render

Render Package

Package render provides a template rendering system for weft. It offers advanced template discovery, block management, partial and include support, collection operations, and an extensive function registry with string manipulation utilities.

Architecture

The render package is organized into eight main components:

• Template Discovery (discovery.go): Configurable template file discovery with pattern matching
• Block Management (blocks.go): Template block definition, override, and inheritance system
• Include System (includes.go): Template inclusion with data passing and circular dependency detection
• Partial Management (partials.go): Partial template loading and registration
• Function Registry (registry.go): Extensible function management with metadata and documentation
• Collection Operations (collections.go): Advanced slice and array manipulation functions
• Function Library (funcs.go): Default and extended template function sets
• String Utilities (strings.go): Comprehensive string manipulation and formatting functions

Basic Usage

Initialize Template Discovery

discovery := render.NewTemplateDiscovery(templateFS)
discovery.AddDefaultRules()
templates, err := discovery.DiscoverTemplates("templates/")

Create Block Manager

blockManager := render.NewBlockManager(templateFS, funcMap)
blockManager.DefineBlock("header", "<h1>{{.Title}}</h1>")

Set Up Function Registry

registry := render.NewFunctionRegistry()
registry.RegisterDefaults()
funcMap := registry.GetFuncMap()

Template Integration

The package provides comprehensive template functions for various operations:

<!-- String manipulation -->
{{ "hello_world" | camel }}     <!-- helloWorld -->
{{ "HelloWorld" | snake }}      <!-- hello_world -->
{{ "hello world" | pascal }}    <!-- HelloWorld -->

<!-- Collection operations -->
{{ .Items | filter (lambda .Active) }}
{{ .Numbers | sort | unique }}
{{ .Users | map (lambda .Name) | join ", " }}

<!-- Block usage -->
{{ block "content" "Default content" }}
{{ override "footer" "Custom footer content" }}

<!-- Include templates -->
{{ include "partials/header" }}
{{ includeWith "partials/user-card" .User }}

Register Function Registry with Templates

registry := render.NewFunctionRegistry()
registry.RegisterDefaults()
registry.RegisterExtended()

tmpl := template.New("main").Funcs(registry.GetFuncMap())

Configuration

Template Discovery Rules

discovery := render.NewTemplateDiscovery(templateFS)

// Add custom discovery rule
rule := render.DiscoveryRule{
    Name:        "components",
    Patterns:    []string{"*.component.tmpl"},
    Extensions:  []string{".tmpl"},
    Directories: []string{"components"},
    Recursive:   true,
    Priority:    25,
}
discovery.AddRule(rule)

Include Manager Configuration

includeManager := render.NewIncludeManager(templateFS, funcMap)
includeManager.SetMaxDepth(20) // Prevent deep nesting

// Preload commonly used includes
templatePaths := []string{"main.tmpl", "layout.tmpl"}
err := includeManager.PreloadIncludes(templatePaths)

Function Registry Setup

registry := render.NewFunctionRegistry()

// Register custom function with metadata
registry.Register("customFunc", myFunction,
    render.WithDescription("Custom processing function"),
    render.WithCategory("custom"),
    render.WithParameters(
        render.ParamInfo{Name: "input", Type: "string", Required: true},
        render.ParamInfo{Name: "options", Type: "map", Required: false},
    ),
    render.WithReturnType("string"),
    render.WithExamples(`{{ "text" | customFunc }}`),
    render.WithSince("2.0.0"))

Template Discovery

Discover templates using configurable rules and patterns:

discovery := render.NewTemplateDiscovery(templateFS)
discovery.AddDefaultRules()

// Discover all templates
templates, err := discovery.DiscoverTemplates("templates/")
for _, tmpl := range templates {
    fmt.Printf("Found: %s (%s)\n", tmpl.Name, tmpl.Path)
}

// Get templates by type
partials, err := discovery.GetTemplatesByType("templates/", "partial")
includes, err := discovery.GetTemplatesByType("templates/", "include")

Discovery Rule Types

Rule Type	Description	Example Pattern
standard-templates	Main template files	*.tmpl, *.tpl
partials	Underscore-prefixed partials	_*.tmpl, _*.tpl
includes	Include directory templates	Files in includes/

Advanced Discovery

// Find templates by pattern
matched, err := discovery.GetTemplatesByPattern("templates/", `user.*\.tmpl$`)

// Get discovery statistics
stats, err := discovery.GetDiscoveryStats("templates/")
fmt.Printf("Total templates: %d\n", stats["total"])
fmt.Printf("Partials: %d\n", stats["partials"])

Block Management

Block Definition and Usage

blockManager := render.NewBlockManager(templateFS, funcMap)

// Define blocks
blockManager.DefineBlock("navigation", `
<nav>
  <ul>
    {{range .NavItems}}
    <li><a href="{{.URL}}">{{.Title}}</a></li>
    {{end}}
  </ul>
</nav>`)

// Override blocks
blockManager.OverrideBlock("navigation", "<nav>Custom navigation</nav>")

Template Block Syntax

<!-- Define a block -->
{{ define "sidebar" }}
<aside>Default sidebar content</aside>
{{ end }}

<!-- Use a block with fallback -->
{{ block "sidebar" "Default content" }}

<!-- Override a block -->
{{ override "sidebar" }}
<aside>Custom sidebar for this template</aside>
{{ end }}

Block Validation

// Validate block references
err := blockManager.ValidateBlocks("templates/main.tmpl")
if err != nil {
    log.Printf("Block validation error: %v", err)
}

// Get block information
blocks := blockManager.GetBlockInfo()
for _, block := range blocks {
    fmt.Printf("Block: %s, Override: %t\n", block.Name, block.Override)
}

Include System

Basic Includes

includeManager := render.NewIncludeManager(templateFS, funcMap)

// Template usage
// {{ include "header" }}
// {{ includeWith "user-profile" .User }}

Include Path Resolution

// Automatic path resolution tries:
// - exact path
// - path + .tmpl
// - path + .tpl  
// - includes/path
// - includes/path.tmpl
// - includes/path.tpl

Include Validation and Dependencies

// Validate includes
err := includeManager.ValidateIncludes("templates/main.tmpl")

// Get include dependency graph
graph, err := includeManager.GetIncludeGraph("templates/main.tmpl", nil)
for template, includes := range graph {
    fmt.Printf("%s includes: %v\n", template, includes)
}

Partial Templates

Partial Discovery and Loading

partialManager := render.NewPartialManager(templateFS, funcMap)

// Find partials in directory
partials, err := partialManager.FindPartials("templates/")

// Create template with partials
tmpl, err := partialManager.ParseTemplateWithPartials("main.tmpl")

Partial Naming Convention

// File: _header.tmpl -> Partial name: "header"
// File: _user-card.tmpl -> Partial name: "user-card"
// File: _navigation.tpl -> Partial name: "navigation"

Partial Template Usage

<!-- In your main template -->
{{ template "header" .HeaderData }}
{{ template "user-card" .User }}
{{ template "navigation" .NavItems }}

Function Library

String Functions

Function	Description	Example
snake	Convert to snake_case	{{ "HelloWorld" | snake }}
camel	Convert to camelCase	{{ "hello_world" | camel }}
pascal	Convert to PascalCase	{{ "hello_world" | pascal }}
kebab	Convert to kebab-case	{{ "HelloWorld" | kebab }}
plural	Pluralize word	{{ "person" | plural }}
singular	Singularize word	{{ "people" | singular }}
humanize	Human readable format	{{ "user_name" | humanize }}
indent	Indent text lines	{{ .Code | indent 4 }}
quote	Add double quotes	{{ .String | quote }}
comment	Add comment prefix	{{ .Text | comment "//" }}

Collection Functions

Function	Description	Example
formatSlice	Format slice with separator	{{ formatSlice .Items ", " "%s" }}
filter	Filter by predicate	{{ .Users | filter .IsActive }}
map	Transform elements	{{ .Items | map .GetName }}
first	Get first element	{{ .Items | first }}
last	Get last element	{{ .Items | last }}
rest	Get all but first	{{ .Items | rest }}
reverse	Reverse order	{{ .Items | reverse }}
sort	Sort elements	{{ .Numbers | sort }}
unique	Remove duplicates	{{ .Items | unique }}
shuffle	Random order	{{ .Cards | shuffle }}
chunk	Split into chunks	{{ sliceChunk .Items 3 }}
zip	Combine slices	{{ sliceZip .Names .Values }}

Math and Utility Functions

Function	Description	Example
add	Add numbers	{{ add 5 3 }}
subtract	Subtract numbers	{{ subtract 10 3 }}
multiply	Multiply numbers	{{ multiply 4 5 }}
divide	Divide numbers	{{ divide 15 3 }}
max	Maximum value	{{ max .Values }}
min	Minimum value	{{ min .Values }}
default	Default value	{{ default "none" .Value }}
coalesce	First non-empty	{{ coalesce .A .B .C }}
ternary	Conditional value	{{ ternary .Condition "yes" "no" }}

Extended Functions

// Register extended functions for additional capabilities
registry.RegisterExtended()

// Available extended functions:
// - UUID generation: {{ uuid }}
// - Hashing: {{ "text" | md5 }}, {{ "text" | sha256 }}
// - Encoding: {{ "text" | base64 }}, {{ .Base64 | base64dec }}
// - Environment: {{ env "HOME" }}, {{ hasEnv "DEBUG" }}
// - Regex: {{ regexMatch "^test" .String }}
// - Path operations: {{ pathJoin .Dir .File }}
// - Semver: {{ semver "v1.2.3" }}
// - Random: {{ randInt 1 100 }}, {{ genPassword 12 }}

Performance Considerations

Optimization Tips

1. Template Caching: Use discovery cache for repeated template lookups
2. Preload Includes: Load commonly used includes at startup
3. Function Registry: Register functions once and reuse FuncMap
4. Block Management: Clear unused blocks and overrides periodically
5. Partial Caching: Cache parsed templates with partials

Performance Settings

// Optimize include depth for your use case
includeManager.SetMaxDepth(5) // Lower depth for simpler templates

// Clear caches periodically in long-running applications
partialManager.ClearCache()
includeManager.ClearCache()
blockManager.ClearAll()

Memory Management

// Monitor registry size
registry := render.NewFunctionRegistry()
fmt.Printf("Registered functions: %d\n", registry.Count())

// Clear discovery cache when templates change
discovery.ClearCache()

// Use selective function registration
registry.RegisterDefaults() // Essential functions only
// registry.RegisterExtended() // Add only if needed

Security Notes

Template Security

• Include path resolution prevents directory traversal attacks
• Function registry validates function types before registration
• Template validation catches syntax errors before execution
• Block validation ensures referenced blocks exist

Security Best Practices

1. Validate all template inputs before rendering
2. Sanitize user-provided data in templates
3. Limit include depth to prevent resource exhaustion
4. Use allow-lists for template discovery paths
5. Regular security audits of custom functions

Input Sanitization

// Use built-in escaping functions
// {{ .UserInput | htmlEscape }}
// {{ .JSValue | jsEscape }}
// {{ .URLParam | urlQuery }}
// {{ .YAMLValue | yamlEscape }}

Thread Safety

All public functions and types in this package are thread-safe and can be used concurrently from multiple goroutines. Internal synchronization is handled automatically.

Concurrent Usage Examples

// Safe concurrent discovery
discovery := render.NewTemplateDiscovery(templateFS)
go func() {
    templates, _ := discovery.DiscoverTemplates("path1")
    // Process templates
}()
go func() {
    templates, _ := discovery.DiscoverTemplates("path2")  
    // Process templates
}()

// Safe concurrent function registration
registry := render.NewFunctionRegistry()
go registry.Register("func1", fn1)
go registry.Register("func2", fn2)

Advanced Features

Custom Discovery Rules

// Create domain-specific discovery rules
emailRule := render.DiscoveryRule{
    Name:        "email-templates",
    Patterns:    []string{"*.email.tmpl"},
    Extensions:  []string{".tmpl"},
    Directories: []string{"emails", "notifications"},
    Recursive:   true,
    Priority:    30,
}
discovery.AddRule(emailRule)

Function Documentation Generation

registry := render.NewFunctionRegistry()
registry.RegisterDefaults()

// Generate function documentation
docs := registry.GetDocumentation()
fmt.Println(docs) // Markdown documentation

// Export function metadata
metadata := registry.ExportJSON()
// Save to file or API

Complex Template Composition

// Combine all managers for full functionality
blockManager := render.NewBlockManager(templateFS, nil)
includeManager := render.NewIncludeManager(templateFS, nil)  
partialManager := render.NewPartialManager(templateFS, nil)
registry := render.NewFunctionRegistry()

// Merge all function maps
funcMap := registry.MergeFuncMap(blockManager.GetFuncMap())
funcMap = registry.MergeFuncMap(includeManager.GetFuncMap())

// Use combined functionality in templates
tmpl := template.New("complex").Funcs(funcMap)

Integration Examples

With Web Applications

func setupTemplateEngine() *template.Template {
    templateFS := os.DirFS("templates")
    
    // Set up discovery
    discovery := render.NewTemplateDiscovery(templateFS)
    discovery.AddDefaultRules()
    
    // Set up managers
    blockManager := render.NewBlockManager(templateFS, nil)
    includeManager := render.NewIncludeManager(templateFS, nil)
    partialManager := render.NewPartialManager(templateFS, nil)
    registry := render.NewFunctionRegistry()
    registry.RegisterDefaults()
    
    // Create combined function map
    funcMap := registry.MergeFuncMap(blockManager.GetFuncMap())
    funcMap = registry.MergeFuncMap(includeManager.GetFuncMap())
    
    // Discover and parse templates
    templates, _ := discovery.DiscoverTemplates(".")
    
    rootTemplate := template.New("app").Funcs(funcMap)
    for _, tmpl := range templates {
        content, _ := fs.ReadFile(templateFS, tmpl.Path)
        rootTemplate.New(tmpl.Name).Parse(string(content))
    }
    
    return rootTemplate
}

With CLI Code Generation

func generateCode(templateDir, outputDir string, data interface{}) error {
    templateFS := os.DirFS(templateDir)
    
    // Set up rendering system
    registry := render.NewFunctionRegistry()
    registry.RegisterDefaults()
    registry.RegisterExtended() // For file operations
    
    discovery := render.NewTemplateDiscovery(templateFS)
    discovery.AddDefaultRules()
    
    // Add code generation specific rules
    codeRule := render.DiscoveryRule{
        Name:        "code-templates", 
        Patterns:    []string{"*.go.tmpl", "*.js.tmpl"},
        Extensions:  []string{".tmpl"},
        Recursive:   true,
        Priority:    20,
    }
    discovery.AddRule(codeRule)
    
    // Generate code files
    templates, err := discovery.DiscoverTemplates(".")
    if err != nil {
        return err
    }
    
    for _, tmpl := range templates {
        output, err := renderTemplate(templateFS, tmpl.Path, data, registry.GetFuncMap())
        if err != nil {
            return fmt.Errorf("rendering %s: %w", tmpl.Path, err)
        }
        
        outputFile := filepath.Join(outputDir, tmpl.Name)
        err = os.WriteFile(outputFile, []byte(output), 0644)
        if err != nil {
            return fmt.Errorf("writing %s: %w", outputFile, err)
        }
    }
    
    return nil
}

With Template Validation Pipeline

func validateTemplateSystem(templateFS fs.FS) error {
    // Set up all components
    discovery := render.NewTemplateDiscovery(templateFS)
    discovery.AddDefaultRules()
    
    blockManager := render.NewBlockManager(templateFS, nil)
    includeManager := render.NewIncludeManager(templateFS, nil)
    partialManager := render.NewPartialManager(templateFS, nil)
    registry := render.NewFunctionRegistry()
    registry.RegisterDefaults()
    
    // Validate discovery
    if err := discovery.ValidateDiscovery("."); err != nil {
        return fmt.Errorf("discovery validation failed: %w", err)
    }
    
    // Get all templates
    templates, err := discovery.DiscoverTemplates(".")
    if err != nil {
        return err
    }
    
    // Validate each template
    for _, tmpl := range templates {
        // Validate blocks
        if err := blockManager.ValidateBlocks(tmpl.Path); err != nil {
            return fmt.Errorf("block validation failed for %s: %w", tmpl.Path, err)
        }
        
        // Validate includes  
        if err := includeManager.ValidateIncludes(tmpl.Path); err != nil {
            return fmt.Errorf("include validation failed for %s: %w", tmpl.Path, err)
        }
        
        // Validate partials
        if err := partialManager.ValidatePartials(tmpl.Path); err != nil {
            return fmt.Errorf("partial validation failed for %s: %w", tmpl.Path, err)
        }
    }
    
    return nil
}