Ivan Pilat | 8ecbed3 | 2015-01-13 21:30:05 -0800 | [diff] [blame] | 1 | // LimitedWriter is an io.Writer wrapper that limits the total number of bytes |
| 2 | // written to the underlying writer. |
| 3 | // |
| 4 | // All attempted writes count against the limit, regardless of whether they |
| 5 | // succeed. |
| 6 | // Not thread-safe. |
| 7 | |
| 8 | package lib |
| 9 | |
| 10 | import ( |
| 11 | "errors" |
| 12 | "io" |
| 13 | "net/http" |
| 14 | "sync" |
| 15 | ) |
| 16 | |
| 17 | var ErrWriteLimitExceeded = errors.New("LimitedWriter: write limit exceeded") |
| 18 | |
| 19 | // Initialize using NewLimitedWriter. |
| 20 | type LimitedWriter struct { |
| 21 | io.Writer |
| 22 | maxLen int |
| 23 | maxLenExceededCb func() |
| 24 | lenWritten int |
| 25 | } |
| 26 | |
| 27 | func NewLimitedWriter(writer io.Writer, maxLen int, maxLenExceededCb func()) *LimitedWriter { |
| 28 | return &LimitedWriter{ |
| 29 | Writer: writer, |
| 30 | maxLen: maxLen, |
| 31 | maxLenExceededCb: maxLenExceededCb, |
| 32 | } |
| 33 | } |
| 34 | |
| 35 | func (t *LimitedWriter) Write(p []byte) (n int, err error) { |
| 36 | if t.lenWritten+len(p) > t.maxLen { |
| 37 | t.lenWritten = t.maxLen |
| 38 | if t.maxLenExceededCb != nil { |
| 39 | t.maxLenExceededCb() |
| 40 | } |
| 41 | return 0, ErrWriteLimitExceeded |
| 42 | } |
| 43 | if len(p) == 0 { |
| 44 | return 0, nil |
| 45 | } |
| 46 | t.lenWritten += len(p) |
| 47 | return t.Writer.Write(p) |
| 48 | } |
| 49 | |
| 50 | var _ http.Flusher = (*LimitedWriter)(nil) |
| 51 | |
| 52 | func (t *LimitedWriter) Flush() { |
| 53 | if f, ok := t.Writer.(http.Flusher); ok { |
| 54 | f.Flush() |
| 55 | } |
| 56 | } |
| 57 | |
| 58 | // Wraps a function to prevent it from executing more than once. |
| 59 | func DoOnce(f func()) func() { |
| 60 | var once sync.Once |
| 61 | return func() { |
| 62 | once.Do(f) |
| 63 | } |
| 64 | } |