buffer: allow .write() offset to be at buffer end

Do not throw if the offset passed to `buf.write()` points to the end of the buffer. Fixes: #8127 PR-URL: #8154 Reviewed-By: James M Snell <[email protected]> Reviewed-By: Colin Ihrig <[email protected]> Reviewed-By: Michaël Zasso <[email protected]>

Author: addaleax

src/node_buffer.cc

@@ -714,7 +714,7 @@ void StringWrite(const FunctionCallbackInfo<Value>& args){
 size_t max_length;
 
 CHECK_NOT_OOB(ParseArrayIndex(args[1], 0, &offset));
-if (offset >= ts_obj_length)
+if (offset > ts_obj_length)
 return env->ThrowRangeError("Offset is out of bounds");
 
 CHECK_NOT_OOB(ParseArrayIndex(args[2], ts_obj_length - offset, &max_length));

test/parallel/test-buffer-alloc.js

@@ -358,6 +358,12 @@ writeTest.write('e', 3, 'ascii');
 writeTest.write('j',4,'ascii');
 assert.equal(writeTest.toString(),'nodejs');
 
+// Offset points to the end of the buffer
+// (see https://github.com/nodejs/node/issues/8127).
+assert.doesNotThrow(()=>{
+Buffer.alloc(1).write('',1,0);
+});
+
 // ASCII slice test
 {
 constasciiString='hello world';