[GitHub] [nifi-minifi-cpp] szaszm commented on a change in pull request #940: MINIFICPP-1373 - Implement ConsumeKafka

[GitBox <gi...@apache.org>]

szaszm commented on a change in pull request #940:
URL: https://github.com/apache/nifi-minifi-cpp/pull/940#discussion_r567675222



##########
File path: extensions/librdkafka/ConsumeKafka.cpp
##########
@@ -0,0 +1,579 @@
+/**
+ * Licensed to the Apache Software Foundation (ASF) under one or more
+ * contributor license agreements.  See the NOTICE file distributed with
+ * this work for additional information regarding copyright ownership.
+ * The ASF licenses this file to You 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.
+ */
+
+#include "ConsumeKafka.h"
+
+#include <algorithm>
+#include <limits>
+
+#include "core/PropertyValidation.h"
+#include "utils/ProcessorConfigUtils.h"
+#include "utils/gsl.h"
+
+namespace org {
+namespace apache {
+namespace nifi {
+namespace minifi {
+namespace core {
+// The upper limit for Max Poll Time is 4 seconds. This is because Watchdog would potentially start
+// reporting issues with the processor health otherwise
+class ConsumeKafkaMaxPollTimeValidator : public TimePeriodValidator {
+ public:
+  ConsumeKafkaMaxPollTimeValidator(const std::string &name) // NOLINT
+      : TimePeriodValidator(name) {
+  }
+  ~ConsumeKafkaMaxPollTimeValidator() override = default;
+
+  ValidationResult validate(const std::string& subject, const std::string& input) const override {
+    uint64_t value;
+    TimeUnit timeUnit;
+    uint64_t value_as_ms;
+    return ValidationResult::Builder::createBuilder().withSubject(subject).withInput(input).isValid(
+        core::TimePeriodValue::StringToTime(input, value, timeUnit) &&
+        org::apache::nifi::minifi::core::Property::ConvertTimeUnitToMS(value, timeUnit, value_as_ms) &&
+        0 < value_as_ms && value_as_ms <= 4000).build();
+  }
+};
+}  // namespace core
+namespace processors {
+
+constexpr const std::size_t ConsumeKafka::DEFAULT_MAX_POLL_RECORDS;
+constexpr char const* ConsumeKafka::DEFAULT_MAX_POLL_TIME;
+
+constexpr char const* ConsumeKafka::TOPIC_FORMAT_NAMES;
+constexpr char const* ConsumeKafka::TOPIC_FORMAT_PATTERNS;
+
+core::Property ConsumeKafka::KafkaBrokers(core::PropertyBuilder::createProperty("Kafka Brokers")
+  ->withDescription("A comma-separated list of known Kafka Brokers in the format <host>:<port>.")
+  ->withDefaultValue("localhost:9092", core::StandardValidators::get().NON_BLANK_VALIDATOR)
+  ->supportsExpressionLanguage(true)
+  ->isRequired(true)
+  ->build());
+
+core::Property ConsumeKafka::SecurityProtocol(core::PropertyBuilder::createProperty("Security Protocol")
+  ->withDescription("This property is currently not supported. Protocol used to communicate with brokers. Corresponds to Kafka's 'security.protocol' property.")
+  ->withAllowableValues<std::string>({SECURITY_PROTOCOL_PLAINTEXT/*, SECURITY_PROTOCOL_SSL, SECURITY_PROTOCOL_SASL_PLAINTEXT, SECURITY_PROTOCOL_SASL_SSL*/ })
+  ->withDefaultValue(SECURITY_PROTOCOL_PLAINTEXT)
+  ->isRequired(true)
+  ->build());
+
+core::Property ConsumeKafka::TopicNames(core::PropertyBuilder::createProperty("Topic Names")
+  ->withDescription("The name of the Kafka Topic(s) to pull from. Multiple topic names are supported as a comma separated list.")
+  ->supportsExpressionLanguage(true)
+  ->isRequired(true)
+  ->build());
+
+core::Property ConsumeKafka::TopicNameFormat(core::PropertyBuilder::createProperty("Topic Name Format")
+  ->withDescription("Specifies whether the Topic(s) provided are a comma separated list of names or a single regular expression.")
+  ->withAllowableValues<std::string>({TOPIC_FORMAT_NAMES, TOPIC_FORMAT_PATTERNS})
+  ->withDefaultValue(TOPIC_FORMAT_NAMES)
+  ->isRequired(true)
+  ->build());
+
+core::Property ConsumeKafka::HonorTransactions(core::PropertyBuilder::createProperty("Honor Transactions")
+  ->withDescription(
+      "Specifies whether or not MiNiFi should honor transactional guarantees when communicating with Kafka. If false, the Processor will use an \"isolation level\" of "
+      "read_uncomitted. This means that messages will be received as soon as they are written to Kafka but will be pulled, even if the producer cancels the transactions. "
+      "If this value is true, MiNiFi will not receive any messages for which the producer's transaction was canceled, but this can result in some latency since the consumer "
+      "must wait for the producer to finish its entire transaction instead of pulling as the messages become available.")
+  ->withDefaultValue<bool>(true)
+  ->isRequired(true)
+  ->build());
+
+core::Property ConsumeKafka::GroupID(core::PropertyBuilder::createProperty("Group ID")
+  ->withDescription("A Group ID is used to identify consumers that are within the same consumer group. Corresponds to Kafka's 'group.id' property.")
+  ->supportsExpressionLanguage(true)
+  ->isRequired(true)
+  ->build());
+
+core::Property ConsumeKafka::OffsetReset(core::PropertyBuilder::createProperty("Offset Reset")
+  ->withDescription("Allows you to manage the condition when there is no initial offset in Kafka or if the current offset does not exist any more on the server (e.g. because that "
+      "data has been deleted). Corresponds to Kafka's 'auto.offset.reset' property.")
+  ->withAllowableValues<std::string>({OFFSET_RESET_EARLIEST, OFFSET_RESET_LATEST, OFFSET_RESET_NONE})
+  ->withDefaultValue(OFFSET_RESET_LATEST)
+  ->isRequired(true)
+  ->build());
+
+core::Property ConsumeKafka::KeyAttributeEncoding(core::PropertyBuilder::createProperty("Key Attribute Encoding")
+  ->withDescription("FlowFiles that are emitted have an attribute named 'kafka.key'. This property dictates how the value of the attribute should be encoded.")
+  ->withAllowableValues<std::string>({KEY_ATTR_ENCODING_UTF_8, KEY_ATTR_ENCODING_HEX})
+  ->withDefaultValue(KEY_ATTR_ENCODING_UTF_8)
+  ->isRequired(true)
+  ->build());
+
+core::Property ConsumeKafka::MessageDemarcator(core::PropertyBuilder::createProperty("Message Demarcator")
+  ->withDescription("Since KafkaConsumer receives messages in batches, you have an option to output FlowFiles which contains all Kafka messages in a single batch "
+      "for a given topic and partition and this property allows you to provide a string (interpreted as UTF-8) to use for demarcating apart multiple Kafka messages. "
+      "This is an optional property and if not provided each Kafka message received will result in a single FlowFile which time it is triggered. ")
+  ->supportsExpressionLanguage(true)
+  ->build());
+
+core::Property ConsumeKafka::MessageHeaderEncoding(core::PropertyBuilder::createProperty("Message Header Encoding")
+  ->withDescription("Any message header that is found on a Kafka message will be added to the outbound FlowFile as an attribute. This property indicates the Character Encoding "
+      "to use for deserializing the headers.")
+  ->withAllowableValues<std::string>({MSG_HEADER_ENCODING_UTF_8, MSG_HEADER_ENCODING_HEX})
+  ->withDefaultValue(MSG_HEADER_ENCODING_UTF_8)
+  ->build());
+
+core::Property ConsumeKafka::HeadersToAddAsAttributes(core::PropertyBuilder::createProperty("Headers To Add As Attributes")
+  ->withDescription("A Regular Expression that is matched against all message headers. Any message header whose name matches the regex will be added to the FlowFile "
+      "as an Attribute. If not specified, no Header values will be added as FlowFile attributes. If two messages have a different value for the same header and that "
+      "header is selected by the provided regex, then those two messages must be added to different FlowFiles. As a result, users should be cautious about using a "
+      "regex like \".*\" if messages are expected to have header values that are unique per message, such as an identifier or timestamp, because it will prevent MiNiFi "
+      "from bundling the messages together efficiently.")
+  ->build());
+
+core::Property ConsumeKafka::DuplicateHeaderHandling(core::PropertyBuilder::createProperty("Duplicate Header Handling")
+  ->withDescription("For headers to be added as attributes, this option specifies how to handle cases where multiple headers are present with the same key. "
+      "For example in case of receiving these two headers: \"Accept: text/html\" and \"Accept: application/xml\" and we want to attach the value of \"Accept\" "
+      "as a FlowFile attribute:\n"
+      " - \"Keep First\" attaches: \"Accept -> text/html\"\n"
+      " - \"Keep Latest\" attaches: \"Accept -> application/xml\"\n"
+      " - \"Comma-separated Merge\" attaches: \"Accept -> text/html, application/xml\"\n")
+  ->withAllowableValues<std::string>({MSG_HEADER_KEEP_FIRST, MSG_HEADER_KEEP_LATEST, MSG_HEADER_COMMA_SEPARATED_MERGE})
+  ->withDefaultValue(MSG_HEADER_KEEP_LATEST)  // Mirroring NiFi behaviour
+  ->build());
+
+core::Property ConsumeKafka::MaxPollRecords(core::PropertyBuilder::createProperty("Max Poll Records")
+  ->withDescription("Specifies the maximum number of records Kafka should return when polling each time the processor is triggered.")
+  ->withDefaultValue<unsigned int>(DEFAULT_MAX_POLL_RECORDS)
+  ->build());
+
+core::Property ConsumeKafka::MaxPollTime(core::PropertyBuilder::createProperty("Max Poll Time")
+  ->withDescription("Specifies the maximum amount of time the consumer can use for polling data from the brokers. "
+      "Polling is a blocking operation, so the upper limit of this value is specified in 4 seconds.")
+  ->withDefaultValue(DEFAULT_MAX_POLL_TIME, std::make_shared<core::ConsumeKafkaMaxPollTimeValidator>(std::string("ConsumeKafkaMaxPollTimeValidator")))
+  ->isRequired(true)
+  ->build());
+
+core::Property ConsumeKafka::SessionTimeout(core::PropertyBuilder::createProperty("Session Timeout")
+  ->withDescription("Client group session and failure detection timeout. The consumer sends periodic heartbeats "
+      "to indicate its liveness to the broker. If no hearts are received by the broker for a group member within "
+      "the session timeout, the broker will remove the consumer from the group and trigger a rebalance. "
+      "The allowed range is configured with the broker configuration properties group.min.session.timeout.ms and group.max.session.timeout.ms.")
+  ->withDefaultValue<core::TimePeriodValue>("60 seconds")
+  ->build());
+
+const core::Relationship ConsumeKafka::Success("success", "Incoming kafka messages as flowfiles. Depending on the demarcation strategy, this can be one or multiple flowfiles per message.");
+
+void ConsumeKafka::initialize() {
+  setSupportedProperties({
+    KafkaBrokers,
+    SecurityProtocol,
+    TopicNames,
+    TopicNameFormat,
+    HonorTransactions,
+    GroupID,
+    OffsetReset,
+    KeyAttributeEncoding,
+    MessageDemarcator,
+    MessageHeaderEncoding,
+    HeadersToAddAsAttributes,
+    DuplicateHeaderHandling,
+    MaxPollRecords,
+    MaxPollTime,
+    SessionTimeout
+  });
+  setSupportedRelationships({
+    Success,
+  });
+}
+
+void ConsumeKafka::onSchedule(core::ProcessContext* context, core::ProcessSessionFactory* /* sessionFactory */) {

Review comment:
       Ideally the processor would take references and then this would not be a problem, but since we need to take pointers here (for JNI support IIRC), the next possible safe solution is a wide contract with preconditions.




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