# A file loader server (?)
# The idea here is that we receive requests with a socket, then respond to each
# with a response (ideally a document.)
# For now, the protocol looks like:
# C: Request
# S: res (0 => success, _ => error)
# if success:
#  S: output ID
#  S: status code
#  S: headers
#  C: resume
#  S: response body
# else:
#  S: error message
#
# The body is passed to the stream as-is, so effectively nothing can follow it.
#
# Note: if the consumer closes the request's body after headers have been
# passed, it will *not* be cleaned up until a `resume' command is
# received. (This allows for passing outputIds to the pager for later
# addCacheFile commands there.)

import std/deques
import std/nativesockets
import std/net
import std/options
import std/os
import std/posix
import std/strutils
import std/tables

import io/bufreader
import io/bufwriter
import io/dynstream
import io/poll
import io/serversocket
import io/stdio
import io/tempfile
import io/urlfilter
import loader/connecterror
import loader/headers
import loader/loaderhandle
import loader/loaderiface
import loader/request
import monoucha/javascript
import types/cookie
import types/formdata
import types/opt
import types/referrer
import types/urimethodmap
import types/url
import utils/twtstr

type
  CachedItem = ref object
    id: int
    refc: int
    offset: int
    path: string

  ClientData = ref object
    pid: int
    key: ClientKey
    # List of cached resources.
    cacheMap: seq[CachedItem]
    # List of file descriptors passed by the client.
    passedFdMap: Table[string, FileHandle] # host -> fd
    config: LoaderClientConfig

  LoaderContext = ref object
    pagerClient: ClientData
    ssock: ServerSocket
    alive: bool
    config: LoaderConfig
    handleMap: seq[LoaderHandle]
    pollData: PollData
    # List of existing clients (buffer or pager) that may make requests.
    clientData: Table[int, ClientData] # pid -> data
    # ID of next output. TODO: find a better allocation scheme
    outputNum: int

  LoaderConfig* = object
    cgiDir*: seq[string]
    uriMethodMap*: URIMethodMap
    w3mCGICompat*: bool
    tmpdir*: string
    sockdir*: string

func isPrivileged(ctx: LoaderContext; client: ClientData): bool =
  return ctx.pagerClient == client

#TODO this may be too low if we want to use urimethodmap for everything
const MaxRewrites = 4

func canRewriteForCGICompat(ctx: LoaderContext; path: string): bool =
  if path.startsWith("/cgi-bin/") or path.startsWith("/$LIB/"):
    return true
  for dir in ctx.config.cgiDir:
    if path.startsWith(dir):
      return true
  return false

proc rejectHandle(handle: InputHandle; code: ConnectErrorCode; msg = "") =
  handle.sendResult(code, msg)
  handle.close()

iterator inputHandles(ctx: LoaderContext): InputHandle {.inline.} =
  for it in ctx.handleMap:
    if it != nil and it of InputHandle:
      yield InputHandle(it)

iterator outputHandles(ctx: LoaderContext): OutputHandle {.inline.} =
  for it in ctx.handleMap:
    if it != nil and it of OutputHandle:
      yield OutputHandle(it)

func findOutput(ctx: LoaderContext; id: int; client: ClientData): OutputHandle =
  assert id != -1
  for it in ctx.outputHandles:
    if it.outputId == id:
      # verify that it's safe to access this handle.
      doAssert ctx.isPrivileged(client) or client.pid == it.ownerPid
      return it
  return nil

func findCachedHandle(ctx: LoaderContext; cacheId: int): InputHandle =
  assert cacheId != -1
  for it in ctx.inputHandles:
    if it.cacheId == cacheId:
      return it
  return nil

func find(cacheMap: seq[CachedItem]; id: int): int =
  for i, it in cacheMap:
    if it.id == id:
      return i
  -1

type PushBufferResult = enum
  pbrDone, pbrUnregister

proc register(ctx: LoaderContext; handle: InputHandle) =
  assert not handle.registered
  ctx.pollData.register(handle.stream.fd, cshort(POLLIN))
  handle.registered = true

proc unregister(ctx: LoaderContext; handle: InputHandle) =
  assert handle.registered
  ctx.pollData.unregister(int(handle.stream.fd))
  handle.registered = false

proc register(ctx: LoaderContext; output: OutputHandle) =
  assert not output.registered
  ctx.pollData.register(int(output.stream.fd), cshort(POLLOUT))
  output.registered = true

proc unregister(ctx: LoaderContext; output: OutputHandle) =
  assert output.registered
  ctx.pollData.unregister(int(output.stream.fd))
  output.registered = false

# Either write data to the target output, or append it to the list of buffers to
# write and register the output in our selector.
proc pushBuffer(ctx: LoaderContext; output: OutputHandle; buffer: LoaderBuffer;
    si: int): PushBufferResult =
  if output.suspended:
    if output.currentBuffer == nil:
      output.currentBuffer = buffer
      output.currentBufferIdx = si
    else:
      # si must be 0 here in all cases. Why? Well, it indicates the first unread
      # position after reading headers, and at that point currentBuffer will
      # be empty.
      #
      # Obviously, this breaks down if anything is pushed into the stream
      # before the header parser destroys itself. For now it never does, so we
      # should be fine.
      doAssert si == 0
      output.buffers.addLast(buffer)
  elif output.currentBuffer == nil:
    var n = si
    try:
      n += output.stream.sendData(buffer, si)
    except ErrorAgain:
      discard
    except ErrorBrokenPipe:
      return pbrUnregister
    if n < buffer.len:
      output.currentBuffer = buffer
      output.currentBufferIdx = n
      ctx.register(output)
  else:
    output.buffers.addLast(buffer)
  pbrDone

proc getOutputId(ctx: LoaderContext): int =
  result = ctx.outputNum
  inc ctx.outputNum

proc redirectToFile(ctx: LoaderContext; output: OutputHandle;
    targetPath: string): bool =
  let ps = newPosixStream(targetPath, O_CREAT or O_WRONLY, 0o600)
  if ps == nil:
    return false
  try:
    if output.currentBuffer != nil:
      let n = ps.sendData(output.currentBuffer, output.currentBufferIdx)
      if unlikely(n < output.currentBuffer.len - output.currentBufferIdx):
        ps.sclose()
        return false
    for buffer in output.buffers:
      let n = ps.sendData(buffer)
      if unlikely(n < buffer.len):
        ps.sclose()
        return false
  except ErrorBrokenPipe:
    # ps is dead; give up.
    ps.sclose()
    return false
  if output.istreamAtEnd:
    ps.sclose()
  elif output.parent != nil:
    output.parent.outputs.add(OutputHandle(
      parent: output.parent,
      stream: ps,
      istreamAtEnd: output.istreamAtEnd,
      outputId: ctx.getOutputId()
    ))
  return true

proc addCacheFile(ctx: LoaderContext; client: ClientData; output: OutputHandle):
    int =
  if output.parent != nil and output.parent.cacheId != -1:
    # may happen e.g. if client tries to cache a `cache:' URL
    return output.parent.cacheId
  let tmpf = getTempFile(ctx.config.tmpdir)
  if ctx.redirectToFile(output, tmpf):
    let cacheId = output.outputId
    if output.parent != nil:
      output.parent.cacheId = cacheId
    client.cacheMap.add(CachedItem(id: cacheId, path: tmpf, refc: 1))
    return cacheId
  return -1

proc findOffset(ps: PosixStream): int =
  try:
    var buffer = default(array[512, char])
    var off = 0
    var lf = 1u # we start at EOL
    while true:
      let n = ps.recvData(buffer)
      if n == 0:
        return off
      for i in 0 ..< n:
        let c = buffer[i]
        if c == '\n':
          inc lf
          if lf == 2:
            return off + i + 1
        elif c != '\r':
          lf = 0
      off += n
  except IOError:
    discard
  return -1

proc openCachedItem(client: ClientData; id: int): (PosixStream, int) =
  let n = client.cacheMap.find(id)
  if n != -1:
    let item = client.cacheMap[n]
    let ps = newPosixStream(client.cacheMap[n].path, O_RDONLY, 0)
    if item.offset == -1:
      let offset = ps.findOffset()
      if offset == -1:
        client.cacheMap.del(n)
        return (nil, -1)
      item.offset = offset
    ps.seek(item.offset)
    return (ps, n)
  return (nil, -1)

proc put(ctx: LoaderContext; handle: LoaderHandle) =
  let fd = int(handle.stream.fd)
  if ctx.handleMap.len <= fd:
    ctx.handleMap.setLen(fd + 1)
  assert ctx.handleMap[fd] == nil
  ctx.handleMap[fd] = handle

proc unset(ctx: LoaderContext; handle: LoaderHandle) =
  let fd = int(handle.stream.fd)
  if fd < ctx.handleMap.len:
    ctx.handleMap[fd] = nil

proc addFd(ctx: LoaderContext; handle: InputHandle) =
  let output = handle.output
  output.stream.setBlocking(false)
  handle.stream.setBlocking(false)
  ctx.register(handle)
  ctx.put(handle)
  ctx.put(output)

type ControlResult = enum
  crDone, crContinue, crError

proc handleFirstLine(handle: InputHandle; line: string; headers: Headers;
    status: var uint16): ControlResult =
  let k = line.until(':')
  if k.len == line.len:
    # invalid
    handle.sendResult(ERROR_CGI_MALFORMED_HEADER)
    return crError
  let v = line.substr(k.len + 1).strip()
  if k.equalsIgnoreCase("Status"):
    handle.sendResult(0) # success
    status = parseUInt16(v, allowSign = false).get(0)
    return crContinue
  if k.equalsIgnoreCase("Cha-Control"):
    if v.startsWithIgnoreCase("Connected"):
      handle.sendResult(0) # success
      return crContinue
    elif v.startsWithIgnoreCase("ConnectionError"):
      let errs = v.split(' ')
      if errs.len <= 1:
        handle.sendResult(ERROR_CGI_INVALID_CHA_CONTROL)
      else:
        let fb = int32(ERROR_CGI_INVALID_CHA_CONTROL)
        let code = int(parseInt32(errs[1]).get(fb))
        var message = ""
        if errs.len > 2:
          message &= errs[2]
          for i in 3 ..< errs.len:
            message &= ' '
            message &= errs[i]
        handle.sendResult(code, message)
      return crError
    elif v.startsWithIgnoreCase("ControlDone"):
      return crDone
    handle.sendResult(ERROR_CGI_INVALID_CHA_CONTROL)
    return crError
  handle.sendResult(0) # success
  headers.add(k, v)
  return crDone

proc handleControlLine(handle: InputHandle; line: string; headers: Headers;
    status: var uint16): ControlResult =
  let k = line.until(':')
  if k.len == line.len:
    # invalid
    return crError
  let v = line.substr(k.len + 1).strip()
  if k.equalsIgnoreCase("Status"):
    status = parseUInt16(v, allowSign = false).get(0)
    return crContinue
  if k.equalsIgnoreCase("Cha-Control"):
    if v.startsWithIgnoreCase("ControlDone"):
      return crDone
    return crError
  headers.add(k, v)
  return crDone

# returns false if transfer was interrupted
proc handleLine(handle: InputHandle; line: string; headers: Headers) =
  let k = line.until(':')
  if k.len == line.len:
    # invalid
    return
  let v = line.substr(k.len + 1).strip()
  headers.add(k, v)

proc parseHeaders0(handle: InputHandle; data: openArray[char]): int =
  let parser = handle.parser
  var s = parser.lineBuffer
  for i, c in data:
    template die =
      handle.parser = nil
      return -1
    if parser.crSeen and c != '\n':
      die
    parser.crSeen = false
    if c == '\r':
      parser.crSeen = true
    elif c == '\n':
      if s == "":
        if parser.state == hpsBeforeLines:
          # body comes immediately, so we haven't had a chance to send result
          # yet.
          handle.sendResult(0)
        handle.sendStatus(parser.status)
        handle.sendHeaders(parser.headers)
        handle.parser = nil
        return i + 1 # +1 to skip \n
      case parser.state
      of hpsBeforeLines:
        case handle.handleFirstLine(s, parser.headers, parser.status)
        of crDone: parser.state = hpsControlDone
        of crContinue: parser.state = hpsAfterFirstLine
        of crError: die
      of hpsAfterFirstLine:
        case handle.handleControlLine(s, parser.headers, parser.status)
        of crDone: parser.state = hpsControlDone
        of crContinue: discard
        of crError: die
      of hpsControlDone:
        handle.handleLine(s, parser.headers)
      s = ""
    else:
      s &= c
  if s != "":
    parser.lineBuffer = s
  return data.len

proc parseHeaders(handle: InputHandle; buffer: LoaderBuffer): int =
  try:
    if buffer == nil:
      return handle.parseHeaders0(['\n'])
    assert buffer.page != nil
    let p = cast[ptr UncheckedArray[char]](buffer.page)
    return handle.parseHeaders0(p.toOpenArray(0, buffer.len - 1))
  except ErrorBrokenPipe:
    handle.parser = nil
    return -1

proc finishParse(handle: InputHandle) =
  discard handle.parseHeaders(nil)

type HandleReadResult = enum
  hrrDone, hrrUnregister, hrrBrokenPipe

# Called whenever there is more data available to read.
proc handleRead(ctx: LoaderContext; handle: InputHandle;
    unregWrite: var seq[OutputHandle]): HandleReadResult =
  var unregs = 0
  let maxUnregs = handle.outputs.len
  while true:
    let buffer = newLoaderBuffer()
    try:
      let n = handle.stream.recvData(buffer)
      if n == 0: # EOF
        return hrrUnregister
      var si = 0
      if handle.parser != nil:
        si = handle.parseHeaders(buffer)
        if si == -1: # died while parsing headers; unregister
          return hrrUnregister
        if si == n: # parsed the entire buffer as headers; skip output handling
          continue
      for output in handle.outputs:
        if output.dead:
          # do not push to unregWrite candidates
          continue
        case ctx.pushBuffer(output, buffer, si)
        of pbrUnregister:
          output.dead = true
          unregWrite.add(output)
          inc unregs
        of pbrDone: discard
      if unregs == maxUnregs:
        # early return: no more outputs to write to
        break
      if n < buffer.cap:
        break
    except ErrorAgain: # retry later
      break
    except ErrorBrokenPipe: # sender died; stop streaming
      return hrrBrokenPipe
  hrrDone

# stream is a regular file, so we can't select on it.
#
# cachedHandle is used for attaching the output handle to another
# InputHandle when loadFromCache is called while a download is still
# ongoing (and thus some parts of the document are not cached yet).
proc loadStreamRegular(ctx: LoaderContext; handle, cachedHandle: InputHandle) =
  assert handle.parser == nil # parser is only used with CGI
  var unregWrite: seq[OutputHandle] = @[]
  let r = ctx.handleRead(handle, unregWrite)
  for output in unregWrite:
    output.parent = nil
    let i = handle.outputs.find(output)
    if output.registered:
      ctx.unregister(output)
    handle.outputs.del(i)
  for output in handle.outputs:
    if r == hrrBrokenPipe:
      output.oclose()
    elif cachedHandle != nil:
      output.parent = cachedHandle
      cachedHandle.outputs.add(output)
      ctx.put(output)
    elif output.registered or output.suspended:
      output.parent = nil
      output.istreamAtEnd = true
      ctx.put(output)
    else:
      assert output.stream.fd >= ctx.handleMap.len or
        ctx.handleMap[output.stream.fd] == nil
      output.oclose()
  handle.outputs.setLen(0)
  handle.iclose()

proc putMappedURL(url: URL) =
  putEnv("MAPPED_URI_SCHEME", url.scheme)
  putEnv("MAPPED_URI_USERNAME", url.username)
  putEnv("MAPPED_URI_PASSWORD", url.password)
  putEnv("MAPPED_URI_HOST", url.hostname)
  putEnv("MAPPED_URI_PORT", url.port)
  putEnv("MAPPED_URI_PATH", url.path.serialize())
  putEnv("MAPPED_URI_QUERY", url.query.get(""))

type CGIPath = object
  basename: string
  pathInfo: string
  cmd: string
  scriptName: string
  requestURI: string
  myDir: string

proc setupEnv(cpath: CGIPath; request: Request; contentLen: int; prevURL: URL;
    config: LoaderClientConfig) =
  let url = request.url
  putEnv("SCRIPT_NAME", cpath.scriptName)
  putEnv("SCRIPT_FILENAME", cpath.cmd)
  putEnv("REQUEST_URI", cpath.requestURI)
  putEnv("REQUEST_METHOD", $request.httpMethod)
  var headers = ""
  for k, v in request.headers:
    headers &= k & ": " & v & "\r\n"
  putEnv("REQUEST_HEADERS", headers)
  if prevURL != nil:
    putMappedURL(prevURL)
  if cpath.pathInfo != "":
    putEnv("PATH_INFO", cpath.pathInfo)
  if url.query.isSome:
    putEnv("QUERY_STRING", url.query.get)
  if request.httpMethod == hmPost:
    if request.body.t == rbtMultipart:
      putEnv("CONTENT_TYPE", request.body.multipart.getContentType())
    else:
      putEnv("CONTENT_TYPE", request.headers.getOrDefault("Content-Type", ""))
    putEnv("CONTENT_LENGTH", $contentLen)
  if "Cookie" in request.headers:
    putEnv("HTTP_COOKIE", request.headers["Cookie"])
  if request.referrer != nil:
    putEnv("HTTP_REFERER", $request.referrer)
  if config.proxy != nil:
    putEnv("ALL_PROXY", $config.proxy)
  if config.insecureSSLNoVerify:
    putEnv("CHA_INSECURE_SSL_NO_VERIFY", "1")
  setCurrentDir(cpath.myDir)

proc parseCGIPath(ctx: LoaderContext; request: Request): CGIPath =
  var path = percentDecode(request.url.pathname)
  if path.startsWith("/cgi-bin/"):
    path.delete(0 .. "/cgi-bin/".high)
  elif path.startsWith("/$LIB/"):
    path.delete(0 .. "/$LIB/".high)
  var cpath = CGIPath()
  if path == "" or request.url.hostname != "":
    return cpath
  if path[0] == '/':
    for dir in ctx.config.cgiDir:
      if path.startsWith(dir):
        cpath.basename = path.substr(dir.len).until('/')
        cpath.pathInfo = path.substr(dir.len + cpath.basename.len)
        cpath.cmd = dir / cpath.basename
        if not fileExists(cpath.cmd):
          continue
        cpath.myDir = dir
        cpath.scriptName = path.substr(0, dir.len + cpath.basename.len)
        cpath.requestURI = cpath.cmd / cpath.pathInfo & request.url.search
        break
  else:
    cpath.basename = path.until('/')
    cpath.pathInfo = path.substr(cpath.basename.len)
    cpath.scriptName = "/cgi-bin/" & cpath.basename
    cpath.requestURI = "/cgi-bin/" & path & request.url.search
    for dir in ctx.config.cgiDir:
      cpath.cmd = dir / cpath.basename
      if fileExists(cpath.cmd):
        cpath.myDir = dir
        break
  return cpath

proc loadCGI(ctx: LoaderContext; client: ClientData; handle: InputHandle;
    request: Request; prevURL: URL; config: LoaderClientConfig) =
  if ctx.config.cgiDir.len == 0:
    handle.sendResult(ERROR_NO_CGI_DIR)
    return
  let cpath = ctx.parseCGIPath(request)
  if cpath.cmd == "" or cpath.basename in ["", ".", ".."] or
      cpath.basename[0] == '~':
    handle.sendResult(ERROR_INVALID_CGI_PATH)
    return
  if not fileExists(cpath.cmd):
    handle.sendResult(ERROR_CGI_FILE_NOT_FOUND)
    return
  # Pipe the response body as stdout.
  var pipefd: array[2, cint] # child -> parent
  if pipe(pipefd) == -1:
    handle.sendResult(ERROR_FAIL_SETUP_CGI)
    return
  let istreamOut = newPosixStream(pipefd[0]) # read by loader
  var ostreamOut = newPosixStream(pipefd[1]) # written by child
  var ostreamOut2: PosixStream = nil
  if request.tocache:
    # Set stdout to a file, and repurpose the pipe as a dummy to detect when
    # the process ends. outputId is the cache id.
    let tmpf = getTempFile(ctx.config.tmpdir)
    ostreamOut2 = ostreamOut
    # RDWR, otherwise mmap won't work
    ostreamOut = newPosixStream(tmpf, O_CREAT or O_RDWR, 0o600)
    if ostreamOut == nil:
      handle.sendResult(ERROR_FAIL_SETUP_CGI)
      return
    let cacheId = handle.output.outputId # welp
    client.cacheMap.add(CachedItem(
      id: cacheId,
      path: tmpf,
      refc: 1,
      offset: -1
    ))
  # Pipe the request body as stdin for POST.
  var istream: PosixStream = nil # child end (read)
  var ostream: PosixStream = nil # parent end (write)
  var istream2: PosixStream = nil # child end (read) for rbtCache
  var cachedHandle: InputHandle = nil # for rbtCache
  var outputIn: OutputHandle = nil # for rbtOutput
  if request.body.t == rbtCache:
    var n: int
    (istream, n) = client.openCachedItem(request.body.cacheId)
    if istream == nil:
      handle.sendResult(ERROR_CGI_CACHED_BODY_NOT_FOUND)
      return
    cachedHandle = ctx.findCachedHandle(request.body.cacheId)
    if cachedHandle != nil: # cached item still open, switch to streaming mode
      istream2 = istream
  elif request.body.t == rbtOutput:
    outputIn = ctx.findOutput(request.body.outputId, client)
    if outputIn == nil:
      handle.sendResult(ERROR_FAIL_SETUP_CGI)
      return
  if request.body.t in {rbtString, rbtMultipart, rbtOutput} or
      request.body.t == rbtCache and istream2 != nil:
    var pipefdRead: array[2, cint] # parent -> child
    if pipe(pipefdRead) == -1:
      handle.sendResult(ERROR_FAIL_SETUP_CGI)
      return
    istream = newPosixStream(pipefdRead[0])
    ostream = newPosixStream(pipefdRead[1])
  let contentLen = request.body.contentLength()
  stderr.flushFile()
  let pid = fork()
  if pid == -1:
    handle.sendResult(ERROR_FAIL_SETUP_CGI)
  elif pid == 0:
    istreamOut.sclose() # close read
    discard dup2(ostreamOut.fd, 1) # dup stdout
    ostreamOut.sclose()
    if ostream != nil:
      ostream.sclose() # close write
    if istream2 != nil:
      istream2.sclose() # close cache file; we aren't reading it directly
    if istream != nil:
      if istream.fd != 0:
        discard dup2(istream.fd, 0) # dup stdin
        istream.sclose()
    else:
      closeStdin()
    # we leave stderr open, so it can be seen in the browser console
    setupEnv(cpath, request, contentLen, prevURL, config)
    # reset SIGCHLD to the default handler. this is useful if the child process
    # expects SIGCHLD to be untouched. (e.g. git dies a horrible death with
    # SIGCHLD as SIG_IGN)
    signal(SIGCHLD, SIG_DFL)
    # let's also reset SIGPIPE, which we ignored in forkserver
    signal(SIGPIPE, SIG_DFL)
    # close the parent handles
    for i in 0 ..< ctx.handleMap.len:
      if ctx.handleMap[i] != nil:
        discard close(cint(i))
    discard execl(cstring(cpath.cmd), cstring(cpath.basename), nil)
    let code = int(ERROR_FAILED_TO_EXECUTE_CGI_SCRIPT)
    stdout.write("Cha-Control: ConnectionError " & $code & " " &
      ($strerror(errno)).deleteChars({'\n', '\r'}))
    quit(1)
  else:
    ostreamOut.sclose() # close write
    if ostreamOut2 != nil:
      ostreamOut2.sclose() # close write
    if request.body.t != rbtNone:
      istream.sclose() # close read
    handle.parser = HeaderParser(headers: newHeaders())
    handle.stream = istreamOut
    case request.body.t
    of rbtString:
      ostream.write(request.body.s)
      ostream.sclose()
    of rbtMultipart:
      let boundary = request.body.multipart.boundary
      for entry in request.body.multipart.entries:
        ostream.writeEntry(entry, boundary)
      ostream.writeEnd(boundary)
      ostream.sclose()
    of rbtOutput:
      ostream.setBlocking(false)
      let output = outputIn.tee(ostream, ctx.getOutputId(), client.pid)
      ctx.put(output)
      output.suspended = false
      if not output.isEmpty:
        ctx.register(output)
    of rbtCache:
      if ostream != nil:
        let handle = newInputHandle(ostream, ctx.getOutputId(), client.pid,
          suspended = false)
        handle.stream = istream2
        ostream.setBlocking(false)
        ctx.loadStreamRegular(handle, cachedHandle)
        assert handle.stream == nil
        handle.close()
    of rbtNone:
      discard

proc loadStream(ctx: LoaderContext; client: ClientData; handle: InputHandle;
    request: Request) =
  client.passedFdMap.withValue(request.url.pathname, fdp):
    handle.sendResult(0)
    handle.sendStatus(200)
    handle.sendHeaders(newHeaders())
    let ps = newPosixStream(fdp[])
    var stats: Stat
    doAssert fstat(fdp[], stats) != -1
    handle.stream = ps
    client.passedFdMap.del(request.url.pathname)
    if S_ISCHR(stats.st_mode) or S_ISREG(stats.st_mode):
      # regular file: e.g. cha <file
      # or character device: e.g. cha </dev/null
      handle.output.stream.setBlocking(false)
      # not loading from cache, so cachedHandle is nil
      ctx.loadStreamRegular(handle, nil)
  do:
    handle.sendResult(ERROR_FILE_NOT_FOUND, "stream not found")

proc loadFromCache(ctx: LoaderContext; client: ClientData; handle: InputHandle;
    request: Request) =
  let id = parseInt32(request.url.pathname).get(-1)
  let startFrom = parseInt32(request.url.query.get("")).get(0)
  let (ps, n) = client.openCachedItem(id)
  if ps != nil:
    if startFrom != 0:
      ps.seek(startFrom)
    handle.stream = ps
    if ps == nil:
      handle.rejectHandle(ERROR_FILE_NOT_IN_CACHE)
      client.cacheMap.del(n)
      return
    handle.sendResult(0)
    handle.sendStatus(200)
    handle.sendHeaders(newHeaders())
    handle.output.stream.setBlocking(false)
    let cachedHandle = ctx.findCachedHandle(id)
    ctx.loadStreamRegular(handle, cachedHandle)
  else:
    handle.sendResult(ERROR_URL_NOT_IN_CACHE)

# Data URL handler.
# Moved back into loader from CGI, because data URLs can get extremely long
# and thus no longer fit into the environment.
proc loadDataSend(ctx: LoaderContext; handle: InputHandle; s, ct: string) =
  handle.sendResult(0)
  handle.sendStatus(200)
  handle.sendHeaders(newHeaders({"Content-Type": ct}))
  let output = handle.output
  if s.len == 0:
    if output.suspended:
      output.istreamAtEnd = true
      ctx.put(output)
    else:
      output.oclose()
    return
  let buffer = newLoaderBuffer(size = s.len)
  buffer.len = s.len
  copyMem(buffer.page, unsafeAddr s[0], s.len)
  case ctx.pushBuffer(output, buffer, 0)
  of pbrUnregister:
    if output.registered:
      ctx.unregister(output)
    output.oclose()
  of pbrDone:
    if output.registered or output.suspended:
      output.istreamAtEnd = true
      ctx.put(output)
    else:
      output.oclose()

proc loadData(ctx: LoaderContext; handle: InputHandle; request: Request) =
  let url = request.url
  var ct = url.path.s.until(',')
  if AllChars - Ascii + Controls - {'\t', ' '} in ct:
    handle.sendResult(ERROR_INVALID_URL, "invalid data URL")
    handle.close()
    return
  let sd = ct.len + 1 # data start
  let body = percentDecode(url.path.s, sd)
  if ct.endsWith(";base64"):
    let d = atob0(body) # decode from ct end + 1
    if d.isNone:
      handle.sendResult(ERROR_INVALID_URL, "invalid data URL")
      handle.close()
      return
    ct.setLen(ct.len - ";base64".len) # remove base64 indicator
    ctx.loadDataSend(handle, d.get, ct)
  else:
    ctx.loadDataSend(handle, body, ct)

proc loadResource(ctx: LoaderContext; client: ClientData;
    config: LoaderClientConfig; request: Request; handle: InputHandle) =
  var redo = true
  var tries = 0
  var prevurl: URL = nil
  while redo and tries < MaxRewrites:
    redo = false
    if ctx.config.w3mCGICompat and request.url.scheme == "file":
      let path = request.url.path.serialize_unicode()
      if ctx.canRewriteForCGICompat(path):
        let newURL = newURL("cgi-bin:" & path & request.url.search)
        if newURL.isSome:
          request.url = newURL.get
          inc tries
          redo = true
          continue
    if request.url.scheme == "cgi-bin":
      ctx.loadCGI(client, handle, request, prevurl, config)
      if handle.stream != nil:
        ctx.addFd(handle)
      else:
        handle.close()
    elif request.url.scheme == "stream":
      ctx.loadStream(client, handle, request)
      if handle.stream != nil:
        ctx.addFd(handle)
      else:
        handle.close()
    elif request.url.scheme == "cache":
      ctx.loadFromCache(client, handle, request)
      assert handle.stream == nil
      handle.close()
    elif request.url.scheme == "data":
      ctx.loadData(handle, request)
    else:
      prevurl = request.url
      case ctx.config.uriMethodMap.findAndRewrite(request.url)
      of ummrSuccess:
        inc tries
        redo = true
      of ummrWrongURL:
        handle.rejectHandle(ERROR_INVALID_URI_METHOD_ENTRY)
      of ummrNotFound:
        handle.rejectHandle(ERROR_UNKNOWN_SCHEME)
  if tries >= MaxRewrites:
    handle.rejectHandle(ERROR_TOO_MANY_REWRITES)

proc setupRequestDefaults(request: Request; config: LoaderClientConfig) =
  for k, v in config.defaultHeaders.table:
    if k notin request.headers.table:
      request.headers.table[k] = v
  if config.cookieJar != nil and config.cookieJar.cookies.len > 0:
    if "Cookie" notin request.headers.table:
      let cookie = config.cookieJar.serialize(request.url)
      if cookie != "":
        request.headers["Cookie"] = cookie
  if request.referrer != nil and "Referer" notin request.headers:
    let r = request.referrer.getReferrer(request.url, config.referrerPolicy)
    if r != "":
      request.headers["Referer"] = r

proc load(ctx: LoaderContext; stream: SocketStream; request: Request;
    client: ClientData; config: LoaderClientConfig) =
  let handle = newInputHandle(stream, ctx.getOutputId(), client.pid)
  when defined(debug):
    handle.url = request.url
    handle.output.url = request.url
  if not config.filter.match(request.url):
    handle.rejectHandle(ERROR_DISALLOWED_URL)
  else:
    request.setupRequestDefaults(config)
    ctx.loadResource(client, config, request, handle)

proc load(ctx: LoaderContext; stream: SocketStream; client: ClientData;
    r: var BufferedReader) =
  var request: Request
  r.sread(request)
  ctx.load(stream, request, client, client.config)

proc loadConfig(ctx: LoaderContext; stream: SocketStream; client: ClientData;
    r: var BufferedReader) =
  var request: Request
  r.sread(request)
  var config: LoaderClientConfig
  r.sread(config)
  ctx.load(stream, request, client, config)

proc getCacheFile(ctx: LoaderContext; stream: SocketStream; client: ClientData;
    r: var BufferedReader) =
  var cacheId: int
  r.sread(cacheId)
  stream.withPacketWriter w:
    let n = client.cacheMap.find(cacheId)
    if n != -1:
      w.swrite(client.cacheMap[n].path)
    else:
      w.swrite("")

proc addClient(ctx: LoaderContext; stream: SocketStream;
    r: var BufferedReader) =
  var key: ClientKey
  var pid: int
  var config: LoaderClientConfig
  var clonedFrom: int
  r.sread(key)
  r.sread(pid)
  r.sread(config)
  r.sread(clonedFrom)
  stream.withPacketWriter w:
    if pid in ctx.clientData or key == default(ClientKey):
      w.swrite(false)
    else:
      let client = ClientData(pid: pid, key: key, config: config)
      ctx.clientData[pid] = client
      if clonedFrom != -1:
        let client2 = ctx.clientData[clonedFrom]
        for item in client2.cacheMap:
          inc item.refc
        client.cacheMap = client2.cacheMap
      w.swrite(true)
  stream.sclose()

proc cleanup(client: ClientData) =
  for it in client.cacheMap:
    dec it.refc
    if it.refc == 0:
      discard unlink(cstring(it.path))

proc removeClient(ctx: LoaderContext; stream: SocketStream;
    r: var BufferedReader) =
  var pid: int
  r.sread(pid)
  if pid in ctx.clientData:
    let client = ctx.clientData[pid]
    client.cleanup()
    ctx.clientData.del(pid)
  stream.sclose()

proc addCacheFile(ctx: LoaderContext; stream: SocketStream; client: ClientData;
    r: var BufferedReader) =
  var outputId: int
  var targetPid: int
  r.sread(outputId)
  #TODO get rid of targetPid
  r.sread(targetPid)
  doAssert ctx.isPrivileged(client) or client.pid == targetPid
  let output = ctx.findOutput(outputId, client)
  assert output != nil
  let targetClient = ctx.clientData[targetPid]
  let id = ctx.addCacheFile(targetClient, output)
  stream.withPacketWriter w:
    w.swrite(id)
  stream.sclose()

proc redirectToFile(ctx: LoaderContext; stream: SocketStream;
    r: var BufferedReader) =
  var outputId: int
  var targetPath: string
  r.sread(outputId)
  r.sread(targetPath)
  let output = ctx.findOutput(outputId, ctx.pagerClient)
  var success = false
  if output != nil:
    success = ctx.redirectToFile(output, targetPath)
  stream.withPacketWriter w:
    w.swrite(success)
  stream.sclose()

proc shareCachedItem(ctx: LoaderContext; stream: SocketStream;
    r: var BufferedReader) =
  # share a cached file with another buffer. this is for newBufferFrom
  # (i.e. view source)
  var sourcePid: int # pid of source client
  var targetPid: int # pid of target client
  var id: int
  r.sread(sourcePid)
  r.sread(targetPid)
  r.sread(id)
  let sourceClient = ctx.clientData[sourcePid]
  let targetClient = ctx.clientData[targetPid]
  let n = sourceClient.cacheMap.find(id)
  let item = sourceClient.cacheMap[n]
  inc item.refc
  targetClient.cacheMap.add(item)
  stream.sclose()

proc openCachedItem(ctx: LoaderContext; stream: SocketStream;
    client: ClientData; r: var BufferedReader) =
  # open a cached item
  var id: int
  r.sread(id)
  let (ps, _) = client.openCachedItem(id)
  stream.withPacketWriter w:
    w.swrite(ps != nil)
    if ps != nil:
      w.sendAux.add(FileHandle(ps.fd))
  if ps != nil:
    ps.sclose()
  stream.sclose()

proc passFd(ctx: LoaderContext; stream: SocketStream; client: ClientData;
    r: var BufferedReader) =
  var id: string
  r.sread(id)
  let fd = stream.recvFileHandle()
  client.passedFdMap[id] = fd
  stream.sclose()

proc removeCachedItem(ctx: LoaderContext; stream: SocketStream;
    client: ClientData; r: var BufferedReader) =
  var id: int
  r.sread(id)
  let n = client.cacheMap.find(id)
  if n != -1:
    let item = client.cacheMap[n]
    client.cacheMap.del(n)
    dec item.refc
    if item.refc == 0:
      discard unlink(cstring(item.path))
  stream.sclose()

proc tee(ctx: LoaderContext; stream: SocketStream; client: ClientData;
    r: var BufferedReader) =
  var sourceId: int
  var targetPid: int
  r.sread(sourceId)
  r.sread(targetPid)
  let outputIn = ctx.findOutput(sourceId, client)
  if outputIn != nil:
    let id = ctx.getOutputId()
    let output = outputIn.tee(stream, id, targetPid)
    ctx.put(output)
    stream.withPacketWriter w:
      w.swrite(id)
    stream.setBlocking(false)
  else:
    stream.withPacketWriter w:
      w.swrite(-1)
    stream.sclose()

proc suspend(ctx: LoaderContext; stream: SocketStream; client: ClientData;
    r: var BufferedReader) =
  var ids: seq[int]
  r.sread(ids)
  for id in ids:
    let output = ctx.findOutput(id, client)
    if output != nil:
      output.suspended = true
      if output.registered:
        # do not waste cycles trying to push into output
        ctx.unregister(output)
  stream.sclose()

proc resume(ctx: LoaderContext; stream: SocketStream; client: ClientData;
    r: var BufferedReader) =
  var ids: seq[int]
  r.sread(ids)
  for id in ids:
    let output = ctx.findOutput(id, client)
    if output != nil:
      output.suspended = false
      ctx.register(output)
  stream.sclose()

proc equalsConstantTime(a, b: ClientKey): bool =
  static:
    doAssert a.len == b.len
  {.push boundChecks:off, overflowChecks:off.}
  var i {.volatile.} = 0
  var res {.volatile.} = 0u8
  while i < a.len:
    res = res or (a[i] xor b[i])
    inc i
  {.pop.}
  return res == 0

proc acceptConnection(ctx: LoaderContext) =
  let stream = ctx.ssock.acceptSocketStream()
  try:
    stream.withPacketReader r:
      var myPid: int
      var key: ClientKey
      r.sread(myPid)
      r.sread(key)
      if myPid notin ctx.clientData:
        # possibly already removed
        stream.sclose()
        return
      let client = ctx.clientData[myPid]
      if not client.key.equalsConstantTime(key):
        # ditto
        stream.sclose()
        return
      var cmd: LoaderCommand
      r.sread(cmd)
      template privileged_command =
        doAssert ctx.isPrivileged(client)
      case cmd
      of lcAddClient:
        privileged_command
        ctx.addClient(stream, r)
      of lcRemoveClient:
        privileged_command
        ctx.removeClient(stream, r)
      of lcShareCachedItem:
        privileged_command
        ctx.shareCachedItem(stream, r)
      of lcOpenCachedItem:
        privileged_command
        ctx.openCachedItem(stream, client, r)
      of lcRedirectToFile:
        privileged_command
        ctx.redirectToFile(stream, r)
      of lcLoadConfig:
        privileged_command
        ctx.loadConfig(stream, client, r)
      of lcGetCacheFile:
        privileged_command
        ctx.getCacheFile(stream, client, r)
      of lcAddCacheFile:
        ctx.addCacheFile(stream, client, r)
      of lcRemoveCachedItem:
        ctx.removeCachedItem(stream, client, r)
      of lcPassFd:
        ctx.passFd(stream, client, r)
      of lcLoad:
        ctx.load(stream, client, r)
      of lcTee:
        ctx.tee(stream, client, r)
      of lcSuspend:
        ctx.suspend(stream, client, r)
      of lcResume:
        ctx.resume(stream, client, r)
  except ErrorBrokenPipe:
    # receiving end died while reading the file; give up.
    assert stream.fd >= ctx.handleMap.len or ctx.handleMap[stream.fd] == nil
    stream.sclose()

proc exitLoader(ctx: LoaderContext) =
  ctx.ssock.close()
  for client in ctx.clientData.values:
    client.cleanup()
  exitnow(1)

var gctx: LoaderContext
proc initLoaderContext(fd: cint; config: LoaderConfig): LoaderContext =
  var ctx = LoaderContext(alive: true, config: config)
  gctx = ctx
  let myPid = getCurrentProcessId()
  # we don't capsicumize loader, so -1 is appropriate here
  ctx.ssock = initServerSocket(config.sockdir, -1, myPid, blocking = true)
  let sfd = int(ctx.ssock.sock.getFd())
  ctx.pollData.register(sfd, POLLIN)
  if sfd >= ctx.handleMap.len:
    ctx.handleMap.setLen(sfd + 1)
  ctx.handleMap[sfd] = LoaderHandle() # pseudo handle
  # The server has been initialized, so the main process can resume execution.
  let ps = newPosixStream(fd)
  ps.write(char(0u8))
  ps.sclose()
  onSignal SIGTERM:
    discard sig
    gctx.exitLoader()
  for dir in ctx.config.cgiDir.mitems:
    if dir.len > 0 and dir[^1] != '/':
      dir &= '/'
  # get pager's key
  let stream = ctx.ssock.acceptSocketStream()
  stream.withPacketReader r:
    block readNullKey:
      var pid: int # ignore pid
      r.sread(pid)
      # pager's key is still null
      var key: ClientKey
      r.sread(key)
      doAssert key == default(ClientKey)
    var cmd: LoaderCommand
    r.sread(cmd)
    doAssert cmd == lcAddClient
    var key: ClientKey
    var pid: int
    var config: LoaderClientConfig
    r.sread(key)
    r.sread(pid)
    r.sread(config)
    stream.withPacketWriter w:
      w.swrite(true)
    ctx.pagerClient = ClientData(key: key, pid: pid, config: config)
    ctx.clientData[pid] = ctx.pagerClient
    stream.sclose()
  # unblock main socket
  ctx.ssock.sock.getFd().setBlocking(false)
  # for CGI
  putEnv("SERVER_SOFTWARE", "Chawan")
  putEnv("SERVER_PROTOCOL", "HTTP/1.0")
  putEnv("SERVER_NAME", "localhost")
  putEnv("SERVER_PORT", "80")
  putEnv("REMOTE_HOST", "localhost")
  putEnv("REMOTE_ADDR", "127.0.0.1")
  putEnv("GATEWAY_INTERFACE", "CGI/1.1")
  putEnv("CHA_INSECURE_SSL_NO_VERIFY", "0")
  return ctx

# This is only called when an OutputHandle could not read enough of one (or
# more) buffers, and we asked select to notify us when it will be available.
proc handleWrite(ctx: LoaderContext; output: OutputHandle;
    unregWrite: var seq[OutputHandle]) =
  while output.currentBuffer != nil:
    let buffer = output.currentBuffer
    try:
      let n = output.stream.sendData(buffer, output.currentBufferIdx)
      output.currentBufferIdx += n
      if output.currentBufferIdx < buffer.len:
        break
      output.bufferCleared() # swap out buffer
    except ErrorAgain: # never mind
      break
    except ErrorBrokenPipe: # receiver died; stop streaming
      unregWrite.add(output)
      break
  if output.isEmpty:
    if output.istreamAtEnd:
      # after EOF, no need to send anything more here
      unregWrite.add(output)
    else:
      # all buffers sent, no need to select on this output again for now
      ctx.unregister(output)

proc finishCycle(ctx: LoaderContext; unregRead: var seq[InputHandle];
    unregWrite: var seq[OutputHandle]) =
  # Unregister handles queued for unregistration.
  # It is possible for both unregRead and unregWrite to contain duplicates. To
  # avoid double-close/double-unregister, we set the istream/ostream of
  # unregistered handles to nil.
  for handle in unregRead:
    if handle.stream != nil:
      ctx.unregister(handle)
      ctx.unset(handle)
      if handle.parser != nil:
        handle.finishParse()
      handle.iclose()
      for output in handle.outputs:
        output.istreamAtEnd = true
        if output.isEmpty:
          unregWrite.add(output)
  for output in unregWrite:
    if output.stream != nil:
      if output.registered:
        ctx.unregister(output)
      ctx.unset(output)
      output.oclose()
      let handle = output.parent
      if handle != nil: # may be nil if from loadStream S_ISREG
        let i = handle.outputs.find(output)
        handle.outputs.del(i)
        if handle.outputs.len == 0 and handle.stream != nil:
          # premature end of all output streams; kill istream too
          ctx.unregister(handle)
          ctx.unset(handle)
          if handle.parser != nil:
            handle.finishParse()
          handle.iclose()

proc runFileLoader*(fd: cint; config: LoaderConfig) =
  var ctx = initLoaderContext(fd, config)
  let fd = int(ctx.ssock.sock.getFd())
  while ctx.alive:
    ctx.pollData.poll(-1)
    var unregRead: seq[InputHandle] = @[]
    var unregWrite: seq[OutputHandle] = @[]
    for event in ctx.pollData.events:
      let efd = int(event.fd)
      if (event.revents and POLLIN) != 0:
        if efd == fd: # incoming connection
          ctx.acceptConnection()
        else:
          let handle = InputHandle(ctx.handleMap[efd])
          case ctx.handleRead(handle, unregWrite)
          of hrrDone: discard
          of hrrUnregister, hrrBrokenPipe: unregRead.add(handle)
      if (event.revents and POLLOUT) != 0:
        let handle = ctx.handleMap[efd]
        ctx.handleWrite(OutputHandle(handle), unregWrite)
      if (event.revents and POLLERR) != 0 or (event.revents and POLLHUP) != 0:
        assert efd != fd
        let handle = ctx.handleMap[efd]
        if handle of InputHandle: # istream died
          unregRead.add(InputHandle(handle))
        else: # ostream died
          unregWrite.add(OutputHandle(handle))
    ctx.finishCycle(unregRead, unregWrite)
  ctx.exitLoader()