cli: Fix reverse-line-wrap in terminals (VPP-1295)

- Terminals do not reverse-line-wrap when the cursor is at the left
  edge and \b tries to make it go left.
- Instead, we have to track the cursor position if we need to emit \b's
  and if we are at the left edge emit an ANSI sequence to relocate
  the cursor. Previously we usually simply calculated the new cursor
  position after a bunch of output had completed.
- Further trickiness is required since most xterm-like terminals also
  defer moving the cursor to the next line when at the right edge[1], and
  then if they receive a \b move the cursor back one character too many.
- This requires intricate reworking of everywhere that \b is emitted
  by the CLI code during command line editing.

[1] Bash counters this issue by tracking the cursor position as output
  is generated and forcing the cursor to the next line (by emitting
  a space followed by \r) if it gets to this phantom cursor position);
  here we effectively do that but only if the user tries to go left
  when in this state.

Change-Id: I7c1d7c0e24c53111a5810cebb504ccfdac743086
Signed-off-by: Chris Luke <chrisy@flirble.org>

1 files changed, 195 insertions, 86 deletions

diff --git a/src/vlib/unix/cli.c b/src/vlib/unix/cli.c
index 512a77aa8f7..6c49d80aabd 100644
--- a/src/vlib/unix/cli.c
+++ b/src/vlib/unix/cli.c
@@ -226,6 +226,20 @@ typedef struct
 
   /** Process node identifier */
   u32 process_node_index;
+
+  /** The current direction of cursor travel.
+   *  This is important since when advancing left-to-right, at the
+   *  right hand edge of the console the terminal typically defers
+   *  wrapping the cursor to the next line until a character is
+   *  actually displayed.
+   *  This messes up our heuristic for whether to use ANSI to return
+   *  the cursor to the end of the line and instead we have to
+   *  nudge the cursor to the next line.
+   *  A Value of @c 0 means we're advancing left-to-right; @c 1 means
+   *  the opposite.
+   */
+  u8 cursor_direction;
+
 } unix_cli_file_t;
 
 /** Resets the pager buffer and other data.
@@ -681,6 +695,69 @@ unix_vlib_cli_output_cooked (unix_cli_file_t * cf,
 	  start = end;
 	}
     }
+
+  /* Use the last character to determine the last direction of the cursor. */
+  if (buffer_bytes > 0)
+    cf->cursor_direction = (buffer[buffer_bytes - 1] == (u8) '\b');
+}
+
+/** @brief Moves the terminal cursor one character to the left, with
+ * special handling when it reaches the left edge of the terminal window.
+ *
+ * Ordinarily we can simply send a '\b' to move the cursor left, however
+ * most terminals will not reverse-wrap to the end of the previous line
+ * if the cursor is in the left-most column. To counter this we must
+ * check the cursor position + prompt length modulo terminal width and
+ * if available use some other means, such as ANSI terminal escape
+ * sequences, to move the cursor.
+ *
+ * @param cf Unix CLI session of the desired stream to write to.
+ * @param uf The Unix file structure of the desired stream to write to.
+ */
+static void
+unix_vlib_cli_output_cursor_left (unix_cli_file_t * cf, clib_file_t * uf)
+{
+  unix_cli_main_t *cm = &unix_cli_main;
+  static u8 *ansi = 0;		/* assumes no reentry */
+  u32 position;
+
+  if (!cf->is_interactive || !cf->ansi_capable || !cf->width)
+    {
+      /* No special handling for dumb terminals */
+      unix_vlib_cli_output_cooked (cf, uf, (u8 *) "\b", 1);
+      return;
+    }
+
+  position = ((u32) vec_len (cm->cli_prompt) + cf->cursor) % cf->width;
+
+  if (position != 0)
+    {
+      /* No special handling required if we're not at the left edge */
+      unix_vlib_cli_output_cooked (cf, uf, (u8 *) "\b", 1);
+      return;
+    }
+
+  if (!cf->cursor_direction)
+    {
+      /* Special handling for when we are at the left edge but
+       * the cursor was going left-to-right, but in this situation
+       * xterm-like terminals actually hide the cursor off the right
+       * edge. A \b here seems to jump one char too many, so let's
+       * force the cursor onto the next line instead.
+       */
+      if (cf->cursor < vec_len (cf->current_command))
+	unix_vlib_cli_output_cooked (cf, uf, &cf->current_command[cf->cursor],
+				     1);
+      else
+	unix_vlib_cli_output_cooked (cf, uf, (u8 *) " ", 1);
+      unix_vlib_cli_output_cooked (cf, uf, (u8 *) "\r", 1);
+    }
+
+  /* Relocate the cursor at the right hand edge one line above */
+  ansi = format (ansi, CSI "A" CSI "%dC", cf->width - 1);
+  unix_vlib_cli_output_cooked (cf, uf, ansi, vec_len (ansi));
+  vec_reset_length (ansi);	/* keep the vec around for next time */
+  cf->cursor_direction = 1;	/* going backwards now */
 }
 
 /** @brief Output the CLI prompt */
@@ -1359,16 +1436,20 @@ unix_cli_line_process_one (unix_cli_main_t * cm,
       if (cf->search_mode == 0)
 	{
 	  /* Erase the current command (if any) */
-	  for (j = 0; j < (vec_len (cf->current_command)); j++)
-	    unix_vlib_cli_output_cooked (cf, uf, (u8 *) "\b \b", 3);
+	  for (; cf->cursor > 0; cf->cursor--)
+	    {
+	      unix_vlib_cli_output_cursor_left (cf, uf);
+	      unix_vlib_cli_output_cooked (cf, uf, (u8 *) " ", 1);
+	      unix_vlib_cli_output_cursor_left (cf, uf);
+	    }
 
 	  vec_reset_length (cf->search_key);
 	  vec_reset_length (cf->current_command);
+
 	  if (action == UNIX_CLI_PARSE_ACTION_REVSEARCH)
 	    cf->search_mode = -1;
 	  else
 	    cf->search_mode = 1;
-	  cf->cursor = 0;
 	}
       else
 	{
@@ -1385,27 +1466,29 @@ unix_cli_line_process_one (unix_cli_main_t * cm,
     case UNIX_CLI_PARSE_ACTION_ERASELINELEFT:
       /* Erase the command from the cursor to the start */
 
-      /* Shimmy forwards to the new end of line position */
+      j = cf->cursor;
+      /* Shimmy backwards to the new end of line position */
       delta = vec_len (cf->current_command) - cf->cursor;
-      for (j = cf->cursor; j > delta; j--)
-	unix_vlib_cli_output_cooked (cf, uf, (u8 *) "\b", 1);
+      for (; cf->cursor > delta; cf->cursor--)
+	unix_vlib_cli_output_cursor_left (cf, uf);
       /* Zap from here to the end of what is currently displayed */
-      for (; j < (vec_len (cf->current_command)); j++)
+      for (; cf->cursor < vec_len (cf->current_command); cf->cursor++)
 	unix_vlib_cli_output_cooked (cf, uf, (u8 *) " ", 1);
       /* Get back to the start of the line */
-      for (j = 0; j < (vec_len (cf->current_command)); j++)
-	unix_vlib_cli_output_cooked (cf, uf, (u8 *) "\b", 1);
+      for (; cf->cursor > 0; cf->cursor--)
+	unix_vlib_cli_output_cursor_left (cf, uf);
 
-      j = vec_len (cf->current_command) - cf->cursor;
-      memmove (cf->current_command, cf->current_command + cf->cursor, j);
-      _vec_len (cf->current_command) = j;
+      /* Delete the desired text from the command */
+      memmove (cf->current_command, cf->current_command + j, delta);
+      _vec_len (cf->current_command) = delta;
 
       /* Print the new contents */
-      unix_vlib_cli_output_cooked (cf, uf, cf->current_command, j);
+      unix_vlib_cli_output_cooked (cf, uf, cf->current_command, delta);
+      cf->cursor = delta;	/* for backspace tracking */
+
       /* Shimmy back to the start */
-      for (j = 0; j < (vec_len (cf->current_command)); j++)
-	unix_vlib_cli_output_cooked (cf, uf, (u8 *) "\b", 1);
-      cf->cursor = 0;
+      for (; cf->cursor > 0; cf->cursor--)
+	unix_vlib_cli_output_cursor_left (cf, uf);
 
       cf->search_mode = 0;
       break;
@@ -1413,12 +1496,13 @@ unix_cli_line_process_one (unix_cli_main_t * cm,
     case UNIX_CLI_PARSE_ACTION_ERASELINERIGHT:
       /* Erase the command from the cursor to the end */
 
+      j = cf->cursor;
       /* Zap from cursor to end of what is currently displayed */
-      for (j = cf->cursor; j < (vec_len (cf->current_command)); j++)
+      for (; cf->cursor < (vec_len (cf->current_command)); cf->cursor++)
 	unix_vlib_cli_output_cooked (cf, uf, (u8 *) " ", 1);
       /* Get back to where we were */
-      for (j = cf->cursor; j < (vec_len (cf->current_command)); j++)
-	unix_vlib_cli_output_cooked (cf, uf, (u8 *) "\b", 1);
+      for (; cf->cursor > j; cf->cursor--)
+	unix_vlib_cli_output_cursor_left (cf, uf);
 
       /* Truncate the line at the cursor */
       _vec_len (cf->current_command) = cf->cursor;
@@ -1429,7 +1513,7 @@ unix_cli_line_process_one (unix_cli_main_t * cm,
     case UNIX_CLI_PARSE_ACTION_LEFT:
       if (cf->cursor > 0)
 	{
-	  unix_vlib_cli_output_cooked (cf, uf, (u8 *) "\b", 1);
+	  unix_vlib_cli_output_cursor_left (cf, uf);
 	  cf->cursor--;
 	}
 
@@ -1454,10 +1538,14 @@ unix_cli_line_process_one (unix_cli_main_t * cm,
 	break;
       cf->search_mode = 0;
       /* Erase the command */
-      for (j = cf->cursor; j < (vec_len (cf->current_command)); j++)
+      for (; cf->cursor < vec_len (cf->current_command); cf->cursor++)
 	unix_vlib_cli_output_cooked (cf, uf, (u8 *) " ", 1);
-      for (j = 0; j < (vec_len (cf->current_command)); j++)
-	unix_vlib_cli_output_cooked (cf, uf, (u8 *) "\b \b", 3);
+      for (; cf->cursor > 0; cf->cursor--)
+	{
+	  unix_vlib_cli_output_cursor_left (cf, uf);
+	  unix_vlib_cli_output_cooked (cf, uf, (u8 *) " ", 1);
+	  unix_vlib_cli_output_cursor_left (cf, uf);
+	}
       vec_reset_length (cf->current_command);
       if (vec_len (cf->command_history))
 	{
@@ -1501,11 +1589,8 @@ unix_cli_line_process_one (unix_cli_main_t * cm,
     case UNIX_CLI_PARSE_ACTION_HOME:
       if (vec_len (cf->current_command) && cf->cursor > 0)
 	{
-	  while (cf->cursor)
-	    {
-	      unix_vlib_cli_output_cooked (cf, uf, (u8 *) "\b", 1);
-	      cf->cursor--;
-	    }
+	  for (; cf->cursor > 0; cf->cursor--)
+	    unix_vlib_cli_output_cursor_left (cf, uf);
 	}
 
       cf->search_mode = 0;
@@ -1528,25 +1613,22 @@ unix_cli_line_process_one (unix_cli_main_t * cm,
     case UNIX_CLI_PARSE_ACTION_WORDLEFT:
       if (vec_len (cf->current_command) && cf->cursor > 0)
 	{
-	  j = cf->cursor;
-
-	  unix_vlib_cli_output_cooked (cf, uf, (u8 *) "\b", 1);
-	  j--;
+	  unix_vlib_cli_output_cursor_left (cf, uf);
+	  cf->cursor--;
 
-	  while (j && isspace (cf->current_command[j]))
+	  while (cf->cursor && isspace (cf->current_command[cf->cursor]))
 	    {
-	      unix_vlib_cli_output_cooked (cf, uf, (u8 *) "\b", 1);
-	      j--;
+	      unix_vlib_cli_output_cursor_left (cf, uf);
+	      cf->cursor--;
 	    }
-	  while (j && !isspace (cf->current_command[j]))
+	  while (cf->cursor && !isspace (cf->current_command[cf->cursor]))
 	    {
-	      if (isspace (cf->current_command[j - 1]))
+	      if (isspace (cf->current_command[cf->cursor - 1]))
 		break;
-	      unix_vlib_cli_output_cooked (cf, uf, (u8 *) "\b", 1);
-	      j--;
+	      unix_vlib_cli_output_cursor_left (cf, uf);
+	      cf->cursor--;
 	    }
 
-	  cf->cursor = j;
 	}
 
       cf->search_mode = 0;
@@ -1577,9 +1659,13 @@ unix_cli_line_process_one (unix_cli_main_t * cm,
 	{
 	  if (cf->cursor == vec_len (cf->current_command))
 	    {
-	      unix_vlib_cli_output_cooked (cf, uf, (u8 *) "\b \b", 3);
-	      _vec_len (cf->current_command)--;
+	      unix_vlib_cli_output_cursor_left (cf, uf);
 	      cf->cursor--;
+	      unix_vlib_cli_output_cooked (cf, uf, (u8 *) " ", 1);
+	      cf->cursor++;
+	      unix_vlib_cli_output_cursor_left (cf, uf);
+	      cf->cursor--;
+	      _vec_len (cf->current_command)--;
 	    }
 	  else if (cf->cursor > 0)
 	    {
@@ -1588,16 +1674,25 @@ unix_cli_line_process_one (unix_cli_main_t * cm,
 	      memmove (cf->current_command + cf->cursor - 1,
 		       cf->current_command + cf->cursor, j);
 	      _vec_len (cf->current_command)--;
-	      cf->cursor--;
+
 	      /* redraw the rest of the line */
-	      unix_vlib_cli_output_cooked (cf, uf, (u8 *) "\b", 1);
+	      unix_vlib_cli_output_cursor_left (cf, uf);
+	      cf->cursor--;
 	      unix_vlib_cli_output_cooked (cf, uf,
 					   cf->current_command + cf->cursor,
 					   j);
-	      unix_vlib_cli_output_cooked (cf, uf, (u8 *) " \b\b", 3);
+	      cf->cursor += j;
+	      /* erase last char */
+	      unix_vlib_cli_output_cooked (cf, uf, (u8 *) " ", 1);
+	      cf->cursor++;
+
 	      /* and shift the terminal cursor back where it should be */
+	      j += 2;		/* account for old string length and offset position */
 	      while (--j)
-		unix_vlib_cli_output_cooked (cf, uf, (u8 *) "\b", 1);
+		{
+		  unix_vlib_cli_output_cursor_left (cf, uf);
+		  cf->cursor--;
+		}
 	    }
 	}
       cf->search_mode = 0;
@@ -1619,13 +1714,21 @@ unix_cli_line_process_one (unix_cli_main_t * cm,
 	      unix_vlib_cli_output_cooked (cf, uf,
 					   cf->current_command + cf->cursor,
 					   j);
-	      unix_vlib_cli_output_cooked (cf, uf, (u8 *) " \b", 2);
+	      cf->cursor += j;
+	      unix_vlib_cli_output_cooked (cf, uf, (u8 *) " ", 1);
+	      cf->cursor++;
+	      unix_vlib_cli_output_cursor_left (cf, uf);
+	      cf->cursor--;
 	      /* and shift the terminal cursor back where it should be */
 	      if (j)
 		{
-		  unix_vlib_cli_output_cooked (cf, uf, (u8 *) "\b", 1);
+		  unix_vlib_cli_output_cursor_left (cf, uf);
+		  cf->cursor--;
 		  while (--j)
-		    unix_vlib_cli_output_cooked (cf, uf, (u8 *) "\b", 1);
+		    {
+		      unix_vlib_cli_output_cursor_left (cf, uf);
+		      cf->cursor--;
+		    }
 		}
 	    }
 	}
@@ -1657,11 +1760,13 @@ unix_cli_line_process_one (unix_cli_main_t * cm,
 
       unix_vlib_cli_output_raw (cf, uf,
 				cm->cli_prompt, vec_len (cm->cli_prompt));
-      unix_vlib_cli_output_raw (cf, uf,
-				cf->current_command,
-				vec_len (cf->current_command));
-      for (j = cf->cursor; j < vec_len (cf->current_command); j++)
-	unix_vlib_cli_output_cooked (cf, uf, (u8 *) "\b", 1);
+      unix_vlib_cli_output_cooked (cf, uf,
+				   cf->current_command,
+				   vec_len (cf->current_command));
+      j = cf->cursor;
+      cf->cursor = vec_len (cf->current_command);
+      for (; cf->cursor > j; cf->cursor--)
+	unix_vlib_cli_output_cursor_left (cf, uf);
 
       break;
 
@@ -1688,14 +1793,15 @@ unix_cli_line_process_one (unix_cli_main_t * cm,
 	vlib_cli_get_possible_completions (cf->current_command);
       if (vec_len (possible_commands) == 1)
 	{
-	  u32 j = cf->cursor;
 	  u8 *completed = possible_commands[0];
+	  j = cf->cursor;
 
 	  /* find the last word of current_command */
 	  while (j >= 1 && !isspace (cf->current_command[j - 1]))
 	    {
+	      unix_vlib_cli_output_cursor_left (cf, uf);
+	      cf->cursor--;
 	      j--;
-	      unix_vlib_cli_output_raw (cf, uf, (u8 *) "\b", 1);
 	    }
 	  _vec_len (cf->current_command) = j;
 
@@ -1703,13 +1809,14 @@ unix_cli_line_process_one (unix_cli_main_t * cm,
 	  vec_append (cf->current_command, completed);
 
 	  /* echo to the terminal */
-	  unix_vlib_cli_output_raw (cf, uf, completed, vec_len (completed));
+	  unix_vlib_cli_output_cooked (cf, uf, completed,
+				       vec_len (completed));
 
 	  /* add one trailing space if needed */
 	  if (vec_len (save) == 0)
 	    {
 	      vec_add1 (cf->current_command, ' ');
-	      unix_vlib_cli_output_raw (cf, uf, (u8 *) " ", 1);
+	      unix_vlib_cli_output_cooked (cf, uf, (u8 *) " ", 1);
 	    }
 
 	  cf->cursor = vec_len (cf->current_command);
@@ -1719,18 +1826,14 @@ unix_cli_line_process_one (unix_cli_main_t * cm,
 	{
 	  u8 **possible_command;
 	  uword max_command_len = 0, min_command_len = ~0;
-	  u32 i, j;
+	  u32 i;
 
 	  vec_foreach (possible_command, possible_commands)
 	  {
 	    if (vec_len (*possible_command) > max_command_len)
-	      {
-		max_command_len = vec_len (*possible_command);
-	      }
+	      max_command_len = vec_len (*possible_command);
 	    if (vec_len (*possible_command) < min_command_len)
-	      {
-		min_command_len = vec_len (*possible_command);
-	      }
+	      min_command_len = vec_len (*possible_command);
 	  }
 
 	  unix_vlib_cli_output_cooked (cf, uf, (u8 *) "\n", 1);
@@ -1743,12 +1846,12 @@ unix_cli_line_process_one (unix_cli_main_t * cm,
 		unix_vlib_cli_output_cooked (cf, uf, (u8 *) "\n", 1);
 		i = 0;
 	      }
-	    unix_vlib_cli_output_raw (cf, uf, *possible_command,
-				      vec_len (*possible_command));
+	    unix_vlib_cli_output_cooked (cf, uf, *possible_command,
+					 vec_len (*possible_command));
 	    for (j = vec_len (*possible_command); j < max_command_len + 2;
 		 j++)
 	      {
-		unix_vlib_cli_output_raw (cf, uf, (u8 *) " ", 1);
+		unix_vlib_cli_output_cooked (cf, uf, (u8 *) " ", 1);
 	      }
 	    i += max_command_len + 2;
 	  }
@@ -1757,8 +1860,8 @@ unix_cli_line_process_one (unix_cli_main_t * cm,
 
 	  /* rewrite prompt */
 	  unix_cli_cli_prompt (cf, uf);
-	  unix_vlib_cli_output_raw (cf, uf, cf->current_command,
-				    vec_len (cf->current_command));
+	  unix_vlib_cli_output_cooked (cf, uf, cf->current_command,
+				       vec_len (cf->current_command));
 
 	  /* count length of last word */
 	  j = cf->cursor;
@@ -1774,6 +1877,7 @@ unix_cli_line_process_one (unix_cli_main_t * cm,
 	    {
 	      u8 common = '\0';
 	      int stop = 0;
+
 	      vec_foreach (possible_command, possible_commands)
 	      {
 		if (common == '\0')
@@ -1786,11 +1890,12 @@ unix_cli_line_process_one (unix_cli_main_t * cm,
 		    break;
 		  }
 	      }
+
 	      if (!stop)
 		{
 		  vec_add1 (cf->current_command, common);
 		  cf->cursor++;
-		  unix_vlib_cli_output_raw (cf, uf, (u8 *) & common, 1);
+		  unix_vlib_cli_output_cooked (cf, uf, (u8 *) & common, 1);
 		}
 	      else
 		{
@@ -1806,11 +1911,10 @@ unix_cli_line_process_one (unix_cli_main_t * cm,
       if (vec_len (save) > 0)
 	{
 	  /* restore remaining input if tab was hit in the middle of a line */
-	  unix_vlib_cli_output_raw (cf, uf, save, vec_len (save));
-	  for (j = 0; j < vec_len (save); j++)
-	    {
-	      unix_vlib_cli_output_raw (cf, uf, (u8 *) "\b", 1);
-	    }
+	  unix_vlib_cli_output_cooked (cf, uf, save, vec_len (save));
+	  cf->cursor += vec_len (save);
+	  for (j = 0; j < vec_len (save); j++, cf->cursor--)
+	    unix_vlib_cli_output_cursor_left (cf, uf);
 	  vec_append (cf->current_command, save);
 	  vec_free (save);
 	}
@@ -2062,7 +2166,7 @@ unix_cli_line_process_one (unix_cli_main_t * cm,
 	{
 	  /* no-op for now */
 	}
-      else if (cf->has_history && cf->search_mode && isprint (input))
+      else if (cf->has_history && cf->search_mode != 0 && isprint (input))
 	{
 	  int k, limit, offset;
 	  u8 *item;
@@ -2097,8 +2201,12 @@ unix_cli_line_process_one (unix_cli_main_t * cm,
 	      goto next;
 
 	    found_at_offset:
-	      for (j = 0; j < vec_len (cf->current_command); j++)
-		unix_vlib_cli_output_cooked (cf, uf, (u8 *) "\b \b", 3);
+	      for (; cf->cursor > 0; cf->cursor--)
+		{
+		  unix_vlib_cli_output_cursor_left (cf, uf);
+		  unix_vlib_cli_output_cooked (cf, uf, (u8 *) " ", 1);
+		  unix_vlib_cli_output_cursor_left (cf, uf);
+		}
 
 	      vec_validate (cf->current_command, vec_len (item) - 1);
 	      clib_memcpy (cf->current_command, item, vec_len (item));
@@ -2129,7 +2237,7 @@ unix_cli_line_process_one (unix_cli_main_t * cm,
 	      cf->cursor++;
 
 	      /* Echo the character back to the client */
-	      unix_vlib_cli_output_raw (cf, uf, &input, 1);
+	      unix_vlib_cli_output_cooked (cf, uf, &input, 1);
 	    }
 	  else
 	    {
@@ -2141,12 +2249,14 @@ unix_cli_line_process_one (unix_cli_main_t * cm,
 	      cf->current_command[cf->cursor] = input;
 	      /* Redraw the line */
 	      j++;
-	      unix_vlib_cli_output_raw (cf, uf,
-					cf->current_command + cf->cursor, j);
+	      unix_vlib_cli_output_cooked (cf, uf,
+					   cf->current_command + cf->cursor,
+					   j);
+	      cf->cursor += j;
+	      j--;
 	      /* Put terminal cursor back */
-	      while (--j)
-		unix_vlib_cli_output_raw (cf, uf, (u8 *) "\b", 1);
-	      cf->cursor++;
+	      for (; j > 0; j--, cf->cursor--)
+		unix_vlib_cli_output_cursor_left (cf, uf);
 	    }
 	}
       else
@@ -3289,7 +3399,6 @@ unix_cli_show_cli_sessions (vlib_main_t * vm,
 			    unformat_input_t * input,
 			    vlib_cli_command_t * cmd)
 {
-  //unix_main_t *um = &unix_main;
   unix_cli_main_t *cm = &unix_cli_main;
   clib_file_main_t *fm = &file_main;
   unix_cli_file_t *cf;