golflog

golflog is a logging utility package built around go-logr. It's main use is a higher level api for building context based logging iteratively and stored in context.Context.

Installation

go get -u github.com/floatme-corp/golflog

Use

As close to your application entry point or initial context creation, create a Configurator and logr.Logger, then set that logger in the context.Context:

import (
    "context"
    "fmt"

    "github.com/floatme-corp/golflog"
)

func main() {
    configurator := golflog.NewZapProductionConfigurator()
    verbosity := 0

    logger, err := golflog.NewLogger(configurator, "RootLoggerName", verbosity)
    if err != nil {
        panic(fmt.Sprintf("runtime error: failed to setup logging: %s", err))
    }

    ctx := golflog.NewContext(context.Background(), logger)

    ...
}

Later if your application has another section, such as a Queue handler, you can set that in the logger name:

func HandleQueue(ctx context.Context) {
    ctx = golflog.ContextWithName(ctx, "Queue")
}

All messages logged from that point forward will have the name added to the existing name: RootLoggerName.Queue.

Additional values can be setup as well for future logging:

func HandleUser(ctx context.Context, userID string) {
    ctx = golflog.ContextWithValues(ctx, "user_id", userID)
}

The name and values can be setup together in one shot:

func HandleUser(ctx context.Context, userID string) {
    ctx = golflog.ContextWithNameAndValues(ctx, "Queue", "user_id", userID)
}

Functions are guaranteed to be able to get a logger from any context:

func randoFunc(ctx context.Context) {
    log := golflog.AlwaysFromContext(ctx)
    log.Info("my log message")
}

If the context does not have a logger associated with it golflog will create a fallback logger with the default configuration. If that fails it will fallback to logging via fmt.Fprintln to os.Stdout

golflog provides helpers to create a log and a context with a name, values, or both:

func randoFunc(ctx context.Context) {
    // for tracing logs from this function
    ctx, log := golflog.WithName(ctx, "randoFunc")
    log.Info("my log message") // logs `randoFunc "msg"="my log message"`
}

// assume you have the important value `foo`
func randoFunc(ctx context.Context, importantValue string) {
    // for always seeing important value in future logs with this context
    ctx, log := golflog.WithValues(ctx, "important-value", importantValue)
    log.Info("my log message")
    // logs `"msg"="my log message" "important-value"="foo"`
}

func randoFunc(ctx context.Context, importantValue string) {
    ctx, log := golflog.WithNameAndValues(
        ctx,
        "randoFunc",
        "important-value", importantValue,
    )
    log.Info("my log message")
    // logs `randoFunc "msg"="my log message" "important-value"="foo"`
}

Logging Convenience Helpers

Info and Error convenience helpers are provided to log or report an error to the logger in the context. A severity key is added to each to invocation automatically to assist log aggregation services.

func randoFunc(ctx context.Context) {
    // Same as:
    // log := golflog.AlwaysFromContext(ctx)
    // log.Info("message", "severity", "info", "key", "value")
    golflog.Info(ctx, "message", "key", "value")

    ...

    // Same as:
    // log := golflog.AlwaysFromContext(ctx)
    // log.Error(err, "message", "severity", "error", "key", "value")
    golflog.Error(ctx, err, "message", "key", "value")
}

A Wrap helper will log the message at the info level and return a new error wrapping the err with message. A WarnWrap helper is also provided to log the message with severity=warning prepended to the list of key/value pairs before returning the wrapped error.

func randoFunc(ctx context.Context) {
    ...

    if err != nil {
        // Same as:
        // golflog.Error(ctx, err, "message", "key", "value")
        // return fmt.Errorf("%s: %w", "message", "err")
        return golflog.Wrap(ctx, err, "message", "key", "value")
    }
    ...

    thingID := "1234"
    if err := findThing(thingID); err != nil {
        // Suppose you expect this error
        if err.As(ErrThingNotFound) {
            // Same as:
            // golflog.Warn(ctx, "message", "thing_id", thingID)
            // return fmt.Errorf("%s: %w", "message", "err")
            return golflog.WarnWrap(ctx, err, "Could not find thing!", "thing_id", thingID)
        }
    }
}

A V helper will return a logger from the context at the level requested.

func randoFunc(ctx context.Context) {
    ...

    // Will be logged at level 1
    golflog.V(ctx, 1).Info("message", "key", "value")
}

A Warn helper will automatically prepend severity=warning to the list of key/value pairs and logs out the message. This helper should be used sparingly, and instead logging levels should be used. It is included to make it easier for log aggregation services to key off.

func randoFunc(ctx context.Context) {
    ...

    // The same as
    // golflog.Info(ctx, "message", "severity", "warning", "key", "value")
    golflog.Warn(ctx, "message", "key", "value")
}

Warning is an alias of Warn.

func randoFunc(ctx context.Context) {
    ...

    // The same as
    // golflog.Info(ctx, "message", "severity", "warning", "key", "value")
    golflog.Warning(ctx, "message", "key", "value")
}

A Debug helper will automatically prepend severity=debug to the list of key/value pairs and logs out the message at a level 1 higher than the level of the logger in the context.Context. This helper should be used sparingly, and instead logging levels should be used. It is included to make it easier for log aggregation services to key off.

func randoFunc(ctx context.Context) {
    ...

    // The same as
    // golflog.V(ctx, 1).Info("message", "severity", "warning", "key", "value")
    golflog.Debug(ctx, "message", "key", "value")
}

Env setup

An alternative to calling golflog.NewLogger with the parameters, is to call NewLoggerFromEnv and give it only the root name:

import (
    "context"
    "fmt"

    "github.com/floatme-corp/golflog
)

func main() {
    logger, err := golflog.NewLoggerFromEnv("RootLoggerName")
    if err != nil {
        panic(fmt.Sprintf("runtime error: failed to setup logging: %s", err))
    }

    ctx := golflog.NewContext(context.Background(), logger)

    ...
}

NewLoggerFromEnv uses the environment variables LOG_PRODUCTION, LOG_IMPLEMENTATION, and LOG_VERBOSITY to configure the logger. If they do not exist, it will default to configuring a production logger, with a zap Configurator at 0 verbosity (normal / info level).

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Released under the Apache 2.0 License.