feat: load model from oci image

vendor/oras.land/oras-go/v2/internal/httputil/seek.go

@@ -0,0 +1,116 @@
+/*
+Copyright The ORAS Authors.
+Licensed under the Apache License, Version 2.0 (the "License");
+you may not use this file except in compliance with the License.
+You may obtain a copy of the License at
+
+http://www.apache.org/licenses/LICENSE-2.0
+
+Unless required by applicable law or agreed to in writing, software
+distributed under the License is distributed on an "AS IS" BASIS,
+WITHOUT WARRANTIES OR CONDITIONS OF ANY KIND, either express or implied.
+See the License for the specific language governing permissions and
+limitations under the License.
+*/
+
+package httputil
+
+import (
+	"errors"
+	"fmt"
+	"io"
+	"net/http"
+)
+
+// Client is an interface for a HTTP client.
+// This interface is defined inside this package to prevent potential import
+// loop.
+type Client interface {
+	// Do sends an HTTP request and returns an HTTP response.
+	Do(*http.Request) (*http.Response, error)
+}
+
+// readSeekCloser seeks http body by starting new connections.
+type readSeekCloser struct {
+	client Client
+	req    *http.Request
+	rc     io.ReadCloser
+	size   int64
+	offset int64
+	closed bool
+}
+
+// NewReadSeekCloser returns a seeker to make the HTTP response seekable.
+// Callers should ensure that the server supports Range request.
+func NewReadSeekCloser(client Client, req *http.Request, respBody io.ReadCloser, size int64) io.ReadSeekCloser {
+	return &readSeekCloser{
+		client: client,
+		req:    req,
+		rc:     respBody,
+		size:   size,
+	}
+}
+
+// Read reads the content body and counts offset.
+func (rsc *readSeekCloser) Read(p []byte) (n int, err error) {
+	if rsc.closed {
+		return 0, errors.New("read: already closed")
+	}
+	n, err = rsc.rc.Read(p)
+	rsc.offset += int64(n)
+	return
+}
+
+// Seek starts a new connection to the remote for reading if position changes.
+func (rsc *readSeekCloser) Seek(offset int64, whence int) (int64, error) {
+	if rsc.closed {
+		return 0, errors.New("seek: already closed")
+	}
+	switch whence {
+	case io.SeekCurrent:
+		offset += rsc.offset
+	case io.SeekStart:
+		// no-op
+	case io.SeekEnd:
+		offset += rsc.size
+	default:
+		return 0, errors.New("seek: invalid whence")
+	}
+	if offset < 0 {
+		return 0, errors.New("seek: an attempt was made to move the pointer before the beginning of the content")
+	}
+	if offset == rsc.offset {
+		return offset, nil
+	}
+	if offset >= rsc.size {
+		rsc.rc.Close()
+		rsc.rc = http.NoBody
+		rsc.offset = offset
+		return offset, nil
+	}
+
+	req := rsc.req.Clone(rsc.req.Context())
+	req.Header.Set("Range", fmt.Sprintf("bytes=%d-%d", offset, rsc.size-1))
+	resp, err := rsc.client.Do(req)
+	if err != nil {
+		return 0, fmt.Errorf("seek: %s %q: %w", req.Method, req.URL, err)
+	}
+	if resp.StatusCode != http.StatusPartialContent {
+		resp.Body.Close()
+		return 0, fmt.Errorf("seek: %s %q: unexpected status code %d", resp.Request.Method, resp.Request.URL, resp.StatusCode)
+	}
+
+	rsc.rc.Close()
+	rsc.rc = resp.Body
+	rsc.offset = offset
+	return offset, nil
+}
+
+// Close closes the content body.
+func (rsc *readSeekCloser) Close() error {
+	if rsc.closed {
+		return nil
+	}
+	rsc.closed = true
+	return rsc.rc.Close()
+}