| 1 | ### -*-python-*- |
| 2 | ### |
| 3 | ### Output machinery |
| 4 | ### |
| 5 | ### (c) 2013 Mark Wooding |
| 6 | ### |
| 7 | |
| 8 | ###----- Licensing notice --------------------------------------------------- |
| 9 | ### |
| 10 | ### This file is part of Chopwood: a password-changing service. |
| 11 | ### |
| 12 | ### Chopwood is free software; you can redistribute it and/or modify |
| 13 | ### it under the terms of the GNU Affero General Public License as |
| 14 | ### published by the Free Software Foundation; either version 3 of the |
| 15 | ### License, or (at your option) any later version. |
| 16 | ### |
| 17 | ### Chopwood is distributed in the hope that it will be useful, |
| 18 | ### but WITHOUT ANY WARRANTY; without even the implied warranty of |
| 19 | ### MERCHANTABILITY or FITNESS FOR A PARTICULAR PURPOSE. See the |
| 20 | ### GNU Affero General Public License for more details. |
| 21 | ### |
| 22 | ### You should have received a copy of the GNU Affero General Public |
| 23 | ### License along with Chopwood; if not, see |
| 24 | ### <http://www.gnu.org/licenses/>. |
| 25 | |
| 26 | from __future__ import with_statement |
| 27 | |
| 28 | import contextlib as CTX |
| 29 | import os as OS |
| 30 | from cStringIO import StringIO |
| 31 | import sys as SYS |
| 32 | |
| 33 | import util as U |
| 34 | |
| 35 | ### There are a number of interesting things to do with output. |
| 36 | ### |
| 37 | ### The remote-service interface needs to prefix its output lines with `INFO' |
| 38 | ### tokens so that they get parsed properly. |
| 39 | ### |
| 40 | ### The CGI interface needs to prefix its output with at least a |
| 41 | ### `Content-Type' header. |
| 42 | |
| 43 | ###-------------------------------------------------------------------------- |
| 44 | ### Utilities. |
| 45 | |
| 46 | def http_headers(**kw): |
| 47 | """ |
| 48 | Generate mostly-formatted HTTP headers. |
| 49 | |
| 50 | KW is a dictionary mapping HTTP header names to values. Each name is |
| 51 | converted to external form by changing underscores `_' to hyphens `-', and |
| 52 | capitalizing each constituent word. The values are converted to strings. |
| 53 | If a value is a list, a header is produced for each element. Subsequent |
| 54 | lines in values containing internal line breaks have a tab character |
| 55 | prepended. |
| 56 | """ |
| 57 | def hack_header(k, v): |
| 58 | return '%s: %s' % ('-'.join(i.title() for i in k.split('_')), |
| 59 | str(v).replace('\n', '\n\t')) |
| 60 | for k, v in kw.iteritems(): |
| 61 | if isinstance(v, list): |
| 62 | for i in v: yield hack_header(k, i) |
| 63 | else: |
| 64 | yield hack_header(k, v) |
| 65 | |
| 66 | ###-------------------------------------------------------------------------- |
| 67 | ### Protocol. |
| 68 | |
| 69 | class BasicOutputDriver (object): |
| 70 | """ |
| 71 | A base class for output drivers, providing trivial implementations of most |
| 72 | of the protocol. |
| 73 | |
| 74 | The main missing piece is the `_write' method, which should write its |
| 75 | argument to the output with as little ceremony as possible. Any fancy |
| 76 | formatting should be applied by overriding `write'. |
| 77 | """ |
| 78 | |
| 79 | def __init__(me): |
| 80 | """Trivial constructor.""" |
| 81 | me.warnings = [] |
| 82 | |
| 83 | def writeln(me, msg): |
| 84 | """Write MSG, as a complete line.""" |
| 85 | me.write(str(msg) + '\n') |
| 86 | |
| 87 | def write(me, msg): |
| 88 | """Write MSG to the output, with any necessary decoration.""" |
| 89 | me._write(str(msg)) |
| 90 | |
| 91 | def warn(me, msg): |
| 92 | """Write MSG as a warning message.""" |
| 93 | SYS.stderr.write('%s: %s\n' % (OS.path.basename(SYS.argv[0]), msg)) |
| 94 | |
| 95 | def close(me): |
| 96 | """Wrap up when everything that needs saying has been said.""" |
| 97 | pass |
| 98 | |
| 99 | def header(me, **kw): |
| 100 | """Emit HTTP-style headers in a distinctive way.""" |
| 101 | for h in http_headers(**kw): |
| 102 | PRINT('[%s]' % h) |
| 103 | |
| 104 | class BasicLineOutputDriver (BasicOutputDriver): |
| 105 | """ |
| 106 | Mixin class for line-oriented output formatting. |
| 107 | |
| 108 | We override `write' to buffer partial lines; complete lines are passed to |
| 109 | `_writeln' to be written, presumably through the low-level `_write' method. |
| 110 | """ |
| 111 | |
| 112 | def __init__(me, *args, **kw): |
| 113 | """Contructor.""" |
| 114 | super(BasicLineOutputDriver, me).__init__(*args, **kw) |
| 115 | me._buf = None |
| 116 | |
| 117 | def _flush(me): |
| 118 | """Write any incomplete line accumulated so far, and clear the buffer.""" |
| 119 | if me._buf: |
| 120 | me._writeln(me._buf.getvalue()) |
| 121 | me._buf = None |
| 122 | |
| 123 | def write(me, msg): |
| 124 | """Write MSG, sending any complete lines to the `_writeln' method.""" |
| 125 | |
| 126 | if '\n' not in msg: |
| 127 | ## If there's not a complete line here then we just accumulate the |
| 128 | ## message into our buffer. |
| 129 | |
| 130 | if not me._buf: me._buf = StringIO() |
| 131 | me._buf.write(msg) |
| 132 | |
| 133 | else: |
| 134 | ## There's at least one complete line here. We take the final |
| 135 | ## incomplete line off the end. |
| 136 | |
| 137 | lines = msg.split('\n') |
| 138 | tail = lines.pop() |
| 139 | |
| 140 | ## If there's a partial line already buffered then add whatever new |
| 141 | ## stuff we have and flush it out. |
| 142 | if me._buf: |
| 143 | me._buf.write(lines[0]) |
| 144 | me._flush() |
| 145 | |
| 146 | ## Write out any other complete lines. |
| 147 | for line in lines: |
| 148 | me._writeln(line) |
| 149 | |
| 150 | ## If there's a proper partial line, then start a new buffer. |
| 151 | if tail: |
| 152 | me._buf = StringIO() |
| 153 | me._buf.write(tail) |
| 154 | |
| 155 | def close(me): |
| 156 | """If there's any partial line buffered, flush it out.""" |
| 157 | me._flush() |
| 158 | |
| 159 | ###-------------------------------------------------------------------------- |
| 160 | ### Implementations. |
| 161 | |
| 162 | class FileOutput (BasicOutputDriver): |
| 163 | """Output driver for writing stuff to a file.""" |
| 164 | def __init__(me, file = SYS.stdout, *args, **kw): |
| 165 | """Constructor: send output to FILE (default is stdout).""" |
| 166 | super(FileOutput, me).__init__(*args, **kw) |
| 167 | me._file = file |
| 168 | def _write(me, text): |
| 169 | """Output protocol: write TEXT to the ouptut file.""" |
| 170 | me._file.write(text) |
| 171 | |
| 172 | class RemoteOutput (FileOutput, BasicLineOutputDriver): |
| 173 | """Output driver for decorating lines with `INFO' tags.""" |
| 174 | def _writeln(me, line): |
| 175 | """Line output protocol: write a complete line with an `INFO' tag.""" |
| 176 | me._write('INFO %s\n' % line) |
| 177 | |
| 178 | ###-------------------------------------------------------------------------- |
| 179 | ### Context. |
| 180 | |
| 181 | class DelegatingOutput (BasicOutputDriver): |
| 182 | """Fake output driver which delegates to some other driver.""" |
| 183 | |
| 184 | def __init__(me, default = None): |
| 185 | """Constructor: send output to DEFAULT.""" |
| 186 | me._fluid = U.Fluid(target = default) |
| 187 | |
| 188 | @CTX.contextmanager |
| 189 | def redirect_to(me, target): |
| 190 | """Temporarily redirect output to TARGET, closing it when finished.""" |
| 191 | try: |
| 192 | with me._fluid.bind(target = target): |
| 193 | yield |
| 194 | finally: |
| 195 | target.close() |
| 196 | |
| 197 | ## Delegating methods. |
| 198 | def write(me, msg): me._fluid.target.write(msg) |
| 199 | def writeln(me, msg): me._fluid.target.writeln(msg) |
| 200 | def close(me): me._fluid.target.close() |
| 201 | def header(me, **kw): me._fluid.target.header(**kw) |
| 202 | def warn(me, msg): me._fluid.target.warn(msg) |
| 203 | |
| 204 | ## Delegating properties. |
| 205 | @property |
| 206 | def headerp(me): return me._fluid.target.headerp |
| 207 | @property |
| 208 | def warnings(me): return me._fluid.target.warnings |
| 209 | |
| 210 | ## The selected output driver. Set this with `output_to'. |
| 211 | OUT = DelegatingOutput() |
| 212 | |
| 213 | def PRINT(msg = ''): |
| 214 | """Write the MSG as a line to the current output.""" |
| 215 | OUT.writeln(msg) |
| 216 | |
| 217 | ###----- That's all, folks -------------------------------------------------- |