Bug: SFTP Testcontainer Times out with default config / RSA key pair

Describe the bug

Using the default config for the SFTP testcontainer, the Script raises a TimeoutError. Seems to only happen with an RSA keypair user, which is included by default.

To Reproduce

Provide a self-contained code snippet that illustrates the bug or unexpected behavior. Ideally, send a Pull Request to illustrate with a test that illustrates the problem.

from testcontainers.sftp import SFTPContainer

with SFTPContainer() as sftp_container:
    print("Hello World")

Results in:

Pulling image testcontainers/ryuk:0.8.1
Container started: cffcdb6f31c4
Waiting for container <Container: cffcdb6f31c4> with image testcontainers/ryuk:0.8.1 to be ready ...
Pulling image atmoz/sftp:alpine
Container started: 170fb1ee983a
Traceback (most recent call last):
  File "/.../minimum_example.py", line 3, in <module>
    with SFTPContainer() as sftp_container:
  File "/.../.venv/lib/python3.12/site-packages/testcontainers/core/container.py", line 134, in __enter__
    return self.start()
           ^^^^^^^^^^^^
  File "/.../.venv/lib/python3.12/site-packages/testcontainers/sftp/__init__.py", line 269, in start
    wait_for_logs(self, f".*Server listening on 0.0.0.0 port {self.port}.*")
  File "/.../.venv/lib/python3.12/site-packages/testcontainers/core/waiting_utils.py", line 125, in wait_for_logs
    raise TimeoutError(f"Container did not emit logs satisfying predicate in {timeout:.3f} " "seconds")
TimeoutError: Container did not emit logs satisfying predicate in 120.000 seconds

Using only a user with a Password Authentication (no RSA key pairs) seems to work fine:

from testcontainers.sftp import SFTPContainer, SFTPUser

sftp_user = SFTPUser(name="user", password="Secret")

with SFTPContainer(users=[sftp_user]) as sftp_container:
    print("Hello World")

Pulling image testcontainers/ryuk:0.8.1
Container started: 22ffa2ac108b
Waiting for container <Container: 22ffa2ac108b> with image testcontainers/ryuk:0.8.1 to be ready ...
Pulling image atmoz/sftp:alpine
Container started: a51c685e2d50
Hello World

Runtime environment

Provide a summary of your runtime environment. Which operating system, python version, and docker version are you using? What is the version of testcontainers-python you are using? You can run the following commands to get the relevant information.

# Get the operating system information (on a unix os).
$ uname -a
Linux aoudad 6.8.0-60-generic #63~22.04.1-Ubuntu SMP PREEMPT_DYNAMIC Tue Apr 22 19:00:15 UTC 2 x86_64 x86_64 x86_64 GNU/Linux

# Get the python version.
$ python --version
Python 3.12.2

# Get the docker version and other docker information.
$ docker info
Client: Docker Engine - Community
 Version:    28.1.1
 Context:    default
 Debug Mode: false
 Plugins:
  buildx: Docker Buildx (Docker Inc.)
    Version:  v0.23.0
    Path:     /usr/libexec/docker/cli-plugins/docker-buildx
  compose: Docker Compose (Docker Inc.)
    Version:  v2.35.1
    Path:     /usr/libexec/docker/cli-plugins/docker-compose

Server:
 Containers: 4
  Running: 0
  Paused: 0
  Stopped: 4
 Images: 10
 Server Version: 28.1.1
 Storage Driver: overlay2
  Backing Filesystem: extfs
  Supports d_type: true
  Using metacopy: false
  Native Overlay Diff: true
  userxattr: false
 Logging Driver: json-file
 Cgroup Driver: systemd
 Cgroup Version: 2
 Plugins:
  Volume: local
  Network: bridge host ipvlan macvlan null overlay
  Log: awslogs fluentd gcplogs gelf journald json-file local splunk syslog
 Swarm: inactive
 Runtimes: runc io.containerd.runc.v2
 Default Runtime: runc
 Init Binary: docker-init
 containerd version: 05044ec0a9a75232cad458027ca83437aae3f4da
 runc version: 
 init version: de40ad0
 Security Options:
  apparmor
  seccomp
   Profile: builtin
  cgroupns
 Kernel Version: 6.8.0-60-generic
 Operating System: Ubuntu Core 22
 OSType: linux
 Architecture: x86_64
 CPUs: 16
 Total Memory: 30.18GiB
 Name: aoudad
 ID: f82c9622-c54f-491c-b224-132a4c383cd9
 Docker Root Dir: /var/snap/docker/common/var-lib-docker
 Debug Mode: false
 Experimental: false
 Insecure Registries:
  ::1/128
  127.0.0.0/8
 Live Restore Enabled: false

# Get all python packages.
$ pip freeze
asttokens==3.0.0
certifi==2025.4.26
cffi==1.17.1
charset-normalizer==3.4.2
comm==0.2.2
cryptography==45.0.3
debugpy==1.8.14
decorator==5.2.1
docker==7.1.0
executing==2.2.0
idna==3.10
ipykernel==6.29.5
ipython==9.3.0
ipython_pygments_lexers==1.1.1
jedi==0.19.2
jupyter_client==8.6.3
jupyter_core==5.8.1
matplotlib-inline==0.1.7
nest-asyncio==1.6.0
packaging==25.0
parso==0.8.4
pexpect==4.9.0
platformdirs==4.3.8
prompt_toolkit==3.0.51
psutil==7.0.0
ptyprocess==0.7.0
pure_eval==0.2.3
pycparser==2.22
Pygments==2.19.1
python-dateutil==2.9.0.post0
python-dotenv==1.1.0
pyzmq==26.4.0
requests==2.32.3
six==1.17.0
stack-data==0.6.3
testcontainers==4.10.0
tornado==6.5.1
traitlets==5.14.3
typing_extensions==4.14.0
urllib3==2.4.0
wcwidth==0.2.13
wrapt==1.17.2

Commencez par testcontainers/sftp/init.py, en particulier SFTPContainer.start, et examinez l’appel à wait_for_logs dans testcontainers/core/waiting_utils.py. Reproduisez la configuration par défaut avec l’utilisateur disposant de la paire de clés RSA, puis vérifiez que le démarrage se termine sans atteindre le délai d’expiration de 120 secondes et ajoutez une couverture pour ce chemin par défaut.