contentenc: add safer "bPool" pool variant; add pBlockPool

bPool verifies the lengths of slices going in and out.

Also, add a plaintext block pool - pBlockPool - and use
it for decryption.

1 files changed, 39 insertions, 0 deletions

diff --git a/internal/contentenc/bpool.go b/internal/contentenc/bpool.go
new file mode 100644
index 0000000..c4517d3
--- /dev/null
+++ b/internal/contentenc/bpool.go
@@ -0,0 +1,39 @@
+package contentenc
+
+import (
+	"log"
+	"sync"
+)
+
+// bPool is a byte slice pool
+type bPool struct {
+	sync.Pool
+	sliceLen int
+}
+
+func newBPool(sliceLen int) bPool {
+	return bPool{
+		Pool: sync.Pool{
+			New: func() interface{} { return make([]byte, sliceLen) },
+		},
+		sliceLen: sliceLen,
+	}
+}
+
+// Put grows the slice "s" to its maximum capacity and puts it into the pool.
+func (b *bPool) Put(s []byte) {
+	s = s[:cap(s)]
+	if len(s) != b.sliceLen {
+		log.Panicf("wrong len=%d, want=%d", len(s), b.sliceLen)
+	}
+	b.Pool.Put(s)
+}
+
+// Get returns a byte slice from the pool.
+func (b *bPool) Get() (s []byte) {
+	s = b.Pool.Get().([]byte)
+	if len(s) != b.sliceLen {
+		log.Panicf("wrong len=%d, want=%d", len(s), b.sliceLen)
+	}
+	return s
+}