offloaded: upload.py: handle forward skips, to allow resumed uploads to send less than all the data. We still read all the data (to hash it, 'paranoid mode'), but we don't send it over the wire

src/allmydata/upload.py

@@ -638,7 +638,7 @@ class RemoteEncryptedUploadable(Referenceable):
     def __init__(self, encrypted_uploadable):
         self._eu = IEncryptedUploadable(encrypted_uploadable)
         self._offset = 0
-        self._bytes_read = 0
+        self._bytes_sent = 0
         self._cutoff = None # set by debug options
         self._cutoff_cb = None
 
@@ -648,14 +648,32 @@ class RemoteEncryptedUploadable(Referenceable):
         return self._eu.get_all_encoding_parameters()
 
     def remote_read_encrypted(self, offset, length):
-        # we don't yet implement seek
+        # we don't support seek backwards, but we allow skipping forwards
+        precondition(offset >= 0, offset)
+        precondition(length >= 0, length)
+        lp = log.msg("remote_read_encrypted(%d-%d)" % (offset, offset+length),
+                     level=log.NOISY)
+        precondition(offset >= self._offset, offset, self._offset)
+        if offset > self._offset:
+            # read the data from disk anyways, to build up the hash tree
+            skip = offset - self._offset
+            log.msg("remote_read_encrypted skipping ahead to %d, skip=%d" %
+                    (self._offset, skip), level=log.UNUSUAL, parent=lp)
+            d = self.remote_read_encrypted(self._offset, skip)
+            def _ignore(strings):
+                size = sum([len(data) for data in strings])
+                self._bytes_sent -= size
+                return self.remote_read_encrypted(offset, length)
+            d.addCallback(_ignore)
+            return d
+
         assert offset == self._offset, "%d != %d" % (offset, self._offset)
         if self._cutoff is not None and offset+length > self._cutoff:
             self._cutoff_cb()
         d = self._eu.read_encrypted(length)
         def _read(strings):
             size = sum([len(data) for data in strings])
-            self._bytes_read += size
+            self._bytes_sent += size
             self._offset += size
             return strings
         d.addCallback(_read)
@@ -729,10 +747,22 @@ class AssistedUploader:
             self.log("helper says we need to upload")
             # we need to upload the file
             reu = RemoteEncryptedUploadable(self._encuploadable)
-            if False: #"debug_stash_RemoteEncryptedUploadable" in self._options:
-                self._options["RemoteEncryptedUploadable"] = reu
-            if False: #"debug_interrupt" in self._options:
-                reu._cutoff = self._options["debug_interrupt"]
+
+            # we have unit tests which want to interrupt the upload so they
+            # can exercise resumability. They indicate this by adding debug_
+            # attributes to the Uploadable.
+            if hasattr(self._encuploadable.original,
+                       "debug_stash_RemoteEncryptedUploadable"):
+                # we communicate back to them the same way. This may look
+                # weird, but, well, ok, it is. However, it is better than the
+                # barrage of options={} dictionaries that were flying around
+                # before. We could also do this by setting attributes on the
+                # class, but that doesn't make it easy to undo when we're
+                # done. TODO: find a cleaner way, maybe just a small options=
+                # dict somewhere.
+                self._encuploadable.original.debug_RemoteEncryptedUploadable = reu
+            if hasattr(self._encuploadable.original, "debug_interrupt"):
+                reu._cutoff = self._encuploadable.original.debug_interrupt
                 def _cutoff():
                     # simulate the loss of the connection to the helper
                     self.log("debug_interrupt killing connection to helper",