python-swiftclient API

The python-swiftclient includes two levels of API. A low level client API that provides simple python wrappers around the various authentication mechanisms, the individual HTTP requests, and a high level service API that provides methods for performing common operations in parallel on a thread pool.

This document aims to provide guidance for choosing between these APIs and examples of usage for the service API.

Important Considerations

This section covers some important considerations, helpful hints, and things to avoid when integrating an object store into your workflow.

An Object Store is not a filesystem

Important

It cannot be stressed enough that your usage of the object store should reflect the use case, and not treat the storage like a filesystem.

There are 2 main restrictions to bear in mind here when designing your use of the object store:

1. Objects cannot be renamed due to the way in which objects are stored and references by the object store. This usually requires multiple copies of the data to be moved between physical storage devices. As a result, a move operation is not provided. If the user wants to move an object they must re-upload to the new location and delete the original.
2. Objects cannot be modified. Objects are stored in multiple locations and are checked for integrity based on the MD5 sum calculated during upload. Object creation is a 1-shot event, and in order to modify the contents of an object the entire new contents must be re-uploaded. In certain special cases it is possible to work around this restriction using large objects, but no general file-like access is available to modify a stored object.

The swiftclient.Connection API

A low level API that provides methods for authentication and methods that correspond to the individual REST API calls described in the swift documentation.

For usage details see the client docs: swiftclient.client.

The swiftclient.SwiftService API

A higher level API aimed at allowing developers an easy way to perform multiple operations asynchronously using a configurable thread pool. Documentation for each service method call can be found here: swiftclient.service.

Configuration

When you create an instance of a SwiftService, you can override a collection of default options to suit your use case. Typically, the defaults are sensible to get us started, but depending on your needs you might want to tweak them to improve performance (options affecting large objects and thread counts can significantly alter performance in the right situation).

Service level defaults and some extra options can also be overridden on a per-operation (or even in some cases per-object) basis, and you will call out which options affect which operations later in the document.

The configuration of the service API is performed using an options dictionary passed to the SwiftService during initialisation. The options available in this dictionary are described below, along with their defaults:

Options

retries: 5

The number of times that the library should attempt to retry HTTP actions before giving up and reporting a failure.

container_threads: 10

object_dd_threads: 10

object_uu_threads: 10

segment_threads: 10

The above options determine the size of the available thread pools for performing swift operations. Container operations (such as listing a container) operate in the container threads, and a similar pattern applies to object and segment threads.

Note

Object threads are separated into two separate thread pools: uu and dd. This stands for “upload/update” and “download/delete”, and the corresponding actions will be run on separate threads pools.

segment_size: None

If specified, this option enables uploading of large objects. Should the object being uploaded be larger than 5G in size, this option is mandatory otherwise the upload will fail. This option should be specified as a size in bytes.

use_slo: False

Used in combination with the above option, use_slo will upload large objects as static rather than dynamic. Only static large objects provide error checking for the downloaded object, so we recommend this option.

segment_container: None

Allows the user to select the container into which large object segments will be uploaded. We do not recommend changing this value as it could make locating orphaned segments more difficult in the case of errors.

leave_segments: False

Setting this option to true means that when deleting or overwriting a large object, its segments will be left in the object store and must be cleaned up manually. This option can be useful when sharing large object segments between multiple objects in more advanced scenarios, but must be treated with care, as it could lead to ever increasing storage usage.

changed: None

This option affects uploads and simply means that those objects which already exist in the object store will not be overwritten if the mtime and size of the source is the same as the existing object.

skip_identical: False

A slightly more thorough case of the above, but rather than mtime and size uses an object’s MD5 sum.

yes_all: False

This options affects only download and delete, and in each case must be specified in order to download/delete the entire contents of an account. This option has no effect on any other calls.

no_download: False

This option only affects download and means that all operations proceed as normal with the exception that no data is written to disk.

header: []

Used with upload and post operations to set headers on objects. Headers are specified as colon separated strings, e.g. “content-type:text/plain”.

meta: []

Used to set metadata on an object similarly to headers.

Note

Setting metadata is a destructive operation, so when updating one of many metadata values all desired metadata for an object must be re-applied.

long: False

Affects only list operations, and results in more metrics being made available in the results at the expense of lower performance.

fail_fast: False

Applies to delete and upload operations, and attempts to abort queued tasks in the event of errors.

prefix: None

Affects list operations; only objects with the given prefix will be returned/affected. It is not advisable to set at the service level, as those operations that call list to discover objects on which they should operate will also be affected.

delimiter: None

Affects list operations, and means that listings only contain results up to the first instance of the delimiter in the object name. This is useful for working with objects containing ‘/’ in their names to simulate folder structures.

dir_marker: False

Affects uploads, and allows empty ‘pseudofolder’ objects to be created when the source of an upload is None.

shuffle: False

When downloading objects, the default behaviour of the CLI is to shuffle lists of objects in order to spread the load on storage drives when multiple clients are downloading the same files to multiple locations (e.g. in the event of distributing an update). When using the SwiftService directly, object downloads are scheduled in the same order as they appear in the container listing. When combined with a single download thread this means that objects are downloaded in lexically-sorted order. Setting this option to True gives the same shuffling behaviour as the CLI.

Other available options can be found in swiftclient/service.py in the source code for python-swiftclient. Each SwiftService method also allows for an optional dictionary to override those specified at init time, and the appropriate docstrings show which options modify each method’s behaviour.

Authentication

This section covers the various options for authenticating with a swift object store. The combinations of options required for each authentication version are detailed below.

Version 1.0 Auth

auth_version: environ.get('ST_AUTH_VERSION')

auth: environ.get('ST_AUTH')

user: environ.get('ST_USER')

key: environ.get('ST_KEY')

Version 2.0 and 3.0 Auth

auth_version: environ.get('ST_AUTH_VERSION')

os_username: environ.get('OS_USERNAME')

os_password: environ.get('OS_PASSWORD')

os_tenant_name: environ.get('OS_TENANT_NAME')

os_auth_url: environ.get('OS_AUTH_URL')

As is evident from the default values, if these options are not set explicitly in the options dictionary, then they will default to the values of the given environment variables. The SwiftService authentication automatically selects the auth version based on the combination of options specified, but having options from different auth versions can cause unexpected behaviour.

Note

Leftover environment variables are a common source of confusion when authorization fails.

Operation Return Values

Each operation provided by the service API may raise a SwiftError or ClientException for any call that fails completely (or a call which performs only one operation at an account or container level). In the case of a successful call an operation returns one of the following:

• A dictionary detailing the results of a single operation.
• An iterator that produces result dictionaries (for calls that perform multiple sub-operations).

A result dictionary can indicate either the success or failure of an individual operation (detailed in the success key), and will either contain the successful result, or an error key detailing the error encountered (usually an instance of Exception).

An example result dictionary is given below:

result = {
    'action': 'download_object',
    'success': True,
    'container': container,
    'object': obj,
    'path': path,
    'start_time': start_time,
    'finish_time': finish_time,
    'headers_receipt': headers_receipt,
    'auth_end_time': conn.auth_end_time,
    'read_length': bytes_read,
    'attempts': conn.attempts
}

All the possible action values are detailed below:

[
    'stat_account',
    'stat_container',
    'stat_object',
    'post_account',
    'post_container',
    'post_object',
    'list_part',          # list yields zero or more 'list_part' results
    'download_object',
    'create_container',   # from upload
    'create_dir_marker',  # from upload
    'upload_object',
    'upload_segment',
    'delete_container',
    'delete_object',
    'delete_segment',     # from delete_object operations
    'capabilities',
]

Stat

Stat can be called against an account, a container, or a list of objects to get account stats, container stats or information about the given objects. In the first two cases a dictionary is returned containing the results of the operation, and in the case of a list of object names being supplied, an iterator over the results generated for each object is returned.

Information returned includes the amount of data used by the given object/container/account and any headers or metadata set (this includes user set data as well as content-type and modification times).

See swiftclient.service.SwiftService.stat for docs generated from the method docstring.

Valid calls for this method are as follows:

• stat([options]): Returns stats for the configured account.
• stat(<container>, [options]): Returns stats for the given container.
• stat(<container>, <object_list>, [options]): Returns stats for each of the given objects in the the given container (through the returned iterator).

Results from stat are dictionaries indicating the success or failure of each operation. In the case of a successful stat against an account or container, the method returns immediately with one of the following results:

{
    'action': 'stat_account',
    'success': True,
    'items': items,
    'headers': headers
}

{
    'action': 'stat_container',
    'container': <container>,
    'success': True,
    'items': items,
    'headers': headers
}

In the case of stat called against a list of objects, the method returns a generator that returns the results of individual object stat operations as they are performed on the thread pool:

{
    'action': 'stat_object',
    'object': <object_name>,
    'container': <container>,
    'success': True,
    'items': items,
    'headers': headers
}

In the case of a failure the dictionary returned will indicate that the operation was not successful, and will include the keys below:

{
    'action': <'stat_object'|'stat_container'|'stat_account'>,
    'object': <'object_name'>,      # Only for stat with objects list
    'container': <container>,       # Only for stat with objects list or container
    'success': False,
    'error': <error>,
    'traceback': <trace>,
    'error_timestamp': <timestamp>
}

Example

The code below demonstrates the use of stat to retrieve the headers for a given list of objects in a container using 20 threads. The code creates a mapping from object name to headers.

import logging

from swiftclient.service import SwiftService

logger = logging.getLogger()
_opts = {'object_dd_threads': 20}
with SwiftService(options=_opts) as swift:
    container = 'container1'
    objects = [ 'object_%s' % n for n in range(0,100) ]
    header_data = {}
    stats_it = swift.stat(container=container, objects=objects)
    for stat_res in stats_it:
        if stat_res['success']:
            header_data[stat_res['object']] = stat_res['headers']
        else:
            logger.error(
                'Failed to retrieve stats for %s' % stat_res['object']
            )

List

List can be called against an account or a container to retrieve the containers or objects contained within them. Each call returns an iterator that returns pages of results (by default, up to 10000 results in each page).

See swiftclient.service.SwiftService.list for docs generated from the method docstring.

If the given container or account does not exist, the list method will raise a SwiftError, but for all other success/failures a dictionary is returned. Each successfully listed page returns a dictionary as described below:

{
    'action': <'list_account_part'|'list_container_part'>,
    'container': <container>,      # Only for listing a container
    'prefix': <prefix>,            # The prefix of returned objects/containers
    'success': True,
    'listing': [Item],             # A list of results
                                   # (only in the event of success)
    'marker': <marker>             # The last item name in the list
                                   # (only in the event of success)
}

Where an item contains the following keys:

{
    'name': <name>,
    'bytes': 10485760,
    'last_modified': '2014-12-11T12:02:38.774540',
    'hash': 'fb938269cbeabe4c234e1127bbd3b74a',
    'content_type': 'application/octet-stream',
    'meta': <metadata>    # Full metadata listing from stat'ing each object
                          # this key only exists if 'long' is specified in options
}

Any failure listing an account or container that exists will return a failure dictionary as described below:

{
    'action': <'list_account_part'|'list_container_part'>,,
    'container': container,         # Only for listing a container
    'prefix': options['prefix'],
    'success': success,
    'marker': marker,
    'error': error,
    'traceback': <trace>,
    'error_timestamp': <timestamp>
}

Example

The code below demonstrates the use of list to list all items in a container that are over 10MiB in size:

container = 'example_container'
minimum_size = 10*1024**2
with SwiftService() as swift:
    try:
        stats_parts_gen = swift.list(container=container)
        for stats in stats_parts_gen:
            if stats["success"]:
                for item in stats["listing"]:
                    i_size = int(item["bytes"])
                    if i_size > minimum_size:
                        i_name = item["name"]
                        i_etag = item["hash"]
                        print(
                            "%s [size: %s] [etag: %s]" %
                            (i_name, i_size, i_etag)
                        )
            else:
                raise stats["error"]
    except SwiftError as e:
        output_manager.error(e.value)

Post

Post can be called against an account, container or list of objects in order to update the metadata attached to the given items. Each element of the object list may be a plain string of the object name, or a SwiftPostObject that allows finer control over the options applied to each of the individual post operations. In the first two cases a single dictionary is returned containing the results of the operation, and in the case of a list of objects being supplied, an iterator over the results generated for each object post is returned. If the given container or account does not exist, the post method will raise a SwiftError.

Successful metadata update results are dictionaries as described below:

{
    'action': <'post_account'|<'post_container'>|'post_object'>,
    'success': True,
    'container': <container>,
    'object': <object>,
    'headers': {},
    'response_dict': <HTTP response details>
}

Note

Updating user metadata keys will not only add any specified keys, but will also remove user metadata that has previously been set. This means that each time user metadata is updated, the complete set of desired key-value pairs must be specified.

Upload

Upload is always called against an account and container and with a list of objects to upload. Each element of the object list may be a plain string detailing the path of the object to upload, or a SwiftUploadObject that allows finer control over some aspects of the individual operations.

When a simple string is supplied to specify a file to upload, the name of the object uploaded is the full path of the specified file and the options used for the upload are those supplied to the call to upload.

Constructing a SwiftUploadObject allows the user to supply an object name for the uploaded file, and modify the options used by upload at the granularity of invidivual files.

If the given container or account does not exist, the upload method will raise a SwiftError, otherwise an iterator over the results generated for each object upload is returned.

See swiftclient.service.SwiftService.upload for docs generated from the method docstring.

For each successfully uploaded object (or object segment), the results returned by the iterator will be a dictionary as described below:

{
    'action': 'upload_object',
    'container': <container>,
    'object': <object name>,
    'success': True,
    'status': <'uploaded'|'skipped-identical'|'skipped-changed'>,
    'attempts': <attempt count>,
    'response_dict': <HTTP response details>
}

{
    'action': 'upload_segment',
    'for_container': <container>,
    'for_object': <object name>,
    'segment_index': <segment_index>,
    'segment_size': <segment_size>,
    'segment_location': <segment_path>
    'segment_etag': <etag>,
    'log_line': <object segment n>
    'success': True,
    'response_dict': <HTTP response details>,
    'attempts': <attempt count>
}

Any failure uploading an object will return a failure dictionary as described below:

{
    'action': 'upload_object',
    'container': <container>,
    'object': <object name>,
    'success': False,
    'attempts': <attempt count>,
    'error': <error>,
    'traceback': <trace>,
    'error_timestamp': <timestamp>,
    'response_dict': <HTTP response details>
}

{
    'action': 'upload_segment',
    'for_container': <container>,
    'for_object': <object name>,
    'segment_index': <segment_index>,
    'segment_size': <segment_size>,
    'segment_location': <segment_path>,
    'log_line': <object segment n>,
    'success': False,
    'error': <error>,
    'traceback': <trace>,
    'error_timestamp': <timestamp>,
    'response_dict': <HTTP response details>,
    'attempts': <attempt count>
}

Example

The code below demonstrates the use of upload to upload all files and folders in /tmp, and renaming each object by replacing /tmp in the object or directory marker names with temporary-objects:

_opts['object_uu_threads'] = 20
with SwiftService(options=_opts) as swift, OutputManager() as out_manager:
    try:
        # Collect all the files and folders in '/tmp'
        objs = []
        dir_markers = []
        dir = '/tmp':
            for (_dir, _ds, _fs) in walk(f):
                if not (_ds + _fs):
                    dir_markers.append(_dir)
                else:
                    objs.extend([join(_dir, _f) for _f in _fs])

        # Now that we've collected all the required files and dir markers
        # build the ``SwiftUploadObject``s for the call to upload
        objs = [
            SwiftUploadObject(
                o, object_name=o.replace(
                    '/tmp', 'temporary-objects', 1
                )
            ) for o in objs
        ]
        dir_markers = [
            SwiftUploadObject(
                None, object_name=d.replace(
                    '/tmp', 'temporary-objects', 1
                ), options={'dir_marker': True}
            ) for d in dir_markers
        ]

        # Schedule uploads on the SwiftService thread pool and iterate
        # over the results
        for r in swift.upload(container, objs + dir_markers):
            if r['success']:
                if 'object' in r:
                    out_manager.print_msg(r['object'])
                elif 'for_object' in r:
                    out_manager.print_msg(
                        '%s segment %s' % (r['for_object'],
                                           r['segment_index'])
                        )
            else:
                error = r['error']
                if r['action'] == "create_container":
                    out_manager.warning(
                        'Warning: failed to create container '
                        "'%s'%s", container, msg
                    )
                elif r['action'] == "upload_object":
                    out_manager.error(
                        "Failed to upload object %s to container %s: %s" %
                        (container, r['object'], error)
                    )
                else:
                    out_manager.error("%s" % error)

    except SwiftError as e:
        out_manager.error(e.value)