Optimize zlib reader and consolidate sync.pools

Expands on the optimisations from https://github.com/fluxcd/go-git/pull/5
and ensures that zlib reader does not need to recreate a deflate
dictionary at every use.

The use of sync pools was consolidated into a new sync utils package.

name       old time/op    new time/op    delta
Parser-16    7.51ms ± 3%    7.71ms ± 6%     ~     (p=0.222 n=5+5)

name       old alloc/op   new alloc/op   delta
Parser-16    4.65MB ± 3%    1.90MB ± 3%  -59.06%  (p=0.008 n=5+5)

name       old allocs/op  new allocs/op  delta
Parser-16     3.48k ± 0%     3.32k ± 0%   -4.57%  (p=0.016 n=5+4)

Signed-off-by: Paulo Gomes <pjbgf@linux.com>

1 files changed, 29 insertions, 0 deletions

diff --git a/utils/sync/bufio.go b/utils/sync/bufio.go
new file mode 100644
index 0000000..5009ea8
--- /dev/null
+++ b/utils/sync/bufio.go
@@ -0,0 +1,29 @@
+package sync
+
+import (
+	"bufio"
+	"io"
+	"sync"
+)
+
+var bufioReader = sync.Pool{
+	New: func() interface{} {
+		return bufio.NewReader(nil)
+	},
+}
+
+// GetBufioReader returns a *bufio.Reader that is managed by a sync.Pool.
+// Returns a bufio.Reader that is resetted with reader and ready for use.
+//
+// After use, the *bufio.Reader should be put back into the sync.Pool
+// by calling PutBufioReader.
+func GetBufioReader(reader io.Reader) *bufio.Reader {
+	r := bufioReader.Get().(*bufio.Reader)
+	r.Reset(reader)
+	return r
+}
+
+// PutBufioReader puts reader back into its sync.Pool.
+func PutBufioReader(reader *bufio.Reader) {
+	bufioReader.Put(reader)
+}