Refactor and export range retry transport (#2012)

This transport had some weirdness about it in terms of using an HTTP
client internally instead of the "usual" transport layering. This fixes
that and also avoids storing a context unnecessarily. That makes the
transport itself stateless and statically usable for clients as well.

Fixes a couple of other nits around the transport as well.

Author: markusthoemmes

pkg/apk/apk/implementation.go

@@ -1384,7 +1384,7 @@ func (a *APK) FetchPackage(ctx context.Context, pkg FetchablePackage) (io.ReadCl
 		}
 
 		// This will return a body that retries requests using Range requests if Read() hits an error.
-		rrt := newRangeRetryTransport(ctx, client)
+		rrt := NewRangeRetryTransport(client.Transport)
 		res, err := rrt.RoundTrip(req)
 		if err != nil {
 			return nil, fmt.Errorf("unable to get package apk at %s: %w", u, err)

pkg/apk/apk/index.go

@@ -321,7 +321,7 @@ func fetchRepositoryIndex(ctx context.Context, u string, etag string, opts *inde
 	}
 
 	// This will return a body that retries requests using Range requests if Read() hits an error.
-	rrt := newRangeRetryTransport(ctx, client)
+	rrt := NewRangeRetryTransport(client.Transport)
 	res, err := rrt.RoundTrip(req)
 	if err != nil {
 		return nil, err

pkg/apk/apk/transport.go

@@ -15,45 +15,40 @@
 package apk
 
 import (
-	"context"
 	"errors"
 	"fmt"
 	"io"
 	"net/http"
 )
 
 type rangeRetryTransport struct {
-	client *http.Client
-	ctx    context.Context
+	base http.RoundTripper
 }
 
-func newRangeRetryTransport(ctx context.Context, client *http.Client) *rangeRetryTransport {
-	return &rangeRetryTransport{
-		client: client,
-		ctx:    ctx,
+// NewRangeRetryTransport returns a transport that retries failed reads using HTTP Range requests.
+func NewRangeRetryTransport(base http.RoundTripper) http.RoundTripper {
+	if base == nil {
+		base = http.DefaultTransport
 	}
+	return &rangeRetryTransport{base: base}
 }
 
 func (t *rangeRetryTransport) RoundTrip(req *http.Request) (*http.Response, error) {
-	r := rangeRetryReader{
-		client: t.client,
-		ctx:    t.ctx,
-		req:    req,
+	r := &rangeRetryReader{
+		base: t.base,
+		req:  req,
 	}
 
 	return r.reset(nil)
 }
 
 type rangeRetryReader struct {
-	client *http.Client
-	ctx    context.Context
-
-	req *http.Request
+	base http.RoundTripper
+	req  *http.Request
 
 	body io.ReadCloser
 
 	progress int64
-	total    int64
 }
 
 func (r *rangeRetryReader) reset(oerr error) (*http.Response, error) {
@@ -62,14 +57,13 @@ func (r *rangeRetryReader) reset(oerr error) (*http.Response, error) {
 		_ = r.body.Close()
 	}
 
-	req := r.req.WithContext(r.ctx)
+	req := r.req.WithContext(r.req.Context())
 
-	rangeHeader := fmt.Sprintf("bytes=%d-", r.progress)
 	if r.progress != 0 {
-		req.Header.Set("Range", rangeHeader)
+		req.Header.Set("Range", fmt.Sprintf("bytes=%d-", r.progress))
 	}
 
-	resp, err := r.client.Do(req)
+	resp, err := r.base.RoundTrip(req)
 	if err != nil {
 		return resp, errors.Join(oerr, err)
 	}
@@ -78,10 +72,6 @@ func (r *rangeRetryReader) reset(oerr error) (*http.Response, error) {
 		return resp, nil
 	}
 
-	if r.total == 0 {
-		r.total = resp.ContentLength
-	}
-
 	if resp.StatusCode == http.StatusOK {
 		// If the upstream doesn't support Range requests for some reason and only returns 200,
 		// we need to discard anything we've already Read().
@@ -91,11 +81,11 @@ func (r *rangeRetryReader) reset(oerr error) (*http.Response, error) {
 			}
 		}
 	} else if resp.StatusCode != http.StatusPartialContent {
-		if oerr != nil {
-			return resp, fmt.Errorf("retrying %w: %s %s (Range: %s): unexpected status code: %d", oerr, req.Method, req.URL.String(), rangeHeader, resp.StatusCode)
+		if r.progress != 0 {
+			return resp, fmt.Errorf("retrying %w: %s %s (Range: %s): unexpected status code: %d", oerr, req.Method, req.URL.String(), req.Header.Get("Range"), resp.StatusCode)
 		}
 
-		return resp, fmt.Errorf("%s %s (Range: %s): unexpected status code: %d", req.Method, req.URL.String(), rangeHeader, resp.StatusCode)
+		return resp, fmt.Errorf("%s %s: unexpected status code: %d", req.Method, req.URL.String(), resp.StatusCode)
 	}
 
 	r.body = resp.Body

pkg/apk/apk/transport_test.go

@@ -16,7 +16,6 @@ package apk
 
 import (
 	"bytes"
-	"context"
 	"fmt"
 	"io"
 	"net/http"
@@ -166,7 +165,7 @@ func TestTransport(t *testing.T) {
 				ranges: tc.ranges,
 			}
 
-			rt := newRangeRetryTransport(context.Background(), &http.Client{Transport: tt})
+			rt := NewRangeRetryTransport(tt)
 
 			req := &http.Request{
 				URL:    &url.URL{},