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3.3.15. Master-Worker connection with MessagePack over WebSocket protocol

Note

This is experimental protocol.

Messages between master and worker are sent using WebSocket protocol in both directions. Data to be sent conceptually is a dictionary and is encoded using MessagePack. One such encoded dictionary corresponds to one WebSocket message.

Authentication happens during opening WebSocket handshake using standard HTTP Basic authentication. Worker credentials are sent in the value of the HTTP “Authorization” header. Master checks if the credentials match and if not - the connection is terminated.

A WebSocket message can be either a request or a response. Request message is sent when one side wants another one to perform an action. Once the action is performed, the other side sends the response message back. A response message is mandatory for every request message.

3.3.15.1. Message key-value pairs

This section describes a general structure of messages. It applies for both master and worker.

Request message

A request message must contain at least these keys: seq_number , op . Additional key-value pairs may be supplied depending on the request type.

seq_number

Value is an integer. seq_number must be unique for every request message coming from a particular side. The purpose of seq_number value is to link the request message with response message. Response message will carry the same seq_number value as in corresponding request message.

op

Value is a string. It must not be response . Each side has a predefined set of commands that another side may invoke. op specifies the command to be invoked by requesting side.

Response message

A response message must contain at least these keys: seq_number , op , result .

seq_number

Value is an integer. It represents a number which was specified in the corresponding request message.

op

Value is a string, always a response .

result

Value is None when success. Otherwise – message of exception.

is_exception

This key-value pair is optional. If request succeeded this key-value pair is absent. Otherwise, its value is a boolean True and the message of exception is specified in the value of result .

3.3.15.2. Messages from master to worker

print

Request

This message requests worker to print a message to its log.

seq_number

Described in section on

Worker prints a message from master to its log.

seq_number

Described in section on

Request

Master sends this message to check if the connection is still working.

seq_number

Described in section on

Response indicates that connection is still working.

seq_number

Described in section on

Request

This message requests worker to collect and send the information about itself back to the master. Only op and seq_number values are sent, because worker does not need any additional arguments for this action.

op

Value is a string get_worker_info .

seq_number

Described in section on

op

Value is a string response .

seq_number

Described in section on

Request

Master sends this message to set worker settings. The settings must be sent from master before first command.

seq_number

Described in section on

seq_number

Described in section on

Request

This message requests worker to start a specific command. Master does not have to wait for completion of previous commands before starting a new one, so many different commands may be running in worker simultaneously.

Each start command request message has a unique command_id value.

Worker may be sending request update messages to master which update master about status of started command. When worker sends a request update message about command, the message takes a command_id value from corresponding start command request message. Accordingly master can match update messages to the commands they correspond to. When command execution in worker is completed, worker sends a request complete message to master with the command_id value of the completed command. It allows master to track which command exactly was completed.

op

Value is a string start_command .

seq_number

Described in section

op

Value is a string response .

seq_number

Described in section

Request

This message requests worker to halt the specified command.

seq_number

Described in section

During this command worker may also send back additional update messages to the master. Update messages are explained in section

Request

This message requests worker to shutdown itself. Action does not require arguments, so only op and seq_number values are sent.

seq_number

Described in section

Worker returns result : None without waiting for completion of shutdown.

op

Value is a string response .

seq_number

Described in section

update

From the start of a command till its completion, worker may be updating master about the processes of commands it requested to start. These updates are sent in an update messages.

Request

seq_number

Described in section

op

Value is a string response .

seq_number

Described in section

Request

op

Value is a string update_upload_file_write .

args

Contents of the chunk from the file that worker read.

command_id

Value is a string which identifies command the update refers to.

Response

op

Value is a string response .

seq_number

Described in section

By this command worker states that no more data will be transferred.

Request

op

Value is a string update_upload_file_close .

command_id

Value is a string which identifies command the update refers to.

Response

op

Value is a string response .

seq_number

Described in section

Request

op

Value is a string update_upload_file_utime .

access_time

Value is a floating point number. It is a number of seconds that passed from the start of the Unix epoch (January 1, 1970, 00:00:00 (UTC)) and last access of path.

modified_time

Value is a floating point number. It is a number of seconds that passed from the start of the Unix epoch (January 1, 1970, 00:00:00 (UTC)) and last modification of path.

command_id

Value is a string which identifies command the update refers to.

Response

op

Value is a string response .

seq_number

Described in section

Request

op

Value is a string update_read_file .

length

Maximum number of bytes of data to read.

command_id

Value is a string which identifies command the update refers to.

Response

op

Value is a string response .

seq_number

Described in section

By this command worker states that no more data will be transferred.

Request

op

Value is a string update_read_file_close .

command_id

Value is a string which identifies command the update refers to.

Response

op

Value is a string response .

seq_number

Described in section

Request

op

Value is a string update_upload_directory_write .

args

Contents of the chunk from the directory that worker read.

command_id

Value is a string which identifies command the update refers to.

Response

op

Value is a string response .

seq_number

Described in section

By this command worker states that no more data will be transferred.

Request

op

Value is a string update_upload_directory_unpack .

command_id

Value is a string which identifies command the update refers to.

Response

op

Value is a string response .

seq_number

Described in section

Notifies master that the remote command has finished.

Request

seq_number

Described in section

op

Value is a string response .

seq_number

Described in section

Request causes worker to start performing an action. There are multiple types of the request each supporting a particular type of worker action. The basic structure of request is the same as explained in section

Runs a shell command on the worker.

workdir

Value is a string. workdir is an absolute path and overrides the builder directory. The resulting path represents the worker directory to run the command in.

env

Value is a dictionary and is optional. It contains key-value pairs that specify environment variables for the environment in which a new command is started.

If the value is of type list, its elements are concatenated to a single string using a platform specific path separator between the elements.

If this dictionary contains “PYTHONPATH” key, path separator and “$PYTHONPATH” is appended to that value.

Resulting environment dictionary sent to the command is created following these rules:

1. If env has value for specific key and it is None , resulting dictionary does not have this key.

 

• If env has value for specific key and it is not None , resulting dictionary contains this value with substitutions applied.

 

Any matches of a pattern ${name} in this value, where name is any number of alphanumeric characters, are substituted with the value of the same key from worker environment.

3. If a specific key from worker environment is not present in env , resulting dictionary contains that key-value pair from worker environment.

want_stdout

Value is a bool and is optional. If value is not specified, the default is True . If value is True , worker sends update log messages to master from the process stdout output.

want_stderr

Value is a bool and is optional. If value is not specified, the default is True. If value is True , worker sends update log messages to the master from the process stderr output.

logfiles

Value is a dictionary and is optional. If the value is not specified, the default is an empty dictionary.

This dictionary specifies logfiles other than stdio.

Keys are the logfile names.

Worker reads this logfile and sends the data with the update message, where logfile name as a key identifies data of different logfiles.

Value is a dictionary. It contains the following keys:

filename

Value is a string. It represents the filename of the logfile, relative to worker directory where the command is run.

follow

Value is a boolean. If True - only follow the file from its current end-of-file, rather than starting from the beginning. The default is False .

timeout

Value is an integer and is optional. If value is not specified, the default is None . It represents, how many seconds a worker should wait before killing a process after it gives no output.

maxTime

Value is an integer and is optional. If value is not specified, the default is None . It represents, how many seconds a worker should wait before killing a process. Even if command is still running and giving the output, maxTime variable sets the maximum time the command is allowed to be performing. If maxTime is set to None , command runs for as long as it needs unless timeout specifies otherwise.

sigtermTime

Value is an integer and is optional. If value is not specified, the default is None . It specifies how to abort the process. If sigtermTime is not None when aborting the process, worker sends a signal SIGTERM. After sending this signal, worker waits for sigtermTime seconds of time and if the process is still alive, sends the signal SIGKILL. If sigtermTime is None , worker does not wait and sends signal SIGKILL to the process immediately.

usePTY

Value is a bool and is optional. If value is not specified, the default is False . True to use a PTY, False to not use a PTY.

logEnviron

Value is a bool and is optional. If value is not specified, the default is True . If True , worker sends to master an update message with process environment key-value pairs at the beginning of a process.

initial_stdin

Value is a string or None . If not None , the value is sent to the process as an initial stdin after process is started. If value is None , no initial stdin is sent.

command

Value is a list of strings or a string. It represents the name of a program to be started and its arguments. If this is a string, it will be invoked via /bin/sh shell by calling it as /bin/sh -c <command> . Otherwise, it must be a list, which will be executed directly.

If command succeeded, worker sends rc value 0 as an update message args key-value pair. It can also send many other update messages with keys such as header , stdout or stderr to inform about command execution. If command failed, it sends rc value with the error number.

The basic structure of worker update message is explained in section

Worker reads the contents of its file and sends them in chunks to write into the file on masters’s side.

path

Value is a string. It specifies the path of the worker file to read from.

maxsize

Value is an integer. Maximum number of bytes to transfer from the worker. The operation will fail if the file exceeds this size. Worker will send messages with data to master until it notices it exceeded maxsize .

blocksize

Value is an integer. Maximum size for each data block to be sent to master.

keepstamp

Value is a bool. It represents whether to preserve “file modified” and “accessed” times. True is for preserving.

Workers sends data to master with one or more update_upload_file_write messages. After reading the file is over, worker sends update_upload_file_close message. If keepstamp was True , workers sends update_upload_file_utime message. If command succeeded, worker sends rc value 0 as an update message args key-value pair. It can also send update messages with key header or stderr to inform about command execution.

If command failed, worker sends update_upload_file_close message and the update message with dictionary args key rc with the error number.

The basic structure of worker update message is explained in section

Similar to upload_file . This command will upload an entire directory to the master, in the form of a tarball.

path

Value is a string. It specifies the path of the worker directory to upload.

maxsize

Value is an integer. Maximum number of bytes to transfer from the worker. The operation will fail if the tarball file exceeds this size. Worker will send messages with data to master until it notices it exceeded maxsize .

blocksize

Value is an integer. Maximum size for each data block to be sent to master.

compress

Compression algorithm to use – one of None , ‘bz2’, or ‘gz’.

Worker sends data to the master with one or more update_upload_directory_write messages. After reading the directory, worker sends update_upload_directory_unpack with no arguments to extract the tarball and rc value 0 as an update message args key-value pair if the command succeeded.

Otherwise, worker sends update message with dictionary args key header with information about the error that occurred and another update message with dictionary args key rc with the error number.

The basic structure of worker update message is explained in section

Downloads a file from master to worker.

path

Value is a string. It specifies the path of the worker file to create.

maxsize

Value is an integer. Maximum number of bytes to transfer from the master. The operation will fail if the file exceeds this size. Worker will request data from master until it notices it exceeded maxsize .

blocksize

Value is an integer. It represents maximum size for each data block to be sent from master to worker.

mode

Value is None or an integer which represents an access mode for the new file.

256 - owner has read permission.

128 - owner has write permission.

64 - owner has execute permission.

32 - group has read permission.

16 - group has write permission.

8 - group has execute permission.

4 - others have read permission.

2 - others have write permission.

1 - others have execute permission.

If None , file has default permissions.

If command succeeded, worker will send rc value 0 as an update message args key-value pair.

Otherwise, worker sends update message with dictionary args key header with information about the error that occurred and another update message with dictionary args key rc with the error number.

The basic structure of worker update message is explained in section

This command reads the directory and returns the list with directory contents.

path

Value is a string. It specifies the path of a directory to list.

If command succeeded, the list containing the names of the entries in the directory given by that path is sent via update message in args key files . Worker will also send rc value 0 as an update message args key-value pair. If command failed, worker sends update message with dictionary args key header with information about the error that occurred and another update message with dictionary args key rc with the error number.

The basic structure of worker update message is explained in section

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

paths

Value is a list of strings. It specifies absolute paths of directories to create.

If command succeeded, worker will send rc value 0 as an update message args key-value pair.

Otherwise, worker sends update message with dictionary args key header with information about the error that occurred and another update message with dictionary args key rc with the error number.

The basic structure of worker update message is explained in section

This command will remove directories or files on the worker.

paths

Value is a list of strings. It specifies absolute paths of directories or files to remove.

logEnviron

Value is a bool and is optional. If value is not specified, the default is True . If True , worker sends to master an update message with process environment key-value pairs at the beginning of a process.

timeout

Value is an integer and is optional. If value is not specified, the default is 120s. It represents how many seconds a worker should wait before killing a process when it gives no output.

maxTime

Value is an integer and is optional. If value is not specified, the default is None . It represents, how many seconds a worker should wait before killing a process. Even if command is still running and giving the output, maxTime variable sets the maximum time the command is allowed to be performing. If maxTime is set to None , command runs for as long as it needs unless timeout specifies otherwise.

If command succeeded, worker sends rc value 0 as an update message args key-value pair. It can also send many update messages with key header , stdout or stderr to inform about command execution. If command failed, worker changes the permissions of a directory and tries the removal once again. If that does not help, worker sends rc value with the error number.

The basic structure of worker update message is explained in section

This command copies a directory from one place in the worker to another.

from_path

Value is a string. It specifies the absolute path to the source directory for the copy operation.

to_path

Value is a string. It specifies the absolute path to the destination directory for the copy operation.

logEnviron

Value is a bool. If True , worker sends to master an update message with process environment key-value pairs at the beginning of a process.

timeout

Value is an integer. If value is not specified, the default is 120s. It represents, how many seconds a worker should wait before killing a process if it gives no output.

maxTime

Value is an integer and is optional. If value is not specified, the default is None . It represents, how many seconds a worker should wait before killing a process. Even if command is still running and giving the output, maxTime variable sets the maximum time the command is allowed to be performing. If maxTime is set to None , command runs for as long as it needs unless timeout specifies otherwise.

If command succeeded, worker sends rc value 0 as an update message args key-value pair. It can also send many update messages with key header , stdout or `stderr` to inform about command execution. If command failed, it sends ``rc value with the error number.

The basic structure of worker update message is explained in section

This command returns status information about workers file or directory.

path

Value is a string. It specifies the path of a file or directory to get the status of.

If command succeeded, status information is sent to the master in an update message, where args has a key stat with a value of a tuple of these 10 elements:

0 - File mode: file type and file mode bits (permissions) in Unix convention.

1 - Platform dependent, but if non-zero, uniquely identifies the file for a specific device.

2 - Unique ID of disc device where this file resides.

3 - Number of hard links.

4 - ID of the file owner.

5 - Group ID of the file owner.

6 - If the file is a regular file or a symbolic link, size of the file in bytes, otherwise unspecified.

Timestamps depend on the platform:

Unix time or the time of Windows creation, expressed in seconds.

7 - time of last access in seconds.

8 - time of last data modification in seconds.

9 - time of last status change in seconds.

If command succeeded, worker also sends rc value 0 as an update message args key-value pair.

Otherwise, worker sends update message with dictionary args key header with information about the error that occurred and another update message with dictionary args key rc with the error number.

The basic structure of worker update message is explained in section

Worker sends to the master a possibly-empty list of path names that match shell-style path specification.

path

Value is a string. It specifies a shell-style path pattern. Path pattern can contain shell-style wildcards and must represent an absolute path.

If command succeeded, the result is sent to the master in an update message, where args has a key file with the value of that possibly-empty path list. This path list may contain broken symlinks as in the shell. It is not specified whether path list is sorted.

Worker also sends rc value 0 as an update message args key-value pair.

Otherwise, worker sends update message with dictionary args key header with information about the error that occurred and another update message with dictionary args key rc with the error number.

The basic structure of worker update message is explained in section

This command removes the specified file.

path

Value is a string. It specifies a path of a file to delete.

If command succeeded, worker sends rc value 0 as an update message args key-value pair.

Otherwise, worker sends update message with dictionary args key header with information about the error that occurred and another update message with dictionary args key rc with the error number.

The basic structure of worker update message is explained in section

The args key-value pair describes information that the request message sends to master. The value is a list of lists. Each sub-list contains a name-value pair and represents a single update. First element in a list represents the name of update (see below) and second element represents its value. Commands may have their own update names so only common ones are described here.

stdout

Value is a standard output of a process as a string. Some of the commands that master requests worker to start, may initiate processes which output a result as a standard output and this result is saved in the value of stdout . The value satisfies the requirements described in a section below.

rc

Value is an integer. It represents an exit code of a process. 0 if the process exit was successful. Any other number represents a failure.

header

Value is a string of a header. It represents additional information about how the command worked. For example, information may include the command name and arguments, working directory and environment or various errors or warnings of a process or other information that may be useful for debugging. The value satisfies the requirements described in a section below.

files

Value is a list of strings.

1. If the update message was a response to master request message start_command with a key value pair command_name and glob , then strings in this list represent path names that matched pathname given by the master.

 

• If the update message was a response to master request message start_command with a key value pair command_name and listdir , then strings in this list represent the names of the entries in the directory given by path, which master sent as an argument.

 

stderr

Value is a standard error of a process as a string. Some of the commands that master requests worker to start may initiate processes which can output a result as a standard error and this result is saved in the value of stderr . The value satisfies the requirements described in a section below.

log

Value is a list where the first element represents the name of the log and the second element is a list, representing the contents of the file. The composition of this second element is described in the section below. This message is used to transfer the contents of the file that master requested worker to read. This file is identified by the name of the log. The same value is sent by master as the key of dictionary represented by logfile key within args dictionary of StartCommand command.

elapsed

Value is an integer. It represents how much time has passed between the start of a command and the completion in seconds.

Requirements for content lists of stdout , stderr , header and log

The lists that represents the contents of the output or a file consist of three elements.

First element is a string with the content, which must be processed using the following algorithm:

• Each value may contain one or more lines (characters with a terminating \n character).

  Each line is not longer than internal maxsize value on worker side. Longer lines are split into multiple lines where each except the last line contains exactly maxsize characters and the last line may contain less.

 

• The lines are run through an internal worker cleanup regex.

 

Second element is a list of indexes, representing the positions of newline characters in the string of first tuple element.

Third element is a list of numbers, representing at what time each line was received as an output while processing the command.

The number of elements in both lists is always the same.