chore(docs): update package docs for internal/homepage

internal/homepage/README.md

@@ -1,6 +1,6 @@
 # Homepage
 
-The homepage package provides the GoDoxy WebUI dashboard with support for categories, favorites, widgets, and dynamic item configuration.
+The homepage package provides the GoDoxy WebUI dashboard with support for categories, favorites, widgets, dynamic item configuration, and icon management.
 
 ## Overview
 
@@ -194,18 +194,6 @@ Widgets can display various types of information:
 - **Links**: Quick access links
 - **Custom**: Provider-specific data
 
-## Icon Handling
-
-Icons are handled via `IconURL` type:
-
-```go
-type IconURL struct {
-    // Icon URL with various sources
-}
-
-// Automatic favicon fetching from item URL
-```
-
 ## Categories
 
 ### Default Categories

internal/homepage/icons/README.md

@@ -0,0 +1,491 @@
+# Icons Package
+
+Icon URL parsing, fetching, and listing for the homepage dashboard.
+
+## Overview
+
+The icons package manages icon resources from multiple sources with support for light/dark variants and multiple image formats. It provides a unified API for parsing icon URLs, checking icon availability, fetching icon data, and searching available icons from CDN repositories.
+
+### Purpose
+
+- Parse and validate icon URLs from various sources
+- Fetch icon data with caching and fallback strategies
+- Maintain a searchable index of available icons from walkxcode and selfh.st CDNs
+- Support light/dark theme variants and multiple image formats (SVG, PNG, WebP)
+
+### Primary Consumers
+
+- `internal/homepage/` - Homepage route management and icon assignment
+- `internal/api/` - Icon search and listing API endpoints
+- `internal/route/` - Route icon resolution for proxy targets
+
+### Non-goals
+
+- Icon generation or modification (only fetching)
+- Authentication for remote icon sources (public CDNs only)
+- Icon validation beyond format checking
+
+### Stability
+
+This package exposes a stable public API. Internal implementations (caching strategies, fetch logic) may change without notice.
+
+## Concepts and Terminology
+
+| Term         | Definition                                                                            |
+| ------------ | ------------------------------------------------------------------------------------- |
+| **Source**   | The origin type of an icon (absolute URL, relative path, walkxcode CDN, selfh.st CDN) |
+| **Variant**  | Theme variant: none, light, or dark                                                   |
+| **Key**      | Unique identifier combining source and reference (e.g., `@walkxcode/nginx`)           |
+| **Meta**     | Metadata describing available formats and variants for an icon                        |
+| **Provider** | Interface for checking icon existence without fetching data                           |
+
+## Public API
+
+### Exported Types
+
+#### Source
+
+Source identifies the origin of an icon. Use the constants defined below.
+
+```go
+type Source string
+
+const (
+    // SourceAbsolute is a full URL (http:// or https://)
+    SourceAbsolute Source = "https://"
+
+    // SourceRelative is a path relative to the target service (@target or leading /)
+    SourceRelative Source = "@target"
+
+    // SourceWalkXCode is the walkxcode dashboard-icons CDN
+    SourceWalkXCode Source = "@walkxcode"
+
+    // SourceSelfhSt is the selfh.st icons CDN
+    SourceSelfhSt Source = "@selfhst"
+)
+```
+
+#### Variant
+
+Variant indicates the theme preference for icons that support light/dark modes.
+
+```go
+type Variant string
+
+const (
+    VariantNone  Variant = ""     // Default, no variant suffix
+    VariantLight Variant = "light" // Light theme variant (-light suffix)
+    VariantDark  Variant = "dark"  // Dark theme variant (-dark suffix)
+)
+```
+
+#### URL
+
+URL represents a parsed icon URL with its source and metadata.
+
+```go
+type URL struct {
+    // Source identifies the icon origin
+    Source `json:"source"`
+
+    // FullURL contains the resolved URL for absolute/relative sources
+    FullURL *string `json:"value,omitempty"`
+
+    // Extra contains metadata for CDN sources (walkxcode/selfhst)
+    Extra *Extra `json:"extra,omitempty"`
+}
+```
+
+**URL Methods:**
+
+- `Parse(v string) error` - Parses an icon URL string (implements `strutils.Parser`)
+- `URL() string` - Returns the absolute URL for fetching
+- `HasIcon() bool` - Checks if the icon exists (requires Provider to be set)
+- `WithVariant(variant Variant) *URL` - Returns a new URL with the specified variant
+- `String() string` - Returns the original URL representation
+- `MarshalText() ([]byte, error)` - Serializes to text (implements `encoding.TextMarshaler`)
+- `UnmarshalText(data []byte) error` - Deserializes from text (implements `encoding.TextUnmarshaler`)
+
+#### Extra
+
+Extra contains metadata for icons from CDN sources.
+
+```go
+type Extra struct {
+    // Key is the unique icon key
+    Key Key `json:"key"`
+
+    // Ref is the icon reference name (without variant suffix)
+    Ref string `json:"ref"`
+
+    // FileType is the image format: "svg", "png", or "webp"
+    FileType string `json:"file_type"`
+
+    // IsLight indicates if this is a light variant
+    IsLight bool `json:"is_light"`
+
+    // IsDark indicates if this is a dark variant
+    IsDark bool `json:"is_dark"`
+}
+```
+
+#### Key
+
+Key is a unique identifier for an icon from a specific source.
+
+```go
+type Key string
+
+// NewKey creates a key from source and reference
+func NewKey(source Source, reference string) Key
+
+// SourceRef extracts the source and reference from a key
+func (k Key) SourceRef() (Source, string)
+```
+
+#### Meta
+
+Meta stores availability metadata for an icon.
+
+```go
+type Meta struct {
+    // Available formats
+    SVG  bool `json:"SVG"`  // SVG format available
+    PNG  bool `json:"PNG"`  // PNG format available
+    WebP bool `json:"WebP"` // WebP format available
+
+    // Available variants
+    Light bool `json:"Light"` // Light variant available
+    Dark  bool `json:"Dark"`  // Dark variant available
+
+    // DisplayName is the human-readable name (selfh.st only)
+    DisplayName string `json:"-"`
+
+    // Tag is the category tag (selfh.st only)
+    Tag string `json:"-"`
+}
+
+// Filenames returns all available filename variants for this icon
+func (icon *Meta) Filenames(ref string) []string
+```
+
+### Exported Functions
+
+```go
+// NewURL creates a URL for a CDN source with the given reference and format
+func NewURL(source Source, refOrName, format string) *URL
+
+// ErrInvalidIconURL is returned when icon URL parsing fails
+var ErrInvalidIconURL = gperr.New("invalid icon url")
+```
+
+### Provider Interface
+
+```go
+type Provider interface {
+    // HasIcon returns true if the icon exists in the provider's catalog
+    HasIcon(u *URL) bool
+}
+
+// SetProvider sets the global icon provider for existence checks
+func SetProvider(p Provider)
+```
+
+The provider pattern allows the icons package to check icon existence without fetching data. The `list` subpackage registers a provider that checks against the cached icon list.
+
+## Architecture
+
+### Core Components
+
+```mermaid
+graph TD
+    subgraph icons/
+        URL["URL"] --> Parser[URL Parser]
+        URL --> VariantHandler[Variant Handler]
+        Key --> Provider
+    end
+
+    subgraph fetch/
+        FetchFavIconFromURL --> FetchIconAbsolute
+        FetchFavIconFromURL --> FindIcon
+        FindIcon --> fetchKnownIcon
+        FindIcon --> findIconSlow
+        fetchKnownIcon --> FetchIconAbsolute
+    end
+
+    subgraph list/
+        InitCache --> updateIcons
+        updateIcons --> UpdateWalkxCodeIcons
+        updateIcons --> UpdateSelfhstIcons
+        SearchIcons --> fuzzyRank[Fuzzy Rank Match]
+        HasIcon --> ListAvailableIcons
+    end
+
+    style URL fill:#22553F,color:#fff
+    style list fill:#22553F,color:#fff
+    style fetch fill:#22553F,color:#fff
+```
+
+### Component Interactions
+
+1. **URL Parsing** (`url.go`): Parses icon URL strings and validates format
+2. **Icon Existence** (`provider.go`): Delegates to registered Provider
+3. **Icon Fetching** (`fetch/fetch.go`): Fetches icon data with caching
+4. **Icon Listing** (`list/list_icons.go`): Maintains cached index of available icons
+
+### Data Flow
+
+```mermaid
+sequenceDiagram
+    participant Client
+    participant URLParser
+    participant Provider
+    participant FetchCache
+    participant ExternalCDN
+
+    Client->>URLParser: Parse("@walkxcode/nginx.svg")
+    URLParser->>Provider: HasIcon(icon)
+    Provider->>FetchCache: Check cached list
+    FetchCache-->>Provider: exists
+    Provider-->>URLParser: true
+    URLParser-->>Client: URL object
+
+    Client->>FetchCache: FetchFavIconFromURL(url)
+    FetchCache->>ExternalCDN: GET https://...
+    ExternalCDN-->>FetchCache: icon data
+    FetchCache-->>Client: Result{Icon: [...], StatusCode: 200}
+```
+
+## Subpackages
+
+### fetch/
+
+Icon fetching implementation with caching and fallback strategies.
+
+```go
+type Result struct {
+    Icon       []byte  // Raw icon image data
+    StatusCode int     // HTTP status code from fetch
+}
+
+// FetchFavIconFromURL fetches an icon from a parsed URL
+func FetchFavIconFromURL(ctx context.Context, iconURL *URL) (Result, error)
+
+// FindIcon finds an icon for a route with variant support
+func FindIcon(ctx context.Context, r route, uri string, variant Variant) (Result, error)
+```
+
+**Key behaviors:**
+
+- `FetchIconAbsolute` is cached with 200 entries and 4-hour TTL
+- `findIconSlow` has infinite retries with 15-second backoff
+- HTML parsing fallback extracts `<link rel=icon>` from target pages
+
+### list/
+
+Icon catalog management with search and caching.
+
+```go
+type IconMap map[Key]*Meta
+type IconMetaSearch struct {
+    *Meta
+    Source Source `json:"Source"`
+    Ref    string `json:"Ref"`
+    rank   int
+}
+
+// InitCache loads icon metadata from cache or remote sources
+func InitCache()
+
+// ListAvailableIcons returns the current icon catalog
+func ListAvailableIcons() IconMap
+
+// SearchIcons performs fuzzy search on icon names
+func SearchIcons(keyword string, limit int) []*IconMetaSearch
+
+// HasIcon checks if an icon exists in the catalog
+func HasIcon(icon *URL) bool
+```
+
+**Key behaviors:**
+
+- Updates from walkxcode and selfh.st CDNs every 2 hours
+- Persists cache to disk for fast startup
+- Fuzzy search uses Levenshtein distance ranking
+
+## Configuration
+
+### Cache Location
+
+Icons cache is stored at the path specified by `common.IconListCachePath`.
+
+### Environment Variables
+
+No direct environment variable configuration. Cache is managed internally.
+
+### Reloading
+
+Icon cache updates automatically every 2 hours in the background. Manual refresh requires program restart.
+
+## Observability
+
+### Logs
+
+- `failed to load icons` - Cache load failure at startup
+- `icons loaded` - Successful cache load with entry count
+- `updating icon data` - Background update started
+- `icons list updated` - Successful cache refresh with entry count
+- `failed to save icons` - Cache persistence failure
+
+### Metrics
+
+No metrics exposed directly. Status codes in `Result` can be monitored via HTTP handlers.
+
+### Tracing
+
+Standard `context.Context` propagation is used throughout. Fetch operations respect context cancellation and deadlines.
+
+## Security Considerations
+
+- **Input Validation**: Icon URLs are strictly validated for format and source
+- **SSRF Protection**: Only absolute URLs passed directly; no arbitrary URL construction
+- **Content-Type**: Detected from response headers or inferred from SVG magic bytes
+- **Size Limits**: Cache limited to 200 entries; no explicit size limit on icon data
+- **Timeouts**: 3-second timeout on favicon fetches, 5-second timeout on list updates
+
+## Performance Characteristics
+
+- **Parsing**: O(1) string parsing with early validation
+- **Caching**: LRU-style cache with TTL for fetched icons
+- **Background Updates**: Non-blocking updates every 2 hours
+- **Search**: O(n) fuzzy match with early exit at rank > 3
+- **Memory**: Icon list typically contains ~2000 entries
+
+## Failure Modes and Recovery
+
+| Failure                | Behavior                                 | Recovery                         |
+| ---------------------- | ---------------------------------------- | -------------------------------- |
+| CDN fetch timeout      | Return cached data or fail               | Automatic retry with backoff     |
+| Cache load failure     | Attempt legacy format, then remote fetch | Manual cache reset if persistent |
+| Icon not found in list | Return error from Parse                  | User must select valid icon      |
+| HTML parse failure     | Return "icon element not found"          | Manual icon selection            |
+
+## Usage Examples
+
+### Basic: Parse and Generate URL
+
+```go
+package main
+
+import (
+    "fmt"
+    "github.com/yusing/godoxy/internal/homepage/icons"
+)
+
+func main() {
+    // Parse a CDN icon URL
+    url := &icons.URL{}
+    err := url.Parse("@walkxcode/nginx.svg")
+    if err != nil {
+        panic(err)
+    }
+
+    // Get the actual fetchable URL
+    fmt.Println(url.URL())
+    // Output: https://cdn.jsdelivr.net/gh/walkxcode/dashboard-icons/svg/nginx.svg
+
+    // Get string representation
+    fmt.Println(url.String())
+    // Output: @walkxcode/nginx.svg
+
+    // Create with dark variant
+    darkUrl := url.WithVariant(icons.VariantDark)
+    fmt.Println(darkUrl.URL())
+    // Output: https://cdn.jsdelivr.net/gh/walkxcode/dashboard-icons/svg/nginx-dark.svg
+}
+```
+
+### Advanced: Fetch Icon Data
+
+```go
+package main
+
+import (
+    "context"
+    "fmt"
+    "net/http"
+
+    "github.com/yusing/godoxy/internal/homepage/icons/fetch"
+)
+
+func main() {
+    // Initialize the icon list cache first
+    iconlist.InitCache()
+
+    // Parse icon URL
+    url := &icons.URL{}
+    if err := url.Parse("@walkxcode/nginx.svg"); err != nil {
+        panic(err)
+    }
+
+    // Fetch icon data
+    ctx := context.Background()
+    result, err := fetch.FetchFavIconFromURL(ctx, url)
+    if err != nil {
+        fmt.Printf("Fetch failed: %v\n", err)
+        return
+    }
+
+    if result.StatusCode != http.StatusOK {
+        fmt.Printf("HTTP %d\n", result.StatusCode)
+        return
+    }
+
+    fmt.Printf("Fetched %d bytes, Content-Type: %s\n",
+        len(result.Icon), result.ContentType())
+}
+```
+
+### Integration: Search Available Icons
+
+```go
+package main
+
+import (
+    "fmt"
+
+    "github.com/yusing/godoxy/internal/homepage/icons/list"
+)
+
+func main() {
+    // Initialize cache
+    list.InitCache()
+
+    // Search for icons matching a keyword
+    results := list.SearchIcons("nginx", 5)
+
+    for _, icon := range results {
+        source, ref := icon.Key.SourceRef()
+        fmt.Printf("[%s] %s - SVG:%v PNG:%v WebP:%v\n",
+            source, ref, icon.SVG, icon.PNG, icon.WebP)
+    }
+}
+```
+
+## Testing Notes
+
+- Unit tests in `url_test.go` validate parsing and serialization
+- Test mode (`common.IsTest`) bypasses existence checks
+- Mock HTTP in list tests via `MockHTTPGet()`
+- Golden tests not used; test fixtures embedded in test cases
+
+## Icon URL Formats
+
+| Format        | Example                        | Output URL                                                            |
+| ------------- | ------------------------------ | --------------------------------------------------------------------- |
+| Absolute      | `https://example.com/icon.png` | `https://example.com/icon.png`                                        |
+| Relative      | `@target/favicon.ico`          | `/favicon.ico`                                                        |
+| WalkXCode     | `@walkxcode/nginx.svg`         | `https://cdn.jsdelivr.net/gh/walkxcode/dashboard-icons/svg/nginx.svg` |
+| Selfh.st      | `@selfhst/adguard-home.webp`   | `https://cdn.jsdelivr.net/gh/selfhst/icons/webp/adguard-home.webp`    |
+| Light variant | `@walkxcode/nginx-light.png`   | `.../nginx-light.png`                                                 |
+| Dark variant  | `@walkxcode/nginx-dark.svg`    | `.../nginx-dark.svg`                                                  |

internal/homepage/types/README.md

@@ -0,0 +1,13 @@
+# Types Package
+
+Configuration types for the homepage package.
+
+## Config
+
+```go
+type Config struct {
+    UseDefaultCategories bool `json:"use_default_categories"`
+}
+
+var ActiveConfig atomic.Pointer[Config]
+```