support reading from a pipe, such as stdin

example.js

@@ -1,14 +1,19 @@
 'use strict';
 
 const lineByLine = require('./readlines.js');
-const liner = new lineByLine('./test/fixtures/normalFile.txt');
+
+const fname = process.argv.length > 2 ? process.argv[2] : './test/fixtures/normalFile.txt';
+const enc   = process.argv.length > 3 ? process.argv[3] : 'ascii';
+console.log('Reading', enc, 'encoded file', fname);
+
+const liner = new lineByLine(fname === '-' ? 0 : fname);
 
 let line;
 let lineNumber = 0;
 
 while (line = liner.next()) {
-    console.log('Line ' + lineNumber + ': ' + line.toString('ascii'));
+    console.log('Line ' + lineNumber + ': ' + line.toString(enc));
     lineNumber++;
 }
 
-console.log('end of line reached');
+console.log('end of file reached');

readlines.js

@@ -47,6 +47,7 @@ class LineByLine {
     reset() {
         this.eofReached = false;
         this.linesCache = [];
+        this.seekable = true;
         this.fdPosition = 0;
     }
 
@@ -87,9 +88,18 @@ class LineByLine {
         let bytesRead;
         const buffers = [];
         do {
-            const readBuffer = new Buffer(this.options.readChunk);
+            const readBuffer = Buffer.alloc(this.options.readChunk);
 
-            bytesRead = fs.readSync(this.fd, readBuffer, 0, this.options.readChunk, this.fdPosition);
+            if (this.seekable) {
+                try {
+                    bytesRead = fs.readSync(this.fd, readBuffer, 0, this.options.readChunk, this.fdPosition);
+                } catch (e) {
+                    this.seekable = false;
+                }
+            }
+            if (!this.seekable) {
+                bytesRead = fs.readSync(this.fd, readBuffer, 0, this.options.readChunk);
+            }
             totalBytesRead = totalBytesRead + bytesRead;
 
             this.fdPosition = this.fdPosition + bytesRead;
@@ -100,10 +110,11 @@ class LineByLine {
         let bufferData = Buffer.concat(buffers);
 
         if (bytesRead < this.options.readChunk) {
-            this.eofReached = true;
             bufferData = bufferData.slice(0, totalBytesRead);
         }
 
+        this.eofReached = bytesRead === 0;
+
         if (totalBytesRead) {
             this.linesCache = this._extractLines(bufferData);
 
@@ -116,11 +127,12 @@ class LineByLine {
     }
 
     next() {
-        if (!this.fd) return false;
+        if (this.fd === null) return false;
 
         let line = false;
 
         if (this.eofReached && this.linesCache.length === 0) {
+            this.close();
             return line;
         }
 

test/readlines.test.js

@@ -127,6 +127,7 @@ test('should correctly processes NULL character in lines', (t) => {
     t.equals(liner.next().toString(), 'line wi'+String.fromCharCode(0)+'th null', 'line 1: line with null');
     t.equals(liner.next().toString(), 'another line without null', 'line 2: another line without null');
 
+    t.equals(liner.next(), false, 'line 3: false');
     t.equals(liner.fd, null, 'fd is null');
     t.end();
 })