From: Zooko O'Whielacronx zooko@zooko.com <zooko@zooko.com>
Date: Sat, 14 Apr 2007 18:19:24 +0000 (+0530)
Subject: pyfec: new filefec with compressed metadata, better error handling, much better unit... 
X-Git-Url: https://git.rkrishnan.org/?a=commitdiff_plain;h=0d4336f613c74afc22aecfa86a75c3849ec28137;p=tahoe-lafs%2Fzfec.git

pyfec: new filefec with compressed metadata, better error handling, much better unit tests

darcs-hash:981818a7904dfb786d05af5503ff59ea2a7d5de2
---

diff --git a/pyfec/README.txt b/pyfec/README.txt
index 59695fc..7420166 100644
--- a/pyfec/README.txt
+++ b/pyfec/README.txt
@@ -17,9 +17,9 @@ whose loss it can tolerate.
 This package is largely based on the old "fec" library by Luigi Rizzo et al.,
 which is a mature and optimized implementation of erasure coding.  The pyfec
 package makes several changes from the original "fec" package, including
-addition of the Python API, refactoring of the C API to be faster (for the way
-that I use it, at least), and a few clean-ups and micro-optimizations of the
-core code itself.
+addition of the Python API, refactoring of the C API to support zero-copy
+operation, and a few clean-ups and micro-optimizations of the core code
+itself.
 
 
  * Community
@@ -52,13 +52,21 @@ and k is required to be at least 1 and at most m.
 degenerates to the equivalent of the Unix "split" utility which simply splits
 the input into successive segments.  Similarly, when k == 1 it degenerates to
 the equivalent of the unix "cp" utility -- each block is a complete copy of the
-input data.)
+input data.  The "fec" command-line tool does not implement these degenerate 
+cases.)
 
 Note that each "primary block" is a segment of the original data, so its size
 is 1/k'th of the size of original data, and each "secondary block" is of the
 same size, so the total space used by all the blocks is m/k times the size of
 the original data (plus some padding to fill out the last primary block to be
-the same size as all the others).
+the same size as all the others).  In addition to the data contained in the 
+blocks themselves there are also a few pieces of metadata which are necessary 
+for later reconstruction.  Those pieces are: 1.  the value of K, 2.  the value 
+of M,  3.  the sharenum of each block,  4.  the number of bytes of padding 
+that were used.  The "fec" command-line tool compresses these pieces of data 
+and prepends them to the beginning of each share, so each the sharefile 
+produced by the "fec" command-line tool is between one and four bytes larger 
+than the share data alone.
 
 The decoding step requires as input k of the blocks which were produced by the
 encoding step.  The decoding step produces as output the data that was earlier
@@ -136,8 +144,11 @@ objects (e.g. Python strings) to hold the data that you pass to pyfec.
 
  * Utilities
 
-See also the filefec.py module which has a utility function for efficiently
-reading a file and encoding it piece by piece.
+The filefec.py module which has a utility function for efficiently reading a
+file and encoding it piece by piece.
+
+The bin/ directory contains two commandline tools "fec" and "unfec".  See
+their usage strings for details.
 
 
  * Dependencies
@@ -180,5 +191,5 @@ licence.
 Enjoy!
 
 Zooko Wilcox-O'Hearn
-2007-08-01
+2007-04-11
 Boulder, Colorado
diff --git a/pyfec/fec/filefec.py b/pyfec/fec/filefec.py
index 6c9ae13..b227962 100644
--- a/pyfec/fec/filefec.py
+++ b/pyfec/fec/filefec.py
@@ -24,77 +24,237 @@
 # Foundation, Inc., 51 Franklin Street, Fifth Floor, Boston, MA  02110-1301, USA.
 
 import easyfec, fec
+from util import fileutil
+from util.mathutil import log_ceil
 
-import array, random
+import array, os, re, struct, traceback
 
-def encode_to_files_easyfec(inf, prefix, k, m):
+CHUNKSIZE = 4096
+
+def _build_header(m, k, pad, sh):
     """
-    Encode inf, writing the shares to a file named $prefix+$sharenum.
+    @param m: the total number of shares; 3 <= m <= 256
+    @param k: the number of shares required to reconstruct; 2 <= k < m
+    @param pad: the number of bytes of padding added to the file before encoding; 0 <= pad < k
+    @param sh: the shnum of this share; 0 <= k < m
+
+    @return: a string (which is hopefully short) encoding m, k, sh, and pad
     """
-    l = [ open(prefix+str(sharenum), "wb") for sharenum in range(m) ]
-    def cb(blocks, length):
-        assert len(blocks) == len(l)
-        for i in range(len(blocks)):
-            l[i].write(blocks[i])
-
-    encode_file_stringy_easyfec(inf, cb, k, m, chunksize=4096)
- 
-def encode_to_files_stringy(inf, prefix, k, m):
+    assert m >= 3
+    assert m <= 2**8
+    assert k >= 2
+    assert k < m
+    assert pad >= 0
+    assert pad < k
+
+    assert sh >= 0
+    assert sh < m
+
+    bitsused = 0
+    val = 0
+
+    val |= (m - 3)
+    bitsused += 8 # the first 8 bits always encode m
+
+    kbits = log_ceil(m-2, 2) # num bits needed to store all possible values of k
+    val <<= kbits
+    bitsused += kbits
+
+    val |= (k - 2)
+
+    padbits = log_ceil(k, 2) # num bits needed to store all possible values of pad
+    val <<= padbits
+    bitsused += padbits
+
+    val |= pad
+
+    shnumbits = log_ceil(m, 2) # num bits needed to store all possible values of shnum
+    val <<= shnumbits
+    bitsused += shnumbits
+
+    val |= sh
+
+    assert bitsused >= 11
+    assert bitsused <= 32
+
+    if bitsused <= 16:
+        val <<= (16-bitsused)
+        cs = struct.pack('>H', val)
+        assert cs[:-2] == '\x00' * (len(cs)-2)
+        return cs[-2:]
+    if bitsused <= 24:
+        val <<= (24-bitsused)
+        cs = struct.pack('>I', val)
+        assert cs[:-3] == '\x00' * (len(cs)-3)
+        return cs[-3:]
+    else:
+        val <<= (32-bitsused)
+        cs = struct.pack('>I', val)
+        assert cs[:-4] == '\x00' * (len(cs)-4)
+        return cs[-4:]
+
+def MASK(bits):
+    return (1<<bits)-1
+
+def _parse_header(inf):
     """
-    Encode inf, writing the shares to a file named named $prefix+$sharenum.
+    @param inf: an object which I can call read(1) on to get another byte
+
+    @return: tuple of (m, k, pad, sh,); side-effect: the first one to four
+        bytes of inf will be read
     """
-    l = [ open(prefix+str(sharenum), "wb") for sharenum in range(m) ]
-    def cb(blocks, length):
-        assert len(blocks) == len(l)
-        for i in range(len(blocks)):
-            l[i].write(blocks[i])
-
-    encode_file_stringy(inf, cb, k, m, chunksize=4096)
- 
-def encode_to_files(inf, prefix, k, m):
+    # The first 8 bits always encode m.
+    byte = ord(inf.read(1))
+    m = byte + 3
+
+    # The next few bits encode k.
+    kbits = log_ceil(m-2, 2) # num bits needed to store all possible values of k
+    b2_bits_left = 8-kbits
+    kbitmask = MASK(kbits) << b2_bits_left
+    byte = ord(inf.read(1))
+    k = ((byte & kbitmask) >> b2_bits_left) + 2
+
+    shbits = log_ceil(m, 2) # num bits needed to store all possible values of shnum
+    padbits = log_ceil(k, 2) # num bits needed to store all possible values of pad
+
+    val = byte & (~kbitmask)
+
+    needed_padbits = padbits - b2_bits_left
+    if needed_padbits > 0:
+        byte = struct.unpack(">B", inf.read(1))[0]
+        val <<= 8
+        val |= byte 
+        needed_padbits -= 8
+    assert needed_padbits <= 0
+    extrabits = -needed_padbits
+    pad = val >> extrabits
+    val &= MASK(extrabits)
+
+    needed_shbits = shbits - extrabits
+    if needed_shbits > 0:
+        byte = struct.unpack(">B", inf.read(1))[0]
+        val <<= 8
+        val |= byte 
+        needed_shbits -= 8
+    assert needed_shbits <= 0
+
+    gotshbits = -needed_shbits
+
+    sh = val >> gotshbits
+
+    return (m, k, pad, sh,)
+
+FORMAT_FORMAT = "%%s.%%0%dd_%%0%dd%%s"
+RE_FORMAT = "%s.[0-9]+_[0-9]+%s"
+def encode_to_files(inf, fsize, dirname, prefix, k, m, suffix=".fec", verbose=False):
     """
-    Encode inf, writing the shares to named $prefix+$sharenum.
+    Encode inf, writing the shares to specially named, newly created files.
+
+    @param fsize: calling read() on inf must yield fsize bytes of data and 
+        then raise an EOFError
+    @param dirname: the name of the directory into which the sharefiles will
+        be written
     """
-    l = [ open(prefix+str(sharenum), "wb") for sharenum in range(m) ]
-    def cb(blocks, length):
-        assert len(blocks) == len(l)
-        for i in range(len(blocks)):
-            l[i].write(blocks[i])
-
-    encode_file(inf, cb, k, m, chunksize=4096)
- 
-def decode_from_files(outf, filesize, prefix, k, m):
+    mlen = len(str(m))
+    format = FORMAT_FORMAT % (mlen, mlen,)
+
+    padbytes = fec.util.mathutil.pad_size(fsize, k)
+
+    fns = []
+    fs = []
+    try:
+        for shnum in range(m):
+            hdr = _build_header(m, k, padbytes, shnum)
+
+            fn = os.path.join(dirname, format % (prefix, shnum, m, suffix,))
+            if verbose:
+                print "Creating share file %r..." % (fn,)
+            fd = os.open(fn, os.O_WRONLY|os.O_CREAT|os.O_EXCL)
+            f = os.fdopen(fd, "wb")
+            f.write(hdr)
+            fs.append(f)
+            fns.append(fn)
+        sumlen = [0]
+        def cb(blocks, length):
+            if verbose:
+                print "Writing %d bytes into share files..." % (length,)
+            assert len(blocks) == len(fs)
+            sumlen[0] += length
+            if sumlen[0] > fsize:
+                raise IOError("Wrong file size -- possibly the size of the file changed during encoding.  Original size: %d, observed size at least: %s" % (fsize, sumlen[0],))
+            for i in range(len(blocks)):
+                data = blocks[i]
+                fs[i].write(data)
+                length -= len(data)
+
+        encode_file_stringy_easyfec(inf, cb, k, m, chunksize=4096)
+    except EnvironmentError, le:
+        print "Cannot complete because of exception: "
+        print le
+        print "Cleaning up..."
+        # clean up
+        while fs:
+            f = fs.pop()
+            f.close() ; del f
+            fn = fns.pop()
+            if verbose:
+                print "Cleaning up: trying to remove %r..." % (fn,)
+            fileutil.remove_if_possible(fn)
+        return 1
+    if verbose:
+        print "Done!"
+    return 0
+
+def decode_from_files(outf, dirname, prefix, suffix=".fec", verbose=False):
     """
-    Decode from the first k files in the current directory whose names begin 
-    with prefix, writing the results to outf.
+    Decode from the first k files in the directory whose names match the
+    pattern, writing the results to outf.
     """
-    import os
+    RE=re.compile(RE_FORMAT % (prefix, suffix,))
+
     infs = []
-    sharenums = []
-    listd = os.listdir(".")
-    random.shuffle(listd)
-    for f in listd:
-        if f.startswith(prefix):
-            infs.append(open(f, "rb"))
-            sharenums.append(int(f[len(prefix):]))
+    shnums = []
+    m = None
+    k = None
+    padlen = None
+
+    for fn in os.listdir(dirname):
+        if RE.match(fn):
+            f = open(os.path.join(dirname, fn), "rb")
+
+            (nm, nk, npadlen, shnum,) = _parse_header(f)
+            if not (m is None or m == nm):
+                raise fec.Error("Share files were corrupted -- share file %s said that m was %s but another share file previously said that m was %s" % (f, nm, m,))
+            m = nm
+            if not (k is None or k == nk):
+                raise fec.Error("Share files were corrupted -- share file %s said that k was %s but another share file previously said that k was %s" % (f, nk, k,))
+            k = nk
+            if not (padlen is None or padlen == npadlen):
+                raise fec.Error("Share files were corrupted -- share file %s said that pad length was %s but another share file previously said that pad length was %s" % (f, npadlen, padlen,))
+            padlen = npadlen
+
+            infs.append(f)
+            shnums.append(shnum)
+
             if len(infs) == k:
                 break
 
-    CHUNKSIZE = 4096
-    dec = fec.Decoder(k, m)
+    dec = easyfec.Decoder(k, m)
+
     while True:
-        x = [ inf.read(CHUNKSIZE) for inf in infs ]
-        decblocks = dec.decode(x, sharenums)
-        for decblock in decblocks:
-            if len(decblock) == 0:
-                raise "error -- probably share was too short -- was it stored in a file which got truncated? chunksizes: %s" % ([len(chunk) for chunk in x],)
-            if filesize >= len(decblock):
-                outf.write(decblock)
-                filesize -= len(decblock)
-                # print "filesize is now %s after subtracting %s" % (filesize, len(decblock),)
-            else: 
-                outf.write(decblock[:filesize])
-                return
+        chunks = [ inf.read(CHUNKSIZE) for inf in infs ]
+        if [ch for ch in chunks if len(ch) != len(chunks[-1])]:
+            raise fec.Error("Share files were corrupted -- all share files are required to be the same length, but they weren't.")
+
+        if len(chunks[-1]) == CHUNKSIZE:
+            # Then this was a full read, so we're still in the sharefiles.
+            resultdata = dec.decode(chunks, shnums, padlen=0)
+            outf.write(resultdata)
+        else:
+            # Then this was a short read, so we've reached the end of the sharefiles.
+            resultdata = dec.decode(chunks, shnums, padlen)
+            outf.write(resultdata)
+            return # Done.
 
 def encode_file(inf, cb, k, m, chunksize=4096):
     """
@@ -128,30 +288,31 @@ def encode_file(inf, cb, k, m, chunksize=4096):
     enc = fec.Encoder(k, m)
     l = tuple([ array.array('c') for i in range(k) ])
     indatasize = k*chunksize # will be reset to shorter upon EOF
+    eof = False
     ZEROES=array.array('c', ['\x00'])*chunksize
-    while indatasize == k*chunksize:
+    while not eof:
         # This loop body executes once per segment.
         i = 0
         while (i<len(l)):
             # This loop body executes once per chunk.
             a = l[i]
-            i += 1
             del a[:]
             try:
                 a.fromfile(inf, chunksize)
+                i += 1
             except EOFError:
+                eof = True
                 indatasize = i*chunksize + len(a)
                 
                 # padding
                 a.fromstring("\x00" * (chunksize-len(a)))
+                i += 1
                 while (i<len(l)):
                     a = l[i]
                     a[:] = ZEROES
                     i += 1
 
-        # print "about to encode()... len(l[0]): %s, l[0]: %s" % (len(l[0]), type(l[0]),),
         res = enc.encode(l)
-        # print "...finished to encode()"
         cb(res, indatasize)
 
 def encode_file_stringy(inf, cb, k, m, chunksize=4096):
@@ -195,50 +356,9 @@ def encode_file_stringy(inf, cb, k, m, chunksize=4096):
                     l.append(ZEROES)
                     i += 1
 
-        # print "about to encode()... len(l[0]): %s, l[0]: %s" % (len(l[0]), type(l[0]),),
         res = enc.encode(l)
-        # print "...finished to encode()"
         cb(res, indatasize)
 
-def encode_file_not_really(inf, cb, k, m, chunksize=4096):
-    """
-    Read in the contents of inf, and call cb with the results.
-
-    @param inf the file object from which to read the data
-    @param cb the callback to be invoked with the results
-    @param k the number of shares required to reconstruct the file
-    @param m the total number of shares created
-    @param chunksize how much data to read from inf for each of the k input 
-        blocks
-    """
-    enc = fec.Encoder(k, m)
-    l = tuple([ array.array('c') for i in range(k) ])
-    indatasize = k*chunksize # will be reset to shorter upon EOF
-    ZEROES=array.array('c', ['\x00'])*chunksize
-    while indatasize == k*chunksize:
-        # This loop body executes once per segment.
-        i = 0
-        while (i<len(l)):
-            # This loop body executes once per chunk.
-            a = l[i]
-            i += 1
-            del a[:]
-            try:
-                a.fromfile(inf, chunksize)
-            except EOFError:
-                indatasize = i*chunksize + len(a)
-                
-                # padding
-                a.fromstring("\x00" * (chunksize-len(a)))
-                while (i<len(l)):
-                    a[:] = ZEROES
-                    i += 1
-
-        # print "about to encode()... len(l[0]): %s, l[0]: %s" % (len(l[0]), type(l[0]),),
-        # res = enc.encode(l)
-        # print "...finished to encode()"
-        cb(l, indatasize)
-
 def encode_file_stringy_easyfec(inf, cb, k, m, chunksize=4096):
     """
     Read in the contents of inf, encode, and call cb with the results.
@@ -262,10 +382,10 @@ def encode_file_stringy_easyfec(inf, cb, k, m, chunksize=4096):
     """
     enc = easyfec.Encoder(k, m)
 
-    indatasize = k*chunksize # will be reset to shorter upon EOF
-    indata = inf.read(indatasize)
+    readsize = k*chunksize
+    indata = inf.read(readsize)
     while indata:
         res = enc.encode(indata)
-        cb(res, indatasize)
-        indata = inf.read(indatasize)
+        cb(res, len(indata))
+        indata = inf.read(readsize)
 
diff --git a/pyfec/fec/test/test_pyfec.py b/pyfec/fec/test/test_pyfec.py
index e536d3b..7731e28 100755
--- a/pyfec/fec/test/test_pyfec.py
+++ b/pyfec/fec/test/test_pyfec.py
@@ -1,5 +1,8 @@
 #!/usr/bin/env python
 
+# import bindann
+# import bindann.monkeypatch.all
+
 # pyfec -- fast forward error correction library with Python interface
 #
 # Copyright (C) 2007 Allmydata, Inc.
@@ -25,11 +28,22 @@
 # along with this program; if not, write to the Free Software
 # Foundation, Inc., 51 Franklin Street, Fifth Floor, Boston, MA  02110-1301, USA.
 
-import random
-import sys
+import cStringIO, os, random, re, sys
 
 import fec
 
+try:
+    from twisted.trial import unittest
+except ImportError:
+    # trial is unavailable, oh well
+    import unittest
+
+global VERBOSE
+VERBOSE=False
+if '-v' in sys.argv:
+    sys.argv.pop(sys.argv.index('-v'))
+    VERBOSE=True
+
 from base64 import b32encode
 def ab(x): # debuggery
     if len(x) >= 3:
@@ -42,124 +56,165 @@ def ab(x): # debuggery
         return "%s:%s" % (len(x), "--empty--",)
 
 def _h(k, m, ss):
-    # sys.stdout.write("k: %s, m: %s,  len(ss): %r, len(ss[0]): %r" % (k, m, len(ss), len(ss[0]),)) ; sys.stdout.flush()
     encer = fec.Encoder(k, m)
-    # sys.stdout.write("constructed.\n") ; sys.stdout.flush()
     nums_and_blocks = list(enumerate(encer.encode(ss)))
-    # sys.stdout.write("encoded.\n") ; sys.stdout.flush()
     assert isinstance(nums_and_blocks, list), nums_and_blocks
     assert len(nums_and_blocks) == m, (len(nums_and_blocks), m,)
     nums_and_blocks = random.sample(nums_and_blocks, k)
     blocks = [ x[1] for x in nums_and_blocks ]
     nums = [ x[0] for x in nums_and_blocks ]
-    # sys.stdout.write("about to construct Decoder.\n") ; sys.stdout.flush()
     decer = fec.Decoder(k, m)
-    # sys.stdout.write("about to decode from %s.\n"%nums) ; sys.stdout.flush()
     decoded = decer.decode(blocks, nums)
-    # sys.stdout.write("decoded.\n") ; sys.stdout.flush()
     assert len(decoded) == len(ss), (len(decoded), len(ss),)
     assert tuple([str(s) for s in decoded]) == tuple([str(s) for s in ss]), (tuple([ab(str(s)) for s in decoded]), tuple([ab(str(s)) for s in ss]),)
 
 def randstr(n):
     return ''.join(map(chr, map(random.randrange, [0]*n, [256]*n)))
 
-def div_ceil(n, d):
-    """
-    The smallest integer k such that k*d >= n.
-    """
-    return (n/d) + (n%d != 0)
-
-def next_multiple(n, k):
-    """
-    The smallest multiple of k which is >= n.
-    """
-    return div_ceil(n, k) * k
-
-def pad_size(n, k):
-    """
-    The smallest number that has to be added to n so that n is a multiple of k.
-    """
-    if n%k:
-        return k - n%k
-    else:
-        return 0
-
-def _test_random():
+def _help_test_random():
     m = random.randrange(1, 257)
     k = random.randrange(1, m+1)
-    l = random.randrange(0, 2**15)
+    l = random.randrange(0, 2**10)
     ss = [ randstr(l/k) for x in range(k) ]
     _h(k, m, ss)
 
-def _test_random_with_l(l):
+def _help_test_random_with_l(l):
     m = 83
     k = 19
     ss = [ randstr(l/k) for x in range(k) ]
     _h(k, m, ss)
 
-def test_random(noisy=True):
-    for i in range(2**5):
-        # sys.stdout.write(",")
-        _test_random()
-        # sys.stdout.write(".")
-    if noisy:
-        print "%d randomized tests pass." % (i+1)
-
-def test_bad_args_enc():
-    encer = fec.Encoder(2, 4)
-    try:
-        encer.encode(["a", "b", ], ["c", "I am not an integer blocknum",])
-    except fec.Error, e:
-        assert "Precondition violation: second argument is required to contain int" in str(e), e
-    else:
-        raise "Should have gotten fec.Error for wrong type of second argument."
-
-    try:
-        encer.encode(["a", "b", ], 98) # not a sequence at all
-    except TypeError, e:
-        assert "Second argument (optional) was not a sequence" in str(e), e
-    else:
-        raise "Should have gotten TypeError for wrong type of second argument."
-
-def test_bad_args_dec():
-    decer = fec.Decoder(2, 4)
-
-    try:
-        decer.decode(98, [0, 1]) # first argument is not a sequence
-    except TypeError, e:
-        assert "First argument was not a sequence" in str(e), e
-    else:
-        raise "Should have gotten TypeError for wrong type of second argument."
-
-    try:
-        decer.decode(["a", "b", ], ["c", "d",])
-    except fec.Error, e:
-        assert "Precondition violation: second argument is required to contain int" in str(e), e
-    else:
-        raise "Should have gotten fec.Error for wrong type of second argument."
-
-    try:
-        decer.decode(["a", "b", ], 98) # not a sequence at all
-    except TypeError, e:
-        assert "Second argument was not a sequence" in str(e), e
-    else:
-        raise "Should have gotten TypeError for wrong type of second argument."
-
-try:
-    from twisted.trial import unittest
-    class TestPyFec(unittest.TestCase):
-        def test_random(self):
-            test_random(False)
-        def test_bad_args_enc(self):
-            test_bad_args_enc()
-        def test_bad_args_dec(self):
-            test_bad_args_dec()
-except ImportError:
-    # trial is unavailable, oh well
-    pass
+class Fec(unittest.TestCase):
+    def test_random(self):
+        for i in range(3):
+            _help_test_random()
+        if VERBOSE:
+            print "%d randomized tests pass." % (i+1)
+
+    def test_bad_args_enc(self):
+        encer = fec.Encoder(2, 4)
+        try:
+            encer.encode(["a", "b", ], ["c", "I am not an integer blocknum",])
+        except fec.Error, e:
+            assert "Precondition violation: second argument is required to contain int" in str(e), e
+        else:
+            raise "Should have gotten fec.Error for wrong type of second argument."
+
+        try:
+            encer.encode(["a", "b", ], 98) # not a sequence at all
+        except TypeError, e:
+            assert "Second argument (optional) was not a sequence" in str(e), e
+        else:
+            raise "Should have gotten TypeError for wrong type of second argument."
+
+    def test_bad_args_dec(self):
+        decer = fec.Decoder(2, 4)
+
+        try:
+            decer.decode(98, [0, 1]) # first argument is not a sequence
+        except TypeError, e:
+            assert "First argument was not a sequence" in str(e), e
+        else:
+            raise "Should have gotten TypeError for wrong type of second argument."
+
+        try:
+            decer.decode(["a", "b", ], ["c", "d",])
+        except fec.Error, e:
+            assert "Precondition violation: second argument is required to contain int" in str(e), e
+        else:
+            raise "Should have gotten fec.Error for wrong type of second argument."
+
+        try:
+            decer.decode(["a", "b", ], 98) # not a sequence at all
+        except TypeError, e:
+            assert "Second argument was not a sequence" in str(e), e
+        else:
+            raise "Should have gotten TypeError for wrong type of second argument."
+
+class FileFec(unittest.TestCase):
+    def test_filefec_header(self):
+        for m in [3, 5, 7, 9, 11, 17, 19, 33, 35, 65, 66, 67, 129, 130, 131, 254, 255, 256,]:
+            for k in [2, 3, 5, 9, 17, 33, 65, 129, 255,]:
+                if k >= m:
+                    continue
+                for pad in [0, 1, k-1,]:
+                    if pad >= k:
+                        continue
+                    for sh in [0, 1, m-1,]:
+                        if sh >= m:
+                            continue
+                        h = fec.filefec._build_header(m, k, pad, sh)
+                        hio = cStringIO.StringIO(h)
+                        (rm, rk, rpad, rsh,) = fec.filefec._parse_header(hio)
+                        assert (rm, rk, rpad, rsh,) == (m, k, pad, sh,), h
+
+    def _help_test_filefec(self, teststr, k, m, numshs=None):
+        if numshs == None:
+            numshs = m
+
+        TESTFNAME = "testfile.txt"
+        PREFIX = "test"
+        SUFFIX = ".fec"
+
+        tempdir = fec.util.fileutil.NamedTemporaryDirectory(cleanup=False)
+        try:
+            tempfn = os.path.join(tempdir.name, TESTFNAME)
+            tempf = open(tempfn, 'wb')
+            tempf.write(teststr)
+            tempf.close()
+            fsize = os.path.getsize(tempfn)
+            assert fsize == len(teststr)
+
+            # encode the file
+            fec.filefec.encode_to_files(open(tempfn, 'rb'), fsize, tempdir.name, PREFIX, k, m, SUFFIX, verbose=VERBOSE)
+
+            # delete some share files
+            fns = os.listdir(tempdir.name)
+            RE=re.compile(fec.filefec.RE_FORMAT % (PREFIX, SUFFIX,))
+            sharefs = [ fn for fn in fns if RE.match(fn) ]
+            random.shuffle(sharefs)
+            while len(sharefs) > numshs:
+                shfn = sharefs.pop()
+                fec.util.fileutil.remove(os.path.join(tempdir.name, shfn))
+
+            # decode from the share files
+            outf = open(os.path.join(tempdir.name, 'recovered-testfile.txt'), 'wb')
+            fec.filefec.decode_from_files(outf, tempdir.name, PREFIX, SUFFIX, verbose=VERBOSE)
+            outf.close()
+
+            tempfn = open(os.path.join(tempdir.name, 'recovered-testfile.txt'), 'rb')
+            recovereddata = tempfn.read()
+            assert recovereddata == teststr
+        finally:
+            tempdir.shutdown()
+
+    def test_filefec_all_shares(self):
+        return self._help_test_filefec("Yellow Whirled!", 3, 8)
+
+    def test_filefec_all_shares_with_padding(self, noisy=VERBOSE):
+        return self._help_test_filefec("Yellow Whirled!A", 3, 8)
+
+    def test_filefec_min_shares_with_padding(self, noisy=VERBOSE):
+        return self._help_test_filefec("Yellow Whirled!A", 3, 8, numshs=3)
 
 if __name__ == "__main__":
-    test_bad_args_dec()
-    test_bad_args_enc()
-    test_random()
-
+    if hasattr(unittest, 'main'):
+        unittest.main()
+    else:
+        sys.path.append(os.getcwd())
+        mods = []
+        fullname = os.path.realpath(os.path.abspath(__file__))
+        for pathel in sys.path:
+            fullnameofpathel = os.path.realpath(os.path.abspath(pathel))
+            if fullname.startswith(fullnameofpathel):
+                relname = fullname[len(fullnameofpathel):]
+                mod = (os.path.splitext(relname)[0]).replace(os.sep, '.').strip('.')
+                mods.append(mod)
+
+        mods.sort(cmp=lambda x, y: cmp(len(x), len(y)))
+        mods.reverse()
+        for mod in mods:
+            cmdstr = "trial %s %s" % (' '.join(sys.argv[1:]), mod)
+            print cmdstr
+            if os.system(cmdstr) == 0:
+                break