Add session.clientdata; allow access to input names via dir()

CHANGELOG.md

@@ -17,6 +17,10 @@ and this project adheres to [Semantic Versioning](https://semver.org/spec/v2.0.0
 
 * `shiny create` includes new and improved `ui.Chat()` template options. Most of these templates leverage the new [`{chatlas}` package](https://posit-dev.github.io/chatlas/), our opinionated approach to interfacing with various LLM. (#1806)
 
+* Client data values (e.g., url info, output sizes/styles, etc.) can now be accessed in the server-side Python code via `session.clientdata`, which is collection of reactive `Inputs`. For example, `session.clientdata.url_search()` reactively reads the URL search parameters. See [this PR](https://github.com/posit-dev/py-shiny/pull/1832) for a more complete example. (#1832)
+
+* Available `input` ids can now be listed via `dir(input)`. This also works on the new `session.clientdata` object. (#1832)
+
 ### Bug fixes
 
 * `ui.Chat()` now correctly handles new `ollama.chat()` return value introduced in `ollama` v0.4. (#1787)

shiny/session/_session.py

@@ -170,6 +170,7 @@ class Session(ABC):
     id: str
     input: Inputs
     output: Outputs
+    clientdata: Inputs
     user: str | None
     groups: list[str] | None
 
@@ -519,6 +520,7 @@ def __init__(
 
         self.input: Inputs = Inputs(dict())
         self.output: Outputs = Outputs(self, self.ns, outputs=dict())
+        self.clientdata: Inputs = Inputs(dict())
 
         self.user: str | None = None
         self.groups: list[str] | None = None
@@ -692,7 +694,12 @@ def _manage_inputs(self, data: dict[str, object]) -> None:
             # The keys[0] value is already a fully namespaced id; make that explicit by
             # wrapping it in ResolvedId, otherwise self.input will throw an id
             # validation error.
-            self.input[ResolvedId(keys[0])]._set(val)
+            k = keys[0]
+            self.input[ResolvedId(k)]._set(val)
+
+            if k.startswith(".clientdata_"):
+                k2 = k.split("_", 1)[1]
+                self.clientdata[ResolvedId(k2)]._set(val)
 
         self.output._manage_hidden()
 
@@ -1352,6 +1359,9 @@ def __contains__(self, key: str) -> bool:
         # creates a reactive dependency, and returns whether the value is set.
         return self[key].is_set()
 
+    def __dir__(self):
+        return list(self._map.keys())
+
 
 # ======================================================================================
 # Outputs

tests/playwright/shiny/session/clientdata/app.py

@@ -0,0 +1,21 @@
+# pyright: reportUnknownMemberType=false, reportUnknownVariableType=false
+import matplotlib.pyplot as plt
+import numpy as np
+
+from shiny.express import input, render, session, ui
+
+with ui.sidebar(open="closed"):
+    ui.input_slider("obs", "Number of observations:", min=0, max=1000, value=500)
+
+
+@render.code
+def clientdatatext():
+    cdata = session.clientdata
+    return "\n".join([f"{name} = {cdata[name]()}" for name in reversed(dir(cdata))])
+
+
+@render.plot
+def myplot():
+    plt.figure()
+    plt.hist(np.random.normal(size=input.obs()))  # type: ignore
+    plt.title("This is myplot")

tests/playwright/shiny/session/clientdata/test_clientdata.py

@@ -0,0 +1,25 @@
+import re
+
+from playwright.sync_api import Page
+
+from shiny.playwright import controller
+from shiny.run import ShinyAppProc
+
+
+def test_output_image_kitchen(page: Page, local_app: ShinyAppProc) -> None:
+
+    page.goto(local_app.url)
+
+    text = controller.OutputTextVerbatim(page, "clientdatatext")
+
+    # This doesn't cover all the clientdata values since some of them
+    # are environment-dependent. However, this at least checks that the
+    # clientdata object is available and that some values are present.
+    text.expect.to_contain_text("url_protocol = http")
+    text.expect.to_contain_text("url_pathname = /")
+    text.expect.to_contain_text(
+        re.compile("url_hostname = (localhost|127\\.0\\.0\\.1)")
+    )
+    text.expect.to_contain_text("output_myplot_hidden = False")
+    text.expect.to_contain_text("output_myplot_bg = rgb(255, 255, 255)")
+    text.expect.to_contain_text("output_clientdatatext_hidden = False")