Move hg from storing files in data with base64 encoding to full

pathnames with .i and .d extensions. This means we naturally get good
FS layout, and cp and tar fix things up nicely rather than pessimizing
layout.

mercurial/hg.py

@@ -1,873 +1,870 b''
 # hg.py - repository classes for mercurial
 #
 # Copyright 2005 Matt Mackall <[e-mail]>
 #
 # This software may be used and distributed according to the terms
 # of the GNU General Public License, incorporated herein by reference.
 
-import sys, struct, sha, socket, os, time, base64, re, urllib2
+import sys, struct, sha, socket, os, time, re, urllib2
 import urllib
 from mercurial import byterange
 from mercurial.transaction import *
 from mercurial.revlog import *
 from difflib import SequenceMatcher
 
 class filelog(revlog):
     def __init__(self, opener, path):
-        s = self.encodepath(path)
-        revlog.__init__(self, opener, os.path.join("data", s + "i"),
-                        os.path.join("data", s))
-
-    def encodepath(self, path):
-        s = sha.sha(path).digest()
-        s = base64.encodestring(s)[:-3]
-        s = re.sub("\+", "%", s)
-        s = re.sub("/", "_", s)
-        return s
+        revlog.__init__(self, opener, path + ".i", path + ".d")
 
     def read(self, node):
         return self.revision(node)
     def add(self, text, transaction, link, p1=None, p2=None):
         return self.addrevision(text, transaction, link, p1, p2)
 
     def annotate(self, node):
         revs = []
         while node != nullid:
             revs.append(node)
             node = self.parents(node)[0]
         revs.reverse()
         prev = []
         annotate = []
         
         for node in revs:
             curr = self.read(node).splitlines(1)
             linkrev = self.linkrev(node)
             sm = SequenceMatcher(None, prev, curr)
             new = []
             for o, m, n, s, t in sm.get_opcodes():
                 if o == 'equal':
                     new += annotate[m:n]
                 else:
                     new += [(linkrev, l) for l in curr[s:t]]
             annotate, prev = new, curr
         return annotate
 
 class manifest(revlog):
     def __init__(self, opener):
         self.mapcache = None
         self.listcache = None
         self.addlist = None
         revlog.__init__(self, opener, "00manifest.i", "00manifest.d")
 
     def read(self, node):
         if self.mapcache and self.mapcache[0] == node:
             return self.mapcache[1].copy()
         text = self.revision(node)
         map = {}
         self.listcache = (text, text.splitlines(1))
         for l in self.listcache[1]:
             (f, n) = l.split('\0')
             map[f] = bin(n[:40])
         self.mapcache = (node, map)
         return map
 
     def diff(self, a, b):
         # this is sneaky, as we're not actually using a and b
         if self.listcache and len(self.listcache[0]) == len(a):
             d = mdiff.diff(self.listcache[1], self.addlist, 1)
             if mdiff.patch(a, d) != b:
                 sys.stderr.write("*** sortdiff failed, falling back ***\n")
                 return mdiff.textdiff(a, b)
             return d
         else:
             return mdiff.textdiff(a, b)
 
     def add(self, map, transaction, link, p1=None, p2=None):
         files = map.keys()
         files.sort()
 
         self.addlist = ["%s\000%s\n" % (f, hex(map[f])) for f in files]
         text = "".join(self.addlist)
 
         n = self.addrevision(text, transaction, link, p1, p2)
         self.mapcache = (n, map)
         self.listcache = (text, self.addlist)
 
         return n
 
 class changelog(revlog):
     def __init__(self, opener):
         revlog.__init__(self, opener, "00changelog.i", "00changelog.d")
 
     def extract(self, text):
         if not text:
             return (nullid, "", "0", [], "")
         last = text.index("\n\n")
         desc = text[last + 2:]
         l = text[:last].splitlines()
         manifest = bin(l[0])
         user = l[1]
         date = l[2]
         files = l[3:]
         return (manifest, user, date, files, desc)
 
     def read(self, node):
         return self.extract(self.revision(node))
 
     def add(self, manifest, list, desc, transaction, p1=None, p2=None):
         user = (os.environ.get("HGUSER") or
                 os.environ.get("EMAIL") or
                 os.environ.get("LOGNAME", "unknown") + '@' + socket.getfqdn())
         date = "%d %d" % (time.time(), time.timezone)
         list.sort()
         l = [hex(manifest), user, date] + list + ["", desc]
         text = "\n".join(l)
         return self.addrevision(text, transaction, self.count(), p1, p2)
 
 class dircache:
     def __init__(self, opener, ui):
         self.opener = opener
         self.dirty = 0
         self.ui = ui
         self.map = None
     def __del__(self):
         if self.dirty: self.write()
     def __getitem__(self, key):
         try:
             return self.map[key]
         except TypeError:
             self.read()
             return self[key]
         
     def read(self):
         if self.map is not None: return self.map
 
         self.map = {}
         try:
             st = self.opener("dircache").read()
         except: return
 
         pos = 0
         while pos < len(st):
             e = struct.unpack(">llll", st[pos:pos+16])
             l = e[3]
             pos += 16
             f = st[pos:pos + l]
             self.map[f] = e[:3]
             pos += l
         
     def update(self, files):
         if not files: return
         self.read()
         self.dirty = 1
         for f in files:
             try:
                 s = os.stat(f)
                 self.map[f] = (s.st_mode, s.st_size, s.st_mtime)
             except IOError:
                 self.remove(f)
 
     def taint(self, files):
         if not files: return
         self.read()
         self.dirty = 1
         for f in files:
             self.map[f] = (0, -1, 0)
 
     def remove(self, files):
         if not files: return
         self.read()
         self.dirty = 1
         for f in files:
             try:
                 del self.map[f]
             except KeyError:
                 self.ui.warn("Not in dircache: %s\n" % f)
                 pass
 
     def clear(self):
         self.map = {}
         self.dirty = 1
 
     def write(self):
         st = self.opener("dircache", "w")
         for f, e in self.map.items():
             e = struct.pack(">llll", e[0], e[1], e[2], len(f))
             st.write(e + f)
         self.dirty = 0
 
     def copy(self):
         self.read()
         return self.map.copy()
 
 # used to avoid circular references so destructors work
 def opener(base):
     p = base
     def o(path, mode="r"):
         if p[:7] == "http://":
             f = os.path.join(p, urllib.quote(path))
             return httprangereader(f)
 
         f = os.path.join(p, path)
 
-        if mode != "r" and os.path.isfile(f):
-            s = os.stat(f)
-            if s.st_nlink > 1:
-                file(f + ".tmp", "w").write(file(f).read())
-                os.rename(f+".tmp", f)
+        if mode != "r":
+            try:
+                s = os.stat(f)
+            except OSError:
+                d = os.path.dirname(f)
+                if not os.path.isdir(d):
+                    os.makedirs(d)
+            else:
+                if s.st_nlink > 1:
+                    file(f + ".tmp", "w").write(file(f).read())
+                    os.rename(f+".tmp", f)
 
         return file(f, mode)
 
     return o
 
 class localrepository:
     def __init__(self, ui, path=None, create=0):
         self.remote = 0
         if path and path[:7] == "http://":
             self.remote = 1
             self.path = path
         else:
             if not path:
                 p = os.getcwd()
                 while not os.path.isdir(os.path.join(p, ".hg")):
                     p = os.path.dirname(p)
                     if p == "/": raise "No repo found"
                 path = p
             self.path = os.path.join(path, ".hg")
 
         self.root = path
         self.ui = ui
 
         if create:
             os.mkdir(self.path)  
             os.mkdir(self.join("data"))
 
         self.opener = opener(self.path)
         self.manifest = manifest(self.opener)
         self.changelog = changelog(self.opener)
         self.ignorelist = None
         self.tags = None
 
         if not self.remote:
             self.dircache = dircache(self.opener, ui)
             try:
                 self.current = bin(self.opener("current").read())
             except IOError:
                 self.current = None
 
     def setcurrent(self, node):
         self.current = node
         self.opener("current", "w").write(hex(node))
       
     def ignore(self, f):
         if self.ignorelist is None:
             self.ignorelist = []
             try:
                 l = open(os.path.join(self.root, ".hgignore"))
                 for pat in l:
                     if pat != "\n":
                         self.ignorelist.append(re.compile(pat[:-1]))
             except IOError: pass
         for pat in self.ignorelist:
             if pat.search(f): return True
         return False
 
     def lookup(self, key):
         if self.tags is None:
             self.tags = {}
             try:
                 fl = self.file(".hgtags")
                 for l in fl.revision(fl.tip()).splitlines():
                     if l:
                         n, k = l.split(" ")
                         self.tags[k] = bin(n)
             except KeyError: pass
         try:
             return self.tags[key]
         except KeyError:
             return self.changelog.lookup(key)
 
     def join(self, f):
         return os.path.join(self.path, f)
 
     def file(self, f):
         return filelog(self.opener, f)
 
     def transaction(self):
         return transaction(self.opener, self.join("journal"),
                            self.join("undo"))
 
     def commit(self, parent, update = None, text = ""):
         tr = self.transaction()
         
         try:
             remove = [ l[:-1] for l in self.opener("to-remove") ]
             os.unlink(self.join("to-remove"))
 
         except IOError:
             remove = []
 
         if update == None:
             update = self.diffdir(self.root, parent)[0]
 
         # check in files
         new = {}
         linkrev = self.changelog.count()
         for f in update:
             self.ui.note(f + "\n")
             try:
                 t = file(f).read()
             except IOError:
                 remove.append(f)
                 continue
             r = self.file(f)
             new[f] = r.add(t, tr, linkrev)
 
         # update manifest
         mmap = self.manifest.read(self.manifest.tip())
         mmap.update(new)
         for f in remove:
             del mmap[f]
         mnode = self.manifest.add(mmap, tr, linkrev)
 
         # add changeset
         new = new.keys()
         new.sort()
 
         edittext = text + "\n"+"".join(["HG: changed %s\n" % f for f in new])
         edittext += "".join(["HG: removed %s\n" % f for f in remove])
         edittext = self.ui.edit(edittext)
 
         n = self.changelog.add(mnode, new, edittext, tr)
         tr.close()
 
         self.setcurrent(n)
         self.dircache.update(new)
         self.dircache.remove(remove)
 
     def checkdir(self, path):
         d = os.path.dirname(path)
         if not d: return
         if not os.path.isdir(d):
             self.checkdir(d)
             os.mkdir(d)
 
     def checkout(self, node):
         # checkout is really dumb at the moment
         # it ought to basically merge
         change = self.changelog.read(node)
         mmap = self.manifest.read(change[0])
 
         l = mmap.keys()
         l.sort()
         stats = []
         for f in l:
             self.ui.note(f + "\n")
             r = self.file(f)
             t = r.revision(mmap[f])
             try:
                 file(f, "w").write(t)
             except:
                 self.checkdir(f)
                 file(f, "w").write(t)
 
         self.setcurrent(node)
         self.dircache.clear()
         self.dircache.update(l)
 
     def diffdir(self, path, changeset):
         changed = []
         mf = {}
         added = []
 
         if changeset:
             change = self.changelog.read(changeset)
             mf = self.manifest.read(change[0])
 
         if changeset == self.current:
             dc = self.dircache.copy()
         else:
             dc = dict.fromkeys(mf)
 
         def fcmp(fn):
             t1 = file(os.path.join(self.root, fn)).read()
             t2 = self.file(fn).revision(mf[fn])
             return cmp(t1, t2)
 
         for dir, subdirs, files in os.walk(self.root):
             d = dir[len(self.root)+1:]
             if ".hg" in subdirs: subdirs.remove(".hg")
             
             for f in files:
                 fn = os.path.join(d, f)
                 try: s = os.stat(os.path.join(self.root, fn))
                 except: continue
                 if fn in dc:
                     c = dc[fn]
                     del dc[fn]
                     if not c:
                         if fcmp(fn):
                             changed.append(fn)
                     elif c[1] != s.st_size:
                         changed.append(fn)
                     elif c[0] != s.st_mode or c[2] != s.st_mtime:
                         if fcmp(fn):
                             changed.append(fn)
                 else:
                     if self.ignore(fn): continue
                     added.append(fn)
 
         deleted = dc.keys()
         deleted.sort()
 
         return (changed, added, deleted)
 
     def diffrevs(self, node1, node2):
         changed, added = [], []
 
         change = self.changelog.read(node1)
         mf1 = self.manifest.read(change[0])
         change = self.changelog.read(node2)
         mf2 = self.manifest.read(change[0])
 
         for fn in mf2:
             if mf1.has_key(fn):
                 if mf1[fn] != mf2[fn]:
                     changed.append(fn)
                 del mf1[fn]
             else:
                 added.append(fn)
                 
         deleted = mf1.keys()
         deleted.sort()
     
         return (changed, added, deleted)
 
     def add(self, list):
         self.dircache.taint(list)
 
     def remove(self, list):
         dl = self.opener("to-remove", "a")
         for f in list:
             dl.write(f + "\n")
 
     def branches(self, nodes):
         if not nodes: nodes = [self.changelog.tip()]
         b = []
         for n in nodes:
             t = n
             while n:
                 p = self.changelog.parents(n)
                 if p[1] != nullid or p[0] == nullid:
                     b.append((t, n, p[0], p[1]))
                     break
                 n = p[0]
         return b
 
     def between(self, pairs):
         r = []
 
         for top, bottom in pairs:
             n, l, i = top, [], 0
             f = 1
 
             while n != bottom:
                 p = self.changelog.parents(n)[0]
                 if i == f:
                     l.append(n) 
                     f = f * 2
                 n = p
                 i += 1
 
             r.append(l)
 
         return r
 
     def newer(self, nodes):
         m = {}
         nl = []
         pm = {}
         cl = self.changelog
         t = l = cl.count()
 
         # find the lowest numbered node
         for n in nodes:
             l = min(l, cl.rev(n))
             m[n] = 1
 
         for i in xrange(l, t):
             n = cl.node(i)
             if n in m: # explicitly listed
                 pm[n] = 1
                 nl.append(n)
                 continue
             for p in cl.parents(n):
                 if p in pm: # parent listed
                     pm[n] = 1
                     nl.append(n)
                     break
 
         return nl
 
     def getchangegroup(self, remote):
         tip = remote.branches([])[0]
         self.ui.debug("remote tip branch is %s:%s\n" %
                       (short(tip[0]), short(tip[1])))
         m = self.changelog.nodemap
         unknown = [tip]
         search = []
         fetch = []
 
         if tip[0] in m:
             self.ui.note("nothing to do!\n")
             return None
 
         while unknown:
             n = unknown.pop(0)
             if n == nullid: break
             if n[1] and n[1] in m: # do we know the base?
                 self.ui.debug("found incomplete branch %s\n" % short(n[1]))
                 search.append(n) # schedule branch range for scanning
             else:
                 if n[2] in m and n[3] in m:
                     if n[1] not in fetch:
                         self.ui.debug("found new changeset %s\n" %
                                       short(n[1]))
                         fetch.append(n[1]) # earliest unknown
                         continue
                 for b in remote.branches([n[2], n[3]]):
                     if b[0] not in m:
                         unknown.append(b)
   
         while search:
             n = search.pop(0)
             l = remote.between([(n[0], n[1])])[0]
             p = n[0]
             f = 1
             for i in l + [n[1]]:
                 if i in m:
                     if f <= 2:
                         self.ui.debug("found new branch changeset %s\n" %
                                           short(p))
                         fetch.append(p)
                     else:
                         self.ui.debug("narrowed branch search to %s:%s\n"
                                       % (short(p), short(i)))
                         search.append((p, i))
                     break
                 p, f = i, f * 2
 
         for f in fetch:
             if f in m:
                 raise "already have", short(f[:4])
 
         self.ui.note("adding new changesets starting at " +
                      " ".join([short(f) for f in fetch]) + "\n")
 
         return remote.changegroup(fetch)
     
     def changegroup(self, basenodes):
         nodes = self.newer(basenodes)
 
         # construct the link map
         linkmap = {}
         for n in nodes:
             linkmap[self.changelog.rev(n)] = n
 
         # construct a list of all changed files
         changed = {}
         for n in nodes:
             c = self.changelog.read(n)
             for f in c[3]:
                 changed[f] = 1
         changed = changed.keys()
         changed.sort()
 
         # the changegroup is changesets + manifests + all file revs
         revs = [ self.changelog.rev(n) for n in nodes ]
 
         yield self.changelog.group(linkmap)
         yield self.manifest.group(linkmap)
 
         for f in changed:
             g = self.file(f).group(linkmap)
             if not g: raise "couldn't find change to %s" % f
             l = struct.pack(">l", len(f))
             yield "".join([l, f, g])
 
     def addchangegroup(self, generator):
         class genread:
             def __init__(self, generator):
                 self.g = generator
                 self.buf = ""
             def read(self, l):
                 while l > len(self.buf):
                     try:
                         self.buf += self.g.next()
                     except StopIteration:
                         break
                 d, self.buf = self.buf[:l], self.buf[l:]
                 return d
                 
         if not generator: return
         source = genread(generator)
 
         def getchunk(add = 0):
             d = source.read(4)
             if not d: return ""
             l = struct.unpack(">l", d)[0]
             return source.read(l - 4 + add)
 
         tr = self.transaction()
         simple = True
 
         self.ui.status("adding changesets\n")
         # pull off the changeset group
         def report(x):
             self.ui.debug("add changeset %s\n" % short(x))
             return self.changelog.count()
             
         csg = getchunk()
         co = self.changelog.tip()
         cn = self.changelog.addgroup(csg, report, tr)
 
         self.ui.status("adding manifests\n")
         # pull off the manifest group
         mfg = getchunk()
         mm = self.manifest.tip()
         mo = self.manifest.addgroup(mfg, lambda x: self.changelog.rev(x), tr)
 
         # do we need a resolve?
         if self.changelog.ancestor(co, cn) != co:
             simple = False
             resolverev = self.changelog.count()
 
         # process the files
         self.ui.status("adding files\n")
         new = {}
         while 1:
             f = getchunk(4)
             if not f: break
             fg = getchunk()
             self.ui.debug("adding %s revisions\n" % f)
             fl = self.file(f)
             o = fl.tip()
             n = fl.addgroup(fg, lambda x: self.changelog.rev(x), tr)
             if not simple:
                 if o == n: continue
                 # this file has changed between branches, so it must be
                 # represented in the merge changeset
                 new[f] = self.merge3(fl, f, o, n, tr, resolverev)
 
         # For simple merges, we don't need to resolve manifests or changesets
         if simple:
             self.ui.debug("simple merge, skipping resolve\n")
             tr.close()
             return
 
         # resolve the manifest to point to all the merged files
         self.ui.status("resolving manifests\n")
         ma = self.manifest.ancestor(mm, mo)
         omap = self.manifest.read(mo) # other
         amap = self.manifest.read(ma) # ancestor
         mmap = self.manifest.read(mm) # mine
         self.ui.debug("ancestor %s local %s remote %s\n" %
                       (short(ma), short(mm), short(mo)))
         nmap = {}
 
         for f, mid in mmap.iteritems():
             if f in omap:
                 if mid != omap[f]:
                     self.ui.debug("%s versions differ\n" % f)
                     if f in new: self.ui.debug("%s updated in resolve\n" % f)
                     # use merged version or local version
                     nmap[f] = new.get(f, mid)
                 else:
                     nmap[f] = mid # keep ours
                 del omap[f]
             elif f in amap:
                 if mid != amap[f]:
                     r = self.ui.prompt(
                         ("local changed %s which remote deleted\n" % f) +
                         "(k)eep or (d)elete?", "[kd]", "k")
                     if r == "k": nmap[f] = mid
                 else:
                     self.ui.debug("other deleted %s\n" % f)
                     pass # other deleted it
             else:
                 self.ui.debug("local created %s\n" %f)
                 nmap[f] = mid # we created it
                 
         del mmap
 
         for f, oid in omap.iteritems():
             if f in amap:
                 if oid != amap[f]:
                     r = self.ui.prompt(
                         ("remote changed %s which local deleted\n" % f) +
                         "(k)eep or (d)elete?", "[kd]", "k")
                     if r == "k": nmap[f] = oid
                 else:
                     pass # probably safe
             else:
                 self.ui.debug("remote created %s\n" % f)
                 nmap[f] = new.get(f, oid) # remote created it
 
         del omap
         del amap
 
         node = self.manifest.add(nmap, tr, resolverev, mm, mo)
 
         # Now all files and manifests are merged, we add the changed files
         # and manifest id to the changelog
         self.ui.status("committing merge changeset\n")
         new = new.keys()
         new.sort()
         if co == cn: cn = -1
 
         edittext = "\nHG: merge resolve\n" + \
                    "".join(["HG: changed %s\n" % f for f in new])
         edittext = self.ui.edit(edittext)
         n = self.changelog.add(node, new, edittext, tr, co, cn)
 
         tr.close()
 
     def merge3(self, fl, fn, my, other, transaction, link):
         """perform a 3-way merge and append the result"""
         
         def temp(prefix, node):
             pre = "%s~%s." % (os.path.basename(fn), prefix)
             (fd, name) = tempfile.mkstemp("", pre)
             f = os.fdopen(fd, "w")
             f.write(fl.revision(node))
             f.close()
             return name
 
         base = fl.ancestor(my, other)
         self.ui.note("resolving %s\n" % fn)
         self.ui.debug("local %s remote %s ancestor %s\n" %
                               (short(my), short(other), short(base)))
 
         if my == base: 
             text = fl.revision(other)
         else:
             a = temp("local", my)
             b = temp("remote", other)
             c = temp("parent", base)
 
             cmd = os.environ["HGMERGE"]
             self.ui.debug("invoking merge with %s\n" % cmd)
             r = os.system("%s %s %s %s" % (cmd, a, b, c))
             if r:
                 raise "Merge failed!"
 
             text = open(a).read()
             os.unlink(a)
             os.unlink(b)
             os.unlink(c)
             
         return fl.addrevision(text, transaction, link, my, other)
 
 class remoterepository:
     def __init__(self, ui, path):
         self.url = path.replace("hg://", "http://", 1)
         self.ui = ui
 
     def do_cmd(self, cmd, **args):
         self.ui.debug("sending %s command\n" % cmd)
         q = {"cmd": cmd}
         q.update(args)
         qs = urllib.urlencode(q)
         cu = "%s?%s" % (self.url, qs)
         return urllib.urlopen(cu)
 
     def branches(self, nodes):
         n = " ".join(map(hex, nodes))
         d = self.do_cmd("branches", nodes=n).read()
         br = [ map(bin, b.split(" ")) for b in d.splitlines() ]
         return br
 
     def between(self, pairs):
         n = "\n".join(["-".join(map(hex, p)) for p in pairs])
         d = self.do_cmd("between", pairs=n).read()
         p = [ map(bin, l.split(" ")) for l in d.splitlines() ]
         return p
 
     def changegroup(self, nodes):
         n = " ".join(map(hex, nodes))
         zd = zlib.decompressobj()
         f = self.do_cmd("changegroup", roots=n)
         while 1:
             d = f.read(4096)
             if not d:
                 yield zd.flush()
                 break
             yield zd.decompress(d)
 
 def repository(ui, path=None, create=0):
     if path and path[:5] == "hg://":
         return remoterepository(ui, path)
     else:
         return localrepository(ui, path, create)
 
 class ui:
     def __init__(self, verbose=False, debug=False, quiet=False,
                  interactive=True):
         self.quiet = quiet and not verbose and not debug
         self.verbose = verbose or debug
         self.debugflag = debug
         self.interactive = interactive
     def write(self, *args):
         for a in args:
             sys.stdout.write(str(a))
     def readline(self):
         return sys.stdin.readline()[:-1]
     def prompt(self, msg, pat, default = "y"):
         if not self.interactive: return default
         while 1:
             self.write(msg, " ")
             r = self.readline()
             if re.match(pat, r):
                 return r
             else:
                 self.write("unrecognized response\n")
     def status(self, *msg):
         if not self.quiet: self.write(*msg)
     def warn(self, msg):
         self.write(*msg)
     def note(self, *msg):
         if self.verbose: self.write(*msg)
     def debug(self, *msg):
         if self.debugflag: self.write(*msg)
     def edit(self, text):
         (fd, name) = tempfile.mkstemp("hg")
         f = os.fdopen(fd, "w")
         f.write(text)
         f.close()
 
         editor = os.environ.get("EDITOR", "vi")
         r = os.system("%s %s" % (editor, name))
         if r:
             raise "Edit failed!"
 
         t = open(name).read()
         t = re.sub("(?m)^HG:.*\n", "", t)
 
         return t
 
     
 class httprangereader:
     def __init__(self, url):
         self.url = url
         self.pos = 0
     def seek(self, pos):
         self.pos = pos
     def read(self, bytes=None):
         opener = urllib2.build_opener(byterange.HTTPRangeHandler())
         urllib2.install_opener(opener)
         req = urllib2.Request(self.url)
         end = ''
         if bytes: end = self.pos + bytes
         req.add_header('Range', 'bytes=%d-%s' % (self.pos, end))
         f = urllib2.urlopen(req)
         return f.read()