Web Services

The CRDS servers support a JSONRPC based service mechanism which enables remote users to make calls to the CRDS server without installing the CRDS Python based client library. See http://json-rpc.org/wiki/specification for more details on the JSONRPC protocol.

Users of the CRDS client library can access these JSONRPC functions using the crds.client module:

>>> from crds import client
>>> client.get_default_context('jwst')

Context Information

The CRDS context is the version of CRDS rules used to select reference files. The default CRDS context is maintained on the CRDS server and reported by the function get_default_context(). Institutional pipelines which are operating decoupled from the CRDS server can post their actual cached context to the CRDS server for retrieval by get_remote_context().

Centralized Default


get_default_context() returns the name of the context which is currently in use by default in the archive pipeline, e.g. ‘jwst_0001.pmap’. This value is set and maintained on the CRDS Server. The actual pipeline context differs from this commanded valuer until the pipeline is synchronized with the CRDS server using cron_sync.

The commanded default can be obtained using the CRDS client library as follows:

 >>> from CRDS import client
 >>> client.get_default_context('jwst')

See the explanation of JSONRPC requests and responses below for a language and library neutral example of calling the same CRDS web service using the command line program “curl”.

Pipeline Echo

get_remote_context(observatory, pipeline_name)

get_remote_context() returns the name of the context last reported as synced by the specified pipeline_name (e.g. ‘jwst-ops-pipeline’). This is the value stored in a pipeline’s CRDS cache and echoed back to the CRDS server when the cache is synchronized. Since this value is inapplicable if a pipeline is run in “remote” mode computing best references on the CRDS Server, the generally preferred value is from get_default_context() since it always reflects the intended operational context regardless of the pipeline’s CRDS mode.

The actual default context for a pipeline can be obtained as follows:

 >>> from CRDS import client
 >>> client.get_remote_context('jwst', 'jwst-ops-pipeline')

Context History

CRDS makes the history of contexts which have been activated in the pipeline as the operational context via the get_context_history() web service:

>>> client.get_context_history("jwst")
[('2012-09-06 00:00:00', 'jwst.pmap', 'Bootstrap mappings'),
 ('2012-09-27 00:00:00',
  'First rules and references from jwst_gentools stub development cloning.'),
 ('2013-04-13 00:00:00', 'jwst_0001.pmap', 'Linearity and dark files.'),
 ('2013-07-31 00:00:00', 'jwst_0002.pmap', 'Dark and Mask files.'),
 ('2013-09-04 00:00:00',
  'Absolute Calibration (photom) additions and replacements.'),
 ('2013-11-25 09:00:03', 'jwst_0005.pmap', 'set by system'),
 ('2014-03-19 10:51:19',
  'Updated for META.INSTRUMENT.TYPE switch to META.INSTRUMENT.NAME\r\nNew linearity files for all instruments\r\nNew saturation files and rmaps for all instruments'),


 ('2015-11-18 12:58:13',
  'Declared various EXP_TYPE as N/A for 15 WCS types for MIRI, NIRCAM, NIRSPEC. Replacement MIRI distortion references for ticket #238.')

Each entry in the context history is a list/tuple of form: (start_date, context, description).

Adjacent entries are consecutive, the start date of the one context is the end date of the previous context.

The context history is in first-to-last order and it is possible that the context will be regressed to a prior version; consequently, there is no guarantee that context names will monotonically increase. At times several file submissions and created contexts are activated en masse via the last created context; consequently, there is no guarantee that pmap serial numbers will increase or decrease by one.

File Information

The CRDS server maintains a catalog of basic metadata for the rules and reference files managed by CRDS. Catalog information cab be

Single File Metadata

get_file_info(pipeline_context, filename)

Return a dictionary of CRDS catalog information about filename. For instance:

>>> get_file_info("jwst", "jwst_miri_flat_0023.fits")
{'activation_date': '2014-09-25 18:30:27',
 'aperture': 'none',
 'blacklisted': 'false',
 'change_level': 'severe',
 'comment': 'cdp-2 from fm testing',
 'creator_name': 'jwst build 3 team',
 'deliverer_user': 'homer',
 'delivery_date': '2014-09-20 07:55:56',
 'derived_from': 'none',
 'description': 'all references from jwst build 3 delivery 2. update miri flats, fringes, straymasks, resets, lastframes, nirspec flat.',
 'filekind': 'flat',
 'instrument': 'miri',
 'name': 'jwst_miri_flat_0023.fits',
 'observatory': 'jwst',
 'pedigree': 'ground',
 'reference_file_type': 'flat',
 'rejected': 'false',
 'replaced_by_filename': '',
 'sha1sum': '3f0c92aae539cb67f8e8823cc6815130018948f7',
 'size': '10592640',
 'state': 'operational',
 'type': 'reference',
 'uploaded_as': 'jwst_miri_flat_0016.fits',
 'useafter_date': '2050-01-01 00:00:00'}

Multiple File Metadata

get_file_info_map(observatory, files=None, fields=None)

get_file_info_map() is a multi-file version of get_info_map() whihch returns the information for several files with one call. If files is not specified then get_file_info_map() returns info for all files.

Return the info:

{ filename : { info, ... }, ... }

on files of observatory.

fields can be used to limit info returned to specified keys:

['activation_date', 'aperture', 'blacklisted', 'change_level', 'comment',
 'creator_name', 'deliverer_user', 'delivery_date', 'derived_from', 'description',
 'filekind', 'instrument', 'name', 'observatory', 'pedigree', 'reference_file_type',
 'rejected', 'replaced_by_filename', 'sha1sum', 'size', 'state', 'type',
 'uploaded_as', 'useafter_date']

If fields is not specified then get_file_info_map() returns all fields.

Best References

Single Header

get_best_references(context, header, reftypes)

get_best_references() matches a set of parameters header against the lookup rules specified by the pipeline mapping context to return a mapping of type names onto recommended reference file names.

A suitable context string can be obtained from get_default_context() above, although any archived CRDS context file can be specified.

The header parameter of get_best_references is nominally a JSON object which maps CRDS parkey names onto dataset file header values. CRDS parkey names can be located by browsing reference mappings (.rmap’s) and looking at the parkey header parameter of the rmap.

For JWST, the rmap parkeys (matching parameter names) are currently specified as JWST stpipe data model dotted identifiers. Example JSON for the get_best_references header parameter for JWST is:

{ "meta.instrument.type":"fgs",
  "meta.instrument.filter":"any" }

For JWST, it is also possible to use the equivalent FITS header keyword, as defined by the data model schema, to determine best references:

{ "instrume":"fgs",
  "filter":"any" }

For HST, GEIS or FITS header keyword names are supported.

reftypes should be a json array of strings, each naming a single desired reference type. If reftypes is passed as null, recommended references for all reference types are returned. Reference types which are defined for an instrument but which are not applicable to the mode defined by header are returned with the value NOT FOUND n/a.

Example JSON for reftypes might be:


Because get_best_references determines references for a list of types, lookup errors are reported by setting the value of a reference type to “NOT FOUND ” + error_message. A value of “NOT FOUND n/a” indicates that CRDS determined that a particular reference type does not apply to the given parameter set.

Multiple Headers

get_best_references_by_header_map(context, header_map, reftypes)

This service is an adaptation of get_best_references() to support returning best references for multiple datasets with a single service call. All parameters are as for get_best_references() with the modification that header above is replaced with a mapping from multiple dataset ids to their corresponding headers, i.e. header_map:

{ dataset_id : header, ... }

The return value is likewise adapted to return best references for multiple datasets:

{ dataset_id : best_references, ... }

Where dataset_id is nominally an HST IPPPSSOOT id (e.g. ‘I9ZF01010’) or JWST dataset identifier (TBD). Since dataset_id is only a keyword not used in best references computations, it can be any unique abstract identifier consisting of alphanumeric characters, period, colon, hyphen, or plus sign of 128 characters or less.

Selection Parameters


Return a mapping from instruments to lists of parameter names required to compute bestrefs under context, i.e. matching header keys:

{ instrument : [ matching_parkey_name, ... ], ... }

In CRDS the matching parameters are defined by each set of rules, e.g. for one HST context (hst_0366.pmap) the reference file selection parameters for all instruments are as follows:

        'REFTYPE', 'SAMP_SEQ', 'TIME-OBS'],

The required parkeys can be used to reduce a complete file header to only those keywords necessary to select references under the given context.

Valid Dataset IDs

get_dataset_ids(context, instrument)

CRDS interacts with the archive to obtain matching parameters for to compute best references for particular datasets. Each parameter set corresponds to a data set ID. A list of the valid dataset IDs with respect to a particular CRDS context (or date) can be obtained as follows.

To obtain current best references specify the context using a date:

>>> get_dataset_ids("2016-01-01T00:00:00", "miri")

Alternately the abstract default context can be specified as “<project>-operational”, as in:

>>> get_dataset_ids("jwst-operational", "miri")

Dataset IDs have a grammar like this for HST:

<product_id> : <exposure_id>

Dataset IDs currently have a grammar like this for JWST:

<id>     :=  <whole>:<part>
<whole>  :=  <filesetname>:<detector>
<part>   :=  <filesetname>:<detector>

As can be seen above, currently JWST IDs are redundant and <whole> and <part> are identical. However, conceptually the IDs have that relationship and may be further elaborated and differentiated in later builds (post-jwst-build-7). In such a case, several exposure level IDs (<parts>’s) might have an identical common root (<whole>).

In both cases it’s possible to specify either half of an ID returned by get_dataset_ids() to request matching parameters or best references using the services below.

For HST requesting parameters using only the <product_id> returns the parameters associated with the full two part ID for every exposure of the product. Requesting the parameters using only the <exposure_id> returns the references associated with processing that exposure.

For JWST, conceptually the same behavior will be preserved, so while either half of an ID will currently return the same parameters, at a future date the <whole> part may return all references associated with all exposures of a single high level product, and the <part> component will only return the references associated with processing that particular exposure.

Matching Parameters By ID

get_dataset_headers_by_id(context_specifier, ids, datasets_since)

CRDS fetches best reference matching parameters indirectly from the archive database. The get_dataset_headers_by_id() function can be used to return the parameters required to compute best references associated with the specified dataset ids:

context_specifier is a date-based CRDS context specifier, e.g.: jwst_0192.pmap, 2015-05-25T00:00:27, jwst-operational

ids is a list of archive dataset id strings as shown above. A maximum of 200 IDs should be requested per call.

datasets_since is an optional cut-off date for datasets. If specified, only datasets acquired after that date are returned.

An example call using the CRDS Python client is:

>>> get_dataset_headers_by_id("2016-01-01", ['JW96090001004_03101_00001.NRCB2'], None)
{'JW96090001004_03101_00001.NRCB2': {'META.EXPOSURE.READPATT': 'BRIGHT1',

AUI Interface for Best References

get_aui_best_references(date, ids)

The CRDS server can compute the best references for a list of data set ids using the get_aui_best_references() function. The dataset ids must be compatible with those returned by get_dataset_ids() above. Examples below are fully functional at this time but actual IDs and parameter sets may change during the course of development; use get_dataset_ids() documented above to obtain up-to-date example IDs.

date is a date-based CRDS context specifier, e.g.: jwst_0192.pmap, 2015-05-25T00:00:27, jwst-operational

ids is a list of valid archive dataset ids. For JWST it’s currently natural and supported to use either half (currently identical) of the dataset IDs as specified in get_dataset_ids() above. Using a “half-ID” is shown below. Ultimately the first half will identify a group of exposures and the second half will identify a single exposure in the group. A maximum of 200 ids should be requested per call.

An examople call using the CRDS Python client is:

>>> get_aui_best_references("2016-01-01", ['JW82500001003_02102_00001.NRCA1','JW82500001003_02102_00001.NRCA3'])
{'JW82500001003_02102_00001.NRCA1': [True,
 'JW82500001003_02102_00001.NRCA3': [True,

The value returned is a mapping from dataset ids to a pair of values. The first value of the id result pair is a boolean with the sense “completed successfully”.

The second value has a variable type depending on the boolean value. If the ID was successful, the second value of the pair is a list of file names. If the ID was unsuccessful, the second value of the pair is a string describing the error:

>>> get_aui_best_references("2016-01-01", ['JW96090001004_03101_00001.NRCB5'])
{'JW96090001004_03101_00001.NRCB5': [False,
  "NOT FOUND dataset ID does not exist 'JW96090001004_03101_00001.NRCB5'"]}

Although it is possible for errors to occur on a per-type basis, for this interface specific types which result in lookup errors (e.g. flat) are dropped from the results. The net effect is that the list of files returned includes only those types that could be successfully assigned with the given context (date) and parameter set. Types which are assigned the value N/A are also silently dropped.

Under the hood the get_aui_best_references() function is a language agnostic JSONRPC call which can be called from the UNIX command line by e.g. “curl” as follows:

% curl -i -X POST -d '{"jsonrpc": "1.0", "method": "get_aui_best_references", "params": ["2016-01-01", ["JW80500017001_02101_00001.MIRIFUSHORT"]], "id": 1}' https://jwst-crds.stsci.edu/json/
HTTP/1.1 200 OK
Date: Mon, 25 Jul 2016 20:03:13 GMT
Vary: Cookie
X-Frame-Options: SAMEORIGIN
Content-Type: application/json-rpc
Via: 1.1 jwst-crds.stsci.edu
Transfer-Encoding: chunked

{"error": null, "jsonrpc": "1.0", "id": 1, "result": {"JW80500017001_02101_00001.MIRIFUSHORT": [true, ["jwst_miri_ipc_0005.fits", "jwst_miri_fringe_0018.fits", "jwst_miri_linearity_0010.fits", "jwst_miri_distortion_0010.asdf", "jwst_miri_specwcs_0003.asdf", "jwst_miri_drizpars_0001.fits", "jwst_miri_v2v3_0003.asdf", "jwst_miri_wavelengthrange_0001.asdf", "jwst_miri_regions_0003.asdf", "jwst_miri_wcsregions_0001.json", "jwst_miri_flat_0036.fits", "jwst_miri_saturation_0013.fits", "jwst_miri_photom_0011.fits", "jwst_miri_dark_0031.fits", "jwst_miri_gain_0004.fits", "jwst_miri_straymask_0006.fits", "jwst_miri_reset_0018.fits", "jwst_miri_lastframe_0018.fits", "jwst_miri_mask_0013.fits", "jwst_miri_readnoise_0005.fits"]]}}

Interface for Calibration S/W Versions

get_system_versions(master_version, context)

The versions of calibration software components for a particular s/w release will nominally be recorded in CRDS as reference files with type CALVER looked up from a corresponding rmap using a master version string. The function of this service is really independent of that representation, but nominally one reference file will describe versions for components of one s/w release.

This get_system_versions() service will return a JSON object corresponding to the contents of the s/w versions reference file. This interface should not however be construed as the definition of the file contents.

master_version is a string naming the overall version number for a calibration software release and used to select a particular versions reference file within a CRDS context.

context is a CRDS context name which is used to interpret master_version to define the versions reference file corresponding to an overall s/w release. Typically the string “null” should be used to select the current CRDS versions translation context in use in the JWST pipeline. It is anticipated that the definitions of software versions should be relatively stable and additive as new contexts are generated.

An example call using the CRDS Python client shows the conceptual nature of the interface, the functional inputs and outputs:

>>> versions_obj = get_system_versions("0.6.0noop.dev307", "null")

Printing the Python client return object in JSON format gives a more language agnostic view of the conceptual return value:

>>> print(json.dumps(versions_obj, indent=4, sort_keys=True))
"CAL_VER": "0.6.0noop.dev307",
"author": "Warren J. Hack",
"descrip": "JWST calibration processing step version reference file",
"history": "Created by cal_ver_steps version 0.7.0.dev",
"instrument": "SYSTEM",
"reftype": "CALVER",
"versions": {
     "AlignRefsStep": null,
     "AmiAnalyzeStep": "0.7.0.dev",
     "AmiAverageStep": "0.7.0.dev",
     "AmiNormalizeStep": "0.7.0.dev",
     "AssignWcsStep": null,

where ... indicates that the full contents of the object are not being displayed.

The alternative abstract context identifier “jwst-versions” may be used en lieu of “null”. The translation of the “jwst-versions” identifier is maintained on the CRDS server as a more literal context name such as “jwst_0059.pmap”. The value associated with “jwst-versions” or “null” will nominally be updated on the CRDS server whenever a new master version is defined.

The intended purpose of the “jwst-versions” tag is to name the most capable context for use in translating calibration master versions. Unlike the abstract name “jwst-operational” that describes the default context used to define calibration references, it is anticipated that “jwst-versions” will never or rarely ever revert to older versions of CRDS rules. This is because “version facts” should not in general change once they’re defined, 0.6.0 should mean the same thing in every epoch, whereas it’s valid for calibration reference assignments to change over time.

Nevertheless, in the case of anomalous situations related to CAL_VER, alternate CRDS contexts may be explicitly named to specify different rules by which to translate master version names. Alternately, the value associated with “jwst-versions” (or “null”) can be redefined on the CRDS server.

The following curl command line shows the full expansion of the same service example wrapped in the JSONRPC protocol in a language agnostic way:

curl -i -X POST -d '{"jsonrpc": "1.0", "method": "get_system_versions", "params": ["0.6.0noop.dev307","null"], "id": 1}' https://jwst-crds-dit.stsci.edu/json/
HTTP/1.1 200 OK
Date: Wed, 24 Aug 2016 22:33:04 GMT
Vary: Cookie
X-Frame-Options: SAMEORIGIN
Content-Type: application/json-rpc
Via: 1.1 jwst-crds-dit.stsci.edu
Transfer-Encoding: chunked

{"error": null, "jsonrpc": "1.0", "id": 1, "result": {"reftype": "CALVER", "author": "Warren J. Hack", "versions": {"TweakRegStep": "0.1.0", "SubtractImagesStep": null, "RSCD_Step": null, "CubeBuildStep": null, "Extract1dStep": null, "AmiAnalyzeStep": "0.7.0.dev", "Extract2dStep": null, "BackgroundStep": null, "SuperBiasStep": null, "DarkCurrentStep": null, "Combine1dStep": null, "SaturationStep": null, "LinearityStep": null, "DQInitStep": null, "ImprintStep": null, "OutlierDetectionStep": null, "AssignWcsStep": null, "KlipStep": null, "StackRefsStep": null, "TweakregCatalogStep": null, "SourceCatalogStep": null, "PersistenceStep": null, "StraylightStep": null, "IPCStep": null, "FlatFieldStep": null, "ResetStep": null, "RefPixStep": null, "ResampleStep": null, "AmiAverageStep": "0.7.0.dev", "FringeStep": null, "AlignRefsStep": null, "LastFrameStep": null, "JumpStep": null, "EmissionStep": null, "WfsCombineStep": null, "AmiNormalizeStep": "0.7.0.dev", "SkyMatchStep": "0.1.0", "PhotomStep": null, "RampFitStep": null, "HlspStep": null}, "instrument": "SYSTEM", "descrip": "JWST calibration processing step version reference file", "CAL_VER": "0.6.0noop.dev307", "history": "Created by cal_ver_steps version 0.7.0.dev"}}

This example shows the structure of a response string for a query with an error, “result” is set to null and “error” describes the problem in more detail, most notably with the response.error.message string:

% curl -i -X POST -d '{"jsonrpc": "1.0", "method": "get_system_versions", "params": ["an,invalid(version)","null"], "id": 1}' https://jwst-crds-dit.stsci.edu/json/
HTTP/1.1 200 OK
Date: Wed, 24 Aug 2016 22:23:11 GMT
Vary: Cookie
X-Frame-Options: SAMEORIGIN
Content-Type: application/json-rpc
Via: 1.1 jwst-crds-dit.stsci.edu
Transfer-Encoding: chunked

{"error": {"message": "OtherError: Invalid version string,  must be 1-128 chars of A-Z, a-z, 0-9, ., -, _", "code": 500, "data": null, "name": "OtherError"}, "jsonrpc": "1.0", "id": 1, "result": null}

JSONRPC Protocol

Sample URL’s

The base URL used for making CRDS JSONRPC method calls is essentially /json/. All further information, including the method name and the parameters, are POSTed using a JSON serialization scheme. Example absolute server URLs are:

Generic Request

JSONRPC requests are made by POST’ing a set of variables to the appropriate URL.

An example CRDS service request can be demonstrated in a language agnostic way using the UNIX command line utility curl:

% curl -i -X POST -d '{"jsonrpc": "1.0", "method": "get_default_context", "params": ["jwst"], "id": 1}' https://jwst-crds.stsci.edu/json/

The jsonrpc attribute is used to specify the version of the JSONRPC standard being used, currently 1.0 for CRDS.

The method attribute specifies the name of the service being called.

The params attribute specifies a JSON array of parameters which are passed positionally to the CRDS method.

The id can be used to associate calls with their responses in asynchronous environments.

Generic Response

The response returned by the server for the above request is the following JSON:

{"error": null, "jsonrpc": "1.0", "id": 1, "result": "jwst_0000.pmap"}

Error Handling

Fatal errors are handled by setting the error attribute of the result object to an error object. Inspect the result.error.message attribute to get descriptive text about the error.

Demo Page

The CRDS servers support demoing the JSONRPC services and calling them interactively by visiting the URL .../json/browse/. This facility is available in development and test environments upon request.

The resulting page is shown here:

jsonrpc browser demo page

An example dialog for get_best_references from the CRDS jsonrpc demo page is shown here with FITS parkey names:

>>> jsonrpc.get_best_references("jwst_0000.pmap", {'INSTRUME':'FGS','DETECTOR':'FGS1', 'FILTER':'ANY'}, null)
Requesting ->
{"id":"jsonrpc", "params":["jwst_0000.pmap", {"INSTRUME":"FGS", "DETECTOR":"FGS1", "FILTER":"ANY"}, null], "method":"get_best_references", "jsonrpc":"1.0"}
Deferred(12, unfired)
Got ->
{"error": null, "jsonrpc": "1.0", "id": "jsonrpc", "result": {"linearity": "jwst_fgs_linearity_0000.fits", "amplifier": "jwst_fgs_amplifier_0000.fits", "mask": "jwst_fgs_mask_0000.fits"}}

And the same query is here with JWST data model parkey names:

>>> jsonrpc.get_best_references("jwst_0000.pmap", {'META.INSTRUMENT.TYPE':'FGS','META.INSTRUMENT.DETECTOR':'FGS1', 'META.INSTRUMENT.FILTER':'ANY'}, null)
Requesting ->
{"id":"jsonrpc", "params":["jwst_0000.pmap", {"META.INSTRUMENT.TYPE":"FGS", "META.INSTRUMENT.DETECTOR":"FGS1", "META.INSTRUMENT.FILTER":"ANY"}, null], "method":"get_best_references", "jsonrpc":"1.0"}
Deferred(14, unfired)
Got ->
{"error": null, "jsonrpc": "1.0", "id": "jsonrpc", "result": {"linearity": "jwst_fgs_linearity_0000.fits", "amplifier": "jwst_fgs_amplifier_0000.fits", "mask": "jwst_fgs_mask_0000.fits"}}