mediocre-go-lib/m/m.go

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// Package m is the glue which holds all the other packages in this project
// together. While other packages in this project are intended to be able to be
// used separately and largely independently, this package combines them in ways
// which I specifically like.
package m
import (
"context"
"os"
"os/signal"
"github.com/mediocregopher/mediocre-go-lib/mcfg"
"github.com/mediocregopher/mediocre-go-lib/mctx"
"github.com/mediocregopher/mediocre-go-lib/merr"
"github.com/mediocregopher/mediocre-go-lib/mlog"
"github.com/mediocregopher/mediocre-go-lib/mrun"
)
type cfgSrcKey int
// ProcessContext returns a Context which should be used as the root Context
// when implementing most processes.
//
// The returned Context will automatically handle setting up global
// configuration parameters like "log-level", as well as an http endpoint where
// debug information about the running process can be accessed.
func ProcessContext() context.Context {
ctx := context.Background()
// embed confuration source which should be used into the context.
ctx = context.WithValue(ctx, cfgSrcKey(0), mcfg.Source(new(mcfg.SourceCLI)))
// set up log level handling
logger := mlog.NewLogger()
ctx = mlog.WithLogger(ctx, logger)
ctx, logLevelStr := mcfg.WithString(ctx, "log-level", "info", "Maximum log level which will be printed.")
ctx = mrun.WithStartHook(ctx, func(context.Context) error {
logLevel := mlog.LevelFromString(*logLevelStr)
if logLevel == nil {
ctx := mctx.Annotate(ctx, "log-level", *logLevelStr)
return merr.New("invalid log level", ctx)
}
logger.SetMaxLevel(logLevel)
return nil
})
return ctx
}
// ServiceContext extends ProcessContext so that it better supports long running
// processes which are expected to handle requests from outside clients.
//
// Additional behavior it adds includes setting up an http endpoint where debug
// information about the running process can be accessed.
func ServiceContext() context.Context {
ctx := ProcessContext()
// services expect to use many different configuration sources
ctx = context.WithValue(ctx, cfgSrcKey(0), mcfg.Source(mcfg.Sources{
new(mcfg.SourceEnv),
new(mcfg.SourceCLI),
}))
// TODO set up the debug endpoint.
return ctx
}
// Start performs the work of populating configuration parameters and triggering
// the start event. It will return once the Start event has completed running.
func Start(ctx context.Context) {
src, _ := ctx.Value(cfgSrcKey(0)).(mcfg.Source)
if src == nil {
mlog.Fatal("ctx not sourced from m package", ctx)
}
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// no logging should happen before populate, primarily because log-level
// hasn't been populated yet, but also because it makes help output on cli
// look weird.
if err := mcfg.Populate(ctx, src); err != nil {
mlog.Fatal("error populating configuration", ctx, merr.Context(err))
} else if err := mrun.Start(ctx); err != nil {
mlog.Fatal("error triggering start event", ctx, merr.Context(err))
}
mlog.Info("start hooks completed", ctx)
}
// StartWaitStop performs the work of populating configuration parameters,
// triggering the start event, waiting for an interrupt, and then triggering the
// stop event. Run will block until the stop event is done. If any errors are
// encountered a fatal is thrown.
func StartWaitStop(ctx context.Context) {
Start(ctx)
{
ch := make(chan os.Signal, 1)
signal.Notify(ch, os.Interrupt)
s := <-ch
mlog.Info("signal received, stopping", mctx.Annotate(ctx, "signal", s))
}
if err := mrun.Stop(ctx); err != nil {
mlog.Fatal("error triggering stop event", ctx, merr.Context(err))
}
mlog.Info("exiting process", ctx)
}