Add a Connect toolbar item linking to the request's trace

When plain.toolbar is installed and connect is exporting, a Trace
button links the current request to its `/t/<trace_id>` page in Plain
Cloud (or shows "Not sampled" when the trace was dropped). Adds the
CONNECT_DASHBOARD_URL setting for the dashboard base URL, and a shared
current_trace() helper used by both the toolbar item and pageviews.

Author: davegaeddert

plain-connect/plain/connect/templates.py

@@ -4,13 +4,13 @@
 from urllib.parse import quote
 
 from jinja2.runtime import Context
-from opentelemetry import trace
 
 from plain.runtime import settings
 from plain.templates import register_template_extension, register_template_global
 from plain.templates.jinja.extensions import InclusionTagExtension
 
 from .identity import encrypt_identity, sign_render_token
+from .tracing import current_trace
 
 if TYPE_CHECKING:
     from plain.http import Request
@@ -43,7 +43,7 @@ def get_context(
             "connect_pageviews_identity": _identity_token(request, secret)
             if token
             else "",
-            "connect_pageviews_trace_id": _current_trace_id() if token else "",
+            "connect_pageviews_trace_id": current_trace().trace_id if token else "",
             "connect_pageviews_route": _current_route(request) if token else "",
         }
 
@@ -89,10 +89,3 @@ def _identity_token(request: Request | None, secret: str) -> str:
     if user is None:
         return ""
     return encrypt_identity(user.id, secret)
-
-
-def _current_trace_id() -> str:
-    span_context = trace.get_current_span().get_span_context()
-    if not span_context.trace_id:
-        return ""
-    return format(span_context.trace_id, "032x")

plain-connect/plain/connect/toolbar.py

@@ -2,22 +2,21 @@
 
 from typing import Any
 
-from opentelemetry import trace
-from opentelemetry.trace import format_trace_id
-
 from plain.runtime import settings
 from plain.toolbar import ToolbarItem, register_toolbar_item
 
+from .tracing import current_trace
+
 
 @register_toolbar_item
 class ConnectToolbarItem(ToolbarItem):
     """Links the current request to its exported trace in Plain Cloud.
 
     This module is only imported when plain.toolbar is installed (it is
-    autodiscovered by the toolbar package), so the import above is safe
-    without a guard. The item is a button-only toolbar entry — no panel —
-    that points at the `/t/<trace_id>` short URL on the dashboard, which
-    resolves the trace back to its app and redirects.
+    autodiscovered by the toolbar package), so the `plain.toolbar` import
+    above is safe without a guard. The item is a button-only toolbar entry —
+    no panel — that points at the `/t/<trace_id>` short URL on the dashboard,
+    which resolves the trace back to its app and redirects.
     """
 
     name = "Connect"
@@ -30,19 +29,11 @@ def is_enabled(self) -> bool:
     def get_template_context(self) -> dict[str, Any]:
         context = super().get_template_context()
 
-        span_context = trace.get_current_span().get_span_context()
-        if not span_context.is_valid:
-            context["sampled"] = None
-            context["trace_url"] = ""
-            return context
-
-        # The sampled flag reflects the final sampling decision, so a
-        # sub-1.0 CONNECT_TRACE_SAMPLE_RATE is accounted for here for free.
-        context["sampled"] = span_context.trace_flags.sampled
-        if span_context.trace_flags.sampled:
+        trace = current_trace()
+        context["sampled"] = trace.sampled
+        if trace.sampled:
             dashboard_url = str(settings.CONNECT_DASHBOARD_URL).rstrip("/")
-            trace_id = format_trace_id(span_context.trace_id)
-            context["trace_url"] = f"{dashboard_url}/t/{trace_id}"
+            context["trace_url"] = f"{dashboard_url}/t/{trace.trace_id}"
         else:
             context["trace_url"] = ""
 

plain-connect/plain/connect/tracing.py

@@ -0,0 +1,34 @@
+from __future__ import annotations
+
+from dataclasses import dataclass
+
+from opentelemetry import trace
+from opentelemetry.trace import format_trace_id
+
+
+@dataclass(frozen=True)
+class CurrentTrace:
+    """The active request's OpenTelemetry trace, as connect needs it.
+
+    `trace_id` is the 32-char hex id, or "" when there is no valid trace —
+    connect only installs an SDK tracer provider when export is configured,
+    so without a token requests get no-op spans with an all-zero id.
+
+    `sampled` is the final sampling decision (so a sub-1.0
+    CONNECT_TRACE_SAMPLE_RATE is accounted for here for free), or None when
+    there is no valid trace.
+    """
+
+    trace_id: str
+    sampled: bool | None
+
+
+def current_trace() -> CurrentTrace:
+    """Read the active span's trace id and sampling decision."""
+    span_context = trace.get_current_span().get_span_context()
+    if not span_context.is_valid:
+        return CurrentTrace(trace_id="", sampled=None)
+    return CurrentTrace(
+        trace_id=format_trace_id(span_context.trace_id),
+        sampled=span_context.trace_flags.sampled,
+    )