Introduce ContractFactory to replace Map<SecureHash, Contract>. It allows for lazy loading of contracts.

src/main/kotlin/contracts/DummyContract.kt

@@ -10,14 +10,14 @@ package contracts
 
 import core.Contract
 import core.ContractState
-import core.crypto.SecureHash
 import core.TransactionForVerification
+import core.crypto.SecureHash
 
 // The dummy contract doesn't do anything useful. It exists for testing purposes.
 
 val DUMMY_PROGRAM_ID = SecureHash.sha256("dummy")
 
-object DummyContract : Contract {
+class DummyContract : Contract {
     class State : ContractState {
         override val programRef: SecureHash = DUMMY_PROGRAM_ID
     }

src/main/kotlin/core/Structures.kt

@@ -134,3 +134,16 @@ interface Contract {
      */
     val legalContractReference: SecureHash
 }
+
+/** A contract factory knows how to lazily load and instantiate contract objects. */
+interface ContractFactory {
+    /**
+     * Loads, instantiates and returns a contract object from its class bytecodes, given the hash of that bytecode.
+     *
+     * @throws UnknownContractException if the hash doesn't map to any known contract.
+     * @throws ClassCastException if the hash mapped to a contract, but it was not of type T
+     */
+    operator fun <T : Contract> get(hash: SecureHash): T
+}
+
+class UnknownContractException : Exception()

src/main/kotlin/core/TransactionVerification.kt

@@ -27,7 +27,7 @@ class TransactionGroup(val transactions: Set<LedgerTransaction>, val nonVerified
     /**
      * Verifies the group and returns the set of resolved transactions.
      */
-    fun verify(programMap: Map<SecureHash, Contract>): Set<TransactionForVerification> {
+    fun verify(programMap: ContractFactory): Set<TransactionForVerification> {
         // Check that every input can be resolved to an output.
         // Check that no output is referenced by more than one input.
         // Cycles should be impossible due to the use of hashes as pointers.
@@ -73,12 +73,12 @@ data class TransactionForVerification(val inStates: List<ContractState>,
      * @throws IllegalStateException if a state refers to an unknown contract.
      */
     @Throws(TransactionVerificationException::class, IllegalStateException::class)
-    fun verify(programMap: Map<SecureHash, Contract>) {
+    fun verify(programMap: ContractFactory) {
         // For each input and output state, locate the program to run. Then execute the verification function. If any
         // throws an exception, the entire transaction is invalid.
         val programHashes = (inStates.map { it.programRef } + outStates.map { it.programRef }).toSet()
         for (hash in programHashes) {
-            val program = programMap[hash] ?: throw IllegalStateException("Unknown program hash $hash")
+            val program: Contract = programMap[hash]
             try {
                 program.verify(this)
             } catch(e: Throwable) {

src/test/kotlin/contracts/CommercialPaperTests.kt

@@ -216,11 +216,11 @@ class CommercialPaperTestsGeneric {
         val validRedemption = makeRedeemTX(TEST_TX_TIME + 31.days)
 
         val e = assertFailsWith(TransactionVerificationException::class) {
-            TransactionGroup(setOf(issueTX, moveTX, tooEarlyRedemption), setOf(corpWalletTX, alicesWalletTX)).verify(TEST_PROGRAM_MAP)
+            TransactionGroup(setOf(issueTX, moveTX, tooEarlyRedemption), setOf(corpWalletTX, alicesWalletTX)).verify(MockContractFactory)
         }
         assertTrue(e.cause!!.message!!.contains("paper must have matured"))
 
-        TransactionGroup(setOf(issueTX, moveTX, validRedemption), setOf(corpWalletTX, alicesWalletTX)).verify(TEST_PROGRAM_MAP)
+        TransactionGroup(setOf(issueTX, moveTX, validRedemption), setOf(corpWalletTX, alicesWalletTX)).verify(MockContractFactory)
     }
 
     // Generate a trade lifecycle with various parameters.

src/test/kotlin/contracts/CrowdFundTests.kt

@@ -157,11 +157,11 @@ class CrowdFundTests {
         val validClose = makeFundedTX(TEST_TX_TIME + 8.days)
 
         val e = assertFailsWith(TransactionVerificationException::class) {
-            TransactionGroup(setOf(registerTX, pledgeTX, tooEarlyClose), setOf(miniCorpWalletTx, aliceWalletTX)).verify(TEST_PROGRAM_MAP)
+            TransactionGroup(setOf(registerTX, pledgeTX, tooEarlyClose), setOf(miniCorpWalletTx, aliceWalletTX)).verify(MockContractFactory)
         }
         assertTrue(e.cause!!.message!!.contains("the closing date has past"))
 
         // This verification passes
-        TransactionGroup(setOf(registerTX, pledgeTX, validClose), setOf(aliceWalletTX)).verify(TEST_PROGRAM_MAP)
+        TransactionGroup(setOf(registerTX, pledgeTX, validClose), setOf(aliceWalletTX)).verify(MockContractFactory)
     }
 }

src/test/kotlin/core/MockServices.kt

@@ -9,6 +9,7 @@
 package core
 
 import core.crypto.DigitalSignature
+import core.crypto.SecureHash
 import core.crypto.generateKeyPair
 import core.crypto.signWithECDSA
 import core.messaging.MessagingService
@@ -18,6 +19,7 @@ import core.node.TimestampingError
 import core.serialization.SerializedBytes
 import core.serialization.deserialize
 import core.testutils.TEST_KEYS_TO_CORP_MAP
+import core.testutils.TEST_PROGRAM_MAP
 import core.testutils.TEST_TX_TIME
 import java.security.KeyPair
 import java.security.PrivateKey
@@ -77,6 +79,14 @@ class MockStorageService : StorageService {
     }
 }
 
+object MockContractFactory : ContractFactory {
+    override operator fun <T : Contract> get(hash: SecureHash): T {
+        val clazz = TEST_PROGRAM_MAP[hash] ?: throw UnknownContractException()
+        @Suppress("UNCHECKED_CAST")
+        return clazz.newInstance() as T
+    }
+}
+
 class MockServices(
         val wallet: WalletService? = null,
         val keyManagement: KeyManagementService? = null,

src/test/kotlin/core/testutils/TestUtils.kt

@@ -52,13 +52,13 @@ val TEST_KEYS_TO_CORP_MAP: Map<PublicKey, Party> = mapOf(
 val TEST_TX_TIME = Instant.parse("2015-04-17T12:00:00.00Z")
 
 // In a real system this would be a persistent map of hash to bytecode and we'd instantiate the object as needed inside
-// a sandbox. For now we just instantiate right at the start of the program.
-val TEST_PROGRAM_MAP: Map<SecureHash, Contract> = mapOf(
-        CASH_PROGRAM_ID to Cash(),
-        CP_PROGRAM_ID to CommercialPaper(),
-        JavaCommercialPaper.JCP_PROGRAM_ID to JavaCommercialPaper(),
-        CROWDFUND_PROGRAM_ID to CrowdFund(),
-        DUMMY_PROGRAM_ID to DummyContract
+// a sandbox. For unit tests we just have a hard-coded list.
+val TEST_PROGRAM_MAP: Map<SecureHash, Class<out Contract>> = mapOf(
+        CASH_PROGRAM_ID to Cash::class.java,
+        CP_PROGRAM_ID to CommercialPaper::class.java,
+        JavaCommercialPaper.JCP_PROGRAM_ID to JavaCommercialPaper::class.java,
+        CROWDFUND_PROGRAM_ID to CrowdFund::class.java,
+        DUMMY_PROGRAM_ID to DummyContract::class.java
 )
 
 ////////////////////////////////////////////////////////////////////////////////////////////////////////////////////
@@ -135,7 +135,7 @@ open class TransactionForTest : AbstractTransactionForTest() {
     protected fun run(time: Instant) {
         val cmds = commandsToAuthenticatedObjects()
         val tx = TransactionForVerification(inStates, outStates.map { it.state }, cmds, SecureHash.randomSHA256())
-        tx.verify(TEST_PROGRAM_MAP)
+        tx.verify(MockContractFactory)
     }
 
     fun accepts(time: Instant = TEST_TX_TIME) = run(time)
@@ -297,7 +297,7 @@ class TransactionGroupDSL<T : ContractState>(private val stateType: Class<T>) {
     fun verify() {
         val group = toTransactionGroup()
         try {
-            group.verify(TEST_PROGRAM_MAP)
+            group.verify(MockContractFactory)
         } catch (e: TransactionVerificationException) {
             // Let the developer know the index of the transaction that failed.
             val ltx: LedgerTransaction = txns.find { it.hash == e.tx.origHash }!!