From f59aec9d526f05bde08f5c90cc4a1c4c1d8766eb Mon Sep 17 00:00:00 2001
From: =?UTF-8?q?Kamil=20Trzci=C5=84ski?= <ayufan@ayufan.eu>
Date: Thu, 20 Aug 2020 17:31:30 +0200
Subject: Refactor ZIP support to be more OOM

---
 internal/vfs/zip/http_range/resource.go | 70 +++++++++++++++++++++++++++++++++
 1 file changed, 70 insertions(+)
 create mode 100644 internal/vfs/zip/http_range/resource.go

(limited to 'internal/vfs/zip/http_range/resource.go')

diff --git a/internal/vfs/zip/http_range/resource.go b/internal/vfs/zip/http_range/resource.go
new file mode 100644
index 00000000..d35563b0
--- /dev/null
+++ b/internal/vfs/zip/http_range/resource.go
@@ -0,0 +1,70 @@
+package http_range
+
+import (
+	"context"
+	"fmt"
+	"io"
+	"io/ioutil"
+	"net/http"
+	"strconv"
+	"strings"
+)
+
+type Resource struct {
+	URL          string
+	Etag         string
+	LastModified string
+	Size         int64
+}
+
+func NewResource(ctx context.Context, URL string) (*Resource, error) {
+	// the `h.URL` is likely presigned only for GET
+	req, err := http.NewRequest("GET", URL, nil)
+	if err != nil {
+		return nil, err
+	}
+
+	req = req.WithContext(ctx)
+
+	// we fetch a single byte and ensure that range requests is additionally supported
+	req.Header.Set("Range", fmt.Sprintf("bytes=%d-%d", 0, 0))
+	res, err := httpClient.Do(req)
+	if err != nil {
+		return nil, err
+	}
+	defer io.Copy(ioutil.Discard, res.Body)
+	defer res.Body.Close()
+
+	resource := &Resource{
+		URL:          URL,
+		Etag:         res.Header.Get("ETag"),
+		LastModified: res.Header.Get("Last-Modified"),
+	}
+
+	switch res.StatusCode {
+	case http.StatusOK:
+		resource.Size = res.ContentLength
+		println(resource.URL, resource.Etag, resource.LastModified, resource.Size)
+		return resource, nil
+
+	case http.StatusPartialContent:
+		contentRange := res.Header.Get("Content-Range")
+		ranges := strings.SplitN(contentRange, "/", 2)
+		if len(ranges) != 2 {
+			return nil, fmt.Errorf("invalid `Content-Range`: %q", contentRange)
+		}
+
+		resource.Size, err = strconv.ParseInt(ranges[1], 0, 64)
+		if err != nil {
+			return nil, err
+		}
+
+		return resource, nil
+
+	case http.StatusRequestedRangeNotSatisfiable:
+		return nil, ErrRangeRequestsNotSupported
+
+	default:
+		return nil, fmt.Errorf("failed with %d: %q", res.StatusCode, res.Status)
+	}
+}
-- 
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