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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.
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;<cookie>h and the suffix sequence is \x1b[?1155l, where \x1b denotes the Escape character and <cookie> 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.
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;<cookie>h<b>Hello World!</b>\x1b[?1155l
The output HTML fragment may optionally begin with a special Graphterm directive which looks like an HTML comment line:
\x1b[?1155;<cookie>h<!--gterm nb_clear all=yes-->\x1b[?1155l
The above string, if output by a program, will clear output from all cells in a notebook. The GraphTerm always begins with string <!--gterm and ends with -->, like an HTML comment line. The directive begins with an action (nb_clear) and optional arguments of the form name=value.
The basic actions and optional arguments are:
data blob=... (create blob with specified random id from data URI content)
display_blob blob=... display=block|fullpage|fullwindow overwrite=yes exit_page=yes (display blob image)
pagelet block=overwrite (display arbitrary HTML page fragment from content)
The pagelet action allows arbitrary HTML fragments to be displayed inline. The following python command will display inline HTML:
print "\x1b[?1155;<cookie>h"+"<!--gterm pagelet-->"+"<b>Hello World!</b>"+"\x1b[?1155l"
The data and display_blob actions are unprivileged, i.e., they can be executed even with a dummy cookie value of 0. This allows “blobs” to be created from data URIs and displayed even across SSH logins. For example, the following two python print statements will display an inline image from a data URL:
print "\x1b[?1155;0h"+"<!--gterm data blob=75543619-->"+"image/png;base64,iVBORw0KGgoAAAANSUhEUgAAAAUAAAAFCAYAAACNbyblAAAAHElEQVQI12P4//8/w38GIAXDIBKE0DHxgljNBAAO9TXL0Y4OHwAAAABJRU5ErkJggg=="+"\x1b[?1155l"
print "\x1b[?1155;0h"<!--gterm display_blob blob=75543619-->"+"\x1b[?1155l
The sample program hello_world.sh in $GTERM_DIR/bin displays the above two strings. Executing the program across an SSH login will still display the red dot.
A displayed inline image can be overwritten. The following two lines will overwrite the last displayed image with a new image containing a single white pixel:
print "\x1b[?1155;0h"+"<!--gterm data blob=84327630-->"+"image/gif;base64,R0lGODlhAQABAIAAAP///wAAACwAAAAAAQABAAACAkQBADs="+"\x1b[?1155l"
print "\x1b[?1155;0h"<!--gterm display_blob blob=84327630
overwrite=yes-->"+"\x1b[?1155l
Additional actions and optional arguments 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)
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 and data etc.:
\x1b[?1155;<cookie>h
{"content_type": "text/html",
"x_gterm_response": "pagelet"}
<div>
Hello World!
</div>
\x1b[?1155l
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).
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("<b>Hello Wordl!</b>")
with open("sample.png") as f:
content = f.read()
blob_url = gterm.create_blob(content, content_type="image/png")
gterm.display_blob(gterm.get_blob_id(blob_url), display="block")
See the toolchain programs gimage, gframe, etc. for examples of this API usage.
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 <a> 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 <a> 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 = '<hr><a class="gterm-link gterm-click" href="" data-gtermmime="" data-gtermcmd="echo %[arg] echoed" data-gtermconfirm="Execute echo command?">Clickable Command</a><hr>'
gterm.write_html(html)
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.Lterm_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.