Repository: fermyon/spin (rust)

Issue:
Add `spin up` option to mount static asset directory directly
Currently, `spin up` always copies static assets into a temporary directory and mounts that into the host.  This creates friction when iteratively developing static assets (e.g. SPAs) since `spin up` must be restarted each time any asset changes in order for the updated asset to be served.

I'm proposing that we add an option, e.g. `--direct-mount` to mount the asset directory directly instead of using a temporary directory, so that changes on the host filesystem are immediately visible to subsequent app invocations, with no restart required.

Pull request:
add `--direct-mounts` option to `spin up`
This option tells `spin up` to directly mount any asset directories specified in the manifest file instead of copying the contents to a temporary directory and mounting that.  This is useful when iteratively developing the static assets in the app, since any modifications to assets are immediately visible to subsequent invocations -- no restart required.

Closes #964.

Signed-off-by: Joel Dice <joel.dice@fermyon.com>

Patch:
diff --git a/crates/loader/src/local/assets.rs b/crates/loader/src/local/assets.rs
index a38f0f0d..174c95be 100644
--- a/crates/loader/src/local/assets.rs
+++ b/crates/loader/src/local/assets.rs
@@ -18,6 +18,26 @@ use super::config::{RawDirectoryPlacement, RawFileMount};
 /// Prepare all local assets given a component ID and its file patterns.
 /// This file will copy all assets into a temporary directory as read-only.
 pub(crate) async fn prepare_component(
+    raw_mounts: &[RawFileMount],
+    src: impl AsRef<Path>,
+    base_dst: Option<impl AsRef<Path>>,
+    id: &str,
+    exclude_files: &[String],
+) -> Result<Vec<DirectoryMount>> {
+    if let Some(base_dst) = base_dst {
+        prepare_component_with_temp_dir(raw_mounts, src, base_dst, id, exclude_files).await
+    } else {
+        tracing::info!("directly mounting local asset directories into guest");
+
+        if !exclude_files.is_empty() {
+            bail!("this component cannot be run with `--direct-mount` because some files are excluded from mounting")
+        }
+
+        prepare_component_with_direct_mounts(raw_mounts)
+    }
+}
+
+async fn prepare_component_with_temp_dir(
     raw_mounts: &[RawFileMount],
     src: impl AsRef<Path>,
     base_dst: impl AsRef<Path>,
@@ -38,6 +58,29 @@ pub(crate) async fn prepare_component(
     Ok(vec![DirectoryMount { guest, host }])
 }
 
+fn prepare_component_with_direct_mounts(
+    raw_mounts: &[RawFileMount],
+) -> Result<Vec<DirectoryMount>> {
+    tracing::info!("directly mounting local asset directories into guest");
+
+    raw_mounts
+        .iter()
+        .map(|mount| match mount {
+            RawFileMount::Placement(placement) => Ok(DirectoryMount {
+                guest: placement
+                    .destination
+                    .to_str()
+                    .context("unable to parse mount destination as UTF-8")?
+                    .to_owned(),
+                host: placement.source.clone(),
+            }),
+            RawFileMount::Pattern(_) => Err(anyhow!(
+                "this component cannot be run with `--direct-mount` because it uses file patterns"
+            )),
+        })
+        .collect()
+}
+
 /// A file that a component requires to be present at runtime.
 #[derive(Debug, Clone)]
 pub struct FileMount {
diff --git a/crates/loader/src/local/mod.rs b/crates/loader/src/local/mod.rs
index 07324642..433f660f 100644
--- a/crates/loader/src/local/mod.rs
+++ b/crates/loader/src/local/mod.rs
@@ -38,7 +38,7 @@ use self::config::FileComponentUrlSource;
 /// otherwise create a new temporary directory.
 pub async fn from_file(
     app: impl AsRef<Path>,
-    base_dst: impl AsRef<Path>,
+    base_dst: Option<impl AsRef<Path>>,
     bindle_connection: &Option<BindleConnectionInfo>,
 ) -> Result<Application> {
     let app = absolutize(app)?;
@@ -91,7 +91,7 @@ pub fn absolutize(path: impl AsRef<Path>) -> Result<PathBuf> {
 async fn prepare_any_version(
     raw: RawAppManifestAnyVersion,
     src: impl AsRef<Path>,
-    base_dst: impl AsRef<Path>,
+    base_dst: Option<impl AsRef<Path>>,
     bindle_connection: &Option<BindleConnectionInfo>,
 ) -> Result<Application> {
     match raw {
@@ -129,7 +129,7 @@ pub fn validate_raw_app_manifest(raw: &RawAppManifestAnyVersion) -> Result<()> {
 async fn prepare(
     raw: RawAppManifest,
     src: impl AsRef<Path>,
-    base_dst: impl AsRef<Path>,
+    base_dst: Option<impl AsRef<Path>>,
     bindle_connection: &Option<BindleConnectionInfo>,
 ) -> Result<Application> {
     let info = info(raw.info, &src);
@@ -145,7 +145,7 @@ async fn prepare(
     let components = future::join_all(
         raw.components
             .into_iter()
-            .map(|c| async { core(c, &src, &base_dst, bindle_connection).await })
+            .map(|c| async { core(c, &src, base_dst.as_ref(), bindle_connection).await })
             .collect::<Vec<_>>(),
     )
     .await
@@ -171,7 +171,7 @@ async fn prepare(
 async fn core(
     raw: RawComponentManifest,
     src: impl AsRef<Path>,
-    base_dst: impl AsRef<Path>,
+    base_dst: Option<impl AsRef<Path>>,
     bindle_connection: &Option<BindleConnectionInfo>,
 ) -> Result<CoreComponent> {
     let id = raw.id;
@@ -227,7 +227,7 @@ async fn core(
     let mounts = match raw.wasm.files {
         Some(f) => {
             let exclude_files = raw.wasm.exclude_files.unwrap_or_default();
-            assets::prepare_component(&f, src, &base_dst, &id, &exclude_files).await?
+            assets::prepare_component(&f, src, base_dst, &id, &exclude_files).await?
         }
         None => vec![],
     };
diff --git a/crates/trigger/src/locked.rs b/crates/trigger/src/locked.rs
index 67de11e3..e485531c 100644
--- a/crates/trigger/src/locked.rs
+++ b/crates/trigger/src/locked.rs
@@ -235,7 +235,7 @@ mod tests {
         std::fs::write("spin.toml", TEST_MANIFEST).expect("write manifest");
         std::fs::write("test-source.wasm", "not actual wasm").expect("write source");
         std::fs::write("static.txt", "content").expect("write static");
-        let app = spin_loader::local::from_file("spin.toml", &tempdir, &None)
+        let app = spin_loader::local::from_file("spin.toml", Some(&tempdir), &None)
             .await
             .expect("load app");
         (app, tempdir)
diff --git a/src/commands/up.rs b/src/commands/up.rs
index 0a83078c..a9c4f855 100644
--- a/src/commands/up.rs
+++ b/src/commands/up.rs
@@ -87,6 +87,14 @@ pub struct UpCommand {
     #[clap(long = "temp")]
     pub tmp: Option<PathBuf>,
 
+    /// For local apps with directory mounts and no excluded files, mount them directly instead of using a temporary
+    /// directory.
+    ///
+    /// This allows you to update the assets on the host filesystem such that the updates are visible to the guest
+    /// without a restart.  This cannot be used with bindle apps or apps which use file patterns and/or exclusions.
+    #[clap(long, takes_value = false, conflicts_with = BINDLE_ID_OPT)]
+    pub direct_mounts: bool,
+
     /// All other args, to be passed through to the trigger
     #[clap(hide = true)]
     pub trigger_args: Vec<OsString>,
@@ -127,10 +135,19 @@ impl UpCommand {
                     .as_deref()
                     .unwrap_or_else(|| DEFAULT_MANIFEST_FILE.as_ref());
                 let bindle_connection = self.bindle_connection();
-                spin_loader::from_file(manifest_file, &working_dir, &bindle_connection).await?
+                let asset_dst = if self.direct_mounts {
+                    None
+                } else {
+                    Some(&working_dir)
+                };
+                spin_loader::from_file(manifest_file, asset_dst, &bindle_connection).await?
             }
             (None, Some(bindle)) => match &self.server {
-                Some(server) => spin_loader::from_bindle(bindle, server, &working_dir).await?,
+                Some(server) => {
+                    assert!(!self.direct_mounts);
+
+                    spin_loader::from_bindle(bindle, server, &working_dir).await?
+                }
                 _ => bail!("Loading from a bindle requires a Bindle server URL"),
             },
             (Some(_), Some(_)) => bail!("Specify only one of app file or bindle ID"),


Test patch:
diff --git a/crates/loader/src/local/tests.rs b/crates/loader/src/local/tests.rs
index ceaff588..3aae011d 100644
--- a/crates/loader/src/local/tests.rs
+++ b/crates/loader/src/local/tests.rs
@@ -11,7 +11,7 @@ async fn test_from_local_source() -> Result<()> {
 
     let temp_dir = tempfile::tempdir()?;
     let dir = temp_dir.path();
-    let app = from_file(MANIFEST, dir, &None).await?;
+    let app = from_file(MANIFEST, Some(dir), &None).await?;
 
     assert_eq!(app.info.name, "spin-local-source-test");
     assert_eq!(app.info.version, "1.0.0");
@@ -157,7 +157,7 @@ async fn test_invalid_manifest() -> Result<()> {
 
     let temp_dir = tempfile::tempdir()?;
     let dir = temp_dir.path();
-    let app = from_file(MANIFEST, dir, &None).await;
+    let app = from_file(MANIFEST, Some(dir), &None).await;
 
     let e = app.unwrap_err().to_string();
     assert!(
@@ -214,7 +214,7 @@ async fn test_duplicate_component_id_is_rejected() -> Result<()> {
 
     let temp_dir = tempfile::tempdir()?;
     let dir = temp_dir.path();
-    let app = from_file(MANIFEST, dir, &None).await;
+    let app = from_file(MANIFEST, Some(dir), &None).await;
 
     assert!(
         app.is_err(),
@@ -236,7 +236,7 @@ async fn test_insecure_allow_all_with_invalid_url() -> Result<()> {
 
     let temp_dir = tempfile::tempdir()?;
     let dir = temp_dir.path();
-    let app = from_file(MANIFEST, dir, &None).await;
+    let app = from_file(MANIFEST, Some(dir), &None).await;
 
     assert!(
         app.is_ok(),
@@ -252,7 +252,7 @@ async fn test_invalid_url_in_allowed_http_hosts_is_rejected() -> Result<()> {
 
     let temp_dir = tempfile::tempdir()?;
     let dir = temp_dir.path();
-    let app = from_file(MANIFEST, dir, &None).await;
+    let app = from_file(MANIFEST, Some(dir), &None).await;
 
     assert!(app.is_err(), "Expected allowed_http_hosts parsing error");