For internal macros used only in this crate we do not need to use
`macro_use` and pollute the top level namespace now that we have edition
2018. We can add a `pub(crate) use` statement to each and then path
imports work for the macros like normal types.
Now we have edition 2018 we do not need to use `macro_use` or `extern
crate`; `pub use` works with macros.
Remove the extern crate statement and replace it with a pub use
statement. Requires fixing up various imports statements and also
requires importing `sha256t_hash_newtype` macro directly instead of
using a qualified path to it.
73bc2bb058 Remove leading colons from ::core::cmp::Ordering (Tobin C. Harding)
bffe0e840d Remove _most_ leading double colons (Tobin C. Harding)
Pull request description:
Leading double colons are a relic of edition 2015. Attempt to remove _all_ leading double colons (assuming I didn't miss any).
- Patch 1 is done mechanically so it can be repeated by reviewers, just search-and-replace ' ::' with '::' (note the leading space).
- Patch 2 does a single other instance of leading `::`
ACKs for top commit:
apoelstra:
ACK 73bc2bb058
sanket1729:
utACK 73bc2bb058.
Tree-SHA512: 8f7aafdda1aed5b69dcc83f544e65085dfec6590765839f0a6f259b99872805d1f00602fd9deac05c80a5cac3bc222d454dde0117dff4484e5cd34ea930fdfa1
a1df62a3d9 Witness human-readable serde test (Dr Maxim Orlovsky)
68577dfb50 Witness human-readable serde (Dr Maxim Orlovsky)
93b66c55b3 Witness serde: test binary encoding to be backward-compatible (Dr Maxim Orlovsky)
b409ae78a4 witness: Refactor import statements (Tobin C. Harding)
e23d3a815c Remove unnecessary whitespace (Tobin C. Harding)
ac55b1017e Add whitespace between functions (Tobin C. Harding)
Pull request description:
This is dr-orlovsky's [PR](https://github.com/rust-bitcoin/rust-bitcoin/pull/899) picked up at his permission in the discussion thread.
I went through the review comments and implemented everything except the perf optimisations. Also includes a patch at the front of the PR that adds a unit test that can be run to see the "before and after", not sure if we want it in, perhaps it should be removed before merge.
This PR implicitly fixes 942.
To test this PR works as advertised run `cargo test display_transaction --features=serde -- --nocapture` after creating a unit test as follows:
```rust
// Used to verify that parts of a transaction pretty print.
// `cargo test display_transaction --features=serde -- --nocapture`
#[cfg(feature = "serde")]
#[test]
fn serde_display_transaction() {
let tx_bytes = Vec::from_hex(
"02000000000101595895ea20179de87052b4046dfe6fd515860505d6511a9004cf12a1f93cac7c01000000\
00ffffffff01deb807000000000017a9140f3444e271620c736808aa7b33e370bd87cb5a078702483045022\
100fb60dad8df4af2841adc0346638c16d0b8035f5e3f3753b88db122e70c79f9370220756e6633b17fd271\
0e626347d28d60b0a2d6cbb41de51740644b9fb3ba7751040121028fa937ca8cba2197a37c007176ed89410\
55d3bcb8627d085e94553e62f057dcc00000000"
).unwrap();
let tx: Transaction = deserialize(&tx_bytes).unwrap();
let ser = serde_json::to_string_pretty(&tx).unwrap();
println!("{}", ser);
}
```
Fixes: #942
ACKs for top commit:
apoelstra:
ACK a1df62a3d9
Kixunil:
ACK a1df62a3d9
Tree-SHA512: d0ef5b8cbf1cf8456eaaea490a793f1ac7dfb18067c4019a2c3a1bdd9627a231a4dd0a0151a4df9af2b32b909d4b384a5bec1dd3e38d44dc6a23f9c40aa4f1f9
e34bc538c3 Add new type for sequence (Noah Lanson)
Pull request description:
#1082
Created a new type for txin sequence field with methods to create sequences with relative time locks from block height or time units.
ACKs for top commit:
Kixunil:
ACK e34bc538c3
tcharding:
ACK e34bc538c3
apoelstra:
ACK e34bc538c3
Tree-SHA512: 6605349d0312cc36ef9a4632f954e59265b3ba5cfd437aa88a37672fe479688aa4a3eff474902f8cc55848efe55caf3f09f321b3a62417842bfc3ec365c40688
f3b2120ec9 Create configuration conditional bench (Tobin C. Harding)
f60c92ca58 Add informative error message to DO_BENCH (Tobin C. Harding)
c6d5a12b60 Add cargo/rustc sanity calls (Tobin C. Harding)
34d5a3141d Put triple ticks on their own line (Tobin C. Harding)
Pull request description:
Currently we are unable to build with all features enabled with a non-nightly toolchain, this is because of the use of
`#![cfg_attr(all(test, feature = "unstable"), feature(test))]`
which causes the following error when building:
error[E0554]: `#![feature]` may not be used on the stable release channel
The "unstable" feature is used to guard bench mark modules, this is widely suggested online but there is a better way.
When running the bench marks use the following incantation:
`RUSTFLAGS='--cfg=bench' cargo bench`
This creates a configuration conditional "bench" that can be used to guard the bench mark modules.
```
#[cfg(bench)]
mod benches {
...
}
```
ACKs for top commit:
Kixunil:
ACK f3b2120ec9
apoelstra:
ACK f3b2120ec9
Tree-SHA512: 7ec2a501a30bfe2ce72601077cd675cf5e5ac2f0f93f97fc7e83cb7401606b69ae909b35bfc0ace8bd1ea771ca4fba70e2ad9ac9ba26f2b6e371494cf694c0a8
Currently we are unable to build with all features enabled with a
non-nightly toolchain, this is because of the use of
`#![cfg_attr(all(test, feature = "unstable"), feature(test))]`
which causes the following error when building:
error[E0554]: `#![feature]` may not be used on the stable release
channel
The "unstable" feature is used to guard bench mark modules, this is
widely suggested online but there is a better way.
When running the bench marks use the following incantation:
`RUSTFLAGS='--cfg=bench' cargo bench`
This creates a configuration conditional "bench" that can be used to
guard the bench mark modules.
#[cfg(bench)]
mod benches {
...
}
Previous implementations of Witness (and Vec<Vec<u8>>) serde serialization
didn't support human-readable representations. This resulted in long unreadable
JSON/YAML byte arrays, which were especially ugly when pretty-printed (a line
per each byte).
Co-authored-by: Tobin C. Harding <me@tobin.cc>
This also removes tests for JSON backward-compatible encoding. Human-readable
encoding will be changed in the next commit and this will break backward
compatibility, thus that part of the test is removed.
91ff2f628c Introduce SPDX license identifiers (Tobin C. Harding)
Pull request description:
When `rust-bitcoin` was started in 2014 the SPDX license list and short identifiers where not a thing. Now that we have short identifiers and they are gaining popularity in other projects we can consider using them.
- Add links to the SPDX website in the readme
- Shorten the author section to a single line
- Remove all the licence information in each file and replace it with an
SPDX ID (see https://spdx.dev/ids/#how)
Of note:
- If the author of a file is explicitly listed, maintain this information
- If the 'author' is listed as the generic 'Rust Bitcoin developers' just remove the attribution, this is implicit. This does loose the date info but that can be seen at any time from the git index using
`git log --follow --format=%ad --date default <FILE> | tail -1`
apoelstra, please confirm that I'm not treading on your toes here, especially, are you ok with the new 'written by' string format?
### Ref
- https://spdx.dev/ids/#how
- https://spdx.org/licenses/CC0-1.0.html
- https://spdx.dev/ids/
ACKs for top commit:
apoelstra:
ACK 91ff2f628c
sanket1729:
ACK 91ff2f628c. I am also in IDGAF camp, but I like more red lines in diff.
Kixunil:
ACK 91ff2f628c
Tree-SHA512: ca8aac00f015c18ec18de83dfeb50dd6f4f840653c7def85daa2436a339021ada5f3c34ad0cdf6b18e3e39c45a6d58a8313742e4001d467785b10eee7fdbc938
Leading double colons are a relic of edition 2015. Remove all leading
double colons that follow a space, done like this so that reviewers can
do the same and verify the diff. Done with
search-and-replace ' ::' '::'
And, for the record:
```bash
function search-and-replace() {
if (($# != 2))
then
echo "Usage: $0 <this> <that>"
return
fi
local this="$1"
local that="$2"
for file in $(git grep -l "$this")
do
perl -pi -e "s/$this/$that/g" "$file"
done
}
```
32cfd93933 Use to_hex when available (Tobin C. Harding)
Pull request description:
We have a bunch of calls to `format!("{:x}", foo)` for types that implement `ToHex`. The code is terser with no loss of clarity if we use the trait method and call `to_hex()`.
ACKs for top commit:
apoelstra:
ACK 32cfd93933
Kixunil:
ACK 32cfd93933
Tree-SHA512: 87cb6660708c11dfafb56bd6e2ea2634043b2226d51903a20806c1ba51c6e7c4f0e4cc25e49f820b5b1236600af7da2a20893c49a5b8845d7652b143fd0ec388
4d2291930b Use fragment-specifier literal (Tobin C. Harding)
Pull request description:
Currently we are using the fragment-specifier `expr` in a bunch of
macros for captures that are only used for literals. If we use `literal`
instead it allows the compiler to give slightly more specific error
messages.
The benefits of this change are minor. Of note, this patch found one
unusual macro call site (removed unnecessary `&`).
The macros changed are all internal macros, this is not a breaking change.
ACKs for top commit:
Kixunil:
ACK 4d2291930b
apoelstra:
ACK 4d2291930b
Tree-SHA512: 51c109fe3a884191bf623508555c1d5ad337a3f3b48538d18aec13e581f2c5fbbd055be49600ced19f38541412c34090bd8bac61fd05d5aa9702c96ff521364f
We have a bunch of calls to `format!("{:x}", foo)` for types that
implement `ToHex`. The code is terser with no loss of clarity if we use
the trait method and call `to_hex()`.
a8e62f249b Remove Uninhabited (Tobin C. Harding)
Pull request description:
Last release, before we had access to `non_exhaustive` we added some fancy types to enable conditionally having a `bitcoinconsensus::Error`.
Now that we have bumped the MSRV and have already added `non_exhaustive` to the `Error` type in question, we can use a compiler attribute to conditionally include the `bitcoinconsensus` error.
Remove `Uninhabited` and its usage.
For more context see the [original attempt ](https://github.com/rust-bitcoin/rust-bitcoin/pull/1025)at using `Infallible` (last comment in discussion thread).
ACKs for top commit:
Kixunil:
ACK a8e62f249b
dunxen:
ACK a8e62f2
apoelstra:
ACK a8e62f249b
Tree-SHA512: 8c03c44d7533af1a9a1185b7f9e0fa2c52369eaac8a45f0e2199e7e1bbd08ba2bfa23d829d2c2abf7f45fe8cc26ccad02f2e1a6d408d2c0fbca23140cafe3801
1fea098dfb Support unsized `R` and `W` in consensus encode/decode (Dawid Ciężarkiewicz)
a24a3b0194 Forward `consensus_decode` to `consensus_decode_from_finite_reader` (Dawid Ciężarkiewicz)
9c754ca4de Take Writer/Reader by `&mut` in consensus en/decoding (Dawid Ciężarkiewicz)
Pull request description:
Fix#1020 (see more relevant discussion there)
This definitely makes the amount of generics compiler
has to generate by avoding generating the same functions
for `R`, `&mut R`, `&mut &mut R` and so on.
old:
```
> ls -al target/release/deps/bitcoin-07a9dabf1f3e0266
-rwxrwxr-x 1 dpc dpc 9947832 Jun 2 22:42 target/release/deps/bitcoin-07a9dabf1f3e0266
> strip target/release/deps/bitcoin-07a9dabf1f3e0266
> ls -al target/release/deps/bitcoin-07a9dabf1f3e0266
-rwxrwxr-x 1 dpc dpc 4463024 Jun 2 22:46 target/release/deps/bitcoin-07a9dabf1f3e0266
```
new:
```
> ls -al target/release/deps/bitcoin-07a9dabf1f3e0266
-rwxrwxr-x 1 dpc dpc 9866800 Jun 2 22:44 target/release/deps/bitcoin-07a9dabf1f3e0266
> strip target/release/deps/bitcoin-07a9dabf1f3e0266
> ls -al target/release/deps/bitcoin-07a9dabf1f3e0266
-rwxrwxr-x 1 dpc dpc 4393392 Jun 2 22:45 target/release/deps/bitcoin-07a9dabf1f3e0266
```
In the unit-test binary itself, it saves ~100KB of data.
I did not expect much performance gains, but turn out I was wrong(*):
old:
```
test blockdata::block::benches::bench_block_deserialize ... bench: 1,072,710 ns/iter (+/- 21,871)
test blockdata::block::benches::bench_block_serialize ... bench: 191,223 ns/iter (+/- 5,833)
test blockdata::block::benches::bench_block_serialize_logic ... bench: 37,543 ns/iter (+/- 732)
test blockdata::block::benches::bench_stream_reader ... bench: 1,872,455 ns/iter (+/- 149,519)
test blockdata::transaction::benches::bench_transaction_deserialize ... bench: 136 ns/iter (+/- 3)
test blockdata::transaction::benches::bench_transaction_serialize ... bench: 51 ns/iter (+/- 8)
test blockdata::transaction::benches::bench_transaction_serialize_logic ... bench: 5 ns/iter (+/- 0)
test blockdata::transaction::benches::bench_transaction_size ... bench: 3 ns/iter (+/- 0)
```
new:
```
test blockdata::block::benches::bench_block_deserialize ... bench: 1,028,574 ns/iter (+/- 10,910)
test blockdata::block::benches::bench_block_serialize ... bench: 162,143 ns/iter (+/- 3,363)
test blockdata::block::benches::bench_block_serialize_logic ... bench: 30,725 ns/iter (+/- 695)
test blockdata::block::benches::bench_stream_reader ... bench: 1,437,071 ns/iter (+/- 53,694)
test blockdata::transaction::benches::bench_transaction_deserialize ... bench: 92 ns/iter (+/- 2)
test blockdata::transaction::benches::bench_transaction_serialize ... bench: 17 ns/iter (+/- 0)
test blockdata::transaction::benches::bench_transaction_serialize_logic ... bench: 5 ns/iter (+/- 0)
test blockdata::transaction::benches::bench_transaction_size ... bench: 4 ns/iter (+/- 0)
```
(*) - I'm benchmarking on a noisy laptop. Take this with a grain of salt. But I think
at least it doesn't make anything slower.
While doing all this manual labor that will probably generate conflicts,
I took a liberty of changing generic type names and variable names to
`r` and `R` (reader) and `w` and `W` for writer.
ACKs for top commit:
RCasatta:
ACK 1fea098dfb tested in downstream lib, space saving in compiled code confirmed
apoelstra:
ACK 1fea098dfb
Tree-SHA512: bc11994791dc97cc468dc9d411b9abf52ad475f23adf5c43d563f323bae0da180c8f57f2f17c1bb7b9bdcf523584b0943763742b81362880206779872ad7489f
b29ff9b715 Rename SchnorrSighashType::from_u8 -> from_consensus_u8 (Tobin C. Harding)
af16286679 Implement TryFrom sha256::Hash for TaprootMerkleBranch (Tobin C. Harding)
6b7b440cff Implement TryFrom<Key> for ProprietaryKey (Tobin C. Harding)
5c49fe775f Implement TryFrom<TaprootBuilder> for TapTree (Tobin C. Harding)
632a5db8d9 Implement TryFrom for WitnessVersion (Tobin C. Harding)
Pull request description:
Audit the whole codebase checking for any method that is of the form `from_foo` where foo is not an interesting identifier (like 'consensus' and 'standard'). Implement `TryFrom` for any such methods, deprecating the original.
Done as separate patches so any can be easily dropped if not liked.
ACKs for top commit:
apoelstra:
ACK b29ff9b715
Kixunil:
ACK b29ff9b715
Tree-SHA512: 40f1d96b505891080df1f7a9b3507979b0279a9e0f9d7cd32598bdc16c866785e6b13d5cb1face5ba50e3bc8484a5cd9c7f430d7abc86db9609962476dacd467
9bf959180b Optimize Witness Serialization (DanGould)
Pull request description:
fix#942
> self.to_vec() allocates, it should be possible to avoid it - just feed the items into serializer.
based on https://github.com/rust-bitcoin/rust-bitcoin/pull/1068
ACKs for top commit:
Kixunil:
ACK 9bf959180b
apoelstra:
ACK 9bf959180b
Tree-SHA512: 14553dfed20aee50bb6361d44986b38556cbb3e112e1b4d9e3b401c3da831b6bdf159089966254cf371c225ae929fc78516c96a6114b40a7bc1fda7305295e4a
We allocated a new vector when serializing a `Witness`. That was
inefficient and unnecessary. Use `serialize_seq` to feed the witness
elements directly into the serializer.
Optimize `Witness` serialization by removing the allocation.
When `rust-bitcoin` was started in 2014 the SPDX license list and short
identifiers where not a thing. Now that we have short identifiers and
they are gaining popularity in other projects we can consider using
them.
- Add links to the SPDX website in the readme
- Shorten the author section to a single line
- Remove all the licence information in each file and replace it with an
SPDX ID (see https://spdx.dev/ids/#how)
Of note:
- If the author of a file is explicitly listed, maintain this
information
- If the 'author' is listed as the generic 'Rust Bitcoin developers'
just remove the attribution, this is implicit. This does loose the date
info but that can be seen at any time from the git index using
`git log --follow --format=%ad --date default <FILE> | tail -1`
Last release, before we had access to `non_exhaustive` we added some
fancy types to enable conditionally having a `bitcoinconsensus::Error`.
Now that we have bumped the MSRV and have already added `non_exhaustive`
to the `Error` type in question, we can use a compiler attribute to
conditionally include the `bitcoinconsensus` error.
Remove `Uninhabited` and its usage.
We have a bunch of 'from' methods that are fallible; `TryFrom` became
available in Rust 1.34 so we can use it now we have bumped our MSRV.
Implement the various `WitnessVersion` from methods using `TryFrom` and
deprecate the originals.
Fix#1020 (see more relevant discussion there)
This definitely makes the amount of generics compiler
has to generate by avoding generating the same functions
for `R`, &mut R`, `&mut &mut R` and so on.
old:
```
> ls -al target/release/deps/bitcoin-07a9dabf1f3e0266
-rwxrwxr-x 1 dpc dpc 9947832 Jun 2 22:42 target/release/deps/bitcoin-07a9dabf1f3e0266
> strip target/release/deps/bitcoin-07a9dabf1f3e0266
> ls -al target/release/deps/bitcoin-07a9dabf1f3e0266
-rwxrwxr-x 1 dpc dpc 4463024 Jun 2 22:46 target/release/deps/bitcoin-07a9dabf1f3e0266
```
new:
```
> ls -al target/release/deps/bitcoin-07a9dabf1f3e0266
-rwxrwxr-x 1 dpc dpc 9866800 Jun 2 22:44 target/release/deps/bitcoin-07a9dabf1f3e0266
> strip target/release/deps/bitcoin-07a9dabf1f3e0266
> ls -al target/release/deps/bitcoin-07a9dabf1f3e0266
-rwxrwxr-x 1 dpc dpc 4393392 Jun 2 22:45 target/release/deps/bitcoin-07a9dabf1f3e0266
```
In the unit-test binary itself, it saves ~100KB of data.
I did not expect much performance gains, but turn out I was wrong(*):
old:
```
test blockdata::block::benches::bench_block_deserialize ... bench: 1,072,710 ns/iter (+/- 21,871)
test blockdata::block::benches::bench_block_serialize ... bench: 191,223 ns/iter (+/- 5,833)
test blockdata::block::benches::bench_block_serialize_logic ... bench: 37,543 ns/iter (+/- 732)
test blockdata::block::benches::bench_stream_reader ... bench: 1,872,455 ns/iter (+/- 149,519)
test blockdata::transaction::benches::bench_transaction_deserialize ... bench: 136 ns/iter (+/- 3)
test blockdata::transaction::benches::bench_transaction_serialize ... bench: 51 ns/iter (+/- 8)
test blockdata::transaction::benches::bench_transaction_serialize_logic ... bench: 5 ns/iter (+/- 0)
test blockdata::transaction::benches::bench_transaction_size ... bench: 3 ns/iter (+/- 0)
```
new:
```
test blockdata::block::benches::bench_block_deserialize ... bench: 1,028,574 ns/iter (+/- 10,910)
test blockdata::block::benches::bench_block_serialize ... bench: 162,143 ns/iter (+/- 3,363)
test blockdata::block::benches::bench_block_serialize_logic ... bench: 30,725 ns/iter (+/- 695)
test blockdata::block::benches::bench_stream_reader ... bench: 1,437,071 ns/iter (+/- 53,694)
test blockdata::transaction::benches::bench_transaction_deserialize ... bench: 92 ns/iter (+/- 2)
test blockdata::transaction::benches::bench_transaction_serialize ... bench: 17 ns/iter (+/- 0)
test blockdata::transaction::benches::bench_transaction_serialize_logic ... bench: 5 ns/iter (+/- 0)
test blockdata::transaction::benches::bench_transaction_size ... bench: 4 ns/iter (+/- 0)
```
(*) - I'm benchmarking on a noisy laptop. Take this with a grain of salt. But I think
at least it doesn't make anything slower.
While doing all this manual labor that will probably generate conflicts,
I took a liberty of changing generic type names and variable names to
`r` and `R` (reader) and `w` and `W` for writer.
clippy emits:
warning: this expression creates a reference which is immediately
dereferenced by the compiler
As suggested, remove the explicit reference.
Currently we are using the fragment-specifier `expr` in a bunch of
macros for captures that are only used for literals. If we use `literal`
instead it allows the compiler to give slightly more specific error
messages.
The benefits of this change are minor. Of note, this patch found one
unusual macro call site (removed unnecessary `&`).
The macros changed are all internal macros, this is not a breaking change.
Clippy emits:
warning: using `clone` on type `blockdata::transaction::OutPoint`
which implements the `Copy` trait
Remove calls to `clone` from types that implement `Copy`.
57dd6739c3 Do not print error when displaying for std builds (Tobin C. Harding)
b80cfeed85 Bind to error_kind instead of e (Tobin C. Harding)
241ec72497 Bind to b instead of e (Tobin C. Harding)
01f481bf5c Bind to s instead of e (Tobin C. Harding)
5c6d369289 network: Remove unused error variants (Tobin C. Harding)
e67e97bb37 Put From impl below std::error::Error impl (Tobin C. Harding)
6ca98e5275 Remove error TODO (Tobin C. Harding)
Pull request description:
As part of the ongoing error improvement work and as a direct result of [this comment](https://github.com/rust-bitcoin/rust-bitcoin/pull/987#issuecomment-1135563287) improve the `Display` implementations of all our error types so as to not repeat the source error when printing.
The first 5 patches are trivial clean ups around the errors. Patch 6 is the real work.
EDIT: ~CC @Kixunil, have I got the right idea here bro?~ Patch 6 now includes a macro as suggested.
ACKs for top commit:
Kixunil:
ACK 57dd6739c3
apoelstra:
ACK 57dd6739c3
sanket1729:
ACK 57dd6739c3. Did not check if we covered all cases. We need to remember to use `write_err!` instead of `write!` in future.
Tree-SHA512: 1ed26b0cc5f9a0f71684c431cbb9f94404c116c9136be696434c56a2f56fd93cb5406b0955edbd0dc6f8612e77345c93fa70a70650118968cc58e680333a41de
1875c912c3 Extend docstring for more types (Dawid Ciężarkiewicz)
325ea8fb7d Add "Relevant BIPs` to `Address` (Dawid Ciężarkiewicz)
7c2ca3d20b Add `BlockHeader` Bitcoin Core reference link (Dawid Ciężarkiewicz)
f4922f6fe7 Update `BlockHeader::version` documentation (Dawid Ciężarkiewicz)
Pull request description:
This is meant to make it more educational, and handy even for experienced developers.
A first step to make https://docs.rs/bitcoin (or `cargo doc --open`) a go-to place for
convenient Bitcoin documentation.
ACKs for top commit:
tcharding:
tACK 1875c912c3
apoelstra:
ACK 1875c912c3
sanket1729:
utACK 1875c912c3. Thanks for doing this.
Tree-SHA512: 8457e120f9979bfd95e55e8b18faf6131610aa2241f8e5fc4630fe61dc7e16ddfc35fb6eff46339804016db7b176465943cc0c02d84dcf478ed55da9f5e06fc5
2e7effc604 Feature `use-serde` renamed to `serde` (Martin Habovstiak)
Pull request description:
Features activating external crates are supposed to have same name as
those crates. However we depend on same feature in other crates so we
need a separate feature. After MSRV bump it is possible to rename the
crates and features so we can now fix this inconsistency.
Sadly, derive can't see that the crate was renamed so all derives must
be told to use the other one.
Replaces #373
ACKs for top commit:
apoelstra:
ACK 2e7effc604
Tree-SHA512: b20364b9e8f30c2269bef915e821b2b2ec929e71dd0e88af2bc3a021821f87011d35e095cb8efe99add77a23dde940a17537eb387fb4582b05c57c8679969eb0
Tobin C. Harding
Andrew Poelstra
Noah Lanson
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