Add HeadId to "Greetings" message (#1622)

<!-- Describe your change here -->

Closes #1557

---

<!-- Consider each and tick it off one way or the other -->
* [x] CHANGELOG updated or not needed
* [x] Documentation updated or not needed
* [x] Haddocks updated or not needed
* [x] No new TODOs introduced or explained herafter

Author: ffakenz

CHANGELOG.md

@@ -14,6 +14,8 @@ changes.
   - Conway formatted transactions can be submitted to the `hydra-node`, while past eras are still supported (except deprecated features like protocol updates).
   - This includes support for `PlutusV3` scripts, but most of the governance-related features have no meaning in the Hydra L2.
 
+- Added head id information into the Greetings message.
+
 - Adds a manual recipient address entry to `hydra-tui` and fixes event handling. [#1607](https://github.com/cardano-scaling/hydra/pull/1607)
 
 ## [0.18.1] - 2024-08-15

hydra-node/golden/ReasonablySized (ServerOutput (Tx ConwayEra)).json

@@ -624,6 +624,8 @@ components:
           $ref: "api.yaml#/components/schemas/Party"
         headStatus:
           $ref: "api.yaml#/components/schemas/HeadStatus"
+        hydraHeadId:
+          $ref: "api.yaml#/components/schemas/HeadId"
         snapshotUtxo:
           $ref: "api.yaml#/components/schemas/UTxO"
         timestamp:

hydra-node/golden/ReasonablySized (TimedServerOutput (Tx ConwayEra)).json

@@ -106,7 +106,7 @@ withAPIServer config party persistence tracer chain pparams callback action =
             . simpleCors
             $ websocketsOr
               defaultConnectionOptions
-              (wsApp party tracer history callback headStatusP snapshotUtxoP responseChannel)
+              (wsApp party tracer history callback headStatusP headIdP snapshotUtxoP responseChannel)
               (httpApp tracer chain pparams (atomically $ getLatest headIdP) (atomically $ getLatest snapshotUtxoP) callback)
       )
       ( do

hydra-node/json-schemas/api.yaml

@@ -120,7 +120,13 @@ data ServerOutput tx
     -- node. Currently used for knowing what signing key the server uses (it
     -- only knows one), 'HeadStatus' and optionally (if 'HeadIsOpen' or
     -- 'SnapshotConfirmed' message is emitted) UTxO's present in the Hydra Head.
-    Greetings {me :: Party, headStatus :: HeadStatus, snapshotUtxo :: Maybe (UTxOType tx), hydraNodeVersion :: String}
+    Greetings
+      { me :: Party
+      , headStatus :: HeadStatus
+      , hydraHeadId :: Maybe HeadId
+      , snapshotUtxo :: Maybe (UTxOType tx)
+      , hydraNodeVersion :: String
+      }
   | PostTxOnChainFailed {postChainTx :: PostChainTx tx, postTxError :: PostTxError tx}
   | IgnoredHeadInitializing
       { headId :: HeadId
@@ -175,10 +181,11 @@ instance (ArbitraryIsTx tx, IsChainState tx) => Arbitrary (ServerOutput tx) wher
     SnapshotConfirmed headId s ms -> SnapshotConfirmed <$> shrink headId <*> shrink s <*> shrink ms
     GetUTxOResponse headId u -> GetUTxOResponse <$> shrink headId <*> shrink u
     InvalidInput r i -> InvalidInput <$> shrink r <*> shrink i
-    Greetings me headStatus snapshotUtxo hydraNodeVersion ->
+    Greetings me headStatus hydraHeadId snapshotUtxo hydraNodeVersion ->
       Greetings
         <$> shrink me
         <*> shrink headStatus
+        <*> shrink hydraHeadId
         <*> shrink snapshotUtxo
         <*> shrink hydraNodeVersion
     PostTxOnChainFailed p e -> PostTxOnChainFailed <$> shrink p <*> shrink e

hydra-node/src/Hydra/API/Server.hs

@@ -15,7 +15,7 @@ import Hydra.API.ClientInput (ClientInput)
 import Hydra.API.Projection (Projection (..))
 import Hydra.API.ServerOutput (
   HeadStatus,
-  ServerOutput (Greetings, InvalidInput, hydraNodeVersion),
+  ServerOutput (Greetings, InvalidInput, hydraHeadId, hydraNodeVersion),
   ServerOutputConfig (..),
   TimedServerOutput (..),
   WithUTxO (..),
@@ -31,6 +31,7 @@ import Hydra.Chain.Direct.State ()
 import Hydra.Logging (Tracer, traceWith)
 import Hydra.Options qualified as Options
 import Hydra.Tx (Party, UTxOType)
+import Hydra.Tx.HeadId (HeadId (..))
 import Network.WebSockets (
   PendingConnection (pendingRequest),
   RequestHead (..),
@@ -52,12 +53,14 @@ wsApp ::
   (ClientInput tx -> IO ()) ->
   -- | Read model to enhance 'Greetings' messages with 'HeadStatus'.
   Projection STM.STM (ServerOutput tx) HeadStatus ->
+  -- | Read model to enhance 'Greetings' messages with 'HeadId'.
+  Projection STM.STM (ServerOutput tx) (Maybe HeadId) ->
   -- | Read model to enhance 'Greetings' messages with snapshot UTxO.
   Projection STM.STM (ServerOutput tx) (Maybe (UTxOType tx)) ->
   TChan (TimedServerOutput tx) ->
   PendingConnection ->
   IO ()
-wsApp party tracer history callback headStatusP snapshotUtxoP responseChannel pending = do
+wsApp party tracer history callback headStatusP headIdP snapshotUtxoP responseChannel pending = do
   traceWith tracer NewAPIConnection
   let path = requestPath $ pendingRequest pending
   queryParams <- uriQuery <$> mkURIBs path
@@ -81,6 +84,7 @@ wsApp party tracer history callback headStatusP snapshotUtxoP responseChannel pe
   forwardGreetingOnly con = do
     seq <- atomically $ nextSequenceNumber history
     headStatus <- atomically getLatestHeadStatus
+    hydraHeadId <- atomically getLatestHeadId
     snapshotUtxo <- atomically getLatestSnapshotUtxo
     time <- getCurrentTime
 
@@ -93,13 +97,15 @@ wsApp party tracer history callback headStatusP snapshotUtxoP responseChannel pe
               Greetings
                 { me = party
                 , headStatus
+                , hydraHeadId
                 , snapshotUtxo
                 , hydraNodeVersion = showVersion Options.hydraNodeVersion
                 } ::
                 ServerOutput tx
           }
 
   Projection{getLatest = getLatestHeadStatus} = headStatusP
+  Projection{getLatest = getLatestHeadId} = headIdP
   Projection{getLatest = getLatestSnapshotUtxo} = snapshotUtxoP
 
   mkServerOutputConfig qp =