[bugfix] ensure timeline limit query is respected (#4141)

# Description

Fixes a bug in the new timeline code in which the limit query parameter wasn't always being fulfilled, in which case some clients like Tusky would then assume it didn't need to add a "load more" placeholder view even when there were more statuses to be loaded. This also fiddles around a bit in the logging middleware handler to add some more code comments, and add logging of full request URIs when it is safe to do so.

## Checklist

- [x] I/we have read the [GoToSocial contribution guidelines](https://codeberg.org/superseriousbusiness/gotosocial/src/branch/main/CONTRIBUTING.md).
- [x] I/we have discussed the proposed changes already, either in an issue on the repository, or in the Matrix chat.
- [x] I/we have not leveraged AI to create the proposed changes.
- [x] I/we have performed a self-review of added code.
- [x] I/we have written code that is legible and maintainable by others.
- [x] I/we have commented the added code, particularly in hard-to-understand areas.
- [ ] I/we have made any necessary changes to documentation.
- [x] I/we have added tests that cover new code.
- [x] I/we have run tests and they pass locally with the changes.
- [x] I/we have run `go fmt ./...` and `golangci-lint run`.

Reviewed-on: https://codeberg.org/superseriousbusiness/gotosocial/pulls/4141
Co-authored-by: kim <grufwub@gmail.com>
Co-committed-by: kim <grufwub@gmail.com>

internal/cache/timeline/status.go

@@ -336,6 +336,14 @@ func (t *StatusTimeline) Load(
 	limit := page.Limit
 	order := page.Order()
 	dir := toDirection(order)
+	if limit <= 0 {
+
+		// a page limit MUST be set!
+		// this shouldn't be possible
+		// but we check anyway to stop
+		// chance of limitless db calls!
+		panic("invalid page limit")
+	}
 
 	// Use a copy of current page so
 	// we can repeatedly update it.
@@ -344,11 +352,11 @@ func (t *StatusTimeline) Load(
 	nextPg.Min.Value = lo
 	nextPg.Max.Value = hi
 
-	// Interstitial meta objects.
-	var metas []*StatusMeta
+	// Preallocate slice of interstitial models.
+	metas := make([]*StatusMeta, 0, limit)
 
-	// Returned frontend API statuses.
-	var apiStatuses []*apimodel.Status
+	// Preallocate slice of required status API models.
+	apiStatuses := make([]*apimodel.Status, 0, limit)
 
 	// TODO: we can remove this nil
 	// check when we've updated all
@@ -362,13 +370,17 @@ func (t *StatusTimeline) Load(
 			return nil, "", "", err
 		}
 
+		// Load a little more than limit to
+		// reduce chance of db calls below.
+		limitPtr := util.Ptr(limit + 10)
+
 		// First we attempt to load status
 		// metadata entries from the timeline
 		// cache, up to given limit.
 		metas = t.cache.Select(
 			util.PtrIf(lo),
 			util.PtrIf(hi),
-			util.PtrIf(limit),
+			limitPtr,
 			dir,
 		)
 
@@ -384,9 +396,6 @@ func (t *StatusTimeline) Load(
 			lo = metas[len(metas)-1].ID
 			hi = metas[0].ID
 
-			// Allocate slice of expected required API models.
-			apiStatuses = make([]*apimodel.Status, 0, len(metas))
-
 			// Prepare frontend API models for
 			// the cached statuses. For now this
 			// also does its own extra filtering.
@@ -399,10 +408,10 @@ func (t *StatusTimeline) Load(
 		}
 	}
 
-	// If no cached timeline statuses
-	// were found for page, we need to
-	// call through to the database.
-	if len(apiStatuses) == 0 {
+	// If not enough cached timeline
+	// statuses were found for page,
+	// we need to call to database.
+	if len(apiStatuses) < limit {
 
 		// Pass through to main timeline db load function.
 		apiStatuses, lo, hi, err = loadStatusTimeline(ctx,
@@ -460,25 +469,31 @@ func loadStatusTimeline(
 	// vals of loaded statuses.
 	var lo, hi string
 
-	// Extract paging params.
+	// Extract paging params, in particular
+	// limit is used separate to nextPg to
+	// determine the *expected* return limit,
+	// not just what we use in db queries.
+	returnLimit := nextPg.Limit
 	order := nextPg.Order()
-	limit := nextPg.Limit
-
-	// Load a little more than
-	// limit to reduce db calls.
-	nextPg.Limit += 10
-
-	// Ensure we have a slice of meta objects to
-	// use in later preparation of the API models.
-	metas = xslices.GrowJust(metas[:0], nextPg.Limit)
-
-	// Ensure we have a slice of required frontend API models.
-	apiStatuses = xslices.GrowJust(apiStatuses[:0], nextPg.Limit)
 
 	// Perform maximum of 5 load
 	// attempts fetching statuses.
 	for i := 0; i < 5; i++ {
 
+		// Update page limit to the *remaining*
+		// limit of total we're expected to return.
+		nextPg.Limit = returnLimit - len(apiStatuses)
+		if nextPg.Limit <= 0 {
+
+			// We reached the end! Set lo paging value.
+			lo = apiStatuses[len(apiStatuses)-1].ID
+			break
+		}
+
+		// But load a bit more than
+		// limit to reduce db calls.
+		nextPg.Limit += 10
+
 		// Load next timeline statuses.
 		statuses, err := loadPage(nextPg)
 		if err != nil {
@@ -519,17 +534,8 @@ func loadStatusTimeline(
 			metas,
 			prepareAPI,
 			apiStatuses,
-			limit,
+			returnLimit,
 		)
-
-		// If we have anything, return
-		// here. Even if below limit.
-		if len(apiStatuses) > 0 {
-
-			// Set returned lo status paging value.
-			lo = apiStatuses[len(apiStatuses)-1].ID
-			break
-		}
 	}
 
 	return apiStatuses, lo, hi, nil