Add an optional length argument to Buffer.write()

Fixes #243.
Fixes #1361.

doc/api/buffers.markdown

@@ -47,12 +47,12 @@ Allocates a new buffer using an `array` of octets.
 
 Allocates a new buffer containing the given `str`.
 
-### buffer.write(string, offset=0, encoding='utf8')
+### buffer.write(string, offset=0, length=buffer.length-offset, encoding='utf8')
 
-Writes `string` to the buffer at `offset` using the given encoding. Returns
-number of octets written.  If `buffer` did not contain enough space to fit
-the entire string, it will write a partial amount of the string.
-The method will not write partial characters.
+Writes `string` to the buffer at `offset` using the given encoding. `length` is
+the number of bytes to write. Returns number of octets written. If `buffer` did
+not contain enough space to fit the entire string, it will write a partial
+amount of the string. The method will not write partial characters.
 
 Example: write a utf8 string into a buffer, then print it
 

lib/buffer.js

@@ -92,15 +92,27 @@ SlowBuffer.prototype.toString = function(encoding, start, end) {
 };
 
 
-SlowBuffer.prototype.hexWrite = function(string, offset) {
-  var len = string.length;
+SlowBuffer.prototype.hexWrite = function(string, offset, length) {
   offset = +offset || 0;
+  var remaining = this.length - offset;
+  if (!length) {
+    length = remaining;
+  } else {
+    length = +length;
+    if (length > remaining) {
+      length = remaining;
+    }
+  }
 
   // must be an even number of digits
-  if (len % 2) {
+  var strLen = string.length;
+  if (strLen % 2) {
     throw new Error('Invalid hex string');
   }
-  for (var i = 0; i < len / 2; i++) {
+  if (length > strLen / 2) {
+    length = strLen / 2;
+  }
+  for (var i = 0; i < length; i++) {
     var byte = parseInt(string.substr(i * 2, 2), 16);
     if (isNaN(byte)) throw new Error('Invalid hex string');
     this[offset + i] = byte;
@@ -109,38 +121,53 @@ SlowBuffer.prototype.hexWrite = function(string, offset) {
 };
 
 
-SlowBuffer.prototype.write = function(string, offset, encoding) {
-  // Support both (string, offset, encoding)
-  // and the legacy (string, encoding, offset)
-  if (!isFinite(offset)) {
+SlowBuffer.prototype.write = function(string, offset, length, encoding) {
+  // Support both (string, offset, length, encoding)
+  // and the legacy (string, encoding, offset, length)
+  if (isFinite(offset)) {
+    if (!isFinite(length)) {
+      encoding = length;
+      length = undefined;
+    }
+  } else {  // legacy
     var swap = encoding;
     encoding = offset;
-    offset = swap;
+    offset = length;
+    length = swap;
   }
 
   offset = +offset || 0;
+  var remaining = this.length - offset;
+  if (!length) {
+    length = remaining;
+  } else {
+    length = +length;
+    if (length > remaining) {
+      length = remaining;
+    }
+  }
   encoding = String(encoding || 'utf8').toLowerCase();
 
   switch (encoding) {
     case 'hex':
-      return this.hexWrite(string, offset);
+      return this.hexWrite(string, offset, length);
 
     case 'utf8':
     case 'utf-8':
-      return this.utf8Write(string, offset);
+      return this.utf8Write(string, offset, length);
 
     case 'ascii':
-      return this.asciiWrite(string, offset);
+      return this.asciiWrite(string, offset, length);
 
     case 'binary':
-      return this.binaryWrite(string, offset);
+      return this.binaryWrite(string, offset, length);
 
     case 'base64':
-      return this.base64Write(string, offset);
+      return this.base64Write(string, offset, length);
 
     case 'ucs2':
     case 'ucs-2':
-      return this.ucs2Write(string, offset);
+      return this.ucs2Write(string, offset, length);
 
     default:
       throw new Error('Unknown encoding');
@@ -271,47 +298,61 @@ Buffer.prototype.set = function set(i, v) {
 };
 
 
-// write(string, offset = 0, encoding = 'utf8')
-Buffer.prototype.write = function(string, offset, encoding) {
-  if (!isFinite(offset)) {
+// write(string, offset = 0, length = buffer.length-offset, encoding = 'utf8')
+Buffer.prototype.write = function(string, offset, length, encoding) {
+  // Support both (string, offset, length, encoding)
+  // and the legacy (string, encoding, offset, length)
+  if (isFinite(offset)) {
+    if (!isFinite(length)) {
+      encoding = length;
+      length = undefined;
+    }
+  } else {  // legacy
     var swap = encoding;
     encoding = offset;
-    offset = swap;
+    offset = length;
+    length = swap;
   }
 
   offset = +offset || 0;
+  var remaining = this.length - offset;
+  if (!length) {
+    length = remaining;
+  } else {
+    length = +length;
+    if (length > remaining) {
+      length = remaining;
+    }
+  }
   encoding = String(encoding || 'utf8').toLowerCase();
 
-  // Make sure we are not going to overflow
-  var maxLength = this.length - offset;
-
   var ret;
   switch (encoding) {
     case 'hex':
-      ret = this.parent.hexWrite(string, this.offset + offset, maxLength);
+      ret = this.parent.hexWrite(string, this.offset + offset, length);
       break;
 
     case 'utf8':
     case 'utf-8':
-      ret = this.parent.utf8Write(string, this.offset + offset, maxLength);
+      ret = this.parent.utf8Write(string, this.offset + offset, length);
       break;
 
     case 'ascii':
-      ret = this.parent.asciiWrite(string, this.offset + offset, maxLength);
+      ret = this.parent.asciiWrite(string, this.offset + offset, length);
       break;
 
     case 'binary':
-      ret = this.parent.binaryWrite(string, this.offset + offset, maxLength);
+      ret = this.parent.binaryWrite(string, this.offset + offset, length);
       break;
 
     case 'base64':
       // Warning: maxLength not taken into account in base64Write
-      ret = this.parent.base64Write(string, this.offset + offset, maxLength);
+      ret = this.parent.base64Write(string, this.offset + offset, length);
       break;
 
     case 'ucs2':
     case 'ucs-2':
-      ret = this.parent.ucs2Write(string, this.offset + offset, maxLength);
+      ret = this.parent.ucs2Write(string, this.offset + offset, length);
       break;
 
     default:
@@ -1019,3 +1060,4 @@ Buffer.prototype.writeDouble = function(value, offset, endian) {
   verifIEEE754(value, 1.7976931348623157E+308, -1.7976931348623157E+308);
   IEEE754.writeIEEE754(buffer, value, offset, endian, 52, 8);
 };
+

test/simple/test-buffer.js

@@ -621,3 +621,50 @@ assert.equal(written, 9);
 written = buf.write('あいう\0'); // 3bytes * 3 + 1byte
 assert.equal(written, 10);
 
+// #243 Test write() with maxLength
+var buf = new Buffer(4);
+buf.fill(0xFF);
+var written = buf.write('abcd', 1, 2, 'utf8');
+console.log(buf);
+assert.equal(written, 2);
+assert.equal(buf[0], 0xFF);
+assert.equal(buf[1], 0x61);
+assert.equal(buf[2], 0x62);
+assert.equal(buf[3], 0xFF);
+
+buf.fill(0xFF);
+written = buf.write('abcd', 1, 4);
+console.log(buf);
+assert.equal(written, 3);
+assert.equal(buf[0], 0xFF);
+assert.equal(buf[1], 0x61);
+assert.equal(buf[2], 0x62);
+assert.equal(buf[3], 0x63);
+
+buf.fill(0xFF);
+written = buf.write('abcd', 'utf8', 1, 2);  // legacy style
+console.log(buf);
+assert.equal(written, 2);
+assert.equal(buf[0], 0xFF);
+assert.equal(buf[1], 0x61);
+assert.equal(buf[2], 0x62);
+assert.equal(buf[3], 0xFF);
+
+buf.fill(0xFF);
+written = buf.write('abcdef', 1, 2, 'hex');
+console.log(buf);
+assert.equal(written, 2);
+assert.equal(buf[0], 0xFF);
+assert.equal(buf[1], 0xAB);
+assert.equal(buf[2], 0xCD);
+assert.equal(buf[3], 0xFF);
+
+buf.fill(0xFF);
+written = buf.write('abcd', 0, 2, 'ucs2');
+console.log(buf);
+assert.equal(written, 2);
+assert.equal(buf[0], 0x61);
+assert.equal(buf[1], 0x00);
+assert.equal(buf[2], 0xFF);
+assert.equal(buf[3], 0xFF);
+