utils: add executable for reading from datapack files

Summary:
Useful for debugging the rust code. I used it to isolate
a bug in the delta patching logic in the rust code.

(Note: this ignores all push blocking failures!)

Reviewed By: xavierd

Differential Revision: D15380387

fbshipit-source-id: 5980d352b85ee4836bd654045eda2eae131e5847

exec/utils/src/bin/datapack.rs

@@ -0,0 +1,30 @@
+// Copyright 2019 Facebook, Inc.
+//
+// This software may be used and distributed according to the terms of the
+// GNU General Public License version 2 or any later version.
+
+use std::path::PathBuf;
+
+use structopt::StructOpt;
+
+use revisionstore::{datapack::DataPack, datastore::DataStore, uniondatastore::UnionDataStore};
+use types::{Key, Node, RepoPathBuf};
+
+#[derive(StructOpt)]
+struct Cli {
+    #[structopt(short = "n", parse(try_from_str = "Node::from_str"))]
+    node: Node,
+    #[structopt(short = "p")]
+    path: PathBuf,
+}
+
+fn main() {
+    let args = Cli::from_args();
+    let pack = DataPack::new(&args.path).unwrap();
+    let mut store = UnionDataStore::new();
+    store.add(pack);
+
+    let key = Key::new(RepoPathBuf::new(), args.node);
+    let result = store.get(&key).unwrap();
+    println!("{:?}", String::from_utf8_lossy(&result));
+}