Catch Ubuntu's snap-based Docker runtime (#118)

Author: bleggett

src/checkers/preinstall/system.rs

@@ -27,6 +27,7 @@ impl SystemChecks {
     }
     pub async fn run_all(&self) -> CheckGroupResult {
         let results = join_all([
+            self.not_snap_docker().boxed(),
             self.enough_memory().boxed(),
             self.enough_disk("/usr".into(), MINIMUM_DISK_GENERAL)
                 .boxed(),
@@ -60,6 +61,24 @@ impl SystemChecks {
         }
     }
 
+    async fn not_snap_docker(&self) -> CheckResult {
+        let name = String::from("Supported Docker Runtime");
+        let is_snap = std::fs::read_to_string("/proc/self/mountinfo")
+            .map(|c| c.contains("snap/docker"))
+            .unwrap_or(false);
+
+        if is_snap {
+            CheckResult::new(
+                &name,
+                Errored(
+                    "Docker is running as a snap: hosts with snap-managed Docker runtimes are not supported installation targets".into(),
+                ),
+            )
+        } else {
+            CheckResult::new(&name, Passed)
+        }
+    }
+
     /// Checks that the `nft` binary, typically from the `nftables` package,
     /// is in PATH. Currently, the installer and `protect-network` rely on this.
     async fn has_nft_bin(&self) -> CheckResult {