[FAB-1360] Introduce ChainPartition for Kafka

https://jira.hyperledger.org/browse/FAB-1360

This changeset introduces ChainPartition, a construct that will be used
to identify the Kafka topic/partition that the ordering shims should
interact with when dealing with a particular chain.

Note that it encodes the given chain ID in base-16 as a means of escaping
characters that are not allowed in Kafka topic names. All the
restrictions for topic names are linked to in line 38. Filtering for
complying chain IDs should probably happen during transaction filtering
at ingress. This is marked as a TODO, and a JIRA issue has been created
for it.

This changeset merely introduces the ChainPartition construct and does
not integrate it with the rest of the code yet. This will happen in a
follow-up changeset.

Change-Id: I33d4e80758d7dfd7e7d827caa385d0507a39a40a
Signed-off-by: Kostas Christidis <kostas@christidis.io>

orderer/kafka/chain_partition.go

@@ -0,0 +1,57 @@
+/*
+Copyright IBM Corp. 2016 All Rights Reserved.
+
+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 kafka
+
+import "fmt"
+
+const rawPartition = 0
+
+// ChainPartition identifies the Kafka partition the orderer interacts with.
+type ChainPartition interface {
+	Topic() string
+	Partition() int32
+	fmt.Stringer
+}
+
+type chainPartitionImpl struct {
+	tpc string
+	prt int32
+}
+
+// Returns a new chain partition for a given chain ID and partition.
+func newChainPartition(chainID string, partition int32) ChainPartition {
+	return &chainPartitionImpl{
+		// TODO https://github.com/apache/kafka/blob/trunk/core/src/main/scala/kafka/common/Topic.scala#L29
+		tpc: fmt.Sprintf("%x", chainID),
+		prt: partition,
+	}
+}
+
+// Topic returns the Kafka topic of this chain partition.
+func (cp *chainPartitionImpl) Topic() string {
+	return cp.tpc
+}
+
+// Partition returns the Kafka partition of this chain partition.
+func (cp *chainPartitionImpl) Partition() int32 {
+	return cp.prt
+}
+
+// String returns a string identifying the chain partition.
+func (cp *chainPartitionImpl) String() string {
+	return fmt.Sprintf("%s/%d", cp.tpc, cp.prt)
+}

orderer/kafka/chain_partition_test.go

@@ -0,0 +1,41 @@
+/*
+Copyright IBM Corp. 2016 All Rights Reserved.
+
+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 kafka
+
+import (
+	"fmt"
+	"strings"
+	"testing"
+
+	"github.com/hyperledger/fabric/orderer/common/bootstrap/static"
+)
+
+func TestChainPartition(t *testing.T) {
+	cp := newChainPartition(static.TestChainID, rawPartition)
+
+	expectedTopic := fmt.Sprintf("%x", static.TestChainID)
+	actualTopic := cp.Topic()
+	if strings.Compare(expectedTopic, actualTopic) != 0 {
+		t.Fatalf("Got the wrong topic, expected %s, got %s instead", expectedTopic, actualTopic)
+	}
+
+	expectedPartition := int32(rawPartition)
+	actualPartition := cp.Partition()
+	if actualPartition != expectedPartition {
+		t.Fatalf("Got the wrong partition, expected %d, got %d instead", expectedPartition, actualPartition)
+	}
+}