API-Docker
view release on metacpan or search on metacpan
lib/API/Docker/API/Containers.pm view on Meta::CPAN
# The Podman compatibility path, and deliberately only that. Podman answers
# GET /containers/{id}/stats for a container that is not running with an error
# object inside a response it has already committed to 200 --
# {"cause":"container is stopped","message":"container is stopped",
# "response":500}, chunked, for the one-shot call and for stream => 1 alike
# (measured on Podman 5.4.2, API 1.41). Neither guard in the transport sees
# it: the >= 400 croak reads the status line, which says 200, and the stream
# check triggers on errorDetail, which this object does not carry. Docker
# 29.7.2 (API 1.55) answers the same call with a real, zero-filled reading and
# never produces this shape at all -- so this belongs here, next to the one
# endpoint and the one engine it was measured on, and not in Role::HTTP, where
# it would be a heuristic on daemon prose sitting under all twelve modules.
#
# All four clauses have to hold. The narrowness is the point, not an accident:
#
# 1. the status was 2xx. True by construction on both paths this guards:
# _request croaks before returning for >= 400, and
# _read_streaming_response reads such a body whole rather than handing it
# to a callback, so nothing that failed the status line reaches here
# 2. the decoded value is a HashRef
# 3. it carries all three of cause, message and response, exactly
# lower-cased. Never case-insensitively, and this is the counter-example
# that fixes it: POST /containers/{id}/wait answers its SUCCESS case with
# a top-level `Error` key -- Podman sends "Error":null on every wait --
# so a rule matching /error/i would turn every successful wait into a
# failure. Measured over fifteen read endpoints per engine and every
# fixture in t/fixtures: no 2xx body on either engine carries even one of
# these three lower-cased at the top level
# 4. `response` is a non-ref scalar reading as an integer >= 400. That is
# what makes the rule self-evidencing rather than a guess about prose:
# the object is an error because Podman says so inside it. Known miss:
# Podman's GET /plugins answers {"cause":"","message":"Path ... is not
# supported","response":0}, which clause 4 rejects -- but it arrives with
# 404 on the status line and the transport croaks it long before this
# runs, so the miss goes in the conservative direction and costs nothing
#
# A bare {message => ...} deliberately does not trigger: that is the ordinary
# Docker error body, and treating one inside a 2xx as a failure would be a
# guess about prose rather than a reading of what the engine said.
sub _podman_error_object {
my ($self, $value) = @_;
return unless ref $value eq 'HASH';
return unless exists $value->{cause}
&& exists $value->{message}
&& exists $value->{response};
my $response = $value->{response};
return if ref $response;
return unless defined $response && $response =~ /\A[0-9]+\z/;
return unless $response >= 400;
return $value;
}
# API::Docker::Error::HTTP rather than ::Stream: the one-shot call is not a
# stream at all, so "Docker API stream error" would be the wrong sentence for
# it and ->events would be a fabricated list. What the caller wants instead is
# exactly what this class carries -- ->status for the code Podman named, and
# ->data for the object, whose `cause` key that attribute's own POD already
# points at. Two of its attributes are left at their defaults on this path, on
# purpose: ->reason, because the status line's reason phrase was "OK" and
# putting that on a 500 would mislead, and ->body, because the bytes were
# decoded by the transport before this check ever saw them.
sub _assert_no_podman_error {
my ($self, $endpoint, $value) = @_;
my $error = $self->_podman_error_object($value) or return $value;
my $reason = $error->{message};
$reason = $error->{cause} unless defined $reason && length $reason;
$reason = 'no message given' unless defined $reason && length $reason;
# Carp appends no location to a message that already ends in a newline.
$reason =~ s/\s+\z//;
# The object goes into a variable first: `croak CLASS->new(...)` is indirect
# object syntax and parses as CLASS->croak(new(...)). Carp hands a reference
# straight back rather than decorating it, so the location is captured by
# hand, naming the frame a croak of a plain string would have named.
my $err = API::Docker::Error::HTTP->new(
message => 'Docker API error (' . $error->{response} . '): ' . $reason
. ' -- reported inside a 200 response to ' . $endpoint,
location => shortmess(''),
status => $error->{response},
data => $error,
);
croak $err;
}
sub stats {
my ($self, $id, %opts) = @_;
croak "Container ID required" unless $id;
my $stream = $opts{stream} ? 1 : 0;
my %params = ( stream => $stream );
# one-shot asks the engine not to wait for a second sampling cycle, which
# only means anything to a single reading. It is sent for the one-shot call
# alone, the way it always was, and never beside stream => 1.
$params{'one-shot'} = 1 unless $stream;
my $endpoint = 'GET /containers/' . $id . '/stats';
# The guard has to sit on both sides of the callback split, because the same
# body arrives either way: buffered it is the return value, streamed it goes
# to the callback and is never returned at all. Wrapping puts the check in
# front of the caller's callback, so no caller is handed the error object as
# though it were a reading. Only a CodeRef is wrapped -- anything else is
# passed through untouched, so the transport still raises its own "on_event
# option must be a CodeRef" instead of this method dying on a closure it
# built around a non-callback.
my $on_event = $opts{on_event};
if (exists $opts{on_event} && ref $on_event eq 'CODE') {
my $cb = $on_event;
$on_event = sub {
my ($reading, $stop) = @_;
$self->_assert_no_podman_error($endpoint, $reading);
return $cb->($reading, $stop);
};
}
my $result = $self->client->get("/containers/$id/stats",
params => \%params,
lib/API/Docker/API/Containers.pm view on Meta::CPAN
my ($self, %opts) = @_;
my %params;
$params{filters} = $self->_normalise_filters($opts{filters})
if defined $opts{filters};
return $self->client->post('/containers/prune', undef,
params => \%params,
%{ $self->_request_options },
);
}
1;
__END__
=pod
=encoding UTF-8
=head1 NAME
API::Docker::API::Containers - Docker Engine Containers API
=head1 VERSION
version 0.004
=head1 SYNOPSIS
my $docker = API::Docker->new;
# List containers
my $containers = $docker->containers->list(all => 1);
for my $container (@$containers) {
say $container->id;
say $container->status;
}
# Create and start a container
my $result = $docker->containers->create(
Image => 'nginx:latest',
name => 'my-nginx',
ExposedPorts => { '80/tcp' => {} },
);
$docker->containers->start($result->{Id});
# Inspect container details
my $container = $docker->containers->inspect($result->{Id});
say $container->name;
# Stop and remove
$docker->containers->stop($result->{Id}, timeout => 10);
$docker->containers->remove($result->{Id});
# View logs (ArrayRef of { stream => 'stdout'|'stderr'|'raw', data => ... })
my $frames = $docker->containers->logs($result->{Id}, tail => 100);
my $text = join '', map { $_->{data} } @$frames;
# Attach one-way: replays the same frames and returns (stream => 0 by
# default -- stream => 1 on a stopped container never returns). On Podman,
# attaching to a container that has ALREADY EXITED destroys its exit
# status; use logs() for that case, see attach()
my $attached = $docker->containers->attach($result->{Id});
# Copy a file out, and a tar archive in (what docker cp is built on)
my $tar = $docker->containers->get_archive($result->{Id},
path => '/etc/hostname');
$docker->containers->put_archive($result->{Id}, $tar, path => '/tmp');
=head1 DESCRIPTION
This module provides methods for managing Docker containers including creation,
lifecycle operations (start, stop, restart), inspection, logs, and more.
C<list> and C<inspect> return generated L<API::Docker::Type> objects carrying
the convenience methods of L<API::Docker::Role::Entity::Container>, so
C<< $container->start >> and C<< $container->logs >> work on either. Which
class each returns, and where the two disagree, is below.
Accessed via C<< $docker->containers >>, or through
L<API::Docker::Role::Using/using> for a run of calls that needs its own
transport bound: C<< $docker->containers->using(read_timeout => 5) >>.
=head2 The two container shapes
The daemon describes a container two ways and the swagger has two
definitions for it, so this class returns two classes:
=over
=item * L</list> returns L<API::Docker::Type::ContainerSummary> objects --
one per entry of C<GET /containers/json>.
=item * L</inspect> returns an L<API::Docker::Type::ContainerInspectResponse>
-- the body of C<GET /containers/{id}/json>.
=back
They overlap but do not line up, and the field names are the swagger's own
spelling in snake_case (C<Id> is C<< ->id >>, C<SizeRootFs> is
C<< ->size_root_fs >>). The differences worth knowing before reading a value
off the wrong one:
=over
=item * C<< ->image >> is the name the container was created from on a
summary (C<nginx:latest>) and the resolved C<sha256:> digest on an inspect.
A summary reports that digest separately as C<< ->image_id >>; an inspect
has no such field.
=item * C<< ->created >> is an integer Unix epoch on a summary and an
RFC 3339 string on an inspect. Same field name, two types -- C<Int> and
C<Str> in the model, which is the swagger's own answer, not a normalisation
this client applies.
=item * C<< ->state >> is the status string (C<running>, C<exited>) on a
summary and an L<API::Docker::Type::ContainerState> object on an inspect,
where that string is C<< ->state->status >> and the flags are
C<< ->state->running >>, C<< ->state->paused >>, C<< ->state->exit_code >>.
L<API::Docker::Role::Entity::Container/is_running> reads whichever it is
lib/API/Docker/API/Containers.pm view on Meta::CPAN
=item * C<< ->command >> is the whole command as one string, on a summary
only. An inspect splits it into C<< ->path >> and C<< ->args >> and keeps
the original C<Cmd> ArrayRef under C<< ->config->cmd >>.
=item * C<< ->labels >> and C<< ->ports >> are top-level on a summary only.
An inspect carries the labels under C<< ->config->labels >> and the port
bindings under C<< ->network_settings->ports >>, which is a map of container
port to host bindings rather than the summary's ArrayRef of
L<API::Docker::Type::Port>.
=item * C<< ->names >> (an ArrayRef, each with a leading C</>) is the
summary's; C<< ->name >> (one string, also with the C</>) is the inspect's.
=item * C<< ->config >>, C<< ->restart_count >>, C<< ->driver >>,
C<< ->platform >>, C<< ->graph_driver >>, C<< ->exec_ids >> and the
C<*_path> fields come from an inspect only.
=item * C<< ->host_config >> and C<< ->network_settings >> exist on both and
are B<different classes>: the summary's are
L<API::Docker::Type::ContainerSummary::HostConfig> (C<NetworkMode> and
C<Annotations>, nothing else) and
L<API::Docker::Type::ContainerSummary::NetworkSettings> (C<Networks> alone),
against the full L<API::Docker::Type::HostConfig> and
L<API::Docker::Type::NetworkSettings> on an inspect.
=item * C<< ->size_rw >> and C<< ->size_root_fs >> are on both, but a
summary only carries them when C<< size => 1 >> was asked for.
=back
A field neither class knows -- a newer engine than the C<spec/v1.51.yaml>
this model was generated from -- is not dropped: it stays under the name it
arrived with in L<API::Docker::Role::Type/unknown_fields> and goes back out
unchanged.
A field whose B<value> disagrees with the swagger is kept the same way and
costs only itself. An engine answering C<State> with the bare status string
rather than the object the spec declares leaves C<< ->state >> C<undef> while
every other field of the inspect reads normally; the raw value is in
C<unknown_fields> under C<State>, and
L<API::Docker::Role::Type/rejected_fields> names it, so "not sent" and "sent
and not usable" are two different answers.
=head2 client
Reference to L<API::Docker> client. Weak reference to avoid circular dependencies.
=head2 list
my $containers = $containers->list(%opts);
List containers. Returns an ArrayRef of
L<API::Docker::Type::ContainerSummary> objects -- see L</"The two container
shapes"> for what a summary carries and L</inspect> does not.
Options:
=over
=item * C<all> - Show all containers (default shows just running)
=item * C<limit> - Limit results to N most recently created containers
=item * C<size> - Include size information
=item * C<filters> - HashRef of filter name to ArrayRef of string values, e.g.
C<< { status => ['running'], label => ['stage=build'] } >>. Shape-checked and
normalised by L<API::Docker::Role::Filters>
=back
=head2 create
my $result = $containers->create(
Image => 'nginx:latest',
name => 'my-nginx',
Cmd => ['/bin/sh'],
Env => ['FOO=bar'],
);
Create a new container. Returns hashref with C<Id> and C<Warnings>.
The C<name> parameter is extracted and passed as query parameter. All other
parameters are Docker container configuration (see Docker API documentation).
Common config keys: C<Image>, C<Cmd>, C<Env>, C<ExposedPorts>, C<HostConfig>.
Boolean flags may be given as a Perl C<1>/C<0> or as a JSON boolean; either
goes out as a real JSON C<true>/C<false>, which the engine's body type-check
requires. This applies to the top-level flags (C<Tty>, C<OpenStdin>,
C<AttachStdin>, C<AttachStdout>, C<AttachStderr>, C<StdinOnce>,
C<NetworkDisabled>, C<ArgsEscaped>) and to the C<HostConfig> flags
(C<Privileged>, C<PublishAllPorts>, C<ReadonlyRootfs>, C<AutoRemove>, C<Init>,
C<OomKillDisable>).
=head2 inspect
my $container = $containers->inspect($id);
Get detailed information about a container. Returns an
L<API::Docker::Type::ContainerInspectResponse> -- see L</"The two container
shapes">.
=head2 start
$containers->start($id);
say 'was already running' unless $containers->start($id);
Start a container. Returns 1 when the container was started and 0 when it was
already running: the engine answers a state change with 204 and a no-op with
B<304 Not Modified>, and both carry an empty body, so until now both came back
as C<undef>.
The no-op keeps the falsy value this method always returned -- 0 where it used
to be C<undef> -- so a caller that ignores the return or tests it for falseness
is unaffected; only a caller testing C<defined> sees a difference. A failure is
still a croak, never a 0.
=head2 stop
$containers->stop($id, timeout => 10);
say 'was already stopped' unless $containers->stop($id);
Stop a container. Returns 1 when the container was stopped and 0 when it was
already stopped -- the engine answers the no-op with B<304 Not Modified>. See
L</start> for what that 0 replaces.
Options:
=over
=item * C<timeout> - Seconds to wait before killing (default 10)
=item * C<signal> - Signal to send (default SIGTERM)
=back
=head2 restart
$containers->restart($id, timeout => 10);
Restart a container. Optionally specify C<timeout> in seconds.
Reports 1/0 like L</start>, but a restart has no no-op state to report: the
engine restarts a stopped container as readily as a running one. Measured
against Podman 5.4.2 (API 1.41) it answers 204 in both cases, and the Docker
Engine API documents no 304 for this endpoint either, so 0 is not expected
here. The value is reported the same way rather than specially, so an engine
that does answer 304 is not silently read as a change.
=head2 kill
$containers->kill($id, signal => 'SIGKILL');
$containers->kill($id, signal => 'SIGUSR1'); # not necessarily a stop
Send a signal to a container. Default signal is C<SIGKILL>.
Returns nothing -- unlike L</start>, L</stop>, L</restart>, L</pause> and
L</unpause>, which report 1/0 through their shared C<_state_change> path.
Those methods have two outcomes worth telling apart: a change (204) and a
no-op (304, where the engine sends one). C<kill> has only one, because
C<_request> croaks on any C<< status >= 400 >>, so the B<409> a non-running
container gets back never reaches this method's C<return>. A boolean with a
single possible value is not worth adding.
More importantly, B<204 does not mean the container stopped.> Measured on
B<both> engines -- Docker 29.7.2 (API 1.55) and rootless Podman 5.4.2 (API
1.41), same machine, identical behavior: sending a signal the container traps
or ignores -- C<< signal => 'SIGUSR1' >> against a process with a handler
installed for it -- is delivered, the container keeps running, the handler's
output turns up in L</logs>, and the engine still answers 204 exactly as it
does for a signal that does end the process. A caller that needs to know
whether the container is still running after a C<kill> has to ask
L</inspect>; that is also why this returns nothing rather than a plain C<1>
-- a 1 here would claim a state change that a trapped signal never made.
B<A paused container is where the two engines part.> Both answer 204 to
C<< signal => 'SIGUSR1' >> against a paused container, and then:
=over
=item * B<Docker unpauses it as a side effect.> L</inspect> reports C<running>
straight afterwards and the handler has already run. A caller that paused the
container and means to unpause it later gets a croak instead: the following
L</unpause> answers B<500> C<Container E<lt>idE<gt> is not paused>
=item * B<Podman leaves it paused> and queues the signal. The state stays
C<paused>, the handler produces nothing until an explicit L</unpause>, and
that L</unpause> succeeds
=back
So C<kill> is a state change for a paused container on Docker and is not one
on Podman -- with the same 204 on both.
Killing a container that is not running -- stopped, exited or just created --
croaks B<409>; it does not return a falsy value. An unknown container ID
croaks B<404>. Neither is reachable through a return value, and no case
answers 304: moby's swagger for this endpoint (C<operationId: ContainerKill>)
documents only 204, 404, 409 and 500.
The B<text> of either is engine prose, so branch on
L<API::Docker::Error::HTTP/status> and not on the message. For one and the
same stopped container:
=over
=item * Docker -- C<cannot kill container: E<lt>nameE<gt>: container E<lt>idE<gt> is
not running>
=item * Podman -- C<can only kill running containers. E<lt>idE<gt> is in state
exited: container state improper>. C<container state improper> is Podman's
separate C<cause> field, reachable as C<< $err->data->{cause} >>, not a
phrase Docker uses anywhere
=back
The 404 differs too, and on Docker it differs I<per endpoint>: C<kill>
against a missing ID answers C<cannot kill container: E<lt>nameE<gt>: No such
container: E<lt>nameE<gt>> where L</inspect> answers the bare C<No such container:
E<lt>nameE<gt>>. Podman sends one sentence for both.
Options:
=over
=item * C<signal> - Signal to send (default C<SIGKILL>)
=back
=head2 remove
$containers->remove($id, force => 1, volumes => 1);
Remove a container.
Options:
=over
=item * C<force> - Force removal (kill if running)
=item * C<volumes> - Remove associated volumes
=item * C<link> - Remove specified link
=back
=head2 logs
my $frames = $containers->logs($id, tail => 100, timestamps => 1);
# stdout and stderr, in the order the engine emitted them
my $text = join '', map { $_->{data} } @$frames;
# stderr only
my @errors = grep { $_->{stream} eq 'stderr' } @$frames;
Get container logs. Returns an ArrayRef of frames, each a HashRef with
C<stream> and C<data>:
[ { stream => 'stdout', data => "OUT\n" },
{ stream => 'stderr', data => "ERR\n" } ]
A container created without a TTY multiplexes stdout and stderr into a single
framed stream, and this method demultiplexes it -- without that, the 8-byte
frame headers end up in the caller's log text. A container created B<with> a
TTY writes to one pty and the engine sends no frame headers, so its whole
output arrives as a single frame with C<< stream => 'raw' >>: with a TTY there
is no stdout/stderr distinction left to report. C<stream> is always a plain
string, so C<< $_->{stream} eq 'stderr' >> is safe on any frame.
Framing is detected from the response bytes, because the engine's
C<Content-Type> cannot be trusted for it -- see
L<API::Docker::Role::HTTP/"Detecting a framed stream"> for the rule and its one
failure mode.
Options:
=over
=item * C<follow> - Keep the connection open and send new output as the
container writes it. Only usable with C<on_frame>; see below
=item * C<stdout> - Include stdout (default 1)
=item * C<stderr> - Include stderr (default 1)
=item * C<since> - Show logs since timestamp
=item * C<until> - Show logs before timestamp
=item * C<timestamps> - Include timestamps
=item * C<tail> - Number of lines from end (e.g., C<100> or C<all>)
=item * C<tty> - Set to 1 when the container was created with a TTY and its
output is binary, to skip demultiplexing. Not needed for text output. The
container's own setting is C<Config.Tty> from C<< $containers->inspect($id) >>.
With C<on_frame> it is a declaration rather than a hint; see below
=item * C<on_frame> - CodeRef called with each frame as it arrives, instead of
the ArrayRef being collected and returned; see below
=back
=head2 Following the log
C<< follow => 1 >> asks the daemon to keep sending as the container writes.
Pass C<on_frame> with it and the frames are handed over as they arrive:
my $summary = $containers->logs($id,
follow => 1,
tail => 0,
on_frame => sub {
my ($frame, $stop) = @_;
print $frame->{data};
$stop->() if $frame->{data} =~ /listening on/;
},
);
$summary; # { delivered => 4, stopped => 1 }
With a callback the return value is that summary HashRef, not the frames:
C<delivered> is how many went to the callback, C<stopped> is 1 when the
callback ended the stream and 0 when the daemon did. Nothing is accumulated --
a followed log is unbounded by construction, and the callback has been handed
every frame already. See
L<API::Docker::Role::HTTP/"Streaming a response as it arrives">.
B<Without a callback, C<< follow => 1 >> blocks> until the container exits or
the daemon closes the connection, because the whole response is read before
anything is parsed. Use it with C<on_frame> or not at all.
C<tty> means something stronger on this path. The buffered path decides
framing by walking the whole body (see
L<API::Docker::Role::HTTP/"Detecting a framed stream">), which is exactly what
a streamed one does not have; so with C<on_frame> the flag is a promise about
the container rather than a hint, and an undeclared stream that turns out not
to be framed croaks instead of being handed back raw. Read C<Config.Tty> from
C<< $containers->inspect($id) >> and pass it. The frame shape is the same
either way -- a TTY stream arrives as a series of C<< stream => 'raw' >>
frames rather than the single one the buffered path builds.
=head2 attach
my $frames = $containers->attach($id);
my $text = join '', map { $_->{data} } @$frames;
Attach to a container's streams and return everything they produced, as an
ArrayRef of frames in the same shape L</logs> returns:
[ { stream => 'stdout', data => "OUT\n" },
{ stream => 'stderr', data => "ERR\n" } ]
A container created without a TTY multiplexes its output into one framed
stream, which this method demultiplexes; one created with a TTY arrives as a
single C<< stream => 'raw' >> frame. See L</logs> and
L<API::Docker::Role::HTTP/"Detecting a framed stream">.
B<The container must be running.> Attaching to one that has already exited
destroys its exit status on Podman, so this method checks first and croaks
rather than attaching -- read the output of a finished container with
L</logs>. Both halves of that are worth knowing before the call: see
L</"On Podman this destroys a stopped container's exit status"> and
L</"This method refuses a container that is not running">.
=head2 On Podman this destroys a stopped container's exit status
B<Attaching to a container that has already exited loses its exit code on
Podman, and nothing reports it.> Measured before and after a single attach
against one container that exited with 4, on Podman 5.4.2 (API 1.41) and
Docker 29.7.2 (API 1.55), same machine:
PODMAN before inspect: exited 4 wait: { StatusCode => 4 }
PODMAN after inspect: created 0 wait: { StatusCode => -1 }
DOCKER before inspect: exited 4 wait: { StatusCode => 4 }
DOCKER after inspect: exited 4 wait: { StatusCode => 4 }
Podman reverts the container to C<created>, resets C<ExitCode> to 0, and
answers a later L</wait> with the sentinel C<-1> inside a 200. The real value
is gone from the engine; there is nothing to read it back from. B<All three
variants do it> -- C<< stream => 1 >> with and without C<logs>, and the
C<< stream => 0, logs => 1 >> this method now sends by default, which is the
one that returns cleanly in milliseconds. It is the call that does it, not
the hang.
L</logs> does B<not> do it, and Docker does not do it at all. So on Podman
the sequence "attach to collect the output, then L</wait> for the exit code"
cannot work: read the output with L</logs> instead, or take the exit code
before attaching.
=head2 This method refuses a container that is not running
Because of the above, C<attach> asks L</inspect> whether the container is
running and B<croaks instead of attaching> when it is not:
API::Docker::API::Containers->attach refused: container x is exited. ...
C<< require_running => 0 >> turns that off and attaches anyway; the check is
then not performed at all, so opting out costs no round trip either.
With the guard off, the hang this section exists to explain becomes reachable:
attaching to a container that has already exited never returns on rootless
Podman (measured 5.4.2, still true on 5.8.4, API 1.44). A bound on the
resource class is how to survive that call instead of blocking on it forever:
$docker->containers->using(read_timeout => 2)
->attach($id, require_running => 0);
See L<API::Docker::Role::Using> and
L<API::Docker::Role::HTTP/"Bounding a request that never ends">.
B<What the check does not do is close the race.> It is a pre-flight question,
and the container can stop between the answer and the attach arriving -- in
which case the exit status is destroyed exactly as it would have been without
the check. The engine offers no attach-if-running, so this cannot be fixed
from a client. What makes the check worth its round trip is that the window is
one round trip wide rather than unbounded, and that the condition it tests is
precisely the condition that does the damage. Measured, one container per row,
each exiting with status 4:
attach to an ALREADY-EXITED container Podman: status destroyed
attach while RUNNING, exits under the call Podman: status intact (4)
either of those Docker: status intact (4)
A container that is still running when the attach is sent therefore stays
safe even when it exits a millisecond later. The damage needs the container to
be stopped B<already>, which is the common case and the one the check catches:
a caller reaching for a container it knows has finished.
Refusing costs a caller nothing that C<attach> could have given them, on
either engine. Against a container that is not running there is no combination
that is both safe and useful: on Podman every variant destroys the exit
status, C<< stream => 1 >> hangs forever on B<both> engines (measured: Docker
was still open when a 10 s probe gave up), and Docker's C<< stream => 0 >>
replay returns the same frames L</logs> returns, with none of the hazard and
with C<tail> and C<since> on top.
The check is engine-independent although the data loss is Podman's alone.
Telling the engines apart would cost a round trip of its own, it would leave
the both-engine C<< stream => 1 >> hang in place, and it would make the safe
call on Docker a call this distribution recommends against anywhere else.
B<This is a behavior change.> Up to and including the previous release the
call went straight to the engine.
=head2 This is the one-way attach
The engine has two attach protocols behind one path. Sent with
C<Upgrade: tcp> and C<Connection: Upgrade>, C<< POST /containers/{id}/attach >>
answers B<101 Switching Protocols> and hands over a bidirectional connection:
that is what C<docker attach> uses, and it is what lets a caller type into the
container's stdin. Sent B<without> those headers -- which is what this method
does -- the engine answers B<200> and streams the container's output one way,
in exactly the frames L</logs> returns.
This method implements the second one only, because the transport here buffers
a whole response before returning it (see
L<API::Docker::Role::HTTP/"What the transport does not do">). Two consequences
a caller has to plan around:
=over
=item * B<You cannot write to the container.> C<< stdin => 1 >> is passed to
the engine, but this client sends no bytes after the request headers and then
reads until the daemon closes, so there is no moment at which input could be
supplied. Use L<API::Docker::API::Exec> to run something interactive-shaped,
or wait for the upgraded variant
=item * B<Without a callback it returns when the stream ends, not before.>
With C<< stream => 1 >>, attaching to a container that keeps running blocks
until it exits or the daemon closes the connection -- and on a container that
is B<not> running it never returns at all, see
L</"The defaults follow the engine"> below. Pass C<on_frame> to read the
stream as it arrives and stop where you like, exactly as L</logs> does under
L</"Following the log">; the return value is then the summary HashRef
C<< { delivered => N, stopped => 0|1 } >> rather than the frames, and C<tty>
becomes a declaration the transport takes at its word -- an undeclared
unframed stream croaks. For a running container that need not be attached to,
L</logs> with C<tail> reads the same output and returns immediately
=back
C</containers/{id}/attach/ws>, the WebSocket variant, is not implemented
either.
=head2 The defaults follow the engine
C<stream> defaults to B<0> -- the engine's own default -- and C<logs> to
B<1>, which is the one flag that keeps the call useful without it. So
C<< $containers->attach($id) >> B<replays> what the container has written and
returns.
B<This is a change.> Up to and including the previous release C<stream>
defaulted to 1, so the same call opened an open-ended subscription; a caller
who wants the live stream now has to ask for it with C<< stream => 1 >>.
The reason is that the subscription has exactly one terminator: the container
ending. C<stream> means I<stream attached streams from the time the request
was made onwards>, so on a container that has B<already exited> that
terminator is in the past and will not happen again. attach also hijacks the
connection -- the response carries no C<Content-Length> and no chunked
terminator -- so HTTP framing cannot signal the end either. The transport
reads until EOF, there is no EOF, and the call hangs. C<on_frame> does not
help: nothing will ever call C<< $stop->() >>.
Measured on Podman 5.4.2 (API 1.41), all four against one and the same
container:
=over
=item * C<?logs=1&stdout=1&stderr=1&stream=0>, exited container -- 200, the
frames, connection closed after 13 ms
=item * C<?logs=1&stdout=1&stderr=1&stream=1>, exited container -- 200, the
same frames, then hangs
=item * the same with C<Upgrade: tcp> -- 101 UPGRADED, the same frames, still
hangs
=item * C<?stream=1> while the container is still B<running> and exits three
seconds later -- closes cleanly after 3 s
=back
B<Docker does exactly the same, and that is measured now too.> Against Docker
29.7.2 (API 1.55): C<?logs=1&stdout=1&stderr=1&stream=1> on an exited
container was still open when a 10 s probe gave up, and
C<?logs=1&stdout=1&stderr=1&stream=0> answered 200 with byte-identical frames
and closed in half a millisecond. So the hang is not a Podman quirk to be
worked around -- it is what both engines do with a subscription whose only
terminator is already in the past, on an endpoint whose reference promises a
close in neither direction. It is unspecified behavior on both, which is the
case for the C<< stream => 0 >> default rather than an argument against it.
One more measured difference: Podman refuses C<< stream => 0 >> together with
C<< logs => 0 >> outright, with B<400> C<at least one of Logs or Stream must
be set>, rather than answering an empty 200.
Options:
=over
=item * C<stream> - Subscribe to what the container writes from the time of
the request onwards. Default B<0>, which is the engine's own default.
C<< stream => 1 >> on a container that is not running never returns; see
L</"The defaults follow the engine">
=item * C<logs> - Replay what the container has already written. Default
B<1>, so the call returns something without subscribing; combined with
C<< stream => 1 >> the replay comes first and then transitions seamlessly
into the live output. C<< logs => 0 >> without C<< stream => 1 >> is the
combination the engine refuses (400 on Podman)
=item * C<stdout> - Attach stdout. Default 1 (engine default: false)
=item * C<stderr> - Attach stderr. Default 1 (engine default: false)
=item * C<stdin> - Attach stdin. Sent as asked, but nothing can be written to
it here; see above
=item * C<tty> - Set to 1 when the container was created with a TTY and its
output is binary, to skip demultiplexing. Same meaning as in L</logs>, and
with C<on_frame> the same promise
=item * C<on_frame> - CodeRef called with each frame as it arrives, instead of
the ArrayRef being collected and returned. Same contract as in L</logs>
=item * C<require_running> - Ask L</inspect> whether the container is running
first, and croak rather than attach when it is not. Default B<1>. Set to 0 to
attach to a stopped container anyway, which also skips the round trip; see
L</"This method refuses a container that is not running"> for what the check
does and does not guarantee
=back
=head2 top
my $processes = $containers->top($id, ps_args => 'aux');
List running processes in a container. Returns hashref with C<Titles> and C<Processes> arrays.
Options:
=over
=item * C<ps_args> - Arguments passed to C<ps> inside the container, e.g.
C<'aux'>. Omitted, the engine uses its own default
=back
=head2 stats
my $stats = $containers->stats($id);
Get container resource usage statistics (CPU, memory, network, I/O). With no
options this is the one-shot call it always was: a single reading, returned as
a HashRef.
For a container that is B<not running> the two engines answer differently and
neither says so in the status line -- on Podman this method croaks, on Docker
it returns zeros that look like a reading. See
L</"A container that is not running: a croak on Podman, zeros on Docker">
before calling it on a container that may have stopped.
=head2 Following the stats
C<< stream => 1 >> asks the engine for a reading per sampling cycle for as long
as the container runs. Pass C<on_event> with it and the readings are handed
over as they arrive:
my $summary = $containers->stats($id,
stream => 1,
on_event => sub {
my ($stats, $stop) = @_;
printf "%.1f MB\n", $stats->{memory_stats}{usage} / 1024 ** 2;
$stop->() if ++$seen >= 5;
},
);
$summary; # { delivered => 5, stopped => 1 }
With a callback the return value is that summary HashRef, not the readings:
C<delivered> is how many went to the callback, C<stopped> is 1 when the
callback ended the stream and 0 when the daemon did. Nothing is accumulated.
See L<API::Docker::Role::HTTP/"Streaming a response as it arrives">.
B<Without a callback, C<< stream => 1 >> blocks> until the container stops or
the daemon closes the connection: the whole response is read before anything
is parsed. It then returns an ArrayRef of readings rather than the single
HashRef the one-shot call returns, which is the other reason to pass a
callback instead.
Unlike L<API::Docker::API::System/events>, this does not turn the stream's
error check off. C</events> is a feed of engine records, where an
C<errorDetail> object would still be data; a stats stream is one container's
readings, and the transport's default is to croak on a failure reported inside
a 200 body (L<API::Docker::Role::HTTP/"Failure inside a 200 response">).
The default is kept on a measurement rather than on that analogy. Against
Podman 5.4.2 (API 1.41) every object a running container's stream carries is
a complete reading -- C<read>, C<cpu_stats>, C<memory_stats>, C<networks> and
the rest -- and killing the container and then removing it while the stream
was open ended the stream on a whole reading, with nothing appended after it.
No C<errorDetail> was sent in either case, and the Engine API reference names
that key for C</build>, C</images/create> and C</images/{name}/push> alone.
So the check has no legitimate reading here it could turn into a croak, and
that -- not an unexamined default -- is why it stays on.
Options:
=over
=item * C<stream> - Ask for a reading per sampling cycle instead of one.
Defaults off and is always sent, so a call with no options is the single
reading it has always been
=item * C<on_event> - CodeRef called with each reading as it arrives, instead
of them being collected and returned; see above
=back
=head2 A container that is not running: a croak on Podman, zeros on Docker
Neither engine answers this with an HTTP error, and they agree on nothing
else. Measured on Podman 5.4.2 (API 1.41) and Docker 29.7.2 (API 1.55), same
machine, one container that had exited.
B<Podman sends an error object inside the 200> -- chunked, for the one-shot
call and for C<< stream => 1 >> alike:
{ cause => 'container is stopped',
message => 'container is stopped',
response => 500 }
B<This method now croaks on it>, with an L<API::Docker::Error::HTTP> carrying
C<< ->status == 500 >> -- the code Podman named in C<response> -- and the
object itself as C<< ->data >>, so C<< $err->data->{cause} >> stays readable.
That is a B<change>: up to and including the previous release the one-shot
call returned this HashRef where a reading was expected, and an C<on_event>
callback was handed it as though it were one. The check runs on the buffered
return value and in front of the callback alike, and only on that exact
shape -- a HashRef inside a 2xx carrying all three of C<cause>, C<message>
and C<response> lower-cased, with C<response> reading as an integer >= 400.
Nothing else in this distribution, in its fixtures, or in a sweep of fifteen
read endpoints per engine carries even one of those keys lower-cased at the
top level. The rule is deliberately B<not> case-insensitive: a I<successful>
L</wait> answers with a top-level C<Error> key, and a looser rule would
report every one of those as a failure.
B<Docker sends a structurally valid reading with everything zeroed> -- 200,
about 825 bytes, no error anywhere in it:
{ id => '...', name => '/...', os_type => 'linux',
read => '0001-01-01T00:00:00Z',
cpu_stats => { cpu_usage => { total_usage => 0, ... }, ... },
memory_stats => {}, pids_stats => {}, num_procs => 0, ... }
So the advice this section used to give -- test for C<read> or C<cpu_stats>
before using what comes back -- is B<wrong on Docker>: both keys are present,
both look plausible, the test passes, and the caller uses zeros as though
they were a measurement. The markers in that body are Go's zero time in
C<read> (C<0001-01-01T00:00:00Z>) and an empty C<memory_stats>, and those are
Docker's shape rather than anybody's contract.
C<num_procs> is B<not> one of them, contrary to what this section said before
it was measured: a one-shot reading taken from a container that was genuinely
B<running> on Docker 29.7.2 carries C<< num_procs => 0 >> as well. It is zero
lib/API/Docker/API/Containers.pm view on Meta::CPAN
{ StatusCode => 4 } # Docker 29.7.2 (API 1.55)
{ StatusCode => 4, Error => undef } # Podman 5.4.2 (API 1.41)
B<The C<Error> key diverges, and C<exists> is the wrong test for it.>
Measured on successful waits on both engines: Docker B<omits> the key
entirely, Podman sends C<"Error": null> on every wait, which decodes to
C<undef>. So C<< exists $result->{Error} >> is false on Docker and true on
Podman for one and the same outcome, while C<< defined $result->{Error} >> is
false on both. Ask C<defined>, never C<exists>, and take C<StatusCode> as the
answer.
A B<non-null> C<Error> was not produced on either engine by any probe behind
this documentation. The Engine API reference documents it as an object
carrying C<Message>; that shape is B<documented but not measured here>, which
is not the same as unreachable -- do not write code that assumes it cannot
appear, and do not trust its shape without checking.
The call blocks in the client for as long as the engine takes to answer: this
endpoint answers only once the condition is met, and the whole response is
read before anything is parsed. There is no timeout, on this method or in the
transport.
Measured on both engines:
=over
=item * A container that has B<already exited> answers immediately with its
real exit status -- with no condition and with C<not-running> alike
=item * A container that was B<created and never started> answers immediately
with an invented one: Docker C<< StatusCode => 0 >>, Podman
C<< StatusCode => -1 >>. There is no exit status to report and the two
engines make up different ones, so a C<0> from this call is not proof that
anything ran
=item * C<< condition => 'next-exit' >> and C<< condition => 'removed' >>
against an exited container B<block> on both engines: the awaited event is in
the future and may never happen
=item * An unrecognised condition croaks B<400> on both (Docker C<invalid
condition: "...">, Podman C<failed to parse query parameter 'condition' ...>),
and an unknown container ID croaks B<404>
=back
Podman also answers C<< StatusCode => -1 >> for a container whose exit status
L</attach> has destroyed -- see
L</"On Podman this destroys a stopped container's exit status">. The value is
that engine's sentinel for "no status", not an exit code.
This endpoint is also the reason the error check on L</stats> matches
C<cause>, C<message> and C<response> case-sensitively: a I<successful> wait
is a 2xx body with a top-level C<Error> key in it, and a rule matching
C<error> case-insensitively would turn every one of them into a failure.
Options:
=over
=item * C<condition> - What to wait for: C<not-running> (the engine's own
default), C<next-exit> or C<removed>. Sent only when given
=back
=head2 pause
$containers->pause($id);
Pause all processes in a container.
Reports 1/0 like L</start>, but pausing an already-paused container is an
error rather than a 304: measured against Podman 5.4.2 (API 1.41) it answers
C<500> with C<< "..." is already paused: container state improper >>, which
croaks. The Docker Engine API documents no 304 for this endpoint either. So
this method returns 1 or croaks in practice.
=head2 unpause
$containers->unpause($id);
Unpause all processes in a container. Reports 1/0 like L</start>; as with
L</pause>, the no-op is an error and not a 304 -- Podman 5.4.2 answers
unpausing a running container with C<500>.
=head2 rename
$containers->rename($id, 'new-name');
Rename a container.
=head2 update
$containers->update($id, Memory => 314572800);
Update container resource limits and configuration.
The boolean flags (C<Init>, C<OomKillDisable>) may be given as a Perl C<1>/C<0>
or as a JSON boolean; either goes out as a real JSON C<true>/C<false>, which
the engine's body type-check requires.
=head2 get_archive
use Path::Tiny;
my $tar = $containers->get_archive($id, path => '/etc/hostname');
path('hostname.tar')->spew_raw($tar);
# and what the path was, without a second request
my %stat;
my $tar = $containers->get_archive($id, path => '/var/log', stat => \%stat);
say $stat{name};
Read a path out of a container as a tar archive -- the outbound half of
C<docker cp>. Returns the raw archive bytes, never decoded and never modified.
A file comes back as a one-member archive named after its basename; a
directory comes back as the directory and everything under it, with paths
relative to its parent. The whole archive is buffered in memory.
Options:
=over
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