History Date: Sun, 23 Sep 2007 23:33:41 -0700 From: "Robert Griesemer" To: "Rob 'Commander' Pike" , [email protected] Subject: prog lang discussion ... *** General: Starting point: C, fix some obvious flaws, remove crud, add a few missing features - no includes, instead: import - no macros (do we need something instead?) - ideally only one file instead of a .h and .c file, module interface should be extracted automatically - statements: like in C, though should fix 'switch' statement - expressions: like in C, though with caveats (do we need ',' expressions?) - essentially strongly typed, but probably w/ support for runtime types - want arrays with bounds checking on always (except perhaps in 'unsafe mode'-see section on GC) - mechanism to hook up GC (I think that most code can live w/ GC, but for a true systems programming language there should be mode w/ full control over memory allocation) - support for interfaces (differentiate between concrete, or implementation types, and abstract, or interface types) - support for nested and anonymous functions/closures (don't pay if not used) - a simple compiler should be able to generate decent code - the various language mechanisms should result in predictable code ...
Go IMO • A breath of fresh air from “kitchen sink” languages — cf. Scala • Simple, orthogonal features that aren't surprising — cf. Node • Efficient by default — cf. Python, Ruby • Predictable runtime behavior — cf. JVM languages • Familiar heritage, syntax, and paradigm — cf. Haskell, Elixir
Problems solved • Team is too large to work effectively on shared codebase • Teams are blocked on other teams, can't make progress • Communication overhead becomes gigantic • Product velocity stalled
Problems caused • Need well-defined business domains for stable APIs • No more shared DB — distributed transactions? • Testing becomes really hard • Require dev/ops culture: devs deploy & operate their work • Job (service) scheduling — manually works, for a while...
Initial goals • A standard library for microservices • Something like Finagle for Go • Adapters, bindings, etc. to common infrastructure components • Play nice in your existing, heterogeneous infrastructure • Structure to tame the beast of incidental complexity
Current goals • Mostly the same • Even less opinionated about infrastructure than anticipated • More opinionated about application architecture than anticipated
Non-goals • Messaging patterns other than RPC • Requiring specific bits of infrastructure or tooling to work • Acting as an all-in service framework • Re-implementing existing, good solutions to problems
Comparisons • Micro (Go) — very opinionated, all-in, framework-ish • Finagle (Scala) — original inspiration, lower-level than Go kit • Spring Boot (Java) — similar abstractions, far more magical • Tokio (Rust) — explicitly a clone of Finagle, lower-level than Go kit
type basicService struct{} func (s basicService) Sum(a, b int) (int, error) { return a + b, nil } func (s basicService) Concat(a, b string) (string, error) { return a + b, nil } Core Business Logic
func (s basicService) ServeHTTP(w http.ResponseWriter, r *http.Request) { switch r.URL.Path { case "/sum": var req struct { A int `json:"a"` B int `json:"b"` } if err := json.NewDecoder(r.Body).Decode(&req); err != nil { http.Error(w, err.Error(), http.StatusBadRequest) return }
Transport Operational Metrics Balancing, Limiting, Safety Business Analytics Application Logging Service Metrics Business Logic Service Endpoint Transport
The central rule of The Clean Architecture is the Dependency Rule, which says source code dependencies can only point inwards. — http://appliedgo.net/di
type Service interface { Sum(ctx context.Context, a, b int) (int, error) Concat(ctx context.Context, a, b string) (string, error) } type basicService struct{}
type Service interface { Sum(ctx context.Context, a, b int) (int, error) Concat(ctx context.Context, a, b string) (string, error) } type basicService struct{} func (s basicService) Sum(_ context.Context, a, b int) (int, error) { if a == 0 && b == 0 { return 0, ErrTwoZeroes } if (b > 0 && a > (intMax-b)) || (b < 0 && a < (intMin-b)) { return 0, ErrIntOverflow } return a + b, nil }
type Service interface { Sum(ctx context.Context, a, b int) (int, error) Concat(ctx context.Context, a, b string) (string, error) } type basicService struct{} func (s basicService) Sum(_ context.Context, a, b int) (int, error) { if a == 0 && b == 0 { return 0, ErrTwoZeroes } if (b > 0 && a > (intMax-b)) || (b < 0 && a < (intMin-b)) { return 0, ErrIntOverflow } return a + b, nil } func (s basicService) Concat(_ context.Context, a, b string) (string, error) { if len(a)+len(b) > maxLen { return "", ErrMaxSizeExceeded } return a+b, nil }
type Middleware func(Service) Service type loggingMiddleware struct { logger log.Logger next Service } func NewLoggingMiddleware(logger log.Logger) Middleware { return func(next Service) Service { return loggingMiddleware{logger, next} } }
type Middleware func(Service) Service type loggingMiddleware struct { logger log.Logger next Service } func NewLoggingMiddleware(logger log.Logger) Middleware { return func(next Service) Service { return loggingMiddleware{logger, next} } } func (mw loggingMiddleware) Sum(ctx context.Context, a, b int) (v int, err error) { defer func() { mw.logger.Log("method", "Sum", "a", a, "b", b, "v", v, "err", err) }() return mw.next.Sum(ctx, a, b) } // Concat is the same
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