The transport dropped a message that failed to parse: it logged the
error and returned, so a peer waiting on that request hung forever and
every message already buffered behind it was discarded. Keep going after
a failed parse, and add ReplyWithParseError so a message that is valid
JSON but not a valid request is answered against its own id. Unparseable
JSON still gets no reply, since it carries no id and JSON-RPC forbids
inventing one.
Method-not-found was raised with createStringError, which converts
through inconvertibleErrorCode() to -32603, so clients could not tell a
misspelled method from a server fault. Use the MethodNotFound error,
which already carries -32601, and give InvalidParams the -32602 code it
was missing.
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