setup shadowsocks server on ubuntu 16.04

install

sudo apt-get install software-properties-common -y
sudo add-apt-repository ppa:max-c-lv/shadowsocks-libev -y
sudo apt-get update
sudo apt install shadowsocks-libev

configure

sudo vim /etc/shadowsocks-libev/config.json
{
    "server":"10.128.0.2",
    "server_port":8911,
    "local_port":1008,
    "password":"jesusislove",
    "timeout":60,
    "method":"chacha20-ietf-poly1305"
}

start server

sudo systemctl start shadowsocks-libev

google compute engine

If the server are running on a google compute engine,
You need to setup a firewall rules for the server port(8911, written in config.json).
shadowsocks
Apply to all
IP ranges: 0.0.0.0/0
tcp:8911, udp:8911
Allow

client configuration

iOS
Android
Shadowsocks for Android / iOS also accepts BASE64 encoded URI format configs:

ss://BASE64-ENCODED-STRING-WITHOUT-PADDING#TAG 

Where the plain URI should be:

ss://method:password@hostname:port 

Quick Guide

他的力量若不够

利未记五7、11

7「他的力量若不够献一只羊羔，就要因所犯的罪，把两只斑鸠或是两只雏鸽带到耶和华面前为赎愆祭：一只作赎罪祭，一只作燔祭。

11「他的力量若不够献两只斑鸠或是两只雏鸽，就要因所犯的罪带供物来，就是细面伊法十分之一为赎罪祭；不可加上油，也不可加上乳香，因为是赎罪祭。

Photo by Brooke Lark / Unsplash

expressjs : implement http file download

Express helper, res.download

Express has a helper for this:

app.get('/xxx', function(req, res){ 

  var file = __dirname + '/xxx'; 

  res.download(file); // Set disposition and send it. 

}); 

http file download header

https://developer.mozilla.org/en-US/docs/Web/HTTP/Headers/Content-Disposition

res.setHeader('Content-disposition', 'attachment; filename=xxx'); 

iptables, clean all rules

command

sudo iptables -P INPUT ACCEPT
sudo iptables -F

list all rules

sudo iptables -L
Chain INPUT (policy ACCEPT)
target prot opt source destination
Chain FORWARD (policy DROP)
target prot opt source destination
Chain OUTPUT (policy ACCEPT)
target prot opt source destination

node.js : file upload via express and multer

Form-based File Upload in HTML

https://tools.ietf.org/html/rfc1867

Express

Fast, unopinionated, minimalist web framework for node.

Multer

Multer is a node.js middleware for handling multipart/form-data, which is primarily used for uploading files. It is written on top of busboy for maximum efficiency.
NOTE: Multer will not process any form which is not multipart (multipart/form-data).

Client Codes(index.html)

<script type="text/javascript">
function upload(postUrl, fieldName, files)
{
  var formData = new FormData();
  formData.append(fieldName, files);

  var req = new XMLHttpRequest();
  req.open("POST", postUrl);
  req.onload = function(event) { console.log(event.target.responseText); };
  req.send(formData);
}
function onchange() {
  for (let i = 0; i < this.files.length; i++) {
    upload('/uploads', 'uploadfile', this.files[i]);
  }
}
window.onload = function () {
var  input = document.getElementById('file');
input.addEventListener('change', onchange);
}
</script>
<input type="file" id="file" name="file" multiple onchange="upload" />

Server Codes

var express = require('express')
var app = express()
var path = require('path')
var tmpdir = require('os').tmpdir
var upload = require('multer')({dest: tmpdir()})

app.get('/', function (req, res) {
  var indexhtml = 'index.html';
  var tmp = path.resolve(indexhtml);
  res.sendFile(tmp);
})

app.post('/uploads', upload.single('uploadfile'), function (req, res, next) {
  var rp = {'file':req.file, 'body' : req.body, 'ip':req.ip};
  res.send(rp);
})

app.listen(3000)

Run express Server

node index.js

Test

As you can see in the console, the file was uploaded to server and saved with file name of "/tmp/e2f2d3ae260814fc4b589a13d5981aec".

Print all combination of that select n elements from 1,2,3,...,m.

"C" is for "combination". A combination is an un-ordered collection of distinct elements, usually of a prescribed size and taken from a given set.

   C(n, r) = n!/[r!(n-r)!] 

#include <stdio.h>
#include <sys/time.h>

int a[1001];

// selected n numbers stored in array a
// a[1], a[2], ... , a[n]
// a[i+1] > a[i]
// a[i] - i <= m - n + 1

void comos(int n, int m) {
  int i,j;
  if (n > m)
    return;
  for (i = 1; i <= n; i++) {
    a[i] = i;
  }
  int cur = n;
  do {
    if (a[cur]-cur <= m - n) {
      for (i = 1; i <= n; i++)
        printf("%d ", a[i]);
      printf("\n");
      a[cur]++;
      continue;
    } else {
      if (cur == 1) {
        break;
      }
      a[--cur]++;
      for (i = 1; i <= (n-cur); i++)
        a[cur+i] = a[cur] + i;
      if (a[cur] - cur < m - n + 1)
        cur=n;
    }
  } while(1);
}

int main() {
  int N, M;
  while (scanf("%d %d", &N, &M) != EOF) {
    if (N <= M) {
      struct timeval begin, end;
      gettimeofday(&begin, 0);
      comos(N, M);
      gettimeofday(&end, 0);
      printf("print comos(%d, %d) used %ld microseconds\n", N, M, end.tv_usec-begin.tv_usec);
    } else {
      printf("Invalid Input, %d <= %d is false\n", N, M);
    }
  }
  return 0;
}

1 5
1
2
3
4
5
print comos(1, 5) used 116 microseconds
2 5
1 2
1 3
1 4
1 5
2 3
2 4
2 5
3 4
3 5
4 5
print comos(2, 5) used 171 microseconds
3 5
1 2 3
1 2 4
1 2 5
1 3 4
1 3 5
1 4 5
2 3 4
2 3 5
2 4 5
3 4 5
print comos(3, 5) used 153 microseconds
4 5
1 2 3 4
1 2 3 5
1 2 4 5
1 3 4 5
2 3 4 5
print comos(4, 5) used 97 microseconds
5 5
1 2 3 4 5
print comos(5, 5) used 33 microseconds

all learning is understanding relationships

James Comer says that no significant learning can occur without a significant relationship.
George Washington Carver says all learning is understanding relationships.

"You were chosen to be in my class because I am the best teacher and you are the best students, they put us all together so we could show everybody else how to do it."

"Really?"

"Really. We have to show the other classes how to do it, so when we walk down the hall, people will notice us, so you can't make noise. You just have to strut."

"I am somebody. I was somebody when I came. I'll be a better somebody when I leave. I am powerful, and I am strong. I deserve the education that I get here. I have things to do, people to impress, and places to go."

"Yeah!"

You say it long enough, it starts to be a part of you.