fix!: docker socket detection on unix (#721)

Docker Desktop on macOS creates the socket in the user's home directory
from version
4.13.0.[[1](https://github.com/docker/for-mac/issues/6529)][[2](https://github.com/testcontainers/testcontainers-java/issues/6165)]

And the Docker team [has the intention to move
away](docker/for-mac#6529 (comment))
from the root-owned `/var/run/docker.sock`

There is a option named `Allow the default Docket Socket to be used
(requires password)` in the Docker Desktop, but the created symbolic
link `/var/run/docker.sock` [doesn't
persist](lando/lando#3533 (comment))
between OS restart or OS upgrade.

Without this patch or creating a symbolic link, macOS devs have to face
the ```called `Result::unwrap()` on an `Err` value:
Client(Init(SocketNotFoundError("/var/run/docker.sock")))``` error.

I have used `Cow` to avoid the need of cloning the fields of `Config`
struct. I am open to suggestion or other approaches.

Thanks!

---------

Co-authored-by: Artem Medvedev <[email protected]>

testcontainers/src/core/client.rs

@@ -312,7 +312,7 @@ impl Client {
     }
 
     pub(crate) async fn docker_hostname(&self) -> Result<url::Host, ClientError> {
-        let docker_host = self.config.docker_host();
+        let docker_host = &self.config.docker_host();
         let docker_host_url = Url::from_str(docker_host)
             .map_err(|e| ConfigurationError::InvalidDockerHost(e.to_string()))?;
 

testcontainers/src/core/client/bollard_client.rs

@@ -8,7 +8,7 @@ use crate::core::env;
 const DEFAULT_TIMEOUT: Duration = Duration::from_secs(2 * 60);
 
 pub(super) fn init(config: &env::Config) -> Result<Docker, bollard::errors::Error> {
-    let host = config.docker_host();
+    let host = &config.docker_host();
     let host_url = Url::from_str(host)?;
 
     match host_url.scheme() {
@@ -36,7 +36,7 @@ fn connect_with_ssl(config: &env::Config) -> Result<Docker, bollard::errors::Err
     let cert_path = config.cert_path().expect("cert path not found");
 
     Docker::connect_with_ssl(
-        config.docker_host(),
+        &config.docker_host(),
         &cert_path.join("key.pem"),
         &cert_path.join("cert.pem"),
         &cert_path.join("ca.pem"),

testcontainers/src/core/env/config.rs

@@ -1,8 +1,11 @@
 use std::{
+    borrow::Cow,
     path::{Path, PathBuf},
     str::FromStr,
 };
 
+use dirs::{home_dir, runtime_dir};
+
 use crate::core::env::GetEnvValue;
 
 #[derive(Debug, thiserror::Error)]
@@ -125,12 +128,45 @@ impl Config {
     ///  1. Docker host from the `tc.host` property in the `~/.testcontainers.properties` file.
     ///  2. `DOCKER_HOST` environment variable.
     ///  3. Docker host from the `docker.host` property in the `~/.testcontainers.properties` file.
-    ///  4. Else, the default Docker socket will be returned.
-    pub(crate) fn docker_host(&self) -> &str {
+    ///  4. Read the default Docker socket path, without the unix schema. E.g. `/var/run/docker.sock`.
+    ///  5. Read the rootless Docker socket path, checking in the following alternative locations:
+    ///     1. `${XDG_RUNTIME_DIR}/.docker/run/docker.sock`.
+    ///     2. `${HOME}/.docker/run/docker.sock`.
+    ///     3. `${HOME}/.docker/desktop/docker.sock`.
+    ///  6. The default Docker socket including schema will be returned if none of the above are set.
+    pub(crate) fn docker_host(&self) -> Cow<'_, str> {
         self.tc_host
             .as_deref()
             .or(self.host.as_deref())
-            .unwrap_or(DEFAULT_DOCKER_HOST)
+            .map(Cow::Borrowed)
+            .unwrap_or_else(|| {
+                if cfg!(unix) {
+                    validate_path("/var/run/docker.sock".into())
+                        .or_else(|| {
+                            runtime_dir().and_then(|dir| {
+                                validate_path(format!("{}/.docker/run/docker.sock", dir.display()))
+                            })
+                        })
+                        .or_else(|| {
+                            home_dir().and_then(|dir| {
+                                validate_path(format!("{}/.docker/run/docker.sock", dir.display()))
+                            })
+                        })
+                        .or_else(|| {
+                            home_dir().and_then(|dir| {
+                                validate_path(format!(
+                                    "{}/.docker/desktop/docker.sock",
+                                    dir.display()
+                                ))
+                            })
+                        })
+                        .map(|p| format!("unix://{p}"))
+                        .map(Cow::Owned)
+                        .unwrap_or(DEFAULT_DOCKER_HOST.into())
+                } else {
+                    DEFAULT_DOCKER_HOST.into()
+                }
+            })
     }
 
     pub(crate) fn tls_verify(&self) -> bool {
@@ -150,6 +186,15 @@ impl Config {
     }
 }
 
+/// Validate the path exists and return it if it does.
+fn validate_path(path: String) -> Option<String> {
+    if Path::new(&path).exists() {
+        Some(path)
+    } else {
+        None
+    }
+}
+
 /// Read the Docker authentication configuration in the following order:
 ///
 /// 1. `DOCKER_AUTH_CONFIG` environment variable, unmarshalling the string value from its JSON representation and using it as the Docker config.

testcontainers/src/lib.rs

@@ -40,7 +40,12 @@
 //! 1. Docker host from the `tc.host` property in the `~/.testcontainers.properties` file.
 //! 2. `DOCKER_HOST` environment variable.
 //! 3. Docker host from the "docker.host" property in the `~/.testcontainers.properties` file.
-//! 4. Else, the default Docker socket will be returned.
+//! 4. Read the default Docker socket path, without the unix schema. E.g. `/var/run/docker.sock`.
+//! 5. Read the rootless Docker socket path, checking in the following alternative locations:
+//!    1. `${XDG_RUNTIME_DIR}/.docker/run/docker.sock`.
+//!    2. `${HOME}/.docker/run/docker.sock`.
+//!    3. `${HOME}/.docker/desktop/docker.sock`.
+//! 6. The default Docker socket including schema will be returned if none of the above are set.
 //!
 //! ### Docker authentication
 //!