Merge branch 'lukeshu/9p-tests'

10 files changed, 612 insertions, 65 deletions

diff --git a/lib9p/tests/client_config/config.h b/lib9p/tests/client_config/config.h
new file mode 100644
index 0000000..65ee9de
--- /dev/null
+++ b/lib9p/tests/client_config/config.h
@@ -0,0 +1,40 @@
+/* config.h - Compile-time configuration for lib9p test clients
+ *
+ * Copyright (C) 2024-2025  Luke T. Shumaker <lukeshu@lukeshu.com>
+ * SPDX-License-Identifier: AGPL-3.0-or-later
+ */
+
+#ifndef _CONFIG_H_
+#define _CONFIG_H_
+
+/* 9P *************************************************************************/
+
+#define CONFIG_9P_MAX_ERR_SIZE          128
+#define CONFIG_9P_MAX_9P2000_e_WELEM    16
+
+#define CONFIG_9P_ENABLE_9P2000         1 /* bool */
+#define CONFIG_9P_ENABLE_9P2000_u       1 /* bool */
+#define CONFIG_9P_ENABLE_9P2000_e       1 /* bool */
+#define CONFIG_9P_ENABLE_9P2000_L       1 /* bool */
+#define CONFIG_9P_ENABLE_9P2000_p9p     1 /* bool */
+
+/* 9P server (unused) *********************************************************/
+
+#define CONFIG_9P_SRV_MAX_MSG_SIZE      ((4*1024)+24)
+#define CONFIG_9P_SRV_MAX_HOSTMSG_SIZE  CONFIG_9P_SRV_MAX_MSG_SIZE+16
+#define CONFIG_9P_SRV_MAX_FIDS          16
+#define CONFIG_9P_SRV_MAX_REQS          2
+#define CONFIG_9P_SRV_MAX_DEPTH         3
+
+/* COROUTINE (unused) *********************************************************/
+
+#define CONFIG_COROUTINE_STACK_SIZE_DEFAULT    (32*1024)
+#define CONFIG_COROUTINE_NAME_LEN              16
+#define CONFIG_COROUTINE_MEASURE_STACK         1 /* bool */
+#define CONFIG_COROUTINE_PROTECT_STACK         1 /* bool */
+#define CONFIG_COROUTINE_DEBUG                 0 /* bool */
+#define CONFIG_COROUTINE_VALGRIND              1 /* bool */
+#define CONFIG_COROUTINE_GDB                   1 /* bool */
+#define CONFIG_COROUTINE_NUM                   2
+
+#endif /* _CONFIG_H_ */
diff --git a/lib9p/tests/runtest b/lib9p/tests/runtest
index fb66a43..6883391 100755
--- a/lib9p/tests/runtest
+++ b/lib9p/tests/runtest
@@ -1,67 +1,50 @@
 #!/usr/bin/env bash
-# lib9p/tests/runtest - Simple tests for the 9P `test_server`
+# lib9p/tests/runtest - Test harness for the 9P `test_server`
 #
 # Copyright (C) 2025  Luke T. Shumaker <lukeshu@lukeshu.com>
 # SPDX-License-Identifier: AGPL-3.0-or-later
 
 set -euE -o pipefail
-set -x
 
 build_aux=$(realpath --canonicalize-missing -- "${BASH_SOURCE[0]}/../../../build-aux")
 
-port=$(python -c 'import socket; s=socket.socket(); s.bind(("", 0)); print(s.getsockname()[1]); s.close()')
-"${build_aux}/valgrind" ./tests/test_server/test_server "$port" &
-server_pid=$!
-# shellcheck disable=SC2064
-trap "kill $server_pid || true; wait $server_pid || true" EXIT
-server_addr="localhost:${port}"
-
-client=(9p -a "$server_addr")
+if [[ $# != 2 ]]; then
+	echo >&2 "Usage: $0 CLIENTSCRIPT EXPLOG"
+	exit 2
+fi
+clientscript="$1"
+explog="$2"
 
-expect_lines() (
+cleanup=()
+cleanup() {
 	{ set +x; } &>/dev/null
-	printf >&2 '+ diff -u expected.txt actual.txt\n'
-	diff -u <(printf '%s\n' "$@") <(printf '%s\n' "$out")
-)
-
-while [[ -d /proc/$server_pid ]] && ! (readlink /proc/$server_pid/fd/* 2>/dev/null | grep -q ^socket:); do sleep 0.1; done
+	local i
+	for ((i = ${#cleanup[@]} - 1; i >= 0; i--)); do
+		eval "set -x; ${cleanup[$i]}"
+		{ set +x; } &>/dev/null
+	done
+}
+trap cleanup EXIT
 
-out=$("${client[@]}" ls -l '')
-expect_lines \
-	'd-r-xr-xr-x M 0 root root   0 Oct  7  2024 Documentation' \
-	'--r--r--r-- M 0 root root 166 Oct  7  2024 README.md' \
-	'---w--w--w- M 0 root root   0 Oct  7  2024 shutdown'
+logfile=$(mktemp -t lib9p-log.XXXXXXXXXX)
+cleanup+=("rm -f -- ${logfile@Q}")
 
-out=$("${client[@]}" ls -l 'Documentation/')
-expect_lines \
-	'--r--r--r-- M 0 root root 166 Oct  7  2024 x'
-
-out=$("${client[@]}" read 'README.md')
-expect_lines \
-	'<!--' \
-	'  README.md - test static file' \
-	'' \
-	'  Copyright (C) 2024-2025  Luke T. Shumaker <lukeshu@lukeshu.com>' \
-	'  SPDX-License-Identifier: AGPL-3.0-or-later' \
-	'-->' \
-	'Hello, world!'
+port=$(python -c 'import socket; s=socket.socket(); s.bind(("", 0)); print(s.getsockname()[1]); s.close()')
 
-out=$("${client[@]}" read 'Documentation/x')
-expect_lines \
-	'<!--' \
-	'  Documentation/x.txt - test static file' \
-	'' \
-	'  Copyright (C) 2024-2025  Luke T. Shumaker <lukeshu@lukeshu.com>' \
-	'  SPDX-License-Identifier: AGPL-3.0-or-later' \
-	'-->' \
-	'foo'
+set -x
 
-out=$("${client[@]}" stat 'Documentation/x')
-expect_lines \
-	"'x' 'root' 'root' 'root' q (0000000000000001 1 ) m 0444 at 1728337905 mt 1728337904 l 166 t 0 d 0"
+"${build_aux}/valgrind" ./tests/test_server/test_server "$port" "$logfile" &
+server_pid=$!
+cleanup+=("kill $server_pid || true; wait $server_pid || true")
+while [[ -d /proc/$server_pid ]] && ! (readlink /proc/$server_pid/fd/* 2>/dev/null | grep -q ^socket:); do sleep 0.1; done
 
-out=$("${client[@]}" write 'shutdown' <<<1)
-expect_lines ''
+if [[ "$(head -c2 -- "$clientscript")" == '#!' ]]; then
+	"$clientscript" "$port"
+else
+	"${build_aux}/valgrind" "$clientscript" "$port"
+fi
 
 wait "$server_pid"
-trap - EXIT
+cleanup=("${cleanup[@]::1}")
+
+diff -u -- <(grep -e '^[<>]' -- "$explog") "$logfile"
diff --git a/lib9p/tests/test_server/CMakeLists.txt b/lib9p/tests/test_server/CMakeLists.txt
index 19c8edb..eb16165 100644
--- a/lib9p/tests/test_server/CMakeLists.txt
+++ b/lib9p/tests/test_server/CMakeLists.txt
@@ -10,6 +10,7 @@ if (PICO_PLATFORM STREQUAL "host")
 add_library(test_server_objs OBJECT
 	main.c
 	fs_shutdown.c
+	fs_slowread.c
 )
 target_include_directories(test_server_objs PUBLIC ${CMAKE_CURRENT_SOURCE_DIR}/config)
 target_include_directories(test_server_objs PRIVATE ${CMAKE_CURRENT_BINARY_DIR})
diff --git a/lib9p/tests/test_server/fs_slowread.c b/lib9p/tests/test_server/fs_slowread.c
new file mode 100644
index 0000000..520edd2
--- /dev/null
+++ b/lib9p/tests/test_server/fs_slowread.c
@@ -0,0 +1,101 @@
+/* lib9p/tests/test_server/fs_slowread.c - slowread API endpoint
+ *
+ * Copyright (C) 2024-2025  Luke T. Shumaker <lukeshu@lukeshu.com>
+ * SPDX-License-Identifier: AGPL-3.0-or-later
+ */
+
+#include "fs_slowread.h"
+
+LO_IMPLEMENTATION_C(lib9p_srv_file, struct slowread_file, slowread_file, static);
+
+LO_IMPLEMENTATION_H(lib9p_srv_fio, struct slowread_file, slowread_file);
+LO_IMPLEMENTATION_C(lib9p_srv_fio, struct slowread_file, slowread_file, static);
+
+/* srv_file *******************************************************************/
+
+static void slowread_file_free(struct slowread_file *self) {
+	assert(self);
+}
+static struct lib9p_qid slowread_file_qid(struct slowread_file *self) {
+	assert(self);
+	return (struct lib9p_qid){
+		.type = LIB9P_QT_FILE,
+		.vers = 1,
+		.path = self->pathnum,
+	};
+}
+
+static struct lib9p_stat slowread_file_stat(struct slowread_file *self, struct lib9p_srv_ctx *ctx) {
+	assert(self);
+	assert(ctx);
+	return (struct lib9p_stat){
+		.kern_type                = 0,
+		.kern_dev                 = 0,
+		.file_qid                 = slowread_file_qid(self),
+		.file_mode                = 0444,
+		.file_atime               = UTIL9P_ATIME,
+		.file_mtime               = UTIL9P_MTIME,
+		.file_size                = 6,
+		.file_name                = lib9p_str(self->name),
+		.file_owner_uid           = lib9p_str("root"),
+		.file_owner_gid           = lib9p_str("root"),
+		.file_last_modified_uid   = lib9p_str("root"),
+		.file_extension           = lib9p_str(NULL),
+		.file_owner_n_uid         = 0,
+		.file_owner_n_gid         = 0,
+		.file_last_modified_n_uid = 0,
+	};
+}
+static void slowread_file_wstat(struct slowread_file *self, struct lib9p_srv_ctx *ctx, struct lib9p_stat) {
+	assert(self);
+	assert(ctx);
+	lib9p_error(&ctx->basectx, LINUX_EROFS, "cannot wstat API file");
+}
+static void slowread_file_remove(struct slowread_file *self, struct lib9p_srv_ctx *ctx) {
+	assert(self);
+	assert(ctx);
+	lib9p_error(&ctx->basectx, LINUX_EROFS, "cannot remove API file");
+}
+
+LIB9P_SRV_NOTDIR(struct slowread_file, slowread_file)
+
+static lo_interface lib9p_srv_fio slowread_file_fopen(struct slowread_file *self, struct lib9p_srv_ctx *ctx, bool, bool, bool) {
+	assert(self);
+	assert(ctx);
+	return lo_box_slowread_file_as_lib9p_srv_fio(self);
+}
+
+/* srv_fio ********************************************************************/
+
+static void slowread_file_iofree(struct slowread_file *self) {
+	assert(self);
+}
+
+static uint32_t slowread_file_iounit(struct slowread_file *self) {
+	assert(self);
+	return 0;
+}
+
+static uint32_t slowread_file_pwrite(struct slowread_file *LM_UNUSED(self),
+                                     struct lib9p_srv_ctx *LM_UNUSED(ctx),
+                                     void *LM_UNUSED(buf), uint32_t LM_UNUSED(byte_count),
+                                     uint64_t LM_UNUSED(offset)) {
+	assert_notreached("not writable");
+}
+static void slowread_file_pread(struct slowread_file *self, struct lib9p_srv_ctx *ctx,
+                                uint32_t byte_count, uint64_t LM_UNUSED(byte_offset),
+                                struct iovec *ret) {
+	assert(self);
+	assert(ctx);
+	assert(ret);
+
+	while (!lib9p_srv_flush_requested(ctx))
+		cr_yield();
+	if (self->flushable)
+		lib9p_srv_acknowledge_flush(ctx);
+	else
+		*ret = (struct iovec){
+			.iov_base = "Sloth\n",
+			.iov_len = 6 < byte_count ? 6 : byte_count,
+		};
+}
diff --git a/lib9p/tests/test_server/fs_slowread.h b/lib9p/tests/test_server/fs_slowread.h
new file mode 100644
index 0000000..ef4b65f
--- /dev/null
+++ b/lib9p/tests/test_server/fs_slowread.h
@@ -0,0 +1,22 @@
+/* lib9p/tests/test_server/fs_slowread.h - slowread API endpoint
+ *
+ * Copyright (C) 2024-2025  Luke T. Shumaker <lukeshu@lukeshu.com>
+ * SPDX-License-Identifier: AGPL-3.0-or-later
+ */
+
+#ifndef _LIB9P_TESTS_TEST_SERVER_FS_SLOWREAD_H_
+#define _LIB9P_TESTS_TEST_SERVER_FS_SLOWREAD_H_
+
+#include <util9p/static.h>
+#include <libhw/host_net.h>
+
+struct slowread_file {
+	char            *name;
+	uint64_t         pathnum;
+
+	bool            flushable;
+};
+LO_IMPLEMENTATION_H(lib9p_srv_file, struct slowread_file, slowread_file);
+#define lo_box_slowread_file_as_lib9p_srv_file(obj) util9p_box(slowread_file, obj)
+
+#endif /* _LIB9P_TESTS_TEST_SERVER_FS_SLOWREAD_H_ */
diff --git a/lib9p/tests/test_server/main.c b/lib9p/tests/test_server/main.c
index 8d22a04..2743629 100644
--- a/lib9p/tests/test_server/main.c
+++ b/lib9p/tests/test_server/main.c
@@ -5,6 +5,8 @@
  */
 
 #include <error.h>
+#include <errno.h>
+#include <stdio.h>
 #include <stdlib.h> /* for atoi() */
 
 #include <lib9p/srv.h>
@@ -18,6 +20,7 @@
 
 #include "static.h"
 #include "fs_shutdown.h"
+#include "fs_slowread.h"
 
 /* configuration **************************************************************/
 
@@ -37,6 +40,7 @@ struct {
 	uint16_t                        port;
 	struct hostnet_tcp_listener     listeners[CONFIG_SRV9P_NUM_CONNS];
 	struct lib9p_srv                srv;
+	FILE                           *logstream;
 } globals = {
 	.srv = (struct lib9p_srv){
 		.rootdir = get_root,
@@ -45,32 +49,33 @@ struct {
 
 /* file tree ******************************************************************/
 
-enum { PATH_BASE = __COUNTER__ };
-#define PATH_COUNTER __COUNTER__ - PATH_BASE
-
-#define STATIC_FILE(STRNAME, SYMNAME)                                      \
-	UTIL9P_STATIC_FILE(PATH_COUNTER, STRNAME,                          \
+#define STATIC_FILE(N, STRNAME, SYMNAME)                                   \
+	UTIL9P_STATIC_FILE(N, STRNAME,                                     \
 	                   .data_start = _binary_static_##SYMNAME##_start, \
 	                   .data_end   = _binary_static_##SYMNAME##_end)
-#define STATIC_DIR(STRNAME, ...)  \
-	UTIL9P_STATIC_DIR(PATH_COUNTER, STRNAME, __VA_ARGS__)
+#define STATIC_DIR(N, STRNAME, ...) \
+	UTIL9P_STATIC_DIR(N, STRNAME, __VA_ARGS__)
 
-#define API_FILE(STRNAME, SYMNAME, ...)                                      \
+#define API_FILE(N, STRNAME, SYMNAME, ...)                                   \
 	lo_box_##SYMNAME##_file_as_lib9p_srv_file(&((struct SYMNAME##_file){ \
 		.name = STRNAME,                                             \
-		.pathnum = PATH_COUNTER                                      \
+		.pathnum = N                                                 \
 		__VA_OPT__(,) __VA_ARGS__                                    \
 	}))
 
 struct lib9p_srv_file root =
-		STATIC_DIR("",
-		           STATIC_DIR("Documentation",
-		                      STATIC_FILE("x", Documentation_x_txt),
+		STATIC_DIR(1, "",
+		           STATIC_DIR(2, "Documentation",
+		                      STATIC_FILE(3, "x", Documentation_x_txt),
 		                      ),
-		           STATIC_FILE("README.md", README_md),
-		           API_FILE("shutdown", shutdown,
+		           STATIC_FILE(4, "README.md", README_md),
+		           API_FILE(5, "shutdown", shutdown,
 		                   .listeners = globals.listeners,
 		                   .nlisteners = LM_ARRAY_LEN(globals.listeners)),
+		           API_FILE(6, "slowread", slowread,
+		                    .flushable = false),
+		           API_FILE(7, "slowread-flushable", slowread,
+		                    .flushable = true),
 		           );
 
 static lo_interface lib9p_srv_file get_root(struct lib9p_srv_ctx *LM_UNUSED(ctx), struct lib9p_s LM_UNUSED(treename)) {
@@ -109,15 +114,41 @@ static COROUTINE init_cr(void *) {
 	cr_exit();
 }
 
+static void log_fct(char character, void *_stream) {
+	FILE *stream = _stream;
+	putc(character, stream);
+	putchar(character);
+}
+
+static void log_msg(struct lib9p_srv_ctx *ctx, enum lib9p_msg_type typ, void *hostmsg) {
+	/* It sucks that %v trips -Wformat and -Wformat-extra-args
+	 * https://gcc.gnu.org/bugzilla/show_bug.cgi?id=47781 */
+#pragma GCC diagnostic push
+#pragma GCC diagnostic ignored "-Wformat"
+#pragma GCC diagnostic ignored "-Wformat-extra-args"
+	fmt_fctprintf(log_fct, globals.logstream,
+	              "%c %v\n", typ % 2 ? '<' : '>',
+	              lo_box_lib9p_msg_as_fmt_formatter(&ctx->basectx, typ, hostmsg));
+#pragma GCC diagnostic pop
+	fflush(globals.logstream);
+}
+
 int main(int argc, char *argv[]) {
-	if (argc != 2)
-		error(2, 0, "usage: %s PORT_NUMBER", argv[0]);
+	if (argc != 3)
+		error(2, 0, "usage: %s PORT_NUMBER LOGFILE", argv[0]);
+
 	globals.port = atoi(argv[1]);
+	globals.logstream = fopen(argv[2], "w");
+	if (!globals.logstream)
+		error(2, errno, "fopen");
+	globals.srv.msglog = log_msg;
+
 	struct hostclock clock_monotonic = {
 		.clock_id = CLOCK_MONOTONIC,
 	};
 	bootclock = lo_box_hostclock_as_alarmclock(&clock_monotonic);
 	coroutine_add("init", init_cr, NULL);
 	coroutine_main();
+	fclose(globals.logstream);
 	return 0;
 }
diff --git a/lib9p/tests/testclient-p9p b/lib9p/tests/testclient-p9p
new file mode 100755
index 0000000..81a7e50
--- /dev/null
+++ b/lib9p/tests/testclient-p9p
@@ -0,0 +1,61 @@
+#!/usr/bin/env bash
+# lib9p/tests/testclient-p9p - Test the 9P `test_server` against Plan 9 Port's `9p` utility
+#
+# Copyright (C) 2025  Luke T. Shumaker <lukeshu@lukeshu.com>
+# SPDX-License-Identifier: AGPL-3.0-or-later
+
+set -euE -o pipefail
+
+if [[ $# != 1 ]]; then
+	echo >&2 "Usage: $0 SERVER_PORT"
+	echo >&2 "Usage: ./runtest $0 EXPLOG"
+	exit 2
+fi
+
+expect_lines() (
+	{ set +x; } &>/dev/null
+	printf >&2 '+ diff -u expected.txt actual.txt\n'
+	diff -u <(printf '%s\n' "$@") <(printf '%s\n' "$out")
+)
+
+set -x
+client=(9p -a "localhost:${1}")
+
+out=$("${client[@]}" ls -l '')
+expect_lines \
+	'd-r-xr-xr-x M 0 root root   0 Oct  7  2024 Documentation' \
+	'--r--r--r-- M 0 root root 166 Oct  7  2024 README.md' \
+	'---w--w--w- M 0 root root   0 Oct  7  2024 shutdown' \
+	'--r--r--r-- M 0 root root   6 Oct  7  2024 slowread' \
+	'--r--r--r-- M 0 root root   6 Oct  7  2024 slowread-flushable'
+
+out=$("${client[@]}" ls -l 'Documentation/')
+expect_lines \
+	'--r--r--r-- M 0 root root 166 Oct  7  2024 x'
+
+out=$("${client[@]}" read 'README.md')
+expect_lines \
+	'<!--' \
+	'  README.md - test static file' \
+	'' \
+	'  Copyright (C) 2024-2025  Luke T. Shumaker <lukeshu@lukeshu.com>' \
+	'  SPDX-License-Identifier: AGPL-3.0-or-later' \
+	'-->' \
+	'Hello, world!'
+
+out=$("${client[@]}" read 'Documentation/x')
+expect_lines \
+	'<!--' \
+	'  Documentation/x.txt - test static file' \
+	'' \
+	'  Copyright (C) 2024-2025  Luke T. Shumaker <lukeshu@lukeshu.com>' \
+	'  SPDX-License-Identifier: AGPL-3.0-or-later' \
+	'-->' \
+	'foo'
+
+out=$("${client[@]}" stat 'Documentation/x')
+expect_lines \
+	"'x' 'root' 'root' 'root' q (0000000000000003 1 ) m 0444 at 1728337905 mt 1728337904 l 166 t 0 d 0"
+
+out=$("${client[@]}" write 'shutdown' <<<1)
+expect_lines ''
diff --git a/lib9p/tests/testclient-p9p.explog b/lib9p/tests/testclient-p9p.explog
new file mode 100644
index 0000000..3bfb0b0
--- /dev/null
+++ b/lib9p/tests/testclient-p9p.explog
@@ -0,0 +1,106 @@
+# lib9p/tests/testclient-p9p.explog - Expected 9P logfile of testclient-p9p
+#
+# Copyright (C) 2025  Luke T. Shumaker <lukeshu@lukeshu.com>
+# SPDX-License-Identifier: AGPL-3.0-or-later
+> Tversion { tag=NOTAG max_msg_size=8192 version="9P2000" }
+< Rversion { tag=NOTAG max_msg_size=4120 version="9P2000" }
+> Tauth { tag=0 afid=0 uname="lukeshu" aname="" n_uid=0 }
+< Rerror { tag=0 errstr="authentication not required" errnum=95 }
+> Tattach { tag=0 fid=0 afid=NOFID uname="lukeshu" aname="" n_uid=0 }
+< Rattach { tag=0 qid={ type=(DIR) vers=1 path=1 } }
+> Twalk { tag=0 fid=0 newfid=1 nwname=0 wname=[ ] }
+< Rwalk { tag=0 nwqid=0 wqid=[ ] }
+> Tstat { tag=0 fid=1 }
+< Rstat { tag=0 stat={ kern_type=0 kern_dev=0 file_qid={ type=(DIR) vers=1 path=1 } file_mode=(DIR|0555) file_atime=1728337905 file_mtime=1728337904 file_size=0 file_name="" file_owner_uid="root" file_owner_gid="root" file_last_modified_uid="root" file_extension="" file_owner_n_uid=0 file_owner_n_gid=0 file_last_modified_n_uid=0 } }
+> Tclunk { tag=0 fid=1 }
+< Rclunk { tag=0 }
+> Twalk { tag=0 fid=0 newfid=1 nwname=0 wname=[ ] }
+< Rwalk { tag=0 nwqid=0 wqid=[ ] }
+> Topen { tag=0 fid=1 mode=(MODE_READ) }
+< Ropen { tag=0 qid={ type=(DIR) vers=1 path=1 } iounit=0 }
+> Tread { tag=0 fid=1 offset=0 count=4096 }
+< Rread { tag=0 count=361 data=<bytedata> }
+> Tread { tag=0 fid=1 offset=361 count=4096 }
+< Rread { tag=0 count=0 data="" }
+> Tclunk { tag=0 fid=1 }
+< Rclunk { tag=0 }
+> Tversion { tag=NOTAG max_msg_size=8192 version="9P2000" }
+< Rversion { tag=NOTAG max_msg_size=4120 version="9P2000" }
+> Tauth { tag=0 afid=0 uname="lukeshu" aname="" n_uid=0 }
+< Rerror { tag=0 errstr="authentication not required" errnum=95 }
+> Tattach { tag=0 fid=0 afid=NOFID uname="lukeshu" aname="" n_uid=0 }
+< Rattach { tag=0 qid={ type=(DIR) vers=1 path=1 } }
+> Twalk { tag=0 fid=0 newfid=1 nwname=1 wname=["Documentation" ] }
+< Rwalk { tag=0 nwqid=1 wqid=[{ type=(DIR) vers=1 path=2 } ] }
+> Tstat { tag=0 fid=1 }
+< Rstat { tag=0 stat={ kern_type=0 kern_dev=0 file_qid={ type=(DIR) vers=1 path=2 } file_mode=(DIR|0555) file_atime=1728337905 file_mtime=1728337904 file_size=0 file_name="Documentation" file_owner_uid="root" file_owner_gid="root" file_last_modified_uid="root" file_extension="" file_owner_n_uid=0 file_owner_n_gid=0 file_last_modified_n_uid=0 } }
+> Tclunk { tag=0 fid=1 }
+< Rclunk { tag=0 }
+> Twalk { tag=0 fid=0 newfid=1 nwname=1 wname=["Documentation" ] }
+< Rwalk { tag=0 nwqid=1 wqid=[{ type=(DIR) vers=1 path=2 } ] }
+> Topen { tag=0 fid=1 mode=(MODE_READ) }
+< Ropen { tag=0 qid={ type=(DIR) vers=1 path=2 } iounit=0 }
+> Tread { tag=0 fid=1 offset=0 count=4096 }
+< Rread { tag=0 count=62 data=<bytedata> }
+> Tread { tag=0 fid=1 offset=62 count=4096 }
+< Rread { tag=0 count=0 data="" }
+> Tclunk { tag=0 fid=1 }
+< Rclunk { tag=0 }
+> Tversion { tag=NOTAG max_msg_size=8192 version="9P2000" }
+< Rversion { tag=NOTAG max_msg_size=4120 version="9P2000" }
+> Tauth { tag=0 afid=0 uname="lukeshu" aname="" n_uid=0 }
+< Rerror { tag=0 errstr="authentication not required" errnum=95 }
+> Tattach { tag=0 fid=0 afid=NOFID uname="lukeshu" aname="" n_uid=0 }
+< Rattach { tag=0 qid={ type=(DIR) vers=1 path=1 } }
+> Twalk { tag=0 fid=0 newfid=1 nwname=1 wname=["README.md" ] }
+< Rwalk { tag=0 nwqid=1 wqid=[{ type=(0) vers=1 path=4 } ] }
+> Topen { tag=0 fid=1 mode=(MODE_READ) }
+< Ropen { tag=0 qid={ type=(0) vers=1 path=4 } iounit=0 }
+> Tread { tag=0 fid=1 offset=0 count=4096 }
+< Rread { tag=0 count=166 data="<!--\n  README.md - test static file\n\n  Copyright ("... }
+> Tread { tag=0 fid=1 offset=166 count=4096 }
+< Rread { tag=0 count=0 data="" }
+> Tclunk { tag=0 fid=1 }
+< Rclunk { tag=0 }
+> Tversion { tag=NOTAG max_msg_size=8192 version="9P2000" }
+< Rversion { tag=NOTAG max_msg_size=4120 version="9P2000" }
+> Tauth { tag=0 afid=0 uname="lukeshu" aname="" n_uid=0 }
+< Rerror { tag=0 errstr="authentication not required" errnum=95 }
+> Tattach { tag=0 fid=0 afid=NOFID uname="lukeshu" aname="" n_uid=0 }
+< Rattach { tag=0 qid={ type=(DIR) vers=1 path=1 } }
+> Twalk { tag=0 fid=0 newfid=1 nwname=2 wname=["Documentation", "x" ] }
+< Rwalk { tag=0 nwqid=2 wqid=[{ type=(DIR) vers=1 path=2 }, { type=(0) vers=1 path=3 } ] }
+> Topen { tag=0 fid=1 mode=(MODE_READ) }
+< Ropen { tag=0 qid={ type=(0) vers=1 path=3 } iounit=0 }
+> Tread { tag=0 fid=1 offset=0 count=4096 }
+< Rread { tag=0 count=166 data="<!--\n  Documentation/x.txt - test static file\n\n  C"... }
+> Tread { tag=0 fid=1 offset=166 count=4096 }
+< Rread { tag=0 count=0 data="" }
+> Tclunk { tag=0 fid=1 }
+< Rclunk { tag=0 }
+> Tversion { tag=NOTAG max_msg_size=8192 version="9P2000" }
+< Rversion { tag=NOTAG max_msg_size=4120 version="9P2000" }
+> Tauth { tag=0 afid=0 uname="lukeshu" aname="" n_uid=0 }
+< Rerror { tag=0 errstr="authentication not required" errnum=95 }
+> Tattach { tag=0 fid=0 afid=NOFID uname="lukeshu" aname="" n_uid=0 }
+< Rattach { tag=0 qid={ type=(DIR) vers=1 path=1 } }
+> Twalk { tag=0 fid=0 newfid=1 nwname=2 wname=["Documentation", "x" ] }
+< Rwalk { tag=0 nwqid=2 wqid=[{ type=(DIR) vers=1 path=2 }, { type=(0) vers=1 path=3 } ] }
+> Tstat { tag=0 fid=1 }
+< Rstat { tag=0 stat={ kern_type=0 kern_dev=0 file_qid={ type=(0) vers=1 path=3 } file_mode=(0444) file_atime=1728337905 file_mtime=1728337904 file_size=166 file_name="x" file_owner_uid="root" file_owner_gid="root" file_last_modified_uid="root" file_extension="" file_owner_n_uid=0 file_owner_n_gid=0 file_last_modified_n_uid=0 } }
+> Tclunk { tag=0 fid=1 }
+< Rclunk { tag=0 }
+> Tversion { tag=NOTAG max_msg_size=8192 version="9P2000" }
+< Rversion { tag=NOTAG max_msg_size=4120 version="9P2000" }
+> Tauth { tag=0 afid=0 uname="lukeshu" aname="" n_uid=0 }
+< Rerror { tag=0 errstr="authentication not required" errnum=95 }
+> Tattach { tag=0 fid=0 afid=NOFID uname="lukeshu" aname="" n_uid=0 }
+< Rattach { tag=0 qid={ type=(DIR) vers=1 path=1 } }
+> Twalk { tag=0 fid=0 newfid=1 nwname=1 wname=["shutdown" ] }
+< Rwalk { tag=0 nwqid=1 wqid=[{ type=(0) vers=1 path=5 } ] }
+> Topen { tag=0 fid=1 mode=(TRUNC|MODE_WRITE) }
+< Ropen { tag=0 qid={ type=(0) vers=1 path=5 } iounit=0 }
+> Twrite { tag=0 fid=1 offset=0 count=2 data="1\n" }
+< Rwrite { tag=0 count=2 }
+> Tclunk { tag=0 fid=1 }
+< Rclunk { tag=0 }
diff --git a/lib9p/tests/testclient-sess.c b/lib9p/tests/testclient-sess.c
new file mode 100644
index 0000000..423dc2c
--- /dev/null
+++ b/lib9p/tests/testclient-sess.c
@@ -0,0 +1,144 @@
+/* lib9p/tests/testclient-sess.c - Test the 9P `test_server`'s sessions
+ *
+ * Copyright (C) 2025  Luke T. Shumaker <lukeshu@lukeshu.com>
+ * SPDX-License-Identifier: AGPL-3.0-or-later
+ */
+
+#include <arpa/inet.h> /* for htons(), inet_addr() */
+#include <errno.h>
+#include <error.h>
+#include <netinet/in.h> /* for struct sockaddr{,_in} */
+#include <stdlib.h> /* for atoi() */
+#include <sys/socket.h> /* for socket(), connect() */
+#include <sys/uio.h> /* for writev() */
+#include <unistd.h> /* for read() */
+
+#include <libmisc/assert.h>
+#include <libmisc/endian.h>
+#include <lib9p/9p.h>
+
+#define MAX_MSG_SIZE (8*1024)
+
+static void _send9p(int fd, struct lib9p_ctx *ctx, enum lib9p_msg_type typ, void *body) {
+	struct lib9p_Tmsg_send_buf buf;
+	bool err = lib9p_Tmsg_marshal(ctx, typ, body, &buf);
+	assert(!err);
+	size_t exp = 0;
+	for (size_t i = 0; i < buf.iov_cnt; i++)
+		exp += buf.iov[i].iov_len;
+	ssize_t act = writev(fd, buf.iov, buf.iov_cnt);
+	if (act < 0)
+		error(1, errno, "writev");
+	assert((size_t)act == exp);
+}
+
+#define send9p(typ, ...) _send9p(fd, &ctx, LIB9P_TYP_##typ, &((struct lib9p_msg_##typ){ __VA_ARGS__ }))
+
+static void _recv9p(int fd) {
+	uint8_t buf[MAX_MSG_SIZE];
+	size_t goal = 4;
+	size_t done = 0;
+	while (done < goal) {
+		ssize_t n = read(fd, &buf[done], goal-done);
+		if (n < 0)
+			error(1, errno, "read");
+		done += n;
+	}
+	goal = uint32le_decode(buf);
+	assert(goal <= MAX_MSG_SIZE);
+	while (done < goal) {
+		ssize_t n = read(fd, &buf[done], goal-done);
+		if (n < 0)
+			error(1, errno, "read");
+		done += n;
+	}
+}
+
+#define recv9p() _recv9p(fd)
+
+int main(int argc, char *argv[]) {
+	if (argc != 2)
+		error(2, 0, "Usage: %s SERVER_PORT", argv[0]);
+	uint16_t server_port = atoi(argv[1]);
+
+	union {
+                struct sockaddr         gen;
+                struct sockaddr_in      in;
+	} server_addr = {};
+	server_addr.in.sin_family = AF_INET;
+	server_addr.in.sin_addr.s_addr = inet_addr("127.0.0.1");
+	server_addr.in.sin_port = htons(server_port);
+
+	int fd = socket(AF_INET, SOCK_STREAM, 0);
+	if (fd < 0)
+		error(1, errno, "socket");
+	if (connect(fd, &server_addr.gen, sizeof(server_addr)) < 0)
+		error(1, errno, "connect");
+
+	struct lib9p_ctx ctx = {
+		.max_msg_size = 16*1024,
+	};
+
+	struct lib9p_s wname[1];
+
+	/* numeric downgrade, unknown ext *************************************/
+	send9p(Tversion, .tag=0, .max_msg_size=57, .version=lib9p_str("9P2025.x"));
+	recv9p(); /* Rversion */
+	ctx.version = LIB9P_VER_9P2000;
+
+	/* numeric downgrade, known ext ***************************************/
+	send9p(Tversion, .tag=0, .max_msg_size=57, .version=lib9p_str("9P2025.u"));
+	recv9p(); /* Rversion */
+	ctx.version = LIB9P_VER_9P2000_u;
+
+	/* ext version ********************************************************/
+	send9p(Tversion, .tag=0, .max_msg_size=57, .version=lib9p_str("9P2000.u"));
+	recv9p(); /* Rversion */
+	ctx.version = LIB9P_VER_9P2000_u;
+
+	/* main session *******************************************************/
+	send9p(Tversion, .tag=0, .max_msg_size=(8*1024), .version=lib9p_str("9P2000"));
+	recv9p(); /* Rversion */
+	ctx.version = LIB9P_VER_9P2000;
+	send9p(Tattach, .tag=0, .fid=0, .afid=LIB9P_FID_NOFID, .uname=lib9p_str("nobody"), .aname=lib9p_str(""));
+	recv9p(); /* Rattach */
+
+	/* flush, but original response comes back first */
+	wname[0] = lib9p_str("slowread"); send9p(Twalk, .tag=0, .fid=0, .newfid=1, .nwname=1, .wname=wname);
+	recv9p(); /* Rwalk */
+	send9p(Topen, .tag=0, .fid=1, .mode=LIB9P_O_MODE_READ);
+	recv9p(); /* Ropen */
+	send9p(Tread, .tag=1, .fid=1, .offset=0, .count=6);
+	send9p(Tflush, .tag=2, .oldtag=1);
+	recv9p(); /* Rread */
+	recv9p(); /* Rflush */
+
+	/* flush, original request is aborted with error */
+	wname[0] = lib9p_str("slowread-flushable"); send9p(Twalk, .tag=1, .fid=0, .newfid=2, .nwname=1, .wname=wname);
+	recv9p(); /* Rwalk */
+	send9p(Topen, .tag=0, .fid=2, .mode=LIB9P_O_MODE_READ);
+	recv9p(); /* Ropen */
+	send9p(Tread, .tag=1, .fid=2, .offset=0, .count=6);
+	send9p(Tflush, .tag=2, .oldtag=1);
+	recv9p(); /* Rerror */
+	recv9p(); /* Rflush */
+
+	/* flush, unknown tag */
+	send9p(Tflush, .tag=0, .oldtag=99);
+	recv9p(); /* Rflush */
+
+	/* shutdown ***********************************************************/
+	send9p(Tversion, .tag=0, .max_msg_size=(8*1024), .version=lib9p_str("9P2000"));
+	recv9p(); /* Rversion */
+	ctx.version = LIB9P_VER_9P2000;
+	send9p(Tattach, .tag=0, .fid=0, .afid=LIB9P_FID_NOFID, .uname=lib9p_str("nobody"), .aname=lib9p_str(""));
+	recv9p(); /* Rattach */
+	/* check the newfid==fid case */
+	wname[0] = lib9p_str("shutdown"); send9p(Twalk, .tag=0, .fid=0, .newfid=0, .nwname=1, .wname=wname);
+	recv9p(); /* Rwalk */
+	send9p(Topen, .tag=0, .fid=0, .mode=LIB9P_O_MODE_WRITE);
+	recv9p(); /* Ropen */
+	send9p(Twrite, .tag=0, .fid=0, .offset=0, .count=2, .data="1\n");
+	recv9p(); /* Rwrite */
+	return 0;
+}
diff --git a/lib9p/tests/testclient-sess.explog b/lib9p/tests/testclient-sess.explog
new file mode 100644
index 0000000..b1f3085
--- /dev/null
+++ b/lib9p/tests/testclient-sess.explog
@@ -0,0 +1,58 @@
+# lib9p/tests/testclient-sess.explog - Expected 9P logfile of testclient-sess.c
+#
+# Copyright (C) 2025  Luke T. Shumaker <lukeshu@lukeshu.com>
+# SPDX-License-Identifier: AGPL-3.0-or-later
+
+# numeric downgrade, unknown ext ###############################################
+> Tversion { tag=0 max_msg_size=57 version="9P2025.x" }
+< Rversion { tag=0 max_msg_size=57 version="9P2000" }
+
+# numeric downgrade, known ext #################################################
+> Tversion { tag=0 max_msg_size=57 version="9P2025.u" }
+< Rversion { tag=0 max_msg_size=57 version="9P2000.u" }
+
+# ext version ##################################################################
+> Tversion { tag=0 max_msg_size=57 version="9P2000.u" }
+< Rversion { tag=0 max_msg_size=57 version="9P2000.u" }
+
+# main session #################################################################
+> Tversion { tag=0 max_msg_size=8192 version="9P2000" }
+< Rversion { tag=0 max_msg_size=4120 version="9P2000" }
+> Tattach { tag=0 fid=0 afid=NOFID uname="nobody" aname="" n_uid=0 }
+< Rattach { tag=0 qid={ type=(DIR) vers=1 path=1 } }
+
+# flush, but original response comes back first
+> Twalk { tag=0 fid=0 newfid=1 nwname=1 wname=["slowread" ] }
+< Rwalk { tag=0 nwqid=1 wqid=[{ type=(0) vers=1 path=6 } ] }
+> Topen { tag=0 fid=1 mode=(MODE_READ) }
+< Ropen { tag=0 qid={ type=(0) vers=1 path=6 } iounit=0 }
+> Tread { tag=1 fid=1 offset=0 count=6 }
+> Tflush { tag=2 oldtag=1 }
+< Rread { tag=1 count=6 data="Sloth\n" }
+< Rflush { tag=2 }
+
+# flush, succeeds
+> Twalk { tag=1 fid=0 newfid=2 nwname=1 wname=["slowread-flushable" ] }
+< Rwalk { tag=1 nwqid=1 wqid=[{ type=(0) vers=1 path=7 } ] }
+> Topen { tag=0 fid=2 mode=(MODE_READ) }
+< Ropen { tag=0 qid={ type=(0) vers=1 path=7 } iounit=0 }
+> Tread { tag=1 fid=2 offset=0 count=6 }
+> Tflush { tag=2 oldtag=1 }
+< Rflush { tag=2 }
+< Rerror { tag=1 errstr="request canceled by flush" errnum=125 }
+
+# flush, unknown tag
+> Tflush { tag=0 oldtag=99 }
+< Rflush { tag=0 }
+
+# shutdown #####################################################################
+> Tversion { tag=0 max_msg_size=8192 version="9P2000" }
+< Rversion { tag=0 max_msg_size=4120 version="9P2000" }
+> Tattach { tag=0 fid=0 afid=NOFID uname="nobody" aname="" n_uid=0 }
+< Rattach { tag=0 qid={ type=(DIR) vers=1 path=1 } }
+> Twalk { tag=0 fid=0 newfid=0 nwname=1 wname=["shutdown" ] }
+< Rwalk { tag=0 nwqid=1 wqid=[{ type=(0) vers=1 path=5 } ] }
+> Topen { tag=0 fid=0 mode=(MODE_WRITE) }
+< Ropen { tag=0 qid={ type=(0) vers=1 path=5 } iounit=0 }
+> Twrite { tag=0 fid=0 offset=0 count=2 data="1\n" }
+< Rwrite { tag=0 count=2 }