RPC-API: add getinfo endpoint.

This commit creates a new endpoint /getinfo which currently returns only
the version of Joinmarket (JM_CORE_VERSION) running in the backend
joinmarketd. In future commits the returned dict may add more
information, for example the current block height of the connected
Bitcoin Core node.

Additionally, this commit fixes the response type of the
/rescanblockchain endpoint as defined in the OpenAPI spec.

docs/api/wallet-rpc.yaml

@@ -138,6 +138,16 @@ paths:
           $ref: '#/components/responses/401-Unauthorized'
         '404':
           $ref: '#/components/responses/404-NotFound'
+  /getinfo:
+    get:
+      security:
+        - {}
+      summary: get info on backend
+      operationId: version
+      description: get information about backend, including the version of Joinmarket running.
+      responses:
+        '200':
+          $ref: "#/components/responses/Getinfo-200-OK"
   /wallet/all:
     get:
       summary: get current available wallets
@@ -754,6 +764,22 @@ components:
       items:
         type: string
         example: "2021/10/26 16:40:21,133986791,1,200000000,2680,2680,0.08,"
+    GetinfoResponse:
+      type: object
+      required:
+        - version
+      properties:
+        version:
+          type: string
+          example: "v0.9.10"
+    RescanBlockchainResponse:
+      type: object
+      required:
+        - walletname
+      properties:
+        walletname:
+          type: string
+          example: "wallet.jmdat"
     SessionResponse:
       type: object
       required:
@@ -1106,12 +1132,18 @@ components:
         application/json:
           schema:
             $ref: "#/components/schemas/SessionResponse"
+    Getinfo-200-OK:
+      description: "successful Joinmarket getinfo response"
+      content:
+        application/json:
+          schema:
+            $ref: "#/components/schemas/GetinfoResponse"
     RescanBlockchain-200-OK:
       description: "Blockchain rescan started successfully"
       content:
         application/json:
           schema:
-            $ref: "#/components/schemas/SessionResponse"
+            $ref: "#/components/schemas/RescanBlockchainResponse"
     Create-201-OK:
       description: "wallet created successfully"
       content:

jmclient/jmclient/wallet_rpc.py

@@ -27,7 +27,7 @@
     tumbler_filter_orders_callback, tumbler_taker_finished_update, \
     validate_address, FidelityBondMixin, BaseWallet, WalletError, \
     ScheduleGenerationErrorNoFunds, BIP39WalletMixin
-from jmbase.support import get_log, utxostr_to_utxo
+from jmbase.support import get_log, utxostr_to_utxo, JM_CORE_VERSION
 
 jlog = get_log()
 
@@ -602,6 +602,10 @@ def rescanblockchain(self, request, walletname, blockheight):
             Note that it technically "shouldn't" require a wallet to be loaded,
             but since we hide all blockchain access behind the wallet service,
             it currently *does* require this.
+            An additional subtlety to bear in mind: the action of rescanblockchain
+            depends on the *currently loaded Bitcoin Core wallet*, that Core wallet
+            load event is currently done on startup of Joinmarket, depending on
+            the setting in the joinmarket.cfg file.
             """
             print_req(request)
             self.check_cookie(request)
@@ -615,6 +619,15 @@ def rescanblockchain(self, request, walletname, blockheight):
                 self.services["wallet"].rescanblockchain(blockheight)
                 return make_jmwalletd_response(request, walletname=walletname)
 
+        @app.route('/getinfo', methods=['GET'])
+        def version(self, request):
+            """ This route sends information about the backend, including
+            the running version of Joinmarket,
+            back to the client. It does *not* pay attention to any state,
+            including authentication tokens.
+            """
+            return make_jmwalletd_response(request,version=JM_CORE_VERSION)
+
         @app.route('/session', methods=['GET'])
         def session(self, request):
             """ This route functions as a heartbeat, and communicates

jmclient/test/test_wallet_rpc.py

@@ -10,7 +10,7 @@
     connectWS
 
 from jmbase import get_nontor_agent, hextobin, BytesProducer, get_log
-from jmbase.support import get_free_tcp_ports
+from jmbase.support import get_free_tcp_ports, JM_CORE_VERSION
 from jmbitcoin import CTransaction
 from jmclient import (
     load_test_config,
@@ -685,6 +685,20 @@ def test_do_coinjoin(self):
         yield self.do_request(agent, b"POST", addr, body,
                               self.process_do_coinjoin_response)
 
+    @defer.inlineCallbacks
+    def test_getinfo(self):
+        agent = get_nontor_agent()
+        addr = self.get_route_root()
+        addr += "/getinfo"
+        addr = addr.encode()
+        yield self.do_request(agent, b"GET", addr, None,
+                              self.process_getinfo_response)
+
+    def process_getinfo_response(self, response, code):
+        assert code==200
+        responseobj = json.loads(response.decode("utf-8"))
+        assert responseobj["version"] == JM_CORE_VERSION
+
     def process_do_coinjoin_response(self, response, code):
         assert code == 202
         # response code is already checked to be 200