restruct

name	Restruct
description	Guide for using the Restruct package for struct-based routing and rendering.

Restruct Package Guide

Restruct is a Go package that provides struct-based routing, automatic parameter extraction, and a view engine with template support. It relies on reflection to map struct methods to HTTP routes and assumes a specific project structure.

Core Concepts

• Service: A struct that represents a group of related routes.
• Method: A method on a Service struct that handles a specific HTTP request.
• View: A component that handles rendering HTML templates and serving static files from an fs.FS.
• Handler: The central component that manages services, middleware, routing (via a Trie-based router), and request/response lifecycles.

Routing

Restruct maps struct methods to HTTP routes using naming conventions and struct tags.

Struct Tags

Use the route tag on struct fields to define the base path for a nested service.

• route:"users" -> Maps the struct to /users
• route:"-" -> Ignores the field (won't be registered as a service).
• route:"" -> Uses the field name (kebab-cased) as the path.

Method Naming Conventions

Method names are automatically converted to route paths:

• CamelCase -> camel-case
• Underscore_Separated -> / separator (e.g., Hello_World -> hello/world)
• Index -> Root of the service (/)
• Any -> Catch-all wildcard /{any*}
• Suffix_Any -> Wildcard after path (e.g., Files_Any -> files/{any*})
• _0, _1, etc. -> Path parameters /{0}, /{1} (e.g., Item_0 -> item/{0})

Examples:

• func (s *Svc) CreateUser() -> .../create-user
• func (s *Svc) Hello_World() -> .../hello/world
• func (s *Svc) Item_0() -> .../item/{0}
• func (s *Svc) Any() -> .../{any*}
• func (s *Svc) Link_Any() -> .../link/{any*}

Explicit Routing (Router interface)

Implement the Routes() []rs.Route method on your struct to explicitly define routes, HTTP methods, and per-route middleware.

Handler accepts a string (method name) or a func (used directly):

func (u *User) Routes() []rs.Route {
    return []rs.Route{
        {Handler: u.CreateUser, Path: ".", Methods: []string{http.MethodPost}},
        {Handler: "ReadUser", Path: "{id}", Methods: []string{http.MethodGet}},
        {Handler: "UpdateUser", Path: "{id}", Methods: []string{http.MethodPut}},
        {Handler: "DeleteUser", Path: "{id}", Methods: []string{http.MethodDelete}},
    }
}

• Handler: "MethodName" — Resolves to the struct method by name.
• Handler: u.MethodName or Handler: myFunc — Uses the func directly (same signature rules as regular handlers).
• Path: "." maps to the service root (e.g., POST /users instead of POST /users/create-user).
• Path: "{id}" adds a parameter segment.
• Omitting Path uses the default naming convention for the handler method name.
• Omitting Methods allows all HTTP methods.
• Middlewares on a Route applies only to that specific route.

Handlers

Handlers are methods on your service structs. Restruct supports dependency injection for handler arguments.

Signatures

Common arguments injected automatically:

• *http.Request
• http.ResponseWriter
• context.Context
• Struct pointers or values (for request body binding via RequestReader)

Return Values:

• No return: Response is not written (you handle it via http.ResponseWriter).
• error: Returns an error response (handled by ResponseWriter).
• any / interface{}: Serialized to JSON by the DefaultWriter.
• *rs.Render: Triggers HTML template rendering at a specific path.
• *rs.Response: Manual control over status, content-type, headers, and body.
• *rs.Json: JSON response with a custom status code.
• (int, any, error): Status code, response body, and error.
• (any, error): Response body and error.

Request Binding

To bind request data (JSON body, query params, form data) to a struct, add the struct pointer or value as an argument to your handler.

type CreateRequest struct {
    Name string `json:"name"`
}

func (s *Service) Create(ctx context.Context, req *CreateRequest) any {
    // req is populated automatically via RequestReader
    return req
}

Inline struct arguments are also supported:

func (c *Calculator) Add(req struct {
    A int `json:"a"`
    B int `json:"b"`
}) int {
    return req.A + req.B
}

Path Parameters

Access path parameters via context:

rs.Params(r)["id"]       // from *http.Request
rs.Vars(ctx)["id"]       // from context.Context
rs.Vars(ctx)["0"]        // for auto-generated numeric params (_0, _1, etc.)
rs.Vars(ctx)["any"]      // for wildcard catch-all routes

Context Values

Store and retrieve arbitrary values from the request context (e.g., in middleware):

// Using *http.Request (returns new *http.Request)
r = rs.SetValue(r, "userID", int64(1))
userID := rs.GetValue(r, "userID").(int64)
vals := rs.GetValues(r) // map[string]interface{}

// Using context.Context directly
ctx = rs.SetVal(ctx, "key", "value")
val := rs.GetVal(ctx, "key")
vals := rs.GetVals(ctx) // map[string]interface{}

Views & Rendering

The rs.View struct implements ResponseWriter and handles template rendering and static file serving.

Setup

Implement the Writer interface on your service to associate a View:

func (s *Server) Writer() rs.ResponseWriter {
    f, _ := fs.Sub(publicFS, "public")
    return &rs.View{
        FS:      f,                          // fs.FS (embed.FS, os.DirFS, etc.)
        Funcs:   template.FuncMap{...},      // Custom template functions
        Skips:   regexp.MustCompile("^layout"), // Skip files matching regex from routing
        Layouts: []string{"layout/*.html"},  // Glob patterns for layout templates
        Error:   "error.html",              // Template for error pages
        Data:    func(r *http.Request) map[string]any { ... }, // Global template data
        Writer:  &rs.DefaultWriter{},       // Fallback writer for non-view responses
    }
}

View Struct Fields

Field	Type	Description
FS	fs.FS	Source file system (required)
Funcs	template.FuncMap	Custom template functions
Skips	*regexp.Regexp	Regex to skip files from being routed
Layouts	[]string	Glob patterns for layout/partial templates
Error	string	Error template path (rendered on errors if Any route matched)
Data	func(*http.Request) map[string]any	Callback for default template data
Writer	ResponseWriter	Fallback writer for non-template responses

Template Data

Templates receive a map[string]any with:

• Request: The current *http.Request
• Path parameters merged in (e.g., {{.id}}, {{.profile}})
• Data from the Data callback
• Handler return data: merged if map[string]any, otherwise available as {{.Data}}

Auto-Routing

If FS implements fs.ReadDirFS, View automatically registers routes for .html and .tmpl files:

• index.html -> /
• about.html -> /about
• blog/post.html -> /blog/post

Explicit Rendering

Return *rs.Render from a handler to render a specific template, regardless of the URL:

func (s *Service) Dashboard(ctx context.Context) (*rs.Render, error) {
    return &rs.Render{
        Path: "dashboard/main.html",
        Data: map[string]interface{}{
            "Title": "Dashboard",
        },
    }, nil
}

Request Reader

The RequestReader interface controls how request data is bound to handler arguments.

type RequestReader interface {
    Read(*http.Request, []reflect.Type) ([]reflect.Value, error)
}

The DefaultReader binds JSON body, URL-encoded forms, and multipart forms. Customize the Bind function to add validation:

h.Reader = &rs.DefaultReader{Bind: func(r *http.Request, out interface{}, methods ...string) error {
    if err := rs.Bind(r, out, methods...); err != nil {
        return err
    }
    return validate.Struct(out)
}}

Bind Functions

• rs.Bind(r, out, methods...) — Main bind: dispatches to JSON, form, or query based on content type.
• rs.BindJson(r, out) — Bind JSON body.
• rs.BindQuery(r, out) — Bind query string params (uses query struct tag).
• rs.BindForm(r, out) — Bind form/multipart data (uses form struct tag).

Response Writer

The ResponseWriter interface controls how handler return values are sent to the client.

type ResponseWriter interface {
    Write(http.ResponseWriter, *http.Request, []reflect.Type, []reflect.Value)
}

DefaultWriter

Handles JSON output with error mapping. Configurable via:

• ErrorHandler func(error) any — Custom error formatting. Return *rs.Response for full control.
• Errors map[error]Error — Map known errors to custom HTTP statuses/messages.
• EscapeJsonHtml bool — Whether to escape HTML in JSON output.

Response Types

• rs.Response: Full control over status, headers, content-type, and body bytes.
• rs.Json: JSON response with a custom status code: rs.Json{Status: 201, Content: obj}.
• rs.Error: Error with status, message, data, and wrapped error.

Middleware

Middleware is the standard func(http.Handler) http.Handler signature.

• Global: h.Use(middleware) in Init.
• Service-level: Implement Middlewares() []rs.Middleware on the service struct.
• Route-level: Specify Middlewares in the Route struct returned from Routes().

Built-in Middleware

• rs.Recovery — Panic recovery middleware; logs stack trace and returns 500 error.

Handler Configuration

Init Interface

Implement Init(*rs.Handler) to configure the handler after creation:

func (s *Server) Init(h *rs.Handler) {
    h.Writer = &rs.DefaultWriter{ErrorHandler: myErrorHandler}
    h.Reader = &rs.DefaultReader{Bind: myBind}
    h.Use(loggingMiddleware)
}

Handler Methods

• rs.Handle(pattern, svc) — Register a service on http.DefaultServeMux.
• rs.NewHandler(svc) — Create a Handler without registering on a mux.
• h.WithPrefix(prefix) — Set a URL prefix for the handler.
• h.AddService(path, svc) — Add a sub-service at runtime.
• h.Routes() — List all registered routes (useful for debugging/docs).
• h.Use(middleware...) — Add global middleware.

Global Variables

• rs.MaxBodySize — Maximum request body size for BindJson (default: 10MB).

Example Usage

package main

import (
    "context"
    "net/http"
    rs "github.com/altlimit/restruct"
)

type API struct {
    User User `route:"users"`
}

type User struct{}

func (u *User) Routes() []rs.Route {
    return []rs.Route{
        {Handler: "Get", Path: "{id}", Methods: []string{"GET"}},
    }
}

func (u *User) Get(ctx context.Context) any {
    id := rs.Vars(ctx)["id"]
    return map[string]string{"id": id}
}

func main() {
    rs.Handle("/", &API{})
    http.ListenAndServe(":8080", nil)
}

Sub-packages

structtag

Utility package for struct tag parsing with caching. Used internally for query and form tag binding.

• structtag.GetFieldsByTag(obj, tagName) — Returns []*StructField for all fields with the given tag.
• structtag.NewStructField(index, tag) — Parses a comma-separated key=value tag string.