Merge #4126

4126: Make the experimental route /metrics activable via HTTP r=dureuill a=braddotcoffee

# Pull Request

## Related issue
Closes #4086

## What does this PR do?
- [x] Make `/metrics` available via HTTP as described in #4086 
- [x] The users can still launch Meilisearch using the `--experimental-enable-metrics` flag.
- [x] If the flag `--experimental-enable-metrics` is activated, a call to the `GET /experimental-features` route right after the launch will show `"metrics": true` even if the user has not called the `PATCH /experimental-features` route yet.
- [x] Even if the --experimental-enable-metrics flag is present at launch, calling the `PATCH /experimental-features` route with `"metrics": false` disables the experimental feature.
- [x] Update the spec
    - I was unable to find docs in this repository to update about the `/experimental-features` endpoint. I'll happily update if you point me in the right direction!

## PR checklist
Please check if your PR fulfills the following requirements:
- [x] Does this PR fix an existing issue, or have you listed the changes applied in the PR description (and why they are needed)?
- [x] Have you read the contributing guidelines?
- [x] Have you made sure that the title is accurate and descriptive of the changes?

Co-authored-by: bwbonanno <bradfordbonanno@gmail.com>
Co-authored-by: Louis Dureuil <louis@meilisearch.com>

meilisearch/tests/auth/authorization.rs

@@ -2,10 +2,12 @@ use std::collections::{HashMap, HashSet};
 
 use ::time::format_description::well_known::Rfc3339;
 use maplit::{hashmap, hashset};
+use meilisearch::Opt;
 use once_cell::sync::Lazy;
+use tempfile::TempDir;
 use time::{Duration, OffsetDateTime};
 
-use crate::common::{Server, Value};
+use crate::common::{default_settings, Server, Value};
 use crate::json;
 
 pub static AUTHORIZATIONS: Lazy<HashMap<(&'static str, &'static str), HashSet<&'static str>>> =
@@ -195,7 +197,9 @@ async fn access_authorized_master_key() {
 
 #[actix_rt::test]
 async fn access_authorized_restricted_index() {
-    let mut server = Server::new_auth().await;
+    let dir = TempDir::new().unwrap();
+    let enable_metrics = Opt { experimental_enable_metrics: true, ..default_settings(dir.path()) };
+    let mut server = Server::new_auth_with_options(enable_metrics, dir).await;
     for ((method, route), actions) in AUTHORIZATIONS.iter() {
         for action in actions {
             // create a new API key letting only the needed action.

meilisearch/tests/common/server.rs

@@ -202,6 +202,10 @@ impl Server {
     pub async fn set_features(&self, value: Value) -> (Value, StatusCode) {
         self.service.patch("/experimental-features", value).await
     }
+
+    pub async fn get_metrics(&self) -> (Value, StatusCode) {
+        self.service.get("/metrics").await
+    }
 }
 
 pub fn default_settings(dir: impl AsRef<Path>) -> Opt {
@@ -221,7 +225,7 @@ pub fn default_settings(dir: impl AsRef<Path>) -> Opt {
             skip_index_budget: true,
             ..Parser::parse_from(None as Option<&str>)
         },
-        experimental_enable_metrics: true,
+        experimental_enable_metrics: false,
         ..Parser::parse_from(None as Option<&str>)
     }
 }

meilisearch/tests/features/mod.rs

@@ -1,4 +1,7 @@
-use crate::common::Server;
+use meilisearch::Opt;
+use tempfile::TempDir;
+
+use crate::common::{default_settings, Server};
 use crate::json;
 
 /// Feature name to test against.
@@ -17,6 +20,7 @@ async fn experimental_features() {
     {
       "scoreDetails": false,
       "vectorStore": false,
+      "metrics": false,
       "exportPuffinReports": false
     }
     "###);
@@ -28,6 +32,7 @@ async fn experimental_features() {
     {
       "scoreDetails": false,
       "vectorStore": true,
+      "metrics": false,
       "exportPuffinReports": false
     }
     "###);
@@ -39,6 +44,7 @@ async fn experimental_features() {
     {
       "scoreDetails": false,
       "vectorStore": true,
+      "metrics": false,
       "exportPuffinReports": false
     }
     "###);
@@ -51,6 +57,7 @@ async fn experimental_features() {
     {
       "scoreDetails": false,
       "vectorStore": true,
+      "metrics": false,
       "exportPuffinReports": false
     }
     "###);
@@ -63,11 +70,72 @@ async fn experimental_features() {
     {
       "scoreDetails": false,
       "vectorStore": true,
+      "metrics": false,
       "exportPuffinReports": false
     }
     "###);
 }
 
+#[actix_rt::test]
+async fn experimental_feature_metrics() {
+    // instance flag for metrics enables metrics at startup
+    let dir = TempDir::new().unwrap();
+    let enable_metrics = Opt { experimental_enable_metrics: true, ..default_settings(dir.path()) };
+    let server = Server::new_with_options(enable_metrics).await.unwrap();
+
+    let (response, code) = server.get_features().await;
+
+    meili_snap::snapshot!(code, @"200 OK");
+    meili_snap::snapshot!(meili_snap::json_string!(response), @r###"
+    {
+      "scoreDetails": false,
+      "vectorStore": false,
+      "metrics": true,
+      "exportPuffinReports": false
+    }
+    "###);
+
+    let (response, code) = server.get_metrics().await;
+    meili_snap::snapshot!(code, @"200 OK");
+
+    // metrics are not returned in json format
+    // so the test server will return null
+    meili_snap::snapshot!(response, @"null");
+
+    // disabling metrics results in invalid request
+    let (response, code) = server.set_features(json!({"metrics": false})).await;
+    meili_snap::snapshot!(code, @"200 OK");
+    meili_snap::snapshot!(response["metrics"], @"false");
+
+    let (response, code) = server.get_metrics().await;
+    meili_snap::snapshot!(code, @"400 Bad Request");
+    meili_snap::snapshot!(meili_snap::json_string!(response), @r###"
+    {
+      "message": "Getting metrics requires enabling the `metrics` experimental feature. See https://github.com/meilisearch/product/discussions/625",
+      "code": "feature_not_enabled",
+      "type": "invalid_request",
+      "link": "https://docs.meilisearch.com/errors#feature_not_enabled"
+    }
+    "###);
+
+    // enabling metrics via HTTP results in valid request
+    let (response, code) = server.set_features(json!({"metrics": true})).await;
+    meili_snap::snapshot!(code, @"200 OK");
+    meili_snap::snapshot!(response["metrics"], @"true");
+
+    let (response, code) = server.get_metrics().await;
+    meili_snap::snapshot!(code, @"200 OK");
+    meili_snap::snapshot!(response, @"null");
+
+    // startup without flag respects persisted metrics value
+    let disable_metrics =
+        Opt { experimental_enable_metrics: false, ..default_settings(dir.path()) };
+    let server_no_flag = Server::new_with_options(disable_metrics).await.unwrap();
+    let (response, code) = server_no_flag.get_metrics().await;
+    meili_snap::snapshot!(code, @"200 OK");
+    meili_snap::snapshot!(response, @"null");
+}
+
 #[actix_rt::test]
 async fn errors() {
     let server = Server::new().await;
@@ -78,7 +146,7 @@ async fn errors() {
     meili_snap::snapshot!(code, @"400 Bad Request");
     meili_snap::snapshot!(meili_snap::json_string!(response), @r###"
     {
-      "message": "Unknown field `NotAFeature`: expected one of `scoreDetails`, `vectorStore`, `exportPuffinReports`",
+      "message": "Unknown field `NotAFeature`: expected one of `scoreDetails`, `vectorStore`, `metrics`, `exportPuffinReports`",
       "code": "bad_request",
       "type": "invalid_request",
       "link": "https://docs.meilisearch.com/errors#bad_request"