Add Logging interface to Autometrics

CHANGELOG.md

@@ -35,6 +35,9 @@ specification.
 - [Generator] The generator now tries to keep going with instrumentation even if some instrumentation
   fails. On error, still _No file will be modified_, and the generator will exit with an error code
   and output all the collected errors instead of only the first one.
+- [All] `autometrics.Init` function takes an additional argument, a logging interface to decide whether
+  and how users want autometrics to log events. Passing `nil` for the argument value will use a "No Op"
+  logger that does not do anything.
 
 ### Deprecated
 

README.md

@@ -98,6 +98,7 @@ And then in your main function initialize the metrics
 		autometrics.DefBuckets,
 		autometrics.BuildInfo{Version: "0.4.0", Commit: "anySHA", Branch: "", Service: "myApp"},
 		nil,
+		nil,
 	)
 	if err != nil {
 		log.Fatalf("could not initialize autometrics: %s", err)
@@ -273,6 +274,7 @@ func main() {
 		autometrics.DefBuckets,
 		autometrics.BuildInfo{Version: "0.4.0", Commit: "anySHA", Branch: "", Service: "myApp"},
 		nil,
+		nil,
 	)
 	http.Handle("/metrics", promhttp.Handler())
 }
@@ -384,6 +386,7 @@ metric. You can use the name of the application or its version for example
 		autometrics.DefBuckets,
 		autometrics.BuildInfo{ Version: "2.1.37", Commit: "anySHA", Branch: "", Service: "myApp" },
 		nil,
+		nil,
 	)
 ```
 
@@ -447,6 +450,7 @@ passing a non `nil` argument to `autometrics.Init` for the `pushConfiguration`:
 +			Period: 1 * time.Second,                       // Period is only relevant when using OpenTelemetry implementation
 +			Timeout: 500 * time.Millisecond,               // Timeout is only relevant when using OpenTelementry implementation
 +		},
+    nil,
 	)
 ```
 
@@ -456,6 +460,35 @@ can contact us so we can setup a managed instance of Prometheus for you. We will
 give you collector URLs, that will work with both OpenTelemetry and Prometheus; and can be 
 visualized easily with our explorer as well!
 
+#### Logging
+
+Monitoring/Observability must not crash the application. 
+
+So when Autometrics encounters
+errors, instead of bubbling it up until the program stops, it will log the error and absorb it.
+To leave choice in the logging implementation (depending on your application dependencies),
+Autometrics exposes a `Logger` interface you can implement and then inject in the `Init` call
+to have the logging you want.
+
+The `Logger` interface is a subset of `slog.Logger` methods, so that most loggers can be used.
+Autometrics also provides 2 simple loggers out of the box:
+- `NoOpLogger`, which is the default logger and does nothing,
+- `PrintLogger` which uses `fmt.Print` to write logging messages on stdout.
+
+To use the `PrintLogger` instead of the `NoOpLogger` for examble, you just have to change
+the `Init` call:
+
+``` patch
+	shutdown, err := autometrics.Init(
+		nil,
+		autometrics.DefBuckets,
+		autometrics.BuildInfo{ Version: "2.1.37", Commit: "anySHA", Branch: "", Service: "myApp" },
+		nil,
+-		nil,
++   autometrics.PrintLogger{},
+	)
+```
+
 #### Git hook
 
 As autometrics is a Go generator that modifies the source code when run, it

examples/otel/cmd/main.go

@@ -51,6 +51,7 @@ func main() {
 			Branch:  Branch,
 		},
 		pushConfiguration,
+		autometrics.PrintLogger{},
 	)
 	if err != nil {
 		log.Fatalf("Failed initialization of autometrics: %s", err)

examples/web/cmd/main.go

@@ -50,6 +50,7 @@ func main() {
 			Branch:  Branch,
 		},
 		pushConfiguration,
+		autometrics.PrintLogger{},
 	)
 	if err != nil {
 		log.Fatalf("Failed initialization of autometrics: %s", err)

examples/web/cmd/main.go.orig

@@ -50,6 +50,7 @@ func main() {
 			Service: "autometrics-go-example-prometheus"
 		},
 		pushConfiguration,
+		autometrics.PrintLogger{},
 	)
 	if err != nil {
 		log.Fatalf("Failed initialization of autometrics: %s", err)

internal/generate/context.go

@@ -320,9 +320,7 @@ func detectContextSelectorImpl(ctx *internal.GeneratorContext, argName string, s
 			}
 		}
 	} else {
-		// TODO: log that autometrics cannot detect multi-nested contexts instead of errorring
-		// continue
-		return true, fmt.Errorf("expecting parent to be an identifier, got %s instead", reflect.TypeOf(selector.X).String())
+		am.GetLogger().Error("expecting parent to be an identifier, got %s instead", reflect.TypeOf(selector.X).String())
 	}
 	return false, nil
 }

otel/autometrics/otel.go

@@ -4,12 +4,12 @@ import (
 	"context"
 	"errors"
 	"fmt"
-	"log"
 	"os"
 	"sync"
 	"time"
 
 	"github.com/autometrics-dev/autometrics-go/pkg/autometrics"
+	"github.com/autometrics-dev/autometrics-go/pkg/autometrics/log"
 
 	"go.opentelemetry.io/otel/attribute"
 	"go.opentelemetry.io/otel/exporters/otlp/otlpmetric/otlpmetricgrpc"
@@ -120,6 +120,17 @@ func completeMeterName(meterName string) string {
 // the current (otel) package imported at the call site.
 type BuildInfo = autometrics.BuildInfo
 
+// Logger is an interface for logging autometrics-related events.
+//
+// This is a reexport to allow using only the current package at call site.
+type Logger = log.Logger
+
+// This is a reexport to allow using only the current package at call site.
+type PrintLogger = log.PrintLogger
+
+// This is a reexport to allow using only the current package at call site.
+type NoOpLogger = log.NoOpLogger
+
 // PushConfiguration holds meta information about the push-to-collector configuration of the instrumented code.
 type PushConfiguration struct {
 	// URL of the collector to push to. It must be non-empty if this struct is built.
@@ -180,14 +191,19 @@ type PushConfiguration struct {
 // Make sure that all the latency targets you want to use for SLOs are
 // present in the histogramBuckets array, otherwise the alerts will fail
 // to work (they will never trigger).
-func Init(meterName string, histogramBuckets []float64, buildInformation BuildInfo, pushConfiguration *PushConfiguration) (context.CancelCauseFunc, error) {
+func Init(meterName string, histogramBuckets []float64, buildInformation BuildInfo, pushConfiguration *PushConfiguration, logger log.Logger) (context.CancelCauseFunc, error) {
 	var err error
 	newCtx, cancelFunc := context.WithCancelCause(context.Background())
 	amCtx = newCtx
 
 	autometrics.SetCommit(buildInformation.Commit)
 	autometrics.SetVersion(buildInformation.Version)
 	autometrics.SetBranch(buildInformation.Branch)
+	if logger == nil {
+		autometrics.SetLogger(log.NoOpLogger{})
+	} else {
+		autometrics.SetLogger(logger)
+	}
 
 	var pushExporter metric.Exporter
 	if pushConfiguration != nil {
@@ -334,7 +350,7 @@ func initProvider(pushExporter metric.Exporter, pushConfiguration *PushConfigura
 			metric.WithResource(autometricsSrc),
 		), nil
 	} else {
-		log.Printf("autometrics: opentelemetry: setting up OTLP push configuration, pushing %s to %s\n",
+		autometrics.GetLogger().Debug("opentelemetry: setting up OTLP push configuration, pushing %s to %s\n",
 			autometrics.GetPushJobName(),
 			autometrics.GetPushJobURL(),
 		)
@@ -368,7 +384,7 @@ func initProvider(pushExporter metric.Exporter, pushConfiguration *PushConfigura
 }
 
 func initPushExporter(pushConfiguration *PushConfiguration) (metric.Exporter, error) {
-	log.Println("autometrics: opentelemetry: Init: detected push configuration")
+	autometrics.GetLogger().Debug("opentelemetry: Init: detected push configuration")
 	if pushConfiguration.CollectorURL == "" {
 		return nil, errors.New("invalid PushConfiguration: the CollectorURL must be set.")
 	}

pkg/autometrics/ctx.go

@@ -269,8 +269,10 @@ func FillTracingAndCallerInfo(ctx context.Context) context.Context {
 	// NOTE: This also means that goroutines that outlive their as the caller will not have access to parent
 	// caller information, but hopefully by that point we got all the necessary accesses done.
 	// If not, it is a convenience we accept to give up to prevent memory usage from exploding.
-	// TODO: once settled on a login library, log the error instead of ignoring it
-	_ = PushFunctionName(ctx, callInfo.Current)
+	err := PushFunctionName(ctx, callInfo.Current)
+	if err != nil {
+		GetLogger().Error("adding a function name to the known spans: %s", err)
+	}
 
 	return ctx
 }

pkg/autometrics/global_state.go

@@ -2,6 +2,8 @@ package autometrics // import "github.com/autometrics-dev/autometrics-go/pkg/aut
 
 import (
 	"fmt"
+
+	"github.com/autometrics-dev/autometrics-go/pkg/autometrics/log"
 )
 
 // These variables are describing the state of the application being autometricized,
@@ -36,13 +38,24 @@ var (
 	pushJobName       string
 	pushJobURL        string
 	instrumentedSpans map[spanKey]FunctionID = make(map[spanKey]FunctionID)
+	logger            log.Logger
 )
 
 type spanKey struct {
 	tid TraceID
 	sid SpanID
 }
 
+// GetLogger returns the current logging interface for Autometrics
+func GetLogger() log.Logger {
+	return logger
+}
+
+// SetLogger sets the logging interface for Autometrics.
+func SetLogger(newLogger log.Logger) {
+	logger = newLogger
+}
+
 // GetVersion returns the version of the codebase being instrumented.
 func GetVersion() string {
 	return version

pkg/autometrics/log/log.go

@@ -0,0 +1,63 @@
+package log // import "github.com/autometrics-dev/autometrics-go/pkg/autometrics/log"
+
+import (
+	"context"
+	"fmt"
+)
+
+// Logger is an interface to implement to be able to inject a logger to Autometrics.
+// The interface follows the interface of slog.Logger
+type Logger interface {
+	Debug(msg string, args ...any)
+	DebugContext(ctx context.Context, msg string, args ...any)
+	Info(msg string, args ...any)
+	InfoContext(ctx context.Context, msg string, args ...any)
+	Warn(msg string, args ...any)
+	WarnContext(ctx context.Context, msg string, args ...any)
+	Error(msg string, args ...any)
+	ErrorContext(ctx context.Context, msg string, args ...any)
+}
+
+// NoOpLogger is the default logger for Autometrics. It does nothing.
+type NoOpLogger struct{}
+
+var _ Logger = NoOpLogger{}
+
+func (_ NoOpLogger) Debug(msg string, args ...any)                             {}
+func (_ NoOpLogger) DebugContext(ctx context.Context, msg string, args ...any) {}
+func (_ NoOpLogger) Info(msg string, args ...any)                              {}
+func (_ NoOpLogger) InfoContext(ctx context.Context, msg string, args ...any)  {}
+func (_ NoOpLogger) Warn(msg string, args ...any)                              {}
+func (_ NoOpLogger) WarnContext(ctx context.Context, msg string, args ...any)  {}
+func (_ NoOpLogger) Error(msg string, args ...any)                             {}
+func (_ NoOpLogger) ErrorContext(ctx context.Context, msg string, args ...any) {}
+
+// PrintLogger is a simple logger implementation that simply prints the events to stdout
+type PrintLogger struct{}
+
+var _ Logger = PrintLogger{}
+
+func (_ PrintLogger) Debug(msg string, args ...any) {
+	fmt.Printf("Autometrics - Debug: %v", fmt.Sprintf(msg, args...))
+}
+func (_ PrintLogger) DebugContext(ctx context.Context, msg string, args ...any) {
+	fmt.Printf("Autometrics - Debug: %v", fmt.Sprintf(msg, args...))
+}
+func (_ PrintLogger) Info(msg string, args ...any) {
+	fmt.Printf("Autometrics - Info: %v", fmt.Sprintf(msg, args...))
+}
+func (_ PrintLogger) InfoContext(ctx context.Context, msg string, args ...any) {
+	fmt.Printf("Autometrics - Info: %v", fmt.Sprintf(msg, args...))
+}
+func (_ PrintLogger) Warn(msg string, args ...any) {
+	fmt.Printf("Autometrics - Warn: %v", fmt.Sprintf(msg, args...))
+}
+func (_ PrintLogger) WarnContext(ctx context.Context, msg string, args ...any) {
+	fmt.Printf("Autometrics - Warn: %v", fmt.Sprintf(msg, args...))
+}
+func (_ PrintLogger) Error(msg string, args ...any) {
+	fmt.Printf("Autometrics - Error: %v", fmt.Sprintf(msg, args...))
+}
+func (_ PrintLogger) ErrorContext(ctx context.Context, msg string, args ...any) {
+	fmt.Printf("Autometrics - Error: %v", fmt.Sprintf(msg, args...))
+}

prometheus/autometrics/prometheus.go

@@ -4,11 +4,11 @@ import (
 	"context"
 	"errors"
 	"fmt"
-	"log"
 	"os"
 	"sync"
 
 	"github.com/autometrics-dev/autometrics-go/pkg/autometrics"
+	"github.com/autometrics-dev/autometrics-go/pkg/autometrics/log"
 	"github.com/prometheus/client_golang/prometheus"
 	"github.com/prometheus/client_golang/prometheus/push"
 	"github.com/prometheus/common/expfmt"
@@ -105,6 +105,17 @@ const (
 // the current (prometheus) package imported at the call site.
 type BuildInfo = autometrics.BuildInfo
 
+// Logger is an interface for logging autometrics-related events.
+//
+// This is a reexport to allow using only the current package at call site.
+type Logger = log.Logger
+
+// This is a reexport to allow using only the current package at call site.
+type PrintLogger = log.PrintLogger
+
+// This is a reexport to allow using only the current package at call site.
+type NoOpLogger = log.NoOpLogger
+
 // PushConfiguration holds meta information about the push-to-collector configuration of the instrumented code.
 //
 // This is a reexport of the autometrics type to allow [Init] to work with only
@@ -131,17 +142,22 @@ type PushConfiguration = autometrics.PushConfiguration
 // Make sure that all the latency targets you want to use for SLOs are
 // present in the histogramBuckets array, otherwise the alerts will fail
 // to work (they will never trigger.)
-func Init(reg *prometheus.Registry, histogramBuckets []float64, buildInformation BuildInfo, pushConfiguration *PushConfiguration) (context.CancelCauseFunc, error) {
+func Init(reg *prometheus.Registry, histogramBuckets []float64, buildInformation BuildInfo, pushConfiguration *PushConfiguration, logger log.Logger) (context.CancelCauseFunc, error) {
 	newCtx, cancelFunc := context.WithCancelCause(context.Background())
 	amCtx = newCtx
 
 	autometrics.SetCommit(buildInformation.Commit)
 	autometrics.SetVersion(buildInformation.Version)
 	autometrics.SetBranch(buildInformation.Branch)
+	if logger == nil {
+		autometrics.SetLogger(log.NoOpLogger{})
+	} else {
+		autometrics.SetLogger(logger)
+	}
 
 	pusher = nil
 	if pushConfiguration != nil {
-		log.Printf("autometrics: Init: detected push configuration to %s", pushConfiguration.CollectorURL)
+		autometrics.GetLogger().Debug("Init: detected push configuration to %s", pushConfiguration.CollectorURL)
 
 		if pushConfiguration.CollectorURL == "" {
 			return nil, errors.New("invalid PushConfiguration: the CollectorURL must be set.")