tomcan.dev

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    <div class="project-card-image-wrapper">
      <img src="/images/posts/pteflow-home.png" alt="PTE Flow landing page screenshot" />
    </div>
    <div class="project-card-content">
      <div class="project-card-header">
        <h3 class="project-card-title">PTE Flow</h3>
        <span class="project-card-badge android">Android</span>
        <span class="project-card-badge native">Native</span>
      </div>
      <p class="project-card-description">
        A native Android app built for PTE learners who want to master <strong>Write From Dictation (WFD)</strong> with fast drills, fewer distractions, and a focused repetition loop.
      </p>
      <div class="project-card-features">
        <ul>
          <li><strong>3-step mastery system</strong>: Build phrases, sort words, and write the full sentence.</li>
          <li><strong>First Letter mode</strong>: Practice fast recall by typing the first character of each word.</li>
          <li><strong>Jetpack Compose</strong>: Built with Kotlin and native Android UI for a smooth learning flow.</li>
        </ul>
      </div>
      <a href="https://pteflow.com" target="_blank" rel="noopener noreferrer" class="project-card-button">
        Visit PTE Flow &rarr;
      </a>
    </div>
  </div>  <div class="project-card">
    <div class="project-card-image-wrapper">
      <img src="/images/posts/humawrite-home.png" alt="HumaWrite landing page screenshot" />
    </div>
    <div class="project-card-content">
      <div class="project-card-header">
        <h3 class="project-card-title">HumaWrite</h3>
        <span class="project-card-badge ai">AI Product</span>
        <span class="project-card-badge web">Web & Mobile</span>
      </div>
      <p class="project-card-description">
        An AI writing tool that helps turn stiff AI-generated drafts into more natural, human-like writing with a cleaner rhythm, voice, and flow.
      </p>
      <div class="project-card-features">
        <ul>
          <li><strong>AI humanization</strong>: Rewrite robotic text into clearer, more natural English.</li>
          <li><strong>Detector-aware editing</strong>: Built for drafts that need to pass stricter AI detector checks.</li>
          <li><strong>Flexible writing modes</strong>: Supports academic, casual, and professional writing styles.</li>
        </ul>
      </div>
      <a href="https://humawrite.app" target="_blank" rel="noopener noreferrer" class="project-card-button">
        Visit HumaWrite &rarr;
      </a>
    </div>
  </div>
</div>


Products and personal projects designed and built by tomcan.dev.

Projects

<p>When I was developing the PTE Flow app, I needed to capture HTTPS traffic to check API requests and mock responses. I tried installing the mitmproxy certificate to the Android emulator the normal way as a User CA. The result was a total failure. The app kept showing connection errors and refused to capture any requests.</p>
<p>From Android 7.0 (API 24), Google blocks apps from trusting user-installed certificates on production builds. If you do not want to edit the app&#39;s <code>network_security_config.xml</code> file (especially when reverse-engineering third-party apps), the only way is to put the mitmproxy certificate directly into the system partition (System CA).</p>
<p>Here is the fastest way to do it. I will also show you how to fix the annoying read-only system error on new Android versions.</p>
<h2>Set up the Android emulator</h2>
<p>To write the certificate to the system folder, you must have root access.</p>
<p>Make sure to choose an Android Emulator using a <strong>Google APIs</strong> image. Do not choose the Google Play Store image because it locks root access over ADB, which makes it impossible to do this.</p>
<p>You also need <code>adb</code> and <code>mitmproxy</code> installed on your computer.</p>
<h2>Step 1: Calculate the hash of the mitmproxy CA certificate</h2>
<p>First, Android manages system certificates in the <code>/system/etc/security/cacerts/</code> folder. The file name must be the hash of the certificate with a <code>.0</code> extension.</p>
<p>When you start mitmproxy for the first time, it generates the CA certificate in the <code>~/.mitmproxy/</code> folder. Use <code>openssl</code> to calculate the hash:</p>
<pre><code class="language-bash">cd ~/.mitmproxy
# Get the old subject hash because Android uses this format
hashed_name=$(openssl x509 -inform PEM -subject_hash_old -in mitmproxy-ca-cert.cer | head -1)
# Copy and rename the certificate
cp mitmproxy-ca-cert.cer $hashed_name.0
</code></pre>
<p>If successful, this command creates a new file like <code>c8750f0d.0</code>.</p>
<h2>Step 2: Start the Android emulator with write permissions</h2>
<p>After renaming the certificate file, the next step is to boot the emulator with system write access. The emulator&#39;s system partition is read-only by default. To write to it, you must start the emulator from the terminal with a special flag:</p>
<pre><code class="language-bash">emulator -avd &lt;your_emulator_name&gt; -writable-system
</code></pre>
<p><em>(You can see your emulator list by running <code>emulator -list-avds</code>)</em>.</p>
<h2>Step 3: Fix the remount failed error on the Android emulator (this is usually the frustrating part)</h2>
<p>After booting with write permissions, the next step is to remount the system partition. This is where the official mitmproxy docs usually ignore, leaving many developers stuck for hours. On new Android versions (Android 9 and above), when you run <code>adb remount</code>, you will see this error:</p>
<pre><code class="language-text">remount of /system failed: Read-only file system
</code></pre>
<p>To fix this, disable Android Verified Boot (AVB) checks by running these commands:</p>
<pre><code class="language-bash">adb root
adb shell avbctl disable-verification
adb reboot
</code></pre>
<p>After the emulator reboots, start the emulator with the <code>-writable-system</code> flag from Step 2 again. Now, running remount will work perfectly:</p>
<pre><code class="language-bash">adb root
adb remount
</code></pre>
<p>When you see <code>remount succeeded</code> on your screen, you are 90% done. It feels as good as getting a reply from your crush.</p>
<h2>Step 4: Copy the mitmproxy certificate to the system partition</h2>
<p>When the system partition is writable, now push the certificate file you renamed in Step 1 to the Android system certificate folder:</p>
<pre><code class="language-bash"># Push the certificate file to Android cacerts folder
adb push ~/.mitmproxy/c8750f0d.0 /system/etc/security/cacerts/
# Set correct read-write permissions (644) for the system certificate
adb shell chmod 644 /system/etc/security/cacerts/c8750f0d.0
</code></pre>
<p><em>Remember to replace <code>c8750f0d.0</code> with the actual hash you calculated in Step 1.</em></p>
<p>Finally, reboot the device to apply the changes:</p>
<pre><code class="language-bash">adb reboot
</code></pre>
<h2>How to verify the mitmproxy certificate on the device</h2>
<p>Finally, after the emulator reboots, go to the settings menu to verify:
<strong>Settings -&gt; Security -&gt; Encryption &amp; credentials -&gt; Trusted credentials</strong>.</p>
<p>Choose the <strong>System</strong> tab and scroll down to find <strong>mitmproxy</strong>.</p>
<p><img src="/images/posts/mitmproxy-system-ca-settings.png" alt="Mitmproxy system CA listed on Android Settings System tab"></p>
<p>If you see it there, you succeeded. Now configure the proxy settings on your emulator to point to your computer&#39;s IP address and start capturing HTTPS traffic.</p>
<h2>Security trade-offs and alternatives</h2>
<p>Disabling AVB verification (<code>avbctl disable-verification</code>) and running <code>-writable-system</code> breaks the Android security sandbox. Malicious root processes can write to your system partition. <strong>Only do this on development emulators</strong>. Never do this on a physical phone with personal data.</p>
<p>If you must debug on a physical phone, a safer alternative is to root your phone with <strong>Magisk</strong> and install the <code>MagiskTrustUserCerts</code> module. This module moves user certificates to the system folder on boot without touching the system partition directly. To install it, download the zip file from the GitHub repository (<code>github.com/Notsure2/MagiskTrustUserCerts</code>), copy it to your phone, and flash it through the Magisk Manager app.</p>
<p>If you want to read more about mobile development or UI bugs on Android, check out my old post on <a href="/cch-sa-li-k-t-u-b-ct-trong-textview-khi-dng-custom-font">how to fix clipped text in Android TextView with custom fonts</a>. Leave a comment below if you have questions or want to share other Magisk modules for bypassing SSL pinning.</p>


Learn how to install mitmproxy CA certificate as a System CA on Android Emulator to capture HTTPS traffic without editing app network security configs.

How to Install mitmproxy as a System CA on Android Emulator

Term

<h1>Privacy Policy for 9Currency</h1>
<p><em><strong>Effective Date:</strong></em>* April 10, 2025*</p>
<p>This Privacy Policy describes how TomCan.Dev (“we,” “us,” or “our”) collects, uses, and shares information in connection with your use of the 9Currency mobile application (the “App”).</p>
<h2>Information We Collect</h2>
<p>We collect the following types of information:</p>
<h2>How We Use Information</h2>
<h2>Third-Party Services</h2>
<p>We may share information with third-party service providers under the following circumstances:</p>
<p>We do not sell, rent, or share your personal information with other third parties for their marketing purposes.</p>
<h2>Data Security</h2>
<p>We implement reasonable administrative and technical security measures designed to protect the information we handle. However, please be aware that no security system is impenetrable, and we cannot guarantee the absolute security of data transmitted over the internet or stored on systems.</p>
<h2>Children&#39;s Privacy</h2>
<p>The App is not intended for use by children under the age of 13 (or the relevant age in your jurisdiction). We do not knowingly collect personal information from children under 13. If you are a parent or guardian and believe that your child has provided us with information without your consent, please contact us using the details below. If we become aware that we have collected personal information from a child under the relevant age threshold, we will take steps to delete such information.</p>
<h2>Your Choices</h2>
<p>Since we do not collect direct PII through the App, your main choices relate to analytics and advertising (if applicable):</p>
<p>If you have questions about our data practices, please contact us.</p>
<h2>Changes to This Policy</h2>
<p>We may update this Privacy Policy from time to time. We will notify you of any changes by posting the new Privacy Policy within the App or making it available through the app store listing. You are advised to review this Privacy Policy periodically for any changes. Changes to this Privacy Policy are effective when they are posted on this page.</p>
<h2>Contact Us</h2>
<p>If you have any questions about this Privacy Policy, please contact us at: <strong><a href="mailto:tomcandev@gmail.com">tomcandev@gmail.com</a></strong></p>


Privacy Policy for 9Currency Effective Date: April 10, 2025 This Privacy Policy describes how TomCan.Dev (“we,” “us,” or “our”) collects, uses, and sh...

Privacy Policy

<p>The best way to get in touch with me is to email <a href="mailto:">tomcandev@gmail.com</a>.</p>
<p><a href="https://twitter.com/tomcandev">Twitter</a> • <a href="https://github.com/tomcandev">GitHub</a></p>


The best way to get in touch with me is to email tomcandev@gmail.com. Twitter • GitHub

Contact

<p>Hi,</p>
<p>I’m a developer. I love Android, iOS, and new technologies.</p>
<p>This blog will share my journey to become a developer and my daily activity as a developer</p>
<p>Thanks,</p>
<p>Tom</p>
<p><a href="https://twitter.com/tomcandev">Twitter</a> • <a href="https://github.com/tomcandev">GitHub</a></p>


Hi, I’m a developer. I love Android, iOS, and new technologies. This blog will share my journey to become a developer and my daily activity as a devel...

About

<p>Chẳng là hôm nay mình gặp 1 bug như hình cover nên chia sẻ lại kinh nghiệm cho các bạn đỡ mất công tìm</p>
<p>Tình hình là em sử dụng 1 custom font trong app và bị vấn đề là mất góc của mốt số kí tự như j, f, e,.. khi nó nằm ở đầu dòng. Em đã gắng dùng thử 1 vài cách để fix như là thêm padding start, padding left,… cho vào 1 layout khác và dùng margin cũng như padding nhưng cũng không ăn thua.</p>
<p>Do đó mình search thử 1 vài từ khóa xem có ai bị giống vậy không. May quá có các bạn ạ, đây là lỗi khi sử dụng 1 custom font trên TextView hoặc EditText. Cách xử lý là phải custom lại TextView bằng cách extend lại AppCompatTextView rồi override lại onDraw sau đó viết code để vẽ lại. Các bạn có thể tham khảo code Kotlin như dưới đây:</p>
<pre><code class="language-kotlin">// This custom text view will avoid cutting off on the sides with custom font
class TextViewWithoutClipping : AppCompatTextView {
    constructor(context: Context) : this(context, null)
    constructor(context: Context, attrs: AttributeSet?) : this(context, attrs, 0)
    constructor(context: Context, attrs: AttributeSet?, defStyleAttr: Int) : super(context, attrs,
            defStyleAttr)

    override fun onDraw(canvas: Canvas) {
        val color: Int = paint.color
        // Draw what you have to in transparent
        // This has to be drawn, otherwise getting values from layout throws exceptions
        setTextColor(Color.TRANSPARENT)
        super.onDraw(canvas)
        // setTextColor invalidates the view and causes an endless cycle
        paint.color = color
        for (i in 0 until layout.lineCount) {
            val start = layout.getLineStart(i)
            val end = layout.getLineEnd(i)
            val line = text.substring(start, end)
            val left = layout.getLineLeft(i)
            val baseLine = layout.getLineBaseline(i)
            canvas.drawText(line,
                    left + totalPaddingLeft,  // The text will not be clipped anymore
                    // You can add a padding here too, faster than string string concatenation
                    baseLine + totalPaddingTop.toFloat(),
                    paint)
        }
    }
}
</code></pre>
<p>Hy vọng bài viết này giúp ích gì đó với các bạn.</p>
<p>Nguồn tham khảo:</p>
<p><a href="https://stackoverflow.com/questions/44074858/android-textview-text-get-cut-off-on-the-sides-with-custom-font/44218468#44218468">https://stackoverflow.com/questions/44074858/android-textview-text-get-cut-off-on-the-sides-with-custom-font/44218468#44218468</a></p>
<p><a href="https://stackoverflow.com/questions/28576797/text-being-cut-off-from-front-for-a-particular-font/28625166#28625166">https://stackoverflow.com/questions/28576797/text-being-cut-off-from-front-for-a-particular-font/28625166#28625166</a></p>


Chẳng là hôm nay mình gặp 1 bug như hình cover nên chia sẻ lại kinh nghiệm cho các bạn đỡ mất công tìm Tình hình là em sử dụng 1 custom font trong app...

Cách sửa lỗi kí tự đầu bị cắt trong TextView khi dùng custom font

<p>I was born and grow up in a small village; the internet is a luxury. I used to only watch my friends play games such as MU, Audition,… But Audition was the best game of our children at that time. We loved it, because it was easy to play, good music and suitable for boys and girls. So I wondering why I don’t create that game and play offline at home, that is a reason why I make it</p>
<p>First of all, I asked my friend to know how to play Audition game. It is a game in which players can play with 4 arrows buttons or 8 buttons with the number pad on music background. Besides, players have to have good eyes and fast fingers to catch a Perfect point on the screen with the space button. When I know the rules of that game, I started very first line codes</p>
<p>When I was a student in secondary school, I created the first version with basic features that players played with 4 arrows buttons, music background, and Perfect feature. The first user was my friend; he tried my game and he really loved my game. He gave me some advice to upgrade the new version. I updated my game with 8 arrows buttons and had a dancing person GIF file. I wrote the next version when I was a student in high school; this version can have 2 players at the same time. On the keyboard, I split into 2 parts, 1 player play on ADWS to play, and other play on arrow key on the right side. It was very fun because I can play with my friend with own music we love and play offline. I also wrote a post to technical paper; they posted it with a little money to me and I had many users. They send me a lot of emails and make a friend with me on Yahoo Messenger. I really really love it because I can make something to everyone</p>
<p>This is one of many reasons I selected to become a developer. I think the big motivation is that I create a valuation for everyone and it makes me happy to do that</p>


I was born and grow up in a small village; the internet is a luxury. I used to only watch my friends play games such as MU, Audition,… But Audition wa...

How I can create a game without playing in Microsoft VisualBasic 6.0

<p>Microsoft Visual Basic 6.0 was a famous IDE in the 1990s. It uses easily, drags and drops view, and build exe file to run on Windows without any Framework like .NET. I had good memories with it</p>
<p>The first my Hello World program is a dialog with the “Hi” message. I drag the button from Toolbox to Windows on the screen -&gt; I double click on the button to show code editor -&gt; I write “MsgBox Hi” -&gt; I click Play button on IDE to build and run app -&gt; It was amazing (I thought so) -&gt; It showed the windows with the button exactly -&gt; I click button -&gt; It showed a dialog with “Hi” message -&gt; It was amazing second times (I thought so)</p>
<p>I learned from my older brother’s Visual Basic book and I found some source code examples from Microsoft in Microsoft Visual Basic 6.0 folder. When the Internet became popular, every Internet store had to install Yahoo Messenger, I knew the <a href="http://caulacbovb.com/">caulacbovb.com</a> forum – for people interest and love VB. Whenever I had free time, I accessed that forum to download and saved a lot of page on that forum and read offline later, because I don’t have enough time and money to stay at Internet store</p>
<p>The first application I was completely that is a music player called “Tan Nhac”. It can play music, search file, and a special feature is that play mp3 file with image animation. I cloned skin from the Windows Media Player.
I send my application to my friend by floppy disk (I called “Disc A”).</p>
<p>It was incredible emotion, I could build my own application that users ran!</p>


Microsoft Visual Basic 6.0 was a famous IDE in the 1990s. It uses easily, drags and drops view, and build exe file to run on Windows without any Frame...

How I become a developer with Visual Basic 6.0

<p>I remember when I was a child in primary school about 10 to 11 year-olds, I played games too much until I wondered how I can make a game like them. That is the first step to become a developer</p>
<p>The very first language is HTML with Microsoft Office FrontPage 2003 editor. I tried any features and buttons on the screen, but I love the most feature that makes a text can move left to right on the screen and change the text style with colors, font size,…</p>
<p>The first game I made is that a test with 4 options to select. When user click on 1 question or 1 answer (option), it will go to the URL into a page. This is the simplest thing that I can think</p>
<p>Day by day, I create a lot of pages and add many codes to the project. However I don’t know, I loved programming so much. When I come back home from school, I will sit down in front of the computer to write the codes that I thought on my way with interesting and happiness. I always think about how to make better to show off my parents and my siblings about my results</p>
<p>This is my journey to become a developer, so I hope it makes you love programing and become a developer</p>


I remember when I was a child in primary school about 10 to 11 year-olds, I played games too much until I wondered how I can make a game like them. Th...