add containerd support

README.md

@@ -23,6 +23,7 @@ In this two minute recording you learn all the basics of cntr:
   * LXD
   * rkt
   * systemd-nspawn
+  * containerd
 - For other container engines cntr also takes process ids (PIDs) instead of container names.
 
 ## Installation
@@ -304,6 +305,50 @@ drwx------   22 nobody nogroup    43 Mar 13 15:09 root
 ...
 ```
 
+### Containerd
+
+For containerd integration the `ctr` binary is required. You can get a binary by running:
+
+``` console
+$ GOPATH=$(mktemp -d)
+$ go get github.com/containerd/containerd/cmd/ctr
+$ $GOPATH/bin/ctr --help
+```
+
+Put the resulting `ctr` binary in your `$PATH`
+
+1: Start container
+```console
+$ ctr images pull docker.io/library/busybox:latest
+$ ctr run docker.io/library/busybox:latest boxbusy
+$ ctr tasks lists
+TASK        PID      STATUS
+boxbusy    24310    RUNNING
+```
+
+2: Attach
+```console
+$ cntr attach boxbusy
+```
+
+It's also possible to run cntr from a container itself.
+This repository contains a example Dockerfile for that:
+
+```console
+$ docker build -f Dockerfile.example . -t cntr
+$ docker save cntr > cntr.tar
+$ ctr images import --base-name cntr ./cntr.tar
+```
+
+In this example we attach to containerd by process id. The proccess id of a task is given in `ctr tasks list`.
+
+```console
+$ ctr run --privileged --with-ns pid:/proc/1/ns/pid --tty docker.io/library/cntr:latest cntr /usr/bin/cntr attach 31523 /bin/sh
+```
+
+To resolve containerd names one also would need to add the `ctr` binary (~12mb) to the Dockerfile.
+
+
 # How it works
 
 Cntr is container-agnostic: Instead of interfacing with container engines, it

src/bin/main.rs

@@ -50,7 +50,7 @@ fn parse_attach_args(args: Vec<String>) -> cntr::AttachOptions {
         ap.refer(&mut container_type).add_option(
             &["-t", "--type"],
             Store,
-            "Container type (process_id|rkt|docker|nspawn|lxc|lxd|command), default: all except command)",
+            "Container type (process_id|rkt|docker|nspawn|lxc|lxd|command|containerd), default: all except command)",
         );
         ap.refer(&mut container_name).required().add_argument(
             "id",

src/container/containerd.rs

@@ -0,0 +1,71 @@
+use libc::pid_t;
+use nix::unistd::Pid;
+use std::process::Command;
+
+use crate::cmd;
+use crate::container::Container;
+use crate::types::{Error, Result};
+
+#[derive(Clone, Debug)]
+pub struct Containerd {}
+
+impl Container for Containerd {
+    fn lookup(&self, container_id: &str) -> Result<Pid> {
+        let command = format!("ctr task list");
+        let output = tryfmt!(
+            Command::new("ctr").args(&["task", "list"]).output(),
+            "Running '{}' failed",
+            command
+        );
+
+        if !output.status.success() {
+            let stderr = String::from_utf8_lossy(&output.stderr);
+            return errfmt!(format!(
+                "Failed to list containers. '{}' exited with {}: {}",
+                command,
+                output.status,
+                stderr.trim_end()
+            ));
+        }
+
+        // $ ctr task list
+        // TASK    PID      STATUS
+        // v2      17515    RUNNING
+        // v1      14602    RUNNING
+        let mut lines = output.stdout.split(|&c| c == b'\n');
+        lines.next(); // skip header
+        let pid_str = lines.find_map(|line| {
+            let line_str = String::from_utf8_lossy(&line);
+            let cols = line_str.split_whitespace().collect::<Vec<&str>>();
+            if cols.len() != 3 {
+                return None;
+            }
+
+            if cols[0] == container_id {
+                Some(String::from(cols[1]))
+            } else {
+                None
+            }
+        });
+        match pid_str {
+            Some(pid_str) => {
+                let pid = tryfmt!(
+                    pid_str.parse::<pid_t>(),
+                    "read invalid pid from ctr task list: '{}'",
+                    pid_str
+                );
+                Ok(Pid::from_raw(pid))
+            }
+            None => {
+                errfmt!(format!("No container with id {} found", container_id))
+            }
+        }
+    }
+    fn check_required_tools(&self) -> Result<()> {
+        if cmd::which("ctr").is_some() {
+            Ok(())
+        } else {
+            errfmt!("ctr not found")
+        }
+    }
+}

src/container/mod.rs

@@ -4,6 +4,7 @@ use std::fmt::Debug;
 use crate::types::{Error, Result};
 
 mod command;
+mod containerd;
 mod docker;
 mod lxc;
 mod lxd;
@@ -24,6 +25,7 @@ pub const AVAILABLE_CONTAINER_TYPES: &[&str] = &[
     "lxc",
     "lxd",
     "command",
+    "containerd",
 ];
 
 fn default_order() -> Vec<Box<dyn Container>> {
@@ -34,6 +36,7 @@ fn default_order() -> Vec<Box<dyn Container>> {
         Box::new(nspawn::Nspawn {}),
         Box::new(lxc::Lxc {}),
         Box::new(lxd::Lxd {}),
+        Box::new(containerd::Containerd {}),
     ];
     containers
         .into_iter()
@@ -49,6 +52,7 @@ pub fn lookup_container_type(name: &str) -> Option<Box<dyn Container>> {
         "nspawn" => Box::new(nspawn::Nspawn {}),
         "lxc" => Box::new(lxc::Lxc {}),
         "lxd" => Box::new(lxd::Lxd {}),
+        "containerd" => Box::new(containerd::Containerd {}),
         "command" => Box::new(command::Command {}),
         _ => return None,
     })