feat: oci tar format, bit-perfect disk storage for config and manifest, concurrent image pulls (#88)

* oci: retain bit-perfect copies of manifest and config on disk

* feat: oci tar format support

* feat: concurrent image pulls

crates/oci/src/progress.rs

@@ -1,7 +1,11 @@
-use std::sync::Arc;
-
 use indexmap::IndexMap;
-use tokio::sync::{mpsc::Sender, Mutex};
+use std::sync::Arc;
+use tokio::{
+    sync::{broadcast, Mutex},
+    task::JoinHandle,
+};
+
+const OCI_PROGRESS_QUEUE_LEN: usize = 100;
 
 #[derive(Clone, Debug)]
 pub struct OciProgress {
@@ -99,16 +103,25 @@ pub enum OciProgressLayerPhase {
 
 #[derive(Clone)]
 pub struct OciProgressContext {
-    sender: Sender<OciProgress>,
+    sender: broadcast::Sender<OciProgress>,
 }
 
 impl OciProgressContext {
-    pub fn new(sender: Sender<OciProgress>) -> OciProgressContext {
+    pub fn create() -> (OciProgressContext, broadcast::Receiver<OciProgress>) {
+        let (sender, receiver) = broadcast::channel(OCI_PROGRESS_QUEUE_LEN);
+        (OciProgressContext::new(sender), receiver)
+    }
+
+    pub fn new(sender: broadcast::Sender<OciProgress>) -> OciProgressContext {
         OciProgressContext { sender }
     }
 
     pub fn update(&self, progress: &OciProgress) {
-        let _ = self.sender.try_send(progress.clone());
+        let _ = self.sender.send(progress.clone());
+    }
+
+    pub fn subscribe(&self) -> broadcast::Receiver<OciProgress> {
+        self.sender.subscribe()
     }
 }
 
@@ -137,4 +150,20 @@ impl OciBoundProgress {
         function(&mut progress);
         self.context.update(&progress);
     }
+
+    pub async fn also_update(&self, context: OciProgressContext) -> JoinHandle<()> {
+        let progress = self.instance.lock().await.clone();
+        context.update(&progress);
+        let mut receiver = self.context.subscribe();
+        tokio::task::spawn(async move {
+            while let Ok(progress) = receiver.recv().await {
+                match context.sender.send(progress) {
+                    Ok(_) => {}
+                    Err(_) => {
+                        break;
+                    }
+                }
+            }
+        })
+    }
 }