Merge bitcoin/bitcoin#17631: Expose block filters over REST

2b64fa3251 Update REST docs with new accessors (Matt Corallo)
ef7c8228fd Expose block filters over REST. (Matt Corallo)

Pull request description:

  This adds a new rest endpoint:
  /rest/blockfilter/filtertype/requesttype/blockhash (eg
  /rest/blockfilter/basic/header/000000000019d6689c085ae165831e934ff763ae46a2a6c172b3f1b60a8ce26f.hex)
  which exposes either the filter "header" or the filter data itself.
  Most of the code is cribbed from the equivalent RPC.

  You can test it at http://bitcoin-rest.bitcoin.ninja/rest//blockfilter/basic/header/000000005b7a58a939b2636f61fa4ddd62258c5fed57667a35d23f2334c4f86d.hex

ACKs for top commit:
  dergoegge:
    ACK 2b64fa3251 - Adding blockfilters to the REST interface is analogous to serving other public data such as transactions or blocks.

Tree-SHA512: d487bc694266375c94d6fcf2e9d788a8a42a3b94e8d3290e46335a64cbcde55084ce5ea6119b79a4065888d94d7c3ae25a59a901fa46e3711f0eb296add12696

doc/REST-interface.md

@@ -52,6 +52,20 @@ With the /notxdetails/ option JSON response will only contain the transaction ha
 Given a block hash: returns <COUNT> amount of blockheaders in upward direction.
 Returns empty if the block doesn't exist or it isn't in the active chain.
 
+#### Blockfilter Headers
+`GET /rest/blockfilterheaders/<FILTERTYPE>/<COUNT>/<BLOCK-HASH>.<bin|hex|json>`
+
+Given a block hash: returns <COUNT> amount of blockfilter headers in upward
+direction for the filter type <FILTERTYPE>.
+Returns empty if the block doesn't exist or it isn't in the active chain.
+
+#### Blockfilters
+`GET /rest/blockfilter/<FILTERTYPE>/<BLOCK-HASH>.<bin|hex|json>`
+
+Given a block hash: returns the block filter of the given block of type
+<FILTERTYPE>.
+Responds with 404 if the block doesn't exist.
+
 #### Blockhash by height
 `GET /rest/blockhashbyheight/<HEIGHT>.<bin|hex|json>`