Consolidate proxy rejection handling in handler.go for consistent logging/tracing/error responses

[Copilot]

internal/proxy/handler.go had repeated inline rejection logic (log + span error + JSON error response) across multiple branches, with inconsistent observability behavior between paths. This change centralizes that pattern so proxy failures are handled uniformly and easier to maintain.

• Centralized rejection path

  • Added rejectProxyRequest(...) to encapsulate:
    • proxy error logging (logger.LogError)
    • span error recording (tracing.RecordSpanError, when span is present)
    • standardized JSON error response (httputil.WriteErrorResponse)

• Replaced duplicated inline error blocks

  • Migrated affected branches to the helper in:
    • GraphQL body read failure
    • guard-not-initialized rejection
    • DIFC pre-phase labeling failure
    • filtered response serialization failure
    • upstream request failure
    • upstream response body read failure

• Focused regression coverage

  • Added TestRejectProxyRequest to validate helper output shape and nil-safe behavior.

func rejectProxyRequest(w http.ResponseWriter, span oteltrace.Span, status int, code, msg string, err error) {
	logger.LogError("proxy", "Request rejected: status=%d code=%s message=%s err=%v", status, code, msg, err)
	if err == nil {
		err = errors.New(msg)
	}
	if span != nil {
		tracing.RecordSpanError(span, err, msg)
	}
	httputil.WriteErrorResponse(w, status, code, msg)
}

[Copilot]

Pull request overview

Centralizes proxy rejection handling to standardize error logging, tracing, and JSON responses.

Changes:

• Adds rejectProxyRequest.
• Migrates six proxy failure paths.
• Adds focused helper regression coverage.

Show a summary per file

File	Description
internal/proxy/handler.go	Consolidates proxy rejection handling.
internal/proxy/handler_test.go	Tests nil-safe standardized responses.

Review details

Tip

Add Copilot custom instructions for smarter, more guided reviews. Learn how to get started.

• Files reviewed: 2/2 changed files
• Comments generated: 4
• Review effort level: Medium

[lpcox]

@copilot address review feedback

[Copilot]

@copilot address review feedback

Done in commit addressing all four review points:

• Normalize err before logging: moved the if err == nil { err = errors.New(msg) } block above the logger.LogError call so both log and span see the same synthesized error.
• Double span recording on fwdSpan: the resp == nil branch in handleWithDIFC now calls tracing.RecordSpanError(difcSpan, …) only, since rejectProxyRequest inside forwardAndReadBody already recorded on fwdSpan.
• Upstream request error context: wraps the error as fmt.Errorf("%s %s: %w", method, path, err) before passing to the helper.
• Body-read error context: wraps as fmt.Errorf("%s %s status=%d: %w", method, path, resp.StatusCode, err) to preserve endpoint and upstream status.