Add direct serving of package content (#25543)

Fixes #24723

Direct serving of content aka HTTP redirect is not mentioned in any of
the package registry specs but lots of official registries do that so it
should be supported by the usual clients.

routers/api/packages/helper/helper.go

@@ -5,8 +5,11 @@ package helper
 
 import (
 	"fmt"
+	"io"
 	"net/http"
+	"net/url"
 
+	packages_model "code.gitea.io/gitea/models/packages"
 	"code.gitea.io/gitea/modules/context"
 	"code.gitea.io/gitea/modules/log"
 	"code.gitea.io/gitea/modules/setting"
@@ -35,3 +38,26 @@ func LogAndProcessError(ctx *context.Context, status int, obj interface{}, cb fu
 		cb(message)
 	}
 }
+
+// Serves the content of the package file
+// If the url is set it will redirect the request, otherwise the content is copied to the response.
+func ServePackageFile(ctx *context.Context, s io.ReadSeekCloser, u *url.URL, pf *packages_model.PackageFile, forceOpts ...*context.ServeHeaderOptions) {
+	if u != nil {
+		ctx.Redirect(u.String())
+		return
+	}
+
+	defer s.Close()
+
+	var opts *context.ServeHeaderOptions
+	if len(forceOpts) > 0 {
+		opts = forceOpts[0]
+	} else {
+		opts = &context.ServeHeaderOptions{
+			Filename:     pf.Name,
+			LastModified: pf.CreatedUnix.AsLocalTime(),
+		}
+	}
+
+	ctx.ServeContent(s, opts)
+}