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. If no port is passed, it will listen on the REST port of 8091 (and will fail if you already have a Couchbase Server running).

By default, the mock will be up and running with the default bucket.

Once the mock has been started, it may be used like a normal Couchbase server, with clients bootstrapping over HTTP using the port specified as --port.

java -jar CouchbaseMock-1.4.7.jar --port 9000

and then in another console:

cbc cat foo -U http://localhost:9000

If you are using CouchbaseMock in automated testing, the test application should open up a control port, pass that port to the mock using the --harakiri-monitor argument and set --port to 0. The randomly assigned HTTP port will be received on the control port once. See the Out of Band Commands section below.

Supported Couchbase Operations

Memcached (Key-Value)

• 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

Administrative REST API

These standard REST API endpoints are supported. See the Couchbase Administration manual for how to use these endpoints. These behave exactly as they would against a real Couchbase cluster.

The username and password are hard-coded into the mock as Administrator and password respectively.

• /pools (GET)
• /pools/default (GET)
• /pools/default/buckets (GET, POST) - allows for bucket creation
• /pools/default/buckets/$bucket (GET, DELETE) - allows for bucket deletion
• /pools/default/buckets/$bucket/ddocs (GET) - allows for listing design documents
• /pools/default/bucketsStreaming/$bucket (GET) - streaming config URI
• /sampleBuckets/install (POST) - allows loading the beer-sample bucket. Note that this endpoint seems to be undocumented.

Note that only SASL-auth buckets may be created. This does not necessarily mean that your bucket must have a password. For example:

curl -XPOST -u Administrator:password \
    localhost:8091/pools/default/buckets \
    -d bucketType=couchbase \
    -d name=newbucket \
    -d authType=sasl \
    -d ramQuotaMB=200

Will create a bucket without a password.

Additionally note that the ramQuotaMB must be specified, though other than being necessary for conforming to server behavior, has no effect.

Views (Map-Reduce)

The following rest endpoints are supported. Note that the view query port (e.g. the capi port) is the same as the administrative port. This should not matter for conforming clients which determine this information from the cluster configuration endpoint.

Both map and reduce functions are supported. Javascript support is provided using Rhino, so view functions which depend on V8-specific functionality may fail.

The beer-sample bucket is available in the mock and may be loaded by passing the -S option on the commandline. It may also be loaded in-situ by using the /sampleBuckets/install REST API, for example:

curl -u Administrator:password localhost:8091/sampleBuckets/install \
    -X POST \
    -H "Content-Type: application/json" \
    -d '["beer-sample"]'

Accessing views may be done by the following endpoints:

• /$bucket/_design/$ddoc (PUT, GET, DELETE) - used to create or remove design documents
• /$bucket/_design/$ddoc/_view/$view - to query a view

The following view parameters are recognized and have effect

• skip
• limit
• reduce
• group
• group_level
• startkey
• startkey_docid
• endkey
• endkey_docid
• key
• keys
• inclusive_start (NOTE: not in Couchbase)
• inclusive_end
• descending
• debug (returns dummy debug info)

The full_set and stale options are ignored.

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

SET_ENHANCED_ERRORS

This command enables or disables Enhanced Error Messages semantics for a group of servers. See SDK-RFC-28 for details.

Parameters:

Name	Meaning	Type
enabled	Whether to enable or disabled Enhanced Errors on the selection criteria	JSON Boolean
bucket	Bucket for which Enhanced Errors 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

SET_COMPRESSION

This command sets compression mode for the group of servers. See SDK-RFC-30 for details.

Parameters:

Name	Meaning	Type
mode	Operating mode for the server: "off", "passive", "active" (see spec for details). It also has extra mode "disabled", which makes mock to behave like it does not know Snappy at all.	String
bucket	Bucket for which Enhanced Errors 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

Retry Verification Commands

The mock can verify whether a client library is properly retrying commands. To use this feature, your client must have the XERROR feature enabled and implemented.

The usage overview is this:

1. Setup retry verification recording before running your test
2. Instruct the mock to inject failures (using the OPFAIL command), which will trigger the retry. Note that you can inject failures using other means as well (e.g. internally at the client level)
3. Execute your operations with failure injection enabled (per step 2)
4. Once the operations are done, request the mock to verify behavior. This will also implicitly undo whatever setup was done in step 1.

You can set up retry verification using the START_RETRY_VERIFY command. This command requires the server index and the bucket name to use for verification.

Because the precise server index must be known, you will need to determine the vBucket for the key that will be used in the commands.

# Pseudo code
test_key = "HelloWorld"
vbucket = vbucket_map(test_key)
server = server_map(vbucket)

In order to trigger the correct error retry behavior, you will need to use special error return codes which are further defined in the Mock itself. If the client is properly implemented and functioning correctly, it should not have explicit knowledge of these error codes - but should be handled dynamically by using the corresponding entry in the error map.

The error codes are:

• 0x7ff0 - defines a constant retry strategy
• 0x7ff1 - defines a linear retry strategy
• 0x7ff2 - defines an exponential retry strategy.

You should test with all three error codes to verify that the client can correctly handle all three strategies.

Then set up the OPFAIL command to be directed towards the correct server:

cmd = {
    'command': 'OPFAIL',
    'payload': {
        'servers': [server],
        'bucket': 'default',
        'count': 100,
        'code': 0x7ff1
    }
}

And then set up the START_RETRY_VERIFY command.

cmd = {
    'command': 'START_RETRY_VERIFY',
    'payload': {
        'idx': server,  # Numeric index of server
        'bucket': 'default'
    }
}

Note that START_RETRY_VERIFY only tells the server to start recording command logs.

Once the OPFAIL is sent, any command directed to the specified servers will cause the server to return the error code specified. For the purposes of testing, a simple GET (0x00) command should suffice to trigger the error behavior.

The command should eventually fail on the client side - after multiple internal retries by the client.

Once the client has failed the command, you should query the mock to determine if the client had behaved as expected. This is done using the CHECK_RETRY_VERIFY command.

The CHECK_RETRY_VERIFY command requires the server index (from above), the error, and the opcode of the test operation. If verification succeeded, the command will return success, and if it failed, it will return an error with some additional information.

The format of CHECK_RETRY_VERIFY is:

'command': {
    'payload': {
        'idx': server,
        'bucket': 'default',
        'errcode': 0x7ff1,
        'opcode': 0x00
    }
}

The mock uses three basic tests to determine if the retries were done according to spec.

1. The first retry should be within after (+/- fuzz) ms of the first error response.
2. The spacing between each interval should be as prescribed (strategy dependent)
3. The last retry should not exceed past (+/- fuzz) ms of the max-duration interval from the receipt of the first error.

The "fuzz" is defined as 10ms. Fuzz is required because not all operating environments (virtual machines, interpreters, clocks, etc.) can guarantee accuracy/resolution within 1 ms.

In the following example, conformance to the constant strategy is verified. We will assume that the clock begins at 0 ms

Here is the spec:

{
    "strategy": "constant",
    "max-duration": 500,
    "interval": 10,
    "after": 50
}

• 0ms: Client receives error response
• 53ms: After waiting ~50ms, the client sends the first retry. This should be within fuzz+after of first error response.
• 60ms: After waiting ~10ms, the client sends the next retry. This should be within fuzz+interval of the previous retry attempt.
• 69ms: Retry
• 75ms: Retry ....
• 484ms: Client sends retry...
• 497ms: Client sends last retry. Should be within interval+fuzz of +500ms (Time since first error response)

Verifying this with linear or exponential retries is similar. Here's an example for linear retry:

{
    "strategy": "linear",
    "max-duration": 500,
    "interval": 10,
    "after": 50,
    "ceil": 200
}

• 0ms: Client receives error response
• 55ms: Client sends first retry
• 62ms: Client sends next retry (interval is 10ms)
• 87ms: Client sends next retry (interval is now 20ms)
• 109ms: Client sends next retry (interval is now 30ms)
• 142ms: Client sends next retry (interval is now 40ms)
• 195ms: Client sends next retry (interval is now 50ms)
• 256ms: Client sends next retry (interval is now 60ms) ...