scope

A small library with context helpers for golang.

Consists of 2 main components:

• Closer
• Group

Closer

Closer tries to loosely fill in gap between new context-aware world and old world of context-less network primitives with blocking operations, whose unblocking and cancellation logic is entirely different. Cancelling such blocking operations is often achieved by Close()-ing corresponding primitives in another goroutine. ContextCloser runs separate goroutine, which closes all io.Closer-s passed to Closer constructor func, when its bind context's Done() channel is closed. This separate goroutine is finished either after context is expired and io.Closer-s are closed or when Cancel() or Close() method of Closer is called, if it happens earlier. Closer must be constructed with scope.Closer or scope.CloserWithErrorGroup func.

To finish Closer's goroutine before context is expired call either Close() or Cancel(), but not both! Close() closes all the io.Closers passed to ContextCloser constructor func regardless of context and finishes goroutine. Cancel() just finishes goroutine and doesn't close anything. Both Close() and Cancel() close inner channel without any check, so calling them both or calling any of them more than once leads to panic! Nevertheless, it is perfectly safe to call either of them once regardless of whether context was already expired or not.

It is convenient to construct Closer and call either Close() or Cancel() at once in defer statement. If io.Closer (e.g. a net.Conn) should be bound not only to context, but also to current func scope, then use Close():

defer scope.Closer(ctx, conn).Close()

If io.Closer (e.g. a net.Conn) should be bound to context only while current goroutine is in the current func (rarer case, that might break structured concurrency principle), then use Cancel():

defer scope.Closer(ctx, conn).Cancel()

Group

Group is basically a convenient wrapper for errgroup.Group and optional Closer-s. Group must be constructed with scope.Group func. Any number of Closer-s can be added to it using Add[After]Closer[Cancelling]() functions.

Another way to look at Group is as at context.Context with its errgroup.Group, where new child goroutines could be run in structured way.