fix: tolerate non-numeric keys in get_fee_estimates (mempool.space deprecation warning)

[Copexit]

mempool.space added a non-numeric "warning" key to its (deprecated) /fee-estimates response:

{"1":4.8, ... ,"1008":0.1,"warning":"This endpoint is deprecated ... use /api/v1/fees/precise"}

get_fee_estimates deserializes the body as HashMap<u16, f64>, so the "warning" key fails to parse and the whole call errors. Any client pointed at a mempool.space Esplora is affected.

The most severe downstream impact is ldk-node: it calls get_fee_estimates during Node::start(), so the failed parse makes the node refuse to start and crash-loop on restart. This is a real production failure mode (see #210).

Fix

Parse /fee-estimates leniently: deserialize into a permissive map and keep only entries whose key is a numeric confirmation target and whose value is a number; ignore anything else (such as the "warning" string). Behavior is unchanged for spec-compliant servers (e.g. Blockstream). Applied to both the async and blocking clients.

Changelog

• Fixed: get_fee_estimates tolerates non-numeric entries in the /fee-estimates response (e.g. mempool.space deprecation warning), which previously broke fee estimation for mempool.space-backed clients and prevented ldk-node from starting.

Refs #210

[luisschwab]

NACK. This client is not responsible for conforming to server implementations that deviate from the specification (https://github.com/Blockstream/esplora/blob/master/API.md#get-fee-estimates).

Instead, Mempool should return 301 Moved Permanently/303 See Other/308 Permanent Redirect.

[Copexit]

Thanks for the review, and fair point on spec purity.

The practical wrinkle: per #210, the mempool team has said they're keeping /fee-estimates (recommending /api/v1/fees/precise but not removing the old one), and they added the warning key rather than redirecting, so a 301/308 from mempool doesn't look like it's coming. In the meantime this breaks node.start() in ldk-node for anyone pointed at a mempool.space backend, which is a very common configuration.

This change is strictly more lenient, Blockstream/spec-compliant responses parse identically; it only drops non-numeric keys. So there's no spec regression for compliant servers. But I'm happy to defer to whatever direction you prefer: fold it into the EsploraMethods / MempoolSpaceMethods split discussed in #200, gate it behind a mempool feature, or close this if you'd rather solve it there. Mostly flagging that real users of downstream crates (ldk-node) are hitting node-startup failures today.

[junderw]

#210 (comment)

As mentioned in this comment I made. We should be pushing a fix shortly.

However, most wallets will be converting "1" to something human readable like "fast" anyways, so it would be best if end users add a normal HTTP client to their apps (use the same version that bdk uses if you don't want to add a new dependency) and just pull Mempool's precise fee API values.

[Copexit]

Closing as mempool/mempool#6546 has been merged.