feat: add AttachmentHandler for downloading attachments

Co-authored-by: Copilot <223556219+Copilot@users.noreply.github.com>

Author: AchoArnold

api/pkg/handlers/attachment_handler.go

@@ -0,0 +1,82 @@
+package handlers
+
+import (
+	"fmt"
+	"path/filepath"
+
+	"github.com/NdoleStudio/httpsms/pkg/repositories"
+	"github.com/NdoleStudio/httpsms/pkg/telemetry"
+	"github.com/gofiber/fiber/v2"
+	"github.com/palantir/stacktrace"
+)
+
+// AttachmentHandler handles attachment download requests
+type AttachmentHandler struct {
+	handler
+	logger  telemetry.Logger
+	tracer  telemetry.Tracer
+	storage repositories.AttachmentStorage
+}
+
+// NewAttachmentHandler creates a new AttachmentHandler
+func NewAttachmentHandler(
+	logger telemetry.Logger,
+	tracer telemetry.Tracer,
+	storage repositories.AttachmentStorage,
+) (h *AttachmentHandler) {
+	return &AttachmentHandler{
+		logger:  logger.WithService(fmt.Sprintf("%T", h)),
+		tracer:  tracer,
+		storage: storage,
+	}
+}
+
+// RegisterRoutes registers the routes for the AttachmentHandler (no auth middleware — public endpoint)
+func (h *AttachmentHandler) RegisterRoutes(router fiber.Router) {
+	router.Get("/v1/attachments/:userID/:messageID/:attachmentIndex/:filename", h.GetAttachment)
+}
+
+// GetAttachment downloads an attachment
+// @Summary      Download a message attachment
+// @Description  Download an MMS attachment by its path components
+// @Tags         Attachments
+// @Produce      octet-stream
+// @Param        userID           path  string  true  "User ID"
+// @Param        messageID        path  string  true  "Message ID"
+// @Param        attachmentIndex  path  string  true  "Attachment index"
+// @Param        filename         path  string  true  "Filename with extension"
+// @Success      200  {file}  binary
+// @Failure      404  {object}  responses.NotFoundResponse
+// @Failure      500  {object}  responses.InternalServerError
+// @Router       /attachments/{userID}/{messageID}/{attachmentIndex}/{filename} [get]
+func (h *AttachmentHandler) GetAttachment(c *fiber.Ctx) error {
+	ctx, span := h.tracer.StartFromFiberCtx(c)
+	defer span.End()
+
+	ctxLogger := h.tracer.CtxLogger(h.logger, span)
+
+	userID := c.Params("userID")
+	messageID := c.Params("messageID")
+	attachmentIndex := c.Params("attachmentIndex")
+	filename := c.Params("filename")
+
+	path := fmt.Sprintf("attachments/%s/%s/%s/%s", userID, messageID, attachmentIndex, filename)
+
+	ctxLogger.Info(fmt.Sprintf("downloading attachment from path [%s]", path))
+
+	data, err := h.storage.Download(ctx, path)
+	if err != nil {
+		msg := fmt.Sprintf("cannot download attachment from path [%s]", path)
+		ctxLogger.Warn(stacktrace.Propagate(err, msg))
+		return h.responseNotFound(c, "attachment not found")
+	}
+
+	ext := filepath.Ext(filename)
+	contentType := repositories.ContentTypeFromExtension(ext)
+
+	c.Set("Content-Type", contentType)
+	c.Set("Content-Disposition", "attachment")
+	c.Set("X-Content-Type-Options", "nosniff")
+
+	return c.Send(data)
+}