diff --git a/src/brei-shared.c b/src/brei-shared.c
index 5426864..e585587 100644
--- a/src/brei-shared.c
+++ b/src/brei-shared.c
@@ -28,8 +28,10 @@
 
 #include "util-mem.h"
 #include "util-io.h"
+#include "util-strings.h"
 
 #include "brei-shared.h"
+#include "brei-proto.h"
 
 struct brei_context {
 	struct object object;
@@ -51,6 +53,59 @@ OBJECT_IMPLEMENT_UNREF_CLEANUP(brei_context);
 OBJECT_IMPLEMENT_SETTER(brei_context, log_func, brei_logfunc_t);
 OBJECT_IMPLEMENT_SETTER(brei_context, log_context, void *);
 
+static void
+brei_result_destroy(struct brei_result *res)
+{
+	free(res->explanation);
+}
+
+static
+OBJECT_IMPLEMENT_CREATE(brei_result);
+OBJECT_IMPLEMENT_GETTER(brei_result, data, void *);
+OBJECT_IMPLEMENT_SETTER(brei_result, data, void *);
+OBJECT_IMPLEMENT_GETTER(brei_result, reason, int);
+OBJECT_IMPLEMENT_GETTER(brei_result, explanation, const char *);
+OBJECT_IMPLEMENT_REF(brei_result);
+OBJECT_IMPLEMENT_UNREF_CLEANUP(brei_result);
+
+struct brei_result *
+brei_result_new(int reason,
+		const char *format,
+		...)
+{
+	struct brei_result *result = brei_result_create(NULL);
+	result->reason = reason;
+	if (format) {
+		va_list args;
+		va_start(args, format);
+		result->explanation = xvaprintf(format, args);
+		va_end(args);
+	} else {
+		assert(reason == 0); /* Any error needs an explanation */
+	}
+	return result;
+}
+
+struct brei_result *
+brei_result_new_success(void *data)
+{
+	struct brei_result *result = brei_result_new(0, NULL);
+
+	result->data = data;
+
+	return result;
+}
+
+struct brei_result *
+brei_result_new_from_neg_errno(int err)
+{
+	if (err >= 0)
+		return NULL;
+
+	return brei_result_new(BREI_CONNECTION_DISCONNECT_REASON_ERROR,
+			       "%s", strerror(-err));
+}
+
 struct brei_context *
 brei_context_new(void *parent_context)
 {
@@ -107,13 +162,14 @@ bytes_to_int32(uint32_t count)
 	return (uint32_t)(((uint64_t)count + 3)/4);
 }
 
-static int
-brei_demarshal(struct brei_context *brei, struct iobuf *buf, const char *signature, union brei_arg **args_out)
+static struct brei_result *
+brei_demarshal(struct brei_context *brei, struct iobuf *buf, const char *signature,
+	       size_t *nargs_out, union brei_arg **args_out)
 {
 	size_t nargs = strlen(signature);
 	if (nargs > 256) {
-		log_bug(brei, "Too many arguments in signature (%zu)", nargs);
-		return -EPROTO;
+		return brei_result_new(BREI_CONNECTION_DISCONNECT_REASON_ERROR,
+				       "Too many arguments in signature (%zu)", nargs);
 	}
 
 	/* This over-allocates if we have more than one char per type but meh */
@@ -146,16 +202,16 @@ brei_demarshal(struct brei_context *brei, struct iobuf *buf, const char *signatu
 
 			uint32_t slen32 = bytes_to_int32(slen);
 			if (end - p < slen32) {
-				log_bug_client(brei, "Invalid string length %zu, only %li bytes remaining", slen, (end - p) * 4);
-				return -EINVAL;
+				return brei_result_new(BREI_CONNECTION_DISCONNECT_REASON_ERROR,
+						       "Invalid string length %zu, only %li bytes remaining", slen, (end - p) * 4);
 			}
 
 			const char *str = (char*)p;
 
 			/* strings must be null-terminated */
 			if (slen && str[slen - 1] != '\0') {
-				log_bug_client(brei, "Message string not zero-terminated");
-				return -EINVAL;
+				return brei_result_new(BREI_CONNECTION_DISCONNECT_REASON_ERROR,
+						       "Message string not zero-terminated");
 			}
 
 			arg->s = str;
@@ -163,8 +219,8 @@ brei_demarshal(struct brei_context *brei, struct iobuf *buf, const char *signatu
 			break;
 			}
 		default:
-			log_bug(brei, "Invalid signature '%c'", *s);
-			return -EBADMSG;
+			return brei_result_new(BREI_CONNECTION_DISCONNECT_REASON_ERROR,
+					       "Invalid signature '%c'", *s);
 		}
 		arg++;
 		s++;
@@ -172,11 +228,12 @@ brei_demarshal(struct brei_context *brei, struct iobuf *buf, const char *signatu
 	}
 
 	*args_out = steal(&args);
+	*nargs_out = nargs;
 
-	return nargs;
+	return NULL;
 }
 
-static int
+static struct brei_result *
 brei_marshal(struct brei_context *brei, struct iobuf *buf, const char *signature, size_t nargs, va_list args)
 {
 	const char *s = signature;
@@ -220,23 +277,22 @@ brei_marshal(struct brei_context *brei, struct iobuf *buf, const char *signature
 			break;
 		}
 		default:
-			log_bug(brei, "Invalid signature '%c'", *s);
-			return -EBADMSG;
+			return brei_result_new(BREI_CONNECTION_DISCONNECT_REASON_ERROR,
+					       "Invalid signature '%c'", *s);
 		}
 		s++;
 	}
 
-	return 0;
+	return NULL;
 }
 
-int
-brei_send_message(struct brei_context *brei,
-		  int fd,
-		  uint32_t id,
-		  uint32_t opcode,
-		  const char *signature,
-		  size_t nargs,
-		  va_list args)
+struct brei_result *
+brei_marshal_message(struct brei_context *brei,
+		     uint32_t id,
+		     uint32_t opcode,
+		     const char *signature,
+		     size_t nargs,
+		     va_list args)
 {
 	uint32_t message_len = 0; /* we'll overwrite this later */
 
@@ -245,31 +301,33 @@ brei_send_message(struct brei_context *brei,
 	iobuf_append(buf, (const char *)&id, 4);
 	iobuf_append(buf, (const char *)&opcode, 4);
 
-	int rc = brei_marshal(brei, buf, signature, nargs, args);
+	_unref_(brei_result) *result = brei_marshal(brei, buf, signature, nargs, args);
+	if (result)
+		return steal(&result);
 
-	if (rc == 0) {
-		/* now write the actual message length, including header */
-		*(uint32_t*)iobuf_data(buf) = iobuf_len(buf);
-		rc = iobuf_send(buf, fd);
-	}
+	/* now write the actual message length, including header */
+	*(uint32_t*)iobuf_data(buf) = iobuf_len(buf);
 
-	return rc;
+	return brei_result_new_success(steal(&buf));
 }
 
-int
+struct brei_result *
 brei_dispatch(struct brei_context *brei,
 	      int fd,
 	      int (*lookup_object)(uint32_t object_id, struct brei_object **object, void *user_data),
 	      void *user_data)
 {
+	_unref_(brei_result) *result = NULL;
 	_cleanup_iobuf_ struct iobuf *buf = iobuf_new(64);
 	int rc = iobuf_recv_from_fd(buf, fd);
 	if (rc == -EAGAIN) {
-		return 0;
+		return NULL;
 	} else if (rc == 0) {
-		return -ECANCELED;
+		return brei_result_new(BREI_CONNECTION_DISCONNECT_REASON_ERROR,
+				       "socket disconnected");
 	} else if (rc < 0) {
-		return rc;
+		return brei_result_new(BREI_CONNECTION_DISCONNECT_REASON_ERROR,
+				       "error: %s", strerror(-rc));
 	}
 
 	while (true) {
@@ -295,8 +353,11 @@ brei_dispatch(struct brei_context *brei,
 			iobuf_pop(buf, msglen);
 			continue;
 		}
-		if (rc < 0)
+		if (rc < 0) {
+			result = brei_result_new(BREI_CONNECTION_DISCONNECT_REASON_ERROR,
+						 "lookup_object failed with %d (%s)", -rc, strerror(-rc));
 			goto error;
+		}
 
 		assert(object);
 
@@ -306,9 +367,9 @@ brei_dispatch(struct brei_context *brei,
 		assert(interface);
 
 		if (opcode >= interface->nincoming) {
-			log_bug_client(brei, "opcode %u exceeds interface %s method count %u",
-				       opcode, interface->name, interface->nincoming);
-			rc = -EINVAL;
+			result = brei_result_new(BREI_CONNECTION_DISCONNECT_REASON_ERROR,
+						 "opcode %u exceeds interface %s method count %u",
+						 opcode, interface->name, interface->nincoming);
 			goto error;
 		}
 
@@ -317,28 +378,28 @@ brei_dispatch(struct brei_context *brei,
 		/* Demarshal the protocol into a set of arguments */
 		_cleanup_free_ union brei_arg * args = NULL;
 		const char *signature = interface->incoming[opcode].signature;
-		int nargs = brei_demarshal(brei, buf, signature, &args);
-		if (nargs < 0) {
-			rc = nargs;
+		size_t nargs = 0;
+		result = brei_demarshal(brei, buf, signature, &nargs, &args);
+		if (result)
 			goto error;
-		}
 
 		log_debug(brei, "dispatching %s.%s() on object %#x", interface->name, interface->incoming[opcode].name, object_id);
 
 		/* Success! Let's pass this on to the
 		 * context to process */
-		rc = interface->dispatcher(object->implementation, opcode, nargs, args);
-		if (rc < 0) {
-			log_error(brei, "dispatch failed with %d (%s)", -rc, strerror(-rc));
+		result = interface->dispatcher(object->implementation, opcode, nargs, args);
+		if (result)
 			goto error;
-		}
 
 		iobuf_pop(buf, msglen - headersize);
 	}
-
-	rc = 0;
 error:
-	return rc;
+	if (result) {
+		log_error(brei, "%s", brei_result_get_explanation(result));
+		return steal(&result);
+	}
+
+	return NULL;
 }
 
 void
@@ -355,15 +416,15 @@ brei_drain_fd(int fd)
 #ifdef _enable_tests_
 #include "util-munit.h"
 
-static int
+static struct brei_result *
 brei_marshal_va(struct brei_context *brei, struct iobuf *buf, const char *signature, size_t nargs, ...)
 {
 	va_list args;
 
 	va_start(args, nargs);
-	int rc = brei_marshal(brei, buf, signature, nargs, args);
+	struct brei_result *result = brei_marshal(brei, buf, signature, nargs, args);
 	va_end(args);
-	return rc;
+	return result;
 }
 
 MUNIT_TEST(test_brei_marshal)
@@ -372,12 +433,16 @@ MUNIT_TEST(test_brei_marshal)
 	_cleanup_iobuf_ struct iobuf *buf = iobuf_new(64);
 	const char *str = "eierspeise";
 
-	int rc = brei_marshal_va(brei, buf, "noiusf", 5, 0xab, 0xcd, -13, 0xfffd, str, 1.45);
-	munit_assert_int(rc, ==, 0);
+	{
+		_unref_(brei_result) *result =  brei_marshal_va(brei, buf, "noiusf", 5, 0xab, 0xcd, -13, 0xfffd, str, 1.45);
+		munit_assert_ptr_null(result);
+	}
 
 	_cleanup_free_ union brei_arg *args = NULL;
-	rc = brei_demarshal(brei, buf, "noiusf", &args);
-	munit_assert_int(rc, ==, 6);
+	size_t nargs = 0;
+	_unref_(brei_result) *result = brei_demarshal(brei, buf, "noiusf", &nargs, &args);
+	munit_assert_ptr_null(result);
+	munit_assert_int(nargs, ==, 6);
 
 	munit_assert_int(args[0].o, ==, 0xab);
 	munit_assert_int(args[1].o, ==, 0xcd);
@@ -395,16 +460,41 @@ MUNIT_TEST(test_brei_marshal_bad_sig)
 	_cleanup_iobuf_ struct iobuf *buf = iobuf_new(64);
 	const char *str = "eierspeise";
 
-	int rc = brei_marshal_va(brei, buf, "noiusf", 5, 0xab, 0xcd, -13, 0xfffd, str, 1.45);
-	munit_assert_int(rc, ==, 0);
+	{
+		_unref_(brei_result) *result  = brei_marshal_va(brei, buf, "noiusf", 5, 0xab, 0xcd, -13, 0xfffd, str, 1.45);
+		munit_assert_ptr_null(result);
+	}
 
 	_cleanup_free_ union brei_arg *args = NULL;
-	rc = brei_demarshal(brei, buf, "nxoiusf", &args);
-	munit_assert_int(rc, ==, -EBADMSG);
+	size_t nargs = 789;
+	_unref_(brei_result) *result = brei_demarshal(brei, buf, "nxoiusf", &nargs, &args);
+	munit_assert_ptr_not_null(result);
+	munit_assert_int(brei_result_get_reason(result), ==,
+			 BREI_CONNECTION_DISCONNECT_REASON_ERROR);
+	munit_assert_int(nargs, ==, 789); /* nargs must not be touched on error */
 
 	return MUNIT_OK;
 }
 
+static int
+brei_send_message(struct brei_context *brei,
+		  int fd,
+		  uint32_t id,
+		  uint32_t opcode,
+		  const char *signature,
+		  size_t nargs,
+		  va_list args)
+{
+	_unref_(brei_result) *result = brei_marshal_message(brei, id, opcode, signature, nargs, args);
+
+	if (brei_result_get_reason(result) != 0)
+		return -EBADMSG;
+
+	_cleanup_iobuf_ struct iobuf *buf = NULL;
+	buf = brei_result_get_data(result);
+	return iobuf_send(buf, fd);
+}
+
 static int
 brei_send_message_va(int fd, uint32_t id, uint32_t opcode,
 		     const char *signature, size_t nargs, ...)
diff --git a/src/brei-shared.h b/src/brei-shared.h
index 0d98b69..fcd13e2 100644
--- a/src/brei-shared.h
+++ b/src/brei-shared.h
@@ -30,6 +30,7 @@
 #include <stdint.h>
 #include <stdarg.h>
 
+#include "util-macros.h"
 #include "util-list.h"
 #include "util-object.h"
 
@@ -39,6 +40,29 @@ struct brei_object;
 
 struct brei_context;
 
+struct brei_result {
+	struct object object;
+	int reason; /* enum ei(s)_connection_disconnect_reason */
+	char *explanation;
+	void *data;
+};
+
+struct brei_result *
+brei_result_new_success(void *data);
+
+struct brei_result *
+brei_result_new_from_neg_errno(int err);
+
+_printf_(2, 3) struct brei_result *
+brei_result_new(int reson, const char *format, ...);
+
+OBJECT_DECLARE_GETTER(brei_result, data, void *);
+OBJECT_DECLARE_SETTER(brei_result, data, void *);
+OBJECT_DECLARE_GETTER(brei_result, reason, int);
+OBJECT_DECLARE_GETTER(brei_result, explanation, const char *);
+OBJECT_DECLARE_REF(brei_result);
+OBJECT_DECLARE_UNREF(brei_result);
+
 enum brei_log_priority {
 	BREI_LOG_PRIORITY_DEBUG = 10,
 	BREI_LOG_PRIORITY_INFO = 20,
@@ -73,8 +97,8 @@ struct brei_message {
 	const struct brei_interface **types;
 };
 
-typedef int (*brei_event_dispatcher)(void *object, uint32_t opcode,
-				     size_t nargs, union brei_arg *args);
+typedef struct brei_result * (*brei_event_dispatcher)(void *object, uint32_t opcode,
+						      size_t nargs, union brei_arg *args);
 
 struct brei_interface {
 	const char *name;
@@ -98,14 +122,18 @@ struct brei_object {
 	struct list link; /* in the ei/eis object list */
 };
 
-int
-brei_send_message(struct brei_context *brei,
-		  int fd,
-		  uint32_t id,
-		  uint32_t opcode,
-		  const char *signature,
-		  size_t nargs,
-		  va_list args);
+/**
+ * Marshal the message for the given object id, opcode and signature into
+ * a struct iobuf. On succes, the returned result has that iobuf
+ * as brei_result_get_data(), otherwise the result is the error.
+ */
+struct brei_result *
+brei_marshal_message(struct brei_context *brei,
+		     uint32_t id,
+		     uint32_t opcode,
+		     const char *signature,
+		     size_t nargs,
+		     va_list args);
 
 /**
  * Dispatch messages for the data on fd.
@@ -115,9 +143,9 @@ brei_send_message(struct brei_context *brei,
  * On success, the callback must return the number of bytes consumed in msgdata
  * On failure, the callback must return a negative errno
  *
- * @return zero on success or a negative errno otherwise
+ * @return NULL on success or a struct with the error reason
  */
-int
+struct brei_result *
 brei_dispatch(struct brei_context *brei,
 	      int fd,
 	      int (*lookup_object)(uint32_t object_id, struct brei_object **object, void *user_data),
diff --git a/src/ei-proto.c.tmpl b/src/ei-proto.c.tmpl
index 2d6e93f..3896be6 100644
--- a/src/ei-proto.c.tmpl
+++ b/src/ei-proto.c.tmpl
@@ -29,6 +29,7 @@
 #include <errno.h>
 #include <sys/types.h>
 #include "brei-shared.h"
+#include "brei-proto.h"
 
 {% if headerfile %}
 #include "{{headerfile}}"
@@ -101,7 +102,7 @@ int
  * The dispatcher for the {{interface.name}} interface is the function called by
  * brei with the messages parsed from the wire.
  */
-static int
+static struct brei_result *
 {{interface.name}}_dispatcher(
 	{{interface.as_arg}},
 	uint32_t opcode,
@@ -116,13 +117,15 @@ static int
 		{% for incoming in interface.incoming %}
 	case {{incoming.fqdn.upper()}}:
 		if (obj->version < {{incoming.fqdn.upper()}}_SINCE_VERSION)
-			return -ENOTSUP;
+			return brei_result_new(BREI_CONNECTION_DISCONNECT_REASON_ERROR,
+					       "Opcode %u not supported in this interface version\n", opcode);
 		assert(interface->{{incoming.name}} != NULL);
 		return interface->{{incoming.name}}({{interface.name}}{% for arg in incoming.arguments %}, (args + {{loop.index - 1}})->{{arg.signature}}{% endfor %});
 		{% endfor %}
 	}
 {% endif %}
-	return -EINVAL;
+	return brei_result_new(BREI_CONNECTION_DISCONNECT_REASON_ERROR,
+			       "Opcode %u not supported in this interface version\n", opcode);
 }
 
 static const struct brei_message {{interface.name}}_requests[] = {
diff --git a/src/ei-proto.h.tmpl b/src/ei-proto.h.tmpl
index 143dfc9..56dc2e0 100644
--- a/src/ei-proto.h.tmpl
+++ b/src/ei-proto.h.tmpl
@@ -89,7 +89,7 @@ extern int
  */
 struct {{interface.name}}_interface {
    {% for incoming in interface.incoming %}
-   int (*{{incoming.name}})({{interface.as_arg}}{%- for arg in incoming.arguments %}, {{arg.as_arg}}{% endfor %});
+   struct brei_result * (*{{incoming.name}})({{interface.as_arg}}{%- for arg in incoming.arguments %}, {{arg.as_arg}}{% endfor %});
    {% endfor %}
 };
 {% endfor %}
diff --git a/src/libei-callback.c b/src/libei-callback.c
index 0968c85..679f468 100644
--- a/src/libei-callback.c
+++ b/src/libei-callback.c
@@ -68,11 +68,11 @@ ei_callback_get_id(struct ei_callback *callback)
 	return callback->proto_object.id;
 }
 
-static int
+static struct brei_result *
 handle_msg_done(struct ei_callback *callback, uint32_t callback_data)
 {
 	callback->func(callback, callback->callback_data, callback_data);
-	return 0;
+	return NULL;
 }
 
 static const struct ei_callback_interface interface = {
diff --git a/src/libei-connection-setup.c b/src/libei-connection-setup.c
index 30f96e5..d888475 100644
--- a/src/libei-connection-setup.c
+++ b/src/libei-connection-setup.c
@@ -100,7 +100,7 @@ ei_connection_setup_initialize(struct ei_connection_setup *setup, uint32_t versi
 	return 0;
 }
 
-static int
+static struct brei_result *
 handle_msg_interface_version(struct ei_connection_setup *setup, const char *name, uint32_t version)
 {
 	struct ei *ei = ei_connection_setup_get_context(setup);
@@ -128,7 +128,7 @@ handle_msg_interface_version(struct ei_connection_setup *setup, const char *name
 
 #undef VERSION_UPDATE
 
-	return 0;
+	return NULL;
 }
 
 static void
@@ -143,7 +143,7 @@ connected(struct ei_connection *connection, void *user_data)
 	ei_connected(ei);
 }
 
-static int
+static struct brei_result *
 handle_msg_connection(struct ei_connection_setup *setup, uint32_t id, uint32_t version)
 {
 	struct ei *ei = ei_connection_setup_get_context(setup);
@@ -159,7 +159,7 @@ handle_msg_connection(struct ei_connection_setup *setup, uint32_t id, uint32_t v
 	 * sync callback, we didn't immediately get disconnected */
 	ei_connection_sync(ei->connection, connected, NULL);
 
-	return 0;
+	return NULL;
 }
 
 static const struct ei_connection_setup_interface interface = {
diff --git a/src/libei-device.c b/src/libei-device.c
index 1f3cffd..e025ccd 100644
--- a/src/libei-device.c
+++ b/src/libei-device.c
@@ -125,44 +125,44 @@ ei_device_get_context(struct ei_device *device)
 	return ei_seat_get_context(ei_device_get_seat(device));
 }
 
-static int
+static struct brei_result *
 handle_msg_destroy(struct ei_device *device)
 {
 	struct ei *ei = ei_device_get_context(device);
 	log_debug(ei, "Removed device %#x", ei_device_get_id(device));
 	ei_device_removed_by_server(device);
-	return 0;
+	return NULL;
 }
 
-static int
+static struct brei_result *
 handle_msg_name(struct ei_device *device, const char *name)
 {
 	ei_device_set_name(device, name);
-	return 0;
+	return NULL;
 }
 
-static int
+static struct brei_result *
 handle_msg_capabilities(struct ei_device *device, uint32_t caps)
 {
 	ei_device_set_capabilities(device, caps);
-	return 0;
+	return NULL;
 }
 
-static int
+static struct brei_result *
 handle_msg_type(struct ei_device *device, enum ei_device_type type)
 {
 	ei_device_set_type(device, type);
-	return 0;
+	return NULL;
 }
 
-static int
+static struct brei_result *
 handle_msg_dimensions(struct ei_device *device, uint32_t width, uint32_t height)
 {
 	ei_device_set_size(device, width, height);
-	return 0;
+	return NULL;
 }
 
-static int
+static struct brei_result *
 handle_msg_region(struct ei_device *device, uint32_t x, uint32_t y,
 		  uint32_t w, uint32_t h, float scale)
 {
@@ -172,10 +172,10 @@ handle_msg_region(struct ei_device *device, uint32_t x, uint32_t y,
 	ei_region_set_physical_scale(r, scale);
 	ei_device_add_region(device, r);
 
-	return 0;
+	return NULL;
 }
 
-static int
+static struct brei_result *
 handle_msg_done(struct ei_device *device)
 {
 	struct ei *ei = ei_device_get_context(device);
@@ -191,37 +191,37 @@ handle_msg_done(struct ei_device *device)
 		  ei_device_has_capability(device, EI_DEVICE_CAP_KEYBOARD) ? "k" : "",
 		  ei_device_has_capability(device, EI_DEVICE_CAP_TOUCH) ? "t" : "",
 		  ei_seat_get_name(ei_device_get_seat(device)));
-	return 0;
+	return NULL;
 }
 
-static int
+static struct brei_result *
 handle_msg_resumed(struct ei_device *device)
 {
 	ei_device_resumed(device);
 	ei_queue_device_resumed_event(device);
 
-	return 0;
+	return NULL;
 }
 
-static int
+static struct brei_result *
 handle_msg_paused(struct ei_device *device)
 {
 	ei_device_paused(device);
 	ei_queue_device_paused_event(device);
 
-	return 0;
+	return NULL;
 }
 
 #define DISCONNECT_IF_SENDER_CONTEXT(device_) do {\
 	struct ei *ei_ = ei_device_get_context(device_); \
 	if (ei_is_sender(ei_)) { \
 		log_bug_client(ei_, "Invalid event from receiver EIS context. Disconnecting"); \
-		return -ECANCELED; \
+		return brei_result_new_from_neg_errno(-ECANCELED); \
 	} \
 } while(0)
 
 
-static int
+static struct brei_result *
 handle_msg_start_emulating(struct ei_device *device, uint32_t sequence)
 {
 	DISCONNECT_IF_SENDER_CONTEXT(device);
@@ -241,10 +241,10 @@ handle_msg_start_emulating(struct ei_device *device, uint32_t sequence)
 		break;
 	}
 
-	return 0;
+	return NULL;
 }
 
-static int
+static struct brei_result *
 handle_msg_stop_emulating(struct ei_device *device)
 {
 	DISCONNECT_IF_SENDER_CONTEXT(device);
@@ -264,50 +264,50 @@ handle_msg_stop_emulating(struct ei_device *device)
 		break;
 	}
 
-	return 0;
+	return NULL;
 }
 
-static int
+static struct brei_result *
 handle_msg_frame(struct ei_device *device, uint32_t time, uint32_t micros)
 {
 	DISCONNECT_IF_SENDER_CONTEXT(device);
 
 	ei_queue_frame_event(device, ms2us(time) + micros);
 
-	return 0;
+	return NULL;
 }
 
-static int
+static struct brei_result *
 handle_msg_pointer(struct ei_device *device, uint32_t id, uint32_t version)
 {
 	if (device->pointer)
-		return -EPROTO;
+		return brei_result_new_from_neg_errno(-EPROTO);
 
 	device->pointer = ei_pointer_new(device, id, version);
 
-	return 0;
+	return NULL;
 }
 
-static int
+static struct brei_result *
 handle_msg_keyboard(struct ei_device *device, uint32_t id, uint32_t version)
 {
 	if (device->keyboard)
-		return -EPROTO;
+		return brei_result_new_from_neg_errno(-EPROTO);
 
 	device->keyboard = ei_keyboard_new(device, id, version);
 
-	return 0;
+	return NULL;
 }
 
-static int
+static struct brei_result *
 handle_msg_touchscreen(struct ei_device *device, uint32_t id, uint32_t version)
 {
 	if (device->touchscreen)
-		return -EPROTO;
+		return brei_result_new_from_neg_errno(-EPROTO);
 
 	device->touchscreen = ei_touchscreen_new(device, id, version);
 
-	return 0;
+	return NULL;
 }
 
 static const struct ei_device_interface interface = {
@@ -334,27 +334,27 @@ ei_device_get_interface(struct ei_device *device)
 	return &interface;
 }
 
-static int
+static struct brei_result *
 handle_msg_pointer_rel(struct ei_pointer *pointer, float x, float y)
 {
 	struct ei_device *device = ei_pointer_get_device(pointer);
 
 	DISCONNECT_IF_SENDER_CONTEXT(device);
 
-	return ei_device_event_pointer_rel(device, x, y);
+	return brei_result_new_from_neg_errno(ei_device_event_pointer_rel(device, x, y));
 }
 
-static int
+static struct brei_result *
 handle_msg_pointer_abs(struct ei_pointer *pointer, float x, float y)
 {
 	struct ei_device *device = ei_pointer_get_device(pointer);
 
 	DISCONNECT_IF_SENDER_CONTEXT(device);
 
-	return ei_device_event_pointer_abs(device, x, y);
+	return brei_result_new_from_neg_errno(ei_device_event_pointer_abs(device, x, y));
 }
 
-static int
+static struct brei_result *
 handle_msg_pointer_button(struct ei_pointer *pointer,
 			  uint32_t button, uint32_t state)
 {
@@ -362,20 +362,20 @@ handle_msg_pointer_button(struct ei_pointer *pointer,
 
 	DISCONNECT_IF_SENDER_CONTEXT(device);
 
-	return ei_device_event_pointer_button(device, button, !!state);
+	return brei_result_new_from_neg_errno(ei_device_event_pointer_button(device, button, !!state));
 }
 
-static int
+static struct brei_result *
 handle_msg_pointer_scroll(struct ei_pointer *pointer, float x, float y)
 {
 	struct ei_device *device = ei_pointer_get_device(pointer);
 
 	DISCONNECT_IF_SENDER_CONTEXT(device);
 
-	return ei_device_event_pointer_scroll(device, x, y);
+	return brei_result_new_from_neg_errno(ei_device_event_pointer_scroll(device, x, y));
 }
 
-static int
+static struct brei_result *
 handle_msg_pointer_scroll_discrete(struct ei_pointer *pointer,
 				   int32_t x, int32_t y)
 {
@@ -383,10 +383,10 @@ handle_msg_pointer_scroll_discrete(struct ei_pointer *pointer,
 
 	DISCONNECT_IF_SENDER_CONTEXT(device);
 
-	return ei_device_event_pointer_scroll_discrete(device, x, y);
+	return brei_result_new_from_neg_errno(ei_device_event_pointer_scroll_discrete(device, x, y));
 }
 
-static int
+static struct brei_result *
 handle_msg_pointer_scroll_stop(struct ei_pointer *pointer,
 			       uint32_t x, uint32_t y, uint32_t is_cancel)
 {
@@ -395,20 +395,20 @@ handle_msg_pointer_scroll_stop(struct ei_pointer *pointer,
 	DISCONNECT_IF_SENDER_CONTEXT(device);
 
 	if (is_cancel)
-		return ei_device_event_pointer_scroll_cancel(device, !!x, !!y);
+		return brei_result_new_from_neg_errno(ei_device_event_pointer_scroll_cancel(device, !!x, !!y));
 	else
-		return ei_device_event_pointer_scroll_stop(device, !!x, !!y);
+		return brei_result_new_from_neg_errno(ei_device_event_pointer_scroll_stop(device, !!x, !!y));
 
-	return -EINVAL;
+	return brei_result_new_from_neg_errno(-EINVAL);
 }
 
-static int
+static struct brei_result *
 handle_msg_pointer_destroy(struct ei_pointer *pointer)
 {
 	struct ei_device *device = ei_pointer_get_device(pointer);
 	ei_pointer_unref(steal(&device->pointer));
 
-	return 0;
+	return NULL;
 }
 
 static const struct ei_pointer_interface pointer_interface = {
@@ -427,27 +427,27 @@ ei_device_get_pointer_interface(struct ei_device *device)
 	return &pointer_interface;
 }
 
-static int
+static struct brei_result *
 handle_msg_keymap(struct ei_keyboard *keyboard, uint32_t keymap_type, uint32_t keymap_sz, int keymap_fd)
 {
 	struct ei_device *device = ei_keyboard_get_device(keyboard);
 
 	ei_device_set_keymap(device, keymap_type, keymap_fd, keymap_sz);
 
-	return 0;
+	return NULL;
 }
 
-static int
+static struct brei_result *
 handle_msg_keyboard_key(struct ei_keyboard *keyboard, uint32_t key, uint32_t state)
 {
 	struct ei_device *device = ei_keyboard_get_device(keyboard);
 
 	DISCONNECT_IF_SENDER_CONTEXT(device);
 
-	return ei_device_event_keyboard_key(device, key, !!state);
+	return brei_result_new_from_neg_errno(ei_device_event_keyboard_key(device, key, !!state));
 }
 
-static int
+static struct brei_result *
 handle_msg_keyboard_modifiers(struct ei_keyboard *keyboard, uint32_t depressed,
 			      uint32_t locked, uint32_t latched, uint32_t group)
 {
@@ -456,7 +456,7 @@ handle_msg_keyboard_modifiers(struct ei_keyboard *keyboard, uint32_t depressed,
 
 	if (!ei_device_has_capability(device, EI_DEVICE_CAP_KEYBOARD)) {
 		log_bug(ei,"Modifier event for non-keyboard");
-		return -EPROTO;
+		return brei_result_new_from_neg_errno(-EPROTO);
 	}
 
 	struct ei_xkb_modifiers mods = {
@@ -468,17 +468,17 @@ handle_msg_keyboard_modifiers(struct ei_keyboard *keyboard, uint32_t depressed,
 
 	ei_queue_keyboard_modifiers_event(device, &mods);
 
-	return 0;
+	return NULL;
 }
 
-static int
+static struct brei_result *
 handle_msg_keyboard_destroy(struct ei_keyboard *keyboard)
 {
 
 	struct ei_device *device = ei_keyboard_get_device(keyboard);
 	ei_keyboard_unref(steal(&device->keyboard));
 
-	return 0;
+	return NULL;
 }
 
 static const struct ei_keyboard_interface keyboard_interface = {
@@ -494,7 +494,7 @@ ei_device_get_keyboard_interface(struct ei_device *device)
 	return &keyboard_interface;
 }
 
-static int
+static struct brei_result *
 handle_msg_touch_down(struct ei_touchscreen *touchscreen,
 		      uint32_t touchid, float x, float y)
 {
@@ -502,10 +502,10 @@ handle_msg_touch_down(struct ei_touchscreen *touchscreen,
 
 	DISCONNECT_IF_SENDER_CONTEXT(device);
 
-	return ei_device_event_touch_down(device, touchid, x, y);
+	return brei_result_new_from_neg_errno(ei_device_event_touch_down(device, touchid, x, y));
 }
 
-static int
+static struct brei_result *
 handle_msg_touch_motion(struct ei_touchscreen *touchscreen,
 			uint32_t touchid, float x, float y)
 {
@@ -513,27 +513,27 @@ handle_msg_touch_motion(struct ei_touchscreen *touchscreen,
 
 	DISCONNECT_IF_SENDER_CONTEXT(device);
 
-	return ei_device_event_touch_motion(device, touchid, x, y);
+	return brei_result_new_from_neg_errno(ei_device_event_touch_motion(device, touchid, x, y));
 }
 
-static int
+static struct brei_result *
 handle_msg_touch_up(struct ei_touchscreen *touchscreen, uint32_t touchid)
 {
 	struct ei_device *device = ei_touchscreen_get_device(touchscreen);
 
 	DISCONNECT_IF_SENDER_CONTEXT(device);
 
-	return ei_device_event_touch_up(device, touchid);
+	return brei_result_new_from_neg_errno(ei_device_event_touch_up(device, touchid));
 }
 
-static int
+static struct brei_result *
 handle_msg_touchscreen_destroy(struct ei_touchscreen *touchscreen)
 {
 
 	struct ei_device *device = ei_touchscreen_get_device(touchscreen);
 	ei_touchscreen_unref(steal(&device->touchscreen));
 
-	return 0;
+	return NULL;
 }
 
 static const struct ei_touchscreen_interface touchscreen_interface = {
diff --git a/src/libei-seat.c b/src/libei-seat.c
index 1e9d65b..9e681a2 100644
--- a/src/libei-seat.c
+++ b/src/libei-seat.c
@@ -69,36 +69,40 @@ ei_seat_get_id(struct ei_seat *seat) {
 	return seat->proto_object.id;
 }
 
-static int handle_msg_destroyed(struct ei_seat *seat)
+static struct brei_result *
+handle_msg_destroyed(struct ei_seat *seat)
 {
 	struct ei *ei = ei_seat_get_context(seat);
 
 	log_debug(ei, "server removed seat %s", seat->name);
 	ei_seat_remove(seat);
 
-	return 0;
+	return NULL;
 }
 
-static int handle_msg_name(struct ei_seat *seat, const char * name)
+static struct brei_result *
+handle_msg_name(struct ei_seat *seat, const char * name)
 {
 	if (seat->name != NULL)
-		return -EPROTO;
+		return brei_result_new_from_neg_errno(-EPROTO);
 
 	seat->name = xstrdup(name);
 
 	return 0;
 }
 
-static int handle_msg_capabilities(struct ei_seat *seat, uint32_t capabilities)
+static struct brei_result *
+handle_msg_capabilities(struct ei_seat *seat, uint32_t capabilities)
 {
 	if (seat->capabilities != 0)
-		return -EPROTO;
+		return brei_result_new_from_neg_errno(-EPROTO);
 
 	seat->capabilities = capabilities;
 	return 0;
 }
 
-static int handle_msg_done(struct ei_seat *seat)
+static struct brei_result *
+handle_msg_done(struct ei_seat *seat)
 {
 	struct ei *ei = ei_seat_get_context(seat);
 
@@ -106,10 +110,11 @@ static int handle_msg_done(struct ei_seat *seat)
 	log_debug(ei, "Added seat '%s' with caps %#x", seat->name, seat->capabilities);
 	ei_add_seat(seat);
 
-	return 0;
+	return NULL;
 }
 
-static int handle_msg_device(struct ei_seat *seat, uint32_t id, uint32_t version)
+static struct brei_result *
+handle_msg_device(struct ei_seat *seat, uint32_t id, uint32_t version)
 {
 	struct ei *ei = ei_seat_get_context(seat);
 
@@ -119,7 +124,7 @@ static int handle_msg_device(struct ei_seat *seat, uint32_t id, uint32_t version
 	/* this list "owns" the ref for this device */
 	list_append(&seat->devices, &device->link);
 
-	return 0;
+	return NULL;
 }
 
 static const struct ei_seat_interface interface = {
diff --git a/src/libei.c b/src/libei.c
index 0718ac0..67993f9 100644
--- a/src/libei.c
+++ b/src/libei.c
@@ -81,6 +81,7 @@ _public_
 OBJECT_IMPLEMENT_GETTER(ei, user_data, void *);
 OBJECT_IMPLEMENT_GETTER(ei, connection, struct ei_connection *);
 
+DEFINE_UNREF_CLEANUP_FUNC(brei_result);
 DEFINE_UNREF_CLEANUP_FUNC(ei_device);
 DEFINE_UNREF_CLEANUP_FUNC(ei_region);
 DEFINE_UNREF_CLEANUP_FUNC(ei_pingpong);
@@ -594,7 +595,7 @@ ei_disconnect(struct ei *ei)
 	ei->source = source_unref(ei->source);
 }
 
-static int
+static struct brei_result *
 handle_msg_seat(struct ei_connection *connection, uint32_t seat_id, uint32_t version)
 {
 	struct ei *ei = ei_connection_get_context(connection);
@@ -608,7 +609,7 @@ handle_msg_seat(struct ei_connection *connection, uint32_t seat_id, uint32_t ver
 	/* seats list owns the ref */
 	list_append(&ei->seats, &seat->link);
 
-	return 0;
+	return NULL;
 }
 
 void
@@ -660,7 +661,7 @@ ei_connected(struct ei *ei)
 	}
 }
 
-static int
+static struct brei_result *
 handle_msg_disconnected(struct ei_connection *connection, uint32_t reason, const char *explanation)
 {
 	struct ei *ei = ei_connection_get_context(connection);
@@ -670,20 +671,20 @@ handle_msg_disconnected(struct ei_connection *connection, uint32_t reason, const
 	else
 		log_info(ei, "Disconnected after error: %s", explanation);
 
-	return -ECANCELED;
+	return brei_result_new_from_neg_errno(-ECANCELED);
 }
 
-static int
+static struct brei_result *
 handle_msg_invalid_object(struct ei_connection *connection, uint32_t object)
 {
 	struct ei *ei = ei_connection_get_context(connection);
 
 	log_bug(ei, "Invalid object %#x, I don't yet know how to handle that", object);
 
-	return 0;
+	return NULL;
 }
 
-static int
+static struct brei_result *
 handle_msg_ping(struct ei_connection *connection, uint32_t id,  uint32_t version)
 {
 	struct ei *ei = ei_connection_get_context(connection);
@@ -691,7 +692,7 @@ handle_msg_ping(struct ei_connection *connection, uint32_t id,  uint32_t version
 
 	ei_pingpong_request_done(pingpong, 0);
 
-	return 0;
+	return NULL;
 }
 
 #define DISCONNECT_IF_SENDER_CONTEXT(ei_) do {\
@@ -738,8 +739,9 @@ connection_dispatch(struct source *source, void *userdata)
 	struct ei *ei = userdata;
 	enum ei_state old_state = ei->state;
 
-	int rc = brei_dispatch(ei->brei, source_get_fd(source), lookup_object, ei);
-	if (rc < 0) {
+	_unref_(brei_result) *result = brei_dispatch(ei->brei, source_get_fd(source),
+						     lookup_object, ei);
+	if (result) {
 		brei_drain_fd(source_get_fd(source));
 		ei_disconnect(ei);
 	}
@@ -752,10 +754,8 @@ connection_dispatch(struct source *source, void *userdata)
 		"DISCONNECTED",
 		"DISCONNECTING",
 	};
-	if (rc == -ECANCELED)
-		log_info(ei, "Disconnected");
-	else if (rc)
-		log_warn(ei, "Connection error: %s", strerror(-rc));
+	if (result)
+		log_warn(ei, "Connection error: %s", brei_result_get_explanation(result));
 
 	if (old_state != ei->state)
 		log_debug(ei, "Connection dispatch: %s -> %s",
@@ -767,8 +767,6 @@ int
 ei_send_message(struct ei *ei, const struct brei_object *object,
 		uint32_t opcode, const char *signature, size_t nargs, ...)
 {
-	int fd = source_get_fd(ei->source);
-
 	log_debug(ei, "sending: object %#x (%s@v%u:%s(%u)) signature '%s'",
 	   object->id,
 	   object->interface->name,
@@ -779,8 +777,22 @@ ei_send_message(struct ei *ei, const struct brei_object *object,
 
 	va_list args;
 	va_start(args, nargs);
-	int rc = brei_send_message(ei->brei, fd, object->id, opcode, signature, nargs, args);
+	_unref_(brei_result) *result = brei_marshal_message(ei->brei,
+							    object->id,
+							    opcode, signature,
+							    nargs, args);
 	va_end(args);
+
+	if (brei_result_get_reason(result) != 0) {
+		log_warn(ei, "failed to marshal message: %s",
+			 brei_result_get_explanation(result));
+		return -EBADMSG;
+	}
+
+	_cleanup_iobuf_ struct iobuf *buf = brei_result_get_data(result);
+	assert(buf);
+	int fd = source_get_fd(ei->source);
+	int rc = iobuf_send(buf, fd);
 	return rc < 0 ? rc : 0;
 }
 
diff --git a/src/libeis-client.c b/src/libeis-client.c
index 1a9c3b3..e4a9f2f 100644
--- a/src/libeis-client.c
+++ b/src/libeis-client.c
@@ -46,6 +46,7 @@
 #include "eis-proto.h"
 
 DEFINE_TRISTATE(started, finished, connected);
+DEFINE_UNREF_CLEANUP_FUNC(brei_result);
 
 static void
 eis_client_destroy(struct eis_client *client)
@@ -147,7 +148,6 @@ eis_client_send_message(struct eis_client *client, const struct brei_object *obj
 			uint32_t opcode, const char *signature, size_t nargs, ...)
 {
 	struct eis *eis = eis_client_get_context(client);
-	int fd = source_get_fd(client->source);
 
 	log_debug(eis, "sending: object %#x (%s@v%u:%s(%u)) signature '%s'",
 	   object->id,
@@ -159,8 +159,22 @@ eis_client_send_message(struct eis_client *client, const struct brei_object *obj
 
 	va_list args;
 	va_start(args, nargs);
-	int rc = brei_send_message(client->brei, fd, object->id, opcode, signature, nargs, args);
+	_unref_(brei_result) *result = brei_marshal_message(client->brei,
+						            object->id,
+							    opcode, signature,
+							    nargs, args);
 	va_end(args);
+
+	if (brei_result_get_reason(result) != 0) {
+		log_warn(eis, "failed to marshal message: %s",
+			 brei_result_get_explanation(result));
+		return -EBADMSG;
+	}
+
+	_cleanup_iobuf_ struct iobuf *buf = brei_result_get_data(result);
+	assert(buf);
+	int fd = source_get_fd(client->source);
+	int rc = iobuf_send(buf, fd);
 	return rc < 0 ? rc : 0;
 }
 
@@ -251,26 +265,26 @@ eis_client_setup_done(struct eis_client *client, const char *name, bool is_sende
 	} \
 } while(0)
 
-static int
+static struct brei_result *
 client_msg_disconnect(struct eis_connection *connection)
 {
 	struct eis_client * client = eis_connection_get_client(connection);
 	client_disconnect(client, EIS_CONNECTION_DISCONNECT_REASON_DISCONNECTED, NULL);
-	return 0;
+	return NULL;
 }
 
-static int
+static struct brei_result *
 client_msg_sync(struct eis_connection *connection, uint32_t new_id)
 {
 	if (new_id == 0)
-		return -EINVAL;
+		return brei_result_new_from_neg_errno(-EINVAL);
 
 	struct eis_client *client = eis_connection_get_client(connection);
 	struct eis_callback *callback = eis_callback_new(client, new_id, client->interface_versions.ei_callback);
 	log_debug(eis_client_get_context(client) , "object %u: connection sync done", new_id);
 	int rc = eis_callback_event_done(callback, 0);
 	eis_callback_unref(callback);
-	return rc;
+	return brei_result_new_from_neg_errno(rc);
 }
 
 static const struct eis_connection_interface intf_state_new = {
@@ -329,12 +343,13 @@ client_dispatch(struct source *source, void *userdata)
 	_unref_(eis_client) *client = eis_client_ref(userdata);
 	enum eis_client_state old_state = client->state;
 
-	int rc = brei_dispatch(client->brei, source_get_fd(source), lookup_object, client);
-	if (rc < 0) {
+	_unref_(brei_result) *result = brei_dispatch(client->brei, source_get_fd(source),
+						     lookup_object, client);
+	if (result) {
 		brei_drain_fd(source_get_fd(source));
 		client_disconnect(client,
-				  EIS_CONNECTION_DISCONNECT_REASON_ERROR,
-				  strerror(-rc));
+				  brei_result_get_reason(result),
+				  brei_result_get_explanation(result));
 	}
 
 	static const char *client_states[] = {
@@ -343,11 +358,9 @@ client_dispatch(struct source *source, void *userdata)
 		"CONNECTED",
 		"DISCONNECTED",
 	};
-	if (rc == -ECANCELED)
-		log_info(eis_client_get_context(client), "Disconnected");
-	else if (rc)
+	if (result)
 		log_warn(eis_client_get_context(client), "Client error: %s",
-			 strerror(-rc));
+			 brei_result_get_explanation(result));
 	if (old_state != client->state) {
 		assert(old_state < ARRAY_LENGTH(client_states));
 		assert(client->state < ARRAY_LENGTH(client_states));
diff --git a/src/libeis-connection-setup.c b/src/libeis-connection-setup.c
index e43cc0d..ff0fad3 100644
--- a/src/libeis-connection-setup.c
+++ b/src/libeis-connection-setup.c
@@ -82,7 +82,7 @@ pong(struct eis_connection *connection, void *user_data)
 	eis_queue_connect_event(client);
 }
 
-static int
+static struct brei_result *
 client_msg_done(struct eis_connection_setup *setup)
 {
 	struct eis_client *client = eis_connection_setup_get_client(setup);
@@ -91,7 +91,7 @@ client_msg_done(struct eis_connection_setup *setup)
 	if (setup->client_versions.ei_connection == 0 ||
 	    setup->client_versions.ei_callback == 0 ||
 	    setup->client_versions.ei_pingpong == 0)
-		return -EPROTO;
+		return brei_result_new_from_neg_errno(-EPROTO);
 
 	/* ei_callback needs a client-created object, so tell the client
 	 * about our version */
@@ -117,21 +117,21 @@ client_msg_done(struct eis_connection_setup *setup)
 
 	client->setup = eis_connection_setup_unref(setup);
 
-	return 0;
+	return NULL;
 }
 
-static int
+static struct brei_result *
 client_msg_name(struct eis_connection_setup *setup, const char *name)
 {
 	if (setup->name)
-		return -EPROTO;
+		return brei_result_new_from_neg_errno(-EPROTO);
 
 	setup->name = xstrdup(name);
 
 	return 0;
 }
 
-static int
+static struct brei_result *
 client_msg_context_type(struct eis_connection_setup *setup, uint32_t type)
 {
 	switch(type) {
@@ -141,10 +141,10 @@ client_msg_context_type(struct eis_connection_setup *setup, uint32_t type)
 		return 0;
 	}
 
-	return -EPROTO;
+	return brei_result_new_from_neg_errno(-EPROTO);
 }
 
-static int
+static struct brei_result *
 client_msg_interface_version(struct eis_connection_setup *setup, const char *name, uint32_t version)
 {
 	struct eis_client *client = eis_connection_setup_get_client(setup);
@@ -174,14 +174,14 @@ client_msg_interface_version(struct eis_connection_setup *setup, const char *nam
 	log_debug(eis, "client %#x supports %s version %u", client->id, name, version);
 
 	if (version == 0)
-		return -EPROTO;
+		return brei_result_new_from_neg_errno(-EPROTO);
 
 	struct v *v;
 	ARRAY_FOR_EACH(version_map, v) {
 		if (streq(v->name, name)) {
 			/* Versions must not be set twice */
 			if (*v->client_version != 0)
-				return -EPROTO;
+				return brei_result_new_from_neg_errno(-EPROTO);
 			*v->client_version = min(*v->server_version, version);
 			return 0;
 		}
diff --git a/src/libeis-device.c b/src/libeis-device.c
index 1538ecc..49689ba 100644
--- a/src/libeis-device.c
+++ b/src/libeis-device.c
@@ -203,11 +203,11 @@ eis_device_get_client(struct eis_device *device)
 	return eis_seat_get_client(eis_device_get_seat(device));
 }
 
-static int
+static struct brei_result *
 client_msg_release(struct eis_device *device)
 {
 	eis_device_closed_by_client(device);
-	return 0;
+	return NULL;
 }
 
 #define DISCONNECT_IF_RECEIVER_CONTEXT(device_) do { \
@@ -215,12 +215,12 @@ client_msg_release(struct eis_device *device)
 	if (!eis_client_is_sender(client_)) { \
 		struct eis *_ctx = eis_client_get_context(client_); \
 		log_bug_client(_ctx, "Invalid event from receiver ei context. Disconnecting client"); \
-		return -EINVAL; \
+		return brei_result_new(EIS_CONNECTION_DISCONNECT_REASON_ERROR, "Invalid event from receiver ei context"); \
 	} \
 } while(0)
 
 
-static int
+static struct brei_result *
 client_msg_start_emulating(struct eis_device *device, uint32_t sequence)
 {
 	DISCONNECT_IF_RECEIVER_CONTEXT(device);
@@ -242,7 +242,7 @@ client_msg_start_emulating(struct eis_device *device, uint32_t sequence)
 	return 0;
 }
 
-static int
+static struct brei_result *
 client_msg_stop_emulating(struct eis_device *device)
 {
 	DISCONNECT_IF_RECEIVER_CONTEXT(device);
@@ -263,17 +263,17 @@ client_msg_stop_emulating(struct eis_device *device)
 	return 0;
 }
 
-static int
+static struct brei_result *
 client_msg_frame(struct eis_device *device, uint32_t time, uint32_t micros)
 {
 	DISCONNECT_IF_RECEIVER_CONTEXT(device);
 
 	if (device->state != EIS_DEVICE_STATE_EMULATING)
-		return -EINVAL;
+		return brei_result_new_from_neg_errno(-EINVAL);
 
 	eis_queue_frame_event(device, ms2us(time) + micros);
 
-	return 0;
+	return NULL;
 }
 
 
@@ -290,57 +290,57 @@ eis_device_get_interface(struct eis_device *device)
 	return &interface;
 }
 
-static int
+static struct brei_result *
 client_msg_pointer_rel(struct eis_pointer *pointer, float x, float y)
 {
 	struct eis_device *device = eis_pointer_get_device(pointer);
 
 	DISCONNECT_IF_RECEIVER_CONTEXT(device);
 
-	return eis_device_event_pointer_rel(device, x, y);
+	return brei_result_new_from_neg_errno(eis_device_event_pointer_rel(device, x, y));
 }
 
-static int
+static struct brei_result *
 client_msg_pointer_abs(struct eis_pointer *pointer, float x, float y)
 {
 	struct eis_device *device = eis_pointer_get_device(pointer);
 
 	DISCONNECT_IF_RECEIVER_CONTEXT(device);
 
-	return eis_device_event_pointer_abs(device, x, y);
+	return brei_result_new_from_neg_errno(eis_device_event_pointer_abs(device, x, y));
 }
 
-static int
+static struct brei_result *
 client_msg_pointer_button(struct eis_pointer *pointer, uint32_t button, uint32_t state)
 {
 	struct eis_device *device = eis_pointer_get_device(pointer);
 
 	DISCONNECT_IF_RECEIVER_CONTEXT(device);
 
-	return eis_device_event_pointer_button(device, button, !!state);
+	return brei_result_new_from_neg_errno(eis_device_event_pointer_button(device, button, !!state));
 }
 
-static int
+static struct brei_result *
 client_msg_pointer_scroll(struct eis_pointer *pointer, float x, float y)
 {
 	struct eis_device *device = eis_pointer_get_device(pointer);
 
 	DISCONNECT_IF_RECEIVER_CONTEXT(device);
 
-	return eis_device_event_pointer_scroll(device, x, y);
+	return brei_result_new_from_neg_errno(eis_device_event_pointer_scroll(device, x, y));
 }
 
-static int
+static struct brei_result *
 client_msg_pointer_scroll_discrete(struct eis_pointer *pointer, int32_t x, int32_t y)
 {
 	struct eis_device *device = eis_pointer_get_device(pointer);
 
 	DISCONNECT_IF_RECEIVER_CONTEXT(device);
 
-	return eis_device_event_pointer_scroll_discrete(device, x, y);
+	return brei_result_new_from_neg_errno(eis_device_event_pointer_scroll_discrete(device, x, y));
 }
 
-static int
+static struct brei_result *
 client_msg_pointer_scroll_stop(struct eis_pointer *pointer,
 			       uint32_t x, uint32_t y, uint32_t is_cancel)
 {
@@ -349,12 +349,12 @@ client_msg_pointer_scroll_stop(struct eis_pointer *pointer,
 	DISCONNECT_IF_RECEIVER_CONTEXT(device);
 
 	if (is_cancel)
-		return eis_device_event_pointer_scroll_cancel(device, !!x, !!y);
+		return brei_result_new_from_neg_errno(eis_device_event_pointer_scroll_cancel(device, !!x, !!y));
 	else
-		return eis_device_event_pointer_scroll_stop(device, !!x, !!y);
+		return brei_result_new_from_neg_errno(eis_device_event_pointer_scroll_stop(device, !!x, !!y));
 }
 
-static int
+static struct brei_result *
 client_msg_pointer_release(struct eis_pointer *pointer)
 {
 	struct eis_device *device = eis_pointer_get_device(pointer);
@@ -379,17 +379,17 @@ eis_device_get_pointer_interface(struct eis_device *device)
 	return &pointer_interface;
 }
 
-static int
+static struct brei_result *
 client_msg_keyboard_key(struct eis_keyboard *keyboard, uint32_t key, uint32_t state)
 {
 	struct eis_device *device = eis_keyboard_get_device(keyboard);
 
 	DISCONNECT_IF_RECEIVER_CONTEXT(device);
 
-	return eis_device_event_keyboard_key(device, key, !!state);
+	return brei_result_new_from_neg_errno(eis_device_event_keyboard_key(device, key, !!state));
 }
 
-static int
+static struct brei_result *
 client_msg_keyboard_release(struct eis_keyboard *keyboard)
 {
 	struct eis_device *device = eis_keyboard_get_device(keyboard);
@@ -409,7 +409,7 @@ eis_device_get_keyboard_interface(struct eis_device *device)
 	return &keyboard_interface;
 }
 
-static int
+static struct brei_result *
 client_msg_touch_down(struct eis_touchscreen *touchscreen,
 		      uint32_t touchid, float x, float y)
 {
@@ -417,10 +417,10 @@ client_msg_touch_down(struct eis_touchscreen *touchscreen,
 
 	DISCONNECT_IF_RECEIVER_CONTEXT(device);
 
-	return eis_device_event_touch_down(device, touchid, x, y);
+	return brei_result_new_from_neg_errno(eis_device_event_touch_down(device, touchid, x, y));
 }
 
-static int
+static struct brei_result *
 client_msg_touch_motion(struct eis_touchscreen *touchscreen,
 			uint32_t touchid, float x, float y)
 {
@@ -428,26 +428,26 @@ client_msg_touch_motion(struct eis_touchscreen *touchscreen,
 
 	DISCONNECT_IF_RECEIVER_CONTEXT(device);
 
-	return eis_device_event_touch_motion(device, touchid, x, y);
+	return brei_result_new_from_neg_errno(eis_device_event_touch_motion(device, touchid, x, y));
 }
 
-static int
+static struct brei_result *
 client_msg_touch_up(struct eis_touchscreen *touchscreen, uint32_t touchid)
 {
 	struct eis_device *device = eis_touchscreen_get_device(touchscreen);
 
 	DISCONNECT_IF_RECEIVER_CONTEXT(device);
 
-	return eis_device_event_touch_up(device, touchid);
+	return brei_result_new_from_neg_errno(eis_device_event_touch_up(device, touchid));
 }
 
-static int
+static struct brei_result *
 client_msg_touchscreen_release(struct eis_touchscreen *touchscreen)
 {
 	struct eis_device *device = eis_touchscreen_get_device(touchscreen);
 	eis_touchscreen_event_destroyed(device->touchscreen);
 	eis_touchscreen_unref(steal(&device->touchscreen));
-	return 0;
+	return NULL;
 }
 
 static const struct eis_touchscreen_interface touchscreen_interface = {
diff --git a/src/libeis-pingpong.c b/src/libeis-pingpong.c
index 2d57c2b..45665d6 100644
--- a/src/libeis-pingpong.c
+++ b/src/libeis-pingpong.c
@@ -80,11 +80,11 @@ eis_pingpong_get_version(struct eis_pingpong *pingpong)
 	return pingpong->proto_object.version;
 }
 
-static int
+static struct brei_result *
 client_msg_done(struct eis_pingpong *pingpong, uint32_t pingpong_data)
 {
 	pingpong->func(pingpong, pingpong->pingpong_data, pingpong_data);
-	return 0;
+	return NULL;
 }
 
 static const struct eis_pingpong_interface interface = {
diff --git a/src/libeis-seat.c b/src/libeis-seat.c
index af61e92..fd24218 100644
--- a/src/libeis-seat.c
+++ b/src/libeis-seat.c
@@ -79,7 +79,7 @@ eis_seat_get_client(struct eis_seat *seat)
 	return eis_seat_parent(seat);
 }
 
-static int
+static struct brei_result *
 client_msg_release(struct eis_seat *seat)
 {
 	/* There is no public API in libei to remove a seat, and there's no
@@ -88,10 +88,10 @@ client_msg_release(struct eis_seat *seat)
 	 * and remove it, that should do the trick.
 	 */
 	eis_seat_drop(seat);
-	return 0;
+	return NULL;
 }
 
-static int
+static struct brei_result *
 client_msg_bind(struct eis_seat *seat, uint32_t caps)
 {
 	uint32_t allowed_caps = 0;
@@ -106,11 +106,11 @@ client_msg_bind(struct eis_seat *seat, uint32_t caps)
 		allowed_caps |= EIS_SEAT_CAPABILITIES_TOUCHSCREEN;
 
 	if (caps & ~allowed_caps)
-		return -EINVAL;
+		return brei_result_new_from_neg_errno(-EINVAL);
 
 	eis_seat_bind(seat, caps);
 
-	return 0;
+	return NULL;
 }
 
 static const struct eis_seat_interface interface = {