Update libkv dependency

vendor/golang.org/x/net/http2/hpack/hpack.go

@@ -61,7 +61,7 @@ func (hf HeaderField) String() string {
 func (hf HeaderField) Size() uint32 {
 	// http://http2.github.io/http2-spec/compression.html#rfc.section.4.1
 	// "The size of the dynamic table is the sum of the size of
-	// its entries.  The size of an entry is the sum of its name's
+	// its entries. The size of an entry is the sum of its name's
 	// length in octets (as defined in Section 5.2), its value's
 	// length in octets (see Section 5.2), plus 32.  The size of
 	// an entry is calculated using the length of the name and
@@ -102,6 +102,7 @@ func NewDecoder(maxDynamicTableSize uint32, emitFunc func(f HeaderField)) *Decod
 		emit:        emitFunc,
 		emitEnabled: true,
 	}
+	d.dynTab.table.init()
 	d.dynTab.allowedMaxSize = maxDynamicTableSize
 	d.dynTab.setMaxSize(maxDynamicTableSize)
 	return d
@@ -154,12 +155,9 @@ func (d *Decoder) SetAllowedMaxDynamicTableSize(v uint32) {
 }
 
 type dynamicTable struct {
-	// ents is the FIFO described at
 	// http://http2.github.io/http2-spec/compression.html#rfc.section.2.3.2
-	// The newest (low index) is append at the end, and items are
-	// evicted from the front.
-	ents           []HeaderField
-	size           uint32
+	table          headerFieldTable
+	size           uint32 // in bytes
 	maxSize        uint32 // current maxSize
 	allowedMaxSize uint32 // maxSize may go up to this, inclusive
 }
@@ -169,95 +167,45 @@ func (dt *dynamicTable) setMaxSize(v uint32) {
 	dt.evict()
 }
 
-// TODO: change dynamicTable to be a struct with a slice and a size int field,
-// per http://http2.github.io/http2-spec/compression.html#rfc.section.4.1:
-//
-//
-// Then make add increment the size. maybe the max size should move from Decoder to
-// dynamicTable and add should return an ok bool if there was enough space.
-//
-// Later we'll need a remove operation on dynamicTable.
-
 func (dt *dynamicTable) add(f HeaderField) {
-	dt.ents = append(dt.ents, f)
+	dt.table.addEntry(f)
 	dt.size += f.Size()
 	dt.evict()
 }
 
-// If we're too big, evict old stuff (front of the slice)
+// If we're too big, evict old stuff.
 func (dt *dynamicTable) evict() {
-	base := dt.ents // keep base pointer of slice
-	for dt.size > dt.maxSize {
-		dt.size -= dt.ents[0].Size()
-		dt.ents = dt.ents[1:]
+	var n int
+	for dt.size > dt.maxSize && n < dt.table.len() {
+		dt.size -= dt.table.ents[n].Size()
+		n++
 	}
-
-	// Shift slice contents down if we evicted things.
-	if len(dt.ents) != len(base) {
-		copy(base, dt.ents)
-		dt.ents = base[:len(dt.ents)]
-	}
-}
-
-// constantTimeStringCompare compares string a and b in a constant
-// time manner.
-func constantTimeStringCompare(a, b string) bool {
-	if len(a) != len(b) {
-		return false
-	}
-
-	c := byte(0)
-
-	for i := 0; i < len(a); i++ {
-		c |= a[i] ^ b[i]
-	}
-
-	return c == 0
-}
-
-// Search searches f in the table. The return value i is 0 if there is
-// no name match. If there is name match or name/value match, i is the
-// index of that entry (1-based). If both name and value match,
-// nameValueMatch becomes true.
-func (dt *dynamicTable) search(f HeaderField) (i uint64, nameValueMatch bool) {
-	l := len(dt.ents)
-	for j := l - 1; j >= 0; j-- {
-		ent := dt.ents[j]
-		if !constantTimeStringCompare(ent.Name, f.Name) {
-			continue
-		}
-		if i == 0 {
-			i = uint64(l - j)
-		}
-		if f.Sensitive {
-			continue
-		}
-		if !constantTimeStringCompare(ent.Value, f.Value) {
-			continue
-		}
-		i = uint64(l - j)
-		nameValueMatch = true
-		return
-	}
-	return
+	dt.table.evictOldest(n)
 }
 
 func (d *Decoder) maxTableIndex() int {
-	return len(d.dynTab.ents) + len(staticTable)
+	// This should never overflow. RFC 7540 Section 6.5.2 limits the size of
+	// the dynamic table to 2^32 bytes, where each entry will occupy more than
+	// one byte. Further, the staticTable has a fixed, small length.
+	return d.dynTab.table.len() + staticTable.len()
 }
 
 func (d *Decoder) at(i uint64) (hf HeaderField, ok bool) {
-	if i < 1 {
+	// See Section 2.3.3.
+	if i == 0 {
 		return
 	}
+	if i <= uint64(staticTable.len()) {
+		return staticTable.ents[i-1], true
+	}
 	if i > uint64(d.maxTableIndex()) {
 		return
 	}
-	if i <= uint64(len(staticTable)) {
-		return staticTable[i-1], true
-	}
-	dents := d.dynTab.ents
-	return dents[len(dents)-(int(i)-len(staticTable))], true
+	// In the dynamic table, newer entries have lower indices.
+	// However, dt.ents[0] is the oldest entry. Hence, dt.ents is
+	// the reversed dynamic table.
+	dt := d.dynTab.table
+	return dt.ents[dt.len()-(int(i)-staticTable.len())], true
 }
 
 // Decode decodes an entire block.
@@ -307,7 +255,7 @@ func (d *Decoder) Write(p []byte) (n int, err error) {
 		err = d.parseHeaderFieldRepr()
 		if err == errNeedMore {
 			// Extra paranoia, making sure saveBuf won't
-			// get too large.  All the varint and string
+			// get too large. All the varint and string
 			// reading code earlier should already catch
 			// overlong things and return ErrStringLength,
 			// but keep this as a last resort.