Async not working as expected - node.js

Question

I have several files that I need to write to remote server. As you can see in my code, I'm reading those files inside async scope and writing them to remote server as they become available. Instead of all files, only the last file is successfully transfer to remote server. I put console output statement inside readfile callback function and check path variable value. It outputs the last filename three times. So I'm suspecting that the last readfile call is overwriting the previous ones. Shouldn't async wait for the callback function call before it moves onto next iteration?
var attachments = ['1.jpg','2.jpg','3.jpg'];
var request = require('request');
var option = {
url: "http://www.xxxxxxx.xxxx",
headers: {"content-type": "multipart/form-data"}
};
async.each(attachments, function(att, callback){
path = imagePath + "\\" + att;
fstat = fs.statSync(path);
fsize = fstat["size"];
fs.readFile(path, function(err, data){
if(err)
{
return callback(err);
}
else{
option.body = data;
request.post(option,function(err,response,body) {
if (err) {
return callback(err);
}
else{
console.log(option);
callback();
}
});
}
});
}, function(err){
if (err) {
console.log(err);
}
else
{
console.log("finish");
}
});

Answer 1

Shouldn't async wait for the callback function call before it moves onto next iteration?
No, you're describing what async.eachSeries does. async.each runs each all tasks in parallel.
Your problem is that here is only one option object here. You perform console.log(option) inside of a function asynchronously run by request.post. That callback function runs after every request.post has been run. Since you only have on option object, it will have the final body value it was assigned by the last fs.readFile callback.
The solution here is to have every each function call create its own option object:
async.each(attachments, function(att, callback){
var option = {
url: "http://www.xxxxxxx.xxxx",
headers: {"content-type": "multipart/form-data"}
};