blob: add tracing (#1143)

* blob: add tracing

Add tracing to methods that (a) make RPCs to the service, and (b) are
unlikely to be called in an inner loop. Specifically, do NOT trace:

- SignedURL, because it doesn't make an RPC
- Read and Write, because they are likely to be called frequently,
  so the trace information would be voluminous.

blob/blob.go

@@ -61,14 +61,16 @@ import (
 	"time"
 
 	"gocloud.dev/blob/driver"
+	"gocloud.dev/internal/trace"
 )
 
 // Reader reads bytes from a blob.
 // It implements io.ReadCloser, and must be closed after
 // reads are finished.
 type Reader struct {
-	b driver.Bucket
-	r driver.Reader
+	b    driver.Bucket
+	r    driver.Reader
+	tctx context.Context // trace context
 }
 
 // Read implements io.Reader (https://golang.org/pkg/io/#Reader).
@@ -79,7 +81,9 @@ func (r *Reader) Read(p []byte) (int, error) {
 
 // Close implements io.Closer (https://golang.org/pkg/io/#Closer).
 func (r *Reader) Close() error {
-	return wrapError(r.b, r.r.Close())
+	err := wrapError(r.b, r.r.Close())
+	trace.EndSpan(r.tctx, err)
+	return err
 }
 
 // ContentType returns the MIME type of the blob.
@@ -170,6 +174,7 @@ type Writer struct {
 	key  string
 	opts *driver.WriterOptions
 	buf  *bytes.Buffer
+	tctx context.Context // context for tracing only
 }
 
 // sniffLen is the byte size of Writer.buf used to detect content-type.
@@ -212,7 +217,8 @@ func (w *Writer) Write(p []byte) (n int, err error) {
 // Close returns with no error.
 // Close may return an error if the context provided to create the Writer is
 // canceled or reaches its deadline.
-func (w *Writer) Close() error {
+func (w *Writer) Close() (err error) {
+	defer func() { trace.EndSpan(w.tctx, err) }()
 	if len(w.contentMD5) > 0 {
 		// Verify the MD5 hash of what was written matches the ContentMD5 provided
 		// by the user.
@@ -401,7 +407,9 @@ func (b *Bucket) As(i interface{}) bool {
 
 // ReadAll is a shortcut for creating a Reader via NewReader with nil
 // ReaderOptions, and reading the entire blob.
-func (b *Bucket) ReadAll(ctx context.Context, key string) ([]byte, error) {
+func (b *Bucket) ReadAll(ctx context.Context, key string) (_ []byte, err error) {
+	defer func() { trace.EndSpan(ctx, err) }()
+
 	r, err := b.NewReader(ctx, key, nil)
 	if err != nil {
 		return nil, err
@@ -434,7 +442,10 @@ func (b *Bucket) List(opts *ListOptions) *ListIterator {
 //
 // If the blob does not exist, Attributes returns an error for which
 // IsNotExist will return true.
-func (b *Bucket) Attributes(ctx context.Context, key string) (Attributes, error) {
+func (b *Bucket) Attributes(ctx context.Context, key string) (_ Attributes, err error) {
+	ctx = trace.StartSpan(ctx, "gocloud.dev/blob.Attributes")
+	defer func() { trace.EndSpan(ctx, err) }()
+
 	a, err := b.b.Attributes(ctx, key)
 	if err != nil {
 		return Attributes{}, wrapError(b.b, err)
@@ -479,23 +490,29 @@ func (b *Bucket) NewReader(ctx context.Context, key string, opts *ReaderOptions)
 // A nil ReaderOptions is treated the same as the zero value.
 //
 // The caller must call Close on the returned Reader when done reading.
-func (b *Bucket) NewRangeReader(ctx context.Context, key string, offset, length int64, opts *ReaderOptions) (*Reader, error) {
+func (b *Bucket) NewRangeReader(ctx context.Context, key string, offset, length int64, opts *ReaderOptions) (_ *Reader, err error) {
 	if offset < 0 {
 		return nil, errors.New("blob.NewRangeReader: offset must be non-negative")
 	}
 	if opts == nil {
 		opts = &ReaderOptions{}
 	}
 	dopts := &driver.ReaderOptions{}
+	tctx := trace.StartSpan(ctx, "gocloud.dev/blob.NewRangeReader")
+	defer func() {
+		if err != nil {
+			trace.EndSpan(tctx, err)
+		}
+	}()
 	r, err := b.b.NewRangeReader(ctx, key, offset, length, dopts)
 	if err != nil {
 		return nil, wrapError(b.b, err)
 	}
-	return &Reader{b: b.b, r: r}, nil
+	return &Reader{b: b.b, r: r, tctx: tctx}, nil
 }
 
 // WriteAll is a shortcut for creating a Writer via NewWriter and writing p.
-func (b *Bucket) WriteAll(ctx context.Context, key string, p []byte, opts *WriterOptions) error {
+func (b *Bucket) WriteAll(ctx context.Context, key string, p []byte, opts *WriterOptions) (err error) {
 	w, err := b.NewWriter(ctx, key, opts)
 	if err != nil {
 		return err
@@ -522,7 +539,7 @@ func (b *Bucket) WriteAll(ctx context.Context, key string, p []byte, opts *Write
 //
 // The caller must call Close on the returned Writer, even if the write is
 // aborted.
-func (b *Bucket) NewWriter(ctx context.Context, key string, opts *WriterOptions) (*Writer, error) {
+func (b *Bucket) NewWriter(ctx context.Context, key string, opts *WriterOptions) (_ *Writer, err error) {
 	var dopts *driver.WriterOptions
 	var w driver.Writer
 	if opts == nil {
@@ -555,6 +572,13 @@ func (b *Bucket) NewWriter(ctx context.Context, key string, opts *WriterOptions)
 		dopts.Metadata = md
 	}
 	ctx, cancel := context.WithCancel(ctx)
+	tctx := trace.StartSpan(ctx, "gocloud.dev/blob.NewWriter")
+	defer func() {
+		if err != nil {
+			trace.EndSpan(tctx, err)
+		}
+	}()
+
 	if opts.ContentType != "" {
 		t, p, err := mime.ParseMediaType(opts.ContentType)
 		if err != nil {
@@ -573,6 +597,7 @@ func (b *Bucket) NewWriter(ctx context.Context, key string, opts *WriterOptions)
 			cancel:     cancel,
 			contentMD5: opts.ContentMD5,
 			md5hash:    md5.New(),
+			tctx:       tctx,
 		}, nil
 	}
 	return &Writer{
@@ -584,14 +609,17 @@ func (b *Bucket) NewWriter(ctx context.Context, key string, opts *WriterOptions)
 		buf:        bytes.NewBuffer([]byte{}),
 		contentMD5: opts.ContentMD5,
 		md5hash:    md5.New(),
+		tctx:       tctx,
 	}, nil
 }
 
 // Delete deletes the blob stored at key.
 //
 // If the blob does not exist, Delete returns an error for which
 // IsNotExist will return true.
-func (b *Bucket) Delete(ctx context.Context, key string) error {
+func (b *Bucket) Delete(ctx context.Context, key string) (err error) {
+	ctx = trace.StartSpan(ctx, "gocloud.dev/blob.Delete")
+	defer func() { trace.EndSpan(ctx, err) }()
 	return wrapError(b.b, b.b.Delete(ctx, key))
 }