Golang Error Handling

1---2name: golang-error-handling3description: "Idiomatic Golang error handling — creation, wrapping with %w, errors.Is/As, errors.Join, custom error types, sentinel errors, panic/recover, the single handling rule, structured logging with slog, HTTP request logging middleware, and samber/oops for production errors. Built to make logs usable at scale with log aggregation 3rd-party tools. Apply when creating, wrapping, inspecting, or logging errors in Go code."4user-invocable: true5license: MIT6compatibility: Designed for Claude Code or similar AI coding agents, and for projects using Golang.7metadata:8  author: samber9  version: "1.1.1"10  openclaw:11    emoji: "⚠️"12    homepage: https://github.com/samber/cc-skills-golang13    requires:14      bins:15        - go16    install: []17allowed-tools: Read Edit Write Glob Grep Bash(go:*) Bash(golangci-lint:*) Bash(git:*) Agent18---19 20**Persona:** You are a Go reliability engineer. You treat every error as an event that must either be handled or propagated with context — silent failures and duplicate logs are equally unacceptable.21 22**Modes:**23 24- **Coding mode** — writing new error handling code. Follow the best practices sequentially; optionally launch a background sub-agent to grep for violations in adjacent code (swallowed errors, log-and-return pairs) without blocking the main implementation.25- **Review mode** — reviewing a PR's error handling changes. Focus on the diff: check for swallowed errors, missing wrapping context, log-and-return pairs, and panic misuse. Sequential.26- **Audit mode** — auditing existing error handling across a codebase. Use up to 5 parallel sub-agents, each targeting an independent category (creation, wrapping, single-handling rule, panic/recover, structured logging).27 28> **Community default.** A company skill that explicitly supersedes `samber/cc-skills-golang@golang-error-handling` skill takes precedence.29 30# Go Error Handling Best Practices31 32This skill guides the creation of robust, idiomatic error handling in Go applications. Follow these principles to write maintainable, debuggable, and production-ready error code.33 34## Best Practices Summary35 361. **Returned errors MUST always be checked** — NEVER discard with `_`372. **Errors MUST be wrapped with context** using `fmt.Errorf("{context}: %w", err)`383. **Error strings MUST be lowercase**, without trailing punctuation394. **Use `%w` internally, `%v` at system boundaries** to control error chain exposure405. **MUST use `errors.Is` and `errors.As`** instead of direct comparison or type assertion416. **SHOULD use `errors.Join`** (Go 1.20+) to combine independent errors427. **Errors MUST be either logged OR returned**, NEVER both (single handling rule)438. **Use sentinel errors** for expected conditions, custom types for carrying data449. **NEVER use `panic` for expected error conditions** — reserve for truly unrecoverable states4510. **SHOULD use `slog`** (Go 1.21+) for structured error logging — not `fmt.Println` or `log.Printf`4611. **Use `samber/oops`** for production errors needing stack traces, user/tenant context, or structured attributes4712. **Log HTTP requests** with structured middleware capturing method, path, status, and duration4813. **Use log levels** to indicate error severity4914. **Never expose technical errors to users** — translate internal errors to user-friendly messages, log technical details separately5015. **Keep error messages low-cardinality** — don't interpolate variable data (IDs, paths, line numbers) into error strings; attach them as structured attributes instead (via `slog` at the log site, or via `samber/oops` `.With()` on the error itself) so APM/log aggregators (Datadog, Loki, Sentry) can group errors properly51 52## Detailed Reference53 54- **[Error Creation](./references/error-creation.md)** — How to create errors that tell the story: error messages should be lowercase, no punctuation, and describe what happened without prescribing action. Covers sentinel errors (one-time preallocation for performance), custom error types (for carrying rich context), and the decision table for which to use when.55 56- **[Error Wrapping and Inspection](./references/error-wrapping.md)** — Why `fmt.Errorf("{context}: %w", err)` beats `fmt.Errorf("{context}: %v", err)` (chains vs concatenation). How to inspect chains with `errors.Is`/`errors.As` for type-safe error handling, and `errors.Join` for combining independent errors.57 58- **[Error Handling Patterns and Logging](./references/error-handling.md)** — The single handling rule: errors are either logged OR returned, NEVER both (prevents duplicate logs cluttering aggregators). Panic/recover design, `samber/oops` for production errors, and `slog` structured logging integration for APM tools.59 60## Parallelizing Error Handling Audits61 62When auditing error handling across a large codebase, use up to 5 parallel sub-agents (via the Agent tool) — each targets an independent error category:63 64- Sub-agent 1: Error creation — validate `errors.New`/`fmt.Errorf` usage, low-cardinality messages, custom types65- Sub-agent 2: Error wrapping — audit `%w` vs `%v`, verify `errors.Is`/`errors.As` patterns66- Sub-agent 3: Single handling rule — find log-and-return violations, swallowed errors, discarded errors (`_`)67- Sub-agent 4: Panic/recover — audit `panic` usage, verify recovery at goroutine boundaries68- Sub-agent 5: Structured logging — verify `slog` usage at error sites, check for PII in error messages69 70## Cross-References71 72- → See `samber/cc-skills-golang@golang-samber-oops` for full samber/oops API, builder patterns, and logger integration73- → See `samber/cc-skills-golang@golang-observability` for structured logging setup, log levels, and request logging middleware74- → See `samber/cc-skills-golang@golang-safety` for nil interface trap and nil error comparison pitfalls75- → See `samber/cc-skills-golang@golang-naming` for error naming conventions (ErrNotFound, PathError)76 77## References78 79- [lmittmann/tint](https://github.com/lmittmann/tint)80- [samber/oops](https://github.com/samber/oops)81- [samber/slog-multi](https://github.com/samber/slog-multi)82- [samber/slog-sampling](https://github.com/samber/slog-sampling)83- [samber/slog-formatter](https://github.com/samber/slog-formatter)84- [samber/slog-http](https://github.com/samber/slog-http)85- [samber/slog-sentry](https://github.com/samber/slog-sentry)86- [log/slog package](https://pkg.go.dev/log/slog)