fix: handle mining.extranonce.subscribe and prevent nil pointer crash

[abs2023]

Summary

Fixes crash loop caused by miners sending unexpected protocol messages during handshake phase before destination connection is initialized.

Root Causes (2 issues found)

Issue #1: Nil Pointer in logWithContext()

New miners added to seller node on 2026-02-10 send mining.extranonce.subscribe Stratum extension message during initial handshake. This legitimate protocol message wasn't explicitly handled, causing it to fall through to the default case.

The default case attempted to log a warning, which called logWithContext(). This logging function accessed p.dest.conn.conn.LocalAddr() which was nil during early handshake, triggering panic at proxy.go:453.

Issue #2: Nil Pointer in dest.Write()

After fixing the logging, a second nil pointer issue was discovered: when unknown/unexpected messages arrive before the destination is initialized (e.g., eth_submitLogin from Ethereum miners connecting to Bitcoin proxy), the code attempts to forward the message via p.proxy.dest.Write() which is nil, causing panic at conn_dest.go:139 via handler_first_connect.go:83.

Changes Made

1. Defensive Logging (proxy.go) - Commit 3d2a337

Made logWithContext() nil-safe by checking all pointer levels before accessing:

• Checks if p.dest is nil
• Checks if p.dest.conn is nil
• Checks if p.dest.conn.conn is nil
• Returns "not-connected" or "not-initialized" instead of panicking

2. Handle mining.extranonce.subscribe (handler_first_connect.go) - Commit 3d2a337

Added explicit case for MiningExtranonceSubscribe messages:

• Logs at debug level for visibility
• Forwards message transparently to pool if dest is initialized
• Prevents falling through to unknown message handler

3. Nil Checks Before Writing (handler_first_connect.go) - Commit 94aba98

Added defensive nil checks before writing to dest:

• Both MiningExtranonceSubscribe case and default case now check if p.proxy.dest != nil
• Messages arriving before destination initialization are safely dropped
• Prevents panic when forwarding unexpected protocol messages

Impact

• ✅ Resolves continuous crash loop since 2026-02-10 13:16 ET (Issue chore(deps): bump google.golang.org/protobuf from 1.30.0 to 1.33.0 #1)
• ✅ Resolves secondary crash discovered at 2026-02-10 20:56 UTC (Issue chore(deps): bump golang.org/x/net from 0.10.0 to 0.17.0 #2)
• ✅ Enables modern miners with extranonce support to connect properly
• ✅ Handles protocol mismatches gracefully (e.g., Ethereum miners on Bitcoin proxy)
• ✅ Future-proofs against similar edge cases with uninitialized connections
• ✅ No performance impact (just pointer checks)

Testing

• Code compiles successfully
• Crash pattern analysis confirms both fixes address exact panic locations
• First fix deployed to production, revealed second issue
• Second fix addresses newly discovered crash pattern

CloudWatch Evidence

First crash pattern (fixed in 3d2a337):

panic: runtime error: invalid memory address or nil pointer dereference
[signal SIGSEGV: segmentation violation code=0x1 addr=0x110 pc=0x90b25f]
at proxy.go:453 in logWithContext()

Preceded by unknown message logs showing mining.extranonce.subscribe.

Second crash pattern (fixed in 94aba98):

panic: runtime error: invalid memory address or nil pointer dereference  
[signal SIGSEGV: segmentation violation code=0x1 addr=0x110 pc=0x8feae6]
at conn_dest.go:139 via handler_first_connect.go:83

Triggered by eth_submitLogin message with our logging showing:
"DstAddr":"not-initialized","DstPort":"not-connected"