mosh-client: Make terminal escape character configurable

Uses environment variable MOSH_ESCAPE_KEY. Defaults to current Ctrl-^
which is somewhat problematic for many non-US keyboards.

Signed-off-by: Timo J. Rinne <tri@iki.fi>

Closes #425. Closes #215.

2 files changed, 89 insertions, 12 deletions

diff --git a/src/frontend/stmclient.cc b/src/frontend/stmclient.cc
index 7d68ab1..c2ff2a5 100644
--- a/src/frontend/stmclient.cc
+++ b/src/frontend/stmclient.cc
@@ -121,6 +121,72 @@ void STMClient::init( void )
     overlays.set_title_prefix( wstring( L"[mosh] " ) );
   }
 
+  /* Set terminal escape key. */
+  const char *escape_key_env;
+  if ( (escape_key_env = getenv( "MOSH_ESCAPE_KEY" )) != NULL ) {
+    if ( strlen( escape_key_env ) == 1 ) {
+      escape_key = (int)escape_key_env[0];
+      if ( (escape_key > 0) || (escape_key < 128) ) {
+	if ( escape_key < 32 ) {
+	  /* If escape is ctrl-something, pass it with repeating the key without ctrl. */
+	  escape_pass_key = escape_key + (int)'@';
+	} else {
+	  /* If escape is something else, pass it with repeating the key itself. */
+	  escape_pass_key = escape_key;
+	}
+	if ( escape_pass_key >= 'A' && escape_pass_key <= 'Z' ) {
+	  /* If escape pass is an upper case character, define optional version
+	     as lower case of the same. */
+	  escape_pass_key2 = escape_pass_key + (int)'a' - (int)'A';
+	} else {
+	  escape_pass_key2 = escape_pass_key;
+	}
+      } else {
+	escape_key = 0x1E;
+	escape_pass_key = '^';
+	escape_pass_key2 = '^';
+      }
+    } else if ( strlen( escape_key_env ) == 0 ) {
+      escape_key = -1;
+    } else {
+      escape_key = 0x1E;
+      escape_pass_key = '^';
+      escape_pass_key2 = '^';
+    }
+  } else {
+    escape_key = 0x1E;
+    escape_pass_key = '^';
+    escape_pass_key2 = '^';
+  }
+
+  /* There are so many better ways to shoot oneself into leg than
+     setting escape key to Ctrl-C, Ctrl-D, NewLine, Ctrl-L or CarriageReturn
+     that we just won't allow that. */
+  if ( escape_key == 0x03 || escape_key == 0x04 || escape_key == 0x0A || escape_key == 0x0C || escape_key == 0x0D ) {
+    escape_key = 0x1E;
+    escape_pass_key = '^';
+    escape_pass_key2 = '^';
+  }
+
+  /* Adjust escape help differently if escape is a control character. */
+  if ( escape_key > 0 ) {
+    char escape_pass_name_buf[16];
+    char escape_key_name_buf[16];
+    sprintf(escape_pass_name_buf, "\"%c\"", escape_pass_key);
+    if (escape_key < 32) {
+      sprintf(escape_key_name_buf, "Ctrl-%c", escape_pass_key);
+      escape_requires_lf = false;
+    } else {
+      sprintf(escape_key_name_buf, "\"%c\"", escape_key);
+      escape_requires_lf = true;
+    }
+    string tmp;
+    tmp = string( escape_pass_name_buf );
+    wstring escape_pass_name = std::wstring(tmp.begin(), tmp.end());
+    tmp = string( escape_key_name_buf );
+    wstring escape_key_name = std::wstring(tmp.begin(), tmp.end());
+    escape_key_help = L"Commands: Ctrl-Z suspends, \".\" quits, " + escape_pass_name + L" gives literal " + escape_key_name;
+  }
   wchar_t tmp[ 128 ];
   swprintf( tmp, 128, L"Nothing received from server on UDP port %d.", port );
   connecting_notification = wstring( tmp );
@@ -255,8 +321,6 @@ bool STMClient::process_user_input( int fd )
 
       overlays.get_prediction_engine().new_user_byte( the_byte, *local_framebuffer );
 
-      const static wstring help_message( L"Commands: Ctrl-Z suspends, \".\" quits, \"^\" gives literal Ctrl-^" );
-
       if ( quit_sequence_started ) {
 	if ( the_byte == '.' ) { /* Quit sequence is Ctrl-^ . */
 	  if ( network->has_remote_addr() && (!network->shutdown_in_progress()) ) {
@@ -266,7 +330,7 @@ bool STMClient::process_user_input( int fd )
 	  } else {
 	    return false;
 	  }
-	} else if ( the_byte == 0x1a ) { /* Suspend sequence is Ctrl-^ Ctrl-Z */
+	} else if ( the_byte == 0x1a ) { /* Suspend sequence is escape_key Ctrl-Z */
 	  /* Restore terminal and terminal-driver state */
 	  swrite( STDOUT_FILENO, display.close().c_str() );
 
@@ -283,30 +347,34 @@ bool STMClient::process_user_input( int fd )
 	  kill( 0, SIGSTOP );
 
 	  resume();
-	} else if ( the_byte == '^' ) {
-	  /* Emulation sequence to type Ctrl-^ is Ctrl-^ ^ */
-	  network->get_current_state().push_back( Parser::UserByte( 0x1E ) );
+	} else if ( (the_byte == escape_pass_key) || (the_byte == escape_pass_key2) ) {
+	  /* Emulation sequence to type escape_key is escape_key +
+	     escape_pass_key (that is escape key without Ctrl) */
+	  network->get_current_state().push_back( Parser::UserByte( escape_key ) );
 	} else {
-	  /* Ctrl-^ followed by anything other than . and ^ gets sent literally */
-	  network->get_current_state().push_back( Parser::UserByte( 0x1E ) );
+	  /* Escape key followed by anything other than . and ^ gets sent literally */
+	  network->get_current_state().push_back( Parser::UserByte( escape_key ) );
 	  network->get_current_state().push_back( Parser::UserByte( the_byte ) );	  
 	}
 
 	quit_sequence_started = false;
 
-	if ( overlays.get_notification_engine().get_notification_string() == help_message ) {
+	if ( overlays.get_notification_engine().get_notification_string() == escape_key_help ) {
 	  overlays.get_notification_engine().set_notification_string( L"" );
 	}
 
 	continue;
       }
 
-      quit_sequence_started = (the_byte == 0x1E);
+      quit_sequence_started = (escape_key > 0) && (the_byte == escape_key) && (lf_entered || (! escape_requires_lf));
       if ( quit_sequence_started ) {
-	overlays.get_notification_engine().set_notification_string( help_message, true, false );
+	lf_entered = false;
+	overlays.get_notification_engine().set_notification_string( escape_key_help, true, false );
 	continue;
       }
 
+      lf_entered = ( (the_byte == 0x0A) || (the_byte == 0x0D) ); /* LineFeed, Ctrl-J, '\n' or CarriageReturn, Ctrl-M, '\r' */
+
       if ( the_byte == 0x0C ) { /* Ctrl-L */
 	repaint_requested = true;
       }
diff --git a/src/frontend/stmclient.h b/src/frontend/stmclient.h
index 51150c6..e4bab9b 100644
--- a/src/frontend/stmclient.h
+++ b/src/frontend/stmclient.h
@@ -48,6 +48,12 @@ private:
   int port;
   std::string key;
 
+  int escape_key;
+  int escape_pass_key;
+  int escape_pass_key2;
+  bool escape_requires_lf;
+  std::wstring escape_key_help;
+
   struct termios saved_termios, raw_termios;
 
   struct winsize window_size;
@@ -58,7 +64,7 @@ private:
   Terminal::Display display;
 
   std::wstring connecting_notification;
-  bool repaint_requested, quit_sequence_started;
+  bool repaint_requested, lf_entered, quit_sequence_started;
   bool clean_shutdown;
 
   void main_init( void );
@@ -79,6 +85,8 @@ private:
 public:
   STMClient( const char *s_ip, int s_port, const char *s_key, const char *predict_mode )
     : ip( s_ip ), port( s_port ), key( s_key ),
+    escape_key( 0x1E ), escape_pass_key( '^' ), escape_pass_key2( '^' ),
+    escape_requires_lf( false ), escape_key_help( L"?" ),
       saved_termios(), raw_termios(),
       window_size(),
       local_framebuffer( NULL ),
@@ -88,6 +96,7 @@ public:
       display( true ), /* use TERM environment var to initialize display */
       connecting_notification(),
       repaint_requested( false ),
+      lf_entered( false ),
       quit_sequence_started( false ),
       clean_shutdown( false )
   {