[images]: reference image by their short digest value

Sources/ContainerClient/Core/ClientImage.swift

@@ -211,6 +211,35 @@ extension ClientImage {
         if let locallyBuiltImage {
             return locallyBuiltImage
         }
+
+        let shortDigestReferencedImage: ClientImage? = try {
+            // Check if we are looking for an image referenced by its short digest.
+            // The assumption is that the short digest is passed like -> <name>:<short-digest>.
+            let r = try Reference.parse(reference)
+            r.normalize()
+
+            guard let shortDigestTag = r.tag else {
+                return nil
+            }
+
+            // Check if the tag is a valid short digest value
+            guard (try? Utility.isShortDigest(shortDigestTag)) == true else {
+                return nil
+            }
+
+            let imageName = String(reference.prefix { $0 != ":" })
+            // Fetch the ClientImage with the correct short digest and image name
+            // The second check for name is in case of duplicate short digests
+            let shortDigestImage: ClientImage? = try all.first(where: { image in
+                try Utility.trimDigest(digest: image.digest) == shortDigestTag + "..." &&
+                imageName == String(Self.denormalizeReference(image.reference).prefix { $0 != ":" })
+            })
+            return shortDigestImage
+        }()
+        if let shortDigestReferencedImage {
+            return shortDigestReferencedImage
+        }
+
         // If we don't find a match, try matching `ImageDescription.name` against the given
         // input string, while also checking against its normalized form.
         // Return the first match.

Sources/ContainerClient/Utility.swift

@@ -53,6 +53,17 @@ public struct Utility {
         }
         return digest
     }
+
+    public static func isShortDigest(_ digest: String) throws -> Bool {
+        // Short digest must be be 24 hexadecimal characters
+        let pattern = "^[0-9a-f]{24}$"
+        let regex = try Regex(pattern)
+        if try regex.firstMatch(in: digest) != nil {
+            return true
+        } else {
+            throw ContainerizationError(.invalidArgument, message: "invalid short sha digest \(digest)")
+        }
+    }
 
     public static func validEntityName(_ name: String) throws {
         let pattern = #"^[a-zA-Z0-9][a-zA-Z0-9_.-]+$"#