tests: cover the app-driven sftp and shell paths

The -A cases in scp.test reach the exec callback and the scp handoff.
These drive the rest: the subsystem callback with the sftp accept, the
shell callback in echo mode, and both accepts on a blocking server.

- sftp.test connects to an -A server blocking and non-blocking
- sshclient.test runs a terminal session and a command session against
  an -A server
- scp.test copies from a blocking -A server, where wolfSSH_SCP_accept()
  completes in one call rather than through the retry loop

scripts/scp.test

@@ -178,6 +178,26 @@ else
     exit 1
 fi
 
+# The same handoff on a blocking server, where wolfSSH_SCP_accept() runs to
+# completion in one call rather than through the retry loop above.
+echo "Test basic copy from server to local, blocking app-driven server"
+./examples/echoserver/echoserver -A -1 -R $ready_file &
+server_pid=$!
+create_port
+$run_client ./examples/scpclient/wolfscp -u jill -P upthehill -p $port -S $PWD/scripts/scp.test:$PWD/scp.test
+RESULT=$?
+remove_ready_file
+stop_server
+check_timeout $RESULT "basic copy from server to local, blocking app-driven server"
+
+if test -e $PWD/scp.test; then
+    rm $PWD/scp.test
+else
+    echo -e "\n\nfailed to get file from blocking app-driven server"
+    do_cleanup
+    exit 1
+fi
+
 echo "Test of getting empty file"
 touch $PWD/scripts/empty
 ./examples/echoserver/echoserver -1 -R $ready_file &

scripts/sftp.test

@@ -112,6 +112,41 @@ if [ $RESULT -ne 0 ]; then
     exit 1
 fi
 
+# With -A the echoserver answers the subsystem request in its own callback
+# and serves the session through wolfSSH_SFTP_accept(); the cases above take
+# the accept() re-entry instead.
+if [ "$nonblockingOnly" = 0 ]; then
+    echo "Test connection to an app-driven server"
+    ./examples/echoserver/echoserver -A -1 -R "$ready_file" &
+    server_pid=$!
+    create_port
+    echo "exit" | ./examples/sftpclient/wolfsftp -u jill -P upthehill -p "$port"
+    RESULT=$?
+    remove_ready_file
+    if [ $RESULT -ne 0 ]; then
+        echo
+        echo "failed to connect to app-driven server"
+        do_cleanup
+        exit 1
+    fi
+fi
+
+# The same handoff on a non-blocking server, which reaches the accept call's
+# want-read and want-write retries.
+echo "Test non blocking connection to an app-driven server"
+./examples/echoserver/echoserver -A -N -1 -R "$ready_file" &
+server_pid=$!
+create_port
+echo "exit" | ./examples/sftpclient/wolfsftp -N -u jill -P upthehill -p "$port"
+RESULT=$?
+remove_ready_file
+if [ $RESULT -ne 0 ]; then
+    echo
+    echo "failed to connect to non blocking app-driven server"
+    do_cleanup
+    exit 1
+fi
+
 # Test want write return from highwater callback
 if [ "$nonblockingOnly" = 0 ]; then
     echo "Test want write return from highwater callback"

scripts/sshclient.test

@@ -83,6 +83,7 @@ trap do_trap INT TERM
 # -f keeps the server in echo mode. Without it a build with shell support
 # tries to fork a login shell for the user, which fails since jill isn't a
 # real account, and the session ends before anything crosses the channel.
+# Any arguments are passed on to the echoserver.
 start_server() {
     # The -1 server exits after its connection, but a client run that failed
     # before connecting leaves one listening. Reap it, server_pid is about
@@ -95,7 +96,7 @@ start_server() {
     fi
 
     rm -f "$ready_file"
-    ./examples/echoserver/echoserver -1 -f -R "$ready_file" \
+    ./examples/echoserver/echoserver -1 -f "$@" -R "$ready_file" \
         > "$work_dir/server.log" 2>&1 &
     server_pid=$!
 
@@ -282,6 +283,25 @@ if [ -s "$work_dir/terminal.log" ]; then
         && fail "the client sent a command it wasn't given"
 fi
 
+# -A hands the session requests to the echoserver's own callbacks: the shell
+# callback claims the channel the worker echoes on, and an exec request that
+# is not a transfer runs as a session through the same callback.
+echo "Test terminal session, app-driven server"
+start_server -A
+run_client "" -E "$work_dir/appterm.log" -p $port jill@127.0.0.1
+[ $? -ne 0 ] && fail "failed to open the terminal session on an app-driven server"
+
+grep -q "hello" "$client_out" \
+    || fail "the app-driven echoserver's reply didn't make it back"
+
+echo "Test a session given a command, app-driven server"
+start_server -A
+run_client "" -E "$work_dir/appcommand.log" -p $port jill@127.0.0.1 "echo three"
+[ $? -ne 0 ] && fail "failed to open the session on an app-driven server"
+
+grep -q "hello" "$client_out" \
+    || fail "the app-driven echoserver's reply didn't make it back"
+
 echo "Test the usage message"
 ./apps/wolfssh/wolfssh -Z 2>&1 | grep -q "usage:" \
     || fail "no usage message for a bad option"