depot/web/fup/fuphttp/metadata.go

// SPDX-FileCopyrightText: 2021 Luke Granger-Brown <depot@lukegb.com>
//
// SPDX-License-Identifier: Apache-2.0

package fuphttp

import (
	"context"
	"fmt"
	"log"
	"strconv"
	"time"

	"gocloud.dev/blob"
	"gocloud.dev/gcerrors"
)

type Metadata struct {
	// ExpiresAt is the expiry time of the object.
	// May be the zero time, if this object does not expire.
	// Stored in expires-at.
	ExpiresAt time.Time

	// Attributes is the underlying gocloud Attributes.
	Attributes *blob.Attributes
}

// WriterOptions returns a new WriterOptions based on the provided metadata.
func (m *Metadata) WriterOptions() *blob.WriterOptions {
	attrs := m.Attributes
	if attrs == nil {
		attrs = &blob.Attributes{}
	}
	if attrs.Metadata == nil {
		attrs.Metadata = make(map[string]string)
	}

	if !m.ExpiresAt.IsZero() {
		attrs.Metadata["expires-at"] = strconv.FormatInt(m.ExpiresAt.Unix(), 10)
	}

	return &blob.WriterOptions{
		BufferSize:         8 * 1024 * 1024, /* 8 MiB */
		CacheControl:       attrs.CacheControl,
		ContentDisposition: attrs.ContentDisposition,
		ContentEncoding:    attrs.ContentEncoding,
		ContentLanguage:    attrs.ContentLanguage,
		ContentType:        attrs.ContentType,
		Metadata:           attrs.Metadata,
	}
}

// metadata retrieves the Metadata for the object.
// Note: if the object is expired, it will delete it.
func metadata(ctx context.Context, bucket *blob.Bucket, filename string) (*Metadata, error) {
	attrs, err := bucket.Attributes(ctx, filename)
	if err != nil {
		return nil, fmt.Errorf("Attributes(%q): %w", filename, err)
	}

	m := Metadata{
		Attributes: attrs,
	}

	var exp time.Time
	if expStr, ok := attrs.Metadata["expires-at"]; ok {
		// Check for expiry.
		expSec, err := strconv.ParseInt(expStr, 10, 64)
		if err != nil {
			return nil, fmt.Errorf("parsing expiration %q for %q: %v", expStr, filename, err)
		}

		exp = time.Unix(expSec, 0)
		if exp.Before(time.Now()) {
			// This file has expired. Delete it from the backing storage.
			err := bucket.Delete(ctx, filename)
			switch errorCode(err) {
			case gcerrors.NotFound:
				// Something probably deleted it before we could get there.
			case gcerrors.OK:
				// This was fine.
			default:
				log.Printf("deleting expired file %q: %v", filename, err)
			}
			return nil, &fupError{
				Code: gcerrors.NotFound,
			}
		}

		m.ExpiresAt = exp
	}

	return &m, nil
}