Prevent writing output file over input file - closes #28

index.js

@@ -107,10 +107,14 @@ Sharp.prototype.resize = function(width, height) {
 
 Sharp.prototype.write = function(output, callback) {
   if (!output || output.length === 0) {
-    throw 'Invalid output';
+    callback('Invalid output');
+  } else {
+    if (this.options.inFile === output) {
+      callback('Cannot use same file for input and output');
     } else {
       this._sharp(output, callback);
     }
+  }
   return this;
 };
 

tests/unit.js

@@ -145,5 +145,12 @@ async.series([
         done();
       });
     });
+  },
+  // Attempt to output to input, should fail
+  function(done) {
+    sharp(inputJpg).write(inputJpg, function(err) {
+      assert(!!err);
+      done();
+    });
   }
 ]);