shavit/handler.go

package main

import (
	"fmt"
	"log"
	"net/url"
	"os"
	"path/filepath"
	"strings"

	gemini "git.sr.ht/~yotam/go-gemini"
)

// GeminiError wrap the standard Go error with a Gemini status code
type GeminiError struct {
	Err    error
	Status int
}

// Error return the string of the inner error to fulfill the error interface
func (e GeminiError) Error() string {
	return e.Err.Error()
}

// Handler is the main handler of the server
type Handler struct {
	source string
}

func (h Handler) urlAbsPath(rawURL string) (string, error) {
	u, err := url.Parse(rawURL)
	if err != nil {
		return "", GeminiError{err, gemini.StatusBadRequest}
	}

	itemPath, err := filepath.Abs(filepath.Join(h.source, u.Path))
	if err != nil {
		return "", GeminiError{err, gemini.StatusTemporaryFailure}
	}

	if !strings.HasPrefix(itemPath, h.source) {
		return "", GeminiError{fmt.Errorf("Permission Denied"), gemini.StatusBadRequest}
	}

	return itemPath, nil
}

func (h Handler) isFile(path string) bool {
	fileInfo, err := os.Stat(path)
	if err != nil {
		return false
	}

	return fileInfo.Mode().IsRegular()
}

func (h Handler) getFilePath(rawURL string) (string, error) {
	itemPath, err := h.urlAbsPath(rawURL)
	if err != nil {
		return "", err
	}

	if h.isFile(itemPath) {
		return itemPath, nil
	}

	indexPath := filepath.Join(itemPath, "index.gemi")
	if h.isFile(indexPath) {
		return indexPath, nil
	}

	return "", GeminiError{fmt.Errorf("File Not Found"), gemini.StatusNotFound}
}

func (h Handler) errorResponse(err error) gemini.Response {
	if err == nil {
		panic("nil error is not a valid parameter")
	}

	if ge, ok := err.(GeminiError); ok {
		return gemini.Response{Status: ge.Status, Meta: ge.Error(), Body: nil}
	}

	return gemini.Response{Status: gemini.StatusTemporaryFailure, Meta: err.Error(), Body: nil}
}

// Handle implement the gemini.Handler interface by serving files from a given source directory
func (h Handler) Handle(r gemini.Request) gemini.Response {
	itemPath, err := h.getFilePath(r.URL)
	if err != nil {
		return h.errorResponse(err)
	}

	log.Println("Serving file from", itemPath)

	file, err := os.Open(itemPath)
	if err != nil {
		return h.errorResponse(err)
	}

	return gemini.Response{Status: gemini.StatusSuccess, Meta: "text/gemini", Body: file}
}