CouchbaseMock - The Couchbase Test Server

CouchbaseMock is a test server implementing some of the memcached protocol which is used by some SDKs (including the C SDK) for basic testing. While it is recommended that testing be done against the real server, CouchbaseMock is useful as being self contained (there is no need to install it to the system) and for allowing extra instrumentation.

CouchbaseMock is implemented in Java and is intended to be used by a single client instance. Testing with any real kind of workload has not been done, and it is not intended to be high performance or reliable (it does not even persist data to the disk). As opposed to [cbgb|http://cbgb.io], this is not intended to be a full implementation and/or replacement for the server.

The repository for CouchbaseMock may be found at https://github.com/couchbase/couchbasemock. This is a maven project and most of us use NetBeans with it.

Basic Usage

Typically the mock is spawned by passing a --port argument as the REST port to listen on, and a list of bucket specifications separated by commas. Passing --help to the CouchbaseMock should show example usage.

Once spawned, it may be used like a normal Couchbase Server. The following commands are currently implemented

• GET
• GETQ
• GAT
• GATQ
• TOUCH
• SET
• APPEND
• PREPEND
• REPLACE
• ADD
• REMOVE
• INCR/DECR
• GETL (From 0.6)
• UNL (From 0.6)
• OBSERVE (From 0.6)
• GET_REPLICA (From 0.6)
• STATS
• VERSION
• VERBOSITY

A views implementation is in progress.

Out-of-band Commands

The Out-Of-Band (OOB or Control) commands are where "special" commands can be sent to the mock to do certain things which can simulate different conditions.

OOBs are sent over the Harakiri Port. The Harakiri Port is a client-side listening port to which the mock will connect to once started up, and once the client close the connection the mock server will perform a harakiri. The normal "handshake" sequence is as follows:

Note that this can be found in tests/server.c in the libcouchbase distribution

1. The client sets up a listening address (typically on a random port -- i.e. passing 0 for sin_port).
2. Call the usual functions, i.e. socket(), bind(), and listen(). Then call getsockname() to get the newly assigned port number
3. Invoke the CouchbaseMock JAR passing the newly assigned listening port as the argument to the --harakiri-monitor option, so e.g. --harakiri-monitor=localhost:42464
4. Additionally, pass --port=0 to the JAR so that it will generate a random REST port (this way we don't have port conflicts)
5. In the client, call accept() on the harakiri port. The mock will connect to it.
6. Read from the new connection until an ASCII NUL is encountered. The data read will be a C string containing the ASCII representation of the newly assigned REST port.
7. Once the REST port has been received, you can use it in normal Couchbase/lcb_t operation to connect to the mock cluster.
8. Send/Receive additional OOB commands on the new harakiri connection established between client and mock

Command Format

The command format consists of JSON objects delimited by newlines. The JSON object will consist of the following keys.

• command: this is the name of the command
• payload: This is an object which contains the payload for the command

The response for the command will be delivered at its most basic level will be a JSON object consisting of the following fields

• status: This indicates the status of the command, it will be "ok" if the command was successful
• payload: (optional) - if there is more than a status to deliver

HTTP API

This is a lightweight API following the semantics of the JSON API; only that it uses HTTP as a transport.

The format of each command is http://localhost:18091/mock/<command>?payload\_param1=payload\_value1&...

Where is the value for the JSON command field, and the query parameters are expanded (URL-Encoded) fields within the payload.

Note that all requests (even those which modify data) use the GET method; this is to make it simple to test using a web browser.

Command Listings

The following commands are supported by the Mock. The payload for each command should contain dictionary keys corresponding to the listed Name of the parameter, and its value should conform to the specified Type.

failover

This command fails over a specific server with a given index (the index is obtained from the REST configuration). It may also be passed a bucket for which the failover should affect (if no bucket is passed, it will be default). Names in bold are required

Parameters:

Name	Meaning	Type
idx	The server index	JSON Number
bucket	The bucket to affect (`"default"`) if unspecified	JSON String

respawn

This command does the opposite of failover. Call this with the same arguments as failover to re-activate the node which was failed over.

hiccup

Schedules an artificial delay after a memcached server has sent a specific amount of data. This is intended to simulate a scenario where a server hangs or stalls after sending out a partial packet.

Parameters:

<tr>
    <td><b>msecs</b></td>
    <td>The duration of the delay in milliseconds</td>
    <td>JSON Number</td>
</tr>
<tr>
    <td><b>offset</b></td>
    <td>Stall after this many bytes have been sent</td>
    <td>JSON Number</td>
</tr>

Name	Meaning	Type

Setting both parameters to 0 disables hiccup

truncate

Chops off data from the end of each packet. As a result it means invalid data will be sent to the client (this may also be used in conjunction with failover to simulate a node sending partial data and then disconnecting)

Parameters:

Name	Meaning	Type
limit	Limit the next write operation to this many bytes	JSON Number

Setting the limit to 0 disables truncate

OpFail

Causes a number of memcached operations to unconditionally fail with a specific error code. This may be used to simulate simple 'OOM' or NOT_MY_VBUCKET errors.

Paramters:

Name	Meaning	Type
code	The Memcached protocol code to force	JSON Number; Must also be recognized by the Mock
count	The number of times this error code should be sent before normal operation is restored. This can be either a positive number (which indicates that this many operations should fail before restoring to normal operation), 0 (which means that normal behavior be restored immediately) or a negative number, in which case commands will fail indefinitely until a 0 is sent again with this command	JSON Number
servers	A list of servers to apply this setting to. Servers are specified as indices into the server array. By default, all servers are used	JSON Number

Time Travel

This command moves the internal clock in the server. The primary purpose for this is to allow the clients to test TTL without having to "sleep". Names in bold are required

Parameters:

Name	Meaning	Type
Offset	The number of seconds to add to the internal clock	JSON Number

SET_CCCP

This command enables or disables CCCP protocol semantics for a group of servers.

Parameters:

Name	Meaning	Type
enabled	Whether to enable or disabled CCCP on the selection criteria	JSON Boolean
bucket	Bucket for which CCCP should be enabled/disabled. If this is empty, then this command affects all buckets	String
servers	An array of server indices for which the enable/disable setting should apply to. If this is not set, then all servers are modified	Array of numbers

GET_MCPORTS

This is a more convenient way to get the memcached ports without parsing the entire vBucket config. This is particularly useful for libcouchbase' tests which at the time of writing don't have access to a simple HTTP implementation

Parameters:

Name	Meaning	Type
bucket	Which bucket to use. If unspecified, default is used	string

The response shall contain in the payload field a JSON array of integers containing port numbers (relative to the Mock's listening addresses) which may be used as memcached ports.

keyinfo

This command returns the information about a given key in the mock server. Names in bold are required

Parameters:

Name	Meaning	Type
key	The key to access	JSON String
Bucket	The bucket in which the key resides	Optional. String. If not specified, "default" is used

The payload contains a JSON object containing the per-node status of a given key. The base object is a JSON array ([]). Each element in the array is a JSON object containing three fields.

The nodes are ordered according to the server list received in the vBucket configuration.

If the server is neither a replica nor a master for the given key, it is present as null.

• Conf: Configuration information about this node in relation to the keys' vBucket. This is a JSON object containing two subfields:

  • Index - the server index in the vBucket map for the given vBucket. If this is a master, the index will be 0
  • Type - Either master or replica

• Cache: This is a JSON object containing the status of the key as it resides in the node's Cache. If the item is not present within the node's cache, the object is empty; otherwise it contains these subfields:

  • CAS The CAS value of the key as present within the storage domain
  • Value the actual value of the key

• Disk: This carries the same semantics as Cache, only that it displays information relating to the node's Disk storage domain.

Key Access Commands

Concepts

Starting with 0.6, the Mock introduces actual storage layers to emulate those of an actual cluster. Specifically, a cluster has one or more nodes, where each node retains a key in both its volatile memory (Cache) and persistent storage (Disk). While from a user perspective this process tends to be transparent, the distinction makes itself known when operating on things such as views (where indices are built from "persisted" items only) and the various OBSERVE and/or durability/persistence-requirement commands as well as get-from-replica.

Note that Cache and Disk represent abstract concepts in the Mock. At the time of writing, the Mock does not actually write anything to the disk, but merely contains a separate storage domain for "Disk".

Thus, whenever an item is stored in the mock it may go through the following steps:

1. The item is inserted into the vBucket master's Cache
2. The item is inserted into the vBucket master's Disk
3. For each vBucket replica, the item is placed inside its Cache
4. For each vBucket replica, the item is placed inside its Disk

Common Parameters

These out-of-band commands allow to modify or retrieve information on a specific key.

They all accept a set of common parameters

Name	Meaning	Type
Key	The key to access	JSON String
OnMaster	Whether to affect the key on the vBucket master	JSON Boolean
OnReplicas	Which replicas should be affected	This can either be a number indicating how many replicas to affect; or it can be a list of specific replica indices to affect
CAS	The new CAS to use	Optional. Number. If not specified, the existing CAS (if the key already exists) of each key entry in its respective storage partition will be used. Otherwise a new CAS is generated
Value	The new value to use	Optional. String. If not specified the items value will be an empty string
Bucket	The bucket in which the key resides	Optional. String. If not specified, "default" is used

Below is a list of commands which accept these common parameters

Commands

persist

This command will store an item to one or more nodes' Disk storage domain. The nodes affected depend on the OnMaster and OnReplicas parameters

unpersist

Remove an item from the Disk storage domain from the selected nodes

cache

Store an item to one or more nodes' Cache

uncache

Remove an item from one or more nodes' Cache

endure

For each affected node, store the item to its Disk and Cache stores. This is equivalent to calling persist and cache on the same item

purge

For each affected node, remove the item from both its Disk and Cache stores. This is equivalent to calling uncache and unpersist on the same item