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Use SSZ union-types in RPC request/response #974

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merged 2 commits into from
May 17, 2019
Merged

Use SSZ union-types in RPC request/response #974

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f7ef9a1
Don't use SSZ in RPC request/response wrappers
mslipper Apr 21, 2019
7f6896c
Update to use union type
mslipper May 16, 2019
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42 changes: 23 additions & 19 deletions specs/networking/rpc-interface.md
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Original file line number Diff line number Diff line change
Expand Up @@ -39,32 +39,36 @@ To facilitate RPC-over-`libp2p`, a single protocol name is used: `/eth/serenity/
Remote method calls are wrapped in a "request" structure:

```
(
id: uint64
method_id: uint16
body: Request
)
0 1 2 3
0 1 2 3 4 5 6 7 8 9 0 1 2 3 4 5 6 7 8 9 0 1 2 3 4 5 6 7 8 9 0 1
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
| |
+ id (uint64) +
| |
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
| method_id (uint16) | body_len (uint32) |
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
| | body (body_len bytes) |
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
```

and their corresponding responses are wrapped in a "response" structure:

```
(
id: uint64
response_code: uint16
result: bytes
)
0 1 2 3
0 1 2 3 4 5 6 7 8 9 0 1 2 3 4 5 6 7 8 9 0 1 2 3 4 5 6 7 8 9 0 1
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
| |
+ id (uint64) +
| |
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
| response_code (uint16) | result_len (uint32) |
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can we keep these aligned a bit? ie life gets easier when types are aligned to their size, which in this case can be had by changing response_code to uint32.. alternatively, stick another uint16 in there for future expansion set to 0 for now

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Sure thing.

+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
| | result (result_len bytes) |
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
```

If an error occurs, a variant of the response structure is returned:

```
(
id: uint64
response_code: uint16
result: bytes
)
```
Note that the above structures are NOT encoded as SSZ but rather as sequences of bytes according to the packet diagrams above. This is because SSZ does not support structures without an explicit schema. Since the `body` and `result` fields depend on the value of `method_id` and `response_code`, a schema for the above structure cannot be known beforehand.

The details of the RPC-Over-`libp2p` protocol are similar to [JSON-RPC 2.0](https://www.jsonrpc.org/specification). Specifically:

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