progress_cache.go
| 1 | package service |
| 2 | |
| 3 | import ( |
| 4 | "strings" |
| 5 | "sync" |
| 6 | ) |
| 7 | |
| 8 | type liveDownload struct { |
| 9 | logs strings.Builder |
| 10 | flushed int // length of logs already persisted to the DB |
| 11 | } |
| 12 | |
| 13 | type ProgressCache struct { |
| 14 | mu sync.RWMutex |
| 15 | data map[int64]*liveDownload |
| 16 | } |
| 17 | |
| 18 | func NewProgressCache() *ProgressCache { |
| 19 | return &ProgressCache{ |
| 20 | data: make(map[int64]*liveDownload), |
| 21 | } |
| 22 | } |
| 23 | |
| 24 | // Start discards anything a previous run of the same id left behind. |
| 25 | func (c *ProgressCache) Start(id int64) { |
| 26 | c.mu.Lock() |
| 27 | defer c.mu.Unlock() |
| 28 | c.data[id] = &liveDownload{} |
| 29 | } |
| 30 | |
| 31 | func (c *ProgressCache) AppendLog(id int64, line string) { |
| 32 | c.mu.Lock() |
| 33 | defer c.mu.Unlock() |
| 34 | if d, ok := c.data[id]; ok { |
| 35 | d.logs.WriteString(line) |
| 36 | d.logs.WriteByte('\n') |
| 37 | } |
| 38 | } |
| 39 | |
| 40 | // Snapshot reads under the lock so it never races AppendLog: strings.Builder is |
| 41 | // not safe for concurrent read/write. Empty string if the download isn't live. |
| 42 | func (c *ProgressCache) Snapshot(id int64) string { |
| 43 | c.mu.RLock() |
| 44 | defer c.mu.RUnlock() |
| 45 | if d, ok := c.data[id]; ok { |
| 46 | return d.logs.String() |
| 47 | } |
| 48 | return "" |
| 49 | } |
| 50 | |
| 51 | func (c *ProgressCache) Delete(id int64) { |
| 52 | c.mu.Lock() |
| 53 | defer c.mu.Unlock() |
| 54 | delete(c.data, id) |
| 55 | } |
| 56 | |
| 57 | // FlushLogs returns only what was appended since the last call and advances the |
| 58 | // mark, so the caller appends to the DB instead of rewriting the whole buffer. |
| 59 | func (c *ProgressCache) FlushLogs(id int64) string { |
| 60 | c.mu.Lock() |
| 61 | defer c.mu.Unlock() |
| 62 | d, ok := c.data[id] |
| 63 | if !ok { |
| 64 | return "" |
| 65 | } |
| 66 | full := d.logs.String() |
| 67 | if d.flushed >= len(full) { |
| 68 | return "" |
| 69 | } |
| 70 | tail := full[d.flushed:] |
| 71 | d.flushed = len(full) |
| 72 | return tail |
| 73 | } |
| 74 |