Refactor IP address extraction using net.SplitHostPort

[danielllek]

Description

It's necessary to add X-Forwarded-For header for any request to proxyd, but looking at the code it shouldn't be needed.

Failing request:

$ curl -X POST http://localhost:8080 \
    -H "Content-Type: application/json" \
    -d '{"jsonrpc":"2.0","method":"eth_blockNumber","params":[],"id":1}'
{"jsonrpc":"2.0","error":{"code":-32600,"message":"request does not include a remote IP"},"id":null}

Request with X-Forwarded-For header works:

$curl -X POST http://localhost:8080     -H "Content-Type: application/json" -H "X-Forwarded-For: 127.0.0.1"    -d '{"jsonrpc":"2.0","method":"eth_blockNumber","params":[],"id":1}'
{"jsonrpc":"2.0","result":"0x178e8e3","id":1}

It seems that's caused by ipv6 stack enabled on my machine - ipv6 can't be parsed with simple strings.Split.

Changing it to net.SplitHostPort should fix the issue.

Tests

Built locally with the change and it works:

$ curl -X POST http://localhost:8080     -H "Content-Type: application/json"     -d '{"jsonrpc":"2.0","method":"eth_blockNumber","params":[],"id":1}'
{"jsonrpc":"2.0","result":"0x178e987","id":1}

Additional context

Metadata

[codecov-commenter]

Codecov Report

✅ All modified and coverable lines are covered by tests.
✅ Project coverage is 57.84%. Comparing base (ed7003d) to head (b06fe46).

Additional details and impacted files

@@            Coverage Diff             @@
##             main     #574      +/-   ##
==========================================
+ Coverage   57.83%   57.84%   +0.01%     
==========================================
  Files          96       96              
  Lines       14501    14500       -1     
==========================================
+ Hits         8386     8387       +1     
+ Misses       5597     5596       -1     
+ Partials      518      517       -1     

Flag	Coverage Δ
proxyd	71.30% <100.00%> (+0.03%)	⬆️

Flags with carried forward coverage won't be shown. Click here to find out more.

Files with missing lines	Coverage Δ
proxyd/server.go	76.54% <100.00%> (-0.03%)	⬇️

... and 1 file with indirect coverage changes

🚀 New features to boost your workflow:

• ❄️ Test Analytics: Detect flaky tests, report on failures, and find test suite problems.
• 📦 JS Bundle Analysis: Save yourself from yourself by tracking and limiting bundle sizes in JS merges.