vmm: Add migration helpers

Signed-off-by: Sebastien Boeuf <sebastien.boeuf@intel.com>

vmm/src/migration.rs

@@ -0,0 +1,61 @@
+// Copyright © 2020 Intel Corporation
+//
+// SPDX-License-Identifier: Apache-2.0
+
+use anyhow::anyhow;
+use std::fs::File;
+use std::io::BufReader;
+use std::path::PathBuf;
+use url::Url;
+use vm_migration::{MigratableError, Snapshot};
+
+pub const VM_SNAPSHOT_FILE: &str = "vm.json";
+
+pub fn url_to_path(url: &Url) -> std::result::Result<PathBuf, MigratableError> {
+    match url.scheme() {
+        "file" => url
+            .to_file_path()
+            .map_err(|_| {
+                MigratableError::MigrateSend(anyhow!("Could not convert file URL to a file path"))
+            })
+            .and_then(|path| {
+                if !path.is_dir() {
+                    return Err(MigratableError::MigrateSend(anyhow!(
+                        "Destination is not a directory"
+                    )));
+                }
+                Ok(path)
+            }),
+
+        _ => Err(MigratableError::MigrateSend(anyhow!(
+            "URL scheme is not file: {}",
+            url.scheme()
+        ))),
+    }
+}
+
+pub fn recv_vm_snapshot(source_url: &str) -> std::result::Result<Snapshot, MigratableError> {
+    let url = Url::parse(source_url).map_err(|e| {
+        MigratableError::MigrateSend(anyhow!("Could not parse destination URL: {}", e))
+    })?;
+
+    match url.scheme() {
+        "file" => {
+            let mut vm_snapshot_path = url_to_path(&url)?;
+            vm_snapshot_path.push(VM_SNAPSHOT_FILE);
+
+            // Try opening the snapshot file
+            let vm_snapshot_file =
+                File::open(vm_snapshot_path).map_err(|e| MigratableError::MigrateSend(e.into()))?;
+            let vm_snapshot_reader = BufReader::new(vm_snapshot_file);
+            let vm_snapshot = serde_json::from_reader(vm_snapshot_reader)
+                .map_err(|e| MigratableError::MigrateReceive(e.into()))?;
+
+            Ok(vm_snapshot)
+        }
+        _ => Err(MigratableError::MigrateSend(anyhow!(
+            "Unsupported VM transport URL scheme: {}",
+            url.scheme()
+        ))),
+    }
+}