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tutorials:crystal_bbs:part_zero
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tutorials:crystal_bbs:part_zero [2017/03/19 12:17] sardaukar |
tutorials:crystal_bbs:part_zero [2017/03/19 12:27] sardaukar |
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| So, the basic idea is that we get a character by character interface, just like a local Linux terminal emulator. Our inputs are sent to the server, and we get an update of the virtual terminal's layout sent back (or not, in case the keystroke does not change the state of the terminal). | So, the basic idea is that we get a character by character interface, just like a local Linux terminal emulator. Our inputs are sent to the server, and we get an update of the virtual terminal's layout sent back (or not, in case the keystroke does not change the state of the terminal). | ||
| - | Usually, network programming involves sending and receiving messages, but for purposes of manipulating this virtual terminal, we'll be sending and receiving more than just text - among the messages we will send (and receive) are things that are not shown in text, like sounding a bell or clearing the screen or moving the cursor to a specific line and column or even detecting the width and height (in columns and lines) of the client. These are [[resources:misc:ansi_escape_codes|ANSI Escape Codes]] and are not specific to Telnet - they govern the behaviour of any "modern" text terminal. You **can** avoid these, but your BBS would not look very nice without screen clearing and cursor positioning and so on. | + | Usually, network programming involves sending and receiving messages, but for purposes of manipulating this virtual terminal, we'll be sending and receiving more than just text - among the messages we will send (and receive) are things that are not shown in text, like sounding a bell or clearing the screen or moving the cursor to a specific line and column. These are [[resources:misc:ansi_escape_codes|ANSI Escape Codes]] and are not specific to Telnet - they govern the behaviour of any "modern" text terminal. You **can** avoid these, but your BBS would not look very nice without screen clearing and cursor positioning and so on. |
| Specific to Telnet, there are factors like terminal size and message flow and so on - negotiating these client capabilities with the server was necessary even back when Telnet was first created as many different terminals, with different features, were prominent in the 1970s and 80s. Examples are the famous [[https://en.wikipedia.org/wiki/VT100|VT100]] and [[https://en.wikipedia.org/wiki/VT220|VT220]] terminals by DEC. | Specific to Telnet, there are factors like terminal size and message flow and so on - negotiating these client capabilities with the server was necessary even back when Telnet was first created as many different terminals, with different features, were prominent in the 1970s and 80s. Examples are the famous [[https://en.wikipedia.org/wiki/VT100|VT100]] and [[https://en.wikipedia.org/wiki/VT220|VT220]] terminals by DEC. | ||
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| And just like that, both client and server agreed that the ''Go Ahead'' feature is not to be used in this connection! Other messages are being exchanged in the full sequence above regarding speed, input type (binary or text) and even NAWS (''Negotiate About Window Size''), which has an awesome name. All of these will be addressed as we need them for our BBS, most on the next part of the tutorial. But you can tell from the design of the protocol that clients can be quite flexible in how they interact with any Telnet server you write, if you reply to feature negotiation messages appropriately! | And just like that, both client and server agreed that the ''Go Ahead'' feature is not to be used in this connection! Other messages are being exchanged in the full sequence above regarding speed, input type (binary or text) and even NAWS (''Negotiate About Window Size''), which has an awesome name. All of these will be addressed as we need them for our BBS, most on the next part of the tutorial. But you can tell from the design of the protocol that clients can be quite flexible in how they interact with any Telnet server you write, if you reply to feature negotiation messages appropriately! | ||
| - | The one problem with this setup is that there is not definitive "end" marker to the negotiation step of the connection, since //at any time// you can receive or send one of these messages to turn features on and off. | + | The one problem with this setup is that there is no definitive "end" marker to the negotiation step of the connection, since //at any time// you can receive or send one of these messages to turn features on and off. |
| So this is Telnet in a nutshell - a text-oriented protocol that has special command messages mixed in. | So this is Telnet in a nutshell - a text-oriented protocol that has special command messages mixed in. | ||
tutorials/crystal_bbs/part_zero.txt ยท Last modified: 2018/03/29 01:58 (external edit)
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