veyron.io/playground: Stream playground output to client in realtime.
Output is streamed as JSONified Events, one per line, similar to
builder output. Output size limit is enforced.
Moved Event writing support into a shared playground lib to make it
accessible to compilerd.
Also changed Docker build to include all builder and lib files in
local file mode.
Change-Id: Iefb0ccfa3d8593d2887d530bcb1750dc728bf568
diff --git a/lib/limited_writer.go b/lib/limited_writer.go
new file mode 100644
index 0000000..a93464b
--- /dev/null
+++ b/lib/limited_writer.go
@@ -0,0 +1,64 @@
+// LimitedWriter is an io.Writer wrapper that limits the total number of bytes
+// written to the underlying writer.
+//
+// All attempted writes count against the limit, regardless of whether they
+// succeed.
+// Not thread-safe.
+
+package lib
+
+import (
+ "errors"
+ "io"
+ "net/http"
+ "sync"
+)
+
+var ErrWriteLimitExceeded = errors.New("LimitedWriter: write limit exceeded")
+
+// Initialize using NewLimitedWriter.
+type LimitedWriter struct {
+ io.Writer
+ maxLen int
+ maxLenExceededCb func()
+ lenWritten int
+}
+
+func NewLimitedWriter(writer io.Writer, maxLen int, maxLenExceededCb func()) *LimitedWriter {
+ return &LimitedWriter{
+ Writer: writer,
+ maxLen: maxLen,
+ maxLenExceededCb: maxLenExceededCb,
+ }
+}
+
+func (t *LimitedWriter) Write(p []byte) (n int, err error) {
+ if t.lenWritten+len(p) > t.maxLen {
+ t.lenWritten = t.maxLen
+ if t.maxLenExceededCb != nil {
+ t.maxLenExceededCb()
+ }
+ return 0, ErrWriteLimitExceeded
+ }
+ if len(p) == 0 {
+ return 0, nil
+ }
+ t.lenWritten += len(p)
+ return t.Writer.Write(p)
+}
+
+var _ http.Flusher = (*LimitedWriter)(nil)
+
+func (t *LimitedWriter) Flush() {
+ if f, ok := t.Writer.(http.Flusher); ok {
+ f.Flush()
+ }
+}
+
+// Wraps a function to prevent it from executing more than once.
+func DoOnce(f func()) func() {
+ var once sync.Once
+ return func() {
+ once.Do(f)
+ }
+}
