Compiler

Introduction

If you want to play around with more complicated spending policies, you'll start to find it harder and harder to manually create the descriptors. This is where the miniscript compiler comes in! The bdk library includes a very simple compiler that can produce a descriptor given a spending policy. The syntax used to encode the spending policy is very well described in this page (opens new window), specifically in the "Policy to Miniscript compiler". The compiler included in BDK does basically the same job, but produces descriptors for rust-miniscript that have some minor differences from the ones made by the C++ implementation used in that website.

Installation

To install the miniscript compiler run the following command:

cargo install --git https://github.com/bitcoindevkit/bdk --features="compiler" --example miniscriptc

Once the command is done, you should have a miniscriptc command available. You can check if that's the case by running miniscriptc --help.

Usage

In this case the interface is very simple: it accepts two arguments called "POLICY" and "TYPE", in this order. The first one, as the name implies, sets the spending policy to compile. The latter defines the type of address that should be used to encapsulate the produced script, like a P2SH, P2WSH, etc.

Optionally, the --parsed_policy flag can be enabled and it will make the compiler print the JSON "human-readable" version of the spending policy, as described in the policies subcommand of the CLI.

The --network flag can be used to change the network encoding of the address shown.

Tip

Keep in mind that since the compiler loads and interprets the descriptor, all the public keys specified in the policy must be valid public keys. This differs from the web tool linked above that also accepts placeholders too. As described in the previous sections of this guide, the keys can be either xpub/xprv with or without metadata and a derivation path, WIF keys or raw hex public keys.

Example

Let's take this policy for example:

miniscriptc --parsed_policy "and(pk(cSQPHDBwXGjVzWRqAHm6zfvQhaTuj1f2bFH58h55ghbjtFwvmeXR),or(50@pk(02e96fe52ef0e22d2f131dd425ce1893073a3c6ad20e8cac36726393dfb4856a4c),older(1000)))" sh-wsh

The compiler should print something like:

[2020-04-29T10:42:05Z INFO  miniscriptc] Compiling policy: and(pk(cSQPHDBwXGjVzWRqAHm6zfvQhaTuj1f2bFH58h55ghbjtFwvmeXR),or(50@pk(02e96fe52ef0e22d2f131dd425ce1893073a3c6ad20e8cac36726393dfb4856a4c),older(1000)))
[2020-04-29T10:42:05Z INFO  miniscriptc] ... Descriptor: sh(wsh(and_v(or_c(c:pk(02e96fe52ef0e22d2f131dd425ce1893073a3c6ad20e8cac36726393dfb4856a4c),v:older(1000)),c:pk(cSQPHDBwXGjVzWRqAHm6zfvQhaTuj1f2bFH58h55ghbjtFwvmeXR))))
[2020-04-29T10:42:05Z INFO  miniscriptc] ... First address: 2MsqrJuZewY3o3ADAy1Uhi5vsBqTANjH3Cf

JSON policy:

{
  "type":"THRESH",
  "items":[
    {
      "type":"THRESH",
      "items":[
        {
          "type":"SIGNATURE",
          "pubkey":"02e96fe52ef0e22d2f131dd425ce1893073a3c6ad20e8cac36726393dfb4856a4c",
          "satisfaction":{
            "type":"NONE"
          },
          "contribution":{
            "type":"NONE"
          }
        },
        {
          "type":"RELATIVETIMELOCK",
          "value":1000,
          "satisfaction":{
            "type":"NONE"
          },
          "contribution":{
            "type":"COMPLETE",
            "condition":{
              "csv":1000
            }
          }
        }
      ],
      "threshold":1,
      "satisfaction":{
        "type":"NONE"
      },
      "contribution":{
        "type":"PARTIALCOMPLETE",
        "n":2,
        "m":1,
        "items":[
          1
        ],
        "conditions":{
          "[1]":[
            {
              "csv":1000
            }
          ]
        }
      }
    },
    {
      "type":"SIGNATURE",
      "pubkey":"02e96fe52ef0e22d2f131dd425ce1893073a3c6ad20e8cac36726393dfb4856a4c",
      "satisfaction":{
        "type":"NONE"
      },
      "contribution":{
        "type":"COMPLETE",
        "condition":{

        }
      }
    }
  ],
  "threshold":2,
  "satisfaction":{
    "type":"NONE"
  },
  "contribution":{
    "type":"PARTIALCOMPLETE",
    "n":2,
    "m":2,
    "items":[
      0,
      1
    ],
    "conditions":{
      "[0, 1]":[
        {
          "csv":1000
        }
      ]
    }
  }
}

Troubleshooting

Nothing is printed

This might mean that you have a RUST_LOG variable set to a value that suppresses the compiler's log. You can try adding miniscriptc=info to your RUST_LOG value and see if that works, or open a new clean shell.