go/zodb/zeo: proto: Use enc.<X> and enc.as<X> to encode/decode type X

This is more uniform and will be followed by all data types in the next patch.
Here rename tid/oid pack/unpack routines correspondingly.
Add docstrings for X=tid|oid.

go/zodb/storage/zeo/proto.go

@@ -38,8 +38,8 @@ import (
 // msg represents 1 message.
 // arg is arbitrary argument(s) passed/received along ZEO call or reply.
 //
-// for objects in arg user code has to obtain them via encoding.*Unpack() and
-// set them via encoding.*Pack() methods that
+// for objects in arg user code has to obtain them via encoding.as*() and
+// set them via encoding.Tid(), encoding.Oid() and other similar methods that
 // convert application-level data into objects properly corresponding to wire
 // encoding of messages.
 type msg struct {
@@ -165,20 +165,24 @@ func (e encoding) xuint64Pack(v uint64) string {
 	}
 }
 
-func (e encoding) tidPack(tid zodb.Tid) string {
+// Tid converts tid into corresponding object appropriate for encoding e.
+func (e encoding) Tid(tid zodb.Tid) string {
 	return e.xuint64Pack(uint64(tid))
 }
 
-func (e encoding) oidPack(oid zodb.Oid) string {
+// Oid converts oid into corresponding object appropriate for encoding e.
+func (e encoding) Oid(oid zodb.Oid) string {
 	return e.xuint64Pack(uint64(oid))
 }
 
-func (e encoding) tidUnpack(xv interface{}) (zodb.Tid, bool) {
+// asTid tries to retrieve Tid from corresponding object decoded via encoding e.
+func (e encoding) asTid(xv interface{}) (zodb.Tid, bool) {
 	v, ok := e.xuint64Unpack(xv)
 	return zodb.Tid(v), ok
 }
 
-func (e encoding) oidUnpack(xv interface{}) (zodb.Oid, bool) {
+// asOid tries to retrieve Oid from corresponding object decoded via encoding e.
+func (e encoding) asOid(xv interface{}) (zodb.Oid, bool) {
 	v, ok := e.xuint64Unpack(xv)
 	return zodb.Oid(v), ok
 }

go/zodb/storage/zeo/zeo.go

@@ -63,7 +63,7 @@ func (z *zeo) Sync(ctx context.Context) (head zodb.Tid, err error) {
 		return zodb.InvalidTid, err
 	}
 
-	head, ok := z.link.enc.tidUnpack(xhead)
+	head, ok := z.link.enc.asTid(xhead)
 	if !ok {
 		return zodb.InvalidTid, rpc.ereplyf("got %v; expect tid", xhead)
 	}
@@ -80,7 +80,7 @@ func (z *zeo) Load(ctx context.Context, xid zodb.Xid) (buf *mem.Buf, serial zodb
 
 	rpc := z.rpc("loadBefore")
 	enc := z.link.enc
-	xres, err := rpc.call(ctx, enc.oidPack(xid.Oid), enc.tidPack(xid.At+1)) // XXX at2Before
+	xres, err := rpc.call(ctx, enc.Oid(xid.Oid), enc.Tid(xid.At+1)) // XXX at2Before
 	if err != nil {
 		return nil, 0, err
 	}
@@ -92,7 +92,7 @@ func (z *zeo) Load(ctx context.Context, xid zodb.Xid) (buf *mem.Buf, serial zodb
 	}
 
 	data, ok1 := res[0].(string)
-	serial, ok2 := enc.tidUnpack(res[1])
+	serial, ok2 := enc.asTid(res[1])
 	// next_serial (res[2]) - just ignore
 
 	if !(ok1 && ok2) {
@@ -184,7 +184,7 @@ func (r rpc) excError(exc string, argv []interface{}) error {
 			return r.ereplyf("poskeyerror: got %#v; expect 1-tuple", argv...)
 		}
 
-		oid, ok := r.zlink.enc.oidUnpack(argv[0])
+		oid, ok := r.zlink.enc.asOid(argv[0])
 		if !ok {
 			return r.ereplyf("poskeyerror: got (%v); expect (oid)", argv[0])
 		}
@@ -361,7 +361,7 @@ func openByURL(ctx context.Context, u *url.URL, opt *zodb.DriverOptions) (_ zodb
 		}
 	}
 
-	lastTid, ok := zlink.enc.tidUnpack(xlastTid) // XXX -> xlastTid -> scan
+	lastTid, ok := zlink.enc.asTid(xlastTid) // XXX -> xlastTid -> scan
 	if !ok {
 		return nil, zodb.InvalidTid, rpc.ereplyf("got %v; expect tid", xlastTid)
 	}