This is the most basic version of what it could look like to sync a cient using era1 files.

We add an optional CLI flag --loadBlocksFromEra1=<path_to_era1_dir>

Set this flag, and point it to a directory with era1 files. We assume that the era1 files are named in such a way that alphabetical order equals chronological order.

New fuction eraSync() will be called during client startup. This function will iterate through the directory of era1 files, store the extracted block data, then run block execution. The end result is a client synced to the height of the final era1 file.

While this process does take time, it is faster than full sync via devp2p. More importantly, this method of syncing can be used in a post 4444 world, where this historical data may not be available over devp2p.

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This concept is far from optimized. A more sophisticated version of era1Sync would avoid storing and recalling these blocks from the client database at all.

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To test:

Download 1 or more era1 files from era1.ethportal.net
Start a client via CLI with the --loadBlocksFromEra1 flag set, pointing towards the era1 directory.
Observe the logs while each file is processed, and the client execution runs in batches of 8192 blocks.