[RFC 1/8] Change wrap buffering to use a std::string

[Tom Tromey <tom at tromey dot com>]

Currently wrap buffering is implemented by allocating a string that is
the same width as the window, and then writing characters into it.
However, if gdb emits terminal escapes, then these could possibly
overflow the buffer.

To prevent this, change the wrap buffer to be a std::string and update
the various uses.

gdb/ChangeLog
2018-09-06  Tom Tromey  <tom@tromey.com>

	* utils.c (filter_initalized): New global.
	(wrap_buffer): Now a std::string.
	(wrap_pointer): Remove.
	(filtered_printing_initialized, set_width, wrap_here)
	(fputs_maybe_filtered): Update.
---
 gdb/ChangeLog |  8 ++++++++
 gdb/utils.c   | 47 ++++++++++++++++-------------------------------
 2 files changed, 24 insertions(+), 31 deletions(-)

diff --git a/gdb/utils.c b/gdb/utils.c
index 7a8c80c64ed..1982fa20e64 100644
--- a/gdb/utils.c
+++ b/gdb/utils.c
@@ -1268,13 +1268,11 @@ static bool pagination_disabled_for_command;
    the end of the line, we spit out a newline, the indent, and then
    the buffered output.  */
 
-/* Malloc'd buffer with chars_per_line+2 bytes.  Contains characters which
-   are waiting to be output (they have already been counted in chars_printed).
-   When wrap_buffer[0] is null, the buffer is empty.  */
-static char *wrap_buffer;
+static bool filter_initalized = false;
 
-/* Pointer in wrap_buffer to the next character to fill.  */
-static char *wrap_pointer;
+/* Contains characters which are waiting to be output (they have
+   already been counted in chars_printed).  */
+static std::string wrap_buffer;
 
 /* String to indent by if the wrap occurs.  Must not be NULL if wrap_column
    is non-zero.  */
@@ -1347,7 +1345,7 @@ init_page_info (void)
 int
 filtered_printing_initialized (void)
 {
-  return wrap_buffer != NULL;
+  return filter_initalized;
 }
 
 set_batch_flag_and_restore_page_info::set_batch_flag_and_restore_page_info ()
@@ -1387,8 +1385,7 @@ set_screen_size (void)
   rl_set_screen_size (rows, cols);
 }
 
-/* Reinitialize WRAP_BUFFER according to the current value of
-   CHARS_PER_LINE.  */
+/* Reinitialize WRAP_BUFFER.  */
 
 static void
 set_width (void)
@@ -1396,14 +1393,8 @@ set_width (void)
   if (chars_per_line == 0)
     init_page_info ();
 
-  if (!wrap_buffer)
-    {
-      wrap_buffer = (char *) xmalloc (chars_per_line + 2);
-      wrap_buffer[0] = '\0';
-    }
-  else
-    wrap_buffer = (char *) xrealloc (wrap_buffer, chars_per_line + 2);
-  wrap_pointer = wrap_buffer;	/* Start it at the beginning.  */
+  wrap_buffer.clear ();
+  filter_initalized = true;
 }
 
 static void
@@ -1546,17 +1537,13 @@ void
 wrap_here (const char *indent)
 {
   /* This should have been allocated, but be paranoid anyway.  */
-  if (!wrap_buffer)
+  if (!filter_initalized)
     internal_error (__FILE__, __LINE__,
 		    _("failed internal consistency check"));
 
-  if (wrap_buffer[0])
-    {
-      *wrap_pointer = '\0';
-      fputs_unfiltered (wrap_buffer, gdb_stdout);
-    }
-  wrap_pointer = wrap_buffer;
-  wrap_buffer[0] = '\0';
+  if (!wrap_buffer.empty ())
+    fputs_unfiltered (wrap_buffer.c_str (), gdb_stdout);
+  wrap_buffer.clear ();
   if (chars_per_line == UINT_MAX)	/* No line overflow checking.  */
     {
       wrap_column = 0;
@@ -1693,7 +1680,7 @@ fputs_maybe_filtered (const char *linebuffer, struct ui_file *stream,
 	  if (*lineptr == '\t')
 	    {
 	      if (wrap_column)
-		*wrap_pointer++ = '\t';
+		wrap_buffer.push_back ('\t');
 	      else
 		fputc_unfiltered ('\t', stream);
 	      /* Shifting right by 3 produces the number of tab stops
@@ -1705,7 +1692,7 @@ fputs_maybe_filtered (const char *linebuffer, struct ui_file *stream,
 	  else
 	    {
 	      if (wrap_column)
-		*wrap_pointer++ = *lineptr;
+		wrap_buffer.push_back (*lineptr);
 	      else
 		fputc_unfiltered (*lineptr, stream);
 	      chars_printed++;
@@ -1735,8 +1722,7 @@ fputs_maybe_filtered (const char *linebuffer, struct ui_file *stream,
 	      if (wrap_column)
 		{
 		  fputs_unfiltered (wrap_indent, stream);
-		  *wrap_pointer = '\0';	/* Null-terminate saved stuff, */
-		  fputs_unfiltered (wrap_buffer, stream); /* and eject it.  */
+		  fputs_unfiltered (wrap_buffer.c_str (), stream);
 		  /* FIXME, this strlen is what prevents wrap_indent from
 		     containing tabs.  However, if we recurse to print it
 		     and count its chars, we risk trouble if wrap_indent is
@@ -1745,8 +1731,7 @@ fputs_maybe_filtered (const char *linebuffer, struct ui_file *stream,
 		     if we are printing a long string.  */
 		  chars_printed = strlen (wrap_indent)
 		    + (save_chars - wrap_column);
-		  wrap_pointer = wrap_buffer;	/* Reset buffer */
-		  wrap_buffer[0] = '\0';
+		  wrap_buffer.clear ();
 		  wrap_column = 0;	/* And disable fancy wrap */
 		}
 	    }
-- 
2.13.6