Allow deserialization from std::io::Read
#10
+365
−58
Add this suggestion to a batch that can be applied as a single commit.
This suggestion is invalid because no changes were made to the code.
Suggestions cannot be applied while the pull request is closed.
Suggestions cannot be applied while viewing a subset of changes.
Only one suggestion per line can be applied in a batch.
Add this suggestion to a batch that can be applied as a single commit.
Applying suggestions on deleted lines is not supported.
You must change the existing code in this line in order to create a valid suggestion.
Outdated suggestions cannot be applied.
This suggestion has been applied or marked resolved.
Suggestions cannot be applied from pending reviews.
Suggestions cannot be applied on multi-line comments.
Suggestions cannot be applied while the pull request is queued to merge.
Suggestion cannot be applied right now. Please check back later.
This Pull Request implements BCS deserialization from implementers of
std::io::Read
.Strategy
The PR aims to maintain a minimal diff over the previous implementation. To that end, the following changes have been made.
Deserializer
generic over an inner typeR
BcsReader
, which implements BCS in terms of a few primitive operations. Implementserde::Deserialize<'de> for Deserializer<R> where Deserializer<R>: BcsReader<'de>
BcsReader<'de>
forDeserializer<&'de [u8]>
using existing codeBcsReader
generically for (a version of)Deserializer<R: Read>
.Implementing
BcsReader
genericallyThe existing implementation is very close to supporting deserialization from readers. There are only two places in which its behavior relied on access to a byte slice was in the implementation of
de::MapAccess
.The first case is
map
deserialization.bcs
needs access to the serialized representation of map keys in order to enforce canonicity. When deserializing from a slice, this is straightforward - the implementation can simply deserialize a map key, and then "look back" at the original input slice to determine its serialized representation. When deserializing from a reader, however, this kind of rewinding is not generally possible. To solve this problem, I introduce a theTeeReader
struct, which wraps aRead
er and optionally copies its bytes into acapture_buffer
for later retrieval. Then, I simply implementBcsReader
forDeserializer<TeeReader<...>>
.The second case is the
end
method, which checks that all input bytes have been consumed. To handle this case, I simply attempt to read one extra byte from theRead
er after deserialization and assert that an EOF error is returned from the underlyingRead
er.Testing
All existing unit tests except for
zero_copy_parse
have been modified to test that deserializationfrom_bytes
andfrom_reader
yield the same output. That test is not applicable since readers are not capable of zero-copy deserialization.