Buffer.copy() should liberally allow empty copies.

src/node_buffer.cc

@@ -305,6 +305,11 @@ Handle<Value> Buffer::Copy(const Arguments &args) {
             "sourceEnd < sourceStart")));
   }
 
+  // Copy 0 bytes; we're done
+  if (source_end == source_start) {
+    return scope.Close(Integer::New(0));
+  }
+
   if (target_start < 0 || target_start >= target->length()) {
     return ThrowException(Exception::Error(String::New(
             "targetStart out of bounds")));

test/simple/test-buffer.js

@@ -94,7 +94,7 @@ assert.strictEqual('sourceStart out of bounds', caught_error.message);
 // try to copy starting after the end of b
 caught_error = null;
 try {
-    var copied = b.copy(c, 0, 1024, 1024);
+    var copied = b.copy(c, 0, 1024, 1025);
 } catch (err) {
     caught_error = err;
 }
@@ -110,6 +110,25 @@ try {
 }
 assert.strictEqual('sourceEnd out of bounds', caught_error.message);
 
+// try to create 0-length buffers
+new Buffer('');
+new Buffer('', 'ascii');
+new Buffer('', 'binary');
+new Buffer(0);
+
+// try to write a 0-length string beyond the end of b
+b.write('', 1024);
+b.write('', 2048);
+
+// try to copy 0 bytes worth of data into an empty buffer
+b.copy(new Buffer(0), 0, 0, 0);
+
+// try to copy 0 bytes past the end of the target buffer
+b.copy(new Buffer(0), 1, 1, 1);
+b.copy(new Buffer(1), 1, 1, 1);
+
+// try to copy 0 bytes from past the end of the source buffer
+b.copy(new Buffer(1), 0, 2048, 2048);
 
 var asciiString = "hello world";
 var offset = 100;