feat: add get_query_param utility method to support pagination

Author: Mike Kistler

ibm_cloud_sdk_core/__init__.py

@@ -29,6 +29,7 @@
     string_to_date: De-serializes a string to a date.
     convert_model: Convert a model object into an equivalent dict.
     convert_list: Convert a list of strings into comma-separated string.
+    get_query_param: Return a query parameter value from a URL
     read_external_sources: Get config object from external sources.
     get_authenticator_from_environment: Get authenticator from external sources.
 """
@@ -42,4 +43,5 @@
 from .utils import datetime_to_string, string_to_datetime, read_external_sources
 from .utils import date_to_string, string_to_date
 from .utils import convert_model, convert_list
+from .utils import get_query_param
 from .get_authenticator import get_authenticator_from_environment

ibm_cloud_sdk_core/utils.py

@@ -19,6 +19,7 @@
 from os import getenv, environ, getcwd
 from os.path import isfile, join, expanduser
 from typing import List, Union
+from urllib.parse import urlparse, parse_qs
 
 import dateutil.parser as date_parser
 
@@ -141,6 +142,29 @@ def string_to_date(string: str) -> datetime.date:
     """
     return date_parser.parse(string).date()
 
+def get_query_param(url_str: str, param: str) -> str:
+    """Return a query parameter value from url_str
+
+    Args:
+        url_str: the URL from which to extract the query
+            parameter value
+        param: the name of the query parameter whose value
+            should be returned
+
+    Returns:
+        the value of the `param` query parameter as a string
+
+    Raises:
+        ValueError: if errors are encountered parsing `url_str`
+    """
+    if not url_str:
+        return None
+    url = urlparse(url_str)
+    if not url.query:
+        return None
+    query = parse_qs(url.query, strict_parsing=True)
+    values = query.get(param)
+    return values[0] if values else None
 
 def convert_model(val: any) -> dict:
     """Convert a model object into an equivalent dict.

test/test_utils.py

@@ -17,11 +17,13 @@
 
 import os
 import datetime
-
 from typing import Optional
+import pytest
+
 from ibm_cloud_sdk_core import string_to_datetime, datetime_to_string, get_authenticator_from_environment
 from ibm_cloud_sdk_core import string_to_date, date_to_string
 from ibm_cloud_sdk_core import convert_model, convert_list
+from ibm_cloud_sdk_core import get_query_param
 from ibm_cloud_sdk_core import read_external_sources
 from ibm_cloud_sdk_core.authenticators import BasicAuthenticator, IAMAuthenticator
 
@@ -122,6 +124,46 @@ def test_date_conversion():
     assert res == '2017-03-06'
     assert date_to_string(None) is None
 
+def test_get_query_param():
+    # Relative URL
+    next_url = '/api/v1/offerings?start=foo&limit=10'
+    page_token = get_query_param(next_url, 'start')
+    assert page_token == 'foo'
+    # Absolute URL
+    next_url = 'https://acme.com/api/v1/offerings?start=bar&limit=10'
+    page_token = get_query_param(next_url, 'start')
+    assert page_token == 'bar'
+    # Missing param
+    next_url = 'https://acme.com/api/v1/offerings?start=bar&limit=10'
+    page_token = get_query_param(next_url, 'token')
+    assert page_token is None
+    # No URL
+    page_token = get_query_param(None, 'start')
+    assert page_token is None
+    # Empty URL
+    page_token = get_query_param('', 'start')
+    assert page_token is None
+    # No query string
+    next_url = '/api/v1/offerings'
+    page_token = get_query_param(next_url, 'start')
+    assert page_token is None
+    # Bad query string
+    next_url = '/api/v1/offerings?start%XXfoo'
+    with pytest.raises(ValueError):
+        page_token = get_query_param(next_url, 'start')
+    # Duplicate param
+    next_url = '/api/v1/offerings?start=foo&start=bar&limit=10'
+    page_token = get_query_param(next_url, 'start')
+    assert page_token == 'foo'
+    # Bad URL - since the behavior for this case varies based on the version of Python
+    # we allow _either_ a ValueError or that the illegal chars are just ignored
+    next_url = 'https://foo.bar\u2100/api/v1/offerings?start=foo'
+    try:
+        page_token = get_query_param(next_url, 'start')
+        assert page_token == 'foo'
+    except ValueError:
+        # This is okay.
+        pass
 
 def test_convert_model():
     class MockModel: