feat(compute/metadata): add debug logging

compute/metadata/go.mod

@@ -2,4 +2,7 @@ module cloud.google.com/go/compute/metadata
 
 go 1.21
 
-require golang.org/x/sys v0.25.0
+require (
+	github.com/googleapis/gax-go/v2 v2.0.0-00010101000000-000000000000
+	golang.org/x/sys v0.25.0
+)

compute/metadata/go.sum

@@ -1,2 +1,4 @@
+github.com/google/go-cmp v0.6.0 h1:ofyhxvXcZhMsU5ulbFiLKl/XBFqE1GSq7atu8tAmTRI=
+github.com/google/go-cmp v0.6.0/go.mod h1:17dUlkBOakJ0+DkrSSNjCkIjxS6bF9zb3elmeNGIjoY=
 golang.org/x/sys v0.25.0 h1:r+8e+loiHxRqhXVl6ML1nO3l1+oFoWbnlu2Ehimmi34=
 golang.org/x/sys v0.25.0/go.mod h1:/VUhepiaJMQUp4+oa/7Zr1D23ma6VTLIYjOOTFZPUcA=

compute/metadata/metadata.go

@@ -24,13 +24,16 @@ import (
 	"encoding/json"
 	"fmt"
 	"io"
+	"log/slog"
 	"net"
 	"net/http"
 	"net/url"
 	"os"
 	"strings"
 	"sync"
 	"time"
+
+	"github.com/googleapis/gax-go/v2/internallog"
 )
 
 const (
@@ -60,7 +63,10 @@ var (
 	instID  = &cachedValue{k: "instance/id", trim: true}
 )
 
-var defaultClient = &Client{hc: newDefaultHTTPClient()}
+var defaultClient = &Client{
+	hc:     newDefaultHTTPClient(),
+	logger: internallog.New(nil),
+}
 
 func newDefaultHTTPClient() *http.Client {
 	return &http.Client{
@@ -408,17 +414,38 @@ func strsContains(ss []string, s string) bool {
 
 // A Client provides metadata.
 type Client struct {
-	hc *http.Client
+	hc     *http.Client
+	logger *slog.Logger
+}
+
+type Options struct {
+	Client *http.Client
+	Logger *slog.Logger
 }
 
 // NewClient returns a Client that can be used to fetch metadata.
 // Returns the client that uses the specified http.Client for HTTP requests.
 // If nil is specified, returns the default client.
 func NewClient(c *http.Client) *Client {
-	if c == nil {
+	client := c
+	if client == nil {
+		client = newDefaultHTTPClient()
+	}
+	return NewWithOptions(&Options{
+		Client: client,
+	})
+}
+
+func NewWithOptions(opts *Options) *Client {
+	if opts == nil {
 		return defaultClient
 	}
-	return &Client{hc: c}
+	client := opts.Client
+	if client == nil {
+		client = newDefaultHTTPClient()
+	}
+	logger := internallog.New(opts.Logger)
+	return &Client{hc: client, logger: logger}
 }
 
 // getETag returns a value from the metadata service as well as the associated ETag.
@@ -448,12 +475,21 @@ func (c *Client) getETag(ctx context.Context, suffix string) (value, etag string
 	req.Header.Set("User-Agent", userAgent)
 	var res *http.Response
 	var reqErr error
+	var body []byte
 	retryer := newRetryer()
 	for {
+		c.logger.DebugContext(ctx, "metadata request", "request", internallog.HTTPRequest(req, nil))
 		res, reqErr = c.hc.Do(req)
 		var code int
 		if res != nil {
 			code = res.StatusCode
+			body, err = io.ReadAll(res.Body)
+			if err != nil {
+				res.Body.Close()
+				return "", "", err
+			}
+			c.logger.DebugContext(ctx, "metadata response", "response", internallog.HTTPResponse(res, body))
+			res.Body.Close()
 		}
 		if delay, shouldRetry := retryer.Retry(code, reqErr); shouldRetry {
 			if res != nil && res.Body != nil {
@@ -469,18 +505,13 @@ func (c *Client) getETag(ctx context.Context, suffix string) (value, etag string
 	if reqErr != nil {
 		return "", "", reqErr
 	}
-	defer res.Body.Close()
 	if res.StatusCode == http.StatusNotFound {
 		return "", "", NotDefinedError(suffix)
 	}
-	all, err := io.ReadAll(res.Body)
-	if err != nil {
-		return "", "", err
-	}
 	if res.StatusCode != 200 {
-		return "", "", &Error{Code: res.StatusCode, Message: string(all)}
+		return "", "", &Error{Code: res.StatusCode, Message: string(body)}
 	}
-	return string(all), res.Header.Get("Etag"), nil
+	return string(body), res.Header.Get("Etag"), nil
 }
 
 // Get returns a value from the metadata service.

compute/metadata/metadata_test.go

@@ -18,7 +18,6 @@ import (
 	"bytes"
 	"context"
 	"io"
-	"log"
 	"net/http"
 	"os"
 	"strings"
@@ -70,7 +69,6 @@ func TestGetFailsOnBadURL(t *testing.T) {
 	c := NewClient(http.DefaultClient)
 	t.Setenv(metadataHostEnv, "host:-1")
 	_, err := c.GetWithContext(ctx, "suffix")
-	log.Printf("%v", err)
 	if err == nil {
 		t.Errorf("got %v, want non-nil error", err)
 	}