go.chromium.org/luci@v0.0.0-20240309015107-7cdc2e660f33/cipd/appengine/ui/cursors.go (about)

     1  // Copyright 2018 The LUCI Authors.
     2  //
     3  // Licensed under the Apache License, Version 2.0 (the "License");
     4  // you may not use this file except in compliance with the License.
     5  // You may obtain a copy of the License at
     6  //
     7  //      http://www.apache.org/licenses/LICENSE-2.0
     8  //
     9  // Unless required by applicable law or agreed to in writing, software
    10  // distributed under the License is distributed on an "AS IS" BASIS,
    11  // WITHOUT WARRANTIES OR CONDITIONS OF ANY KIND, either express or implied.
    12  // See the License for the specific language governing permissions and
    13  // limitations under the License.
    14  
    15  package ui
    16  
    17  import (
    18  	"context"
    19  	"crypto/sha256"
    20  	"encoding/base64"
    21  	"time"
    22  
    23  	"go.chromium.org/luci/common/logging"
    24  	"go.chromium.org/luci/server/caching"
    25  )
    26  
    27  type cursorKind string
    28  
    29  const instancesListing cursorKind = "v1:instances"
    30  
    31  // cursorKey is a cache key for items that link cursor to a previous page.
    32  func (k cursorKind) cursorKey(pkg, cursor string) string {
    33  	blob := sha256.Sum224([]byte(pkg + ":" + cursor))
    34  	return string(k) + ":" + base64.RawStdEncoding.EncodeToString(blob[:])
    35  }
    36  
    37  // storePrevCursor stores mapping cursor => prev, so that prev can be fetched
    38  // later by fetchPrevCursor.
    39  //
    40  // Logs and ignores errors. Cursor mapping is non-essential functionality.
    41  func (k cursorKind) storePrevCursor(ctx context.Context, pkg, cursor, prev string) {
    42  	if err := storeInCache(ctx, k.cursorKey(pkg, cursor), []byte(prev)); err != nil {
    43  		logging.Errorf(ctx, "Failed to store prev cursor %q in the cache: %s", k, err)
    44  	}
    45  }
    46  
    47  // fetchPrevCursor returns a cursor stored by storePrevCursor.
    48  //
    49  // Logs and ignores errors. Cursor mapping is non-essential functionality.
    50  func (k cursorKind) fetchPrevCursor(ctx context.Context, pkg, cursor string) string {
    51  	blob, err := loadFromCache(ctx, k.cursorKey(pkg, cursor))
    52  	if err != nil {
    53  		logging.Errorf(ctx, "Failed to fetch the prev cursor %q from the cache: %s", k, err)
    54  		return ""
    55  	}
    56  	return string(blob)
    57  }
    58  
    59  // localCursorCache is used as a replacement for the global cache when running
    60  // locally during development.
    61  var localCursorCache = caching.RegisterLRUCache[string, string](1)
    62  
    63  // storeInCache puts the value in the global memory cache.
    64  //
    65  // If there's no global cache available (e.g. when running locally) uses the
    66  // process cache.
    67  func storeInCache(ctx context.Context, key string, blob []byte) error {
    68  	if global := caching.GlobalCache(ctx, "cursors"); global != nil {
    69  		return global.Set(ctx, key, blob, 24*time.Hour)
    70  	}
    71  	localCursorCache.LRU(ctx).Put(ctx, key, string(blob), time.Hour)
    72  	return nil
    73  }
    74  
    75  // loadFromCache loads the value previously stored with storeInCache.
    76  //
    77  // If there's no such value, returns (nil, nil).
    78  func loadFromCache(ctx context.Context, key string) ([]byte, error) {
    79  	if global := caching.GlobalCache(ctx, "cursors"); global != nil {
    80  		val, err := global.Get(ctx, key)
    81  		if err == caching.ErrCacheMiss {
    82  			return nil, nil
    83  		}
    84  		return val, err
    85  	}
    86  	if val, ok := localCursorCache.LRU(ctx).Get(ctx, key); ok {
    87  		return []byte(val), nil
    88  	}
    89  	return nil, nil
    90  }