The Unsinkable Molly Brown: a full-featured Gemini server implemented in Go
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package main
import (
"bufio"
"crypto/tls"
"errors"
"fmt"
"github.com/BurntSushi/toml"
"io/ioutil"
"mime"
"net"
"net/url"
"os"
"path/filepath"
"regexp"
"strconv"
"strings"
"time"
)
func handleGeminiRequest(conn net.Conn, config Config, accessLogEntries chan LogEntry, errorLogEntries chan string) {
defer conn.Close()
var tlsConn (*tls.Conn) = conn.(*tls.Conn)
var log LogEntry
log.Time = time.Now()
log.RemoteAddr = conn.RemoteAddr()
log.RequestURL = "-"
log.Status = 0
defer func() { accessLogEntries <- log }()
// Read request
URL, err := readRequest(conn, &log, errorLogEntries)
if err != nil {
return
}
// Enforce client certificate validity
clientCerts := tlsConn.ConnectionState().PeerCertificates
enforceCertificateValidity(clientCerts, conn, &log)
if log.Status != 0 {
return
}
// 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
if URL.Hostname() != config.Hostname || (URL.Port() != "" && URL.Port() != strconv.Itoa(config.Port)) {
conn.Write([]byte("53 No proxying to other hosts or ports!\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 := resolvePath(URL.Path, config)
// Paranoid security measures:
// Fail ASAP if the URL has mapped to a sensitive file
if path == config.CertPath || path == config.KeyPath || path == config.AccessLog || path == config.ErrorLog {
conn.Write([]byte("51 Not found!\r\n"))
log.Status = 51
return
}
// Read Molly files
if config.ReadMollyFiles {
parseMollyFiles(path, &config, errorLogEntries)
}
// Check for redirects
handleRedirects(URL, config, conn, &log)
if log.Status != 0 {
return
}
// Check whether this URL is in a certificate zone
handleCertificateZones(URL, clientCerts, config, conn, &log)
if log.Status != 0 {
return
}
// Check whether this URL is in a configured CGI path
for _, cgiPath := range config.CGIPaths {
inCGIPath, err := regexp.Match(cgiPath, []byte(path))
if err == nil && inCGIPath {
handleCGI(config, path, URL, &log, errorLogEntries, conn)
if log.Status != 0 {
return
}
}
}
// Check whether this URL is mapped to an SCGI app
for scgi_url, scgi_socket := range config.SCGIPaths {
matched, err := regexp.Match(scgi_url, []byte(URL.Path))
if matched && err == nil {
handleSCGI(scgi_socket, config, URL, &log, conn)
return
}
}
// Fail if file does not exist or perms aren't right
info, err := os.Stat(path)
if os.IsNotExist(err) || os.IsPermission(err) {
conn.Write([]byte("51 Not found!\r\n"))
log.Status = 51
return
} else if err != nil {
1 year ago
conn.Write([]byte("40 Temporary 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
}
// Don't serve Molly files
if filepath.Base(path) == ".molly" {
conn.Write([]byte("51 Not found!\r\n"))
log.Status = 51
return
}
// Finally, serve the file or directory
if info.IsDir() {
serveDirectory(URL, path, &log, conn, config, errorLogEntries)
} else {
serveFile(path, &log, conn, config, errorLogEntries)
}
}
func readRequest(conn net.Conn, log *LogEntry, errorLog chan string) (*url.URL, error) {
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 nil, errors.New("Request too long")
} else if err != nil {
errorLog <- "Error reading request: " + err.Error()
conn.Write([]byte("40 Unknown error reading request!\r\n"))
log.Status = 40
return nil, errors.New("Error reading request")
}
// Parse request as URL
URL, err := url.Parse(string(request))
if err != nil {
errorLog <- "Error parsing request URL " + string(request) + ": " + err.Error()
conn.Write([]byte("59 Error parsing URL!\r\n"))
log.Status = 59
return nil, errors.New("Bad URL in request")
}
log.RequestURL = URL.String()
// Set implicit scheme
if URL.Scheme == "" {
URL.Scheme = "gemini"
}
return URL, nil
}
func resolvePath(path string, config Config) string {
// 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)
path = filepath.Clean(path)
} else {
path = filepath.Join(config.DocBase, path)
}
return path
}
func parseMollyFiles(path string, config *Config, errorLogEntries chan string) {
// Build list of directories to check
var dirs []string
dirs = append(dirs, path)
for {
if path == filepath.Clean(config.DocBase) {
break
}
subpath := filepath.Dir(path)
dirs = append(dirs, subpath)
path = subpath
}
// Initialise MollyFile using main Config
var mollyFile MollyFile
mollyFile.GeminiExt = config.GeminiExt
mollyFile.DefaultLang = config.DefaultLang
mollyFile.DirectorySort = config.DirectorySort
mollyFile.DirectoryReverse = config.DirectoryReverse
mollyFile.DirectoryTitles = config.DirectoryTitles
// Parse files in reverse order
for i := len(dirs) - 1; i >= 0; i-- {
dir := dirs[i]
// Break out of the loop if a directory doesn't exist
_, err := os.Stat(dir)
if os.IsNotExist(err) {
break
}
// Construct path for a .molly file in this dir
mollyPath := filepath.Join(dir, ".molly")
_, err = os.Stat(mollyPath)
if err != nil {
continue
}
// If the file exists and we can read it, try to parse it
_, err = toml.DecodeFile(mollyPath, &mollyFile)
if err != nil {
errorLogEntries <- "Error parsing .molly file " + mollyPath + ": " + err.Error()
continue
}
// Overwrite main Config using MollyFile
config.GeminiExt = mollyFile.GeminiExt
config.DefaultLang = mollyFile.DefaultLang
config.DirectorySort = mollyFile.DirectorySort
config.DirectoryReverse = mollyFile.DirectoryReverse
config.DirectoryTitles = mollyFile.DirectoryTitles
for key, value := range mollyFile.TempRedirects {
config.TempRedirects[key] = value
}
for key, value := range mollyFile.PermRedirects {
config.PermRedirects[key] = value
}
for key, value := range mollyFile.MimeOverrides {
config.MimeOverrides[key] = value
}
for key, value := range mollyFile.CertificateZones {
config.CertificateZones[key] = value
}
}
}
func handleRedirects(URL *url.URL, config Config, conn net.Conn, log *LogEntry) {
for src, dst := range config.TempRedirects {
if URL.Path == src {
URL.Path = dst
conn.Write([]byte("30 " + URL.String() + "\r\n"))
log.Status = 30
return
}
}
for src, dst := range config.PermRedirects {
if URL.Path == src {
URL.Path = dst
conn.Write([]byte("31 " + URL.String() + "\r\n"))
log.Status = 31
return
}
}
}
func serveDirectory(URL *url.URL, path string, log *LogEntry, conn net.Conn, config Config, errorLogEntries chan string) {
// 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
}
// Check for index.gmi if path is a directory
index_path := filepath.Join(path, "index."+config.GeminiExt)
index_info, err := os.Stat(index_path)
if err == nil && uint64(index_info.Mode().Perm())&0444 == 0444 {
serveFile(index_path, log, conn, config, errorLogEntries)
// Serve a generated listing
} else {
conn.Write([]byte("20 text/gemini\r\n"))
log.Status = 20
conn.Write([]byte(generateDirectoryListing(URL, path, config)))
}
}
func serveFile(path string, log *LogEntry, conn net.Conn, config Config, errorLog chan string) {
// Get MIME type of files
ext := filepath.Ext(path)
var mimeType string
if ext == "."+config.GeminiExt {
mimeType = "text/gemini"
} else {
mimeType = mime.TypeByExtension(ext)
}
// Override extension-based MIME type
for pathRegex, newType := range config.MimeOverrides {
overridden, err := regexp.Match(pathRegex, []byte(path))
if err == nil && overridden {
mimeType = newType
}
}
// Set a generic MIME type if the extension wasn't recognised
if mimeType == "" {
mimeType = "application/octet-stream"
}
// Add lang parameter
if mimeType == "text/gemini" && config.DefaultLang != "" {
mimeType += "; lang=" + config.DefaultLang
}
contents, err := ioutil.ReadFile(path)
if err != nil {
conn.Write([]byte("50 Error!\r\n"))
log.Status = 50
return
}
conn.Write([]byte(fmt.Sprintf("20 %s\r\n", mimeType)))
log.Status = 20
conn.Write(contents)
}