diff --git a/instructions/go.instructions.md b/instructions/go.instructions.md index ce4cdba..8b171a4 100644 --- a/instructions/go.instructions.md +++ b/instructions/go.instructions.md @@ -17,6 +17,8 @@ Follow idiomatic Go practices and community standards when writing Go code. Thes - Make the zero value useful - Document exported types, functions, methods, and packages - Use Go modules for dependency management +- Leverage the Go standard library instead of reinventing the wheel (e.g., use `strings.Builder` for string concatenation, `filepath.Join` for path construction) +- Prefer standard library solutions over custom implementations when functionality exists ## Naming Conventions @@ -27,6 +29,8 @@ Follow idiomatic Go practices and community standards when writing Go code. Thes - Choose names that describe what the package provides, not what it contains - Avoid generic names like `util`, `common`, or `base` - Package names should be singular, not plural +- When editing an existing `.go` file, preserve the current `package` declaration and do not insert a second `package` line +- When creating a new `.go` file, match the package name used by other files in the same directory (or the directory name if new), and ensure exactly one `package` declaration at the top ### Variables and Functions @@ -105,11 +109,14 @@ Follow idiomatic Go practices and community standards when writing Go code. Thes - Use struct tags for JSON, XML, database mappings - Prefer explicit type conversions - Use type assertions carefully and check the second return value +- Prefer generics over unconstrained types; when an unconstrained type is truly needed, use the predeclared alias `any` instead of `interface{}` (Go 1.18+) ### Pointers vs Values -- Use pointers for large structs or when you need to modify the receiver -- Use values for small structs and when immutability is desired +- Use pointer receivers for large structs or when you need to modify the receiver +- Use value receivers for small structs and when immutability is desired +- Use pointer parameters when you need to modify the argument or for large structs +- Use value parameters for small structs and when you want to prevent modification - Be consistent within a type's method set - Consider the zero value when choosing pointer vs value receivers @@ -125,7 +132,8 @@ Follow idiomatic Go practices and community standards when writing Go code. Thes ### Goroutines -- Don't create goroutines in libraries; let the caller control concurrency +- Be cautious about creating goroutines in libraries; prefer letting the caller control concurrency +- If you must create goroutines in libraries, provide clear documentation and cleanup mechanisms - Always know how a goroutine will exit - Use `sync.WaitGroup` or channels to wait for goroutines - Avoid goroutine leaks by ensuring cleanup @@ -143,8 +151,11 @@ Follow idiomatic Go practices and community standards when writing Go code. Thes - Use `sync.Mutex` for protecting shared state - Keep critical sections small - Use `sync.RWMutex` when you have many readers -- Prefer channels over mutexes when possible +- Choose between channels and mutexes based on the use case: use channels for communication, mutexes for protecting state - Use `sync.Once` for one-time initialization +- WaitGroup usage by Go version: + - If `go >= 1.25` in `go.mod`, use the new `WaitGroup` pattern + - If `go < 1.25`, use the classic `Add`/`Done` pattern ## Error Handling Patterns @@ -172,6 +183,9 @@ Follow idiomatic Go practices and community standards when writing Go code. Thes - Use middleware for cross-cutting concerns - Set appropriate status codes and headers - Handle errors gracefully and return appropriate error responses +- Router usage by Go version: + - If `go >= 1.22`, prefer the enhanced `net/http` `ServeMux` with pattern-based routing and method matching + - If `go < 1.22`, use the classic `ServeMux` and handle methods/paths manually (or use a third-party router when justified) ### JSON APIs @@ -181,6 +195,15 @@ Follow idiomatic Go practices and community standards when writing Go code. Thes - Consider using `json.RawMessage` for delayed parsing - Handle JSON errors appropriately +### HTTP Clients + +- Keep the client struct focused on configuration and dependencies only (e.g., base URL, `*http.Client`, auth, default headers). It must not store per-request state +- Do not store or cache `*http.Request` inside the client struct, and do not persist request-specific state across calls; instead, construct a fresh request per method invocation +- Methods should accept `context.Context` and input parameters, assemble the `*http.Request` locally (or via a short-lived builder/helper created per call), then call `c.httpClient.Do(req)` +- If request-building logic is reused, factor it into unexported helper functions or a per-call builder type; never keep `http.Request` (URL params, body, headers) as fields on the long-lived client +- Ensure the underlying `*http.Client` is configured (timeouts, transport) and is safe for concurrent use; avoid mutating `Transport` after first use +- Always set headers on the request instance you’re sending, and close response bodies (`defer resp.Body.Close()`), handling errors appropriately + ## Performance Optimization ### Memory Management @@ -191,6 +214,33 @@ Follow idiomatic Go practices and community standards when writing Go code. Thes - Preallocate slices when size is known - Avoid unnecessary string conversions +### I/O: Readers and Buffers + +- Most `io.Reader` streams are consumable once; reading advances state. Do not assume a reader can be re-read without special handling +- If you must read data multiple times, buffer it once and recreate readers on demand: + - Use `io.ReadAll` (or a limited read) to obtain `[]byte`, then create fresh readers via `bytes.NewReader(buf)` or `bytes.NewBuffer(buf)` for each reuse + - For strings, use `strings.NewReader(s)`; you can `Seek(0, io.SeekStart)` on `*bytes.Reader` to rewind +- For HTTP requests, do not reuse a consumed `req.Body`. Instead: + - Keep the original payload as `[]byte` and set `req.Body = io.NopCloser(bytes.NewReader(buf))` before each send + - Prefer configuring `req.GetBody` so the transport can recreate the body for redirects/retries: `req.GetBody = func() (io.ReadCloser, error) { return io.NopCloser(bytes.NewReader(buf)), nil }` +- To duplicate a stream while reading, use `io.TeeReader` (copy to a buffer while passing through) or write to multiple sinks with `io.MultiWriter` +- Reusing buffered readers: call `(*bufio.Reader).Reset(r)` to attach to a new underlying reader; do not expect it to “rewind” unless the source supports seeking +- For large payloads, avoid unbounded buffering; consider streaming, `io.LimitReader`, or on-disk temporary storage to control memory + +- Use `io.Pipe` to stream without buffering the whole payload: + - Write to `*io.PipeWriter` in a separate goroutine while the reader consumes + - Always close the writer; use `CloseWithError(err)` on failures + - `io.Pipe` is for streaming, not rewinding or making readers reusable + +- **Warning:** When using `io.Pipe` (especially with multipart writers), all writes must be performed in strict, sequential order. Do not write concurrently or out of order—multipart boundaries and chunk order must be preserved. Out-of-order or parallel writes can corrupt the stream and result in errors. + +- Streaming multipart/form-data with `io.Pipe`: + - `pr, pw := io.Pipe()`; `mw := multipart.NewWriter(pw)`; use `pr` as the HTTP request body + - Set `Content-Type` to `mw.FormDataContentType()` + - In a goroutine: write all parts to `mw` in the correct order; on error `pw.CloseWithError(err)`; on success `mw.Close()` then `pw.Close()` + - Do not store request/in-flight form state on a long-lived client; build per call + - Streamed bodies are not rewindable; for retries/redirects, buffer small payloads or provide `GetBody` + ### Profiling - Use built-in profiling tools (`pprof`) @@ -214,7 +264,7 @@ Follow idiomatic Go practices and community standards when writing Go code. Thes - Name tests descriptively using `Test_functionName_scenario` - Use subtests with `t.Run` for better organization - Test both success and error cases -- Use `testify` or similar libraries sparingly +- Consider using `testify` or similar libraries when they add value, but don't over-complicate simple tests ### Test Helpers @@ -238,7 +288,7 @@ Follow idiomatic Go practices and community standards when writing Go code. Thes - Use standard library crypto packages - Don't implement your own cryptography - Use crypto/rand for random number generation -- Store passwords using bcrypt or similar +- Store passwords using bcrypt, scrypt, or argon2 (consider golang.org/x/crypto for additional options) - Use TLS for network communication ## Documentation @@ -265,7 +315,7 @@ Follow idiomatic Go practices and community standards when writing Go code. Thes - `go fmt`: Format code - `go vet`: Find suspicious constructs -- `golint` or `golangci-lint`: Additional linting +- `golangci-lint`: Additional linting (golint is deprecated) - `go test`: Run tests - `go mod`: Manage dependencies - `go generate`: Code generation @@ -288,5 +338,5 @@ Follow idiomatic Go practices and community standards when writing Go code. Thes - Not understanding nil interfaces vs nil pointers - Forgetting to close resources (files, connections) - Using global variables unnecessarily -- Over-using empty interfaces (`interface{}`) +- Over-using unconstrained types (e.g., `any`); prefer specific types or generic type parameters with constraints. If an unconstrained type is required, use `any` rather than `interface{}` - Not considering the zero value of types