crypto: free excessive memory in NodeBIO

Before this commit NodeBIO never shrank, possibly consuming a lot of
memory (depending on reader's haste).

All buffers between write_head's child and read_head should be
deallocated on read, leaving only space left in write_head and in the
next buffer.

1 files changed, 24 insertions, 0 deletions

diff --git a/src/node_crypto_bio.cc b/src/node_crypto_bio.cc
index 52e5e78274..64d9efaf04 100644
--- a/src/node_crypto_bio.cc
+++ b/src/node_crypto_bio.cc
@@ -210,10 +210,34 @@ size_t NodeBIO::Read(char* out, size_t size) {
   assert(expected == bytes_read);
   length_ -= bytes_read;
 
+  // Free all empty buffers, but write_head's child
+  FreeEmpty();
+
   return bytes_read;
 }
 
 
+void NodeBIO::FreeEmpty() {
+  Buffer* child = write_head_->next_;
+  if (child == write_head_ || child == read_head_)
+    return;
+  Buffer* cur = child->next_;
+  if (cur == write_head_ || cur == read_head_)
+    return;
+
+  while (cur != read_head_) {
+    assert(cur != write_head_);
+    assert(cur->write_pos_ == cur->read_pos_);
+
+    Buffer* next = cur->next_;
+    child->next_ = next;
+    delete cur;
+
+    cur = next;
+  }
+}
+
+
 size_t NodeBIO::IndexOf(char delim, size_t limit) {
   size_t bytes_read = 0;
   size_t max = Length() > limit ? limit : Length();