feat: support file:// URLs for snapshot locations

.gitignore

@@ -16,3 +16,5 @@ mithril-infra/terraform.tfstate*
 mithril-infra/*.tfvars
 justfile
 
+# Outputs of nix-build:
+result

CHANGELOG.md

@@ -11,6 +11,7 @@ As a minor extension, we have adopted a slightly different versioning convention
 
 - Support for Mithril nodes footprint support in Prometheus monitoring in infrastructure
 - Add support for custom HTTP headers in Mithril client WASM library
+- Support `file://` URLs for snapshot locations
 
 - **UNSTABLE** Cardano stake distribution certification:
 

mithril-client/Cargo.toml

@@ -1,6 +1,6 @@
 [package]
 name = "mithril-client"
-version = "0.8.14"
+version = "0.8.15"
 description = "Mithril client library"
 authors = { workspace = true }
 edition = { workspace = true }

mithril-client/src/snapshot_downloader.rs

@@ -10,9 +10,13 @@
 use anyhow::{anyhow, Context};
 use async_trait::async_trait;
 use futures::StreamExt;
+use reqwest::Url;
 use reqwest::{Response, StatusCode};
 use slog::{debug, Logger};
+use std::fs;
 use std::path::Path;
+use tokio::fs::File;
+use tokio::io::AsyncReadExt;
 
 #[cfg(test)]
 use mockall::automock;
@@ -78,6 +82,74 @@ impl HttpSnapshotDownloader {
             status_code => Err(anyhow!("Unhandled error {status_code}")),
         }
     }
+
+    fn file_scheme_to_local_path(file_url: &str) -> Option<String> {
+        Url::parse(file_url)
+            .ok()
+            .filter(|url| url.scheme() == "file")
+            .and_then(|url| url.to_file_path().ok())
+            .map(|path| path.to_string_lossy().into_owned())
+    }
+
+    async fn download_local_file<F, Fut>(
+        &self,
+        local_path: &str,
+        sender: &flume::Sender<Vec<u8>>,
+        report_progress: F,
+    ) -> MithrilResult<()>
+    where
+        F: Fn(u64) -> Fut,
+        Fut: std::future::Future<Output = ()>,
+    {
+        // Stream the `location` directly from the local filesystem
+        let mut downloaded_bytes: u64 = 0;
+        let mut file = File::open(local_path).await?;
+
+        loop {
+            // We can either allocate here each time, or clone a shared buffer into sender.
+            // A larger read buffer is faster, less context switches:
+            let mut buffer = vec![0; 16 * 1024 * 1024];
+            let bytes_read = file.read(&mut buffer).await?;
+            if bytes_read == 0 {
+                break;
+            }
+            buffer.truncate(bytes_read);
+            sender.send_async(buffer).await.with_context(|| {
+                format!(
+                    "Local file read: could not write {} bytes to stream.",
+                    bytes_read
+                )
+            })?;
+            downloaded_bytes += bytes_read as u64;
+            report_progress(downloaded_bytes).await
+        }
+        Ok(())
+    }
+
+    async fn download_remote_file<F, Fut>(
+        &self,
+        location: &str,
+        sender: &flume::Sender<Vec<u8>>,
+        report_progress: F,
+    ) -> MithrilResult<()>
+    where
+        F: Fn(u64) -> Fut,
+        Fut: std::future::Future<Output = ()>,
+    {
+        let mut downloaded_bytes: u64 = 0;
+        let mut remote_stream = self.get(location).await?.bytes_stream();
+        while let Some(item) = remote_stream.next().await {
+            let chunk = item.with_context(|| "Download: Could not read from byte stream")?;
+
+            sender.send_async(chunk.to_vec()).await.with_context(|| {
+                format!("Download: could not write {} bytes to stream.", chunk.len())
+            })?;
+
+            downloaded_bytes += chunk.len() as u64;
+            report_progress(downloaded_bytes).await
+        }
+        Ok(())
+    }
 }
 
 #[cfg_attr(test, automock)]
@@ -97,8 +169,6 @@ impl SnapshotDownloader for HttpSnapshotDownloader {
                     .context("Download-Unpack: prerequisite error"),
             )?;
         }
-        let mut downloaded_bytes: u64 = 0;
-        let mut remote_stream = self.get(location).await?.bytes_stream();
         let (sender, receiver) = flume::bounded(5);
 
         let dest_dir = target_dir.to_path_buf();
@@ -107,21 +177,22 @@ impl SnapshotDownloader for HttpSnapshotDownloader {
             unpacker.unpack_snapshot(receiver, compression_algorithm, &dest_dir)
         });
 
-        while let Some(item) = remote_stream.next().await {
-            let chunk = item.with_context(|| "Download: Could not read from byte stream")?;
-
-            sender.send_async(chunk.to_vec()).await.with_context(|| {
-                format!("Download: could not write {} bytes to stream.", chunk.len())
-            })?;
-
-            downloaded_bytes += chunk.len() as u64;
+        let report_progress = |downloaded_bytes: u64| async move {
             self.feedback_sender
                 .send_event(MithrilEvent::SnapshotDownloadProgress {
                     download_id: download_id.to_owned(),
                     downloaded_bytes,
                     size: snapshot_size,
                 })
                 .await
+        };
+
+        if let Some(local_path) = Self::file_scheme_to_local_path(location) {
+            self.download_local_file(&local_path, &sender, report_progress)
+                .await?;
+        } else {
+            self.download_remote_file(location, &sender, report_progress)
+                .await?;
         }
 
         drop(sender); // Signal EOF
@@ -143,15 +214,21 @@ impl SnapshotDownloader for HttpSnapshotDownloader {
     async fn probe(&self, location: &str) -> MithrilResult<()> {
         debug!(self.logger, "HEAD Snapshot location='{location}'.");
 
-        let request_builder = self.http_client.head(location);
-        let response = request_builder.send().await.with_context(|| {
-            format!("Cannot perform a HEAD for snapshot at location='{location}'")
-        })?;
+        if let Some(local_path) = Self::file_scheme_to_local_path(location) {
+            fs::metadata(local_path)
+                .with_context(|| format!("Local snapshot location='{location}' not found"))
+                .map(drop)
+        } else {
+            let request_builder = self.http_client.head(location);
+            let response = request_builder.send().await.with_context(|| {
+                format!("Cannot perform a HEAD for snapshot at location='{location}'")
+            })?;
 
-        match response.status() {
-            StatusCode::OK => Ok(()),
-            StatusCode::NOT_FOUND => Err(anyhow!("Snapshot location='{location} not found")),
-            status_code => Err(anyhow!("Unhandled error {status_code}")),
+            match response.status() {
+                StatusCode::OK => Ok(()),
+                StatusCode::NOT_FOUND => Err(anyhow!("Snapshot location='{location} not found")),
+                status_code => Err(anyhow!("Unhandled error {status_code}")),
+            }
         }
     }
 }