feat(model-client): added IModelClientV2.pullHash

If you only want to check what the latest version on the server is
without receiving all the data of it.

Author: slisson

model-client/src/commonMain/kotlin/org/modelix/model/client2/IModelClientV2.kt

@@ -53,5 +53,7 @@ interface IModelClientV2 {
 
     suspend fun pull(branch: BranchReference, lastKnownVersion: IVersion?): IVersion
 
+    suspend fun pullHash(branch: BranchReference): String
+
     suspend fun poll(branch: BranchReference, lastKnownVersion: IVersion?): IVersion
 }

model-client/src/commonMain/kotlin/org/modelix/model/client2/ModelClientV2.kt

@@ -165,6 +165,18 @@ class ModelClientV2(
         return receivedVersion
     }
 
+    override suspend fun pullHash(branch: BranchReference): String {
+        val response = httpClient.get {
+            url {
+                takeFrom(baseUrl)
+                appendPathSegmentsEncodingSlash("repositories", branch.repositoryId.id, "branches", branch.branchName, "hash")
+            }
+        }
+        val receivedHash: String = response.body()
+//        LOG.debug { "${clientId.toString(16)}.pullHash($branch) -> $receivedHash" }
+        return receivedHash
+    }
+
     override suspend fun poll(branch: BranchReference, lastKnownVersion: IVersion?): IVersion {
         require(lastKnownVersion is CLVersion?)
         LOG.debug { "${clientId.toString(16)}.poll($branch, $lastKnownVersion)" }

model-server/src/main/kotlin/org/modelix/model/server/handlers/ModelReplicationServer.kt

@@ -127,6 +127,18 @@ class ModelReplicationServer(val repositoriesManager: RepositoriesManager) {
                             }
                             call.respondDelta(versionHash, baseVersionHash)
                         }
+                        get("hash") {
+                            val branch = branchRef()
+                            val versionHash = repositoriesManager.getVersionHash(branch)
+                            if (versionHash == null) {
+                                call.respondText(
+                                    "Branch '${branch.branchName}' doesn't exist in repository '${branch.repositoryId.id}'",
+                                    status = HttpStatusCode.NotFound,
+                                )
+                                return@get
+                            }
+                            call.respondText(versionHash)
+                        }
                         post {
                             val deltaFromClient = call.receive<VersionDelta>()
                             deltaFromClient.checkObjectHashes()