Implement large object support

This patch implements large object support as described in
http://www.postgresql.org/docs/current/static/largeobjects.html

fastpath.go

@@ -0,0 +1,110 @@
+package pgx
+
+import (
+	"encoding/binary"
+)
+
+type fastpathArg []byte
+
+func newFastpath(cn *Conn) *fastpath {
+	return &fastpath{cn: cn, fns: make(map[string]Oid)}
+}
+
+type fastpath struct {
+	cn  *Conn
+	fns map[string]Oid
+}
+
+func (f *fastpath) functionOID(name string) Oid {
+	return f.fns[name]
+}
+
+func (f *fastpath) addFunction(name string, oid Oid) {
+	f.fns[name] = oid
+}
+
+func (f *fastpath) addFunctions(rows *Rows) error {
+	for rows.Next() {
+		var name string
+		var oid Oid
+		if err := rows.Scan(&name, &oid); err != nil {
+			return err
+		}
+		f.addFunction(name, oid)
+	}
+	return rows.Err()
+}
+
+type fpArg []byte
+
+func fpIntArg(n int32) fpArg {
+	res := make([]byte, 4)
+	binary.BigEndian.PutUint32(res, uint32(n))
+	return res
+}
+
+func fpInt64Arg(n int64) fpArg {
+	res := make([]byte, 8)
+	binary.BigEndian.PutUint64(res, uint64(n))
+	return res
+}
+
+func (f *fastpath) Call(oid Oid, args []fpArg) (res []byte, err error) {
+	wbuf := newWriteBuf(f.cn.wbuf[:0], 'F') // function call
+	wbuf.WriteInt32(int32(oid))             // function object id
+	wbuf.WriteInt16(1)                      // # of argument format codes
+	wbuf.WriteInt16(1)                      // format code: binary
+	wbuf.WriteInt16(int16(len(args)))       // # of arguments
+	for _, arg := range args {
+		wbuf.WriteInt32(int32(len(arg))) // length of argument
+		wbuf.WriteBytes(arg)             // argument value
+	}
+	wbuf.WriteInt16(1) // response format code (binary)
+	wbuf.closeMsg()
+
+	if _, err := f.cn.conn.Write(wbuf.buf); err != nil {
+		return nil, err
+	}
+
+	for {
+		var t byte
+		var r *msgReader
+		t, r, err = f.cn.rxMsg()
+		if err != nil {
+			return nil, err
+		}
+		switch t {
+		case 'V': // FunctionCallResponse
+			data := r.readBytes(r.readInt32())
+			res = make([]byte, len(data))
+			copy(res, data)
+		case 'Z': // Ready for query
+			f.cn.rxReadyForQuery(r)
+			// done
+			return
+		default:
+			if err := f.cn.processContextFreeMsg(t, r); err != nil {
+				return nil, err
+			}
+		}
+	}
+}
+
+func (f *fastpath) CallFn(fn string, args []fpArg) ([]byte, error) {
+	return f.Call(f.functionOID(fn), args)
+}
+
+func fpInt32(data []byte, err error) (int32, error) {
+	if err != nil {
+		return 0, err
+	}
+	n := int32(binary.BigEndian.Uint32(data))
+	return n, nil
+}
+
+func fpInt64(data []byte, err error) (int64, error) {
+	if err != nil {
+		return 0, err
+	}
+	return int64(binary.BigEndian.Uint64(data)), nil
+}