When implementing HTTP/TCP/WebSocket/networking logic, treat protocol semantics as “correctness-critical”: don’t rely on accidental behavior, and don’t assume inputs are single-valued.

Apply these rules: 1) Be consistent about connection lifecycle

• If you use a higher-level HTTP client (e.g., lua-resty-http), assume it manages keepalive/SSL as documented; don’t partially override by mixing raw socket operations unless you fully own SSL/keepalive/close behavior.
• For correctness tests/connection reuse issues, prefer fully closing the underlying socket over half-close patterns.

2) Defensively handle multi-value headers

• In OpenResty, the same header name can yield a string or a table when the client sends duplicates. Pick a deterministic rule (e.g., “take first” or “ignore if duplicated”) and enforce it.

3) Normalize outbound URLs

• Ensure URL paths are absolute (e.g., prepend “/” when missing) before passing to request/builders.

4) Avoid fragile query parsing/merging

• Naive string parsing can drop duplicate keys and mishandle encoding/edge cases. If correct merging semantics are unclear, avoid merging or use a proper query parser that preserves duplicates.

5) Parse WebSocket subprotocol lists correctly

• For Sec-WebSocket-Protocol, treat it as a list of tokens and compare exact compatible values—don’t use substring matching.

Example (multi-value header handling):

local function first_header_value(v)
  if type(v) == "table" then
    return v[1]
  end
  return v
end

local instana_t = first_header_value(headers["x-instana-t"])
local instana_s = first_header_value(headers["x-instana-s"])