From 121656b11f462e62c24730119036f51b2e4adc72 Mon Sep 17 00:00:00 2001
From: Jean-Paul Calderone <exarkun@twistedmatrix.com>
Date: Fri, 11 Oct 2019 15:03:13 -0400
Subject: [PATCH] comments about client logic for
slot_testv_and_readv_and_writev
---
src/_zkapauthorizer/_storage_client.py | 25 +++++++++++++++++++++++++
1 file changed, 25 insertions(+)
diff --git a/src/_zkapauthorizer/_storage_client.py b/src/_zkapauthorizer/_storage_client.py
index 237f52f..8269a64 100644
--- a/src/_zkapauthorizer/_storage_client.py
+++ b/src/_zkapauthorizer/_storage_client.py
@@ -177,29 +177,54 @@ class ZKAPAuthorizerStorageClient(object):
r_vector,
):
if has_writes(tw_vectors):
+ # When performing writes, if we're increasing the storage
+ # requirement, we need to spend more passes. Unfortunately we
+ # don't know what the current storage requirements are at this
+ # layer of the system. It's *likely* that a higher layer does but
+ # that doesn't help us, even if it were guaranteed. So, instead,
+ # ask the server. Invoke a ZKAPAuthorizer-supplied remote method
+ # on the storage server that will give us a really good estimate
+ # of the current size of all of the specified shares (keys of
+ # tw_vectors).
current_size = yield self._rref.callRemote(
"slot_share_sizes",
storage_index,
set(tw_vectors),
)
if current_size is None:
+ # The server says it doesn't even know about these shares for
+ # this storage index. Thus, we have not yet paid anything for
+ # it and we're about to create it.
current_pass_count = 0
else:
+ # Compute how much has already been paid for the storage
+ # that's already allocated. We're not required to pay this
+ # again.
current_pass_count = required_passes(BYTES_PER_PASS, {0}, current_size)
+
+ # Determine what the share size which will result from the write
+ # we're about to perform.
implied_sizes = (
get_implied_data_length(data_vector, length)
for (_, data_vector, length)
in tw_vectors.values()
)
+ # Total that across all of the shares and figure how many passes
+ # it it would cost if we had to pay for all of it.
new_size = sum(implied_sizes, 0)
new_pass_count = required_passes(BYTES_PER_PASS, {0}, new_size)
+ # Now compute how much hasn't yet been paid.
pass_count_increase = new_pass_count - current_pass_count
+ # And prepare to pay it.
passes = self._get_encoded_passes(
slot_testv_and_readv_and_writev_message(storage_index),
pass_count_increase,
)
else:
+ # Non-write operations on slots are free.
passes = []
+
+ # Perform the operation with the passes we determined are required.
returnValue((
yield self._rref.callRemote(
"slot_testv_and_readv_and_writev",
--
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