molly-brown/handler.go

package main

import (
		"bufio"
		"context"
		"fmt"
		"io"
		"io/ioutil"
		"log"
		"mime"
		"net"
		"net/url"
		"os"
		"os/exec"
		"path/filepath"
		"regexp"
		"strconv"
		"strings"
		"time"
)

func handleGeminiRequest(conn net.Conn, config Config, logEntries chan LogEntry) {
	defer conn.Close()
	var log LogEntry
	log.Time = time.Now()
	log.RemoteAddr = conn.RemoteAddr()
	log.RequestURL = "-"
	log.Status = 0
	defer func() { logEntries <- log }()

	// Read request
	reader := bufio.NewReaderSize(conn, 1024)
	request, overflow, err := reader.ReadLine()
	if overflow {
		conn.Write([]byte("59 Request too long!r\n"))
		log.Status = 59
		return
	} else if err != nil {
		conn.Write([]byte("40 Unknown error reading request!r\n"))
		log.Status = 40
		return
	}

	// Parse request as URL
	URL, err := url.Parse(string(request))
	if err != nil {
		conn.Write([]byte("59 Error parsing URL!r\n"))
		log.Status = 59
		return
	}
	log.RequestURL = URL.String()

	// Set implicit scheme
	if URL.Scheme == "" {
		URL.Scheme = "gemini"
	}

	// Reject non-gemini schemes
	if URL.Scheme != "gemini" {
		conn.Write([]byte("53 No proxying to non-Gemini content!\r\n"))
		log.Status = 53
		return
	}

	// Reject requests for content from other servers
	requestHostname := strings.Split(URL.Host, ":")[0] // Shave off port
	if requestHostname != config.Hostname {
		conn.Write([]byte("53 No proxying to other hosts!\r\n"))
		log.Status = 53
		return
	}

	// Fail if there are dots in the path
	if strings.Contains(URL.Path, "..") {
		conn.Write([]byte("50 Your directory traversal technique has been defeated!\r\n"))
		log.Status = 50
		return
	}

	}

	// Resolve URI path to actual filesystem path
	path, info, err := resolvePath(URL.Path, config)

	// Fail if file does not exist or perms aren't right
	if os.IsNotExist(err) || os.IsPermission(err) {
		conn.Write([]byte("51 Not found!\r\n"))
		log.Status = 51
		return
	} else if err != nil {
		conn.Write([]byte("40 Temporaray failure!\r\n"))
		log.Status = 40
		return
	} else if uint64(info.Mode().Perm())&0444 != 0444 {
		conn.Write([]byte("51 Not found!\r\n"))
		log.Status = 51
		return
	}

	// Handle directories
	if info.IsDir() {
		// Redirect to add trailing slash if missing
		// (otherwise relative links don't work properly)
		if !strings.HasSuffix(URL.Path, "/") {
			conn.Write([]byte(fmt.Sprintf("31 %s\r\n", URL.String()+"/")))
			log.Status = 31
			return
		}
		// Serve a generated listing
		conn.Write([]byte("20 text/gemini\r\n"))
		log.Status = 20
		conn.Write([]byte(generateDirectoryListing(path)))
		return
	}

	// If this file is executable, get dynamic content
	inCGIPath, err := regexp.Match(config.CGIPath, []byte(path))
	if inCGIPath && info.Mode().Perm() & 0111 == 0111 {
		handleCGI(path, URL, log, conn)
		return
	}

	// Otherwise, serve the file contents
	serveFile(path, log, conn)
	return

}

func resolvePath(path string, config Config) (string, os.FileInfo, error) {
	// Handle tildes
	if strings.HasPrefix(path, "/~") {
	    bits := strings.Split(path, "/")
		username := bits[1][1:]
		new_prefix := filepath.Join(config.DocBase, config.HomeDocBase, username)
		path = strings.Replace(path, bits[1], new_prefix, 1)
	} else {
		path = filepath.Join(config.DocBase, path)
	}
	// Make sure this file exists and is readable
	info, err := os.Stat(path)
	if err != nil {
		return "", nil, err
	}
	// Check for index.gmi if path is a directory
	if info.IsDir() {
		index_path := filepath.Join(path, "index.gmi")
		index_info, err := os.Stat(index_path)
		if err == nil {
			path = index_path
			info = index_info
		} else if os.IsPermission(err) {
			return "", nil, err
		}
	}
	return path, info, nil
}

func generateDirectoryListing(path string) string {
	var listing string
	files, err := ioutil.ReadDir(path)
	if err != nil {
		log.Fatal(err)
	}
	listing = "# Directory listing\n\n"
	for _, file := range files {
		// Skip dotfiles
		if strings.HasPrefix(file.Name(), ".") {
			continue
		}
		// Only list world readable files
		if uint64(file.Mode().Perm())&0444 != 0444 {
			continue
		}
		listing += fmt.Sprintf("=> %s %s\n", url.PathEscape(file.Name()), file.Name())
	}
	return listing
}

func serveFile(path string, log LogEntry, conn net.Conn) {
	// Get MIME type of files
	ext := filepath.Ext(path)
	var mimeType string
	if ext == ".gmi" {
		mimeType = "text/gemini"
	} else {
		mimeType = mime.TypeByExtension(ext)
	}
	contents, err := ioutil.ReadFile(path)
	if err != nil {
		conn.Write([]byte("50 Error!\r\n"))
		log.Status = 50
	}
	conn.Write([]byte(fmt.Sprintf("20 %s\r\n", mimeType)))
	log.Status = 20
	conn.Write(contents)
}

func handleCGI(path string, URL *url.URL, log LogEntry, conn net.Conn) {
	ctx, cancel := context.WithTimeout(context.Background(), 10*time.Second)
	defer cancel()
	cmd := exec.CommandContext(ctx, path)
	stdin, err := cmd.StdinPipe()
	if err != nil {
		conn.Write([]byte("42 CGI error!\r\n"))
		log.Status = 42
		return
	}
	defer stdin.Close()
	io.WriteString(stdin, URL.String())
	io.WriteString(stdin, "\r\n")
	stdin.Close()
	response, err := cmd.Output()
	if ctx.Err() == context.DeadlineExceeded {
		conn.Write([]byte("42 CGI process timed out!\r\n"))
		log.Status = 42
		return
	}
	if err != nil {
		conn.Write([]byte("42 CGI error!\r\n"))
		log.Status = 42
		return
	}
	// Extract response header
	header, _, err := bufio.NewReader(strings.NewReader(string(response))).ReadLine()
	status, err2 := strconv.Atoi(strings.Fields(string(header))[0])
	if err != nil || err2 != nil {
		conn.Write([]byte("42 CGI error!\r\n"))
		log.Status = 42
		return
	}
	log.Status = status
	// Write response
	conn.Write(response)
}