Merge #730: Update compiler example to a Policy example

97b6fb0 Add a policy example (rajarshimaitra)
da76708 Update compiler example. (rajarshimaitra)

Pull request description:

  ### Description

  Fixes #729.

  There is an "unmaintained" warning in a old version of clap, which triggered the issue.

  Ideally, we should not have clap in bdk's dependency. It was only used for the `compiler.rs` example, which was a very tiny clap app compiling miniscript policies, and it wasn't really an example for bdk.

  This PR rewrites the example as a `policy.rs` which demos the BDK's Policy module and policy structures.

   - Use a `wsh(multi(2, Privkey, Pubkey))` descriptor, which has only one part private and other part public.
   - use `into_wallet_descriptor()` to turn that into a `Descriptor` and `KeyMap`.
   - Use the `KeyMap` to create a custom signer.
   - Extract the descriptor `Policy` structure from the given keymap.

   I am not very sure on how much this example is helpful. I still find it hard to read the Policy structure visually. But if Policy is something we want the user to know about descriptors and bdk wallets, this shows how to extract it for a simple multisig condition.

  Note: There is no use of `bdk::wallet` in the example. BDK uses the Policy extraction internally while transaction creation. But all these are exposed publicly, so can be used independently too.

  ### Questions:

  - Should we still have a `minscript::policy::compile()` example?  Which IIUC is very different from `bdk::policy:Policy`.  I didn't include it in this PR, because I am not sure if it fits inside bdk example categories.

   - Should we expose `extract_policy` as an wallet API? All though its possible to get policy without creating a wallet, why not let the wallet also spit one out for itself, if its useful?

  ### Checklists

  #### All Submissions:

  * [x] I've signed all my commits
  * [x] I followed the [contribution guidelines](https://github.com/bitcoindevkit/bdk/blob/master/CONTRIBUTING.md)
  * [x] I ran `cargo fmt` and `cargo clippy` before committing

ACKs for top commit:
  afilini:
    ACK 97b6fb0

Tree-SHA512: 8e3719fdad308a347d22377050b2f29e02a884ff7d4e57a05a06d078de0709b5bf70bbcb1a696d1e1cdfe02cdb470e5af643da7c775b67fe318046bd6b80f440

Author: afilini

Cargo.toml

@@ -100,7 +100,6 @@ test-hardware-signer = ["hardware-signer"]
 [dev-dependencies]
 lazy_static = "1.4"
 env_logger = "0.7"
-clap = "2.33"
 electrsd = "0.20"
 
 [[example]]
@@ -114,6 +113,10 @@ name = "miniscriptc"
 path = "examples/compiler.rs"
 required-features = ["compiler"]
 
+[[example]]
+name = "policy"
+path = "examples/policy.rs"
+
 [[example]]
 name = "rpcwallet"
 path = "examples/rpcwallet.rs"

examples/compiler.rs

@@ -11,7 +11,6 @@
 
 extern crate bdk;
 extern crate bitcoin;
-extern crate clap;
 extern crate log;
 extern crate miniscript;
 extern crate serde_json;
@@ -21,8 +20,6 @@ use std::str::FromStr;
 
 use log::info;
 
-use clap::{App, Arg};
-
 use bitcoin::Network;
 use miniscript::policy::Concrete;
 use miniscript::Descriptor;
@@ -31,75 +28,49 @@ use bdk::database::memory::MemoryDatabase;
 use bdk::wallet::AddressIndex::New;
 use bdk::{KeychainKind, Wallet};
 
+/// Miniscript policy is a high level abstraction of spending conditions. Defined in the
+/// rust-miscript library here  https://docs.rs/miniscript/7.0.0/miniscript/policy/index.html
+/// rust-miniscript provides a `compile()` function that can be used to compile any miniscript policy
+/// into a descriptor. This descriptor then in turn can be used in bdk a fully functioning wallet
+/// can be derived from the policy.
+///
+/// This example demonstrates the interaction between a bdk wallet and miniscript policy.
+
 fn main() -> Result<(), Box<dyn Error>> {
     env_logger::init_from_env(
         env_logger::Env::default().filter_or(env_logger::DEFAULT_FILTER_ENV, "info"),
     );
 
-    let matches = App::new("Miniscript Compiler")
-        .arg(
-            Arg::with_name("POLICY")
-                .help("Sets the spending policy to compile")
-                .required(true)
-                .index(1),
-        )
-        .arg(
-            Arg::with_name("TYPE")
-                .help("Sets the script type used to embed the compiled policy")
-                .required(true)
-                .index(2)
-                .possible_values(&["sh", "wsh", "sh-wsh"]),
-        )
-        .arg(
-            Arg::with_name("parsed_policy")
-                .long("parsed_policy")
-                .short("p")
-                .help("Also return the parsed spending policy in JSON format"),
-        )
-        .arg(
-            Arg::with_name("network")
-                .short("n")
-                .long("network")
-                .help("Sets the network")
-                .takes_value(true)
-                .default_value("testnet")
-                .possible_values(&["testnet", "regtest", "bitcoin", "signet"]),
-        )
-        .get_matches();
-
-    let policy_str = matches.value_of("POLICY").unwrap();
-    info!("Compiling policy: {}", policy_str);
+    // We start with a generic miniscript policy string
+    let policy_str = "or(10@thresh(4,pk(029ffbe722b147f3035c87cb1c60b9a5947dd49c774cc31e94773478711a929ac0),pk(025f05815e3a1a8a83bfbb03ce016c9a2ee31066b98f567f6227df1d76ec4bd143),pk(025625f41e4a065efc06d5019cbbd56fe8c07595af1231e7cbc03fafb87ebb71ec),pk(02a27c8b850a00f67da3499b60562673dcf5fdfb82b7e17652a7ac54416812aefd),pk(03e618ec5f384d6e19ca9ebdb8e2119e5bef978285076828ce054e55c4daf473e2)),1@and(older(4209713),thresh(2,pk(03deae92101c790b12653231439f27b8897264125ecb2f46f48278603102573165),pk(033841045a531e1adf9910a6ec279589a90b3b8a904ee64ffd692bd08a8996c1aa),pk(02aebf2d10b040eb936a6f02f44ee82f8b34f5c1ccb20ff3949c2b28206b7c1068))))";
+    info!("Compiling policy: \n{}", policy_str);
 
+    // Parse the string as a [`Concrete`] type miniscript policy.
     let policy = Concrete::<String>::from_str(policy_str)?;
 
-    let descriptor = match matches.value_of("TYPE").unwrap() {
-        "sh" => Descriptor::new_sh(policy.compile()?)?,
-        "wsh" => Descriptor::new_wsh(policy.compile()?)?,
-        "sh-wsh" => Descriptor::new_sh_wsh(policy.compile()?)?,
-        _ => panic!("Invalid type"),
-    };
+    // Create a `wsh` type descriptor from the policy.
+    // `policy.compile()` returns the resulting miniscript from the policy.
+    let descriptor = Descriptor::new_wsh(policy.compile()?)?;
 
-    info!("... Descriptor: {}", descriptor);
+    info!("Compiled into following Descriptor: \n{}", descriptor);
 
     let database = MemoryDatabase::new();
 
-    let network = matches
-        .value_of("network")
-        .map(Network::from_str)
-        .transpose()
-        .unwrap()
-        .unwrap_or(Network::Testnet);
-    let wallet = Wallet::new(&format!("{}", descriptor), None, network, database)?;
-
-    info!("... First address: {}", wallet.get_address(New)?);
-
-    if matches.is_present("parsed_policy") {
-        let spending_policy = wallet.policies(KeychainKind::External)?;
-        info!(
-            "... Spending policy:\n{}",
-            serde_json::to_string_pretty(&spending_policy)?
-        );
-    }
+    // Create a new wallet from this descriptor
+    let wallet = Wallet::new(&format!("{}", descriptor), None, Network::Regtest, database)?;
+
+    info!(
+        "First derived address from the descriptor: \n{}",
+        wallet.get_address(New)?
+    );
+
+    // BDK also has it's own `Policy` structure to represent the spending condition in a more
+    // human readable json format.
+    let spending_policy = wallet.policies(KeychainKind::External)?;
+    info!(
+        "The BDK spending policy: \n{}",
+        serde_json::to_string_pretty(&spending_policy)?
+    );
 
     Ok(())
 }

examples/policy.rs

@@ -0,0 +1,66 @@
+// Bitcoin Dev Kit
+// Written in 2020 by Alekos Filini <alekos.filini@gmail.com>
+//
+// Copyright (c) 2020-2021 Bitcoin Dev Kit Developers
+//
+// This file is licensed under the Apache License, Version 2.0 <LICENSE-APACHE
+// or http://www.apache.org/licenses/LICENSE-2.0> or the MIT license
+// <LICENSE-MIT or http://opensource.org/licenses/MIT>, at your option.
+// You may not use this file except in accordance with one or both of these
+// licenses.
+
+extern crate bdk;
+extern crate env_logger;
+extern crate log;
+use std::error::Error;
+
+use bdk::bitcoin::Network;
+use bdk::descriptor::{policy::BuildSatisfaction, ExtractPolicy, IntoWalletDescriptor};
+use bdk::wallet::signer::SignersContainer;
+
+/// This example describes the use of the BDK's [`bdk::descriptor::policy`] module.
+///
+/// Policy is higher abstraction representation of the wallet descriptor spending condition.
+/// This is useful to express complex miniscript spending conditions into more human readable form.
+/// The resulting `Policy` structure  can be used to derive spending conditions the wallet is capable
+/// to spend from.
+///
+/// This example demos a Policy output for a 2of2 multisig between between 2 parties, where the wallet holds
+/// one of the Extend Private key.
+
+fn main() -> Result<(), Box<dyn Error>> {
+    env_logger::init_from_env(
+        env_logger::Env::default().filter_or(env_logger::DEFAULT_FILTER_ENV, "info"),
+    );
+
+    let secp = bitcoin::secp256k1::Secp256k1::new();
+
+    // The descriptor used in the example
+    // The form is "wsh(multi(2, <privkey>, <pubkey>))"
+    let desc = "wsh(multi(2,tprv8ZgxMBicQKsPdpkqS7Eair4YxjcuuvDPNYmKX3sCniCf16tHEVrjjiSXEkFRnUH77yXc6ZcwHHcLNfjdi5qUvw3VDfgYiH5mNsj5izuiu2N/1/*,tpubD6NzVbkrYhZ4XHndKkuB8FifXm8r5FQHwrN6oZuWCz13qb93rtgKvD4PQsqC4HP4yhV3tA2fqr2RbY5mNXfM7RxXUoeABoDtsFUq2zJq6YK/1/*))";
+
+    // Use the descriptor string to derive the full descriptor and a keymap.
+    // The wallet descriptor can be used to create a new bdk::wallet.
+    // While the `keymap` can be used to create a `SignerContainer`.
+    //
+    // The `SignerContainer` can sign for `PSBT`s.
+    // a bdk::wallet internally uses these to handle transaction signing.
+    // But they can be used as independent tools also.
+    let (wallet_desc, keymap) = desc.into_wallet_descriptor(&secp, Network::Testnet)?;
+
+    log::info!("Example Descriptor for policy analysis : {}", wallet_desc);
+
+    // Create the signer with the keymap and descriptor.
+    let signers_container = SignersContainer::build(keymap, &wallet_desc, &secp);
+
+    // Extract the Policy from the given descriptor and signer.
+    // Note that Policy is a wallet specific structure. It depends on the the descriptor, and
+    // what the concerned wallet with a given signer can sign for.
+    let policy = wallet_desc
+        .extract_policy(&signers_container, BuildSatisfaction::None, &secp)?
+        .expect("We expect a policy");
+
+    log::info!("Derived Policy for the descriptor {:#?}", policy);
+
+    Ok(())
+}