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Agent Instructions

Development Environment

Use Docker to develop and test the application. Do not rely on locally installed Go toolchains.

  • Go version: 1.24 (latest stable)
  • Dependency management: Go modules (go mod)

Build Commands

# Build the image
docker build -t mbproxy .

# Run the proxy
docker run --rm -e MODBUS_UPSTREAM=192.168.1.100:502 mbproxy

# Run with debug logging
docker run --rm -e MODBUS_UPSTREAM=192.168.1.100:502 -e LOG_LEVEL=DEBUG mbproxy

Testing

# Run all tests with race detector (uses full golang image)
docker build --target test .

# Or run tests interactively (without race detector in alpine)
docker run --rm -v $(pwd):/app -w /app golang:1.24 go test -v ./...

# With race detector (requires full golang image, not alpine)
docker run --rm -v $(pwd):/app -w /app golang:1.24 go test -v -race ./...

Note: Race detector requires CGO, which is not available in alpine images. The Dockerfile test stage uses the full golang image for this reason.

CI Checks

Run the full CI suite locally before committing:

# Run all CI checks (format, vet, test with race detector)
docker run --rm -v $(pwd):/app -w /app golang:1.24 sh -c "go fmt ./... && go vet ./... && go test -v -race ./..."

The CI pipeline runs:

  1. Format check: go fmt ./... followed by git diff --exit-code (fails if formatting changes files)
  2. Vet: go vet ./...
  3. Test: go test -v -race ./...

Code Style

  • Run go fmt on all code before committing
  • Run go vet to catch common issues
  • Keep functions small and focused
  • Use meaningful variable names
  • Add comments for non-obvious logic

Commit Conventions

  • Use present tense: "add feature" not "added feature"
  • Keep subject line under 50 characters
  • Format: <type>: <description>
  • Types: feat, fix, refactor, test, docs, chore
  • Always commit topic by topic (one logical change per commit)
  • Never push automatically; always wait for explicit user approval

Examples:

feat: add request coalescing for cache misses
fix: handle upstream connection timeout
refactor: extract cache logic to separate package

Debugging

Set LOG_LEVEL=DEBUG to enable verbose logging:

LOG_LEVEL=DEBUG docker run --rm -e MODBUS_UPSTREAM=... mbproxy

Debug logs include:

  • Cache hits/misses
  • Upstream request timing
  • Connection events
  • Request coalescing activity

Go Best Practices

Error Handling

  • Always handle errors; never discard with _
  • Return errors instead of panicking for normal error handling
  • Error strings should be lowercase, no punctuation: fmt.Errorf("connection failed") not "Connection failed."
  • Indent error handling, keep happy path at minimal indentation: 
    // Good
if err != nil {
    return err
}
// normal code

// Bad
if err != nil {
    // error handling
} else {
    // normal code
}

Naming

  • Variable names: short for local scope (c not lineCount), descriptive for wider scope
  • Receiver names: 1-2 letter abbreviation (c for Client), never this/self/me
  • Initialisms: ID, URL, HTTP stay uppercase (userID not userId)

Goroutines

  • Document when and whether goroutines exit
  • Ensure goroutines don't leak by blocking on channels
  • Prefer synchronous functions; let callers add concurrency if needed

Imports

  • Group standard library first, blank line, then external packages
  • Use goimports to auto-format

Slices and Interfaces

  • Prefer var t []string over t := []string{} for empty slices
  • Define interfaces where used, not where implemented