Add code example for each supported backend

[w0xlt]

This PR adds code example for connecting to Esplora, Electrum Server, Neutrino and Bitcoin Core.
Also shows how to retrieve balance, sign and broadcast transactions.

To test:

cd examples/backend/
cargo run electrum
cargo run esplora
cargo run neutrino
cargo run rpc_core

[rajarshimaitra]

Concept ACK on adding more example to the project. But I think its possible without adding a new cargo project in the workspace.

Can't we just have running examples like this #519?

[notmandatory]

Hi, please rebase to pickup changes in #596. Thanks!

[w0xlt]

@notmandatory sorry for the delay.

I force pushed a new version that adds examples just for Electrum and Esplora, as there are already examples for Compact Filter and RPC backends.

I also updated the code to 0.20.1 and addressed @rajarshimaitra's suggestion not to add a new cargo project.

[w0xlt]

The new push added the documentation suggested in #685, explaining how to use use-esplora-reqwest.

[rajarshimaitra]

Concept ACK.. Few more fixes needs to be done..

[rajarshimaitra]

Code looks good.. It need few more fixes to work.. Sorry if I reviewed prematurely.

[rajarshimaitra]

tACK 95e9b7f

Code loos good.. Thanks for the quick update.. One last comment..

[rajarshimaitra]

ACK f13d5e6

One last fix to pass the tests..

[rajarshimaitra]

tACK c7e1247

LGTM.. One suggestion maybe for a future PR.

[rajarshimaitra]

Sorry I have missed this before. Nothing major, feel free to ignore for this PR.

Even though the calls are async in reqwest they are still blocking in our impl, using the await_or_block macro like this,

bdk/src/blockchain/esplora/reqwest.rs

Line 126 in 06310f1

Ok(await_or_block!(self.url_client._get_tx(txid))?)

So to actually make the wallet calls async in the example you need to use the async-interface feature too.. In that case you will have await in your wallets calls in the example..

This PR is good to go on its own.. Maybe as a future PR an idea.

• Transform this to a blocking example using ureq.
• Create another fully async example using reqwest.

[w0xlt]

That would be great. But, as mentioned above, the command cargo run --features="use-esplora-reqwest, reqwest-default-tls, async-interface" --example esplora_backend results in error.

I think the problem is here (src/lib:210)

#[cfg(all(feature = "async-interface", feature = "electrum"))]
compile_error!(
    "Features async-interface and electrum are mutually exclusive and cannot be enabled together"
);

Even there is no electrum in the features, it seems this is enabled by default. Is there a way to disable it ?

[notmandatory]

You can disable the default features (which are "key-value-db", "electrum") by adding --no-default-features, eg:

cargo run --no-default-features --features=use-esplora-reqwest,reqwest-default-tls,async-interface --example esplora_backend

[w0xlt]

@notmandatory this worked. Thanks.

@rajarshimaitra I created two files examples/esplora_backend_synchronous.rs and examples/esplora_backend_asynchronous.rs in a2b6a40.

[w0xlt]

I don't know why CI / Rust fmt (pull_request) failed. I ran cargo fmt --all before committing.

[rajarshimaitra]

ACK a2b6a40

Thanks for the split.. This now looks complete.. Few more nits..

[rajarshimaitra]

I don't know why CI / Rust fmt (pull_request) failed. I ran cargo fmt --all before committing.

It was some temporary problem with rust update server.. I restarted the tests and it passed..

[rajarshimaitra]

tACK e50fcb6

[w0xlt]

Rebased.
Is any additional action required ?

[rajarshimaitra]

Sorry took me some time to get back to this.. Thanks for pushing this through..

tACK f99a6b9

All looks good to me, and great work separating the blocking and async example separate. This is good to go, no more changes should be required..

[22f-cy]

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