Aim Wang

2025/02/18

C Check that the pointer is in range of the memory.

It's hard to say. It's important to protect yourself.

// Function to check if a pointer is within the process's mapped memory regions
int is_pointer_in_memory_range(void *ptr) {
    FILE *fp = fopen("/proc/self/maps", "r");
    if (!fp) {
        perror("fopen");
        return 0;
    }

    char line[256];
    uintptr_t addr = (uintptr_t)ptr;
    uintptr_t start, end;
    while (fgets(line, sizeof(line), fp)) {
        if (sscanf(line, "%lx-%lx", &start, &end) == 2) {
            if (addr >= start && addr < end) {
                fclose(fp);
                return 1; // Pointer is in a valid range
            }
        }
    }

    fclose(fp);
    return 0; // Pointer is not in the mapped memory range
}

2024/10/08

LINE Notify 的替代方案

LINE Notify 割韭菜了.

只好拿稍微麻煩一點的 pushbullet 來用.

產生 token:

登入 pushbullet 主頁.

在帳號的設定頁面建立 token.

請牢記你的 token, 保管好並且不要洩漏.

然後點選你想接收訊息的裝置

URL 最後就是你的裝置 ID.

接下來就是透過 curl 傳遞我們想要傳送的訊息:

curl -X POST https://api.pushbullet.com/v2/pushes \
-H "Authorization: Bearer ${你的token}>" \
-H "Content-Type: application/json" \
-d "{\"type\": \"note\", \"title\": \"${訊息抬頭}\", \"body\": \"${訊息內容}\", \"device_iden\": \"${你的裝置ID}\"}"

2024/04/18

[C] chek cpu endian

#include <stdint.h>

static uint8_t is_little_endian(void)
{
    uint16_t value = 0x0001;
    uint8_t *byte_ptr = (uint8_t *)&value;
    return (*byte_ptr == 0x01); // If the system is little endian, the least significant byte is 0x01.
}

2024/04/09

[C] Create a folder even if the parent folder does not exist.

static int my_dirname(char *path) {
    char *p = strrchr(path, '/');
    if (p == NULL || p == path) {
        return -1;
    }
    *p = '\0';
    return 0;
}

static int my_mkdir(char *path) {
    struct  stat    st;
    char            p[128];
    char            l[128];

    mkdir(path, 0775);
    while ((stat(path, &st) != 0)) {
        memset(p, 0, 128);
        memcpy(p, path, strlen(path));
        if (0 != my_dirname(p)) {
            return (-1);
        }
        while ((stat(p, &st) != 0)) {
            memset(l, 0, 128);
            memcpy(l, p, strlen(p));  // save the last not exist parent path.
            if (0 != my_dirname(p)) {
                return (-1);
            }
        }
        mkdir(l, 0775);
        if (stat(l, &st) != 0) {
            return (-1);
        }
        mkdir(path, 0775);
    }
    return (0);
}

2023/06/20

Use tc and netem to simulate network delay, jitter and packet loss.

netem relies on kernel module:
CONFIG_IFB
CONFIG_NET_SCHED
CONFIG_NET_SCH_NETEM.

tc qdisc add dev br-lan root handle 1: htb

This will create a root qdisc on the br-lan interface for htb

tc class add dev br-lan parent 1: classid 1:1 htb rate 1000mbit
tc qdisc add dev br-lan parent 1:1 netem delay 100ms 10ms
tc filter add dev br-lan parent 1:0 protocol ip u32 match ip sport 5101 0xffff flowid 1:1

Create a class 1:1 under 1: of br-lan and set the speed limit to 1000bps.
For class 1:1 set its netem to delay 100ms and jitter 10ms.
Direct the packet with src port 5101 of the br-lan interface to class 1:1.

tc class add dev br-lan parent 1: classid 1:2 htb rate 1000mbit
tc qdisc add dev br-lan parent 1:2 netem loss 0% duplicate 0% delay 30ms 20ms
tc filter add dev br-lan parent 1:0 protocol ip u32 match ip sport 5001 0xffff flowid 1:2

Create a class 1:2 under 1: of br-lan and set the speed limit to 1000bps.
For class 1:2 set its netem to loss 0%, duplicate 0%, delay 30ms and jitter 20ms.
Direct the packet with src port 5001 of the br-lan interface to class 1:2.