fix: revisit errors package, match the error

cmd/sql_exporter/promhttp.go

@@ -5,7 +5,6 @@ import (
 	"compress/gzip"
 	"context"
 	"errors"
-	"fmt"
 	"io"
 	"net/http"
 	"strconv"
@@ -24,6 +23,13 @@ const (
 	contentLengthHeader   string = "Content-Length"
 	contentEncodingHeader string = "Content-Encoding"
 	acceptEncodingHeader  string = "Accept-Encoding"
+	scrapeTimeoutHeader   string = "X-Prometheus-Scrape-Timeout-Seconds"
+)
+
+const (
+	prometheusHeaderErr = "Failed to parse timeout from Prometheus header"
+	noMetricsGathered   = "No metrics gathered"
+	noMetricsEncoded    = "No metrics encoded"
 )
 
 // ExporterHandlerFor returns an http.Handler for the provided Exporter.
@@ -36,15 +42,19 @@ func ExporterHandlerFor(exporter sql_exporter.Exporter) http.Handler {
 		gatherer := prometheus.Gatherers{exporter.WithContext(ctx)}
 		mfs, err := gatherer.Gather()
 		if err != nil {
-			if errors.Is(err, context.DeadlineExceeded) {
-				klog.Errorf("Timeout collecting metrics from target: %s", err)
-			}
 			if len(mfs) == 0 {
-				klog.Errorf("No metrics gathered: %s", err)
-				http.Error(w, "No metrics gathered, "+err.Error(), http.StatusInternalServerError)
+				klog.Errorf("%s: %s", noMetricsGathered, err)
+				http.Error(w, noMetricsGathered+", "+err.Error(), http.StatusInternalServerError)
 				return
 			}
-			klog.Errorf("Error gathering metrics: %s", err)
+			multierr := err.(prometheus.MultiError)
+			for _, err := range multierr {
+				if errors.Is(err, context.DeadlineExceeded) {
+					klog.Errorf("%s: timeout collecting metrics", err)
+				} else {
+					klog.Errorf("Error gathering metrics: %s", err)
+				}
+			}
 		}
 
 		contentType := expfmt.Negotiate(req.Header)
@@ -63,12 +73,13 @@ func ExporterHandlerFor(exporter sql_exporter.Exporter) http.Handler {
 			closer.Close()
 		}
 		if errs.MaybeUnwrap() != nil && buf.Len() == 0 {
-			http.Error(w, "No metrics encoded, "+errs.Error(), http.StatusInternalServerError)
+			klog.Errorf("%s: %s", noMetricsEncoded, errs)
+			http.Error(w, noMetricsEncoded+", "+errs.Error(), http.StatusInternalServerError)
 			return
 		}
 		header := w.Header()
 		header.Set(contentTypeHeader, string(contentType))
-		header.Set(contentLengthHeader, fmt.Sprint(buf.Len()))
+		header.Set(contentLengthHeader, strconv.Itoa(buf.Len()))
 		if encoding != "" {
 			header.Set(contentEncodingHeader, encoding)
 		}
@@ -80,19 +91,14 @@ func contextFor(req *http.Request, exporter sql_exporter.Exporter) (context.Cont
 	timeout := time.Duration(0)
 	configTimeout := time.Duration(exporter.Config().Globals.ScrapeTimeout)
 	// If a timeout is provided in the Prometheus header, use it.
-	if v := req.Header.Get("X-Prometheus-Scrape-Timeout-Seconds"); v != "" {
+	if v := req.Header.Get(scrapeTimeoutHeader); v != "" {
 		timeoutSeconds, err := strconv.ParseFloat(v, 64)
 		if err != nil {
-			parseError := errors.Unwrap(err)
 			switch {
-			case errors.Is(parseError, strconv.ErrSyntax):
-				{
-					klog.Errorf("Failed to parse timeout from Prometheus header: unsupported value")
-				}
-			case errors.Is(parseError, strconv.ErrRange):
-				{
-					klog.Errorf("Failed to parse timeout from Prometheus header: value is out of range")
-				}
+			case errors.Is(err, strconv.ErrSyntax):
+				klog.Errorf("%s: unsupported value", prometheusHeaderErr)
+			case errors.Is(err, strconv.ErrRange):
+				klog.Errorf("%s: value out of range", prometheusHeaderErr)
 			}
 		} else {
 			timeout = time.Duration(timeoutSeconds * float64(time.Second))

errors/errors.go

@@ -12,23 +12,24 @@ type WithContext interface {
 	error
 
 	Context() string
-	RawError() string
+	RawError() error
+	Unwrap() error
 }
 
 // withContext implements WithContext.
 type withContext struct {
 	context string
-	err     string
+	err     error
 }
 
 // New creates a new WithContext.
-func New(context, err string) WithContext {
-	return &withContext{context, err}
+func New(context string, err string) WithContext {
+	return &withContext{context, fmt.Errorf(err)}
 }
 
 // Errorf formats according to a format specifier and returns a new WithContext.
 func Errorf(context, format string, a ...any) WithContext {
-	return &withContext{context, fmt.Sprintf(format, a...)}
+	return &withContext{context, fmt.Errorf(format, a...)}
 }
 
 // Wrap returns a WithContext wrapping err. If err is nil, it returns nil. If err is a WithContext, it is returned
@@ -40,7 +41,7 @@ func Wrap(context string, err error) WithContext {
 	if w, ok := err.(WithContext); ok {
 		return w
 	}
-	return &withContext{context, err.Error()}
+	return &withContext{context, err}
 }
 
 // Wrapf returns a WithContext that prepends a formatted message to err.Error(). If err is nil, it returns nil. If err
@@ -55,17 +56,17 @@ func Wrapf(context string, err error, format string, a ...any) WithContext {
 		prefix = fmt.Sprintf(format, a...)
 	}
 	if w, ok := err.(WithContext); ok {
-		return &withContext{w.Context(), prefix + ": " + w.RawError()}
+		return &withContext{w.Context(), fmt.Errorf("%s: %w", prefix, w.RawError())}
 	}
-	return &withContext{context, prefix + ": " + err.Error()}
+	return &withContext{context, err}
 }
 
 // Error implements error.
 func (w *withContext) Error() string {
 	if len(w.context) == 0 {
-		return w.err
+		return w.err.Error()
 	}
-	return "[" + w.context + "] " + w.err
+	return "[" + w.context + "] " + w.err.Error()
 }
 
 // Context implements WithContext.
@@ -74,6 +75,11 @@ func (w *withContext) Context() string {
 }
 
 // RawError implements WithContext.
-func (w *withContext) RawError() string {
+func (w *withContext) RawError() error {
 	return w.err
 }
+
+// Unwrap implements WithContext.
+func (w *withContext) Unwrap() error {
+	return fmt.Errorf("[%s] %w", w.context, w.err)
+}

go.mod

@@ -118,4 +118,4 @@ require (
 	howett.net/plist v0.0.0-20181124034731-591f970eefbb // indirect
 )
 
-replace k8s.io/klog/v2 => github.com/simonpasquier/klog-gokit/v3 v3.1.0
+replace k8s.io/klog/v2 => github.com/simonpasquier/klog-gokit/v3 v3.3.0

go.sum

@@ -288,8 +288,8 @@ github.com/satori/go.uuid v1.2.0/go.mod h1:dA0hQrYB0VpLJoorglMZABFdXlWrHn1NEOzdh
 github.com/shopspring/decimal v0.0.0-20180709203117-cd690d0c9e24/go.mod h1:M+9NzErvs504Cn4c5DxATwIqPbtswREoFCre64PpcG4=
 github.com/shopspring/decimal v1.2.0 h1:abSATXmQEYyShuxI4/vyW3tV1MrKAJzCZ/0zLUXYbsQ=
 github.com/shopspring/decimal v1.2.0/go.mod h1:DKyhrW/HYNuLGql+MJL6WCR6knT2jwCFRcu2hWCYk4o=
-github.com/simonpasquier/klog-gokit/v3 v3.1.0 h1:xQGqjZdgo1lFA4eZ9PcGnKKXgIPz9t+jc25q/fXooIE=
-github.com/simonpasquier/klog-gokit/v3 v3.1.0/go.mod h1:+WRhGy707Lp2Q4r727m9Oc7FxazOHgW76FIyCr23nus=
+github.com/simonpasquier/klog-gokit/v3 v3.3.0 h1:HMzH999kO5gEgJTaWWO+xjncW5oycspcsBnjn9b853Q=
+github.com/simonpasquier/klog-gokit/v3 v3.3.0/go.mod h1:uSbnWC3T7kt1dQyY9sjv0Ao1SehMAJdVnUNSKhjaDsg=
 github.com/sirupsen/logrus v1.4.1/go.mod h1:ni0Sbl8bgC9z8RoU9G6nDWqqs/fq4eDPysMBDgk/93Q=
 github.com/sirupsen/logrus v1.4.2/go.mod h1:tLMulIdttU9McNUspp0xgXVQah82FyeX6MwdIuYE2rE=
 github.com/sirupsen/logrus v1.9.0 h1:trlNQbNUG3OdDrDil03MCb1H2o9nJ1x4/5LYw7byDE0=