Return the plugin-apis to this repo (#1900)

* Return plugin-api to the main repo
* Spotless
* Migrate all external plugin-api references to the project in this repo
* Add licence header
* Update repo reference for publish, even if commented
* Use real configuration for publishing plugin-api

This was tested with the
`:plugins:publishMavenJavaPublicationToMavenLocal` task and checking the
local Maven repo to make sure it was using the correct paths

Signed-off-by: Edward Evans <edward.evans@consensys.net>

Signed-off-by: Adrian Sutton <adrian.sutton@consensys.net>

acceptance-tests/build.gradle

@@ -33,6 +33,7 @@ dependencies {
   testImplementation project(':metrics:core')
   testImplementation project(':pantheon')
   testImplementation project(path: ':pantheon', configuration: 'testArtifacts')
+  testImplementation project(':plugins')
   testImplementation project(':services:kvstore')
   testImplementation project(':testutil')
   testImplementation project(':util')
@@ -55,7 +56,6 @@ dependencies {
   testImplementation 'tech.pegasys.ethsigner.internal:core'
   testImplementation 'tech.pegasys.ethsigner.internal:file-based'
   testImplementation 'tech.pegasys.ethsigner.internal:signing-api'
-  testImplementation 'tech.pegasys.pantheon:plugin-api'
 }
 
 test.enabled = false

build.gradle

@@ -272,6 +272,9 @@ allprojects {
 
 task deploy() {}
 
+tasks.register('checkPluginAPIChanges', DefaultTask) { }
+checkPluginAPIChanges.dependsOn(':plugins:checkAPIChanges')
+check.dependsOn('checkPluginAPIChanges')
 
 subprojects {
 

consensus/common/build.gradle

@@ -26,7 +26,7 @@ jar {
 }
 
 dependencies {
-  api 'tech.pegasys.pantheon:plugin-api'
+  api project(':plugins')
 
   implementation project(':ethereum:core')
   implementation project(':ethereum:jsonrpc')

crypto/build.gradle

@@ -26,10 +26,10 @@ jar {
 }
 
 dependencies {
+  api project(':plugins')
   api project(':util')
 
   api 'org.bouncycastle:bcprov-jdk15on'
-  api 'tech.pegasys.pantheon:plugin-api'
 
   implementation 'com.google.guava:guava'
   implementation 'org.apache.logging.log4j:log4j-api'

ethereum/core/build.gradle

@@ -32,13 +32,13 @@ dependencies {
   implementation project(':ethereum:rlp')
   implementation project(':ethereum:trie')
   implementation project(':metrics:core')
+  implementation project(':plugins')
   implementation project(':services:kvstore')
 
   implementation 'com.fasterxml.jackson.core:jackson-databind'
   implementation 'com.google.guava:guava'
   implementation 'io.vertx:vertx-core'
   implementation 'org.apache.logging.log4j:log4j-api'
-  implementation 'tech.pegasys.pantheon:plugin-api'
 
   runtime 'org.apache.logging.log4j:log4j-core'
 

ethereum/mock-p2p/build.gradle

@@ -26,7 +26,7 @@ jar {
 }
 
 dependencies {
-  api 'tech.pegasys.pantheon:plugin-api'
+  api project(':plugins')
 
   implementation project(':ethereum:p2p')
   implementation project(':ethereum:permissioning')

ethereum/rlp/build.gradle

@@ -26,8 +26,8 @@ jar {
 }
 
 dependencies {
+  api project(':plugins')
   api project(':util')
-  api 'tech.pegasys.pantheon:plugin-api'
 
   implementation 'com.google.guava:guava'
   implementation 'io.vertx:vertx-core'

gradle/versions.gradle

@@ -95,7 +95,5 @@ dependencyManagement {
     dependency "tech.pegasys.ethsigner.internal:core:0.3.0"
     dependency "tech.pegasys.ethsigner.internal:file-based:0.3.0"
     dependency "tech.pegasys.ethsigner.internal:signing-api:0.3.0"
-
-      dependency "tech.pegasys.pantheon:plugin-api:1.2.3"
   }
 }

metrics/core/build.gradle

@@ -33,6 +33,8 @@ publishing {
 
 
 dependencies {
+  implementation project(':plugins')
+
   implementation 'com.google.guava:guava'
   implementation 'io.prometheus:simpleclient'
   implementation 'io.prometheus:simpleclient_common'
@@ -41,7 +43,6 @@ dependencies {
   implementation 'io.vertx:vertx-core'
   implementation 'io.vertx:vertx-web'
   implementation 'org.apache.logging.log4j:log4j-api'
-  implementation 'tech.pegasys.pantheon:plugin-api'
 
   runtime 'org.apache.logging.log4j:log4j-core'
 

metrics/rocksdb/build.gradle

@@ -27,12 +27,11 @@ jar {
 
 dependencies {
   implementation project(':metrics:core')
+  implementation project(':plugins')
   implementation project(':services:util')
 
   implementation 'com.google.guava:guava'
   implementation 'io.prometheus:simpleclient'
   implementation 'org.apache.logging.log4j:log4j-api'
   implementation 'org.rocksdb:rocksdbjni'
-
-  implementation 'tech.pegasys.pantheon:plugin-api'
 }

pantheon/build.gradle

@@ -44,6 +44,7 @@ dependencies {
   implementation project(':ethereum:rlp')
   implementation project(':metrics:core')
   implementation project(':nat')
+  implementation project(':plugins')
   implementation project(':services:kvstore')
 
   implementation 'com.fasterxml.jackson.core:jackson-databind'
@@ -56,7 +57,6 @@ dependencies {
   implementation 'net.consensys.cava:cava-toml'
   implementation 'org.apache.logging.log4j:log4j-api'
   implementation 'org.springframework.security:spring-security-crypto'
-  implementation 'tech.pegasys.pantheon:plugin-api'
 
   runtime 'org.apache.logging.log4j:log4j-core'
   runtime 'org.apache.logging.log4j:log4j-slf4j-impl'

plugins/build.gradle

@@ -0,0 +1,78 @@
+/*
+ * Copyright 2019 ConsenSys AG.
+ *
+ * Licensed under the Apache License, Version 2.0 (the "License"); you may not use this file except in compliance with
+ * the License. You may obtain a copy of the License at
+ *
+ * http://www.apache.org/licenses/LICENSE-2.0
+ *
+ * Unless required by applicable law or agreed to in writing, software distributed under the License is distributed on
+ * an "AS IS" BASIS, WITHOUT WARRANTIES OR CONDITIONS OF ANY KIND, either express or implied. See the License for the
+ * specific language governing permissions and limitations under the License.
+ */
+
+import net.ltgt.gradle.errorprone.CheckSeverity
+import java.security.MessageDigest
+
+apply plugin: 'java-library'
+jar {
+  baseName 'plugin-api'
+  manifest {
+    attributes(
+      'Specification-Title': baseName,
+      'Specification-Version': project.version,
+      'Implementation-Title': baseName,
+      'Implementation-Version': calculateVersion()
+      )
+  }
+}
+
+
+dependencies {
+}
+
+configurations { testArtifacts }
+artifacts { testSupportArtifacts testSupportJar }
+
+class FileStateChecker extends DefaultTask {
+  Set<File> files
+  String knownHash
+
+  @TaskAction
+  def CheckState() {
+    def digestor = MessageDigest.getInstance("SHA-256")
+
+    this.files.sort().each {
+      digestor.update(it.readBytes())
+    }
+    def currentHash = digestor.digest()encodeBase64().toString()
+    if (this.knownHash != currentHash) {
+      throw new GradleException("""For the Plugin APIs the checksum of the project did not match what was expected.
+
+If this is a deliberate change where you have thought through backwards compatibility,
+then update "Expected" for "Calculated" in the appropriate build.gradle as the knownHash for this task.
+Expected   : ${this.knownHash}
+Calculated : ${currentHash}
+""")
+    }
+  }
+}
+
+tasks.register('checkAPIChanges', FileStateChecker) {
+  description = "Checks that the API for the Plugin-API project does not change without deliberate thought"
+  files = sourceSets.main.allJava.files
+  knownHash = 'PBo0D4R6/1EYXEn+k0nmWHW4TkklUWQbQGNqgWzslfw='
+}
+check.dependsOn('checkAPIChanges')
+
+publishing {
+  publications {
+    mavenJava(MavenPublication) {
+      groupId 'tech.pegasys.pantheon.plugin-api'
+      pom {
+        name = 'Pantheon Plugins Library'
+        description = 'Core Plugins Libraries for Pantheon'
+      }
+    }
+  }
+}

plugins/src/main/java/tech/pegasys/pantheon/plugin/PantheonContext.java

@@ -0,0 +1,42 @@
+/*
+ * Copyright 2019 ConsenSys AG.
+ *
+ * Licensed under the Apache License, Version 2.0 (the "License"); you may not use this file except in compliance with
+ * the License. You may obtain a copy of the License at
+ *
+ * http://www.apache.org/licenses/LICENSE-2.0
+ *
+ * Unless required by applicable law or agreed to in writing, software distributed under the License is distributed on
+ * an "AS IS" BASIS, WITHOUT WARRANTIES OR CONDITIONS OF ANY KIND, either express or implied. See the License for the
+ * specific language governing permissions and limitations under the License.
+ */
+package tech.pegasys.pantheon.plugin;
+
+import java.util.Optional;
+
+/** Allows plugins to access Pantheon services. */
+public interface PantheonContext {
+
+  /**
+   * Get the requested service, if it is available. There are a number of reasons that a service may
+   * not be available:
+   *
+   * <ul>
+   *   <li>The service may not have started yet. Most services are not available before the {@link
+   *       PantheonPlugin#start()} method is called
+   *   <li>The service is not supported by this version of Pantheon
+   *   <li>The service may not be applicable to the current configuration. For example some services
+   *       may only be available when a proof of authority network is in use
+   * </ul>
+   *
+   * <p>Since plugins are automatically loaded, unless the user has specifically requested
+   * functionality provided by the plugin, no error should be raised if required services are
+   * unavailable.
+   *
+   * @param serviceType the class defining the requested service.
+   * @param <T> the service type
+   * @return an optional containing the instance of the requested service, or empty if the service
+   *     is unavailable
+   */
+  <T> Optional<T> getService(Class<T> serviceType);
+}

plugins/src/main/java/tech/pegasys/pantheon/plugin/PantheonPlugin.java

@@ -0,0 +1,53 @@
+/*
+ * Copyright 2019 ConsenSys AG.
+ *
+ * Licensed under the Apache License, Version 2.0 (the "License"); you may not use this file except in compliance with
+ * the License. You may obtain a copy of the License at
+ *
+ * http://www.apache.org/licenses/LICENSE-2.0
+ *
+ * Unless required by applicable law or agreed to in writing, software distributed under the License is distributed on
+ * an "AS IS" BASIS, WITHOUT WARRANTIES OR CONDITIONS OF ANY KIND, either express or implied. See the License for the
+ * specific language governing permissions and limitations under the License.
+ */
+package tech.pegasys.pantheon.plugin;
+
+/**
+ * Base interface for Pantheon plugins.
+ *
+ * <p>Plugins are discovered and loaded using {@link java.util.ServiceLoader} from jar files within
+ * Pantheon's plugin directory. See the {@link java.util.ServiceLoader} documentation for how to
+ * register plugins.
+ */
+public interface PantheonPlugin {
+
+  /**
+   * Called when the plugin is first registered with Pantheon. Plugins are registered very early in
+   * the Pantheon life-cycle and should use this callback to register any command line options
+   * required via the PicoCLIOptions service.
+   *
+   * <p>The <code>context</code> parameter should be stored in a field in the plugin. This is the
+   * only time it will be provided to the plugin and is how the plugin will interact with Pantheon.
+   *
+   * <p>Typically the plugin will not begin operation until the {@link #start()} method is called.
+   *
+   * @param context the context that provides access to Pantheon services.
+   */
+  void register(PantheonContext context);
+
+  /**
+   * Called once Pantheon has loaded configuration and is starting up. The plugin should begin
+   * operation, including registering any event listener with Pantheon services and starting any
+   * background threads the plugin requires.
+   */
+  void start();
+
+  /**
+   * Called when the plugin is being stopped. This method will be called as part of Pantheon
+   * shutting down but may also be called at other times to disable the plugin.
+   *
+   * <p>The plugin should remove any registered listeners and stop any background threads it
+   * started.
+   */
+  void stop();
+}

plugins/src/main/java/tech/pegasys/pantheon/plugin/Unstable.java

@@ -0,0 +1,28 @@
+/*
+ * Copyright 2019 ConsenSys AG.
+ *
+ * Licensed under the Apache License, Version 2.0 (the "License"); you may not use this file except in compliance with
+ * the License. You may obtain a copy of the License at
+ *
+ * http://www.apache.org/licenses/LICENSE-2.0
+ *
+ * Unless required by applicable law or agreed to in writing, software distributed under the License is distributed on
+ * an "AS IS" BASIS, WITHOUT WARRANTIES OR CONDITIONS OF ANY KIND, either express or implied. See the License for the
+ * specific language governing permissions and limitations under the License.
+ */
+package tech.pegasys.pantheon.plugin;
+
+import static java.lang.annotation.ElementType.METHOD;
+import static java.lang.annotation.ElementType.TYPE;
+import static java.lang.annotation.RetentionPolicy.CLASS;
+
+import java.lang.annotation.Retention;
+
+/**
+ * This annotation is an indicator that the interface or method may evolve in a way that it not
+ * backwards compatible. Such as deleting methods, changing signatures, and adding checked
+ * exceptions. Authors are advised to exercise caution when using these APIs.
+ */
+@Retention(CLASS)
+@java.lang.annotation.Target({METHOD, TYPE})
+public @interface Unstable {}

plugins/src/main/java/tech/pegasys/pantheon/plugin/data/Address.java

@@ -0,0 +1,19 @@
+/*
+ * Copyright 2019 ConsenSys AG.
+ *
+ * Licensed under the Apache License, Version 2.0 (the "License"); you may not use this file except in compliance with
+ * the License. You may obtain a copy of the License at
+ *
+ * http://www.apache.org/licenses/LICENSE-2.0
+ *
+ * Unless required by applicable law or agreed to in writing, software distributed under the License is distributed on
+ * an "AS IS" BASIS, WITHOUT WARRANTIES OR CONDITIONS OF ANY KIND, either express or implied. See the License for the
+ * specific language governing permissions and limitations under the License.
+ */
+package tech.pegasys.pantheon.plugin.data;
+
+import tech.pegasys.pantheon.plugin.Unstable;
+
+/** An interface for {@link BinaryData} that also represents an Ethereum account address. */
+@Unstable
+public interface Address extends UnformattedData {}

plugins/src/main/java/tech/pegasys/pantheon/plugin/data/BinaryData.java

@@ -0,0 +1,46 @@
+/*
+ * Copyright 2019 ConsenSys AG.
+ *
+ * Licensed under the Apache License, Version 2.0 (the "License"); you may not use this file except in compliance with
+ * the License. You may obtain a copy of the License at
+ *
+ * http://www.apache.org/licenses/LICENSE-2.0
+ *
+ * Unless required by applicable law or agreed to in writing, software distributed under the License is distributed on
+ * an "AS IS" BASIS, WITHOUT WARRANTIES OR CONDITIONS OF ANY KIND, either express or implied. See the License for the
+ * specific language governing permissions and limitations under the License.
+ */
+package tech.pegasys.pantheon.plugin.data;
+
+import tech.pegasys.pantheon.plugin.Unstable;
+
+/** Super class for all types that are ultimately represented by binary data. */
+@Unstable
+public interface BinaryData {
+
+  /**
+   * The byte level representation of the binary data. This array should be treated as read only
+   * constant data as any changes will not be reflected in the source.
+   *
+   * @return a read-only array of the bytes of the binary data.
+   */
+  byte[] getByteArray();
+
+  /**
+   * A hex string representation of the data. This hex string will represent the hex of the entire
+   * binary data and will be "<code>0x</code>" prefixed. APIs that depend on shortend forms will
+   * need to process the string.
+   *
+   * @return A string repsenting the hex encodeing of the data.
+   */
+  String getHexString();
+
+  /**
+   * The size, in bytes, of the contained binary data. Because {@link #getByteArray()} may cause the
+   * underlying data to be copied using this size method is preferred when such a check would avoid
+   * a call to {@link #getByteArray()} or {@link #getHexString()}.
+   *
+   * @return The length of the binary data in bytes.
+   */
+  int size();
+}

plugins/src/main/java/tech/pegasys/pantheon/plugin/data/BlockHeader.java

@@ -0,0 +1,156 @@
+/*
+ * Copyright 2019 ConsenSys AG.
+ *
+ * Licensed under the Apache License, Version 2.0 (the "License"); you may not use this file except in compliance with
+ * the License. You may obtain a copy of the License at
+ *
+ * http://www.apache.org/licenses/LICENSE-2.0
+ *
+ * Unless required by applicable law or agreed to in writing, software distributed under the License is distributed on
+ * an "AS IS" BASIS, WITHOUT WARRANTIES OR CONDITIONS OF ANY KIND, either express or implied. See the License for the
+ * specific language governing permissions and limitations under the License.
+ */
+package tech.pegasys.pantheon.plugin.data;
+
+import tech.pegasys.pantheon.plugin.Unstable;
+
+/**
+ * The minimum set of data for a BlockHeader, as defined in the <a href=
+ * "https://ethereum.github.io/yellowpaper/paper.pdf">Ethereum Yellow Paper</a>.
+ */
+@Unstable
+public interface BlockHeader {
+
+  /**
+   * The Keccak 256-bit hash of the parent block’s header, in its entirety.
+   *
+   * @return The Keccak 256-bit hash of the parent block’s header, in its entirety.
+   */
+  Hash getParentHash();
+
+  /**
+   * The Keccak 256-bit hash of the ommers list portion of this block.
+   *
+   * @return The Keccak 256-bit hash of the ommers list portion of this block.
+   */
+  Hash getOmmersHash();
+
+  /**
+   * The 160-bit address to which all fees collected from the successful mining of this block be
+   * transferred.
+   *
+   * <p>The name in the yellow paper is beneficiary.
+   *
+   * @return The 160-bit address to which all fees collected from the successful mining of this
+   *     block be transferred.
+   */
+  Address getCoinbase();
+
+  /**
+   * The Keccak 256-bit hash of the root node of the state trie, after all transactions are executed
+   * and finalisations applied.
+   *
+   * @return The Keccak 256-bit hash of the root node of the state trie, after all transactions are
+   *     executed and finalisations applied.
+   */
+  Hash getStateRoot();
+
+  /**
+   * The Keccak 256-bit hash of theroot node of the trie structure populated with each transaction
+   * in the transactions list portion of the block.
+   *
+   * @return The Keccak 256-bit hash of theroot node of the trie structure populated with each
+   *     transaction in the transactions list portion of the block.
+   */
+  Hash getTransactionsRoot();
+
+  /**
+   * The Keccak 256-bit hash of the root node of the trie structure populated with the receipts of
+   * each transaction in the transactions list portion of the block.
+   *
+   * @return The Keccak 256-bit hash of the root node of the trie structure populated with the
+   *     receipts of each transaction in the transactions list portion of the block.
+   */
+  Hash getReceiptsRoot();
+
+  /**
+   * The Bloom filter composed from indexable information (logger address and log topics) contained
+   * in each log entry from the receipt of each transaction in the transactions list.
+   *
+   * @return The Bloom filter composed from indexable information (logger address and log topics)
+   *     contained in each log entry from the receipt of each transaction in the transactions list.
+   */
+  UnformattedData getLogsBloom();
+
+  /**
+   * A scalar value corresponding to the difficulty level of this block. This can be calculated from
+   * the previous block’s difficulty level and the timestamp.
+   *
+   * @return A scalar value corresponding to the difficulty level of this block. This can be
+   *     calculated from the previous block’s difficulty level and the timestamp.
+   */
+  Quantity getDifficulty();
+
+  /**
+   * A scalar value equal to the number of ancestor blocks. The genesis block has a number of zero.
+   *
+   * @return A scalar value equal to the number of ancestor blocks. The genesis block has a number
+   *     of zero.
+   */
+  long getNumber();
+
+  /**
+   * A scalar value equal to the current limit of gas expenditure per block.
+   *
+   * @return A scalar value equal to the current limit of gas expenditure per block.
+   */
+  long getGasLimit();
+
+  /**
+   * A scalar value equal to the total gas used in transactions in this block.
+   *
+   * @return A scalar value equal to the total gas used in transactions in this block.
+   */
+  long getGasUsed();
+
+  /**
+   * A scalar value equal to the reasonable output of Unix’s time() at this block’s inception.
+   *
+   * @return A scalar value equal to the reasonable output of Unix’s time() at this block’s
+   *     inception.
+   */
+  long getTimestamp();
+
+  /**
+   * An arbitrary byte array containing data relevant to this block. This must be 32 bytes or fewer.
+   *
+   * @return An arbitrary byte array containing data relevant to this block. This must be 32 bytes
+   *     or fewer.
+   */
+  UnformattedData getExtraData();
+
+  /**
+   * A 256-bit hash which, combined with the nonce, proves that a sufficient amount of computation
+   * has been carried out on this block.
+   *
+   * @return A 256-bit hash which, combined with the nonce, proves that a sufficient amount of
+   *     computation has been carried out on this block.
+   */
+  Hash getMixHash();
+
+  /**
+   * A 64-bit value which, combined with the mixhash, proves that a sufficient amount of computation
+   * has been carried out on this block.
+   *
+   * @return A 64-bit value which, combined with the mixhash, proves that a sufficient amount of
+   *     computation has been carried out on this block.
+   */
+  long getNonce();
+
+  /**
+   * The Keccak 256-bit hash of this header.
+   *
+   * @return The Keccak 256-bit hash of this header.
+   */
+  Hash getBlockHash();
+}

plugins/src/main/java/tech/pegasys/pantheon/plugin/data/Hash.java

@@ -0,0 +1,23 @@
+/*
+ * Copyright 2019 ConsenSys AG.
+ *
+ * Licensed under the Apache License, Version 2.0 (the "License"); you may not use this file except in compliance with
+ * the License. You may obtain a copy of the License at
+ *
+ * http://www.apache.org/licenses/LICENSE-2.0
+ *
+ * Unless required by applicable law or agreed to in writing, software distributed under the License is distributed on
+ * an "AS IS" BASIS, WITHOUT WARRANTIES OR CONDITIONS OF ANY KIND, either express or implied. See the License for the
+ * specific language governing permissions and limitations under the License.
+ */
+package tech.pegasys.pantheon.plugin.data;
+
+import tech.pegasys.pantheon.plugin.Unstable;
+
+/**
+ * A marker interface indicating that this {@link UnformattedData} represents a hash of some sort.
+ * The particular algorithm depends on the source, it may be ripemd, keccak, or some other
+ * algorithm.
+ */
+@Unstable
+public interface Hash extends UnformattedData {}

plugins/src/main/java/tech/pegasys/pantheon/plugin/data/Log.java

@@ -0,0 +1,43 @@
+/*
+ * Copyright 2019 ConsenSys AG.
+ *
+ * Licensed under the Apache License, Version 2.0 (the "License"); you may not use this file except in compliance with
+ * the License. You may obtain a copy of the License at
+ *
+ * http://www.apache.org/licenses/LICENSE-2.0
+ *
+ * Unless required by applicable law or agreed to in writing, software distributed under the License is distributed on
+ * an "AS IS" BASIS, WITHOUT WARRANTIES OR CONDITIONS OF ANY KIND, either express or implied. See the License for the
+ * specific language governing permissions and limitations under the License.
+ */
+package tech.pegasys.pantheon.plugin.data;
+
+import tech.pegasys.pantheon.plugin.Unstable;
+
+import java.util.List;
+
+/** A Log entry from a transaction execution. */
+@Unstable
+public interface Log {
+
+  /**
+   * The address of the contract writing this log message.
+   *
+   * @return The loggers address.
+   */
+  Address getLogger();
+
+  /**
+   * The list of 32 byte log topics, possibly empty.
+   *
+   * @return The list, possibly zero length, of log topics.
+   */
+  List<? extends UnformattedData> getTopics();
+
+  /**
+   * The data, of possibly unlimited length, for this log entry.
+   *
+   * @return The log data.
+   */
+  UnformattedData getData();
+}

plugins/src/main/java/tech/pegasys/pantheon/plugin/data/Quantity.java

@@ -0,0 +1,35 @@
+/*
+ * Copyright 2019 ConsenSys AG.
+ *
+ * Licensed under the Apache License, Version 2.0 (the "License"); you may not use this file except in compliance with
+ * the License. You may obtain a copy of the License at
+ *
+ * http://www.apache.org/licenses/LICENSE-2.0
+ *
+ * Unless required by applicable law or agreed to in writing, software distributed under the License is distributed on
+ * an "AS IS" BASIS, WITHOUT WARRANTIES OR CONDITIONS OF ANY KIND, either express or implied. See the License for the
+ * specific language governing permissions and limitations under the License.
+ */
+package tech.pegasys.pantheon.plugin.data;
+
+import tech.pegasys.pantheon.plugin.Unstable;
+
+/**
+ * An interface to mark the {@link BinaryData} that also represents a disceete quantity, such as an
+ * unsigned integer value.
+ */
+@Unstable
+public interface Quantity extends BinaryData {
+
+  /**
+   * Returns the numeric value of the quantity.
+   *
+   * <p>The specific class returned may be the boxed Java primitives, however plugin authors should
+   * not rely on the underlying number always being castable to that primitive in all cases and
+   * should instead rely on APIs such as {@link Number#longValue()} to cast to primitive values.
+   * Similarly the underlying object based values may evolve over time.
+   *
+   * @return The boxed or object based value of the quantity.
+   */
+  Number getValue();
+}

plugins/src/main/java/tech/pegasys/pantheon/plugin/data/Transaction.java

@@ -0,0 +1,130 @@
+/*
+ * Copyright 2019 ConsenSys AG.
+ *
+ * Licensed under the Apache License, Version 2.0 (the "License"); you may not use this file except in compliance with
+ * the License. You may obtain a copy of the License at
+ *
+ * http://www.apache.org/licenses/LICENSE-2.0
+ *
+ * Unless required by applicable law or agreed to in writing, software distributed under the License is distributed on
+ * an "AS IS" BASIS, WITHOUT WARRANTIES OR CONDITIONS OF ANY KIND, either express or implied. See the License for the
+ * specific language governing permissions and limitations under the License.
+ */
+package tech.pegasys.pantheon.plugin.data;
+
+import tech.pegasys.pantheon.plugin.Unstable;
+
+import java.math.BigInteger;
+import java.util.Optional;
+
+/**
+ * A transaction is a single cryptographically-signed instruction constructed by an actor externally
+ * to the scope of Ethereum. While it is assumed that the ultimate external actor will be human in
+ * nature, software tools will be used in its construction and dissemination.
+ *
+ * <p>There are two types of transactions: those which result in message calls and those which
+ * result in the creation of new accounts with associated code (known informally as ‘contract
+ * creation’). Message call transactions will have an address present in the {@link #getTo} method
+ * whereas contract creation transactions will not.
+ */
+@Unstable
+public interface Transaction {
+
+  /**
+   * A scalar value equal to the number of transactions sent by the sender.
+   *
+   * @return the number of transactions sent by the sender.
+   */
+  long getNonce();
+
+  /**
+   * A scalar value equal to the number of Wei to be paid per unit of gas for all computation costs
+   * incurred as a result of the execution of this transaction.
+   *
+   * @return the quantity of Wei per gas unit paid.
+   */
+  Quantity getGasPrice();
+
+  /**
+   * A scalar value equal to the maximum amount of gas that should be used in executing this
+   * transaction. This is paid up-front, before any computation is done and may not be increased
+   * later.
+   *
+   * @return the maximum amount of gas that should be used in executing this * transaction.
+   */
+  long getGasLimit();
+
+  /**
+   * The 160-bit address of the message call’s recipient. For a contract creation transaction this
+   * address will not be present.
+   *
+   * @return address of the recipient
+   */
+  Optional<? extends Address> getTo();
+
+  /**
+   * A scalar value equal to the number of Wei to be transferred to the message call’s recipient or,
+   * in the case of contract creation, as an endowment to the newly created account
+   *
+   * @return value equal to the number of Wei to be transferred
+   */
+  Quantity getValue();
+
+  /**
+   * Value corresponding to the 'V' component of the signature of the transaction.
+   *
+   * @return the 'V' component of the signature
+   */
+  BigInteger getV();
+
+  /**
+   * Value corresponding to the 'V' component of the signature of the transaction.
+   *
+   * @return the 'V' component of the signature
+   */
+  BigInteger getR();
+
+  /**
+   * Value corresponding to the 'V' component of the signature of the transaction.
+   *
+   * @return the 'V' component of the signature
+   */
+  BigInteger getS();
+
+  /**
+   * The 160-bit address of the account sending the transaction, extracted from the v, r, s
+   * parameters.
+   *
+   * @return The address of the account that sent this transaction.
+   */
+  Address getSender();
+
+  /**
+   * The chainId, computed from the 'V' portion of the signature. Used for replay protection. If
+   * replay protection is not enabled this value will not be present.
+   *
+   * @return The chainId for transaction.
+   */
+  Optional<BigInteger> getChainId();
+
+  /**
+   * An unlimited size byte array specifying the EVM-code for the account // initialisation
+   * procedure.
+   *
+   * <p>Only present if this is a contract creation transaction, which is only true if {@link
+   * #getTo} is empty.
+   *
+   * @return if present, the contract init code.
+   */
+  Optional<? extends UnformattedData> getInit();
+
+  /**
+   * An unlimited size byte array specifying theinput data of the message call.
+   *
+   * <p>Only present if this is a message call transaction, which is only true if {@link #getTo} is
+   * present.
+   *
+   * @return if present, the message call data
+   */
+  Optional<? extends UnformattedData> getData();
+}

plugins/src/main/java/tech/pegasys/pantheon/plugin/data/UnformattedData.java

@@ -0,0 +1,19 @@
+/*
+ * Copyright 2019 ConsenSys AG.
+ *
+ * Licensed under the Apache License, Version 2.0 (the "License"); you may not use this file except in compliance with
+ * the License. You may obtain a copy of the License at
+ *
+ * http://www.apache.org/licenses/LICENSE-2.0
+ *
+ * Unless required by applicable law or agreed to in writing, software distributed under the License is distributed on
+ * an "AS IS" BASIS, WITHOUT WARRANTIES OR CONDITIONS OF ANY KIND, either express or implied. See the License for the
+ * specific language governing permissions and limitations under the License.
+ */
+package tech.pegasys.pantheon.plugin.data;
+
+import tech.pegasys.pantheon.plugin.Unstable;
+
+/** An interface to mark BinaryData that is not a scalar {@link Quantity}. */
+@Unstable
+public interface UnformattedData extends BinaryData {}

plugins/src/main/java/tech/pegasys/pantheon/plugin/services/MetricsSystem.java

@@ -0,0 +1,119 @@
+/*
+ * Copyright 2018 ConsenSys AG.
+ *
+ * Licensed under the Apache License, Version 2.0 (the "License"); you may not use this file except in compliance with
+ * the License. You may obtain a copy of the License at
+ *
+ * http://www.apache.org/licenses/LICENSE-2.0
+ *
+ * Unless required by applicable law or agreed to in writing, software distributed under the License is distributed on
+ * an "AS IS" BASIS, WITHOUT WARRANTIES OR CONDITIONS OF ANY KIND, either express or implied. See the License for the
+ * specific language governing permissions and limitations under the License.
+ */
+package tech.pegasys.pantheon.plugin.services;
+
+import tech.pegasys.pantheon.plugin.services.metrics.Counter;
+import tech.pegasys.pantheon.plugin.services.metrics.LabelledMetric;
+import tech.pegasys.pantheon.plugin.services.metrics.MetricCategory;
+import tech.pegasys.pantheon.plugin.services.metrics.OperationTimer;
+
+import java.util.function.DoubleSupplier;
+import java.util.function.IntSupplier;
+import java.util.function.LongSupplier;
+
+/** An interface for creating various Metrics components. */
+public interface MetricsSystem {
+
+  /**
+   * Creates a Counter.
+   *
+   * @param category The {@link MetricCategory} this counter is assigned to.
+   * @param name A name for this metric.
+   * @param help A human readable description of the metric.
+   * @return The created Counter instance.
+   */
+  default Counter createCounter(
+      final MetricCategory category, final String name, final String help) {
+    return createLabelledCounter(category, name, help, new String[0]).labels();
+  }
+
+  /**
+   * Creates a Counter with assigned labels.
+   *
+   * @param category The {@link MetricCategory} this counter is assigned to.
+   * @param name A name for this metric.
+   * @param help A human readable description of the metric.
+   * @param labelNames An array of labels to assign to the Counter.
+   * @return The created LabelledMetric instance.
+   */
+  LabelledMetric<Counter> createLabelledCounter(
+      MetricCategory category, String name, String help, String... labelNames);
+
+  /**
+   * Creates a Timer.
+   *
+   * @param category The {@link MetricCategory} this timer is assigned to.
+   * @param name A name for this metric.
+   * @param help A human readable description of the metric.
+   * @return The created Timer instance.
+   */
+  default OperationTimer createTimer(
+      final MetricCategory category, final String name, final String help) {
+    return createLabelledTimer(category, name, help, new String[0]).labels();
+  }
+
+  /**
+   * Creates a Timer with assigned labels.
+   *
+   * @param category The {@link MetricCategory} this timer is assigned to.
+   * @param name A name for this metric.
+   * @param help A human readable description of the metric.
+   * @param labelNames An array of labels to assign to the Timer.
+   * @return The created LabelledMetric instance.
+   */
+  LabelledMetric<OperationTimer> createLabelledTimer(
+      MetricCategory category, String name, String help, String... labelNames);
+
+  /**
+   * Creates a gauge for displaying double vales. A gauge is a metric to report the current value.
+   * The metric value may go up or down.
+   *
+   * @param category The {@link MetricCategory} this gauge is assigned to.
+   * @param name A name for this metric.
+   * @param help A human readable description of the metric.
+   * @param valueSupplier A supplier for the double value to be presented.
+   */
+  void createGauge(MetricCategory category, String name, String help, DoubleSupplier valueSupplier);
+
+  /**
+   * Creates a gauge for displaying integer values.
+   *
+   * @param category The {@link MetricCategory} this gauge is assigned to.
+   * @param name A name for this metric.
+   * @param help A human readable description of the metric.
+   * @param valueSupplier A supplier for the integer value to be presented.
+   */
+  default void createIntegerGauge(
+      final MetricCategory category,
+      final String name,
+      final String help,
+      final IntSupplier valueSupplier) {
+    createGauge(category, name, help, () -> (double) valueSupplier.getAsInt());
+  }
+
+  /**
+   * Creates a gauge for displaying long values.
+   *
+   * @param category The {@link MetricCategory} this gauge is assigned to.
+   * @param name A name for this metric.
+   * @param help A human readable description of the metric.
+   * @param valueSupplier A supplier for the long value to be presented.
+   */
+  default void createLongGauge(
+      final MetricCategory category,
+      final String name,
+      final String help,
+      final LongSupplier valueSupplier) {
+    createGauge(category, name, help, () -> (double) valueSupplier.getAsLong());
+  }
+}

plugins/src/main/java/tech/pegasys/pantheon/plugin/services/PantheonConfiguration.java

@@ -0,0 +1,36 @@
+/*
+ * Copyright 2019 ConsenSys AG.
+ *
+ * Licensed under the Apache License, Version 2.0 (the "License"); you may not use this file except in compliance with
+ * the License. You may obtain a copy of the License at
+ *
+ * http://www.apache.org/licenses/LICENSE-2.0
+ *
+ * Unless required by applicable law or agreed to in writing, software distributed under the License is distributed on
+ * an "AS IS" BASIS, WITHOUT WARRANTIES OR CONDITIONS OF ANY KIND, either express or implied. See the License for the
+ * specific language governing permissions and limitations under the License.
+ */
+package tech.pegasys.pantheon.plugin.services;
+
+import java.net.URI;
+import java.nio.file.Path;
+import java.util.Optional;
+
+/** Generally useful configuration provided by Pantheon. */
+public interface PantheonConfiguration {
+
+  /**
+   * Location of the working directory of the storage in the file system running the client.
+   *
+   * @return location of the storage in the file system of the client.
+   */
+  Path getStoragePath();
+
+  /**
+   * Url of the enclave that stores private transaction data.
+   *
+   * @return an optional containing the url of the enclave Pantheon is connected to, or empty if
+   *     privacy is not enabled.
+   */
+  Optional<URI> getEnclaveUrl();
+}

plugins/src/main/java/tech/pegasys/pantheon/plugin/services/PantheonEvents.java

@@ -0,0 +1,117 @@
+/*
+ * Copyright 2019 ConsenSys AG.
+ *
+ * Licensed under the Apache License, Version 2.0 (the "License"); you may not use this file except in compliance with
+ * the License. You may obtain a copy of the License at
+ *
+ * http://www.apache.org/licenses/LICENSE-2.0
+ *
+ * Unless required by applicable law or agreed to in writing, software distributed under the License is distributed on
+ * an "AS IS" BASIS, WITHOUT WARRANTIES OR CONDITIONS OF ANY KIND, either express or implied. See the License for the
+ * specific language governing permissions and limitations under the License.
+ */
+package tech.pegasys.pantheon.plugin.services;
+
+import tech.pegasys.pantheon.plugin.Unstable;
+import tech.pegasys.pantheon.plugin.data.BlockHeader;
+import tech.pegasys.pantheon.plugin.data.Transaction;
+
+/**
+ * This service allows plugins to attach to various events during the normal operation of Pantheon.
+ *
+ * <p>Currently supported events
+ *
+ * <ul>
+ *   <li><b>newBlockPropagated</b> - Fired when a new block header has been received and validated
+ *       and is about to be sent out to other peers, but before the body of the block has been
+ *       evaluated and validated.
+ *   <li><b>newTransactionAdded</b> - Fired when a new transaction has been added to the node.
+ * </ul>
+ */
+@Unstable
+public interface PantheonEvents {
+
+  /**
+   * Add a listener watching new blocks propagated.
+   *
+   * @param newBlockPropagatedListener The listener that will accept a BlockHeader as the event.
+   * @return an object to be used as an identifier when de-registering the event.
+   */
+  Object addNewBlockPropagatedListener(NewBlockPropagatedListener newBlockPropagatedListener);
+
+  /**
+   * Remove the blockAdded listener from pantheon notifications.
+   *
+   * @param listenerIdentifier The instance that was returned from addBlockAddedListener;
+   */
+  void removeNewBlockPropagatedListener(Object listenerIdentifier);
+
+  /**
+   * Add a listener watching new transactions added to the node.
+   *
+   * @param newTransactionAddedListener The listener that will accept the Transaction object as the
+   *     event.
+   * @return an object to be used as an identifier when de-registering the event.
+   */
+  Object addNewTransactionAddedListener(NewTransactionAddedListener newTransactionAddedListener);
+
+  /**
+   * Remove the blockAdded listener from pantheon notifications.
+   *
+   * @param listenerIdentifier The instance that was returned from addNewTransactionAddedListener;
+   */
+  void removeNewTransactionAddedListener(Object listenerIdentifier);
+
+  /**
+   * Add a listener watching dropped transactions.
+   *
+   * @param newTransactionDroppedListener The listener that will accept the Transaction object as
+   *     the event.
+   * @return an object to be used as an identifier when de-registering the event.
+   */
+  Object addNewTransactionDroppedListener(TransactionDroppedListener newTransactionDroppedListener);
+
+  /**
+   * Remove the transactionDropped listener from pantheon notifications.
+   *
+   * @param listenerIdentifier The instance that was returned from addTransactionDroppedListener;
+   */
+  void removeTransactionDroppedListener(Object listenerIdentifier);
+
+  /** The listener interface for receiving new block propagated events. */
+  interface NewBlockPropagatedListener {
+
+    /**
+     * Invoked when a new block header has been received and validated and is about to be sent out
+     * to other peers, but before the body of the block has been evaluated and validated.
+     *
+     * <p>The block may not have been imported to the local chain yet and may fail later
+     * validations.
+     *
+     * @param newBlockHeader the new block header.
+     */
+    void newBlockPropagated(BlockHeader newBlockHeader);
+  }
+
+  /** The listener interface for receiving new transaction added events. */
+  interface NewTransactionAddedListener {
+
+    /**
+     * Invoked when a new transaction has been added to the node.
+     *
+     * @param transaction the new transaction.
+     */
+    void newTransactionAdded(Transaction transaction);
+  }
+
+  /** The listener interface for receiving transaction dropped events. */
+  interface TransactionDroppedListener {
+
+    /**
+     * Invoked when a transaction is dropped from the node.
+     *
+     * @param transaction the dropped transaction.
+     */
+    void newTransactionDropped(Transaction transaction);
+  }
+}

plugins/src/main/java/tech/pegasys/pantheon/plugin/services/PicoCLIOptions.java

@@ -0,0 +1,37 @@
+/*
+ * Copyright 2019 ConsenSys AG.
+ *
+ * Licensed under the Apache License, Version 2.0 (the "License"); you may not use this file except in compliance with
+ * the License. You may obtain a copy of the License at
+ *
+ * http://www.apache.org/licenses/LICENSE-2.0
+ *
+ * Unless required by applicable law or agreed to in writing, software distributed under the License is distributed on
+ * an "AS IS" BASIS, WITHOUT WARRANTIES OR CONDITIONS OF ANY KIND, either express or implied. See the License for the
+ * specific language governing permissions and limitations under the License.
+ */
+package tech.pegasys.pantheon.plugin.services;
+
+/**
+ * A service that plugins can use to add CLI options and commands to the PantheonCommand. The
+ * PicoCLI library annotations will be inspected and the object will be passed into a
+ * picocli.CommandLine.addMixin call.
+ *
+ * <p>This service will be available during the registration callbacks.
+ *
+ * <p>CLI arguments should conform to the <a
+ * href="https://github.com/PegaSysEng/pantheon/blob/master/CLI-STYLE-GUIDE.md">CLI-STYLE-GUIDE.md</a>
+ * conventions.
+ */
+public interface PicoCLIOptions {
+
+  /**
+   * During the registration callback plugins can register CLI options that should be added to
+   * Pantheon's CLI startup.
+   *
+   * @param namespace A namespace prefix. All registered options must start with this prefix
+   * @param optionObject The instance of the object to be inspected. PicoCLI will reflect the fields
+   *     of this object to extract the CLI options.
+   */
+  void addPicoCLIOptions(String namespace, Object optionObject);
+}

plugins/src/main/java/tech/pegasys/pantheon/plugin/services/StorageService.java

@@ -0,0 +1,38 @@
+/*
+ * Copyright 2019 ConsenSys AG.
+ *
+ * Licensed under the Apache License, Version 2.0 (the "License"); you may not use this file except in compliance with
+ * the License. You may obtain a copy of the License at
+ *
+ * http://www.apache.org/licenses/LICENSE-2.0
+ *
+ * Unless required by applicable law or agreed to in writing, software distributed under the License is distributed on
+ * an "AS IS" BASIS, WITHOUT WARRANTIES OR CONDITIONS OF ANY KIND, either express or implied. See the License for the
+ * specific language governing permissions and limitations under the License.
+ */
+package tech.pegasys.pantheon.plugin.services;
+
+import tech.pegasys.pantheon.plugin.Unstable;
+import tech.pegasys.pantheon.plugin.services.storage.KeyValueStorageFactory;
+import tech.pegasys.pantheon.plugin.services.storage.SegmentIdentifier;
+
+import java.util.List;
+
+/** This service allows plugins to register as an available storage engine. */
+@Unstable
+public interface StorageService {
+
+  /**
+   * Registers a factory as available for creating key-value storage instances.
+   *
+   * @param factory creates instances providing key-value storage.
+   */
+  void registerKeyValueStorage(KeyValueStorageFactory factory);
+
+  /**
+   * Retrieves the identifiers for the isolation segments that could be requested during operation.
+   *
+   * @return full set of possible segments required from the storage service.
+   */
+  List<SegmentIdentifier> getAllSegmentIdentifiers();
+}

plugins/src/main/java/tech/pegasys/pantheon/plugin/services/exception/StorageException.java

@@ -0,0 +1,47 @@
+/*
+ * Copyright 2019 ConsenSys AG.
+ *
+ * Licensed under the Apache License, Version 2.0 (the "License"); you may not use this file except in compliance with
+ * the License. You may obtain a copy of the License at
+ *
+ * http://www.apache.org/licenses/LICENSE-2.0
+ *
+ * Unless required by applicable law or agreed to in writing, software distributed under the License is distributed on
+ * an "AS IS" BASIS, WITHOUT WARRANTIES OR CONDITIONS OF ANY KIND, either express or implied. See the License for the
+ * specific language governing permissions and limitations under the License.
+ */
+package tech.pegasys.pantheon.plugin.services.exception;
+
+/** Base exception class for problems encountered in the domain for storage. */
+public class StorageException extends RuntimeException {
+
+  /**
+   * Constructs a new storage exception with the specified cause.
+   *
+   * @param cause saved for later retrieval by the {@link #getCause()} method). (A {@code null}
+   *     value is permitted, and indicates that the cause is nonexistent or unknown.)
+   */
+  public StorageException(final Throwable cause) {
+    super(cause);
+  }
+
+  /**
+   * Constructs a new storage exception with the specified detail message and cause.
+   *
+   * @param message the detail that may be retrieved later by Throwable.getMessage().
+   * @param cause saved for later retrieval by the {@link #getCause()} method). (A {@code null}
+   *     value is permitted, and indicates that the cause is nonexistent or unknown.)
+   */
+  public StorageException(final String message, final Throwable cause) {
+    super(message, cause);
+  }
+
+  /**
+   * Constructs a new storage exception with the specified detail message.
+   *
+   * @param message the detail that may be retrieved later by Throwable.getMessage().
+   */
+  public StorageException(final String message) {
+    super(message);
+  }
+}

plugins/src/main/java/tech/pegasys/pantheon/plugin/services/metrics/Counter.java

@@ -0,0 +1,30 @@
+/*
+ * Copyright 2018 ConsenSys AG.
+ *
+ * Licensed under the Apache License, Version 2.0 (the "License"); you may not use this file except in compliance with
+ * the License. You may obtain a copy of the License at
+ *
+ * http://www.apache.org/licenses/LICENSE-2.0
+ *
+ * Unless required by applicable law or agreed to in writing, software distributed under the License is distributed on
+ * an "AS IS" BASIS, WITHOUT WARRANTIES OR CONDITIONS OF ANY KIND, either express or implied. See the License for the
+ * specific language governing permissions and limitations under the License.
+ */
+package tech.pegasys.pantheon.plugin.services.metrics;
+
+/**
+ * A counter is a metric to track counts of events or running totals etc. The value of the counter
+ * can only increase.
+ */
+public interface Counter {
+
+  /** Increment the counter by 1. */
+  void inc();
+
+  /**
+   * Increment the counter by a specified amount.
+   *
+   * @param amount The amount to increment the counter by. Must be greater than or equal to 0.
+   */
+  void inc(long amount);
+}

plugins/src/main/java/tech/pegasys/pantheon/plugin/services/metrics/LabelledMetric.java

@@ -0,0 +1,31 @@
+/*
+ * Copyright 2018 ConsenSys AG.
+ *
+ * Licensed under the Apache License, Version 2.0 (the "License"); you may not use this file except in compliance with
+ * the License. You may obtain a copy of the License at
+ *
+ * http://www.apache.org/licenses/LICENSE-2.0
+ *
+ * Unless required by applicable law or agreed to in writing, software distributed under the License is distributed on
+ * an "AS IS" BASIS, WITHOUT WARRANTIES OR CONDITIONS OF ANY KIND, either express or implied. See the License for the
+ * specific language governing permissions and limitations under the License.
+ */
+package tech.pegasys.pantheon.plugin.services.metrics;
+
+/**
+ * A metric with labels associated. Values for the associated labels can be provided to access the
+ * underlying metric.
+ *
+ * @param <T> The type of metric the labels are applied to.
+ */
+public interface LabelledMetric<T> {
+
+  /**
+   * Returns a metric tagged with the specified label values.
+   *
+   * @param labels An array of label values in the same order as the labels when creating this
+   *     metric. The number of values provided must match the number of labels.
+   * @return A metric tagged with the specified labels.
+   */
+  T labels(String... labels);
+}

plugins/src/main/java/tech/pegasys/pantheon/plugin/services/metrics/MetricCategory.java

@@ -0,0 +1,43 @@
+/*
+ * Copyright 2019 ConsenSys AG.
+ *
+ * Licensed under the Apache License, Version 2.0 (the "License"); you may not use this file except in compliance with
+ * the License. You may obtain a copy of the License at
+ *
+ * http://www.apache.org/licenses/LICENSE-2.0
+ *
+ * Unless required by applicable law or agreed to in writing, software distributed under the License is distributed on
+ * an "AS IS" BASIS, WITHOUT WARRANTIES OR CONDITIONS OF ANY KIND, either express or implied. See the License for the
+ * specific language governing permissions and limitations under the License.
+ */
+package tech.pegasys.pantheon.plugin.services.metrics;
+
+import java.util.Optional;
+
+/**
+ * A MetricCategory is used to group related metrics. Every metric belongs to one and only one
+ * MetricCategory.
+ *
+ * <p>Categories must be registered with the {@link MetricCategoryRegistry} during plugin
+ * initialisation.
+ */
+public interface MetricCategory {
+
+  /**
+   * Gets the name of this MetricCategory.
+   *
+   * @return The name of this MetricCategory.
+   */
+  String getName();
+
+  /**
+   * Gets the application-specific MetricCategory prefix. An empty Optional may be returned if this
+   * category is not application specific.
+   *
+   * <p>The prefix, if present, is prepended to the category name when creating a single combined
+   * name for metrics.
+   *
+   * @return An optional application prefix.
+   */
+  Optional<String> getApplicationPrefix();
+}

plugins/src/main/java/tech/pegasys/pantheon/plugin/services/metrics/MetricCategoryRegistry.java

@@ -0,0 +1,29 @@
+/*
+ * Copyright 2019 ConsenSys AG.
+ *
+ * Licensed under the Apache License, Version 2.0 (the "License"); you may not use this file except in compliance with
+ * the License. You may obtain a copy of the License at
+ *
+ * http://www.apache.org/licenses/LICENSE-2.0
+ *
+ * Unless required by applicable law or agreed to in writing, software distributed under the License is distributed on
+ * an "AS IS" BASIS, WITHOUT WARRANTIES OR CONDITIONS OF ANY KIND, either express or implied. See the License for the
+ * specific language governing permissions and limitations under the License.
+ */
+package tech.pegasys.pantheon.plugin.services.metrics;
+
+/**
+ * Allow registration of {@link MetricCategory} instances so they are recognised by the metrics
+ * system and can be enabled.
+ *
+ * <p>Categories must be registered during plugin initialisation.
+ */
+public interface MetricCategoryRegistry {
+
+  /**
+   * Registers a {@link MetricCategory}.
+   *
+   * @param newMetricCategory The {@link MetricCategory} that is being registered.
+   */
+  public void addMetricCategory(final MetricCategory newMetricCategory);
+}

plugins/src/main/java/tech/pegasys/pantheon/plugin/services/metrics/OperationTimer.java

@@ -0,0 +1,43 @@
+/*
+ * Copyright 2018 ConsenSys AG.
+ *
+ * Licensed under the Apache License, Version 2.0 (the "License"); you may not use this file except in compliance with
+ * the License. You may obtain a copy of the License at
+ *
+ * http://www.apache.org/licenses/LICENSE-2.0
+ *
+ * Unless required by applicable law or agreed to in writing, software distributed under the License is distributed on
+ * an "AS IS" BASIS, WITHOUT WARRANTIES OR CONDITIONS OF ANY KIND, either express or implied. See the License for the
+ * specific language governing permissions and limitations under the License.
+ */
+package tech.pegasys.pantheon.plugin.services.metrics;
+
+import java.io.Closeable;
+
+/** A timer metric that records duration of operations for metrics purposes. */
+public interface OperationTimer {
+
+  /**
+   * Starts the timer.
+   *
+   * @return The produced TimingContext, which must be stopped or closed when the operation being
+   *     timed has completed.
+   */
+  TimingContext startTimer();
+
+  /** An interface for stopping the timer and returning elapsed time. */
+  interface TimingContext extends Closeable {
+
+    /**
+     * Stops the timer and returns the elapsed time.
+     *
+     * @return Elapsed time in seconds.
+     */
+    double stopTimer();
+
+    @Override
+    default void close() {
+      stopTimer();
+    }
+  }
+}

plugins/src/main/java/tech/pegasys/pantheon/plugin/services/storage/KeyValueStorage.java

@@ -0,0 +1,78 @@
+/*
+ * Copyright 2019 ConsenSys AG.
+ *
+ * Licensed under the Apache License, Version 2.0 (the "License"); you may not use this file except in compliance with
+ * the License. You may obtain a copy of the License at
+ *
+ * http://www.apache.org/licenses/LICENSE-2.0
+ *
+ * Unless required by applicable law or agreed to in writing, software distributed under the License is distributed on
+ * an "AS IS" BASIS, WITHOUT WARRANTIES OR CONDITIONS OF ANY KIND, either express or implied. See the License for the
+ * specific language governing permissions and limitations under the License.
+ */
+package tech.pegasys.pantheon.plugin.services.storage;
+
+import tech.pegasys.pantheon.plugin.Unstable;
+import tech.pegasys.pantheon.plugin.services.exception.StorageException;
+
+import java.io.Closeable;
+import java.util.Optional;
+import java.util.function.Predicate;
+
+/**
+ * Responsible for storing values against keys.
+ *
+ * <p>Behaviour expected with regard to key to value mapping is that of a map, one key maps to one
+ * value, when a new value is added with an existing key, that key now points at the new value.
+ *
+ * <p>All keys and values must be non-null.
+ */
+@Unstable
+public interface KeyValueStorage extends Closeable {
+
+  /**
+   * Deletes all keys and values from the storage.
+   *
+   * @throws StorageException problem encountered when attempting to clear storage.
+   */
+  void clear() throws StorageException;
+
+  /**
+   * Whether the key-value storage contains the given key.
+   *
+   * @param key a key that might be contained in the key-value storage.
+   * @return <code>true</code> when the given key is present in keyset, <code>false</code>
+   *     otherwise.
+   * @throws StorageException problem encountered when interacting with the key set.
+   */
+  boolean containsKey(byte[] key) throws StorageException;
+
+  /**
+   * Retrieves the value associated with a given key.
+   *
+   * @param key whose associated value is being retrieved.
+   * @return an {@link Optional} containing the value associated with the specified key, otherwise
+   *     empty.
+   * @throws StorageException problem encountered during the retrieval attempt.
+   */
+  Optional<byte[]> get(byte[] key) throws StorageException;
+
+  /**
+   * Performs an evaluation against each key in the store, keeping the entries that pass, removing
+   * those that fail.
+   *
+   * @param retainCondition predicate to evaluate each key against, unless the result is {@code
+   *     null}, both the key and associated value must be removed.
+   * @return the number of keys removed.
+   * @throws StorageException problem encountered when removing data.
+   */
+  long removeAllKeysUnless(Predicate<byte[]> retainCondition) throws StorageException;
+
+  /**
+   * Begins a fresh transaction, for sequencing operations for later atomic execution.
+   *
+   * @return transaciton to sequence key-value operations.
+   * @throws StorageException problem encountered when starting a new transaction.
+   */
+  KeyValueStorageTransaction startTransaction() throws StorageException;
+}

plugins/src/main/java/tech/pegasys/pantheon/plugin/services/storage/KeyValueStorageFactory.java

@@ -0,0 +1,57 @@
+/*
+ * Copyright 2019 ConsenSys AG.
+ *
+ * Licensed under the Apache License, Version 2.0 (the "License"); you may not use this file except in compliance with
+ * the License. You may obtain a copy of the License at
+ *
+ * http://www.apache.org/licenses/LICENSE-2.0
+ *
+ * Unless required by applicable law or agreed to in writing, software distributed under the License is distributed on
+ * an "AS IS" BASIS, WITHOUT WARRANTIES OR CONDITIONS OF ANY KIND, either express or implied. See the License for the
+ * specific language governing permissions and limitations under the License.
+ */
+package tech.pegasys.pantheon.plugin.services.storage;
+
+import tech.pegasys.pantheon.plugin.Unstable;
+import tech.pegasys.pantheon.plugin.services.exception.StorageException;
+
+/** Factory for creating key-value storage instances. */
+@Unstable
+public interface KeyValueStorageFactory {
+
+  /**
+   * Retrieves the identity of the key-value storage factory.
+   *
+   * @return the storage identifier, used when selecting the appropriate storage service.
+   */
+  String getName();
+
+  /**
+   * Creates a new key-value storage instance, appropriate for the given segment.
+   *
+   * <p>When segment isolation is not supported, the create will still be called with each of the
+   * required segments, where the same storage instance should be returned.
+   *
+   * <p>New segments may be introduced in future releases and should result in a new empty
+   * key-space. Segments created with the identifier of an existing segment should have the same
+   * data as that existing segment.
+   *
+   * @param segment identity of the isolation segment, an identifier for the data set the storage
+   *     will contain.
+   * @return the storage instance reserved for the given segment.
+   * @exception StorageException problem encountered when creating storage for the segment.
+   */
+  KeyValueStorage create(SegmentIdentifier segment) throws StorageException;
+
+  /**
+   * Whether storage segment isolation is supported by the factory created instances.
+   *
+   * <p>As supporting segment isolation is similar to a separating keys into distinct namespaces,
+   * where operations only affect within that segment i.e. the same key from two segments point to
+   * separate values.
+   *
+   * @return <code>true</code> when the created storage instances are isolated from each other,
+   *     <code>false</code> when keys of different segments can collide with each other.
+   */
+  boolean isSegmentIsolationSupported();
+}

plugins/src/main/java/tech/pegasys/pantheon/plugin/services/storage/KeyValueStorageTransaction.java

@@ -0,0 +1,49 @@
+/*
+ * Copyright 2019 ConsenSys AG.
+ *
+ * Licensed under the Apache License, Version 2.0 (the "License"); you may not use this file except in compliance with
+ * the License. You may obtain a copy of the License at
+ *
+ * http://www.apache.org/licenses/LICENSE-2.0
+ *
+ * Unless required by applicable law or agreed to in writing, software distributed under the License is distributed on
+ * an "AS IS" BASIS, WITHOUT WARRANTIES OR CONDITIONS OF ANY KIND, either express or implied. See the License for the
+ * specific language governing permissions and limitations under the License.
+ */
+package tech.pegasys.pantheon.plugin.services.storage;
+
+import tech.pegasys.pantheon.plugin.Unstable;
+import tech.pegasys.pantheon.plugin.services.exception.StorageException;
+
+/** A transaction that can atomically commit a sequence of operations to a key-value store. */
+@Unstable
+public interface KeyValueStorageTransaction {
+
+  /**
+   * Associates the specified value with the specified key.
+   *
+   * <p>If a previously value had been store against the given key, the old value is replaced by the
+   * given value.
+   *
+   * @param key the given value is to be associated with.
+   * @param value associated with the specified key.
+   */
+  void put(byte[] key, byte[] value);
+
+  /**
+   * When the given key is present, the key and mapped value will be removed from storage.
+   *
+   * @param key the key and mapped value that will be removed.
+   */
+  void remove(byte[] key);
+
+  /**
+   * Performs an atomic commit of all the operations queued in the transaction.
+   *
+   * @throws StorageException problem was encountered preventing the commit
+   */
+  void commit() throws StorageException;
+
+  /** Reset the transaction to a state prior to any operations being queued. */
+  void rollback();
+}

plugins/src/main/java/tech/pegasys/pantheon/plugin/services/storage/SegmentIdentifier.java

@@ -0,0 +1,30 @@
+/*
+ * Copyright 2019 ConsenSys AG.
+ *
+ * Licensed under the Apache License, Version 2.0 (the "License"); you may not use this file except in compliance with
+ * the License. You may obtain a copy of the License at
+ *
+ * http://www.apache.org/licenses/LICENSE-2.0
+ *
+ * Unless required by applicable law or agreed to in writing, software distributed under the License is distributed on
+ * an "AS IS" BASIS, WITHOUT WARRANTIES OR CONDITIONS OF ANY KIND, either express or implied. See the License for the
+ * specific language governing permissions and limitations under the License.
+ */
+package tech.pegasys.pantheon.plugin.services.storage;
+
+import tech.pegasys.pantheon.plugin.Unstable;
+
+/**
+ * A namespace identifier for the storage instance segment, a grouping of data that should be kept
+ * isolated from the data of other segments.
+ */
+@Unstable
+public interface SegmentIdentifier {
+
+  /**
+   * Identifier for the segment consistent throughout the lifetime of the segment.
+   *
+   * @return unique name of the segment.
+   */
+  String getName();
+}

services/kvstore/build.gradle

@@ -26,10 +26,9 @@ jar {
 }
 
 dependencies {
+  api project(':plugins')
   api project(':util')
 
-  api 'tech.pegasys.pantheon:plugin-api'
-
   implementation project(':metrics:core')
   implementation project(':metrics:rocksdb')
   implementation project(':services:util')

services/pipeline/build.gradle

@@ -28,10 +28,10 @@ jar {
 dependencies {
   api project(':util')
   implementation project(':metrics:core')
+  implementation project(':plugins')
 
   implementation 'org.apache.logging.log4j:log4j-api'
   implementation 'com.google.guava:guava'
-  implementation 'tech.pegasys.pantheon:plugin-api'
 
   runtime 'org.apache.logging.log4j:log4j-core'
 

services/tasks/build.gradle

@@ -26,10 +26,9 @@ jar {
 }
 
 dependencies {
+  api project(':plugins')
   api project(':util')
 
-  api 'tech.pegasys.pantheon:plugin-api'
-
   compileOnly 'org.openjdk.jmh:jmh-generator-annprocess'
 
   implementation project(':metrics:core')

settings.gradle

@@ -37,6 +37,7 @@ include 'metrics:core'
 include 'metrics:rocksdb'
 include 'nat'
 include 'pantheon'
+include 'plugins'
 include 'services:kvstore'
 include 'services:pipeline'
 include 'services:tasks'

util/build.gradle

@@ -26,10 +26,10 @@ jar {
 }
 
 dependencies {
+  implementation project(':plugins')
   implementation 'com.google.guava:guava'
   implementation 'io.vertx:vertx-core'
   implementation 'org.apache.logging.log4j:log4j-api'
-  implementation 'tech.pegasys.pantheon:plugin-api'
 
   runtime 'org.apache.logging.log4j:log4j-core'