🔥 feat: Add OpenAPI middleware

app.go

@@ -15,6 +15,8 @@ import (
 	"errors"
 	"fmt"
 	"io"
+	"maps"
+	"mime"
 	"net"
 	"net/http"
 	"net/http/httputil"
@@ -706,6 +708,200 @@ func (app *App) Name(name string) Router {
 	return app
 }
 
+// Summary assigns a short summary to the most recently added route.
+func (app *App) Summary(sum string) Router {
+	app.mutex.Lock()
+	app.latestRoute.Summary = sum
+	app.mutex.Unlock()
+	return app
+}
+
+// Description assigns a description to the most recently added route.
+func (app *App) Description(desc string) Router {
+	app.mutex.Lock()
+	app.latestRoute.Description = desc
+	app.mutex.Unlock()
+	return app
+}
+
+// Consumes assigns a request media type to the most recently added route.
+func (app *App) Consumes(typ string) Router {
+	if typ != "" {
+		if _, _, err := mime.ParseMediaType(typ); err != nil || !strings.Contains(typ, "/") {
+			panic("invalid media type: " + typ)
+		}
+	}
+	app.mutex.Lock()
+	app.latestRoute.Consumes = typ
+	app.mutex.Unlock()
+	return app
+}
+
+// Produces assigns a response media type to the most recently added route.
+func (app *App) Produces(typ string) Router {
+	if typ != "" {
+		if _, _, err := mime.ParseMediaType(typ); err != nil || !strings.Contains(typ, "/") {
+			panic("invalid media type: " + typ)
+		}
+	}
+	app.mutex.Lock()
+	app.latestRoute.Produces = typ
+	app.mutex.Unlock()
+	return app
+}
+
+// RequestBody documents the request payload for the most recently added route.
+func (app *App) RequestBody(description string, required bool, mediaTypes ...string) Router {
+	sanitized := sanitizeRequiredMediaTypes(mediaTypes)
+
+	app.mutex.Lock()
+	app.latestRoute.RequestBody = &RouteRequestBody{
+		Description: description,
+		Required:    required,
+		MediaTypes:  append([]string(nil), sanitized...),
+	}
+	if len(sanitized) > 0 {
+		app.latestRoute.Consumes = sanitized[0]
+	}
+	app.mutex.Unlock()
+
+	return app
+}
+
+// Parameter documents an input parameter for the most recently added route.
+func (app *App) Parameter(name, in string, required bool, schema map[string]any, description string) Router {
+	if strings.TrimSpace(name) == "" {
+		panic("parameter name is required")
+	}
+
+	location := strings.ToLower(strings.TrimSpace(in))
+	switch location {
+	case "path", "query", "header", "cookie":
+	default:
+		panic("invalid parameter location: " + in)
+	}
+
+	if schema == nil {
+		schema = map[string]any{"type": "string"}
+	}
+
+	schemaCopy := make(map[string]any, len(schema))
+	maps.Copy(schemaCopy, schema)
+	if _, ok := schemaCopy["type"]; !ok {
+		schemaCopy["type"] = "string"
+	}
+
+	if location == "path" {
+		required = true
+	}
+
+	param := RouteParameter{
+		Name:        name,
+		In:          location,
+		Required:    required,
+		Description: description,
+		Schema:      schemaCopy,
+	}
+
+	app.mutex.Lock()
+	app.latestRoute.Parameters = append(app.latestRoute.Parameters, param)
+	app.mutex.Unlock()
+
+	return app
+}
+
+// Response documents an HTTP response for the most recently added route.
+func (app *App) Response(status int, description string, mediaTypes ...string) Router {
+	if status != 0 && (status < 100 || status > 599) {
+		panic("invalid status code")
+	}
+
+	sanitized := sanitizeMediaTypes(mediaTypes)
+
+	if description == "" {
+		if status == 0 {
+			description = "Default response"
+		} else if text := http.StatusText(status); text != "" {
+			description = text
+		} else {
+			description = "Status " + strconv.Itoa(status)
+		}
+	}
+
+	key := "default"
+	if status > 0 {
+		key = strconv.Itoa(status)
+	}
+
+	resp := RouteResponse{Description: description}
+	if len(sanitized) > 0 {
+		resp.MediaTypes = append([]string(nil), sanitized...)
+	}
+
+	app.mutex.Lock()
+	if app.latestRoute.Responses == nil {
+		app.latestRoute.Responses = make(map[string]RouteResponse)
+	}
+	app.latestRoute.Responses[key] = resp
+	if status == StatusOK && len(resp.MediaTypes) > 0 {
+		app.latestRoute.Produces = resp.MediaTypes[0]
+	}
+	app.mutex.Unlock()
+
+	return app
+}
+
+func sanitizeMediaTypes(mediaTypes []string) []string {
+	if len(mediaTypes) == 0 {
+		return nil
+	}
+
+	seen := make(map[string]struct{}, len(mediaTypes))
+	sanitized := make([]string, 0, len(mediaTypes))
+	for _, typ := range mediaTypes {
+		trimmed := strings.TrimSpace(typ)
+		if trimmed == "" {
+			continue
+		}
+		if _, _, err := mime.ParseMediaType(trimmed); err != nil || !strings.Contains(trimmed, "/") {
+			panic("invalid media type: " + typ)
+		}
+		if _, ok := seen[trimmed]; ok {
+			continue
+		}
+		seen[trimmed] = struct{}{}
+		sanitized = append(sanitized, trimmed)
+	}
+	if len(sanitized) == 0 {
+		return nil
+	}
+	return sanitized
+}
+
+func sanitizeRequiredMediaTypes(mediaTypes []string) []string {
+	sanitized := sanitizeMediaTypes(mediaTypes)
+	if len(sanitized) == 0 {
+		panic("at least one media type must be provided")
+	}
+	return sanitized
+}
+
+// Tags assigns tags to the most recently added route.
+func (app *App) Tags(tags ...string) Router {
+	app.mutex.Lock()
+	app.latestRoute.Tags = tags
+	app.mutex.Unlock()
+	return app
+}
+
+// Deprecated marks the most recently added route as deprecated.
+func (app *App) Deprecated() Router {
+	app.mutex.Lock()
+	app.latestRoute.Deprecated = true
+	app.mutex.Unlock()
+	return app
+}
+
 // GetRoute Get route by name
 func (app *App) GetRoute(name string) Route {
 	for _, routes := range app.stack {

docs/middleware/openapi.md

@@ -0,0 +1,138 @@
+---
+id: openapi
+---
+
+# OpenAPI
+
+OpenAPI middleware for [Fiber](https://github.com/gofiber/fiber) that generates an OpenAPI specification based on the routes registered in your application.
+
+## Signatures
+
+```go
+func New(config ...Config) fiber.Handler
+```
+
+## Examples
+
+Import the middleware package that is part of the Fiber web framework
+
+```go
+import (
+    "github.com/gofiber/fiber/v3"
+    "github.com/gofiber/fiber/v3/middleware/openapi"
+)
+```
+
+After you initiate your Fiber app, you can use the following possibilities:
+
+```go
+// Initialize default config. Register the middleware *after* all routes
+// so that the spec includes every handler.
+app.Use(openapi.New())
+
+// Or extend your config for customization
+app.Use(openapi.New(openapi.Config{
+    Title:   "My API",
+    Version: "1.0.0",
+    ServerURL: "https://example.com",
+}))
+
+// Customize metadata for specific operations
+app.Use(openapi.New(openapi.Config{
+    Operations: map[string]openapi.Operation{
+        "GET /users": {
+            Summary:     "List users",
+            Description: "Returns all users",
+            Produces:    fiber.MIMEApplicationJSON,
+        },
+    },
+}))
+
+// Routes may optionally document themselves using Summary, Description,
+// RequestBody, Parameter, Response, Tags, Deprecated, Produces and Consumes.
+app.Post("/users", createUser).
+    Summary("Create user").
+    Description("Creates a new user").
+    RequestBody("User payload", true, fiber.MIMEApplicationJSON).
+    Parameter("trace-id", "header", true, nil, "Tracing identifier").
+    Response(fiber.StatusCreated, "Created", fiber.MIMEApplicationJSON).
+    Tags("users", "admin").
+    Produces(fiber.MIMEApplicationJSON)
+
+// If not specified, routes default to an empty summary and description, no tags,
+// not deprecated, and a "text/plain" request and response media type.
+// Consumes and Produces will panic if provided an invalid media type.
+```
+
+Each documented route automatically includes a `200` response with the description `OK` to satisfy the minimum OpenAPI requirements. Additional responses can be declared via the `Response` helper or the middleware configuration.
+
+`CONNECT` routes are ignored because the OpenAPI specification does not define a `connect` operation.
+
+## Config
+
+| Property    | Type                    | Description                                                     | Default            |
+|:------------|:------------------------|:----------------------------------------------------------------|:------------------:|
+| Next        | `func(fiber.Ctx) bool`  | Next defines a function to skip this middleware when returned true. | `nil` |
+| Title       | `string`                | Title is the title for the generated OpenAPI specification.     | `"Fiber API"`     |
+| Version     | `string`                | Version is the version for the generated OpenAPI specification. | `"1.0.0"`         |
+| Description | `string`                | Description is the description for the generated specification. | `""`             |
+| ServerURL   | `string`                | ServerURL is the server URL used in the generated specification.| `""`             |
+| Path        | `string`                | Path is the route where the specification will be served.       | `"/openapi.json"` |
+| Operations  | `map[string]Operation`  | Per-route metadata keyed by `METHOD /path`.                     | `nil`             |
+
+## Default Config
+
+```go
+var ConfigDefault = Config{
+    Next:        nil,
+    Operations:  nil,
+    Title:       "Fiber API",
+    Version:     "1.0.0",
+    Description: "",
+    ServerURL:   "",
+    Path:        "/openapi.json",
+}
+```
+
+### Operation
+
+```go
+type Operation struct {
+    RequestBody *RequestBody
+    Responses   map[string]Response
+    Parameters  []Parameter
+    Tags        []string
+
+    ID          string
+    Summary     string
+    Description string
+    Consumes    string
+    Produces    string
+    Deprecated  bool
+}
+
+type Parameter struct {
+    Schema      map[string]any
+    Name        string
+    In          string
+    Description string
+    Required    bool
+}
+
+type Media struct {
+    Schema map[string]any
+}
+
+type Response struct {
+    Content     map[string]Media
+    Description string
+}
+
+type RequestBody struct {
+    Content     map[string]Media
+    Description string
+    Required    bool
+}
+```
+
+Refer to the type definitions above when customizing OpenAPI operations in your configuration.

docs/whats_new.md

@@ -1288,6 +1288,10 @@ Deprecated fields `Duration`, `Store`, and `Key` have been removed in v3. Use `E
 
 Monitor middleware is migrated to the [Contrib package](https://github.com/gofiber/contrib/tree/main/monitor) with [PR #1172](https://github.com/gofiber/contrib/pull/1172).
 
+### OpenAPI
+
+Introduces an `openapi` middleware that inspects registered routes and serves a generated OpenAPI 3.0 specification. Each operation includes a summary and default `200` response. Routes may attach descriptions, parameters, request bodies, and custom responses—alongside request/response media types—directly or configure them globally.
+
 ### Proxy
 
 The proxy middleware has been updated to improve consistency with Go naming conventions. The `TlsConfig` field in the configuration struct has been renamed to `TLSConfig`. Additionally, the `WithTlsConfig` method has been removed; you should now configure TLS directly via the `TLSConfig` property within the `Config` struct.