#620: storage: allow mutable shares to be deleted, with a writev where new_length=0

src/allmydata/interfaces.py

@@ -207,7 +207,7 @@ class RIStorageServer(RemoteInterface):
         can be used to pre-allocate space for a series of upcoming writes, or
         truncate existing data. If the container is growing, new_length will
         be applied before datav. If the container is shrinking, it will be
-        applied afterwards.
+        applied afterwards. If new_length==0, the share will be deleted.
 
         The read vector is used to extract data from all known shares,
         *before* any writes have been applied. The same vector is used for

src/allmydata/introducer/client.py

@@ -34,6 +34,7 @@ class RemoteServiceConnector:
         "storage": { "http://allmydata.org/tahoe/protocols/storage/v1" :
                      { "maximum-immutable-share-size": 2**32,
                        "tolerates-immutable-read-overrun": False,
+                       "delete-mutable-shares-with-zero-length-writev": False,
                        },
                      "application-version": "unknown: no get_version()",
                      },

src/allmydata/storage.py

@@ -963,6 +963,7 @@ class StorageServer(service.MultiService, Referenceable):
         version = { "http://allmydata.org/tahoe/protocols/storage/v1" :
                     { "maximum-immutable-share-size": remaining_space,
                       "tolerates-immutable-read-overrun": True,
+                      "delete-mutable-shares-with-zero-length-writev": True,
                       },
                     "application-version": str(allmydata.__version__),
                     }
@@ -1218,27 +1219,37 @@ class StorageServer(service.MultiService, Referenceable):
         for sharenum, share in shares.items():
             read_data[sharenum] = share.readv(read_vector)
 
+        ownerid = 1 # TODO
+        expire_time = time.time() + 31*24*60*60   # one month
+        lease_info = LeaseInfo(ownerid,
+                               renew_secret, cancel_secret,
+                               expire_time, self.my_nodeid)
+
         if testv_is_good:
             # now apply the write vectors
             for sharenum in test_and_write_vectors:
                 (testv, datav, new_length) = test_and_write_vectors[sharenum]
-                if sharenum not in shares:
-                    # allocate a new share
-                    allocated_size = 2000 # arbitrary, really
-                    share = self._allocate_slot_share(bucketdir, secrets,
-                                                      sharenum,
-                                                      allocated_size,
-                                                      owner_num=0)
-                    shares[sharenum] = share
-                shares[sharenum].writev(datav, new_length)
-            # and update the leases on all shares
-            ownerid = 1 # TODO
-            expire_time = time.time() + 31*24*60*60   # one month
-            lease_info = LeaseInfo(ownerid,
-                                   renew_secret, cancel_secret,
-                                   expire_time, self.my_nodeid)
-            for share in shares.values():
-                share.add_or_renew_lease(lease_info)
+                if new_length == 0:
+                    if sharenum in shares:
+                        shares[sharenum].unlink()
+                else:
+                    if sharenum not in shares:
+                        # allocate a new share
+                        allocated_size = 2000 # arbitrary, really
+                        share = self._allocate_slot_share(bucketdir, secrets,
+                                                          sharenum,
+                                                          allocated_size,
+                                                          owner_num=0)
+                        shares[sharenum] = share
+                    shares[sharenum].writev(datav, new_length)
+                    # and update the lease
+                    shares[sharenum].add_or_renew_lease(lease_info)
+
+            if new_length == 0:
+                # delete empty bucket directories
+                if not os.listdir(bucketdir):
+                    os.rmdir(bucketdir)
+
 
         # all done
         self.add_latency("writev", time.time() - start)

src/allmydata/test/test_storage.py

@@ -1150,6 +1150,50 @@ class MutableServer(unittest.TestCase):
         self.failUnlessRaises(IndexError,
                               ss.remote_cancel_lease, "si2", "nonsecret")
 
+    def test_remove(self):
+        ss = self.create("test_remove")
+        self.allocate(ss, "si1", "we1", self._lease_secret.next(),
+                      set([0,1,2]), 100)
+        readv = ss.remote_slot_readv
+        writev = ss.remote_slot_testv_and_readv_and_writev
+        secrets = ( self.write_enabler("we1"),
+                    self.renew_secret("we1"),
+                    self.cancel_secret("we1") )
+        # delete sh0 by setting its size to zero
+        answer = writev("si1", secrets,
+                        {0: ([], [], 0)},
+                        [])
+        # the answer should mention all the shares that existed before the
+        # write
+        self.failUnlessEqual(answer, (True, {0:[],1:[],2:[]}) )
+        # but a new read should show only sh1 and sh2
+        self.failUnlessEqual(readv("si1", [], [(0,10)]),
+                             {1: [""], 2: [""]})
+
+        # delete sh1 by setting its size to zero
+        answer = writev("si1", secrets,
+                        {1: ([], [], 0)},
+                        [])
+        self.failUnlessEqual(answer, (True, {1:[],2:[]}) )
+        self.failUnlessEqual(readv("si1", [], [(0,10)]),
+                             {2: [""]})
+
+        # delete sh2 by setting its size to zero
+        answer = writev("si1", secrets,
+                        {2: ([], [], 0)},
+                        [])
+        self.failUnlessEqual(answer, (True, {2:[]}) )
+        self.failUnlessEqual(readv("si1", [], [(0,10)]),
+                             {})
+        # and the bucket directory should now be gone
+        si = base32.b2a("si1")
+        # note: this is a detail of the storage server implementation, and
+        # may change in the future
+        prefix = si[:2]
+        prefixdir = os.path.join(self.workdir("test_remove"), "shares", prefix)
+        bucketdir = os.path.join(prefixdir, si)
+        self.failUnless(os.path.exists(prefixdir))
+        self.failIf(os.path.exists(bucketdir))
 
 class Stats(unittest.TestCase):