# 3.3.14. Master-Worker API

This section describes the master-worker interface. It covers the communication protocol of the “classic” remote Worker. Notice there are other types of workers which behave a bit differently, such as Local Worker and Latent Worker.

## 3.3.14.1. Connection

The interface is based on Twisted’s Perspective Broker, which operates over TCP connections.

The worker connects to the master, using the parameters supplied to buildbot-worker create-worker. It uses a reconnecting process with an exponential backoff, and will automatically reconnect on disconnection.

Once connected, the worker authenticates with the Twisted Cred (newcred) mechanism, using the username and password supplied to buildbot-worker create-worker. The mind behind the worker is the worker bot instance (class `buildbot_worker.pb.BotPb`).

On the master side, the realm is implemented by `buildbot.pbmanager.Dispatcher`, which examines the username of incoming avatar requests. There are special cases for `change` and `debug`, which are not discussed here. For all other usernames, the botmaster is consulted, and if a worker with that name is configured, its `buildbot.worker.Worker` instance is returned as the perspective.

## 3.3.14.2. Workers

At this point, the master-side Worker object has a pointer to the remote worker-side Bot object in its `self.worker`, and the worker-side Bot object has a reference to the master-side Worker object in its `self.perspective`.

### Bot methods

The worker-side Bot object has the following remote methods:

`remote_getCommands`

  Returns a dictionary for all commands the worker recognizes: the key of the dictionary is the command name and the command version is the value.

`remote_setBuilderList`

  Given a list of builders and their build directories, ensures that those builders, and only those builders, are running. This can be called after the initial connection is established, with a new list, to add or remove builders.

  This method returns a dictionary of `WorkerForBuilder` objects - see below.

`remote_print`

  Adds a message to the worker logfile.

`remote_getWorkerInfo`

  Returns a dictionary with the contents of the worker’s `info/` directory (i.e. file name is used as key and file contents as the value). This dictionary also contains the following keys:

  `environ`

  > copy of the workers environment

  `system`

  > OS the worker is running (extracted from Python’s `os.name`)

  `basedir`

  > base directory where the worker is running

  `numcpus`

  > number of CPUs on the worker, either as configured or as detected (since `buildbot-worker` version 0.9.0)

  `version`

  > worker’s version (same as the result of `remote_getVersion` call)

  `worker_commands`

  > worker supported commands (same as the result of `remote_getCommands` call)

`remote_getVersion`

  Returns the worker’s version.

`remote_shutdown`

  Shuts down the worker cleanly.

### Worker methods

The master-side object has the following method:

`perspective_keepalive`

  Does nothing - used to keep traffic flowing over the TCP connection

## 3.3.14.3. Setup

After the initial connection and trading of a mind (`buildbot_worker.pb.BotPb`) for an avatar (Worker), the master calls the Bot’s `setBuilderList` method to set up the proper builders on the worker side. This method returns a reference to each of the new worker-side `WorkerForBuilderPb` objects, described below. Each of these is handed to the corresponding master-side `WorkerForBuilder` object.

This immediately calls the remote `setMaster` method, and then the `print` method.

## 3.3.14.4. Pinging

To ping a remote Worker, the master calls its `print` method.

## 3.3.14.5. Building

When a build starts, the master calls the worker’s `startBuild` method. Each BuildStep instance will subsequently call the `startCommand` method, passing a reference to itself as the `stepRef` parameter. The `startCommand` method returns immediately, and the end of the command is signalled with a call to a method on the master-side BuildStep object.

## 3.3.14.6. Worker For Builders

Each worker has a set of builders which can run on it. These are represented by distinct classes on the master and worker, just like the Worker and Bot objects described above.

On the worker side, builders are represented as instances of the `buildbot_worker.pb.WorkerForBuilderPb` class. On the master side, they are represented by the `buildbot.process.workerforbuilder.WorkerForBuilder` class. The identical names are a source of confusion. The following will refer to these as the worker-side and master-side Worker For Builder classes. Each object keeps a reference to its opposite in `self.remote`.

### Worker-Side `WorkerForBuilderPb` Methods

`remote_setMaster`

  Provides a reference to the master-side Worker For Builder

`remote_print`

  Adds a message to the worker logfile; used to check round-trip connectivity

`remote_startBuild`

  Indicates that a build is about to start, and that any subsequent commands are part of that build

`remote_startCommand`

  Invokes a command on the worker side

`remote_interruptCommand`

  Interrupts the currently-running command

### Master-side `WorkerForBuilder` Methods

The master side does not have any remotely-callable methods.

## 3.3.14.7. Commands

The actual work done by the worker is represented on the master side by a `buildbot.process.remotecommand.RemoteCommand` instance.

The command instance keeps a reference to the worker-side `buildbot_worker.pb.WorkerForBuilderPb`, and calls methods like `remote_startCommand` to start new commands. Once that method is called, the `WorkerForBuilderPb` instance keeps a reference to the command, and calls the following methods on it:

### Master-Side RemoteCommand Methods

`remote_update`

  Update information about the running command. See below for the format.

`remote_complete`

  Signal that the command is complete, either successfully or with a Twisted failure.

## 3.3.14.8. Updates

Updates from the worker, sent via `remote_update`, are a list of individual update elements. Each update element is, in turn, a list of the form `[data, 0]`, where the 0 is present for historical reasons. The data is a dictionary, with keys describing the contents. The updates are handled by `remote_update`.

Updates with different keys can be combined into a single dictionary or delivered sequentially as list elements, at the worker’s option.

To summarize, an `updates` parameter to `remote_update` might look like this:

    [
        [ { 'header' : 'running command..' }, 0 ],
        [ { 'stdout' : 'abcd', 'stderr' : 'local modifications' }, 0 ],
        [ { 'log' : ( 'cmd.log', 'cmd invoked at 12:33 pm\n' ) }, 0 ],
        [ { 'rc' : 0 }, 0 ],
    ]

### Defined Commands

The following commands are defined on the workers.

#### shell

Runs a shell command on the worker. This command takes the following arguments:

`command`

> The command to run. If this is a string, it will be passed to the system shell as a string. Otherwise, it must be a list, which will be executed directly.

`workdir`

> The directory in which to run the command, relative to the builder dir.

`env`

> A dictionary of environment variables to augment or replace the existing environment on the worker. In this dictionary, `PYTHONPATH` is treated specially: it should be a list of path components, rather than a string, and will be prepended to the existing Python path.

`initial_stdin`

> A string which will be written to the command’s standard input before it is closed.

`want_stdout`

> If false, then no updates will be sent for stdout.

`want_stderr`

> If false, then no updates will be sent for stderr.

`usePTY`

> If true, the command should be run with a PTY (POSIX only). This defaults to False.

`not_really`

> If true, skip execution and return an update with rc=0.

`timeout`

> Maximum time without output before the command is killed.

`maxTime`

> Maximum overall time from the start before the command is killed.

`max_lines`

> Maximum overall produced lines by the command, then it is killed.

`logfiles`

> A dictionary specifying logfiles other than stdio. Keys are the logfile names, and values give the workdir-relative filename of the logfile. Alternately, a value can be a dictionary; in this case, the dictionary must have a `filename` key specifying the filename, and can also have the following keys:

> `follow`

> > Only follow the file from its current end-of-file, rather that starting from the beginning.

`logEnviron`

> If false, the command’s environment will not be logged.

The `shell` command sends the following updates:

`stdout`

> The data is a bytestring which represents a continuation of the stdout stream. Note that the bytestring boundaries are not necessarily aligned with newlines.

`stderr`

> Similar to `stdout`, but for the error stream.

`header`

> Similar to `stdout`, but containing data for a stream of Buildbot-specific metadata.

`rc`

> The exit status of the command, where – in keeping with UNIX tradition – 0 indicates success and any nonzero value is considered a failure. No further updates should be sent after an `rc`.

`failure_reason`

> Value is a string and describes additional scenarios when a process failed. The value of the `failure_reason` key can be one of the following:

> > - `timeout` if the command timed out due to time specified by the `maxTime` parameter being exceeded.

> > - `timeout_without_output` if the command timed out due to time specified by the `timeout` parameter being exceeded.

> > - `max_lines_failure` if the command is killed due to the number of lines specified by the `max_lines` parameter being exceeded.

`log`

> This update contains data for a logfile other than stdio. The data associated with the update is a tuple of the log name and the data for that log. Note that non-stdio logs do not distinguish output, error, and header streams.

#### uploadFile

Upload a file from the worker to the master. The arguments are

`workdir`

> Base directory for the filename, relative to the builder’s basedir.

`workersrc`

> Name of the filename to read from, relative to the workdir.

`writer`

> A remote reference to a writer object, described below.

`maxsize`

> Maximum size, in bytes, of the file to write. The operation will fail if the file exceeds this size.

`blocksize`

> The block size with which to transfer the file.

`keepstamp`

> If true, preserve the file modified and accessed times.

The worker calls a few remote methods on the writer object. First, the `write` method is called with a bytestring containing data, until all of the data has been transmitted. Then, the worker calls the writer’s `close`, followed (if `keepstamp` is true) by a call to `upload(atime, mtime)`.

This command sends `rc` and `stderr` updates, as defined for the `shell` command.

#### uploadDirectory

Similar to `uploadFile`, this command will upload an entire directory to the master, in the form of a tarball. It takes the following arguments:

`workdir` `workersrc` `writer` `maxsize` `blocksize`

> See `uploadFile` for these arguments.

`compress`

> Compression algorithm to use – one of `None`, `'bz2'`, or `'gz'`.

The writer object is treated similarly to the `uploadFile` command, but after the file is closed, the worker calls the master’s `unpack` method with no arguments to extract the tarball.

This command sends `rc` and `stderr` updates, as defined for the `shell` command.

#### downloadFile

This command will download a file from the master to the worker. It takes the following arguments:

`workdir`

> Base directory for the destination filename, relative to the builder basedir.

`workerdest`

> Filename to write to, relative to the workdir.

`reader`

> A remote reference to a reader object, described below.

`maxsize`

> Maximum size of the file.

`blocksize`

> The block size with which to transfer the file.

`mode`

> Access mode for the new file.

The reader object’s `read(maxsize)` method will be called with a maximum size, which will return no more than that number of bytes as a bytestring. At EOF, it will return an empty string. Once EOF is received, the worker will call the remote `close` method.

This command sends `rc` and `stderr` updates, as defined for the `shell` command.

#### mkdir

This command will create a directory on the worker. It will also create any intervening directories required. It takes the following argument:

`dir`

> Directory to create.

The `mkdir` command produces the same updates as `shell`.

#### rmdir

This command will remove a directory or file on the worker. It takes the following arguments:

`dir`

> Directory to remove.

`timeout` `maxTime`

> See `shell` above.

The `rmdir` command produces the same updates as `shell`.

#### cpdir

This command will copy a directory from one place to another place on the worker. It takes the following arguments:

`fromdir`

> Source directory for the copy operation, relative to the builder’s basedir.

`todir`

> Destination directory for the copy operation, relative to the builder’s basedir.

`timeout` `maxTime`

> See `shell` above.

The `cpdir` command produces the same updates as `shell`.

#### stat

This command returns status information about a file or directory. It takes a single parameter, `file`, specifying the filename relative to the builder’s basedir.

It produces two status updates:

`stat`

> The return value from Python’s `os.stat`.

`rc`

> 0 if the file is found, otherwise 1.

#### glob

This command finds all pathnames matching a specified pattern that uses shell-style wildcards. It takes a single parameter, `path`, specifying the pattern to pass to Python’s `glob.glob` function.

It produces two status updates:

`files`

> The list of matching files returned from `glob.glob`

`rc`

> 0 if the `glob.glob` does not raise exception, otherwise 1.

#### listdir

This command reads the directory and returns the list with directory contents. It takes a single parameter, `dir`, specifying the directory relative to the builder’s basedir.

It produces two status updates:

`files`

> The list of files in the directory returned from `os.listdir`

`rc`

> 0 if the `os.listdir` does not raise exception, otherwise 1.

#### rmfile

This command removes the file in the worker base directory. It takes a single parameter, `path`, specifying the file path relative to the builder’s basedir.

It produces one status update:

`rc`

> 0 if the `os.remove` does not raise exception, otherwise the corresponding errno.