Add locking to patricia tree

Fixes race conditions in matchers. Impact on benchmarks:

name               old time/op    new time/op    delta
CMuxConnHTTP1-4       664ns ±19%     849ns ± 6%  +27.91%         (p=0.000 n=9+10)
CMuxConnHTTP2-4       745ns ±16%     699ns ± 9%     ~            (p=0.075 n=9+10)
CMuxConnHTTP1n2-4     930ns ±28%    1079ns ± 4%  +16.00%         (p=0.022 n=10+9)
CMuxConnHTTP2n1-4    1.18µs ±52%    0.98µs ±13%     ~           (p=1.000 n=10+10)

name               old alloc/op   new alloc/op   delta
CMuxConnHTTP1-4        256B ± 0%      256B ± 0%     ~     (all samples are equal)
CMuxConnHTTP2-4        288B ± 0%      288B ± 0%     ~     (all samples are equal)
CMuxConnHTTP1n2-4      288B ± 0%      288B ± 0%     ~     (all samples are equal)
CMuxConnHTTP2n1-4      288B ± 0%      288B ± 0%     ~     (all samples are equal)

name               old allocs/op  new allocs/op  delta
CMuxConnHTTP1-4        3.00 ± 0%      3.00 ± 0%     ~     (all samples are equal)
CMuxConnHTTP2-4        4.00 ± 0%      4.00 ± 0%     ~     (all samples are equal)
CMuxConnHTTP1n2-4      4.00 ± 0%      4.00 ± 0%     ~     (all samples are equal)
CMuxConnHTTP2n1-4      4.00 ± 0%      4.00 ± 0%     ~     (all samples are equal)

patricia.go

@@ -17,14 +17,18 @@ package cmux
 import (
 	"bytes"
 	"io"
+	"sync"
 )
 
 // patriciaTree is a simple patricia tree that handles []byte instead of string
 // and cannot be changed after instantiation.
 type patriciaTree struct {
 	root *ptNode
+	mu   struct {
+		sync.Mutex
 		buf []byte // preallocated buffer to read data while matching
 	}
+}
 
 func newPatriciaTree(bs ...[]byte) *patriciaTree {
 	max := 0
@@ -33,10 +37,10 @@ func newPatriciaTree(bs ...[]byte) *patriciaTree {
 			max = len(b)
 		}
 	}
-	return &patriciaTree{
+	t := patriciaTree{root: newNode(bs)}
-		root: newNode(bs),
+	t.mu.buf = make([]byte, max+1)
-		buf:  make([]byte, max+1),
+
-	}
+	return &t
 }
 
 func newPatriciaTreeString(strs ...string) *patriciaTree {
@@ -48,13 +52,19 @@ func newPatriciaTreeString(strs ...string) *patriciaTree {
 }
 
 func (t *patriciaTree) matchPrefix(r io.Reader) bool {
-	n, _ := io.ReadFull(r, t.buf)
+	t.mu.Lock()
-	return t.root.match(t.buf[:n], true)
+	defer t.mu.Unlock()
+
+	n, _ := io.ReadFull(r, t.mu.buf)
+	return t.root.match(t.mu.buf[:n], true)
 }
 
 func (t *patriciaTree) match(r io.Reader) bool {
-	n, _ := io.ReadFull(r, t.buf)
+	t.mu.Lock()
-	return t.root.match(t.buf[:n], false)
+	defer t.mu.Unlock()
+
+	n, _ := io.ReadFull(r, t.mu.buf)
+	return t.root.match(t.mu.buf[:n], false)
 }
 
 type ptNode struct {