metrics: add build command duration metric

This adds a build duration metric for the build command with attributes
related to the buildx driver, the error type (if any), and which options
were used to perform the build from a subset of the options.

This also refactors some of the utility methods used by the git tool to
determine filepaths into its own separate package so they can be reused
in another place.

Also adds a test to ensure the resource is initialized correctly and
doesn't error. The otel handler logging message is suppressed on buildx
invocations so we never see the error if there's a problem with the
schema url. It's so easy to mess up the schema url when upgrading OTEL
that we need a proper test to make sure we haven't broken the
functionality.

Signed-off-by: Jonathan A. Sternberg <jonathan.sternberg@docker.com>

commands/build.go

@@ -3,8 +3,10 @@ package commands
 import (
 	"bytes"
 	"context"
+	"crypto/sha256"
 	"encoding/base64"
 	"encoding/csv"
+	"encoding/hex"
 	"encoding/json"
 	"fmt"
 	"io"
@@ -13,6 +15,8 @@ import (
 	"path/filepath"
 	"strconv"
 	"strings"
+	"sync"
+	"time"
 
 	"github.com/containerd/console"
 	"github.com/docker/buildx/build"
@@ -28,9 +32,11 @@ import (
 	"github.com/docker/buildx/store/storeutil"
 	"github.com/docker/buildx/util/buildflags"
 	"github.com/docker/buildx/util/cobrautil"
+	"github.com/docker/buildx/util/confutil"
 	"github.com/docker/buildx/util/desktop"
 	"github.com/docker/buildx/util/ioset"
 	"github.com/docker/buildx/util/metricutil"
+	"github.com/docker/buildx/util/osutil"
 	"github.com/docker/buildx/util/progress"
 	"github.com/docker/buildx/util/tracing"
 	"github.com/docker/cli-docs-tool/annotation"
@@ -52,6 +58,8 @@ import (
 	"github.com/sirupsen/logrus"
 	"github.com/spf13/cobra"
 	"github.com/spf13/pflag"
+	"go.opentelemetry.io/otel/attribute"
+	"go.opentelemetry.io/otel/metric"
 	"google.golang.org/grpc/codes"
 )
 
@@ -211,6 +219,52 @@ func (o *buildOptions) toDisplayMode() (progressui.DisplayMode, error) {
 	return progress, nil
 }
 
+func buildMetricAttributes(dockerCli command.Cli, b *builder.Builder, options *buildOptions) attribute.Set {
+	return attribute.NewSet(
+		attribute.String("command.name", "build"),
+		attribute.Stringer("command.options.hash", &buildOptionsHash{
+			buildOptions: options,
+			configDir:    confutil.ConfigDir(dockerCli),
+		}),
+		attribute.String("driver.name", options.builder),
+		attribute.String("driver.type", b.Driver),
+	)
+}
+
+// buildOptionsHash computes a hash for the buildOptions when the String method is invoked.
+// This is done so we can delay the computation of the hash until needed by OTEL using
+// the fmt.Stringer interface.
+type buildOptionsHash struct {
+	*buildOptions
+	configDir  string
+	result     string
+	resultOnce sync.Once
+}
+
+func (o *buildOptionsHash) String() string {
+	o.resultOnce.Do(func() {
+		target := o.target
+		contextPath := o.contextPath
+		dockerfile := o.dockerfileName
+		if dockerfile == "" {
+			dockerfile = "Dockerfile"
+		}
+
+		if contextPath != "-" && osutil.IsLocalDir(contextPath) {
+			contextPath = osutil.ToAbs(contextPath)
+		}
+		salt := confutil.TryNodeIdentifier(o.configDir)
+
+		h := sha256.New()
+		for _, s := range []string{target, contextPath, dockerfile, salt} {
+			_, _ = io.WriteString(h, s)
+			h.Write([]byte{0})
+		}
+		o.result = hex.EncodeToString(h.Sum(nil))
+	})
+	return o.result
+}
+
 func runBuild(ctx context.Context, dockerCli command.Cli, options buildOptions) (err error) {
 	mp, err := metricutil.NewMeterProvider(ctx, dockerCli)
 	if err != nil {
@@ -279,6 +333,8 @@ func runBuild(ctx context.Context, dockerCli command.Cli, options buildOptions)
 		return err
 	}
 
+	attributes := buildMetricAttributes(dockerCli, b, &options)
+	done := timeBuildCommand(mp, attributes)
 	var resp *client.SolveResponse
 	var retErr error
 	if isExperimental() {
@@ -290,6 +346,8 @@ func runBuild(ctx context.Context, dockerCli command.Cli, options buildOptions)
 	if err := printer.Wait(); retErr == nil {
 		retErr = err
 	}
+
+	done(retErr)
 	if retErr != nil {
 		return retErr
 	}
@@ -933,3 +991,38 @@ func maybeJSONArray(v string) []string {
 	}
 	return []string{v}
 }
+
+// timeBuildCommand will start a timer for timing the build command. It records the time when the returned
+// function is invoked into a metric.
+func timeBuildCommand(mp metric.MeterProvider, attrs attribute.Set) func(err error) {
+	meter := metricutil.Meter(mp)
+	counter, _ := meter.Float64Counter("command.time",
+		metric.WithDescription("Measures the duration of the build command."),
+		metric.WithUnit("ms"),
+	)
+
+	start := time.Now()
+	return func(err error) {
+		dur := float64(time.Since(start)) / float64(time.Millisecond)
+		extraAttrs := attribute.NewSet()
+		if err != nil {
+			extraAttrs = attribute.NewSet(
+				attribute.String("error.type", otelErrorType(err)),
+			)
+		}
+		counter.Add(context.Background(), dur,
+			metric.WithAttributeSet(attrs),
+			metric.WithAttributeSet(extraAttrs),
+		)
+	}
+}
+
+// otelErrorType returns an attribute for the error type based on the error category.
+// If nil, this function returns an invalid attribute.
+func otelErrorType(err error) string {
+	name := "generic"
+	if errors.Is(err, context.Canceled) {
+		name = "canceled"
+	}
+	return name
+}