********************************************************************************* Extending GraphTerm ********************************************************************************* .. contents:: .. index:: extending GraphTerm, API, hello_gterm.sh, graphterm-aware commands, toolchain The GraphTerm toolchain can be extended by writing additional executable commands in any language, much like a `CGI `_ script. The program `hello_gterm.sh `_ is a simple example. See also the programs ``gls``, ``gimage``, ``gframe``, ``gvi``, ``gfeed``, ``yweather``, ``ec2launch`` and ``ec2list`` for examples of GraphTerm API usage. You can use the ``which gls`` command to figure out where these programs are located. The file ``gterm.py`` contains many helper functions for accessing the GraphTerm API. *Note:* The GraphTerm Application Programming Interface (API) is rather poorly documented, because it is still evolving. If you develop a non-trivial application using this API, please be aware that some of the details may change. GraphTerm comment directive ----------------------------------------------------------------------- A `graphterm-aware program `_ communicates with GraphTerm following the standard protocol for Unix programs to communicate with the terminal, i.e., by writing some text to the standard output, prefixed and suffixed by special *escape* sequences. The prefix sequence is the string ``\x1b[?1155;h`` and the suffix sequence is ``\x1b[?1155l``, where ``\x1b`` denotes the Escape character and ```` denotes a numeric value stored in the environment variable ``GTERM_COOKIE``. This is a security measure that prevents malicious files from accessing GraphTerm. Only executable scripts and programs will be able generate the special escape sequences. *Note*: On a remote machine accessed via SSH, the cookie value will not be available. In that case, the dummy value ``0`` may be used to access basic GraphTerm features like displaying images and HTML within a frame. (For security reasons, advanced features of GraphTerm, such as command execution, cannot be accessed using the dummy cookie value of zero.) If the text output by the program (excluding the escape sequences) starts with the left-angle bracket (``<``), it is interpreted as being an HTML fragment to be displayed within GraphTerm as output of the command. For example, outputting the following string will display the text ``Hello World`` in bold face:: \x1b[?1155;hHello World!\x1b[?1155l The output HTML fragment may optionally begin with a special *Graphterm directive* which looks like an HTML comment line:: \x1b[?1155;h\x1b[?1155l The above string, if output by a program, will clear output from the terminal. The GraphTerm always begins with string ````, like an HTML comment line. The directive begins with an action (``clear_terminal``) and may be followed by optional arguments of the form ``name=value``. The basic actions and optional arguments are: ``data display=block|fullwindow autoerase=yes overwrite=yes exit_page=yes`` (display data URI content; typically used for images) ``pagelet display=block overwrite=yes`` (display arbitrary HTML page fragment from content following the directive) The ``overwrite`` option allows previously displayed content to be overwritten, enabling simple animations etc. The ``autoerase`` option automatically erases the content when the command ends. The ``data`` action allows `data URIs `_ to be displayed (even across SSH logins). The ``pagelet`` action allows arbitrary HTML fragments to be displayed inline. The following python command will display inline HTML:: print "\x1b[?1155;h"+""+"Hello World!"+"\x1b[?1155l" The ``data`` and ``pagelet`` actions are unprivileged, i.e., they can be executed even with a dummy cookie value of 0. However, pagelets without a valid cookie value are treated specially, because they are untrusted. They are always displayed in the full window mode, using a separate "web origin" for security. For example, the following Python ``print`` statement will display an inline image from a data URL:: print "\x1b[?1155;0h"+""+"image/png;base64,iVBORw0KGgoAAAANSUhEUgAAAAUAAAAFCAYAAACNbyblAAAAHElEQVQI12P4//8/w38GIAXDIBKE0DHxgljNBAAO9TXL0Y4OHwAAAABJRU5ErkJggg=="+"\x1b[?1155l" The sample program ``hello_world.sh`` in ``$GTERM_DIR/bin`` displays the above string. Executing the program across an SSH login will still display the red dot. A displayed inline image can be overwritten. The following line will overwrite the last displayed image with a new image containing a single white pixel:: print "\x1b[?1155;0h"+""+"image/gif;base64,R0lGODlhAQABAIAAAP///wAAACwAAAAAAQABAAACAkQBADs="+"\x1b[?1155l" Other useful actions are: ``clear_terminal`` (*gclear*: clear the terminal) ``error_message`` (display content as plain text error message in browser window) ``menu_op target=view_menubar value=on|off`` (*gmenu*: execute menu operation) ``nb_clear all=yes`` (clear notebook cell output) ``open_url width=400 height=300 target=...`` (*gopen*: open URL) GraphTerm JSON headers ----------------------------------------------------------------------- The HTML comment directive format is the simplest way for programs to communicate with GraphTerm, and would suffice for most purposes. An alternative JSON header format is also available to handle more complex options, data etc.:: \x1b[?1155;h {"content_type": "text/html", "x_gterm_response": "pagelet", "x_gterm_parameters": {"display": "fullwindow"} }
Hello World!
\x1b[?1155l This is equivalent to the HTML comment directive::
Hello World!
Note that for the JSON header format, the opening escape sequence is followed by a *dictionary* of header names and values, using JSON format. This must be followed by a single *blank line* and then any content data (such as the HTML fragment to be displayed). gterm API module ----------------------------------------------------------------------- The Python module ``$GTERM_DIR/bin/gterm.py`` contains many convenience functions for accessing the textual GraphTerm API. The following Python code will display some raw HTML followed by an image:: import grapherm.bin.gterm as gterm gterm.write_html("Hello Wordl!") with open("sample.png") as f: content = f.read() gterm.display_data("image/png", content, display="block") See the toolchain programs ``gimage``, ``gframe``, etc. for examples of this API usage. The file ``$GTERM_DIR/bin/gterm.R`` provides convenience wrapper functions for ``R``. Clickable links for generating commands ----------------------------------------------------------------------- A program can display clickable HTML links that can automatically generate a command line and paste it into the terminal. See the ``ec2list`` and ``gls`` programs for examples of this usage. Basically a clickable HTML ```` element is identified by the ``class`` attribute ``gterm-click`` and also contains a special attribute ``data-gtermcmd`` that represents the command to be executed. If this command ends with a space, the displayed text of the element (such as a file name) is appended as an argument to the command. (If the ``href`` attribute of the ```` element represents a file URI, then the file path is appended instead.) To insert the argument elsewhere in the command, the special escape sequence ``%[arg]`` can be used in the command string. See the script ``hello_gterm.sh`` or the sample Python code below:: import graphterm.bin.gterm as gterm html = '
Clickable Command
' gterm.write_html(html) .. index:: command line parsing Mapping command line arguments to HTML form elements ----------------------------------------------------------------------- Any Python program that parses command line options and arguments can be trivially modified to generate an HTML form to request input. The ``gterm`` module provides a ``FormParser`` object that can be used as an almost drop-in replacement for standard command line parsing using ``optparse.OptionParser``. Here's some example code of this usage (modified from ``ec2launch``):: import sys import grapherm.bin.gterm as gterm # Create FormParser object form_parser = gterm.FormParser(usage=usage, title="Create Amazon EC2 instance with hostname: ", command="ec2launch -f") # First argument (required) form_parser.add_argument(label="", help="Instance tagname") # Choice option form_parser.add_option("type", ("m3.medium", "m3.large", "c3.large"), help="Instance type") # String option form_parser.add_option("gmail_addr", "", help="Full gmail address, user@gmail.com") # Boolean option form_parser.add_option("https", False, help="Use https for security") # Raw options (not displayed in form) form_parser.add_option("form", False, help="Force form display", raw=True) form_parser.add_option("fullpage", False, short="f", help="Fullpage display", raw=True) form_parser.add_option("text", False, short="t", help="Text only", raw=True) (options, args) = form_parser.parse_args() if not gterm.Cookie or not sys.stdout.isatty(): # Not running within GraphTerm or stdout is piped; text only options.text = True if not args or options.form: # Invoked with no arguments or with force form display option if options.text: # Display text help and quit sys.exit(form_parser.get_usage()) # Display form, prefilling it if need be gterm.write_form(form_parser.create_form(prefill=(options, args) if options.form else None), command="ec2launch -f") sys.exit(1) # ... code for processing arguments and options See the source for toolchain commands ``ec2launch``, ``gadmin``, ``gframe``, ``gncplot``, ``greveal``, and ``ystock`` for more examples.