From 5ba7ce6802eccabb15acf01f0f57b25d60e0f3f4 Mon Sep 17 00:00:00 2001
From: Jonas 'Sortie' Termansen <sortie@maxsi.org>
Date: Sun, 27 Dec 2015 21:43:41 +0100
Subject: [PATCH] Add backwards support to pager(1).

---
 utils/pager.cpp | 619 +++++++++++++++++++++++++++++-------------------
 1 file changed, 381 insertions(+), 238 deletions(-)

diff --git a/utils/pager.cpp b/utils/pager.cpp
index c8615207..a1efb52d 100644
--- a/utils/pager.cpp
+++ b/utils/pager.cpp
@@ -45,9 +45,11 @@ enum control_state
 	CONTROL_STATE_COMMAND,
 };
 
-struct display_entry
+struct line
 {
-	wchar_t c;
+	char* content;
+	size_t content_used;
+	size_t content_length;
 };
 
 struct pager
@@ -55,27 +57,36 @@ struct pager
 	int tty_fd;
 	unsigned int tty_fd_old_termmode;
 	int out_fd;
-	bool out_fd_tty;
+	bool out_fd_is_tty;
 	struct winsize out_fd_winsize;
-	struct display_entry* display;
-	struct wincurpos begun_wcp;
-	struct wincurpos current_wcp;
 	mbstate_t in_ps;
 	mbstate_t out_ps;
 	const char* input_prompt_name;
+	size_t possible_lines;
 	size_t allowed_lines;
 	bool quiting;
 	bool flag_raw_control_chars;
 	bool flag_color_sequences;
 	enum control_state control_state;
-	unsigned char control_sequence[CONTROL_SEQUENCE_MAX];
+	wchar_t control_sequence[CONTROL_SEQUENCE_MAX];
 	size_t control_sequence_length;
 	bool input_set_color;
+	struct line* lines;
+	size_t lines_used;
+	size_t lines_length;
+	enum control_state incoming_control_state;
+	struct line* incoming_line;
+	size_t incoming_line_width;
+	size_t current_line;
+	size_t current_line_offset;
+	bool allowance_ever_exhausted;
+	bool skipping_to_end;
 };
 
-void pager_init(struct pager* pager)
+static void pager_init(struct pager* pager)
 {
-	if ( !isatty(pager->tty_fd = 0) )
+	pager->tty_fd = 0;
+	if ( !isatty(pager->tty_fd) )
 	{
 		if ( (pager->tty_fd = open("/dev/tty", O_RDONLY)) < 0 )
 			error(1, errno, "/dev/tty");
@@ -85,41 +96,36 @@ void pager_init(struct pager* pager)
 	gettermmode(pager->tty_fd, &pager->tty_fd_old_termmode);
 	settermmode(pager->tty_fd, TERMMODE_KBKEY | TERMMODE_UNICODE | TERMMODE_SIGNAL);
 
-	if ( (pager->out_fd_tty = isatty(pager->out_fd = 1)) )
+	pager->out_fd = 1;
+	if ( (pager->out_fd_is_tty = isatty(pager->out_fd)) )
 	{
 		tcgetwinsize(pager->out_fd, &pager->out_fd_winsize);
-		size_t display_length = (size_t) pager->out_fd_winsize.ws_col *
-		                        (size_t) pager->out_fd_winsize.ws_row;
-		pager->display = (struct display_entry*)
-			calloc(display_length, sizeof(struct display_entry));
-		if ( !pager->display )
-		{
-			error(0, errno, "malloc");
-			settermmode(pager->tty_fd, pager->tty_fd_old_termmode);
-			exit(1);
-		}
-		tcgetwincurpos(pager->out_fd, &pager->begun_wcp);
-		memcpy(&pager->current_wcp, &pager->begun_wcp, sizeof(struct wincurpos));
-		pager->allowed_lines = pager->out_fd_winsize.ws_row - 1;
+		pager->possible_lines = pager->out_fd_winsize.ws_row - 1;
+		pager->allowed_lines = pager->possible_lines;
 	}
 
 	memset(&pager->in_ps, 0, sizeof(pager->in_ps));
 	memset(&pager->out_ps, 0, sizeof(pager->out_ps));
 }
 
-void pager_end(struct pager* pager)
+static void pager_end(struct pager* pager)
 {
+	for ( size_t i = 0; i < pager->lines_used; i++ )
+		free(pager->lines[i].content);
+	free(pager->lines);
 	settermmode(pager->tty_fd, pager->tty_fd_old_termmode);
 	if ( pager->tty_fd != 0 )
 		close(pager->tty_fd);
 }
 
-void pager_prompt(struct pager* pager)
+static void pager_prompt(struct pager* pager, bool at_end)
 {
-	if ( pager->input_prompt_name[0] && pager->input_set_color )
-		dprintf(pager->out_fd, "%s\e[J", pager->input_prompt_name);
-	else if ( pager->input_prompt_name[0] && !pager->input_set_color )
-		dprintf(pager->out_fd, "\e[47;30m%s\e[m\e[J", pager->input_prompt_name);
+	const char* pre = pager->input_set_color ? "" : "\e[47;30m";
+	const char* post = pager->input_set_color ? "" : "\e[m";
+	if ( at_end )
+		dprintf(pager->out_fd, "%s(END)%s\e[J", pre, post);
+	else if ( pager->input_prompt_name[0] )
+		dprintf(pager->out_fd, "%s%s%s\e[J", pre, pager->input_prompt_name, post);
 	else
 		dprintf(pager->out_fd, ":");
 	uint32_t codepoint;
@@ -132,20 +138,57 @@ void pager_prompt(struct pager* pager)
 			return;
 		}
 
+		if ( KBKEY_DECODE(codepoint) == KBKEY_UP )
+		{
+			if ( pager->current_line <= pager->possible_lines )
+				continue;
+			dprintf(pager->out_fd, "\e[2J\e[H");
+			pager->current_line -= pager->possible_lines + 1;
+			pager->current_line_offset = 0;
+			pager->allowed_lines = pager->possible_lines;
+			return;
+		}
+
 		if ( codepoint == L' ' || KBKEY_DECODE(codepoint) == KBKEY_PGDOWN )
 		{
 			dprintf(pager->out_fd, "\r\e[J");
-			pager->allowed_lines = pager->out_fd_winsize.ws_row - 1;
+			pager->allowed_lines = pager->possible_lines;
+			return;
+		}
+
+		if ( KBKEY_DECODE(codepoint) == KBKEY_PGUP )
+		{
+			if ( pager->current_line <= pager->possible_lines )
+				continue;
+			size_t distance = pager->possible_lines;
+			if ( pager->current_line - pager->possible_lines < distance )
+				distance = pager->current_line - pager->possible_lines;
+			dprintf(pager->out_fd, "\e[2J\e[H");
+			pager->current_line -= pager->possible_lines + distance;
+			pager->current_line_offset = 0;
+			pager->allowed_lines = pager->possible_lines;
 			return;
 		}
 
 		if ( KBKEY_DECODE(codepoint) == KBKEY_END )
 		{
 			dprintf(pager->out_fd, "\r\e[J");
+			pager->skipping_to_end = true;
 			pager->allowed_lines = SIZE_MAX;
 			return;
 		}
 
+		if ( KBKEY_DECODE(codepoint) == KBKEY_HOME )
+		{
+			if ( pager->current_line <= pager->possible_lines )
+				continue;
+			dprintf(pager->out_fd, "\e[2J\e[H");
+			pager->current_line = 0;
+			pager->current_line_offset = 0;
+			pager->allowed_lines = pager->possible_lines;
+			return;
+		}
+
 		if ( codepoint == L'q' || codepoint == L'Q' )
 		{
 			dprintf(pager->out_fd, "\r\e[J");
@@ -158,187 +201,208 @@ void pager_prompt(struct pager* pager)
 	exit(1);
 }
 
-bool pager_would_push_newline_scroll(struct pager* pager)
+static void pager_line_push_char(struct pager* pager, struct line* line, char c)
 {
-	return pager->out_fd_winsize.ws_row <= pager->current_wcp.wcp_row + 1;
-}
-
-bool pager_would_push_char_overflow(struct pager* pager, wchar_t wc)
-{
-	if ( wc == L'\r' )
-		return false;
-	return pager->out_fd_winsize.ws_col <= pager->current_wcp.wcp_col;
-}
-
-bool pager_would_push_char_scroll(struct pager* pager, wchar_t wc)
-{
-	if ( wc == L'\n' )
-		return pager_would_push_newline_scroll(pager);
-	if ( pager_would_push_char_overflow(pager, wc) )
-		return pager_would_push_newline_scroll(pager);
-	return false;
-}
-
-void pager_push_newline(struct pager* pager)
-{
-	if ( 0 < pager->allowed_lines && pager->allowed_lines != SIZE_MAX )
-		pager->allowed_lines--;
-	if ( pager->current_wcp.wcp_row + 1 < pager->out_fd_winsize.ws_row )
+	if ( line->content_used == line->content_length )
 	{
-		pager->current_wcp.wcp_row++;
-	}
-	else
-	{
-		if ( 0 < pager->begun_wcp.wcp_row )
-			pager->begun_wcp.wcp_row--;
-	}
-	pager->current_wcp.wcp_col = 0;
-}
-
-bool pager_is_out_of_allowed_lines(struct pager* pager, wchar_t wc)
-{
-	if ( pager->allowed_lines == 1 && wc != L'\n' &&
-	     pager_would_push_char_overflow(pager, wc) )
-		return true;
-	return pager->allowed_lines == 0;
-}
-
-void pager_push_final_char(struct pager* pager, wchar_t wc)
-{
-	if ( pager->quiting || !wc )
-		return;
-
-	while ( pager_is_out_of_allowed_lines(pager, wc) )
-	{
-		pager_prompt(pager);
-		if ( pager->quiting )
-			return;
-	}
-
-	mbstate_t ps;
-	memcpy(&ps, &pager->out_ps, sizeof(mbstate_t));
-	char mb[MB_CUR_MAX];
-	size_t mb_size = wcrtomb(mb, wc, &ps);
-	if ( mb_size == (size_t) -1 )
-	{
-		memset(&pager->out_ps, 0, sizeof(pager->out_ps));
-		return;
-	}
-
-	if ( writeall(pager->out_fd, mb, mb_size) < mb_size )
-	{
-		error(0, errno, "write: <stdout>");
-		pager_end(pager);
-		exit(1);
-	}
-	memcpy(&pager->out_ps, &ps, sizeof(mbstate_t));
-
-	if ( wc == L'\n' )
-	{
-		pager_push_newline(pager);
-	}
-	else if ( wc == L'\t' )
-	{
-		if ( pager_would_push_char_overflow(pager, ' ') )
-			pager_push_newline(pager);
-		do
+		size_t new_length = 2 * line->content_length;
+		if ( new_length == 0 )
+			new_length = 128;
+		char* new_content = (char*) realloc(line->content, new_length);
+		if ( !new_content )
 		{
-			if ( pager_would_push_char_overflow(pager, ' ') )
-				break;
-			pager->current_wcp.wcp_col++;
-		} while ( pager->current_wcp.wcp_col % 8 != 0 );
-	}
-	else if ( wc == L'\r' )
-	{
-		pager->current_wcp.wcp_col = 0;
-	}
-	else
-	{
-		if ( pager_would_push_char_overflow(pager, wc) )
-			pager_push_newline(pager);
-		pager->current_wcp.wcp_col++;
-	}
-}
-
-void pager_push_char(struct pager* pager, wchar_t wc)
-{
-	if ( wc == L'\b' &&
-	     (pager->flag_raw_control_chars || pager->flag_color_sequences) )
-	{
-		dprintf(pager->out_fd, "\b");
-		tcgetwincurpos(pager->out_fd, &pager->current_wcp);
-	}
-	else if ( wc < 32 && wc != L'\t' && wc != L'\n' )
-	{
-		if ( !pager->input_set_color )
-			dprintf(pager->out_fd, "\e[97m");
-		pager_push_final_char(pager, L'^');
-		pager_push_final_char(pager, L'@' + wc);
-		if ( !pager->input_set_color )
-			dprintf(pager->out_fd, "\e[m");
-	}
-	else
-	{
-		pager_push_final_char(pager, wc);
-	}
-}
-
-void pager_control_sequence_begin(struct pager* pager)
-{
-	pager->control_sequence_length = 0;
-}
-
-void pager_control_sequence_accept(struct pager* pager)
-{
-	unsigned char* cs = pager->control_sequence;
-	size_t cs_length = pager->control_sequence_length;
-	if ( writeall(pager->out_fd, cs, cs_length) < cs_length )
-	{
-		error(0, errno, "write: <stdout>");
-		pager_end(pager);
-		exit(1);
-	}
-	pager->control_sequence_length = 0;
-	pager->control_state = CONTROL_STATE_NONE;
-}
-
-void pager_control_sequence_reject(struct pager* pager)
-{
-	for ( size_t i = 0; i < pager->control_sequence_length; i++ )
-	{
-		wint_t wc = btowc(pager->control_sequence[i]);
-		if ( wc != WEOF )
-			pager_push_char(pager, wc);
-	}
-	pager->control_sequence_length = 0;
-	pager->control_state = CONTROL_STATE_NONE;
-}
-
-void pager_control_sequence_push(struct pager* pager, unsigned char byte)
-{
-	if ( CONTROL_SEQUENCE_MAX <= pager->control_sequence_length )
-	{
-		if ( !pager->flag_raw_control_chars )
-			return pager_control_sequence_reject(pager);
-		unsigned char* cs = pager->control_sequence;
-		size_t cs_length = pager->control_sequence_length;
-		if ( writeall(pager->out_fd, cs, cs_length) < cs_length )
-		{
-			error(0, errno, "write: <stdout>");
+			error(0, errno, "malloc");
 			pager_end(pager);
 			exit(1);
 		}
-		pager->control_sequence_length = 0;
+		line->content = new_content;
+		line->content_length = new_length;
 	}
-	pager->control_sequence[pager->control_sequence_length++] = byte;
+	line->content[line->content_used++] = c;
 }
 
-void pager_control_sequence_finish(struct pager* pager, unsigned char byte)
+static struct line* pager_continue_line(struct pager* pager)
 {
-	pager_control_sequence_push(pager, byte);
+	if ( pager->incoming_line )
+		return pager->incoming_line;
+	if ( pager->lines_used == pager->lines_length )
+	{
+		size_t new_length = 2 * pager->lines_length;
+		if ( new_length == 0 )
+			new_length = 128;
+		struct line* new_lines = (struct line*)
+			reallocarray(pager->lines, new_length, sizeof(struct line));
+		if ( !new_lines )
+		{
+			error(0, errno, "malloc");
+			pager_end(pager);
+			exit(1);
+		}
+		pager->lines = new_lines;
+		pager->lines_length = new_length;
+	}
+	pager->incoming_line = &pager->lines[pager->lines_used++];
+	memset(pager->incoming_line, 0, sizeof(*pager->incoming_line));
+	pager->incoming_line_width = 0;
+	return pager->incoming_line;
+}
+
+static void pager_finish_line(struct pager* pager)
+{
+	struct line* line = pager->incoming_line;
+	assert(line);
+	char* final_content = (char*) realloc(line->content, line->content_used);
+	if ( final_content )
+		line->content = final_content;
+	pager->incoming_line = NULL;
+	pager->incoming_line_width = 0;
+}
+
+static struct line* pager_next_line(struct pager* pager)
+{
+	pager_finish_line(pager);
+	return pager_continue_line(pager);
+}
+
+static void pager_push_wchar(struct pager* pager, wchar_t wc)
+{
+	bool newline = false;
+	int width;
+	struct line* line = pager_continue_line(pager);
+
+	if ( pager->incoming_control_state == CONTROL_STATE_CSI )
+	{
+		if ( wc == '[' )
+			pager->incoming_control_state = CONTROL_STATE_COMMAND;
+	}
+	else if ( pager->incoming_control_state == CONTROL_STATE_COMMAND )
+	{
+		pager->incoming_control_state = CONTROL_STATE_NONE;
+		if ( ('0' <= wc && wc <= '9') ||
+		     wc == L';' || wc == L':' || wc == L'?' )
+			pager->incoming_control_state = CONTROL_STATE_COMMAND;
+	}
+	else if ( wc == L'\b' )
+	{
+		if ( pager->incoming_line_width )
+			pager->incoming_line_width--;
+	}
+	else if ( wc == L'\e' )
+	{
+		pager->incoming_control_state = CONTROL_STATE_CSI;
+	}
+	else if ( wc == L'\n' )
+	{
+		newline = true;
+	}
+	else if ( wc == L'\t' )
+	{
+		if ( pager->out_fd_winsize.ws_col == pager->incoming_line_width )
+			line = pager_next_line(pager);
+		do
+		{
+			if ( pager->out_fd_winsize.ws_col == pager->incoming_line_width )
+				break;
+			pager->incoming_line_width++;
+		} while ( pager->incoming_line_width % 8 != 0 );
+	}
+	else if ( wc == L'\r' )
+	{
+		pager->incoming_line_width = 0;
+	}
+	else if ( wc == 127 )
+	{
+	}
+	else if ( 0 <= (width = wcwidth(wc)) )
+	{
+		size_t left = pager->out_fd_winsize.ws_col - pager->incoming_line_width;
+		if ( left < (size_t) width )
+			line = pager_next_line(pager);
+		else
+			pager->incoming_line_width += width;
+	}
+	else
+	{
+		// TODO: What can cause this and how to handle it?
+	}
+
+	char mb[MB_CUR_MAX];
+	size_t amount = wcrtomb(mb, wc, &pager->out_ps);
+	if ( amount != (size_t) -1 )
+	{
+		for ( size_t i = 0; i < amount; i++ )
+			pager_line_push_char(pager, line, mb[i]);
+	}
+
+	if ( newline )
+		pager_finish_line(pager);
+}
+
+static bool pager_push_wchar_is_escaped(struct pager* pager, wchar_t wc)
+{
+	if ( wc == '\b' &&
+	    (pager->flag_raw_control_chars || pager->flag_color_sequences) )
+		return false;
+	return wc < 32 && wc != L'\t' && wc != L'\n';
+}
+
+static void pager_push_wchar_escape(struct pager* pager, wchar_t wc)
+{
+	if ( pager_push_wchar_is_escaped(pager, wc) )
+	{
+		pager_push_wchar(pager, L'^');
+		//pager_push_wchar(pager, L'\b');
+		//pager_push_wchar(pager, L'^');
+		pager_push_wchar(pager, L'@' + wc);
+		//pager_push_wchar(pager, L'\b');
+		//pager_push_wchar(pager, L'@' + wc);
+	}
+	else
+	{
+		pager_push_wchar(pager, wc);
+	}
+}
+
+static void pager_control_sequence_begin(struct pager* pager)
+{
+	pager->control_sequence_length = 0;
+}
+
+static void pager_control_sequence_accept(struct pager* pager)
+{
+	for ( size_t i = 0; i < pager->control_sequence_length; i++ )
+		pager_push_wchar(pager, pager->control_sequence[i]);
+	pager->control_sequence_length = 0;
+	pager->control_state = CONTROL_STATE_NONE;
+}
+
+static void pager_control_sequence_reject(struct pager* pager)
+{
+	for ( size_t i = 0; i < pager->control_sequence_length; i++ )
+		pager_push_wchar_escape(pager, pager->control_sequence[i]);
+	pager->control_sequence_length = 0;
+	pager->control_state = CONTROL_STATE_NONE;
+}
+
+static void pager_control_sequence_push(struct pager* pager, wchar_t wc)
+{
+	if ( pager->flag_raw_control_chars )
+		return pager_push_wchar(pager, wc);
+	if ( CONTROL_SEQUENCE_MAX <= pager->control_sequence_length )
+	{
+		pager_control_sequence_reject(pager);
+		pager_push_wchar_escape(pager, wc);
+		return;
+	}
+	pager->control_sequence[pager->control_sequence_length++] = wc;
+}
+
+static void pager_control_sequence_finish(struct pager* pager, wchar_t wc)
+{
+	pager_control_sequence_push(pager, wc);
 	if ( pager->control_state == CONTROL_STATE_NONE )
 		return;
-	if ( byte == 'm' )
+	if ( wc == 'm' )
 	{
 		pager->input_set_color = true;
 		return pager_control_sequence_accept(pager);
@@ -346,28 +410,24 @@ void pager_control_sequence_finish(struct pager* pager, unsigned char byte)
 	if ( !pager->flag_raw_control_chars )
 		return pager_control_sequence_reject(pager);
 	pager_control_sequence_accept(pager);
-	tcgetwincurpos(pager->out_fd, &pager->current_wcp);
 }
 
-void pager_push_byte(struct pager* pager, unsigned char byte)
+static void pager_push_wchar_filter(struct pager* pager, wchar_t wc)
 {
-	if ( pager->quiting )
-		return;
-
-	if ( byte == '\e' && mbsinit(&pager->in_ps) &&
+	if ( wc == L'\e' &&
 	     (pager->flag_raw_control_chars || pager->flag_color_sequences) &&
 	     pager->control_state == CONTROL_STATE_NONE )
 	{
 		pager_control_sequence_begin(pager);
-		pager_control_sequence_push(pager, byte);
+		pager_control_sequence_push(pager, wc);
 		pager->control_state = CONTROL_STATE_CSI;
 		return;
 	}
 	else if ( pager->control_state == CONTROL_STATE_CSI )
 	{
-		if ( byte == '[' )
+		if ( wc == L'[' )
 		{
-			pager_control_sequence_push(pager, byte);
+			pager_control_sequence_push(pager, wc);
 			pager->control_state = CONTROL_STATE_COMMAND;
 			return;
 		}
@@ -375,15 +435,22 @@ void pager_push_byte(struct pager* pager, unsigned char byte)
 	}
 	else if ( pager->control_state == CONTROL_STATE_COMMAND )
 	{
-		if ( ('0' <= byte && byte <= '9') ||
-		     byte == ';' || byte == ':' || byte == '?' )
+		if ( ('0' <= wc && wc <= '9') ||
+		     wc == L';' || wc == L':' || wc == L'?' )
 		{
-			pager_control_sequence_push(pager, byte);
+			pager_control_sequence_push(pager, wc);
 			return;
 		}
-		pager_control_sequence_finish(pager, byte);
+		pager_control_sequence_finish(pager, wc);
 		return;
 	}
+	pager_push_wchar_escape(pager, wc);
+}
+
+static void pager_push_byte(struct pager* pager, unsigned char byte)
+{
+	if ( pager->quiting )
+		return;
 
 	wchar_t wc;
 	size_t amount = mbrtowc(&wc, (const char*) &byte, 1, &pager->in_ps);
@@ -394,23 +461,38 @@ void pager_push_byte(struct pager* pager, unsigned char byte)
 		wc = 0xFFFD /* REPLACEMENT CHARACTER */;
 		memset(&pager->in_ps, 0, sizeof(pager->in_ps));
 	}
-	pager_push_char(pager, wc);
+	pager_push_wchar_filter(pager, wc);
 }
 
-void pager_simple_output_fd(struct pager* pager, int fd, const char* fdpath)
+static bool pager_read_fd(struct pager* pager, int fd, const char* fdpath)
 {
 	unsigned char buffer[4096];
-	ssize_t in_amount;
-	while ( 0 < (in_amount = read(fd, buffer, sizeof(buffer))) )
+	ssize_t amount = read(fd, buffer, sizeof(buffer));
+	if ( amount < 0 )
 	{
-		if ( writeall(pager->out_fd, buffer, in_amount) < (size_t) in_amount )
+		error(0, errno, "%s", fdpath);
+		pager_end(pager);
+		exit(1);
+	}
+	for ( ssize_t i = 0; i < amount; i++ )
+		pager_push_byte(pager, buffer[i]);
+	return amount != 0;
+}
+
+static void pager_simple_fd(struct pager* pager, int fd, const char* fdpath)
+{
+	unsigned char buffer[4096];
+	ssize_t amount = 0;
+	while ( 0 < (amount = read(fd, buffer, sizeof(buffer))) )
+	{
+		if ( writeall(pager->out_fd, buffer, amount) < (size_t) amount )
 		{
 			error(0, errno, "<stdout>");
 			pager_end(pager);
 			exit(1);
 		}
 	}
-	if ( in_amount < 0 )
+	if ( amount < 0 )
 	{
 		error(0, errno, "%s", fdpath);
 		pager_end(pager);
@@ -418,46 +500,83 @@ void pager_simple_output_fd(struct pager* pager, int fd, const char* fdpath)
 	}
 }
 
-void pager_push_fd(struct pager* pager, int fd, const char* fdpath)
+static bool pager_can_page(struct pager* pager)
+{
+	if ( pager->lines_used <= pager->current_line )
+		return false;
+	struct line* line = &pager->lines[pager->current_line];
+	if ( line->content_used <= pager->current_line_offset )
+		return false;
+	return true;
+}
+
+static void pager_page(struct pager* pager)
+{
+	struct line* line = &pager->lines[pager->current_line];
+	if ( pager->current_line_offset < line->content_used )
+	{
+		const char* buffer = line->content + pager->current_line_offset;
+		size_t amount = line->content_used - pager->current_line_offset;
+		if ( writeall(pager->out_fd, buffer, amount) < amount )
+		{
+			error(0, errno, "write: <stdout>");
+			pager_end(pager);
+			exit(1);
+		}
+		pager->current_line_offset = line->content_used;
+	}
+	if ( pager->current_line + 1 < pager->lines_used )
+	{
+		if ( pager->allowed_lines != SIZE_MAX )
+			pager->allowed_lines--;
+		pager->current_line++;
+		pager->current_line_offset = 0;
+	}
+}
+
+static void pager_push_fd(struct pager* pager, int fd, const char* fdpath)
 {
 	if ( pager->quiting )
 		return;
-
 	if ( !strcmp(fdpath, "<stdin>") )
 		pager->input_prompt_name = "";
 	else
 		pager->input_prompt_name = fdpath;
 	// TODO: In this case, we should disable echoing and read from the terminal
-	//       anyways.
+	//       anyways. Remember to enable it again.
 	if ( isatty(fd) )
 	{
-		error(0, errno, "/dev/tty");
+		error(0, 0, "/dev/tty: Is a terminal");
 		pager_end(pager);
 		exit(1);
 	}
-	if ( !pager->out_fd_tty )
-		return pager_simple_output_fd(pager, fd, fdpath);
-	unsigned char buffer[4096];
-	ssize_t in_amount = 0;
-	while ( !pager->quiting &&
-	        0 < (in_amount = read(fd, buffer, sizeof(buffer))) )
+	if ( !pager->out_fd_is_tty )
+		return pager_simple_fd(pager, fd, fdpath);
+	bool eof = false;
+	while ( !pager->quiting )
 	{
-		for ( ssize_t i = 0; i < in_amount; i++ )
-			pager_push_byte(pager, buffer[i]);
-	}
-	if ( in_amount < 0 )
-	{
-		error(0, errno, "%s", fdpath);
-		pager_end(pager);
-		exit(1);
+		if ( !pager->skipping_to_end && pager->allowed_lines == 0 )
+		{
+			pager->allowance_ever_exhausted = true;
+			pager_prompt(pager, false);
+			continue;
+		}
+		if ( !pager->skipping_to_end && pager_can_page(pager) )
+		{
+			pager_page(pager);
+			continue;
+		}
+		if ( eof )
+			break;
+		if ( !pager_read_fd(pager, fd, fdpath) )
+			eof = true;
 	}
 }
 
-void pager_push_path(struct pager* pager, const char* path)
+static void pager_push_path(struct pager* pager, const char* path)
 {
 	if ( pager->quiting )
 		return;
-
 	if ( !strcmp(path, "-") )
 		return pager_push_fd(pager, 0, "<stdin>");
 	int fd = open(path, O_RDONLY);
@@ -573,6 +692,30 @@ int main(int argc, char* argv[])
 		pager_push_path(&pager, argv[i]);
 	}
 
+	while ( pager.out_fd_is_tty &&
+	        pager.allowance_ever_exhausted &&
+	        !pager.quiting )
+	{
+		if ( pager.skipping_to_end )
+		{
+			dprintf(pager.out_fd, "\e[2J\e[H");
+			size_t line = 0;
+			if ( pager.possible_lines <= pager.lines_used )
+				line = pager.lines_used - pager.possible_lines;
+			pager.current_line = line;
+			pager.current_line_offset = 0;
+			pager.allowed_lines = pager.possible_lines;
+			pager.skipping_to_end = false;
+		}
+		bool cant_page = !pager_can_page(&pager);
+		if ( cant_page || pager.allowed_lines == 0 )
+		{
+			pager_prompt(&pager, cant_page);
+			continue;
+		}
+		pager_page(&pager);
+	}
+
 	pager_end(&pager);
 
 	return 0;