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186 lines
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HTML
186 lines
12 KiB
HTML
<!DOCTYPE html>
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<html class="">
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<head>
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<meta charset="utf-8">
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<title>Styled text with message entities</title>
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<meta property="description" content="How to create styled text with message entities">
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<div class="dev_page_bread_crumbs"><ul class="breadcrumb clearfix"><li><a href="/api" >API</a></li><i class="icon icon-breadcrumb-divider"></i><li><a href="/api/entities" >Styled text with message entities</a></li></ul></div>
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<h1 id="dev_page_title">Styled text with message entities</h1>
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<div id="dev_page_content"><!-- scroll_nav -->
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<p>Telegram supports styled text using <a href="/type/MessageEntity">message entities</a>.</p>
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<p>A client that wants to send styled messages would simply have to integrate a <a href="https://en.wikipedia.org/wiki/Markdown">Markdown</a>/<a href="https://en.wikipedia.org/wiki/HTML">HTML</a> parser, and generate an array of message entities by iterating through the parsed tags. </p>
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<p>Nested entities are supported.</p>
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<h3><a class="anchor" href="#entity-length" id="entity-length" name="entity-length"><i class="anchor-icon"></i></a>Entity length</h3>
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<p>Special care must be taken to consider the length of strings when generating message entities as the number of <a href="https://en.wikipedia.org/wiki/UTF-16">UTF-16</a> code units, even if the message itself must be encoded using UTF-8. </p>
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<p>Example implementations: <a href="https://github.com/tdlib/td/tree/master/td/telegram/MessageEntity.cpp">tdlib</a>, <a href="https://github.com/danog/telegram-entities/blob/master/src/Entities.php">MadelineProto</a>.</p>
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<h4><a class="anchor" href="#unicode-codepoints-and-encoding" id="unicode-codepoints-and-encoding" name="unicode-codepoints-and-encoding"><i class="anchor-icon"></i></a>Unicode codepoints and encoding</h4>
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<p>A <a href="https://en.wikipedia.org/wiki/Unicode">Unicode</a> <a href="https://en.wikipedia.org/wiki/Code_point">code point</a> is a number ranging from <code>0x0</code> to <code>0x10FFFF</code>, usually represented using <code>U+0000</code> to <code>U+10FFFF</code> syntax.<br>
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Unicode defines a codespace of 1,112,064 assignable code points within the <code>U+0000</code> to <code>U+10FFFF</code> range.<br>
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Each of the assignable codepoints, once assigned by the Unicode consortium, maps to a specific character, emoji or control symbol. </p>
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<p>The Unicode codespace is further subdivided into 17 planes:</p>
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<ul>
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<li>Plane 1: <code>U+0000</code> to <code>U+FFFF</code>: Basic Multilingual Plane (BMP)</li>
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<li>Planes 2-17: <code>U+00000</code> to <code>U+10FFFF</code>: Multiple supplementary planes as specified <a href="https://en.wikipedia.org/wiki/Plane_(Unicode)">by the Unicode standard</a></li>
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</ul>
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<p>Since storing a 21-bit number for each letter would result in a waste of space, the Unicode consortium defines multiple encodings that allow storing a code point into a smaller <em>code unit</em>: </p>
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<h4><a class="anchor" href="#utf-8" id="utf-8" name="utf-8"><i class="anchor-icon"></i></a>UTF-8</h4>
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<p><a href="https://en.wikipedia.org/wiki/UTF-8">UTF-8 »</a> is a Unicode encoding that allows storing a 21-bit Unicode code point into <em>code units</em> as small as 8 bits.<br>
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UTF-8 is used by the MTProto and Bot API when transmitting and receiving fields of type <a href="/type/string">string</a>. </p>
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<h4><a class="anchor" href="#utf-16" id="utf-16" name="utf-16"><i class="anchor-icon"></i></a>UTF-16</h4>
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<p><a href="https://en.wikipedia.org/wiki/UTF-16">UTF-16 »</a> is a Unicode encoding that allows storing a 21-bit Unicode code point into one or two 16-bit <em>code units</em>. </p>
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<p>UTF-16 is used when computing the length and offsets of entities in the MTProto and bot APIs, by counting the number of UTF-16 code units (<strong>not</strong> code points).</p>
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<h4><a class="anchor" href="#computing-entity-length" id="computing-entity-length" name="computing-entity-length"><i class="anchor-icon"></i></a>Computing entity length</h4>
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<ul>
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<li>Code points in the BMP (<code>U+0000</code> to <code>U+FFFF</code>) count as 1, because they are encoded into a single UTF-16 code unit</li>
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<li>Code points in all other planes count as 2, because they are encoded into two UTF-16 code units (also called surrogate pairs)</li>
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</ul>
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<p>A simple, but not very efficient way of computing the entity length is converting the text to UTF-16, and then taking the byte length divided by 2 (=number of UTF-16 code units).</p>
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<p>However, since UTF-8 encodes codepoints in non-BMP planes as a 32-bit code unit starting with <code>0b11110</code>, a more efficient way to compute the entity length without converting the message to UTF-16 is the following: </p>
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<ul>
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<li>If the byte marks the beginning of a 32-bit UTF-8 code unit (all bytes starting with <code>0b11110</code>) increment the count by 2, otherwise</li>
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<li>If the byte marks the beginning of a UTF-8 code unit (all bytes not starting with <code>0b10</code>) increment the count by 1.</li>
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</ul>
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<p>Example: </p>
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<pre><code>length := 0
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for byte in text {
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if (byte & 0xc0) != 0x80 {
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length += (byte >= 0xf0 ? 2 : 1)
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}
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}</code></pre>
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<p><strong>Note</strong>: the <em>length</em> of an entity <strong>must not</strong> include the length of trailing newlines or whitespaces, <code>rtrim</code> entities before computing their length: however, the next <em>offset</em> <strong>must</strong> include the length of newlines or whitespaces that precede it. </p>
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<p>Example implementations: <a href="https://github.com/tdlib/td/tree/master/td/telegram/MessageEntity.cpp">tdlib</a>, <a href="https://github.com/danog/telegram-entities/blob/master/src/Entities.php">MadelineProto</a>.</p>
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<h3><a class="anchor" href="#allowed-entities" id="allowed-entities" name="allowed-entities"><i class="anchor-icon"></i></a>Allowed entities</h3>
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<p>For example the following HTML/Markdown aliases for message entities can be used:</p>
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<ul>
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<li><a href="https://core.telegram.org/constructor/messageEntityBold"><strong>messageEntityBold</strong></a> => <code><b>bold</b></code>, <code><strong>bold</strong></code>, <code>**bold**</code></li>
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<li><a href="https://core.telegram.org/constructor/messageEntityItalic"><em>messageEntityItalic</em></a> => <code><i>italic</i></code>, <code><em>italic</em></code> <code>*italic*</code></li>
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<li><a href="https://core.telegram.org/constructor/messageEntityCode"><code>messageEntityCode</code> »</a> => <code><code>code</code></code>, <code>`code`</code></li>
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<li><a href="https://core.telegram.org/constructor/messageEntityStrike"><del>messageEntityStrike</del></a> => <code><s>strike</s></code>, <code><strike>strike</strike></code>, <code><del>strike</del></code>, <code>~~strike~~</code></li>
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<li><a href="https://core.telegram.org/constructor/messageEntityUnderline"><u>messageEntityUnderline</u></a> => <code><u>underline</u></code></li>
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<li><a href="https://core.telegram.org/constructor/messageEntityPre"><code>messageEntityPre</code> »</a> => <code><pre language="c++">code</pre></code>, </li>
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</ul>
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<pre>
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```c++
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code
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```
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</pre>
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<p>The following entities can also be used to <a href="/api/mentions">mention</a> users:</p>
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<ul>
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<li><a href="/constructor/inputMessageEntityMentionName">inputMessageEntityMentionName</a> => <a href="https://t.me/botfather">Mention a user</a></li>
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<li><a href="/constructor/inputMessageEntityMentionName">messageEntityMention</a> => <a href="https://t.me/botfather">@botfather</a> (this mention is generated automatically server-side for @usernames in messages)</li>
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</ul>
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<p>Also, <a href="/constructor/messageEntityCustomEmoji">messageEntityCustomEmoji</a> entities are used for <a href="/api/custom-emoji">custom emojis »</a>.</p>
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<p>A number of other entities are also available, see the <a href="/type/MessageEntity">type page for the full list »</a>.</p></div>
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<h5>Telegram</h5>
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Telegram is a cloud-based mobile and desktop messaging app with a focus on security and speed.
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