hypha: implement image cache

hypha/src/image/cache.rs

@@ -0,0 +1,51 @@
+use crate::image::{ImageInfo, Result};
+use log::debug;
+use oci_spec::image::ImageManifest;
+use std::fs;
+use std::path::{Path, PathBuf};
+
+pub struct ImageCache {
+    cache_dir: PathBuf,
+}
+
+impl ImageCache {
+    pub fn new(cache_dir: &Path) -> Result<ImageCache> {
+        Ok(ImageCache {
+            cache_dir: cache_dir.to_path_buf(),
+        })
+    }
+
+    pub fn recall(&self, digest: &str) -> Result<Option<ImageInfo>> {
+        let mut squashfs_path = self.cache_dir.clone();
+        let mut manifest_path = self.cache_dir.clone();
+        squashfs_path.push(format!("{}.squashfs", digest));
+        manifest_path.push(format!("{}.json", digest));
+        Ok(if squashfs_path.exists() && manifest_path.exists() {
+            let squashfs_metadata = fs::metadata(&squashfs_path)?;
+            let manifest_metadata = fs::metadata(&manifest_path)?;
+            if squashfs_metadata.is_file() && manifest_metadata.is_file() {
+                let manifest_text = fs::read_to_string(&manifest_path)?;
+                let manifest: ImageManifest = serde_json::from_str(manifest_text.as_str())?;
+                debug!("cache hit digest={}", digest);
+                Some(ImageInfo::new(squashfs_path.clone(), manifest)?)
+            } else {
+                None
+            }
+        } else {
+            debug!("cache miss digest={}", digest);
+            None
+        })
+    }
+
+    pub fn store(&self, digest: &str, info: &ImageInfo) -> Result<ImageInfo> {
+        debug!("cache store digest={}", digest);
+        let mut squashfs_path = self.cache_dir.clone();
+        let mut manifest_path = self.cache_dir.clone();
+        squashfs_path.push(format!("{}.squashfs", digest));
+        manifest_path.push(format!("{}.json", digest));
+        fs::copy(&info.squashfs, &squashfs_path)?;
+        let manifest_text = serde_json::to_string_pretty(&info.manifest)?;
+        fs::write(&manifest_path, manifest_text)?;
+        ImageInfo::new(squashfs_path.clone(), info.manifest.clone())
+    }
+}