)
     fd2 = eventfd(initval=8)
 
-    hdr = vfio_user_header(VFIO_USER_DEVICE_SET_IRQS, size=len(payload))
-    sock.sendmsg([hdr + payload], [(socket.SOL_SOCKET, socket.SCM_RIGHTS,
-                 struct.pack("II", fd1, fd2))])
-    vfu_run_ctx(ctx)
-    get_reply(sock)
+    msg(ctx, sock, VFIO_USER_DEVICE_SET_IRQS, payload, fds=[fd1, fd2])
 
     payload = vfio_irq_set(argsz=argsz, flags=VFIO_IRQ_SET_ACTION_TRIGGER |
                            VFIO_IRQ_SET_DATA_NONE, index=VFU_DEV_MSIX_IRQ,
                            start=1, count=1)
 
-    hdr = vfio_user_header(VFIO_USER_DEVICE_SET_IRQS, size=len(payload))
-    sock.send(hdr + payload)
-    vfu_run_ctx(ctx)
-    get_reply(sock)
+    msg(ctx, sock, VFIO_USER_DEVICE_SET_IRQS, payload)
 
     assert struct.unpack("Q", os.read(fd1, 8))[0] == 4
     assert struct.unpack("Q", os.read(fd2, 8))[0] == 9
@@ -331,21 +259,14 @@ def test_device_set_irqs_enable_trigger_bool():
     fd1 = eventfd(initval=4)
     fd2 = eventfd(initval=8)
 
-    hdr = vfio_user_header(VFIO_USER_DEVICE_SET_IRQS, size=len(payload))
-    sock.sendmsg([hdr + payload], [(socket.SOL_SOCKET, socket.SCM_RIGHTS,
-                 struct.pack("II", fd1, fd2))])
-    vfu_run_ctx(ctx)
-    get_reply(sock)
+    msg(ctx, sock, VFIO_USER_DEVICE_SET_IRQS, payload, fds=[fd1, fd2])
 
     payload = vfio_irq_set(argsz=argsz + 2, flags=VFIO_IRQ_SET_ACTION_TRIGGER |
                            VFIO_IRQ_SET_DATA_BOOL, index=VFU_DEV_MSIX_IRQ,
                            start=0, count=2)
     payload = bytes(payload) + struct.pack("??", False, True)
 
-    hdr = vfio_user_header(VFIO_USER_DEVICE_SET_IRQS, size=len(payload))
-    sock.send(hdr + payload)
-    vfu_run_ctx(ctx)
-    get_reply(sock)
+    msg(ctx, sock, VFIO_USER_DEVICE_SET_IRQS, payload)
 
     assert struct.unpack("Q", os.read(fd1, 8))[0] == 4
     assert struct.unpack("Q", os.read(fd2, 8))[0] == 9
diff --git a/test/py/test_dirty_pages.py b/test/py/test_dirty_pages.py
index 25a73da..193e694 100644
--- a/test/py/test_dirty_pages.py
+++ b/test/py/test_dirty_pages.py
@@ -77,38 +77,24 @@ def test_dirty_pages_setup():
         flags=(VFIO_USER_F_DMA_REGION_READ | VFIO_USER_F_DMA_REGION_WRITE),
         offset=0, addr=0x10000, size=0x10000)
 
-    hdr = vfio_user_header(VFIO_USER_DMA_MAP, size=len(payload))
-
-    sock.sendmsg([hdr + payload], [(socket.SOL_SOCKET, socket.SCM_RIGHTS,
-                 struct.pack("I", f.fileno()))])
-    vfu_run_ctx(ctx)
-    get_reply(sock)
+    msg(ctx, sock, VFIO_USER_DMA_MAP, payload, fds=[f.fileno()])
 
 def test_dirty_pages_short_write():
     payload = struct.pack("I", 8)
 
-    hdr = vfio_user_header(VFIO_USER_DIRTY_PAGES, size=len(payload))
-    sock.send(hdr + payload)
-    vfu_run_ctx(ctx)
-    get_reply(sock, expect=errno.EINVAL)
+    msg(ctx, sock, VFIO_USER_DIRTY_PAGES, payload, expect=errno.EINVAL)
 
 def test_dirty_pages_bad_argsz():
     payload = vfio_user_dirty_pages(argsz=4,
         flags=VFIO_IOMMU_DIRTY_PAGES_FLAG_START)
 
-    hdr = vfio_user_header(VFIO_USER_DIRTY_PAGES, size=len(payload))
-    sock.send(hdr + payload)
-    vfu_run_ctx(ctx)
-    get_reply(sock, expect=errno.EINVAL)
+    msg(ctx, sock, VFIO_USER_DIRTY_PAGES, payload, expect=errno.EINVAL)
 
 def test_dirty_pages_start_no_migration():
     payload = vfio_user_dirty_pages(argsz=len(vfio_user_dirty_pages()),
         flags=VFIO_IOMMU_DIRTY_PAGES_FLAG_START)
 
-    hdr = vfio_user_header(VFIO_USER_DIRTY_PAGES, size=len(payload))
-    sock.send(hdr + payload)
-    vfu_run_ctx(ctx)
-    get_reply(sock, expect=errno.ENOTSUP)
+    msg(ctx, sock, VFIO_USER_DIRTY_PAGES, payload, expect=errno.ENOTSUP)
 
 def test_dirty_pages_start_bad_flags():
     #
@@ -121,44 +107,31 @@ def test_dirty_pages_start_bad_flags():
         flags=(VFIO_IOMMU_DIRTY_PAGES_FLAG_START |
                VFIO_IOMMU_DIRTY_PAGES_FLAG_STOP))
 
-    hdr = vfio_user_header(VFIO_USER_DIRTY_PAGES, size=len(payload))
-    sock.send(hdr + payload)
-    vfu_run_ctx(ctx)
-    get_reply(sock, expect=errno.EINVAL)
+    msg(ctx, sock, VFIO_USER_DIRTY_PAGES, payload, expect=errno.EINVAL)
 
     payload = vfio_user_dirty_pages(argsz=len(vfio_user_dirty_pages()),
         flags=(VFIO_IOMMU_DIRTY_PAGES_FLAG_START |
                VFIO_IOMMU_DIRTY_PAGES_FLAG_GET_BITMAP))
 
-    hdr = vfio_user_header(VFIO_USER_DIRTY_PAGES, size=len(payload))
-    sock.send(hdr + payload)
-    vfu_run_ctx(ctx)
-    get_reply(sock, expect=errno.EINVAL)
+    msg(ctx, sock, VFIO_USER_DIRTY_PAGES, payload, expect=errno.EINVAL)
 
 
 def start_logging():
     payload = vfio_user_dirty_pages(argsz=len(vfio_user_dirty_pages()),
                                     flags=VFIO_IOMMU_DIRTY_PAGES_FLAG_START)
 
-    hdr = vfio_user_header(VFIO_USER_DIRTY_PAGES, size=len(payload))
-    sock.send(hdr + payload)
-    vfu_run_ctx(ctx)
-    get_reply(sock)
-
+    msg(ctx, sock, VFIO_USER_DIRTY_PAGES, payload)
 
 def test_dirty_pages_start():
     start_logging()
-    start_logging() # should be idempotent
-
+    # should be idempotent
+    start_logging()
 
 def test_dirty_pages_get_short_read():
     payload = vfio_user_dirty_pages(argsz=len(vfio_user_dirty_pages()),
         flags=VFIO_IOMMU_DIRTY_PAGES_FLAG_GET_BITMAP)
 
-    hdr = vfio_user_header(VFIO_USER_DIRTY_PAGES, size=len(payload))
-    sock.send(hdr + payload)
-    vfu_run_ctx(ctx)
-    get_reply(sock, expect=errno.EINVAL)
+    msg(ctx, sock, VFIO_USER_DIRTY_PAGES, payload, expect=errno.EINVAL)
 
 #
 # This should in fact work; update when it does.
@@ -170,11 +143,9 @@ def test_dirty_pages_get_sub_range():
     bitmap = vfio_user_bitmap(pgsize=0x1000, size=8)
     br = vfio_user_bitmap_range(iova=0x11000, size=0x1000, bitmap=bitmap)
 
-    hdr = vfio_user_header(VFIO_USER_DIRTY_PAGES,
-                           size=len(dirty_pages) + len(br))
-    sock.send(hdr + dirty_pages + br)
-    vfu_run_ctx(ctx)
-    get_reply(sock, expect=errno.ENOTSUP)
+    payload = bytes(dirty_pages) + bytes(br)
+
+    msg(ctx, sock, VFIO_USER_DIRTY_PAGES, payload, expect=errno.ENOTSUP)
 
 def test_dirty_pages_get_bad_page_size():
     argsz = len(vfio_user_dirty_pages()) + len(vfio_user_bitmap_range()) + 8
@@ -183,11 +154,9 @@ def test_dirty_pages_get_bad_page_size():
     bitmap = vfio_user_bitmap(pgsize=0x2000, size=8)
     br = vfio_user_bitmap_range(iova=0x10000, size=0x10000, bitmap=bitmap)
 
-    hdr = vfio_user_header(VFIO_USER_DIRTY_PAGES,
-                           size=len(dirty_pages) + len(br))
-    sock.send(hdr + dirty_pages + br)
-    vfu_run_ctx(ctx)
-    get_reply(sock, expect=errno.EINVAL)
+    payload = bytes(dirty_pages) + bytes(br)
+
+    msg(ctx, sock, VFIO_USER_DIRTY_PAGES, payload, expect=errno.EINVAL)
 
 def test_dirty_pages_get_bad_bitmap_size():
     argsz = len(vfio_user_dirty_pages()) + len(vfio_user_bitmap_range()) + 8
@@ -196,11 +165,9 @@ def test_dirty_pages_get_bad_bitmap_size():
     bitmap = vfio_user_bitmap(pgsize=0x1000, size=1)
     br = vfio_user_bitmap_range(iova=0x10000, size=0x10000, bitmap=bitmap)
 
-    hdr = vfio_user_header(VFIO_USER_DIRTY_PAGES,
-                           size=len(dirty_pages) + len(br))
-    sock.send(hdr + dirty_pages + br)
-    vfu_run_ctx(ctx)
-    get_reply(sock, expect=errno.EINVAL)
+    payload = bytes(dirty_pages) + bytes(br)
+
+    msg(ctx, sock, VFIO_USER_DIRTY_PAGES, payload, expect=errno.EINVAL)
 
 def test_dirty_pages_get_short_reply():
     dirty_pages = vfio_user_dirty_pages(argsz=len(vfio_user_dirty_pages()),
@@ -208,11 +175,9 @@ def test_dirty_pages_get_short_reply():
     bitmap = vfio_user_bitmap(pgsize=0x1000, size=8)
     br = vfio_user_bitmap_range(iova=0x10000, size=0x10000, bitmap=bitmap)
 
-    hdr = vfio_user_header(VFIO_USER_DIRTY_PAGES,
-                           size=len(dirty_pages) + len(br))
-    sock.send(hdr + dirty_pages + br)
-    vfu_run_ctx(ctx)
-    result = get_reply(sock)
+    payload = bytes(dirty_pages) + bytes(br)
+
+    result = msg(ctx, sock, VFIO_USER_DIRTY_PAGES, payload)
 
     assert len(result) == len(vfio_user_dirty_pages())
 
@@ -231,11 +196,9 @@ def test_dirty_pages_get_unmodified():
     bitmap = vfio_user_bitmap(pgsize=0x1000, size=8)
     br = vfio_user_bitmap_range(iova=0x10000, size=0x10000, bitmap=bitmap)
 
-    hdr = vfio_user_header(VFIO_USER_DIRTY_PAGES,
-                           size=len(dirty_pages) + len(br))
-    sock.send(hdr + dirty_pages + br)
-    vfu_run_ctx(ctx)
-    result = get_reply(sock)
+    payload = bytes(dirty_pages) + bytes(br)
+
+    result = msg(ctx, sock, VFIO_USER_DIRTY_PAGES, payload)
 
     assert len(result) == argsz
 
@@ -261,11 +224,9 @@ def get_dirty_page_bitmap():
     bitmap = vfio_user_bitmap(pgsize=0x1000, size=8)
     br = vfio_user_bitmap_range(iova=0x10000, size=0x10000, bitmap=bitmap)
 
-    hdr = vfio_user_header(VFIO_USER_DIRTY_PAGES,
-                           size=len(dirty_pages) + len(br))
-    sock.send(hdr + dirty_pages + br)
-    vfu_run_ctx(ctx)
-    result = get_reply(sock)
+    payload = bytes(dirty_pages) + bytes(br)
+
+    result = msg(ctx, sock, VFIO_USER_DIRTY_PAGES, payload)
 
     dirty_pages, result = vfio_user_dirty_pages.pop_from_buffer(result)
     br, result = vfio_user_bitmap_range.pop_from_buffer(result)
@@ -312,18 +273,12 @@ def stop_logging():
     payload = vfio_user_dirty_pages(argsz=len(vfio_user_dirty_pages()),
                                     flags=VFIO_IOMMU_DIRTY_PAGES_FLAG_STOP)
 
-    hdr = vfio_user_header(VFIO_USER_DIRTY_PAGES, size=len(payload))
-    sock.send(hdr + payload)
-    vfu_run_ctx(ctx)
-    get_reply(sock)
+    msg(ctx, sock, VFIO_USER_DIRTY_PAGES, payload)
 
     payload = vfio_user_dirty_pages(argsz=len(vfio_user_dirty_pages()),
                                     flags=VFIO_IOMMU_DIRTY_PAGES_FLAG_STOP)
 
-    hdr = vfio_user_header(VFIO_USER_DIRTY_PAGES, size=len(payload))
-    sock.send(hdr + payload)
-    vfu_run_ctx(ctx)
-    get_reply(sock)
+    msg(ctx, sock, VFIO_USER_DIRTY_PAGES, payload)
 
 
 def test_dirty_pages_stop():
diff --git a/test/py/test_dma_map.py b/test/py/test_dma_map.py
index 3358abc..fe48c45 100644
--- a/test/py/test_dma_map.py
+++ b/test/py/test_dma_map.py
@@ -68,11 +68,7 @@ def test_dma_region_too_big():
                VFIO_USER_F_DMA_REGION_WRITE),
         offset=0, addr=0x10000, size=MAX_DMA_SIZE + 4096)
 
-    hdr = vfio_user_header(VFIO_USER_DMA_MAP, size=len(payload))
-
-    sock.send(hdr + payload)
-    vfu_run_ctx(ctx)
-    get_reply(sock, expect=errno.ENOSPC)
+    msg(ctx, sock, VFIO_USER_DMA_MAP, payload, expect=errno.ENOSPC)
 
     disconnect_client(ctx, sock)
 
@@ -85,15 +81,12 @@ def test_dma_region_too_many():
                    VFIO_USER_F_DMA_REGION_WRITE),
             offset=0, addr=0x1000 * i, size=4096)
 
-        hdr = vfio_user_header(VFIO_USER_DMA_MAP, size=len(payload))
-
-        sock.send(hdr + payload)
-        vfu_run_ctx(ctx)
-
         if i == MAX_DMA_REGIONS + 1:
-            get_reply(sock, expect=errno.EINVAL)
+            expect=errno.EINVAL
         else:
-            get_reply(sock)
+            expect=0
+
+        msg(ctx, sock, VFIO_USER_DMA_MAP, payload, expect=expect)
 
     disconnect_client(ctx, sock)
 
diff --git a/test/py/test_irq_trigger.py b/test/py/test_irq_trigger.py
index 422eb3e..02bc90a 100644
--- a/test/py/test_irq_trigger.py
+++ b/test/py/test_irq_trigger.py
@@ -72,11 +72,7 @@ def test_irq_trigger():
 
     fd = eventfd(initval=4)
 
-    hdr = vfio_user_header(VFIO_USER_DEVICE_SET_IRQS, size=len(payload))
-    sock.sendmsg([hdr + payload], [(socket.SOL_SOCKET, socket.SCM_RIGHTS,
-                 struct.pack("I", fd))])
-    vfu_run_ctx(ctx)
-    get_reply(sock)
+    msg(ctx, sock, VFIO_USER_DEVICE_SET_IRQS, payload, fds=[fd])
 
     ret = vfu_irq_trigger(ctx, 8)
 
diff --git a/test/py/test_negotiate.py b/test/py/test_negotiate.py
index a3f2a8a..524f59f 100644
--- a/test/py/test_negotiate.py
+++ b/test/py/test_negotiate.py
@@ -41,6 +41,7 @@ def client_version_json(expect=0, json=''):
 
     payload = struct.pack("HH%dsc" % len(json),
                           LIBVFIO_USER_MAJOR, LIBVFIO_USER_MINOR, json, b'\0')
+
     hdr = vfio_user_header(VFIO_USER_VERSION, size=len(payload))
     sock.send(hdr + payload)
     vfu_attach_ctx(ctx, expect=expect)