Here's how the C++ code calculates the block digest:

• digest_type::hash(*this) serializes the block into a binary form, then runs the binary through sha-256.
• block.hpp#L125 identifies the order that the fields are serialized in.
• The types of these fields is at block.hpp#L18
• Each type has its own serialization procedure. Most of them live in libraries/fc.

Note: many users of the JSON RPC API have to serialize objects to binary form, so I suspect someone will create documentation of this process.

Note: the block fields may still change. I pointed to the master branch as of 2018-05-08.

Here's how the C++ code calculates the block digest:

• digest_type::hash(*this) serializes the block into a binary form, then runs the binary through sha-256.
• block.hpp#L125 identifies the order that the fields are serialized in.
• The types of these fields is at block.hpp#L18
• Each type has its own serialization procedure. Most of them live in libraries/fc.
• Here's an example of how it serializes an unsigned_int. This is a 32-bit type which serializes to 1-5 bytes depending on value: raw.hpp#L210

Note: many users of the JSON RPC API have to serialize objects to binary form, so I suspect someone will create documentation of this process.

Note: the block fields may still change. I pointed to the master branch as of 2018-05-08.