memfault_demo_shell.c

//! @file
//!
//! Copyright (c) Memfault, Inc.
//! See LICENSE for details
//!
//! @brief
//! Minimal shell/console implementation for platforms that do not include one.
//! NOTE: For simplicity, ANSI escape sequences are not dealt with!

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

#include "memfault/config.h"
#include "memfault/core/compiler.h"
#include "memfault/demo/shell.h"
#include "memfault/demo/shell_commands.h"

#define MEMFAULT_SHELL_MAX_ARGS (16)
#define MEMFAULT_SHELL_PROMPT "mflt> "

#if defined(MEMFAULT_DEMO_SHELL_COMMAND_EXTENSIONS)
  // When the extension list is enabled, iterate over both the core commands and
  // the extension commands. This construct, despite being pretty intricate,
  // saves about ~28 bytes of code space over running the iteration twice in a
  // row, and keeps the iterator in one macro, instead of two.
  #define MEMFAULT_SHELL_FOR_EACH_COMMAND(command)                                                 \
    const sMemfaultShellCommand *command = g_memfault_shell_commands;                              \
    for (size_t i = 0; i < g_memfault_num_shell_commands + s_mflt_shell.num_extension_commands;    \
         ++i, command = (i < g_memfault_num_shell_commands) ?                                      \
                          &g_memfault_shell_commands[i] :                                          \
                          (s_mflt_shell.extension_commands ?                                       \
                             &s_mflt_shell.extension_commands[i - g_memfault_num_shell_commands] : \
                             NULL))
#else
  #define MEMFAULT_SHELL_FOR_EACH_COMMAND(command)                         \
    for (const sMemfaultShellCommand *command = g_memfault_shell_commands; \
         command < &g_memfault_shell_commands[g_memfault_num_shell_commands]; ++command)
#endif

static struct MemfaultShellContext {
  int (*send_char)(char c);
  size_t rx_size;
  // the char we will ignore when received end-of-line sequences
  char eol_ignore_char;
  char rx_buffer[MEMFAULT_DEMO_SHELL_RX_BUFFER_SIZE];
#if defined(MEMFAULT_DEMO_SHELL_COMMAND_EXTENSIONS)
  const sMemfaultShellCommand *extension_commands;
  size_t num_extension_commands;
#endif
} s_mflt_shell;

static bool prv_booted(void) {
  return s_mflt_shell.send_char != NULL;
}

static void prv_send_char(char c) {
  if (!prv_booted()) {
    return;
  }
  s_mflt_shell.send_char(c);
}

static void prv_echo(char c) {
  if (c == '\n') {
    prv_send_char('\r');
    prv_send_char('\n');
  } else if ('\b' == c) {
    prv_send_char('\b');
    prv_send_char(' ');
    prv_send_char('\b');
  } else {
    prv_send_char(c);
  }
}

static char prv_last_char(void) {
  return s_mflt_shell.rx_buffer[s_mflt_shell.rx_size - 1];
}

static bool prv_is_rx_buffer_full(void) {
  return s_mflt_shell.rx_size >= MEMFAULT_DEMO_SHELL_RX_BUFFER_SIZE;
}

static void prv_reset_rx_buffer(void) {
  memset(s_mflt_shell.rx_buffer, 0, sizeof(s_mflt_shell.rx_buffer));
  s_mflt_shell.rx_size = 0;
}

static void prv_echo_str(const char *str) {
  for (const char *c = str; *c != '\0'; ++c) {
    prv_echo(*c);
  }
}

static void prv_send_prompt(void) {
  prv_echo_str(MEMFAULT_SHELL_PROMPT);
}

static const sMemfaultShellCommand *prv_find_command(const char *name) {
  MEMFAULT_SHELL_FOR_EACH_COMMAND (command) {
    if (strcmp(command->command, name) == 0) {
      return command;
    }
  }
  return NULL;
}

static void prv_process(void) {
  if (prv_last_char() != '\n' && !prv_is_rx_buffer_full()) {
    return;
  }

  char *argv[MEMFAULT_SHELL_MAX_ARGS] = { 0 };
  int argc = 0;

  char *next_arg = NULL;
  for (size_t i = 0; i < s_mflt_shell.rx_size && argc < MEMFAULT_SHELL_MAX_ARGS; ++i) {
    char *const c = &s_mflt_shell.rx_buffer[i];
    if (*c == ' ' || *c == '\n' || i == s_mflt_shell.rx_size - 1) {
      *c = '\0';
      if (next_arg) {
        argv[argc++] = next_arg;
        next_arg = NULL;
      }
    } else if (!next_arg) {
      next_arg = c;
    }
  }

  if (s_mflt_shell.rx_size == MEMFAULT_DEMO_SHELL_RX_BUFFER_SIZE) {
    prv_echo('\n');
  }

  if (argc >= 1) {
    const sMemfaultShellCommand *command = prv_find_command(argv[0]);
    if (!command) {
      prv_echo_str("Unknown command: ");
      prv_echo_str(argv[0]);
      prv_echo('\n');
      prv_echo_str("Type 'help' to list all commands\n");
    } else {
      command->handler(argc, argv);
    }
  }
  prv_reset_rx_buffer();
  prv_send_prompt();
}

void memfault_demo_shell_boot(const sMemfaultShellImpl *impl) {
  s_mflt_shell.eol_ignore_char = 0;
  s_mflt_shell.send_char = impl->send_char;
  prv_reset_rx_buffer();
  prv_echo_str("\n" MEMFAULT_SHELL_PROMPT);
}

#if defined(MEMFAULT_DEMO_SHELL_COMMAND_EXTENSIONS)
void memfault_shell_command_set_extensions(const sMemfaultShellCommand *const commands,
                                           size_t num_commands) {
  s_mflt_shell.extension_commands = commands;
  s_mflt_shell.num_extension_commands = num_commands;
}
#endif

//! Logic to deal with CR, LF, CRLF, or LFCR end-of-line (EOL) sequences
//! @return true if the character should be ignored, false otherwise
static bool prv_should_ignore_eol_char(char c) {
  if (s_mflt_shell.eol_ignore_char != 0) {
    return (c == s_mflt_shell.eol_ignore_char);
  }

  //
  // Check to see if we have encountered our first newline character since the shell was booted
  // (either a CR ('\r') or LF ('\n')). Once found, we will use this character as our EOL delimiter
  // and ignore the opposite character if we see it in the future.
  //

  if (c == '\r') {
    s_mflt_shell.eol_ignore_char = '\n';
  } else if (c == '\n') {
    s_mflt_shell.eol_ignore_char = '\r';
  }
  return false;
}

void memfault_demo_shell_receive_char(char c) {
  if (prv_should_ignore_eol_char(c) || prv_is_rx_buffer_full() || !prv_booted()) {
    return;
  }

  const bool is_backspace = (c == '\b');
  if (is_backspace && s_mflt_shell.rx_size == 0) {
    return;  // nothing left to delete so don't echo the backspace
  }

  // CR are our EOL delimiter. Remap as a LF here since that's what internal handling logic expects
  if (c == '\r') {
    c = '\n';
  }

  prv_echo(c);

  if (is_backspace) {
    s_mflt_shell.rx_buffer[--s_mflt_shell.rx_size] = '\0';
    return;
  }

  s_mflt_shell.rx_buffer[s_mflt_shell.rx_size++] = c;

  prv_process();
}

int memfault_shell_help_handler(MEMFAULT_UNUSED int argc, MEMFAULT_UNUSED char *argv[]) {
  MEMFAULT_SHELL_FOR_EACH_COMMAND (command) {
    prv_echo_str(command->command);
    prv_echo_str(": ");
    prv_echo_str(command->help);
    prv_echo('\n');
  }
  return 0;
}