Handle when etag changes on remote archive

go.mod

@@ -5,6 +5,7 @@ go 1.21
 require (
 	github.com/RoaringBitmap/roaring v1.5.0
 	github.com/alecthomas/kong v0.8.0
+	github.com/aws/aws-sdk-go v1.45.12
 	github.com/caddyserver/caddy/v2 v2.7.5
 	github.com/dustin/go-humanize v1.0.1
 	github.com/paulmach/orb v0.10.0
@@ -38,7 +39,6 @@ require (
 	github.com/Microsoft/go-winio v0.6.0 // indirect
 	github.com/antlr/antlr4/runtime/Go/antlr/v4 v4.0.0-20230305170008-8188dc5388df // indirect
 	github.com/aryann/difflib v0.0.0-20210328193216-ff5ff6dc229b // indirect
-	github.com/aws/aws-sdk-go v1.45.12 // indirect
 	github.com/aws/aws-sdk-go-v2 v1.20.0 // indirect
 	github.com/aws/aws-sdk-go-v2/aws/protocol/eventstream v1.4.11 // indirect
 	github.com/aws/aws-sdk-go-v2/config v1.18.32 // indirect

main.go

@@ -146,7 +146,7 @@ func main() {
 			}
 			w.WriteHeader(statusCode)
 			w.Write(body)
-			logger.Printf("served %s in %s", r.URL.Path, time.Since(start))
+			logger.Printf("served %d %s in %s", statusCode, r.URL.Path, time.Since(start))
 		})
 
 		logger.Printf("Serving %s %s on port %d and interface %s with Access-Control-Allow-Origin: %s\n", cli.Serve.Bucket, cli.Serve.Path, cli.Serve.Port, cli.Serve.Interface, cli.Serve.Cors)

pmtiles/bucket.go

@@ -1,65 +1,159 @@
 package pmtiles
 
 import (
+	"bytes"
 	"context"
+	"crypto/md5"
+	"encoding/hex"
+	"errors"
 	"fmt"
-	"gocloud.dev/blob"
 	"io"
 	"net/http"
 	"net/url"
 	"os"
 	"path"
 	"path/filepath"
 	"strings"
+
+	"github.com/aws/aws-sdk-go/aws/awserr"
+	"github.com/aws/aws-sdk-go/service/s3"
+	"gocloud.dev/blob"
 )
 
 // Bucket is an abstration over a gocloud or plain HTTP bucket.
 type Bucket interface {
 	Close() error
 	NewRangeReader(ctx context.Context, key string, offset int64, length int64) (io.ReadCloser, error)
+	NewRangeReaderEtag(ctx context.Context, key string, offset int64, length int64, etag string) (io.ReadCloser, string, error)
+}
+
+// RefreshRequiredError is an error that indicates the etag has chanced on the remote file
+type RefreshRequiredError struct {
+	StatusCode int
+}
+
+func (m *RefreshRequiredError) Error() string {
+	return fmt.Sprintf("HTTP error indicates file has changed: %d", m.StatusCode)
+}
+
+type mockBucket struct {
+	items map[string][]byte
+}
+
+func (m mockBucket) Close() error {
+	return nil
+}
+
+func (m mockBucket) NewRangeReader(ctx context.Context, key string, offset int64, length int64) (io.ReadCloser, error) {
+	body, _, err := m.NewRangeReaderEtag(ctx, key, offset, length, "")
+	return body, err
+
+}
+func (m mockBucket) NewRangeReaderEtag(_ context.Context, key string, offset int64, length int64, etag string) (io.ReadCloser, string, error) {
+	bs, ok := m.items[key]
+	if !ok {
+		return nil, "", fmt.Errorf("Not found %s", key)
+	}
+
+	hash := md5.Sum(bs)
+	resultEtag := hex.EncodeToString(hash[:])
+	if len(etag) > 0 && resultEtag != etag {
+		return nil, "", &RefreshRequiredError{}
+	}
+	if offset+length > int64(len(bs)) {
+		return nil, "", &RefreshRequiredError{416}
+	}
+
+	return io.NopCloser(bytes.NewReader(bs[offset:(offset + length)])), resultEtag, nil
+}
+
+// HTTPClient is an interface that lets you swap out the default client with a mock one in tests
+type HTTPClient interface {
+	Do(req *http.Request) (*http.Response, error)
 }
 
 type HTTPBucket struct {
 	baseURL string
+	client  HTTPClient
 }
 
-func (b HTTPBucket) NewRangeReader(_ context.Context, key string, offset, length int64) (io.ReadCloser, error) {
+func (b HTTPBucket) NewRangeReader(ctx context.Context, key string, offset, length int64) (io.ReadCloser, error) {
+	body, _, err := b.NewRangeReaderEtag(ctx, key, offset, length, "")
+	return body, err
+}
+
+func (b HTTPBucket) NewRangeReaderEtag(ctx context.Context, key string, offset, length int64, etag string) (io.ReadCloser, string, error) {
 	reqURL := b.baseURL + "/" + key
 
-	req, err := http.NewRequest("GET", reqURL, nil)
+	req, err := http.NewRequestWithContext(ctx, "GET", reqURL, nil)
 	if err != nil {
-		return nil, err
+		return nil, "", err
 	}
 
 	req.Header.Set("Range", fmt.Sprintf("bytes=%d-%d", offset, offset+length-1))
+	if len(etag) > 0 {
+		req.Header.Set("If-Match", etag)
+	}
 
-	resp, err := http.DefaultClient.Do(req)
+	resp, err := b.client.Do(req)
 	if err != nil {
-		return nil, err
+		return nil, "", err
 	}
 
 	if resp.StatusCode != http.StatusOK && resp.StatusCode != http.StatusPartialContent {
 		resp.Body.Close()
-		return nil, fmt.Errorf("HTTP error: %d", resp.StatusCode)
+		if isRefreshRequredCode(resp.StatusCode) {
+			err = &RefreshRequiredError{resp.StatusCode}
+		} else {
+			err = fmt.Errorf("HTTP error: %d", resp.StatusCode)
+		}
+		return nil, "", err
 	}
 
-	return resp.Body, nil
+	return resp.Body, resp.Header.Get("ETag"), nil
 }
 
 func (b HTTPBucket) Close() error {
 	return nil
 }
 
+func isRefreshRequredCode(code int) bool {
+	return code == http.StatusPreconditionFailed || code == http.StatusRequestedRangeNotSatisfiable
+}
+
 type BucketAdapter struct {
 	Bucket *blob.Bucket
 }
 
 func (ba BucketAdapter) NewRangeReader(ctx context.Context, key string, offset, length int64) (io.ReadCloser, error) {
-	reader, err := ba.Bucket.NewRangeReader(ctx, key, offset, length, nil)
+	body, _, err := ba.NewRangeReaderEtag(ctx, key, offset, length, "")
+	return body, err
+}
+
+func (ba BucketAdapter) NewRangeReaderEtag(ctx context.Context, key string, offset, length int64, etag string) (io.ReadCloser, string, error) {
+	reader, err := ba.Bucket.NewRangeReader(ctx, key, offset, length, &blob.ReaderOptions{
+		BeforeRead: func(asFunc func(interface{}) bool) error {
+			var req *s3.GetObjectInput
+			if len(etag) > 0 && asFunc(&req) {
+				req.IfMatch = &etag
+			}
+			return nil
+		},
+	})
 	if err != nil {
-		return nil, err
+		var resp awserr.RequestFailure
+		errors.As(err, &resp)
+		if resp != nil && isRefreshRequredCode(resp.StatusCode()) {
+			return nil, "", &RefreshRequiredError{resp.StatusCode()}
+		}
+		return nil, "", err
+	}
+	resultETag := ""
+	var resp s3.GetObjectOutput
+	if reader.As(&resp) {
+		resultETag = *resp.ETag
 	}
-	return reader, nil
+	return reader, resultETag, nil
 }
 
 func (ba BucketAdapter) Close() error {
@@ -101,7 +195,7 @@ func NormalizeBucketKey(bucket string, prefix string, key string) (string, strin
 
 func OpenBucket(ctx context.Context, bucketURL string, bucketPrefix string) (Bucket, error) {
 	if strings.HasPrefix(bucketURL, "http") {
-		bucket := HTTPBucket{bucketURL}
+		bucket := HTTPBucket{bucketURL, http.DefaultClient}
 		return bucket, nil
 	}
 	bucket, err := blob.OpenBucket(ctx, bucketURL)

pmtiles/bucket_test.go

@@ -1,10 +1,14 @@
 package pmtiles
 
 import (
-	"github.com/stretchr/testify/assert"
+	"context"
+	"io"
+	"net/http"
 	"os"
 	"strings"
 	"testing"
+
+	"github.com/stretchr/testify/assert"
 )
 
 func TestNormalizeLocalFile(t *testing.T) {
@@ -35,3 +39,78 @@ func TestNormalizePathPrefixServer(t *testing.T) {
 	assert.True(t, strings.HasSuffix(bucket, "/foo"))
 	assert.True(t, strings.HasPrefix(bucket, "file://"))
 }
+
+type ClientMock struct {
+	request  *http.Request
+	response *http.Response
+}
+
+func (c *ClientMock) Do(req *http.Request) (*http.Response, error) {
+	c.request = req
+	return c.response, nil
+}
+
+func TestHttpBucketRequestNormal(t *testing.T) {
+	mock := ClientMock{}
+	header := http.Header{}
+	header.Add("ETag", "etag")
+	bucket := HTTPBucket{"http://tiles.example.com/tiles", &mock}
+	mock.response = &http.Response{
+		StatusCode: 200,
+		Body:       io.NopCloser(strings.NewReader("abc")),
+		Header:     header,
+	}
+	data, etag, err := bucket.NewRangeReaderEtag(context.Background(), "a/b/c", 100, 3, "")
+	assert.Equal(t, "", mock.request.Header.Get("If-Match"))
+	assert.Equal(t, "bytes=100-102", mock.request.Header.Get("Range"))
+	assert.Equal(t, "http://tiles.example.com/tiles/a/b/c", mock.request.URL.String())
+	assert.Nil(t, err)
+	b, err := io.ReadAll(data)
+	assert.Nil(t, err)
+	assert.Equal(t, "abc", string(b))
+	assert.Equal(t, "etag", etag)
+	assert.Nil(t, err)
+}
+
+func TestHttpBucketRequestRequestEtag(t *testing.T) {
+	mock := ClientMock{}
+	header := http.Header{}
+	header.Add("ETag", "etag2")
+	bucket := HTTPBucket{"http://tiles.example.com/tiles", &mock}
+	mock.response = &http.Response{
+		StatusCode: 200,
+		Body:       io.NopCloser(strings.NewReader("abc")),
+		Header:     header,
+	}
+	data, etag, err := bucket.NewRangeReaderEtag(context.Background(), "a/b/c", 0, 3, "etag1")
+	assert.Equal(t, "etag1", mock.request.Header.Get("If-Match"))
+	assert.Nil(t, err)
+	b, err := io.ReadAll(data)
+	assert.Nil(t, err)
+	assert.Equal(t, "abc", string(b))
+	assert.Equal(t, "etag2", etag)
+	assert.Nil(t, err)
+}
+
+func TestHttpBucketRequestRequestEtagFailed(t *testing.T) {
+	mock := ClientMock{}
+	header := http.Header{}
+	header.Add("ETag", "etag2")
+	bucket := HTTPBucket{"http://tiles.example.com/tiles", &mock}
+	mock.response = &http.Response{
+		StatusCode: 412,
+		Body:       io.NopCloser(strings.NewReader("abc")),
+		Header:     header,
+	}
+	_, _, err := bucket.NewRangeReaderEtag(context.Background(), "a/b/c", 0, 3, "etag1")
+	assert.Equal(t, "etag1", mock.request.Header.Get("If-Match"))
+	assert.True(t, isRefreshRequredError(err))
+
+	mock.response.StatusCode = 416
+	_, _, err = bucket.NewRangeReaderEtag(context.Background(), "a/b/c", 0, 3, "etag1")
+	assert.True(t, isRefreshRequredError(err))
+
+	mock.response.StatusCode = 404
+	_, _, err = bucket.NewRangeReaderEtag(context.Background(), "a/b/c", 0, 3, "etag1")
+	assert.False(t, isRefreshRequredError(err))
+}