Update ImageName::as_path escaping for digest reference case (#134)

Add escape rule of image name into path for #128 case:

```text
quay.io/jitesoft/alpine:sha256:6755355f801f8e3694bffb1a925786813462cea16f1ce2b0290b6a48acf2500c
```

will escape into

```
quay.io/jitesoft/alpine/__sha256__6755355f801f8e3694bffb1a925786813462cea16f1ce2b0290b6a48acf2500c
```

Author: termoshtt

ocipkg/src/distribution/reference.rs

@@ -6,7 +6,7 @@ use std::fmt;
 /// Reference of container image stored in the repository
 ///
 /// In [OCI distribution spec](https://github.com/opencontainers/distribution-spec/blob/main/spec.md):
-/// > `<reference>`  MUST be either (a) the digest of the manifest or (b) a tag
+/// > `<reference>` MUST be either (a) the digest of the manifest or (b) a tag
 /// > `<reference>` as a tag MUST be at most 128 characters
 /// > in length and MUST match the following regular expression:
 /// > ```text

ocipkg/src/image_name.rs

@@ -74,6 +74,30 @@ use url::Url;
 /// # Ok::<(), anyhow::Error>(())
 /// ```
 ///
+/// [Reference] can be a digest:
+///
+/// ```text
+/// quay.io/jitesoft/alpine:sha256:6755355f801f8e3694bffb1a925786813462cea16f1ce2b0290b6a48acf2500c
+/// ^^^^^^^-------------------- hostname
+///         ^^^^^^^^^^^^^^^---- name
+///            reference ---^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^
+/// ```
+///
+/// ```
+/// use ocipkg::{ImageName, distribution::{Name, Reference}};
+/// let name = ImageName::parse("quay.io/jitesoft/alpine:sha256:6755355f801f8e3694bffb1a925786813462cea16f1ce2b0290b6a48acf2500c")?;
+/// assert_eq!(
+///     name,
+///     ImageName {
+///         hostname: "quay.io".to_string(),
+///         port: None,
+///         name: Name::new("jitesoft/alpine")?,
+///         reference: Reference::new("sha256:6755355f801f8e3694bffb1a925786813462cea16f1ce2b0290b6a48acf2500c")?,
+///     }
+/// );
+/// # Ok::<(), anyhow::Error>(())
+/// ```
+///
 /// Default values
 /// ---------------
 /// If `hostname` is absent, use `registry-1.docker.io` for docker compatibility:
@@ -175,13 +199,11 @@ impl ImageName {
 
     /// Encode image name into a path by `{hostname}/{name}/__{reference}` or `{hostname}__{port}/{name}/__{reference}` if port is specified.
     pub fn as_path(&self) -> PathBuf {
+        let reference = self.reference.replace(':', "__");
         PathBuf::from(if let Some(port) = self.port {
-            format!(
-                "{}__{}/{}/__{}",
-                self.hostname, port, self.name, self.reference
-            )
+            format!("{}__{}/{}/__{}", self.hostname, port, self.name, reference)
         } else {
-            format!("{}/{}/__{}", self.hostname, self.name, self.reference)
+            format!("{}/{}/__{}", self.hostname, self.name, reference)
         })
     }
 
@@ -217,9 +239,10 @@ impl ImageName {
         let name = Name::new(&components[1..n - 1].join("/"))?;
 
         let reference = Reference::new(
-            components[n - 1]
+            &components[n - 1]
                 .strip_prefix("__")
-                .with_context(|| anyhow!("Missing tag in path: {}", path.display()))?,
+                .with_context(|| anyhow!("Missing tag in path: {}", path.display()))?
+                .replace("__", ":"),
         )?;
 
         Ok(ImageName {
@@ -266,6 +289,10 @@ mod test {
             "registry-1.docker.io/ubuntu/__20.04".as_ref(),
         )?;
         test_as_path("alpine", "registry-1.docker.io/alpine/__latest".as_ref())?;
+        test_as_path(
+            "quay.io/jitesoft/alpine:sha256:6755355f801f8e3694bffb1a925786813462cea16f1ce2b0290b6a48acf2500c",
+            "quay.io/jitesoft/alpine/__sha256__6755355f801f8e3694bffb1a925786813462cea16f1ce2b0290b6a48acf2500c".as_ref()
+        )?;
         Ok(())
     }
 }