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Completed basic console implementation
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@danieldegrasse
danieldegrasse committed Aug 8, 2020
1 parent 488a20b commit 413c520
Showing 1 changed file with 203 additions and 130 deletions.
333 changes: 203 additions & 130 deletions cli.c
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Original file line number Diff line number Diff line change
Expand Up @@ -7,11 +7,20 @@
* This code assumes that the connected terminal emulates a VT-100.
*/

#include <stdbool.h>
#include <string.h>

#include "cli.h"

#define CLI_EMPTY_LINELEN -1 // Signifies an "unused" history buffer.
#define CLI_PROMPT "-> "

// Static functions to handle sub cases for the CLI.
static void cli_handle_return(CLIContext *context);
static void cli_handle_esc(CLIContext *context);
static void cli_handle_backspace(CLIContext *context);
// Helper functions
static void move_line_index(CLIContext *context, bool forwards);

/**
* Initializes memory for a CLI context.
Expand All @@ -33,160 +42,46 @@ void cli_context_init(CLIContext *context) {
* @param context: CLI context for I/O.
*/
void start_cli(CLIContext *context) {
char input, esc_buf[2], *line_buf;
int new_idx;
CLI_Line *current_line;
char prompt[] = "-> ";
char input;
/*
* CLI loop, reads a line of data then handles it according to
* avaliable targets.
*/
while (1) {
// Print prompt.
context->cli_write(prompt, sizeof(prompt) - 1);
context->cli_write(CLI_PROMPT, sizeof(CLI_PROMPT) - 1);
current_line = &(context->lines[context->current_line]);
// Initialize cursor location to start of buffer.
context->cursor = line_buf = current_line->line_buf;
context->cursor = current_line->line_buf;
// Zero length of buffer.
current_line->len = 0;
/*
* Set history entry after this one to unused.
* This is why we need one more entry in history buffer than
* we actually use.
*/
new_idx = context->current_line + 1;
if (new_idx == CLI_BUFCNT)
new_idx = 0;
context->lines[new_idx].len = CLI_EMPTY_LINELEN;
move_line_index(context, true);
context->lines[context->current_line].len = CLI_EMPTY_LINELEN;
// Revert change to current line idx.
move_line_index(context, false);
// Read data until a LF is found.
do {
context->cli_read(&input, 1);
switch (input) {
case '\r': // CR, or enter on most consoles.
context->cli_write("\r\n", 2);
// Null terminate the command.
line_buf[current_line->len] = '\0';
/**
* If line is empty, do not advance to next line buffer or
* handle command.
* Else, advance to the next index in the line buffer.
*/
if (current_line->len == 0) {
current_line->len = CLI_EMPTY_LINELEN;
break;
}
// simulate modulo here.
new_idx = context->current_line + 1;
if (new_idx == CLI_BUFCNT)
new_idx = 0;
context->current_line = new_idx;
// TODO: handle command.
context->cli_write("Got Data:", 9);
context->cli_write(current_line->line_buf, strlen(line_buf));
context->cli_write("\r\n", 2);
cli_handle_return(context);
break;
case '\b':
/**
* Backspace: send backspace and space to clear
* character. Edit the value in the command buffer as well.
*/
// Ensure that the cursor is at the end of the line.
if (context->cursor - line_buf == current_line->len &&
context->cursor != line_buf) {
context->cli_write("\b\x20\b", 3);
// Move cursor back, and clear the character there.
context->cursor--;
*(context->cursor) = '\0';
// Lower the line length.
current_line->len--;
}
cli_handle_backspace(context);
break;
case '\x1b':
/**
* Escape sequence. Read more characters from the
* input to see if we can handle it.
*/
context->cli_read(esc_buf, sizeof(esc_buf));
if (esc_buf[0] != '[') {
/**
* Not an escape sequence we understand. Print the buffer
* contents to the terminal and bail.
*/
context->cli_write(esc_buf, sizeof(esc_buf));
break;
}
/*
* If the escape sequence starts with '\x33]',
* switch on next char.
*/
switch (esc_buf[1]) {
case 'A': // Up arrow
/**
* If enough history exists, move the CLI commandline
* to the prior command.
*/
// Simulate modulo here, rather than using directly.
new_idx = context->current_line - 1;
if (new_idx < 0)
new_idx = new_idx + CLI_BUFCNT;
if (context->lines[new_idx].len != CLI_EMPTY_LINELEN) {
// Update the line buffer, cursor, and current line.
current_line = &(context->lines[new_idx]);
context->current_line = new_idx;
context->cursor = line_buf = current_line->line_buf;
// Clear line of console and write line from history.
// Clear line, and reset cursor.
context->cli_write("\x1b[2K\r", 5);
// Write prompt
context->cli_write(prompt, sizeof(prompt) - 1);
context->cli_write(line_buf, current_line->len);
break;
}
break;
case 'B': // Down arrow
/**
* If enough history exists, move the CLI commandline
* to the next command.
*/
// Simulate modulo here, rather than using directly.
new_idx = context->current_line + 1;
if (new_idx == CLI_BUFCNT)
new_idx = 0;
if (context->lines[new_idx].len != CLI_EMPTY_LINELEN) {
// Update the line buffer, cursor, and current line.
current_line = &(context->lines[new_idx]);
context->current_line = new_idx;
context->cursor = line_buf = current_line->line_buf;
// Clear line of console and write line from history.
// Clear line, and reset cursor.
context->cli_write("\x1b[2K\r", 5);
// Write prompt
context->cli_write(prompt, sizeof(prompt) - 1);
context->cli_write(line_buf, current_line->len);
break;
}
break;
case 'C': // Right arrow
if (context->cursor - line_buf != current_line->len) {
// Move cursor and print the forward control seq.
(context->cursor)++;
context->cli_write(&input, 1);
context->cli_write(esc_buf, sizeof(esc_buf));
}
break;
case 'D': // Left arrow
if (context->cursor != line_buf) {
// Move cursor and print the backward control seq.
(context->cursor)--;
context->cli_write(&input, 1);
context->cli_write(esc_buf, sizeof(esc_buf));
}
default:
// Ignore other escape sequences.
break;
}
cli_handle_esc(context);
break;
default:
if (current_line->len >= CLI_MAX_LINE - 1) {
break; // Do not echo any more data, nor write to buffer.
}
// Simply echo character, and set in buffer
context->cli_write(&input, 1);
*(context->cursor) = input;
Expand All @@ -196,11 +91,189 @@ void start_cli(CLIContext *context) {
* If we have added to the end of the buffer, increase
* line length
*/
if (context->cursor - line_buf > current_line->len) {
current_line->len = context->cursor - line_buf;
if (context->cursor - current_line->line_buf >
current_line->len) {
current_line->len =
context->cursor - current_line->line_buf;
}
break;
}
} while (input != '\r' && current_line->len < CLI_MAX_LINE);
} while (input != '\r');
}
}

/**
* Handles a return character ('\r') on the CLI.
* Will submit the null terminated command string to a CLI handler function.
* Following return of handler, will advance CLI history buffer to next entry
* and return.
* @param context: CLI context to use for this command.
*/
static void cli_handle_return(CLIContext *context) {
CLI_Line *current_line = &context->lines[context->current_line];
// Write a newline and carriage return to the console.
context->cli_write("\r\n", 2);
// Null terminate the command.
current_line->line_buf[current_line->len] = '\0';
/**
* If line is empty, do not advance to next line buffer or
* handle command.
* Else, advance to the next index in the line buffer.
*/
if (current_line->len == 0) {
current_line->len = CLI_EMPTY_LINELEN;
return;
}
move_line_index(context, true);
// TODO: handle command.
context->cli_write("Got Data:", 9);
context->cli_write(current_line->line_buf, current_line->len);
context->cli_write("\r\n", 2);
}

/**
* Handles a backspace ('\b') character on the commandline.
* If the cursor is at the end of the current statement and there are
* characters to remove, deletes a character from the screen and buffer, and
* moves the buffer pointer as well as cursor backwards.
* @param context: CLI context to use
*/
static void cli_handle_backspace(CLIContext *context) {
CLI_Line *current_line = &context->lines[context->current_line];
/*
* Backspace: send backspace and space to clear
* character. Edit the value in the command buffer as well.
*/
/*
* Ensure that the cursor is at the end of the line,
* and there is data to delete.
*/
if (context->cursor - current_line->line_buf == current_line->len &&
context->cursor != current_line->line_buf) {
// This moves the cursor back, writes a space, and moves it again
// Effectively, this clears the character before the cursor.
context->cli_write("\b\x20\b", 3);
// Move cursor back, and nullify the character there.
context->cursor--;
*(context->cursor) = '\0';
// Lower the line length.
current_line->len--;
}
}

/**
* Handles an escape character (typically will resolve to a control code) on
* the commandline.
* @param context: Context escape character recieved on.
*/
static void cli_handle_esc(CLIContext *context) {
CLI_Line *current_line = &context->lines[context->current_line];
char esc_buf[2];
/**
* Escape sequence. Read more characters from the
* input to see if we can handle it.
*/
context->cli_read(esc_buf, sizeof(esc_buf));
if (esc_buf[0] != '[') {
/**
* Not an escape sequence we understand. Print the buffer
* contents to the terminal and bail.
*/
context->cli_write(esc_buf, sizeof(esc_buf));
return;
}
/*
* If the escape sequence starts with '\x1b]',
* switch on next char.
*/
switch (esc_buf[1]) {
case 'A': // Up arrow
/**
* If enough history exists, move the CLI commandline
* to the prior command.
*/
move_line_index(context, false);
if (context->lines[context->current_line].len != CLI_EMPTY_LINELEN) {
// Update the line buffer and current line.
current_line = &(context->lines[context->current_line]);
// Set cursor to end of line buffer.
context->cursor = &current_line->line_buf[current_line->len];
// Clear line of console and write line from history.
// Clear line, and reset cursor.
context->cli_write("\x1b[2K\r", 5);
// Write prompt
context->cli_write(CLI_PROMPT, sizeof(CLI_PROMPT) - 1);
context->cli_write(current_line->line_buf, current_line->len);
} else {
// Reset current line idx.
move_line_index(context, true);
}
break;
case 'B': // Down arrow
/**
* If enough history exists, move the CLI commandline
* to the next command.
*/
move_line_index(context, true);
if (context->lines[context->current_line].len != CLI_EMPTY_LINELEN) {
// Update the line buffer, cursor, and current line.
current_line = &(context->lines[context->current_line]);
// Set cursor to end of line buffer.
context->cursor = &current_line->line_buf[current_line->len];
// Clear line of console and write line from history.
// Clear line, and reset cursor.
context->cli_write("\x1b[2K\r", 5);
// Write prompt
context->cli_write(CLI_PROMPT, sizeof(CLI_PROMPT) - 1);
context->cli_write(current_line->line_buf, current_line->len);
} else {
// Reset current line idx.
move_line_index(context, false);
}
break;
case 'C': // Right arrow
if (context->cursor - current_line->line_buf != current_line->len) {
// Move cursor and print the forward control seq.
(context->cursor)++;
context->cli_write("\x1b", 1);
context->cli_write(esc_buf, sizeof(esc_buf));
}
break;
case 'D': // Left arrow
if (context->cursor != current_line->line_buf) {
// Move cursor and print the backward control seq.
(context->cursor)--;
context->cli_write("\x1b", 1);
context->cli_write(esc_buf, sizeof(esc_buf));
}
break;
default:
// Ignore other escape sequences.
break;
}
}

/**
* Moves the index of the CLI line history buffer.
* Sets the index only. Does not edit remainder of context.
* @param context: CLI context to manipulate
* @param forwards: should the index be moved one buffer forwards or back?
*/
static void move_line_index(CLIContext *context, bool forwards) {
int new_idx;
/*
* This function simulates modulo, since we are aware exactly how far
* forwards or back we are moving the index, and our modulo is constant.
*/
if (forwards) {
new_idx = context->current_line + 1;
if (new_idx == CLI_BUFCNT)
new_idx = 0;
context->current_line = new_idx;
} else {
new_idx = context->current_line - 1;
if (new_idx < 0)
new_idx = CLI_BUFCNT - 1;
context->current_line = new_idx;
}
}

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