stream: Raise readable high water mark in powers of 2

This prevents excessively raising the buffer level in tiny increments in
pathological cases.

1 files changed, 17 insertions, 2 deletions

diff --git a/lib/_stream_readable.js b/lib/_stream_readable.js
index bf646f99ac..c4405314a4 100644
--- a/lib/_stream_readable.js
+++ b/lib/_stream_readable.js
@@ -161,6 +161,19 @@ Readable.prototype.setEncoding = function(enc) {
   this._readableState.decoder = new StringDecoder(enc);
 };
 
+// Don't raise the hwm > 128MB
+var MAX_HWM = 0x800000;
+function roundUpToNextPowerOf2(n) {
+  if (n >= MAX_HWM) {
+    n = MAX_HWM;
+  } else {
+    // Get the next highest power of 2
+    n--;
+    for (var p = 1; p < 32; p <<= 1) n |= n >> p;
+    n++;
+  }
+  return n;
+}
 
 function howMuchToRead(n, state) {
   if (state.length === 0 && state.ended)
@@ -181,9 +194,11 @@ function howMuchToRead(n, state) {
     return 0;
 
   // If we're asking for more than the target buffer level,
-  // then raise the water mark.
+  // then raise the water mark.  Bump up to the next highest
+  // power of 2, to prevent increasing it excessively in tiny
+  // amounts.
   if (n > state.highWaterMark)
-    state.highWaterMark = n;
+    state.highWaterMark = roundUpToNextPowerOf2(n);
 
   // don't have that much.  return null, unless we've ended.
   if (n > state.length) {