Add admin commands to get and reset tracing filters

book/changelog.md

@@ -261,9 +261,10 @@ This will be the first release of Grapevine since it was forked from Conduit
    ([!46](https://gitlab.computer.surgery/matrix/grapevine/-/merge_requests/46))
 10. Recognize the `!admin` prefix to invoke admin commands.
     ([!45](https://gitlab.computer.surgery/matrix/grapevine/-/merge_requests/45))
-11. Add the `set-tracing-filter` admin command to change log/metrics/flame
+11. Add the `tracing-filter` admin command to view and change log/metrics/flame
     filters dynamically at runtime.
-    ([!49](https://gitlab.computer.surgery/matrix/grapevine/-/merge_requests/49))
+    ([!49](https://gitlab.computer.surgery/matrix/grapevine/-/merge_requests/49),
+    [!164](https://gitlab.computer.surgery/matrix/grapevine/-/merge_requests/164))
 12. Add more configuration options.
     ([!49](https://gitlab.computer.surgery/matrix/grapevine/-/merge_requests/49))
     * `observability.traces.filter`: The `tracing` filter to use for

src/config/env_filter_clone.rs

@@ -15,7 +15,7 @@ use tracing_subscriber::EnvFilter;
 /// Use [`FromStr`] or [`Deserialize`] to construct this type, then [`From`] or
 /// [`Into`] to convert it into an [`EnvFilter`] when needed.
 #[derive(Debug, Clone)]
-pub(crate) struct EnvFilterClone(String);
+pub(crate) struct EnvFilterClone(pub(crate) String);
 
 impl FromStr for EnvFilterClone {
     type Err = <EnvFilter as FromStr>::Err;

src/observability.rs

@@ -21,6 +21,7 @@ use opentelemetry_sdk::{
     Resource,
 };
 use strum::{AsRefStr, IntoStaticStr};
+use thiserror::Error;
 use tokio::time::Instant;
 use tracing::{subscriber::SetGlobalDefaultError, Span};
 use tracing_flame::{FlameLayer, FlushGuard};
@@ -78,9 +79,67 @@ impl<L, S> ReloadHandle<L> for reload::Handle<L, S> {
     }
 }
 
-/// A type-erased [reload handle][reload::Handle] for an [`EnvFilter`].
-pub(crate) type FilterReloadHandle =
-    Box<dyn ReloadHandle<EnvFilter> + Send + Sync>;
+/// Error returned from [`FilterReloadHandle::set_filter()`]
+#[allow(clippy::missing_docs_in_private_items)]
+#[derive(Debug, Error)]
+pub(crate) enum SetFilterError {
+    #[error("invalid filter string")]
+    InvalidFilter(#[from] tracing_subscriber::filter::ParseError),
+    #[error("failed to reload filter layer")]
+    Reload(#[from] reload::Error),
+}
+
+/// A wrapper around a tracing filter [reload handle][reload::Handle] that
+/// remembers the filter string that was last set.
+pub(crate) struct FilterReloadHandle {
+    /// The actual [`reload::Handle`] that can be used to modify the filter
+    /// [`Layer`]
+    inner: Box<dyn ReloadHandle<EnvFilter> + Send + Sync>,
+    /// Filter string that was last applied to `inner`
+    current_filter: String,
+    /// Filter string that was initially loaded from the configuration
+    initial_filter: String,
+}
+
+impl FilterReloadHandle {
+    /// Creates a new [`FilterReloadHandle`] from a filter string, returning the
+    /// filter layer itself and the handle that can be used to modify it.
+    pub(crate) fn new<S: tracing::Subscriber>(
+        filter: EnvFilterClone,
+    ) -> (impl tracing_subscriber::layer::Filter<S>, Self) {
+        let (layer, handle) = reload::Layer::new(EnvFilter::from(&filter));
+        let handle = Self {
+            inner: Box::new(handle),
+            current_filter: filter.0.clone(),
+            initial_filter: filter.0,
+        };
+        (layer, handle)
+    }
+
+    /// Sets the filter string for the linked filter layer. Can fail if the
+    /// filter string is invalid or when the link to the layer has been
+    /// broken.
+    pub(crate) fn set_filter(
+        &mut self,
+        filter: String,
+    ) -> Result<(), SetFilterError> {
+        self.inner.reload(filter.parse()?)?;
+        self.current_filter = filter;
+        Ok(())
+    }
+
+    /// Returns the filter string that the underlying filter layer is currently
+    /// configured for.
+    pub(crate) fn get_filter(&self) -> &str {
+        &self.current_filter
+    }
+
+    /// Returns the filter string that the underlying filter layer was
+    /// initialized with.
+    pub(crate) fn get_initial_filter(&self) -> &str {
+        &self.initial_filter
+    }
+}
 
 /// Collection of [`FilterReloadHandle`]s, allowing the filters for tracing
 /// backends to be changed dynamically. Handles may be [`None`] if the backend
@@ -153,9 +212,9 @@ where
         return Ok((None, None, None));
     }
 
-    let (filter, handle) = reload::Layer::new(EnvFilter::from(filter));
+    let (filter, handle) = FilterReloadHandle::new(filter.clone());
     let (layer, data) = init()?;
-    Ok((Some(layer.with_filter(filter)), Some(Box::new(handle)), Some(data)))
+    Ok((Some(layer.with_filter(filter)), Some(handle), Some(data)))
 }
 
 /// Initialize observability

src/service/admin.rs

@@ -1,6 +1,6 @@
 use std::{collections::BTreeMap, fmt::Write, sync::Arc, time::Instant};
 
-use clap::{Parser, ValueEnum};
+use clap::{Parser, Subcommand, ValueEnum};
 use regex::Regex;
 use ruma::{
     api::appservice::Registration,
@@ -205,10 +205,41 @@ enum AdminCommand {
     VerifyJson,
 
     /// Dynamically change a tracing backend's filter string
-    SetTracingFilter {
+    TracingFilter {
+        #[command(subcommand)]
+        cmd: TracingFilterCommand,
+    },
+}
+
+#[derive(Debug, Subcommand)]
+enum TracingFilterCommand {
+    Get {
+        backend: TracingBackend,
+    },
+    Set {
         backend: TracingBackend,
         filter: String,
     },
+    Reset {
+        backend: TracingBackend,
+    },
+}
+
+impl TracingFilterCommand {
+    fn backend(&self) -> &TracingBackend {
+        match self {
+            TracingFilterCommand::Get {
+                backend,
+            }
+            | TracingFilterCommand::Set {
+                backend,
+                ..
+            }
+            | TracingFilterCommand::Reset {
+                backend,
+            } => backend,
+        }
+    }
 }
 
 #[derive(Debug)]
@@ -1167,9 +1198,8 @@ impl Service {
                     )
                 }
             }
-            AdminCommand::SetTracingFilter {
-                backend,
-                filter,
+            AdminCommand::TracingFilter {
+                cmd,
             } => {
                 let Some(handles) = &services().globals.reload_handles else {
                     return Ok(RoomMessageEventContent::text_plain(
@@ -1177,7 +1207,7 @@ impl Service {
                     ));
                 };
                 let mut handles = handles.write().await;
-                let handle = match backend {
+                let handle = match cmd.backend() {
                     TracingBackend::Log => &mut handles.log,
                     TracingBackend::Flame => &mut handles.flame,
                     TracingBackend::Traces => &mut handles.traces,
@@ -1187,15 +1217,27 @@ impl Service {
                         "Backend is disabled",
                     ));
                 };
-                let filter = match filter.parse() {
-                    Ok(filter) => filter,
-                    Err(e) => {
+
+                let filter = match cmd {
+                    TracingFilterCommand::Set {
+                        filter,
+                        ..
+                    } => filter,
+                    TracingFilterCommand::Reset {
+                        ..
+                    } => handle.get_initial_filter().to_owned(),
+                    TracingFilterCommand::Get {
+                        ..
+                    } => {
                         return Ok(RoomMessageEventContent::text_plain(
-                            format!("Invalid filter string: {e}"),
+                            format!(
+                                "Current filter string: {}",
+                                handle.get_filter()
+                            ),
                         ));
                     }
                 };
-                if let Err(e) = handle.reload(filter) {
+                if let Err(e) = handle.set_filter(filter) {
                     return Ok(RoomMessageEventContent::text_plain(format!(
                         "Failed to reload filter: {e}"
                     )));