Andrew's git - logparse.git/blob

c7b7c30388a025aa612623ec4a9f5bab59903ff9
   1#
   2#   format.py
   3#   
   4#   This file contains global functions for formatting and printing data. This
   5#   file should be imported into individual log-parsing scripts located in
   6#   logs/*. Data is formatted in HTML or plaintext. Writing to disk and/or
   7#   emailng data is left to __main__.py.
   8#
   9
  10import os
  11import re
  12import locale
  13from string import Template
  14from math import floor, ceil
  15from tabulate import tabulate
  16
  17import logparse
  18from . import interface, util, config, mail
  19
  20import logging
  21logger = logging.getLogger(__name__)
  22
  23
  24locale.setlocale(locale.LC_ALL, '') # inherit system locale
  25#DEG = "&deg;".encode('unicode_escape')
  26DEG = u'\N{DEGREE SIGN}'
  27CEL = "C"
  28TIMEFMT = "%X"
  29DATEFMT = "%x"
  30CORNERCHARS_DOUBLE = ['╚', '╝', '╗', '╔']
  31CORNERCHARS_SINGLE = ['└', '┘', '┐', '┌']
  32LINECHARS_DOUBLE = ['║', '═']
  33LINECHARS_SINGLE = ['│', '─']
  34JXNCHARS_DOUBLE = ['╠', '╣', '╦', '╩', '╬']
  35JXNCHARS_SINGLE = ['├', '┤', '┬', '┴', '┼']
  36BULLET = "• "
  37INDENT = "  "
  38
  39
  40class Output:
  41    """
  42    Base class for a data processor. 
  43    """
  44    
  45    def __init__(self):
  46        self.content = ""
  47        self.destination = ""
  48
  49    def append(self, content):
  50        """
  51        Add a string
  52        """
  53        self.content += content
  54
  55    def write(self, destination=""):
  56        """
  57        Output contents into a file
  58        """
  59        if destination == "":
  60            destination = self.destination
  61        if destination == "":
  62            logger.warning("No destination path provided")
  63            return 1
  64        with open(destination, 'w') as f:
  65            f.write(self.content)
  66            logger.info("Written output to {}".format(destination))
  67
  68
  69class PlaintextOutput(Output):
  70    """
  71    Processes & outputs data in a plaintext form which can be read with cat or plaintext email.
  72    """
  73
  74    def __init__(self, linewidth=80):
  75        self.content = ""
  76        self.destination = ""
  77        self.linewidth = linewidth;
  78
  79    def append_header(self, template=''):
  80        """
  81        Print details with some primitive formatting
  82        """
  83        init_varfilter()
  84        box = PlaintextBox(content=Template("$title $version on $hostname\n\n$time $date").safe_substitute(varsubst), vpadding=2, hpadding="\t\t", linewidth=config.prefs['linewidth'])
  85        line = PlaintextLine(self.linewidth)
  86        self.append(box.draw() + line.draw())
  87
  88    def append_footer(self):
  89        """
  90        Append a horizontal line and some details
  91        """
  92        init_varfilter()
  93        self.append(PlaintextLine(self.linewidth, vpadding=1).draw())
  94        self.append(Template("$hostname $time $date").safe_substitute(varsubst))
  95
  96    def append_section(self, section):
  97        """
  98        Call the appropriate methods to format a section (provided by a parser).
  99        This should be run by interface.py after every instance of parse_log().
 100        """
 101        self.append(PlaintextBox(content=section.title, double=False, fullwidth=False, vpadding=0, hpadding=" ").draw())
 102        self.append('\n'*2)
 103        for data in section.data:
 104            self.append(self._fmt_data(data.subtitle, data.items))
 105            self.append('\n')
 106        for table in section.tables:
 107            self.append(table.draw_plain())
 108        self.append("\n")
 109
 110    def _fmt_data(self, subtitle, data = None):   # write title and data
 111        """
 112        Format the properties of a data object into usable plaintext form with a few fancy symbols/formatting tricks.
 113        Subtitle is required, data is not. If only subtitle is supplied or subtitle + one data item, a single line will be printed.
 114        """
 115        if (subtitle == ""):
 116            logger.warning("No subtitle provided.. skipping section")
 117            return
 118
 119        if (data == None or len(data) == 0):
 120            logger.debug("No data provided.. just printing subtitle")
 121            return subtitle + '\n'
 122        else:
 123            logger.debug("Received data " + str(data))
 124            subtitle += ':'
 125            if (len(data) == 1):
 126                return subtitle + ' ' + data[0] + '\n'
 127            else:
 128                itemoutput = subtitle + '\n'
 129                for datum in data:
 130                    datum = BULLET + datum
 131                    if len(datum) > config.prefs['linewidth'] - 3:
 132                        words = datum.split()
 133                        if max(map(len, words)) > config.prefs['linewidth'] - len(INDENT):
 134                            continue
 135                        res, part, others = [], words[0], words[1:]
 136                        for word in others:
 137                            if 1 + len(word) > config.prefs['linewidth'] - len(part):
 138                                res.append(part)
 139                                part = word
 140                            else:
 141                                part += ' ' + word
 142                        if part:
 143                            res.append(part)
 144                        datum = ('\n    ').join(res)
 145                    datum = INDENT + datum
 146                    itemoutput += datum + '\n'
 147                return itemoutput
 148
 149class HtmlOutput(Output):
 150    """
 151    Process and output data in HTML format.
 152    All HTML formatting functions now reside in this class to differentiate them from plaintext.
 153    """
 154
 155    def __init__(self):
 156        self.content = ""
 157        self.destination = ""
 158        self.css = ""
 159
 160    def embed_css(self, css):
 161        """
 162        Convert stylesheet to inline tags
 163        """
 164        self.content = mail.mailprep(self.content, css)
 165        return self.content
 166
 167    def append_header(self, template):
 168        """
 169        Insert variables into header template file and append HTML tags
 170        """
 171        init_varfilter()
 172        headercontent = Template(open(template, 'r').read())
 173        self.append(headercontent.safe_substitute(varsubst))
 174        self.append(opentag('div', id='main'))
 175
 176    def append_footer(self):
 177        """
 178        Close HTML tags that were opened in the template.
 179        TODO: add footer template similar to header template.
 180        """
 181        self.append(closetag('div') + closetag('body') + closetag('html'))
 182
 183    def append_section(self, section):
 184        """
 185        Call the appropriate methods to generate HTML tags for a section (provided by a parser).
 186        This should be run by interface.py after every instance of parse_log().
 187        """
 188        self.append(opentag('div', 1, section.title, 'section'))
 189        self.append(self._gen_title(section.title))
 190        for data in section.data:
 191            self.append(self._fmt_data(data.subtitle, data.items))
 192        for table in section.tables:
 193            self.append(table.draw_html())
 194        self.append(closetag('div', 1))
 195
 196    def _gen_title(self, title):
 197        """
 198        Format the title for a section
 199        """
 200        if (title == '' or '\n' in title):
 201            logger.error("Invalid title")
 202            raise ValueError 
 203        logger.debug("Writing title for " + title)
 204        return tag('h2', False, title)
 205
 206    def _fmt_data(self, subtitle, data = None):
 207        """
 208        Format the properties of a data object into usable HTML tags.
 209        Subtitle is required, data is not. If only subtitle is supplied or subtitle + one data item, a single line will be printed.
 210        """
 211        if (subtitle == ""):
 212            logger.warning("No subtitle provided.. skipping section")
 213            return
 214
 215        if (data == None or len(data) == 0):
 216            logger.debug("No data provided.. just printing subtitle")
 217            return tag('p', False, subtitle)
 218        else:
 219            logger.debug("Received data " + str(data))
 220            subtitle += ':'
 221            if (len(data) == 1):
 222                return tag('p', False, subtitle + ' ' + data[0])
 223            else:
 224                output = ""
 225                output += tag('p', False, subtitle)
 226                output += opentag('ul', 1)
 227                coderegex = re.compile('`(.*)`')
 228                for datum in data:
 229                    if datum == "" or datum == None:
 230                        continue
 231                    datum = coderegex.sub(r"<code>\1</code>", str(datum))
 232                    output += tag('li', False, datum)
 233                output += closetag('ul', True)
 234                return output
 235
 236
 237class Section:
 238    """
 239    Each parser should output a Section() which contains the title and returned data.
 240    """
 241
 242    def __init__(self, title):
 243        self.title = title
 244        self.data = []
 245        self.tables = []
 246
 247    def append_data(self, data):
 248        self.data.append(data)
 249
 250    def append_table(self, table):
 251        self.tables.append(table)
 252
 253
 254class Data:
 255    """
 256    Each section (parser) can have one or more Data() objects which are essentially glorified lists.
 257    """
 258    
 259    def __init__(self, subtitle="", items=[]):
 260        self.subtitle = subtitle
 261        self.items = items 
 262
 263    def truncl(self, limit):      # truncate list
 264        """
 265        Truncate self.items to a specified value and state how many items are hidden.
 266        """
 267        if (len(self.items) > limit):
 268            more = str(len(self.items) - limit)
 269            self.items = self.items[:limit]
 270            self.items.append("+ {0} more".format(more))
 271
 272    def orderbyfreq(self):
 273        """
 274        Order a list by frequency of each item, then remove duplicates and append frequency in parentheses.
 275        """
 276        unsorted = list(self.items)
 277        self.items = ["{0} ({1})".format(y, unsorted.count(y)) for y in sorted(set(unsorted), key = lambda x: -unsorted.count(x))]
 278
 279class Table(object):
 280    """
 281    A wrapper for python-tabulate's Tabulate type.
 282    """
 283    
 284    def __init__(self, double=False, borders=False, hpadding=" ", maxwidth=80, headers=[]):
 285        self.rows =  []     # List of row objects
 286        self.keymap = {}    # For fast lookup of row by value of first column 
 287        self.double = double
 288        self.borders = borders
 289        self.align_cols = []
 290        self.hpadding = hpadding
 291        self.maxwidth = maxwidth
 292        self.headers = headers
 293        self._align_cols = []
 294
 295    def add_row(self, row):
 296
 297        self.rows.append(row)
 298        if len(row.columns) > 0:
 299            self.keymap[row.columns[0]] = row
 300
 301        logger.debug("Added row with {0} columns".format(str(len(row.columns))))
 302
 303    def align_column(self, i, align):
 304        while len(self._align_cols) -1 < i:
 305            self._align_cols.append("")
 306        self._align_cols[i] = align
 307        for row in self.rows:
 308            row.columns[i].align = align
 309        logger.debug("Column alignment is now {0}".format(str(self._align_cols)))
 310
 311    def _gen_list(self):
 312        hierarchy = []
 313        for row in self.rows:
 314            row_data = []
 315            for column in row.columns:
 316                row_data.append(column.content)
 317            hierarchy.append(row_data)
 318        return hierarchy
 319
 320    def draw_html(self):
 321        output = tabulate(self._gen_list(), self.headers, tablefmt="html", colalign=tuple(self._align_cols))
 322        return output
 323
 324    def draw_plain(self):
 325        output = tabulate(self._gen_list(), self.headers, tablefmt="fancy_grid" if self.borders else "plain", colalign=tuple(self._align_cols))
 326        return output
 327
 328
 329class Table0(object):
 330    """
 331    A two-dimensional information display.
 332    This is a hacky implementation - Table() now relies on the Tabulate package which is much more reliable.
 333    """
 334
 335    def __init__(self, double=False, borders=True, hpadding="+", maxwidth=80):
 336        self.rows =  []     # List of row objects
 337        self.keymap = {}    # For fast lookup of row by value of first column 
 338        self.double = double
 339        self.borders = borders
 340        self.align_cols = []
 341        self.hpadding = hpadding
 342        self.maxwidth = maxwidth
 343        self._colwidths = []
 344
 345    def add_row(self, row):
 346        self.rows.append(row)
 347        for i, col in enumerate(row.columns):
 348            if len(self._colwidths) >= i + 1:
 349                self._colwidths[i] = max([self._colwidths[i], len(col.content)])
 350            else:
 351                self._colwidths.append(len(col.content))
 352        logger.debug("Added row with {0} columns. Column widths are now {1}.".format(str(len(row.columns)), str(self._colwidths)))
 353        if len(row.columns) > 0:
 354            self.keymap[row.columns[0]] = row
 355    
 356    def align_column(self, i, align):
 357        for row in self.rows:
 358            row.columns[i].align = align
 359        
 360
 361    def draw_html(self):
 362        output = ""
 363        output += opentag("table", True, cl="data_table") 
 364        for row in self.rows:
 365            if row.header:
 366                output += opentag("th", block=True, cl="header")
 367            else:
 368                output += opentag("tr", block=True)
 369            for column in row.columns:
 370                output += tag("td", content=column.content, style={"text-align": column.align} if column.align else {})
 371            if row.header:
 372                output += closetag("th", True)
 373            else:
 374                output += closetag("tr", True)
 375        output += closetag("table", True)
 376        logger.debug("Built table with {0} rows and {1} columns".format(str(len(self.rows)), str(max([x.n for x in self.rows]))))
 377        return output
 378
 379    def draw_plain(self):
 380        output = ""
 381        cols = [list(x) for x in zip(self.rows)]
 382        logger.debug("Cols are " + str(cols))
 383
 384        if self.double == True:
 385            cornerchars = CORNERCHARS_DOUBLE
 386            linechars = LINECHARS_DOUBLE
 387            jxnchars = JXNCHARS_DOUBLE
 388        else:
 389            cornerchars = CORNERCHARS_SINGLE
 390            linechars = LINECHARS_SINGLE
 391            jxnchars = JXNCHARS_SINGLE
 392        
 393        lengths = []
 394        row_lengths = []
 395        for row in self.rows:
 396            for i, col in enumerate(row.columns):
 397                if len(lengths) >= i + 1:
 398                    lengths[i] = max([lengths[i], len(col.content)])
 399                else:
 400                    lengths.append(len(col.content))
 401
 402        logger.debug("Lengths are " + str(lengths))
 403
 404        for i, row in enumerate(self.rows):
 405            l = (len(INDENT) + len(self.hpadding)*2*len(row.columns) + ((1+len(row.columns)) if self.borders else 0) + sum([len(col.content) for col in row.columns]))
 406            if l > self.maxwidth:
 407                logger.debug("Line overflow for cell in row {0} of table".format(str(i)))
 408                words = row.columns[-1].content.split()
 409                if max(map(len, words)) > self.maxwidth:
 410                    continue
 411                res, part, others = [], words[0], words[1:]
 412                for word in others:
 413                    if l - len(word) < self.maxwidth:
 414                        res.append(part)
 415                        part = word
 416                    else:
 417                        part += ' ' + word
 418                if part:
 419                    res.append(part)
 420                self._colwidths[-1] = max([len(f) for f in res] + [len(r.columns[-1].content) for r in self.rows if r != row])
 421                if self.borders:
 422                    row.columns[-1].content = res[0][:-1] + self.hpadding + " "*(self._colwidths[-1]-len(res[0])+1) + linechars[0]
 423                    for fragment in res[1:]:
 424                        row.columns[-1].content += "\n" + INDENT + "".join([(linechars[0] + self.hpadding + " "*x + self.hpadding) for x in lengths]) + linechars[0] + self.hpadding + fragment + " " * (max(self._colwidths) - len(fragment))
 425
 426        if self.borders:
 427            top = INDENT + cornerchars[3] + jxnchars[2].join(linechars[1] * (l+2) for l in self._colwidths) + cornerchars[2] + "\n"
 428            bottom = INDENT + cornerchars[0] + jxnchars[3].join(linechars[1] * (l+2) for l in self._colwidths) + cornerchars[1] + "\n"
 429            rowtext = INDENT + linechars[0] + linechars[0].join("{:>%d}" % l for l in self._colwidths) + linechars[0] + "\n"
 430            line = INDENT + jxnchars[0] + jxnchars[4].join(linechars[1] * (l+2) for l in self._colwidths) + jxnchars[1] + "\n"
 431        else:
 432            top = bottom = line = ""
 433            rowtext = " ".join("{:>%d}" % l for l in self._colwidths) + "\n"
 434
 435        for i, row in enumerate(self.rows):
 436            logger.debug("Processing row {0} of {1}".format(str(i), str(len(self.rows)-1)))
 437            row_output = ""
 438            if i == 0:
 439                row_output += top
 440            row_output += (INDENT + linechars[0] if self.borders else "")
 441            for j, column in enumerate(row.columns):
 442                if column.align == "right":
 443                    cell_output = self.hpadding + " "*(self._colwidths[j]-len(column.content)) + column.content + self.hpadding + (linechars[0] if self.borders else "")
 444                elif column.align == "left":
 445                    cell_output = self.hpadding + column.content + " "*(self._colwidths[j]-len(column.content)) + self.hpadding + (linechars[0] if self.borders else "")
 446                elif column.align == "center":
 447                    n_whitespace = (self._colwidths[j]-len(column.content))/2
 448                    cell_output = self.hpadding + " "*(floor(n_whitespace) if len(column.content) % 2 == 0 else ceil(n_whitespace)) + column.content + " "*(ceil(n_whitespace) if len(column.content) % 2 == 0 else floor(n_whitespace)) + self.hpadding + (linechars[0] if self.borders else "")
 449                else:
 450                    logger.warning("Couldn't find alignment value for cell {0} of row {1} with content \"{2}\"".format(str(j), str(i), column.content()))
 451                    continue
 452                row_output += cell_output
 453                if len(row_output) > self.maxwidth:
 454                    logger.warning("Line overflow for row {0} of table".format(str(i)))
 455
 456            output += row_output + "\n"
 457            if i == len(self.rows)-1:
 458                output += (bottom if self.borders else "")
 459            else:
 460                output += (line if self.borders else "")
 461
 462        return output
 463
 464class Row(object):
 465    
 466    def __init__(self, columns=[], header=False):
 467        self.columns = columns
 468        self.header = header
 469        self.n = len(self.columns)
 470
 471    def add_column(self, column):
 472        self.columns.append(column)
 473        self.n += 1
 474
 475    def rm_column(self, column):
 476        self.remove(column)
 477        self.n -= 1
 478
 479class Column(object):
 480
 481    def __init__(self, content="", align="right"):
 482        self.content = content
 483        self.align = align
 484
 485class PlaintextLine:
 486    """
 487    Draw a horizontal line for plain text format, with optional padding/styling.
 488    """
 489
 490    def __init__(self, linewidth=80, double=True, vpadding=1, hpadding=""):
 491        self.linewidth = linewidth
 492        self.double = False
 493        self.vpadding = vpadding
 494        self.hpadding = hpadding
 495
 496    def draw(self):
 497        line = (LINECHARS_DOUBLE[1] if self.double else LINECHARS_SINGLE[1])
 498        return "\n" * self.vpadding + self.hpadding +  line * (self.linewidth - 2 * len(self.hpadding)) + self.hpadding + "\n" * self.vpadding
 499
 500
 501class PlaintextBox:
 502    """
 503    Draw a rectangular box around text, with customisable padding/size/style
 504    """
 505
 506    def __init__(self, content="", double=True, fullwidth=True, linewidth=80, hpadding="\t", vpadding=1):
 507        self.content = content
 508        self.fullwidth = fullwidth
 509        self.linewidth = linewidth
 510        self.hpadding = hpadding 
 511        self.vpadding = vpadding
 512        self.double = double
 513
 514    def draw(self):
 515
 516        if self.double == True:
 517            cornerchars = CORNERCHARS_DOUBLE
 518            linechars = LINECHARS_DOUBLE
 519        else:
 520            cornerchars = CORNERCHARS_SINGLE
 521            linechars = LINECHARS_SINGLE
 522
 523        # Check hpadding has a definite width
 524        self.hpadding = self.hpadding.replace("\t", " "*4)
 525
 526        # Calculate number of characters per line
 527        contentlines = self.content.splitlines()
 528        contentwidth = int((self.linewidth if self.linewidth > 0 else 80) if self.content.splitlines() else len(max(contentlines, key=len)))
 529        logger.debug("Contentwidth is {0}".format(str(contentwidth)))
 530        logger.debug("Longest line is {0}".format(len(max(contentlines, key=len))))
 531        contentwidth += -2*(len(self.hpadding)+1)
 532        if not self.fullwidth:
 533            longestline = len(max(contentlines, key=len))
 534            if longestline <= self.linewidth - 2*(len(self.hpadding)+1):
 535                contentwidth = longestline
 536
 537        # Split lines that are too long
 538        for i, line in enumerate(contentlines):
 539            if len(line) > contentwidth:
 540                words = line.split()
 541                if max(map(len, words)) > contentwidth:
 542                    continue
 543                res, part, others = [], words[0], words[1:]
 544                for word in others:
 545                    if len(' ') + len(word) > contentwidth - len(part):
 546                        res.append(part)
 547                        part = word
 548                    else:
 549                        part += ' ' + word
 550                if part:
 551                    res.append(part)
 552                contentlines[i] = res
 553
 554        # Flatten list
 555        #   Note list comprehension doesn't work here, so we must iterate through each item
 556        newlines = []
 557        for line in contentlines:
 558            if isinstance(line, list):
 559                for subline in line:
 560                    newlines.append(subline)
 561            else:
 562                newlines.append(line)
 563        contentlines = newlines
 564               
 565        # Add vertical padding
 566        for _ in range(self.vpadding):
 567            contentlines.insert(0, ' '*contentwidth)
 568            contentlines.append(' '*contentwidth)
 569
 570        # Insert horizontal padding on lines that are too short
 571        contentlines = [linechars[0] + self.hpadding + x + ' '*(self.linewidth-(len(x)+2*len(self.hpadding)+2) if len(x) < contentwidth else 0) + self.hpadding + linechars[0] for x in contentlines]
 572        contentlines.insert(0, cornerchars[3] + linechars[1] * (contentwidth + len(self.hpadding)*2) + cornerchars[2])
 573        contentlines.append(cornerchars[0] + linechars[1] * (contentwidth + len(self.hpadding)*2) + cornerchars[1])
 574        return ('\n').join(contentlines)
 575
 576
 577def init_varfilter():
 578    global varfilter
 579    global varpattern
 580    global varsubst
 581    varfilter = {"$title$": config.prefs['title'], "$date$": interface.start.strftime(DATEFMT),"$time$": interface.start.strftime(TIMEFMT), "$hostname$": util.hostname(config.prefs['hostname-path']), "$version$": logparse.__version__, "$css$": os.path.relpath(config.prefs['css'], os.path.dirname(config.prefs['output']))}
 582    varfilter = dict((re.escape(k), v) for k, v in varfilter.items())
 583    varpattern = re.compile("|".join(varfilter.keys()))
 584    varsubst = dict(title=config.prefs['title'], date=interface.start.strftime(DATEFMT), time=interface.start.strftime(TIMEFMT), hostname=util.hostname(config.prefs['hostname-path']), version=logparse.__version__, css=os.path.relpath(config.prefs['css'], os.path.dirname(config.prefs['output'])))
 585
 586def backticks(l):
 587    return ["`" + x + "`" for x in l]
 588
 589
 590def plural(noun, quantity):
 591    """
 592    Return "1 noun" or "n nouns"
 593    """
 594    if (quantity == 1):
 595        return(str(quantity) + " " + noun)
 596    else:
 597        return(str(quantity) + " " + noun + "s")
 598
 599
 600def parsesize(num, suffix='B'):
 601    """
 602    Return human-readable size from number of bytes
 603    """
 604    for unit in ['','Ki','Mi','Gi','Ti','Pi','Ei','Zi']:
 605        if abs(num) < 1024.0:
 606            return "%3.1f %s%s" % (num, unit, suffix)
 607        num /= 1024.0
 608    return "%.1f%s%s" % (num, 'Yi', suffix)
 609
 610
 611def fsubject(template):
 612    """
 613    Replace variables in the title template provided in config
 614    """
 615    r = varpattern.sub(lambda m: varfilter[re.escape(m.group(0))], template)
 616    logger.debug("Returning subject line " + r)
 617    return r
 618
 619def opentag(tag, block=False, id=None, cl=None, style=None):
 620    """
 621    Write HTML opening tag
 622    """
 623    output = ""
 624    if block:
 625        output += '\n'
 626    output += '<' + tag
 627    if id:
 628        output += " id='" + id + "'"
 629    if cl:
 630        output += " class='" + cl + "'"
 631    if style:
 632        output += " style='"
 633        output += " ".join("{0}: {1};".format(attr, value) for attr, value in style.items())
 634        output += "'"
 635    output += '>'
 636    if block:
 637        output += '\n'
 638    return output
 639
 640def closetag(tag, block=False):
 641    """
 642    Write HTML closing tag
 643    """
 644    if block:
 645        return "\n</" + tag + ">\n"
 646    else:
 647        return "</" + tag + ">"
 648
 649def tag(tag, block=False, content="", id=None, cl=None, style=None):
 650    """
 651    Write HTML opening tag, content, and closing tag
 652    """
 653    o = opentag(tag, block, id, cl, style)
 654    c = closetag(tag, block)
 655    return o + content + c
 656