[spec] ☿️ gemini — a minimalist gemini protocol

[Petite Abeille]

All details are similar to gemini itself, ? some minor adjustments.

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??://??

By default, a ?? gemini service runs over plain TCP, at port 1961.

A ?? gemini:// request is one-line ?4,096 bytes long at most, UTF-8 encoded? containing a fully qualified, normalized Internationalized Resource Identifier (IRI):

gemini://host.xyz:1961/

An IRI is an UTF-8 version of an Uniform Resource Identifier (URI). 
An URI can be either an Uniform Resource Locator (URL), or Uniform Resource Name (URN).

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An example of a ?? gemini request, followed by a ?? text/gemini response:

# echo -e 'gemini://gemini.xyz:1961/\r\n' | nc 127.0.0.1 1961
20 text/gemini;charset=utf-8;
Hello ?? Gemini!

=> gemini://host.xyz:1961/license CC0-1.0 
<end of connection> 

A successful ?? gemini response is a one-line with status 20?optionally followed by a content type, plus associated attributes, such as encoding:  

20 text/gemini;charset=utf-8;

The content type is optional ? defaulting to ?? text/gemini, UTF-8 encoded.

The content itself follow the  20 status line ? terminated by the service dropping the network connection.

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There are 3 status codes:

20 SUCCESS ? one-line, with optional content type, plus attributes, 4,096 bytes long at most, UTF-8 encoded
20 text/gemini;charset=utf-8;

30 REDIRECT ? one-line IRI, fully qualified, and normalized, 4,096 bytes long at most, UTF-8 encoded
30 gemini://host.xyz:1961/

40 ERROR ? one-line, 4,096 bytes long at most, UTF-8 encoded, with optional description 
40 ??????

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A ?? text/gemini consists of two line types: text, and link. 

A link is denoted as one-line, starting with the arrow symbol (=>), followed by a space, followed by a fully qualified, and normalized IRI ? optionally followed by a space separated description:

=> gemini://host.xyz/license CC0-1.0

All other lines are regular text lines.

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That's all folks.

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