kilo, the minimal text editor

Project status: finished & fully working; probably will not receive further updates, except for bug fixes.

Overview

kilo is a minimal (1200 soc) yet somewhat full-featured text editor. It supports basic editing, (incremental) searching, creating new files, syntax highlighting, and many more.

Build & Run

• nix develop to enable Nix env with all dependencies
• cmake . -B build
• cmake --build build
• ./build/src/kilo to create and open a new file
• ./build/src/kilo <existing-file> to open an existing file

Dev Notes

• by default the terminal starts in canonical mode, a.k.a. cooked mode
  • keyboard input only sent to the program if user presses <Enter>
• we want the raw mode
• type reset then <Enter> in terminal resets it back to normal
• by default ICANON is set
• Escape sequence
  • 3 or 4 bytes
  • starts with the 27 byte
    • which is the <Esc> key
• <Ctrl-Z> takes job to background
  • type fg to bring it to the front
• <Ctrl-S> - stop sending me output
  • XOFF
  • press <Ctrl-Q> to resume sending me output
    • XON
• <Ctrl-C> sends SIGINT
• <Ctrl-Z> sends SIGSTP
• <Ctrl-C> represents byte 3
• <Ctrl-D> represents byte 3
• <Ctrl-Z> represents byte 26
• IXON
  • I - input flag
• <Ctrl-S> represents byte 19
• <Ctrl-Q> represents byte 17
• <Ctrl-V>
  • terminal waits for another character input
  • then sends that character literally
  • IEXTEN flag
• <Ctrl-M>
  • represented as 10 byte
  • <Ctrl-J> also represents 10
  • so does <Enter>
• Terminal translates any carriage returns (13, \r) inputted by user into newlines (10, \n)
  • ICRNL
    • I - input flag
    • CR - carriage return
    • NL - new line
• Terminal translates each newline ("\n") users print into a carriage return followed by a newline - "\r\n"
  • both "\r" and "\n" are required to start a new line
  • carriage return moves the cursor back to the beginning of the current line
  • newline moves cursor down a line, scrolling the screen if necessary
• Likely the only output processing feature turned on by default: "\n" -> "\r\n"
• OPOST - the output processing flag
• BRKINT - a break condition will cause a SIGINT sent to the program
  • similar to <Ctrl-C>
• INPCK - enables parity checking
• ISTRIP - sets the 8th bit of each input byte to be 0
  • most likely already turned off
• CS8 - a bit mask, not a flag
  • sets the character size (CS) to 8 bits per byte
• EAGAIN - resource temporarily unavailable
• In C, bitmasks generally specified in hex
• use J command to clear the screen
• VT100 User Guide
• If a tilde (~) is in a row - row is not part of the file and cannot contain any text
• To get window size of terminal,
  • ioctl - control device
  • the TIOCGWINSZ request
    • Terminal IOCtl Get WINdow SiZe
  • from <sys/ioctl.h>
• However, ioctl() is not guaranteed to query the window size on all systems
• Use "\x1b[K" to clear the line after the "~", instead of clearing the entire screen
• snprintf() - writes to the buffer string at most number of chars
• How to move cursors around?
  • keep track of cursor's x and y position
  • move cursor to position stored in E.cx and E.cy in editor_refresh_screen()
• Use JKHL to move cursors, like Vim
• Pressing Ctrl with another key
  • clears the 6th and 7th bits of the char presses with Ctrl
• Page up & Page down keys
  • <esc>[5~ - Page up
  • <esc>[6~ - Page down
• Home & End keys
  • Home could be sent as:
    • <esc>[1~
    • <esc>[7~
    • <esc>[H
    • <esc>OH
  • End could be sent as:
    • <esc>[4~
    • <esc>[8~
    • <esc>[F
    • <esc>OF
• Delete key - <esc>[3~
• Create a data type for storing a row of text in the editor
• getline() - read lines from a file while how much memory is allocated is unknown
  • takes care memory management for you
  • returns length of the read line; -1 if error
• Strategy for vertical scrolling for long text
  • check if cursor has moved out of the visible window
  • if so, adjust E.rowoff so that cursor is just inside the visible window
• We allow users to scroll one line/column pass the edge - allowing users to insert lines/characters
• Rendering tabs
  • we want to render tabs as multiple spaces
  • tab stop - a column that's divisible by 8
  • each tab must advance the cursor forward at least one column
• Page Up & Page Down should scroll up/down an entire page
• Status bar
  • display file name & current row number
  • Select Graphic Rendition (SGR)
  • ESC [ Ps ; . . . ; Ps m
• status message & timestamp
• Originally, Backspace was mapped to Ctrl-H - control code 8
  • but now mapped to 127
  • DEL mapped to <esc>[3~
• <Ctrl-L> - refresh screen in terminal programs
• O_TRUNC
  • truncates the file to zero length
  • normally a file is overwritten by passing O_TRUNC to open()
    • truncates the file completely
    • then write data to it
• Syntax Highlighting
  • now we have to feed the substring of render to print into abuf_append()
  • but character-by-character
• Filetype detection
  • call editor_select_syntax_highlight() whenever/wherever filename changes
• the audible bell character - 7
• We need to translate nonprintable characters into printable ones
  • we render them using inverted colors (black on white)