feat(tvix/store): add size() and digest() functions for Directory

Change-Id: I3a9e3c77da1d5d7bfb93da0cd7bce8d48dbc8cd4
Reviewed-on: https://cl.tvl.fyi/c/depot/+/7254
Reviewed-by: Adam Joseph <adam@westernsemico.com>
Reviewed-by: tazjin <tazjin@tvl.su>
Tested-by: BuildkiteCI

tvix/store/src/lib.rs

@@ -1,3 +0,0 @@
-pub mod protos {
-    include!(concat!(env!("OUT_DIR"), "/tvix.store.v1.rs"));
-}

tvix/store/src/main.rs

@@ -1,3 +1,5 @@
+mod proto;
+
 fn main() {
     println!("Hello, world!");
 }

tvix/store/src/proto.rs

@@ -0,0 +1,105 @@
+use prost::Message;
+
+include!(concat!(env!("OUT_DIR"), "/tvix.store.v1.rs"));
+
+impl Directory {
+    // The size of a directory is the number of all regular and symlink elements,
+    // the number of directory elements, and their size fields.
+    pub fn size(&self) -> u32 {
+        self.files.len() as u32
+            + self.symlinks.len() as u32
+            + self
+                .directories
+                .iter()
+                .fold(0, |acc: u32, e| (acc + 1 + e.size) as u32)
+    }
+
+    pub fn digest(&self) -> Vec<u8> {
+        let mut hasher = blake3::Hasher::new();
+
+        hasher.update(&self.encode_to_vec()).finalize().as_bytes()[..].to_vec()
+    }
+}
+
+#[cfg(test)]
+mod tests {
+    use super::{Directory, DirectoryNode, FileNode, SymlinkNode};
+
+    #[test]
+    fn test_directory_size() {
+        {
+            let d = Directory {
+                directories: vec![],
+                files: vec![],
+                symlinks: vec![],
+            };
+            assert_eq!(d.size(), 0);
+        }
+        {
+            let d = Directory {
+                directories: vec![DirectoryNode {
+                    name: String::from("foo"),
+                    digest: vec![],
+                    size: 0,
+                }],
+                files: vec![],
+                symlinks: vec![],
+            };
+            assert_eq!(d.size(), 1);
+        }
+        {
+            let d = Directory {
+                directories: vec![DirectoryNode {
+                    name: String::from("foo"),
+                    digest: vec![],
+                    size: 4,
+                }],
+                files: vec![],
+                symlinks: vec![],
+            };
+            assert_eq!(d.size(), 5);
+        }
+        {
+            let d = Directory {
+                directories: vec![],
+                files: vec![FileNode {
+                    name: String::from("foo"),
+                    digest: vec![],
+                    size: 42,
+                    executable: false,
+                }],
+                symlinks: vec![],
+            };
+            assert_eq!(d.size(), 1);
+        }
+        {
+            let d = Directory {
+                directories: vec![],
+                files: vec![],
+                symlinks: vec![SymlinkNode {
+                    name: String::from("foo"),
+                    target: String::from("bar"),
+                }],
+            };
+            assert_eq!(d.size(), 1);
+        }
+    }
+
+    #[test]
+    fn test_digest() {
+        let d = Directory {
+            directories: vec![],
+            files: vec![],
+            symlinks: vec![],
+        };
+
+        assert_eq!(
+            d.digest(),
+            vec![
+                0xaf, 0x13, 0x49, 0xb9, 0xf5, 0xf9, 0xa1, 0xa6, 0xa0, 0x40, 0x4d, 0xea, 0x36, 0xdc,
+                0xc9, 0x49, 0x9b, 0xcb, 0x25, 0xc9, 0xad, 0xc1, 0x12, 0xb7, 0xcc, 0x9a, 0x93, 0xca,
+                0xe4, 0x1f, 0x32, 0x62
+            ]
+        )
+    }
+}