calendar_monthschedulea few secondscategory其他

【程式語言】What's new in C++17

Structured Bindings

1
auto [a, b, c] = tuple('a', 1, 0.5);
1
2
3
4
5
map<int, int> mymap = {{1, 2}, {3, 4}};

for (const auto& [key, value] : mymap) {
    // ...
}
1
2
3
for (auto [a, b] = tuple(0, 'a'); a < 5; a++) {
    // ...
}

Template Argument Deduction

c++17
1
auto p = pair(2, 4.5);
c++14
1
auto p = pair<int, double>(2, 4.5);

Selection Initialization

1
2
3
if (auto a = getval(); a < 10) {
    // ...
}
1
2
3
switch (auto ch = getnext(); ch) {
    // ...
}
  1. https://www.fluentcpp.com/2018/06/19/3-simple-c17-features-that-will-make-your-code-simpler/
  2. https://hackernoon.com/a-tour-of-c-17-if-constexpr-3ea62f62ff65
  3. https://stackoverflow.com/questions/38060436/what-are-the-new-features-in-c17
Read more
calendar_monthschedule3 minutescategory其他

【程式語言】Python 的奇淫技巧

列了一些我新發現的各種花招

Function Attributes (python 2.1)

PEP 232

1
2
3
4
5
6
7
8
9
def a():
    a.count += 1

a.count = 0

for i in range(10):
    a()

print(a.count) # 10

跟 C++ 中，在 function 裡面宣告 static 變數差不多

Keyword-Only Arguments (python 3.0)

PEP 3102

1
2
def func(a, b, *, c = None):
    pass
  • func(1, 2, 3) 不行
  • func(1, 2, c = 3) 這樣才合法

Additional Unpacking Generalizations (python 3.5)

PEP 448

1
2
3
a = [1, 2, 3]
b = [*a, 4, 5]
print(b) # [1, 2, 3, 4, 5]

Merge Dicts

1
2
3
4
a = {1: 2}
b = {3: 4}
c = {**a, **b}
print(c) # {1: 2, 3: 4}

Metaclasses

Python Metaclasses

1
2
3
4
5
6
7
8
9
10
11
12
13
class A:
    pass

B = type('B',
         (A,),
         {
            'attr': 10,
            'func': lambda obj: obj.attr
         })

b = B()
print(b.attr)   # 10
print(b.func()) # 10
正常寫法
1
2
3
4
5
6
7
8
9
10
11
class A:
    pass

class B(A):
    attr = 10
    def func(self):
        return self.attr

b = B()
print(b.attr)   # 10
print(b.func()) # 10

看看就好xD

shallow vs deep copy

Shallow vs Deep Copying of Python Objects

assign

1
2
3
4
5
6
7
8
9
10
a = [[1, 2, 3], [4, 5, 6]]
b = a

b.append('hello')
b[0].append('world')

print(a)
# [[1, 2, 3, 'world'], [4, 5, 6], 'hello']
print(b)
# [[1, 2, 3, 'world'], [4, 5, 6], 'hello']

copy

1
2
3
4
5
6
7
8
9
10
11
12
import copy

a = [[1, 2, 3], [4, 5, 6]]
b = copy.copy(a)

b.append('hello')
b[0].append('world')

print(a)
# [[1, 2, 3, 'world'], [4, 5, 6]]
print(b)
# [[1, 2, 3, 'world'], [4, 5, 6], 'new object']

deepcopy

1
2
3
4
5
6
7
8
9
10
11
12
import copy

a = [[1, 2, 3], [4, 5, 6]]
b = copy.deepcopy(a)

b.append('hello')
b[0].append('world')

print(a)
# [[1, 2, 3], [4, 5, 6]]
print(b)
# [[1, 2, 3, 'world'], [4, 5, 6], 'new object']

  • copy.copy (shallow) 只複製該物件，不會複製子物件
  • copy.deepcopy (deep) 會遞迴複製所有子物件

shallow copy on list

1
2
a = [1, 2, 3]
b = list(a)
1
2
a = [1, 2, 3]
b = a[:]
1
2
a = [1, 2, 3]
b = a.copy()
1
2
3
4
import copy

a = [1, 2, 3]
b = copy.copy(a)

annotations

function annotations

1
2
3
4
5
def func(a: int, b: list) -> int:
    pass

print(func.__annotations__)
# {'a': <class 'int'>, 'b': <class 'list'>, 'return': <class 'int'>}

class annotations

1
2
3
4
5
class A():
    var: int

print(A.__annotations__)
# {'var': <class 'int'>}

variable annotations

1
2
3
4
5
a: int
b: int = 2

print(__annotations__)
# {'a': <class 'int'>, 'b': <class 'int'>}

intern string

1
2
s = 'hello'
s = sys.intern(s)

把字串存進快取池，相同的字串只會存一次
做字串比對會比較快且節省空間

  1. http://guilload.com/python-string-interning/
  2. http://www.laurentluce.com/posts/python-string-objects-implementation/
Read more
calendar_monthschedule7 minutescategory其他

【指令怎麼用】SSH 的十大妙用

ssh config

~/.ssh/config
1
2
3
4
Host vps
    HostName 123.45.67.89
    User oalieno
    Port 22000

每次都打一長串的參數很麻煩，可以先在 ~/.ssh/config 設定好
像上面這樣設定好後 ssh vps 就等同於 ssh -p 22000 oalieno@123.45.67.89

IdentityFile

~/.ssh/config
1
2
3
4
Host vps
    HostName 123.45.67.89
    User oalieno
    IdentityFile ~/.ssh/id_rsa

IdentityFile 就是指定要用哪個 key，等同於 -i ~/.ssh/id_rsa
預設會抓 id_*.pub 中最新的 ( /usr/bin/ssh-copy-id 59 行 )

local port forwarding ( ssh tunnel )

~/.ssh/config
1
2
3
4
Host vps
    HostName 123.45.67.89
    User oalieno
    LocalForward 5555 127.0.0.1:6666

設定好後可以直接打以下指令

1
2
3
ssh -f -N vps
# -f : run in background
# -N : not execute remote command, useful for forwarding ports

就會等同於以下指令

1
2
3
ssh -f -N -L 5555:127.0.0.1:6666 oalieno@123.45.67.89
# -f : run in background
# -N : not execute remote command, useful for forwarding ports

local:5555 -> remote:127.0.0.1:6666
執行這個指令，就會在 local 聽 5555 port 然後把流量都導到 remote 的 127.0.0.1 的 6666 port

remote port forwarding ( reverse ssh tunnel )

~/.ssh/config
1
2
3
4
Host vps
    HostName 123.45.67.89
    User oalieno
    RemoteForward 6666 127.0.0.1:5555

設定好後可以直接打以下指令

1
2
3
ssh -f -N vps
# -f : run in background
# -N : not execute remote command, useful for forwarding ports

就會等同於以下指令

1
2
3
ssh -f -N -R 6666:127.0.0.1:5555 oalieno@123.45.67.89
# -f : run in background
# -N : not execute remote command, useful for forwarding ports

remote:6666 -> local:127.0.0.1:5555
執行這個指令之後，就會在 remote 聽 6666 port 然後把流量都導到 local 的 127.0.0.1 的 5555 port

dynamic port forwarding

~/.ssh/config
1
2
3
4
Host vps
    HostName 123.45.67.89
    User oalieno
    DynamicForward 9999

設定好後可以直接打以下指令

1
2
3
ssh -f -N vps
# -f : run in background
# -N : not execute remote command, useful for forwarding ports

就會等同於打以下指令

1
2
3
ssh -f -N -D 9999 oalieno@123.45.67.89
# -f : run in background
# -N : not execute remote command, useful for forwarding ports

會開一個 SOCKS 代理伺服器聽在 local 的 9999 port，把流量都轉從 remote 的機器出去

情境一：存取內網資源

你在你租的 vps 伺服器上面跑了一個 mattermost 在測試
但你不想讓 mattermost 聽在 0.0.0.0 公開在網路上讓大家都可以連，有風險
所以你開在 127.0.0.1 只有 vps 本地可以連
但是你又想用你的筆電上的瀏覽器測試
這時候就可以用到 local port forwarding 把 local:8065 -> remote:127.0.0.1:8065
設定如下之後，執行 ssh -f -N vps-mattermost
就可以在本地瀏覽器上面輸入 http://localhost:8065 連到你架好的 mattermost 了

~/.ssh/config
1
2
3
4
Host vps-mattermost
    HostName 123.45.67.89
    User oalieno
    LocalForward 8065 127.0.0.1:8065

情境二：透過跳板 ssh 到沒有 public ip 的機器

你在家裡組了一台桌機，但是這台桌機沒有 public ip，所以在外面的時候沒辦法 ssh 連到家裡的桌機
不過你剛好租了一台有 public ip 的 vps 伺服器
這時候就可以用到 remote port forwarding 把 remote:22000 -> local:127.0.0.1:22
設定如下之後，在桌機上執行 ssh -f -N vps-reverse-ssh
就可以從你的筆電先 ssh 到 vps
然後再從 vps 通過 remote port forwarding ssh 到桌機了
有 public ip 的 vps 伺服器在這裡扮演了跳板的角色

~/.ssh/config (桌機)
1
2
3
4
Host vps-reverse-ssh
    HostName 123.45.67.89
    User oalieno
    RemoteForward 22000 127.0.0.1:22
~/.ssh/config (vps)
1
2
3
4
Host home
    HostName 127.0.0.1
    User oalieno
    Port 22000

autossh

autossh 可以幫你自動重連

~/.ssh/config
1
2
3
4
5
6
7
Host vps
    HostName 123.45.67.89
    User oalieno
    IdentityFile ~/.ssh/id_rsa
    LocalForward 5555 127.0.0.1:6666
    ServerAliveInterval 30
    ServerAliveCountMax 3

設定好後可以直接打以下指令

1
2
3
4
autossh -M 0 -f -N vps
# -M 0 : autossh echo port, recommend disable it by setting it to 0
# -f : run in background
# -N : not execute remote command, useful for forwarding ports

就會等同於打以下指令

1
2
3
4
autossh -M 0 -f -N -o "ServerAliveInterval 30" -o "ServerAliveCountMax 3" -L 5555:localhost:6666 oalieno@123.45.67.89
# -M 0 : autossh echo port, recommend disable it by setting it to 0
# -f : run in background
# -N : not execute remote command, useful for forwarding ports

escape sequence

有時候連線斷掉後，畫面就會卡在那裡
這時候就可以直接在鍵盤上打 ~. 這個 escape sequences 就可以直接跳出來啦，感覺像是在逃脫 vim 呢xD
下面還有更多的神秘金手指可以打

1
2
3
4
5
6
7
8
9
10
11
12
Supported escape sequences:
     ~.   - terminate connection (and any multiplexed sessions)
     ~B   - send a BREAK to the remote system
     ~C   - open a command line
     ~R   - request rekey
     ~V/v - decrease/increase verbosity (LogLevel)
     ~^Z  - suspend ssh
     ~#   - list forwarded connections
     ~&   - background ssh (when waiting for connections to terminate)
     ~?   - this message
     ~~   - send the escape character by typing it twice
(Note that escapes are only recognized immediately after newline.)
  1. https://linux.die.net/man/5/ssh_config
  2. https://nerderati.com/2011/03/17/simplify-your-life-with-an-ssh-config-file/
  3. https://www.everythingcli.org/ssh-tunnelling-for-fun-and-profit-local-vs-remote/
  4. https://askubuntu.com/questions/29942/how-can-i-break-out-of-ssh-when-it-locks
  5. https://johnliu55.tw/ssh-tunnel.html
Read more
Follow

Categories

Recents

Archives

Tags

GIL1
RSA2
adb1
ai1
algorithm4
android3
blockchain2
blog4
bloom1
burp1
c++1
chatgpt1
command1
crypto5
ctf7
cve2
dapper labs1
drony1
flare1
flare-on1
flow1
frida2
gdb1
hexo4
hitcon1
icarus4
kernel4
linux3
llm1
nord1
nox1
osint1
pe1
powerlevel10k1
powerlevel9k1
powershell1
proxy1
pwn3
pyc1
python3
reverse5
reverse engineering1
reverse ssh1
rootkit1
rsa1
security16
seo1
srop1
ssh1
tunnel1
ubuntu1
windows3
writeups6
zimfw1
zsh1
×