Execution Pipeline

Spine's execution pipeline receives a request, selects a handler, binds its arguments, and turns its return value into a response. Use this flow to understand when interceptors run and how far execution proceeds when an error occurs.

This document describes the HTTP execution order in Spine v0.6.0. HTTP, event consumers, and WebSocket use the same pipeline implementation, but their input resolvers and response handling configurations differ.

The controller examples are code to add to a project generated by the CLI. Receive request DTOs as pointers and return ordinary success responses as httpx.Response[T] from github.com/NARUBROWN/spine/pkg/httpx. Register constructors and routes in BuildApplication.

HTTP Request Execution Order

A successful request follows this sequence. Each interceptor's PreHandle runs in registration order, and its post-processing methods run in reverse order.

A success response returned by the handler is not sent immediately. The pipeline prepares it in a buffer, then writes it to the actual HTTP response after post-processing and BeforeResponse finish. If an error occurs along the way, the pipeline can replace the pending response with an error response.

Creating the Request Context

The HTTP adapter creates a core.ExecutionContext for each request. The pipeline uses this object to read the request method and path, share values stored by interceptors, and collect events that belong to the request.

Components use the same context with different scopes of access.

Component	Context usage
Router	Find the handler by method and path, and store path parameters
Interceptor	Read request information, store execution state, and run processing before and after the response
Argument resolver	Create controller arguments from the context
Return value handler	Prepare the response with the response writer attached to the context
Controller	Receive only the values it needs through semantic types, context.Context, and read-only spine.Ctx

Controllers do not receive core.ExecutionContext directly. Use pkg/spine.Ctx when a controller needs to read values stored by an interceptor. Execution Context explains the scope of access for each method.

Global Interceptors: Processing Before Routing

The PreHandle methods of global interceptors registered with app.Interceptor() run first. Since no handler has been selected yet, these calls receive an empty core.HandlerMeta{}.

Use this stage for work that must happen before route selection, such as CORS preflight. For example, a CORS interceptor can prepare a response to an allowed OPTIONS request and return core.ErrAbortPipeline to stop further execution.

Keep these constraints in mind in global PreHandle:

• The controller and method to execute have not been determined yet.
• The Spine router has not stored path parameters yet.
• Request DTOs and other controller arguments, such as path.Int, have not been created yet.

After routing succeeds, PostHandle, BeforeResponse, and AfterCompletion receive the selected handler's metadata. If execution stops or fails before routing, it finishes with empty metadata.

Router: Selecting the Handler and Path Parameters

The router uses ctx.Method() and ctx.Path() to find a registered handler. If no handler matches, it returns a 404 error. If the path contains parameters, the router stores their values in the context and preserves their declaration order in the metadata.

HandlerMeta contains the execution target and route configuration.

// core/handler_meta.go
type HandlerMeta struct {
    ControllerType reflect.Type   // 의존성 컨테이너에서 찾을 컨트롤러 타입
    Method         reflect.Method // 호출할 메서드
    PathKeys       []string       // 라우트에 선언한 경로 매개변수의 순서
    Interceptors   []Interceptor  // 해당 핸들러에 적용할 인터셉터
}

HandlerMeta does not instruct the pipeline to create a new controller for each request. The Invoker uses this information to find the target in the dependency container and pass arguments to its method. See HandlerMeta for details about its fields.

Argument Binding: ParameterMeta and ArgumentResolver

After selecting a handler, the pipeline reads its method signature and builds ParameterMeta to describe the type and position of each argument. The first registered resolver that supports the type then creates its value.

If a resolver cannot create a value, or no resolver supports the type, the pipeline moves to error handling without invoking the controller. This stage runs before the route interceptor's PreHandle. Do not assume that a route interceptor performs checks before body binding.

Path Parameters Bind in Declaration Order

path.Int, path.String, and path.Boolean bind in the order of the parameters declared in the route. They do not match by Go argument name.

// 라우트: /users/:userId/posts/:postId
// userId에는 첫 번째 경로 값, postId에는 두 번째 경로 값이 들어갑니다.
func GetPost(userId path.Int, postId path.Int) (httpx.Response[Post], error)

Keep the path types in the correct order even when arguments of other types appear between them. When changing the number or types of path parameters, check both the route declaration and the method signature.

Supported HTTP Arguments

Resolver	Controller argument type	Value provided
StdContextResolver	context.Context	Request cancellation and timeout information, and the context used to publish events
ControllerContextResolver	spine.Ctx, core.ControllerContext	Read-only view of the interceptor store
HeaderResolver	header.Values	HTTP header view
PathIntResolver	path.Int	Integer parsed from a path value
PathStringResolver	path.String	String from the path
PathBooleanResolver	path.Boolean	Boolean parsed from a path value
PaginationResolver	query.Pagination	The page and size query values
QueryValuesResolver	query.Values	View of all query values
DTOResolver	*struct	DTO bound from the HTTP body
FormDTOResolver	*struct with a form tag	DTO bound from a form or multipart body
UploadedFilesResolver	multipart.UploadedFiles	Uploaded files

header, path, query, and multipart are packages under github.com/NARUBROWN/spine/pkg/. Distinguish multipart.UploadedFiles in the table from the types in Go's standard mime/multipart package.

Declare HTTP DTOs as struct pointers. If any field has a form tag, the ordinary DTO resolver skips the type and the form DTO resolver handles it. If page or size in query.Pagination is omitted or cannot be parsed as an integer, it defaults to 1 or 20, respectively.

Resolver Contract

Internal resolvers follow this contract. You do not need to copy and register this interface or the internal/ packages in your app.

type ArgumentResolver interface {
    Supports(parameterMeta ParameterMeta) bool
    Resolve(ctx core.ExecutionContext, parameterMeta ParameterMeta) (any, error)
}

A resolver receives the shared ExecutionContext, then checks for core.HttpRequestContext when it needs HTTP input. Consumer and WebSocket resolvers read message bodies from their respective protocol contexts.

Route Interceptors: Processing Before Handler Invocation

Interceptors registered with route.WithInterceptors() apply only to a specific handler. Their PreHandle runs after routing and argument binding, so they can use the selected HandlerMeta and path parameters.

Scope	Registration	When PreHandle runs	Metadata provided
Global	app.Interceptor()	Before routing	Empty HandlerMeta{}
Route	route.WithInterceptors()	After argument binding, before handler invocation	Selected HandlerMeta

Both kinds implement the four methods of core.Interceptor.

// core/interceptor.go
type Interceptor interface {
    PreHandle(ctx ExecutionContext, meta HandlerMeta) error
    PostHandle(ctx ExecutionContext, meta HandlerMeta)
    BeforeResponse(ctx ExecutionContext, meta HandlerMeta, executionErr error) error
    AfterCompletion(ctx ExecutionContext, meta HandlerMeta, err error)
}

If PreHandle returns an ordinary error, execution moves to error handling. If it returns core.ErrAbortPipeline, the pipeline treats the request as deliberately terminated. In this case, the interceptor must prepare the required response itself. In both cases, subsequent PreHandle methods and the controller do not run.

See the interceptor tutorial for a registration example.

Invoker: Calling the Controller

The Invoker retrieves the controller instance from the dependency container and calls its method with the bound arguments. The controller validates input, calls services, and returns a result or an error.

The following method is an example to add to an app that defines UserController, User, and c.repo. Import path, httpx, and httperr from Spine's respective pkg/ packages.

func (c *UserController) GetUser(userId path.Int) (httpx.Response[User], error) {
    if userId.Value <= 0 {
        return httpx.Response[User]{}, httperr.BadRequest("유효하지 않은 사용자 ID")
    }
    user, err := c.repo.FindByID(userId.Value)
    if err != nil {
        return httpx.Response[User]{}, err
    }
    return httpx.Response[User]{Body: user}, nil
}

The numeric conversion of userId finishes before the controller is invoked. The BadRequest above runs only when the parsed number is zero or less. Do not assume that a path value that cannot be parsed as a number reaches this check.

ReturnValueHandler: Converting Return Values into Responses

The pipeline first looks for a non-nil error among the return values. If it finds one, it moves to the error response path without processing success values. Otherwise, it passes the first non-nil success value to a return value handler that supports it.

Pointers and interfaces that contain a typed nil are also skipped. Returning an unsupported success type causes an error. Wrap ordinary structs in httpx.Response[T] instead of returning them directly.

Return value handler	Supported return type	HTTP response
RedirectReturnValueHandler	httpx.Redirect or a pointer to it	Location header and status code; defaults to 302
BinaryReturnHandler	httpx.Binary or a pointer to it	Binary body
StringReturnHandler	httpx.Response[string] or a pointer to it	Text body
JSONReturnHandler	httpx.Response[T] with a non-string body, or a pointer to it	JSON body
ErrorReturnHandler	error	JSON containing the status code and message

Use ResponseOptions to set the status code, headers, and cookies. If serialization or cookie validation fails during response preparation, the success response is not sent.

Internal return value handlers follow this contract.

type ReturnValueHandler interface {
    Supports(returnType reflect.Type) bool
    Handle(value any, ctx core.ExecutionContext) error
}

PostExecutionHook: Processing Events

Once the success return value has been serialized and the response validated, the pipeline runs registered PostExecutionHook hooks. The domain event dispatch hook takes events from the request's EventBus and passes them to the dispatcher.

Execution does not reach this stage if the handler returns an error or success response preparation fails. If a hook itself returns an error, the pipeline also treats it as an execution failure and skips the subsequent PostHandle methods.

Completion of this stage does not mean that the HTTP response has been sent. BeforeResponse and the actual response transmission run later. See EventBus in Execution Context for how to collect and publish events.

Interceptor Processing Before and After the Response

PostHandle

The pipeline calls PostHandle when the handler, success response preparation, and post-execution hooks all succeed. It runs route interceptors in reverse order, then global interceptors in reverse order.

PostHandle cannot return an error. Use BeforeResponse for work whose outcome must affect the final response, such as committing a transaction.

BeforeResponse

On both success and failure paths, the pipeline calls BeforeResponse only for interceptors whose PreHandle succeeded. It runs route interceptors in reverse order, then global interceptors in reverse order.

executionErr contains the errors that have occurred up to that point. If BeforeResponse returns a new error, the pipeline combines it with the existing error and passes it to the next interceptor and final error handling. A transaction interceptor can use the execution outcome at this stage to commit or roll back.

An interceptor whose own PreHandle returned an error or core.ErrAbortPipeline is not included in the BeforeResponse calls.

AfterCompletion

After response processing, the pipeline calls AfterCompletion. If a route was selected, it calls all route interceptors in reverse order, then all global interceptors in reverse order. Success, errors, and deliberate termination all go through this cleanup stage.

Its scope differs from BeforeResponse. AfterCompletion can also run for interceptors whose PreHandle never ran or failed. Write cleanup code that works even when the resource was never created. If execution ends before routing, no route interceptors have been selected, so only global cleanup runs.

Use this stage for logging, metrics collection, and resource cleanup. It runs after the attempt to write the HTTP response, so an error in AfterCompletion cannot change a response that has already been sent.

Error Responses and Response Transmission

After BeforeResponse finishes, execution errors are converted into HTTP error responses. If a success response has already been prepared, the pipeline rolls it back and prepares an error response. It then writes the buffered response to the actual response writer.

Error condition	HTTP handling
No registered handler found	404
Valid httperr.HTTPError	Specified status code and message
http.MaxBytesError from exceeding the request body limit	413
Execution error without a separate mapping	500, Internal server error
Actual response already committed	Do not write a second response

Spine v0.6.0 with Echo platform v0.1.0 returns HTTP 400 for malformed JSON and invalid numeric or boolean path values, 415 for unsupported body Content-Type, and 413 when the request-body limit is exceeded. Binding fails before the controller runs. Distinguish these failures from business validation and verify them with actual requests.

An error during actual response transmission becomes part of the final execution error. If the response has not yet been committed, the pipeline attempts to write a 500 response. A response that has already been sent cannot be rolled back.

Execution Scope at Each Stopping Point

The following examples assume one global interceptor and one route interceptor. before means BeforeResponse, and after means AfterCompletion.

Successful Processing

pre:global → routing → binding → pre:route → handler
→ return → hook → post:route → post:global
→ before:route → before:global → flush → after:route → after:global

Termination in Route PreHandle

pre:global → routing → binding → pre:route(terminated)
→ before:global → flush → after:route → after:global

The controller is not invoked. The route interceptor that terminated execution does not receive BeforeResponse, but it does receive AfterCompletion.

Termination in Global PreHandle

pre:global(terminated) → flush → after:global

The router and argument binding do not run. In this example, no PreHandle has succeeded, so BeforeResponse does not run either.

Failure During Argument Binding

pre:global → routing → binding(failed)
→ before:global → prepare error response → flush → after:route → after:global

Since the route interceptor has been selected, its AfterCompletion runs. Its PreHandle has not run yet, so the route BeforeResponse does not run.

Execution Beyond HTTP

Event consumers and WebSocket use the same execution structure in separate pipeline instances. The HTTP resolvers and return value handlers do not apply unchanged.

Execution type	Routing criteria	Default arguments	Response handling
HTTP	HTTP method and request path	context.Context, spine.Ctx, path and query types, DTOs, and others	Prepare responses with HTTP return value handlers
Event consumer	EVENT and event name	context.Context, event name, raw payload, struct DTO	Handle execution results in the consumer runtime
WebSocket	WS and connection request path	context.Context, ws.ConnectionID, raw payload, struct DTO	Use the message handler's send API

In particular, HTTP DTOs use pointers, while the default consumer and WebSocket DTO resolvers support struct values. The HTTP spine.Ctx resolver is also not registered in the default consumer or WebSocket pipelines. See Execution Context for differences in context and input between protocols.