Foreign API: Bulk block request

[yeastplume]

As requested, a foreign API function that returns a number of blocks (if they exist) based on the height at which they were applied.

Note this is WIP and subject to review and change, and we may need some form of limitation here to avoid an obvious DOS vector.

[yeastplume]

Tested and ready for review, note there's a hardcoded max of 1000 blocks, similar to the existing max in get_unspent_outputs. Note this function doesn't lock the hashset, it's pure database lookup and should have less potential for interruption than existing foreign API functions.

/// Returns a BlockListing of available blocks
/// between min_height and max_height
/// The method will query the database for blocks starting at the block height min_height
/// and continue until max_height, skipping any blocks that aren't available.
///
/// # Arguments
/// * start_height - starting height to lookup.
/// * end_height - ending height to to lookup.
/// * 'max - The max number of blocks to return. /// Note this is overriden with BLOCK_TRANSFER_LIMIT if BLOCK_TRANSFER_LIMIT is exceeded /// /// # Returns /// * Result Containing: /// * A [BlockListing](types/struct.BlockListing.html) /// * or [Error`](struct.Error.html) if an error is encountered.
///

[yeastplume]

• Move logic into blocks_api::BlockHandler
• Don't error if hash doesn't exist for given height
• if start height < recorded tail in db, change start height to tail to avoid scanning entire DB for first existing block

[phyro]

As I understand it, we'll skip blocks we can't find, which is ok, but do we expect to arrive at this state for some blocks or is it just defensive programming?

[yeastplume]

I don't think there's a particular guarantee that there won't be gaps in the stored blocks, so no harm just handling the case.

[phyro]

Only left a minor question, other than that the code looks good to me. I am unable to test it at the moment, but have asked a few days ago vegycslol to do it and he confirmed it works for him on a non-archive node.