[Issue 304][Reader] fixed panic in CreateReader API using custom MessageID for ReaderOptions

[nitishv]

Fixes #304

Motivation

User of the client's client's CreateReader API can use a custom type satisfying the MessageID interface, when using it as a value for StartMessageID in ReaderOptions argument for the mentioned API.

The current reader creation does an untested type assertion here, when preparing the consumerOptions needed for creating a partitionConsumer.
https://github.com/apache/pulsar-client-go/blob/master/pulsar/reader_impl.go#L64

This assertion of MessageID as *messageID will fail unless an instance of MessageID is created from one of these exported APIs because messageID is unexported
https://github.com/apache/pulsar-client-go/blob/master/pulsar/message.go#L114-#L126
Note: newMessageID returns *messageID which satisfies MessageID interface as well.

Modifications

Test the type assertion of MessageID as *messageID, if it fails, re-create a new MessageID using this

pulsar-client-go/pulsar/impl_message.go

Line 97 in 975eb37

func deserializeMessageID(data []byte) (MessageID, error) {

This will ensure that the custom type can be re-created as a *messageID which can be used by partitionConsumerOpts

Verifying this change

• Make sure that the change passes the CI checks.

This change added tests and can be verified as follows:

Added unit test TestReaderOnSpecificMessageWithCustomMessageID in github.com/apache/pulsar-client-go/pulsar package.
Test uses a custom StartMessageID in ReaderOptions while creating a new reader to read from a specific message ID, rather than the pre-canned earliest/latest options.

CI script test result snippet below.

-- Ready to start tests
+ go test -race -coverprofile=/tmp/coverage -timeout=20m ./...
?       github.com/apache/pulsar-client-go/examples/consumer    [no test files]
?       github.com/apache/pulsar-client-go/examples/consumer-listener   [no test files]
?       github.com/apache/pulsar-client-go/examples/producer    [no test files]
?       github.com/apache/pulsar-client-go/examples/reader      [no test files]
ok      github.com/apache/pulsar-client-go/integration-tests    1.732s  coverage: 0.0% of statements
?       github.com/apache/pulsar-client-go/perf [no test files]

ok      github.com/apache/pulsar-client-go/pulsar       141.199s        coverage: 81.2% of statements
ok      github.com/apache/pulsar-client-go/pulsar/internal      1.658s  coverage: 30.7% of statements
ok      github.com/apache/pulsar-client-go/pulsar/internal/auth 1.028s  coverage: 31.3% of statements
ok      github.com/apache/pulsar-client-go/pulsar/internal/compression  1.041s  coverage: 55.7% of statements
?       github.com/apache/pulsar-client-go/pulsar/internal/pulsar_proto [no test files]
+ go tool cover -html=/tmp/coverage -o coverage.html

Does this pull request potentially affect one of the following parts:

• Dependencies (does it add or upgrade a dependency): no
• The public API: yes
• The schema: no
• The default values of configurations: no
• The wire protocol: no

Documentation

• Does this pull request introduce a new feature? : No

[nitishv]

@wolfstudy @sijie @Ghatage please have a look

[wolfstudy]

Cool, Thanks @nitishv work for this, LGTM +1

[Ghatage]

Great stuff @nitishv! Excited to have you involved in the Pulsar community!