fs: refactor fs module

PR-URL: #20764 Reviewed-By: Michaël Zasso <[email protected]> Reviewed-By: Joyee Cheung <[email protected]> Backport-PR-URL: #21172

Author: jasnell

lib/fs.js

@@ -0,0 +1,108 @@
+'use strict';
+
+const{ Buffer }=require('buffer');
+const{ FSReqWrap, close, read }=process.binding('fs');
+
+constkReadFileBufferLength=8*1024;
+
+functionreadFileAfterRead(err,bytesRead){
+constcontext=this.context;
+
+if(err)
+returncontext.close(err);
+
+if(bytesRead===0)
+returncontext.close();
+
+context.pos+=bytesRead;
+
+if(context.size!==0){
+if(context.pos===context.size)
+context.close();
+else
+context.read();
+}else{
+// unknown size, just read until we don't get bytes.
+context.buffers.push(context.buffer.slice(0,bytesRead));
+context.read();
+}
+}
+
+functionreadFileAfterClose(err){
+constcontext=this.context;
+constcallback=context.callback;
+letbuffer=null;
+
+if(context.err||err)
+returncallback(context.err||err);
+
+try{
+if(context.size===0)
+buffer=Buffer.concat(context.buffers,context.pos);
+elseif(context.pos<context.size)
+buffer=context.buffer.slice(0,context.pos);
+else
+buffer=context.buffer;
+
+if(context.encoding)
+buffer=buffer.toString(context.encoding);
+}catch(err){
+returncallback(err);
+}
+
+callback(null,buffer);
+}
+
+classReadFileContext{
+constructor(callback,encoding){
+this.fd=undefined;
+this.isUserFd=undefined;
+this.size=undefined;
+this.callback=callback;
+this.buffers=null;
+this.buffer=null;
+this.pos=0;
+this.encoding=encoding;
+this.err=null;
+}
+
+read(){
+letbuffer;
+letoffset;
+letlength;
+
+if(this.size===0){
+buffer=this.buffer=Buffer.allocUnsafeSlow(kReadFileBufferLength);
+offset=0;
+length=kReadFileBufferLength;
+}else{
+buffer=this.buffer;
+offset=this.pos;
+length=Math.min(kReadFileBufferLength,this.size-this.pos);
+}
+
+constreq=newFSReqWrap();
+req.oncomplete=readFileAfterRead;
+req.context=this;
+
+read(this.fd,buffer,offset,length,-1,req);
+}
+
+close(err){
+constreq=newFSReqWrap();
+req.oncomplete=readFileAfterClose;
+req.context=this;
+this.err=err;
+
+if(this.isUserFd){
+process.nextTick(functiontick(){
+req.oncomplete(null);
+});
+return;
+}
+
+close(this.fd,req);
+}
+}
+
+module.exports=ReadFileContext;