feat: daemon: Auto-resume interrupted snapshot imports

cmd/lotus/daemon.go

@@ -10,7 +10,6 @@ import (
 	"encoding/json"
 	"fmt"
 	"io"
-	"net/http"
 	"os"
 	"path"
 	"runtime/pprof"
@@ -43,6 +42,7 @@ import (
 	lcli "github.com/filecoin-project/lotus/cli"
 	"github.com/filecoin-project/lotus/journal"
 	"github.com/filecoin-project/lotus/journal/fsjournal"
+	"github.com/filecoin-project/lotus/lib/httpreader"
 	"github.com/filecoin-project/lotus/lib/peermgr"
 	"github.com/filecoin-project/lotus/lib/ulimit"
 	"github.com/filecoin-project/lotus/metrics"
@@ -434,18 +434,13 @@ func ImportChain(ctx context.Context, r repo.Repo, fname string, snapshot bool)
 	var rd io.Reader
 	var l int64
 	if strings.HasPrefix(fname, "http://") || strings.HasPrefix(fname, "https://") {
-		resp, err := http.Get(fname) //nolint:gosec
+		rrd, err := httpreader.NewResumableReader(ctx, fname)
 		if err != nil {
-			return err
-		}
-		defer resp.Body.Close() //nolint:errcheck
-
-		if resp.StatusCode != http.StatusOK {
-			return xerrors.Errorf("fetching chain CAR failed with non-200 response: %d", resp.StatusCode)
+			return xerrors.Errorf("fetching chain CAR failed: setting up resumable reader: %w", err)
 		}
 
-		rd = resp.Body
-		l = resp.ContentLength
+		rd = rrd
+		l = rrd.ContentLength()
 	} else {
 		fname, err = homedir.Expand(fname)
 		if err != nil {

lib/httpreader/resumable.go

@@ -0,0 +1,112 @@
+package httpreader
+
+import (
+	"context"
+	"fmt"
+	"io"
+	"net/http"
+	"strconv"
+
+	"golang.org/x/xerrors"
+)
+
+type ResumableReader struct {
+	ctx           context.Context
+	initialURL    string
+	finalURL      *string
+	position      int64
+	contentLength int64
+	client        *http.Client
+	reader        io.ReadCloser
+}
+
+func NewResumableReader(ctx context.Context, url string) (*ResumableReader, error) {
+	finalURL := ""
+
+	client := &http.Client{
+		CheckRedirect: func(req *http.Request, via []*http.Request) error {
+			finalURL = req.URL.String()
+			if len(via) >= 10 {
+				return xerrors.New("stopped after 10 redirects")
+			}
+			return nil
+		},
+	}
+
+	r := &ResumableReader{
+		ctx:        ctx,
+		initialURL: url,
+		finalURL:   &finalURL,
+		position:   0,
+		client:     client,
+	}
+
+	req, err := http.NewRequestWithContext(ctx, "GET", url, nil)
+	if err != nil {
+		return nil, err
+	}
+
+	resp, err := r.client.Do(req)
+	if err != nil {
+		return nil, err
+	}
+
+	if resp.StatusCode != http.StatusOK {
+		return nil, fmt.Errorf("failed to fetch resource, status code: %d", resp.StatusCode)
+	}
+
+	contentLength, err := strconv.ParseInt(resp.Header.Get("Content-Length"), 10, 64)
+	if err != nil {
+		resp.Body.Close()
+		return nil, err
+	}
+
+	r.contentLength = contentLength
+	r.reader = resp.Body
+
+	return r, nil
+}
+
+func (r *ResumableReader) ContentLength() int64 {
+	return r.contentLength
+}
+
+func (r *ResumableReader) Read(p []byte) (n int, err error) {
+	for {
+		if r.reader == nil {
+			reqURL := r.initialURL
+			if *r.finalURL != "" {
+				reqURL = *r.finalURL
+			}
+
+			req, err := http.NewRequestWithContext(r.ctx, "GET", reqURL, nil)
+			if err != nil {
+				return 0, err
+			}
+			req.Header.Set("Range", fmt.Sprintf("bytes=%d-", r.position))
+			resp, err := r.client.Do(req)
+			if err != nil {
+				return 0, err
+			}
+
+			if resp.StatusCode != http.StatusOK && resp.StatusCode != http.StatusPartialContent {
+				return 0, fmt.Errorf("non-resumable status code: %d", resp.StatusCode)
+			}
+			r.reader = resp.Body
+		}
+
+		n, err = r.reader.Read(p)
+		r.position += int64(n)
+
+		if err == io.EOF {
+			if r.position == r.contentLength {
+				r.reader.Close()
+				return n, err
+			}
+			r.reader.Close()
+			r.reader = nil
+		} else {
+			return n, err
+		}
+	}
+}