Add filtering functionality to server list endpoint (#374)

## Summary
- Adds `updated_since`, `search`, and `version` query parameters to `GET
/v0/servers`
- Enables incremental synchronization via RFC3339 timestamp filtering
- Provides simple substring search on server names
- Supports latest version filtering with `version=latest`

This implementation provides the core filtering capabilities needed for
efficient registry synchronization and improved server discovery.

Fixes #291
Fixes #135

internal/database/database.go

@@ -3,6 +3,7 @@ package database
 import (
 	"context"
 	"errors"
+	"time"
 
 	apiv0 "github.com/modelcontextprotocol/registry/pkg/api/v0"
 )
@@ -19,8 +20,12 @@ var (
 
 // ServerFilter defines filtering options for server queries
 type ServerFilter struct {
-	Name      *string // for finding versions of same server
-	RemoteURL *string // for duplicate URL detection
+	Name          *string    // for finding versions of same server
+	RemoteURL     *string    // for duplicate URL detection
+	UpdatedSince  *time.Time // for incremental sync filtering
+	SubstringName *string    // for substring search on name
+	Version       *string    // for exact version matching
+	IsLatest      *bool      // for filtering latest versions only
 }
 
 // Database defines the interface for database operations

internal/database/memory.go

@@ -4,6 +4,7 @@ import (
 	"context"
 	"fmt"
 	"sort"
+	"strings"
 	"sync"
 
 	apiv0 "github.com/modelcontextprotocol/registry/pkg/api/v0"
@@ -164,6 +165,7 @@ func (db *MemoryDB) filterAndSort(allEntries []*apiv0.ServerJSON, filter *Server
 }
 
 // matchesFilter checks if an entry matches the provided filter
+//nolint:cyclop // Filter matching logic is inherently complex but clear
 func (db *MemoryDB) matchesFilter(entry *apiv0.ServerJSON, filter *ServerFilter) bool {
 	if filter == nil {
 		return true
@@ -188,6 +190,44 @@ func (db *MemoryDB) matchesFilter(entry *apiv0.ServerJSON, filter *ServerFilter)
 		}
 	}
 
+	// Check updatedSince filter
+	if filter.UpdatedSince != nil {
+		if entry.Meta == nil || entry.Meta.Official == nil {
+			return false
+		}
+		if entry.Meta.Official.UpdatedAt.Before(*filter.UpdatedSince) ||
+			entry.Meta.Official.UpdatedAt.Equal(*filter.UpdatedSince) {
+			return false
+		}
+	}
+
+	// Check name search filter (substring match)
+	if filter.SubstringName != nil {
+		// Case-insensitive substring search
+		searchLower := strings.ToLower(*filter.SubstringName)
+		nameLower := strings.ToLower(entry.Name)
+		if !strings.Contains(nameLower, searchLower) {
+			return false
+		}
+	}
+
+	// Check exact version filter
+	if filter.Version != nil {
+		if entry.VersionDetail.Version != *filter.Version {
+			return false
+		}
+	}
+
+	// Check is_latest filter
+	if filter.IsLatest != nil {
+		if entry.Meta == nil || entry.Meta.Official == nil {
+			return false
+		}
+		if entry.Meta.Official.IsLatest != *filter.IsLatest {
+			return false
+		}
+	}
+
 	return true
 }
 

internal/database/postgres.go

@@ -40,6 +40,7 @@ func NewPostgreSQL(ctx context.Context, connectionURI string) (*PostgreSQL, erro
 	}, nil
 }
 
+//nolint:cyclop // Database filtering logic is inherently complex but clear
 func (db *PostgreSQL) List(
 	ctx context.Context,
 	filter *ServerFilter,
@@ -71,6 +72,26 @@ func (db *PostgreSQL) List(
 			args = append(args, *filter.RemoteURL)
 			argIndex++
 		}
+		if filter.UpdatedSince != nil {
+			whereConditions = append(whereConditions, fmt.Sprintf("(value->'_meta'->'io.modelcontextprotocol.registry/official'->>'updated_at')::timestamp > $%d", argIndex))
+			args = append(args, *filter.UpdatedSince)
+			argIndex++
+		}
+		if filter.SubstringName != nil {
+			whereConditions = append(whereConditions, fmt.Sprintf("value->>'name' ILIKE $%d", argIndex))
+			args = append(args, "%"+*filter.SubstringName+"%")
+			argIndex++
+		}
+		if filter.Version != nil {
+			whereConditions = append(whereConditions, fmt.Sprintf("(value->'version_detail'->>'version') = $%d", argIndex))
+			args = append(args, *filter.Version)
+			argIndex++
+		}
+		if filter.IsLatest != nil {
+			whereConditions = append(whereConditions, fmt.Sprintf("(value->'_meta'->'io.modelcontextprotocol.registry/official'->>'is_latest')::boolean = $%d", argIndex))
+			args = append(args, *filter.IsLatest)
+			argIndex++
+		}
 	}
 
 	// Add cursor pagination using registry metadata ID