Merge #13697: Support output descriptors in scantxoutset

f6b7fc349ccf9cfbeb7e91e19c20e2a2fcc9026f Support h instead of ' in hardened descriptor paths (Pieter Wuille)
fddea672eb8f63012f2e9ce04fa477e5d4140750 Add experimental warning to scantxoutset (Jonas Schnelli)
6495849bfd362d6a2f128bac5982fa9e3e2e3396 [QA] Extend tests to more combinations (Pieter Wuille)
1af237faefc316bd708e25d6901ee6f17b706e57 [QA] Add xpub range tests in scantxoutset tests (Jonas Schnelli)
151600bb4972f7bab4ed4a03d1f67c38e081fefe Swap in descriptors support into scantxoutset (Pieter Wuille)
0652c3284fe12941b28624dbbf5e0862c5d0dbc3 Descriptor tests (Pieter Wuille)
fe8a7dcd78cfeedc9a7c705e91384f793822912b Output descriptors module (Pieter Wuille)
e54d76044b3a2c625e53f2116c5f6a7c40105d5d Add simple FlatSigningProvider (Pieter Wuille)
29943a904a11607787d28b1f4288f500bd076dde Add more methods to Span class (Pieter Wuille)

Pull request description:

  As promised, here is an implementation of my output descriptor concept (https://gist.github.com/sipa/e3d23d498c430bb601c5bca83523fa82) and integration within the `scantxoutset` RPC that was just added through #12196.

  It changes the RPC to use descriptors for everything; I hope the interface is simple enough to encompass all use cases. It includes support for P2PK, P2PKH, P2WPKH, P2SH, P2WSH, multisig, xpubs, xprvs, and chains of keys - combined in every possible way.

Tree-SHA512: 63b54a96e7a72f5b04a8d645b8517d43ecd6a65a41f9f4e593931ce725a8845ab0baa1e9db6a7243190d8ac841f6e7e2f520d98c539312d78f7fd687d2c7b88f

1 files changed, 102 insertions, 0 deletions

diff --git a/src/script/descriptor.h b/src/script/descriptor.h
new file mode 100644
index 0000000000..e079c72e92
--- /dev/null
+++ b/src/script/descriptor.h
@@ -0,0 +1,102 @@
+// Copyright (c) 2018 The Bitcoin Core developers
+// Distributed under the MIT software license, see the accompanying
+// file COPYING or http://www.opensource.org/licenses/mit-license.php.
+
+#ifndef BITCOIN_SCRIPT_DESCRIPTOR_H
+#define BITCOIN_SCRIPT_DESCRIPTOR_H
+
+#include <script/script.h>
+#include <script/sign.h>
+
+#include <vector>
+
+// Descriptors are strings that describe a set of scriptPubKeys, together with
+// all information necessary to solve them. By combining all information into
+// one, they avoid the need to separately import keys and scripts.
+//
+// Descriptors may be ranged, which occurs when the public keys inside are
+// specified in the form of HD chains (xpubs).
+//
+// Descriptors always represent public information - public keys and scripts -
+// but in cases where private keys need to be conveyed along with a descriptor,
+// they can be included inside by changing public keys to private keys (WIF
+// format), and changing xpubs by xprvs.
+//
+// 1. Examples
+//
+// A P2PK descriptor with a fixed public key:
+// - pk(0279be667ef9dcbbac55a06295ce870b07029bfcdb2dce28d959f2815b16f81798)
+//
+// A P2SH-P2WSH-P2PKH descriptor with a fixed public key:
+// - sh(wsh(pkh(02e493dbf1c10d80f3581e4904930b1404cc6c13900ee0758474fa94abe8c4cd13)))
+//
+// A bare 1-of-2 multisig descriptor:
+// - multi(1,022f8bde4d1a07209355b4a7250a5c5128e88b84bddc619ab7cba8d569b240efe4,025cbdf0646e5db4eaa398f365f2ea7a0e3d419b7e0330e39ce92bddedcac4f9bc)
+//
+// A chain of P2PKH outputs (this needs the corresponding private key to derive):
+// - pkh(xpub68Gmy5EdvgibQVfPdqkBBCHxA5htiqg55crXYuXoQRKfDBFA1WEjWgP6LHhwBZeNK1VTsfTFUHCdrfp1bgwQ9xv5ski8PX9rL2dZXvgGDnw/1'/2/*)
+//
+// 2. Grammar description:
+//
+// X: xpub or xprv encoded extended key
+// I: decimal encoded integer
+// H: Hex encoded byte array
+// A: Address in P2PKH, P2SH, or Bech32 encoding
+//
+// S (Scripts):
+// * pk(P): Pay-to-pubkey (P2PK) output for public key P.
+// * pkh(P): Pay-to-pubkey-hash (P2PKH) output for public key P.
+// * wpkh(P): Pay-to-witness-pubkey-hash (P2WPKH) output for public key P.
+// * sh(S): Pay-to-script-hash (P2SH) output for script S
+// * wsh(S): Pay-to-witness-script-hash (P2WSH) output for script S
+// * combo(P): combination of P2PK, P2PKH, P2WPKH, and P2SH-P2WPKH for public key P.
+// * multi(I,L): k-of-n multisig for given public keys
+// * addr(A): Output to address
+// * raw(H): scriptPubKey with raw bytes
+//
+// P (Public keys):
+// * H: fixed public key (or WIF-encoded private key)
+// * E: extended public key
+// * E/*: (ranged) all unhardened direct children of an extended public key
+// * E/*': (ranged) all hardened direct children of an extended public key
+//
+// L (Comma-separated lists of public keys):
+// * P
+// * L,P
+//
+// E (Extended public keys):
+// * X
+// * E/I: unhardened child
+// * E/I': hardened child
+// * E/Ih: hardened child (alternative notation)
+//
+// The top level is S.
+
+/** Interface for parsed descriptor objects. */
+struct Descriptor {
+    virtual ~Descriptor() = default;
+
+    /** Whether the expansion of this descriptor depends on the position. */
+    virtual bool IsRange() const = 0;
+
+    /** Convert the descriptor back to a string, undoing parsing. */
+    virtual std::string ToString() const = 0;
+
+    /** Convert the descriptor to a private string. This fails if the provided provider does not have the relevant private keys. */
+    virtual bool ToPrivateString(const SigningProvider& provider, std::string& out) const = 0;
+
+    /** Expand a descriptor at a specified position.
+     *
+     * pos: the position at which to expand the descriptor. If IsRange() is false, this is ignored.
+     * provider: the provider to query for private keys in case of hardened derivation.
+     * output_script: the expanded scriptPubKeys will be put here.
+     * out: scripts and public keys necessary for solving the expanded scriptPubKeys will be put here (may be equal to provider).
+     */
+    virtual bool Expand(int pos, const SigningProvider& provider, std::vector<CScript>& output_scripts, FlatSigningProvider& out) const = 0;
+};
+
+/** Parse a descriptor string. Included private keys are put in out. Returns nullptr if parsing fails. */
+std::unique_ptr<Descriptor> Parse(const std::string& descriptor, FlatSigningProvider& out);
+
+#endif // BITCOIN_SCRIPT_DESCRIPTOR_H
+