From: Lennart Poettering <lennart@poettering.net>
Date: Wed, 31 Jan 2024 17:48:53 +0000 (+0100)
Subject: ptyfwd: tweaks to background tinting logic
X-Git-Tag: v256-rc1~893^2~6
X-Git-Url: http://git.ipfire.org/gitweb.cgi?a=commitdiff_plain;h=d0aa368c85adf2efa29c363a6671927fe7e8e76f;p=thirdparty%2Fsystemd.git

ptyfwd: tweaks to background tinting logic

This makes two changes:

1. it resets the background color not only on NL (aka LF) but also on
   CR, but without erasing things to the end of the line. This increases
   compatbility with tools such as "less" which use CR to jump back to
   the beginning of the line.

2. previously we'd not process series of newlines or ansi sequences
   without intermediate other characters correctly, we'd always assume
   what follows is regular text. Fix that, and correctly determine the
   right state from the subsequent character.
---

diff --git a/src/shared/ptyfwd.c b/src/shared/ptyfwd.c
index c05ce794892..32147495958 100644
--- a/src/shared/ptyfwd.c
+++ b/src/shared/ptyfwd.c
@@ -34,6 +34,7 @@ typedef enum AnsiColorState  {
         ANSI_COLOR_STATE_ESC,
         ANSI_COLOR_STATE_CSI_SEQUENCE,
         ANSI_COLOR_STATE_NEWLINE,
+        ANSI_COLOR_STATE_CARRIAGE_RETURN,
         _ANSI_COLOR_STATE_MAX,
         _ANSI_COLOR_STATE_INVALID = -EINVAL,
 } AnsiColorState;
@@ -230,9 +231,7 @@ static char *background_color_sequence(PTYForward *f) {
         assert(f);
         assert(f->background_color);
 
-        /* This sets the background color to the desired one, and erase the rest of the line with it */
-
-        return strjoin("\x1B[", f->background_color, "m", ANSI_ERASE_TO_END_OF_LINE);
+        return strjoin("\x1B[", f->background_color, "m");
 }
 
 static int insert_string(PTYForward *f, size_t offset, const char *s) {
@@ -257,12 +256,33 @@ static int insert_string(PTYForward *f, size_t offset, const char *s) {
         return (int) l;
 }
 
-static int insert_erase_newline(PTYForward *f, size_t offset) {
+static int insert_newline_color_erase(PTYForward *f, size_t offset) {
         _cleanup_free_ char *s = NULL;
 
         assert(f);
         assert(f->background_color);
 
+        /* When we see a newline (ASCII 10) then this sets the background color to the desired one, and erase the rest
+         * of the line with it */
+
+        s = background_color_sequence(f);
+        if (!s)
+                return -ENOMEM;
+
+        if (!strextend(&s, ANSI_ERASE_TO_END_OF_LINE))
+                return -ENOMEM;
+
+        return insert_string(f, offset, s);
+}
+
+static int insert_carriage_return_color(PTYForward *f, size_t offset) {
+        _cleanup_free_ char *s = NULL;
+
+        assert(f);
+        assert(f->background_color);
+
+        /* When we see a carriage return (ASCII 13) this this sets only the background */
+
         s = background_color_sequence(f);
         if (!s)
                 return -ENOMEM;
@@ -369,31 +389,36 @@ static int pty_forward_ansi_process(PTYForward *f, size_t offset) {
                 switch (f->ansi_color_state) {
 
                 case ANSI_COLOR_STATE_TEXT:
-                        if (c == '\n')
-                                f->ansi_color_state = ANSI_COLOR_STATE_NEWLINE;
-                        if (c == 0x1B) /* ESC */
-                                f->ansi_color_state = ANSI_COLOR_STATE_ESC;
                         break;
 
                 case ANSI_COLOR_STATE_NEWLINE: {
                         /* Immediately after a newline insert an ANSI sequence to erase the line with a background color */
 
-                        r = insert_erase_newline(f, i);
+                        r = insert_newline_color_erase(f, i);
                         if (r < 0)
                                 return r;
 
                         i += r;
+                        break;
+                }
 
-                        f->ansi_color_state = ANSI_COLOR_STATE_TEXT;
+                case ANSI_COLOR_STATE_CARRIAGE_RETURN: {
+                        /* Immediately after a carriage return insert an ANSI sequence set the background color back */
+
+                        r = insert_carriage_return_color(f, i);
+                        if (r < 0)
+                                return r;
+
+                        i += r;
                         break;
                 }
 
                 case ANSI_COLOR_STATE_ESC: {
 
-                        if (c == '[')
+                        if (c == '[') {
                                 f->ansi_color_state = ANSI_COLOR_STATE_CSI_SEQUENCE;
-                        else
-                                f->ansi_color_state = ANSI_COLOR_STATE_TEXT;
+                                continue;
+                        }
 
                         break;
                 }
@@ -408,7 +433,7 @@ static int pty_forward_ansi_process(PTYForward *f, size_t offset) {
                                         /* Safety check: lets not accept unbounded CSI sequences */
 
                                         f->csi_sequence = mfree(f->csi_sequence);
-                                        f->ansi_color_state = ANSI_COLOR_STATE_TEXT;
+                                        break;
                                 } else if (!strextend(&f->csi_sequence, CHAR_TO_STR(c)))
                                         return -ENOMEM;
                         } else {
@@ -427,12 +452,21 @@ static int pty_forward_ansi_process(PTYForward *f, size_t offset) {
                                 f->ansi_color_state = ANSI_COLOR_STATE_TEXT;
                         }
 
-                        break;
+                        continue;
                 }
 
                 default:
                         assert_not_reached();
                 }
+
+                if (c == '\n')
+                        f->ansi_color_state = ANSI_COLOR_STATE_NEWLINE;
+                else if (c == '\r')
+                        f->ansi_color_state = ANSI_COLOR_STATE_CARRIAGE_RETURN;
+                else if (c == 0x1B) /* ESC */
+                        f->ansi_color_state = ANSI_COLOR_STATE_ESC;
+                else
+                        f->ansi_color_state = ANSI_COLOR_STATE_TEXT;
         }
 
         return 0;
@@ -450,6 +484,9 @@ static int shovel(PTYForward *f) {
                 if (!f->out_buffer)
                         return pty_forward_done(f, log_oom());
 
+                if (!strextend(&f->out_buffer, ANSI_ERASE_TO_END_OF_LINE))
+                        return pty_forward_done(f, log_oom());
+
                 f->out_buffer_full = strlen(f->out_buffer);
                 f->out_buffer_size = MALLOC_SIZEOF_SAFE(f->out_buffer);
         }