Go Create Chi Handler

Generate Chi HTTP handler implementations for a Go backend.

Handler Structure

Location: internal/modules/<module>/http/chi/handler/<resource>_handler.go

package handler

import (
	"net/http"
	"strconv"

	"github.com/cristiano-pacheco/bricks/pkg/http/request"
	"github.com/cristiano-pacheco/bricks/pkg/http/response"
	"github.com/cristiano-pacheco/bricks/pkg/logger"
	"github.com/cristiano-pacheco/pingo/internal/modules/<module>/http/dto"
	"github.com/cristiano-pacheco/pingo/internal/modules/<module>/usecase"
	"github.com/go-chi/chi/v5"
)

type ResourceHandler struct {
	resourceCreateUseCase *usecase.ResourceCreateUseCase
	resourceListUseCase   *usecase.ResourceListUseCase
	resourceUpdateUseCase *usecase.ResourceUpdateUseCase
	resourceDeleteUseCase *usecase.ResourceDeleteUseCase
	errorHandler          response.ErrorHandler
	logger                logger.Logger
}

func NewResourceHandler(
	resourceCreateUseCase *usecase.ResourceCreateUseCase,
	resourceListUseCase   *usecase.ResourceListUseCase,
	resourceUpdateUseCase *usecase.ResourceUpdateUseCase,
	resourceDeleteUseCase *usecase.ResourceDeleteUseCase,
	errorHandler response.ErrorHandler,
	logger logger.Logger,
) *ResourceHandler {
	return &ResourceHandler{
		resourceCreateUseCase: resourceCreateUseCase,
		resourceListUseCase:   resourceListUseCase,
		resourceUpdateUseCase: resourceUpdateUseCase,
		resourceDeleteUseCase: resourceDeleteUseCase,
		errorHandler:          errorHandler,
		logger:                logger,
	}
}

DTOs (Data Transfer Objects)

Request and response DTOs are defined in internal/modules/<module>/http/dto/<resource>_dto.go.

Typical DTO structure:

package dto

type CreateResourceRequest struct {
	Field1 string `json:"field1"`
	Field2 int    `json:"field2"`
}

type CreateResourceResponse struct {
	ID     uint64 `json:"id"`
	Field1 string `json:"field1"`
	Field2 int    `json:"field2"`
}

type UpdateResourceRequest struct {
	Field1 string `json:"field1"`
	Field2 int    `json:"field2"`
}

type ResourceResponse struct {
	ID     uint64 `json:"id"`
	Field1 string `json:"field1"`
	Field2 int    `json:"field2"`
}

Key points:

•DTOs live in the HTTP transport layer, separate from use case inputs or models
•Use JSON tags for serialization
•Keep DTOs focused on HTTP contract, not domain logic

Handler Method Patterns

List (GET /resource)

// @Summary		List resources
// @Description	Retrieves all resources
// @Tags		Resources
// @Accept		json
// @Produce		json
// @Security 	BearerAuth
// @Success		200	{object}	response.Envelope[[]dto.ResourceResponse]	"Successfully retrieved resources"
// @Failure		401	{object}	errs.Error	"Invalid credentials"
// @Failure		500	{object}	errs.Error	"Internal server error"
// @Router		/api/v1/resources [get]
func (h *ResourceHandler) ListResources(w http.ResponseWriter, r *http.Request) {
	ctx := r.Context()

	output, err := h.resourceListUseCase.Execute(ctx)
	if err != nil {
		h.logger.Error("failed to list resources", logger.Error(err))
		h.errorHandler.Error(w, err)
		return
	}

	resources := make([]dto.ResourceResponse, len(output.Resources))
	for i, resource := range output.Resources {
		resources[i] = dto.ResourceResponse{
			ID:   resource.ID,
			Name: resource.Name,
			// ... map other fields
		}
	}

	err = response.JSON(w, http.StatusOK, resources, http.Header{})
	if err != nil {
		h.logger.Error("failed to write response", logger.Error(err))
		h.errorHandler.Error(w, err)
		return
	}
}

Create (POST /resource)

// @Summary		Create resource
// @Description	Creates a new resource
// @Tags		Resources
// @Accept		json
// @Produce		json
// @Security 	BearerAuth
// @Param		request	body	dto.CreateResourceRequest	true	"Resource data"
// @Success		201	{object}	response.Envelope[dto.CreateResourceResponse]	"Successfully created resource"
// @Failure		422	{object}	errs.Error	"Invalid request format or validation error"
// @Failure		401	{object}	errs.Error	"Invalid credentials"
// @Failure		500	{object}	errs.Error	"Internal server error"
// @Router		/api/v1/resources [post]
func (h *ResourceHandler) CreateResource(w http.ResponseWriter, r *http.Request) {
	ctx := r.Context()
	var createRequest dto.CreateResourceRequest

	err := request.ReadJSON(w, r, &createRequest)
	if err != nil {
		h.logger.Error("failed to parse request body", logger.Error(err))
		h.errorHandler.Error(w, err)
		return
	}

	input := usecase.ResourceCreateInput{
		Name: createRequest.Name,
		// ... map other fields
	}

	output, err := h.resourceCreateUseCase.Execute(ctx, input)
	if err != nil {
		h.logger.Error("failed to create resource", logger.Error(err))
		h.errorHandler.Error(w, err)
		return
	}

	createResponse := dto.CreateResourceResponse{
		ID:   output.ID,
		Name: output.Name,
		// ... map other fields
	}

	err = response.JSON(w, http.StatusCreated, createResponse, http.Header{})
	if err != nil {
		h.logger.Error("failed to write response", logger.Error(err))
		h.errorHandler.Error(w, err)
		return
	}
}

Update (PUT /resource/:id)

// @Summary		Update resource
// @Description	Updates an existing resource
// @Tags		Resources
// @Accept		json
// @Produce		json
// @Security 	BearerAuth
// @Param		id		path	int	true	"Resource ID"
// @Param		request	body	dto.UpdateResourceRequest	true	"Resource data"
// @Success		204		"Successfully updated resource"
// @Failure		422	{object}	errs.Error	"Invalid request format or validation error"
// @Failure		401	{object}	errs.Error	"Invalid credentials"
// @Failure		404	{object}	errs.Error	"Resource not found"
// @Failure		500	{object}	errs.Error	"Internal server error"
// @Router		/api/v1/resources/{id} [put]
func (h *ResourceHandler) UpdateResource(w http.ResponseWriter, r *http.Request) {
	ctx := r.Context()
	var updateRequest dto.UpdateResourceRequest

	err := request.ReadJSON(w, r, &updateRequest)
	if err != nil {
		h.logger.Error("failed to parse request body", logger.Error(err))
		h.errorHandler.Error(w, err)
		return
	}

	idStr := chi.URLParam(r, "id")
	id, err := strconv.ParseUint(idStr, 10, 64)
	if err != nil {
		h.logger.Error("invalid resource ID", logger.Error(err))
		h.errorHandler.Error(w, err)
		return
	}

	input := usecase.ResourceUpdateInput{
		ID:   id,
		Name: updateRequest.Name,
		// ... map other fields
	}

	err = h.resourceUpdateUseCase.Execute(ctx, input)
	if err != nil {
		h.logger.Error("failed to update resource", logger.Error(err))
		h.errorHandler.Error(w, err)
		return
	}

	response.NoContent(w)
}

Delete (DELETE /resource/:id)

// @Summary		Delete resource
// @Description	Deletes an existing resource
// @Tags		Resources
// @Accept		json
// @Produce		json
// @Security 	BearerAuth
// @Param		id	path	int	true	"Resource ID"
// @Success		204		"Successfully deleted resource"
// @Failure		401	{object}	errs.Error	"Invalid credentials"
// @Failure		404	{object}	errs.Error	"Resource not found"
// @Failure		500	{object}	errs.Error	"Internal server error"
// @Router		/api/v1/resources/{id} [delete]
func (h *ResourceHandler) DeleteResource(w http.ResponseWriter, r *http.Request) {
	ctx := r.Context()

	idStr := chi.URLParam(r, "id")
	id, err := strconv.ParseUint(idStr, 10, 64)
	if err != nil {
		h.logger.Error("invalid resource ID", logger.Error(err))
		h.errorHandler.Error(w, err)
		return
	}

	input := usecase.ResourceDeleteInput{
		ID: id,
	}

	err = h.resourceDeleteUseCase.Execute(ctx, input)
	if err != nil {
		h.logger.Error("failed to delete resource", logger.Error(err))
		h.errorHandler.Error(w, err)
		return
	}

	response.NoContent(w)
}

Get by ID (GET /resource/:id)

// @Summary		Get resource
// @Description	Retrieves a resource by ID
// @Tags		Resources
// @Accept		json
// @Produce		json
// @Security 	BearerAuth
// @Param		id	path	int	true	"Resource ID"
// @Success		200	{object}	response.Envelope[dto.ResourceResponse]	"Successfully retrieved resource"
// @Failure		401	{object}	errs.Error	"Invalid credentials"
// @Failure		404	{object}	errs.Error	"Resource not found"
// @Failure		500	{object}	errs.Error	"Internal server error"
// @Router		/api/v1/resources/{id} [get]
func (h *ResourceHandler) GetResource(w http.ResponseWriter, r *http.Request) {
	ctx := r.Context()

	idStr := chi.URLParam(r, "id")
	id, err := strconv.ParseUint(idStr, 10, 64)
	if err != nil {
		h.logger.Error("invalid resource ID", logger.Error(err))
		h.errorHandler.Error(w, err)
		return
	}

	input := usecase.ResourceGetInput{
		ID: id,
	}

	output, err := h.resourceGetUseCase.Execute(ctx, input)
	if err != nil {
		h.logger.Error("failed to get resource", logger.Error(err))
		h.errorHandler.Error(w, err)
		return
	}

	resourceResponse := dto.ResourceResponse{
		ID:   output.ID,
		Name: output.Name,
		// ... map other fields
	}

	err = response.JSON(w, http.StatusOK, resourceResponse, http.Header{})
	if err != nil {
		h.logger.Error("failed to write response", logger.Error(err))
		h.errorHandler.Error(w, err)
		return
	}
}

Swagger Annotation Rules

•@Summary: Brief action description (e.g., "List resources", "Create resource")
•@Description: Full description of what the endpoint does
•@Tags: Plural resource name (e.g., "Resources", "Contacts")
•@Accept: Always json
•@Produce: Always json
•@Security: Add BearerAuth if authentication required
•
@Param: Define path params and request body
- •Path param: @Param id path int true "Resource ID"
- •Request body: @Param request body dto.CreateResourceRequest true "Resource data"
•
@Success: Status code with response type
- •200: {object} response.Envelope[dto.ResourceResponse]
- •201: {object} response.Envelope[dto.CreateResourceResponse]
- •204: No content, just description string
•@Failure: Common errors (401, 404, 422, 500) with {object} errs.Error
•@Router: /api/v1/resources/{id} [method]

Request/Response Mapping

Handler methods bridge HTTP requests/responses (DTOs from internal/modules/<module>/http/dto) with use case inputs/outputs.

Request to Use Case Input

// Decode request
var req dto.CreateResourceRequest

err := request.ReadJSON(w, r, &req)
if err != nil {
	h.logger.Error("failed to parse request body", logger.Error(err))
	h.errorHandler.Error(w, err)
	return
}

// Map to use case input
input := usecase.ResourceCreateInput{
	Field1: req.Field1,
	Field2: req.Field2,
}

Use Case Output to Response

// Execute use case
output, err := h.resourceCreateUseCase.Execute(ctx, input)
if err != nil {
	h.logger.Error("failed to create resource", logger.Error(err))
	h.errorHandler.Error(w, err)
	return
}

// Map to response DTO
response := dto.CreateResourceResponse{
	ID:     output.ID,
	Field1: output.Field1,
	Field2: output.Field2,
}

Error Handling Pattern

Every error follows this pattern:

if err != nil {
	h.logger.Error("descriptive error message", logger.Error(err))
	h.errorHandler.Error(w, err)
	return
}

Error messages:

•"failed to parse request body" - JSON decode error
•"invalid resource ID" - URL param parsing error
•"failed to list resources" - List use case error
•"failed to create resource" - Create use case error
•"failed to update resource" - Update use case error
•"failed to delete resource" - Delete use case error
•"failed to get resource" - Get use case error
•"failed to write response" - JSON response write error

Fx Wiring

Add to internal/modules/<module>/fx.go:

fx.Provide(handler.NewResourceHandler),

The handler is typically provided to the router, not exposed as a port.

Critical Rules

•Struct: Include all use cases, response.ErrorHandler, and logger.Logger
•Constructor: MUST return pointer *ResourceHandler
•Context: Always get from request: ctx := r.Context()
•Request decoding: Use request.ReadJSON(w, r, &dto) - declare variable first, then call ReadJSON
•URL params: Use chi.URLParam(r, "paramName") and strconv.ParseUint for IDs
•Error handling: Always log error and call h.errorHandler.Error(w, err) then return
•Response mapping: Map use case output to DTO, don't return use case outputs directly
•
Success responses:
- •List/Get: Use response.JSON(w, http.StatusOK, data, http.Header{})
- •Create: Use response.JSON(w, http.StatusCreated, data, http.Header{})
- •Update/Delete: Use response.NoContent(w)
•Swagger: MUST add complete swagger annotations for every handler method
•No comments: Do not add redundant comments inside method bodies
•Validation: Run make lint and make update-swagger after generation

Workflow

•Create handler struct with use case dependencies
•Implement constructor NewResourceHandler
•Implement handler methods following patterns above
•Add swagger annotations to all methods
•Add Fx wiring to module's fx.go
•Run make lint and make nilaway to verify the static tests
•Run make update-swagger to regenerate swagger docs