syndicate_utils/src/drivers/http_driver.nim

# SPDX-FileCopyrightText: ☭ Emery Hemingway
# SPDX-License-Identifier: Unlicense

import std/[httpcore, options, parseutils, sets, streams, strutils, tables, times, uri]
import pkg/sys/ioqueue
import pkg/preserves
import pkg/syndicate
import pkg/syndicate/protocols/http
import taps
import ../schema/config

const
  SP = { ' ', '\x09', '\x0b', '\x0c', '\x0d' }
  SupportedVersion = "HTTP/1.1"
  IMF = initTimeFormat"ddd, dd MMM yyyy HH:mm:ss"

proc echo(args: varargs[string, `$`]) =
  stderr.writeLine(args)

proc `$`(b: seq[byte]): string = cast[string](b)

# a Date header on responses must be present if a clock is available

# An upgrade header can be used to switch over to native syndicate protocol.

# Check the response encoding matches or otherwise return 415

type HandlerEntity = ref object of Entity
  handler: proc (turn: var Turn; req: HttpRequest; cap: Cap)

method publish(e: HandlerEntity; turn: var Turn; a: AssertionRef; h: Handle) =
  var ctx = a.value.preservesTo HttpContext
  if ctx.isSome:
    var res = ctx.get.res.unembed Cap
    if res.isSome:
      e.handler(turn, ctx.get.req, res.get)
    else:
      echo "HandlerEntity got a non-Cap ", ctx.get.res
  else:
    echo "HandlerEntity got a non-HttpContext ", a.value

proc respond404(turn: var Turn; req: HttpRequest; cap: Cap) =
  message(turn, cap, HttpResponse(
      orKind: HttpResponseKind.status,
      status: HttpResponseStatus(
        code: 404,
        message: "resource not found",
    )))
  message(turn, cap, HttpResponse(
      orKind: HttpResponseKind.header,
      header: HttpResponseHeader(
        name: Symbol"content-length",
        value: "0",
    )))
  message(turn, cap, HttpResponse(orKind: HttpResponseKind.done))

proc bind404Handler(turn: var Turn; ds: Cap; port: Port) =
  stderr.writeLine "bind 404 handler to ", port
  var b: HttpBinding
  b.host = HostPattern(orKind: HostPatternKind.any)
  b.port = BiggestInt port
  b.method = MethodPattern(orKind: MethodPatternKind.any)
  b.path = @[PathPatternElement(orKind: PathPatternElementKind.rest)]
  b.handler = newCap(turn, HandlerEntity(handler: respond404)).toPreserves
  discard publish(turn, ds, b)

proc badRequest(conn: Connection; msg: string) =
  conn.send(SupportedVersion & " 400 " & msg, endOfMessage = true)
  close(conn)

proc extractQuery(s: var string): Table[Symbol, seq[QueryValue]] =
  let start = succ skipUntil(s, '?')
  if start < s.len:
    var query = s[start..s.high]
    s.setLen(start)
    for key, val in uri.decodeQuery(query):
      var list = result.getOrDefault(Symbol key)
      list.add QueryValue(orKind: QueryValueKind.string, string: val)
      result[Symbol key] = list

proc parseRequest(conn: Connection; text: string): (int, HttpRequest) =
  ## Parse an `HttpRequest` request out of a `text` from a `Connection`.
  var
    token: string
    off: int

  template advanceSp =
    let n = skipWhile(text, SP, off)
    if n < 1:
      badRequest(conn, "invalid request")
      return
    inc(off, n)

  # method
  off.inc parseUntil(text, token, SP, off)
  result[1].method = token.toLowerAscii.Symbol
  advanceSp()

  # target
  if text[off] == '/': inc(off) #TODO: always a leading slash?
  off.inc parseUntil(text, token, SP, off)
  advanceSp()

  block:
    var version: string
    off.inc parseUntil(text, version, SP, off)
    advanceSp()
    if version != SupportedVersion:
      badRequest(conn, "version not supported")
      return

  result[1].query = extractQuery(token)

  result[1].path = split(token, '/')
  for p in result[1].path.mitems:
    # normalize the path
    for i, c in p:
      if c in {'A'..'Z'}:
        p[i] = char c.ord + 0x20

  template advanceLine =
    inc off, skipWhile(text, {'\x0d'}, off)
    if text.high < off or text[off] != '\x0a':
      badRequest(conn, "invalid request")
      return
    inc off, 1

  advanceLine()
  while off < text.len:
    off.inc parseUntil(text, token, {'\x0d', '\x0a'}, off)
    if token == "": break
    advanceLine()
    var
      (key, vals) = httpcore.parseHeader(token)
      k = key.toLowerAscii.Symbol
      v = result[1].headers.getOrDefault(k)
    for e in vals.mitems:
      e = e.toLowerAscii
      if k == Symbol"host":
        result[1].host = e
      if v == "": v = move e
      else:
        v.add ", "
        v.add e
      if k == Symbol"host":
        result[1].host = v
      result[1].headers[k] = v

  result[0] = off

proc send(conn: Connection; chunk: Chunk) =
  case chunk.orKind
  of ChunkKind.string:
    conn.send(chunk.string, endOfMessage = false)
  of ChunkKind.bytes:
    conn.send(chunk.bytes, endOfMessage = false)

type
  Driver = ref object
    facet: Facet
    ds: Cap
    bindings: seq[HttpBinding]
  Session = ref object
    facet: Facet
    driver: Driver
    conn: Connection
    port: Port
  Exchange = ref object of Entity
    ses: Session
    req: HttpRequest
    stream: StringStream
    mode: HttpResponseKind

proc match(b: HttpBinding, r: HttpRequest): bool =
  ## Check if `HttpBinding` `b` matches `HttpRequest` `r`.
  result =
    (b.host.orKind == HostPatternKind.any or
      b.host.host == r.host) and
    (b.port == r.port) and
    (b.method.orKind == MethodPatternKind.any or
        b.method.specific == r.method)
  if result:
    for i, p in b.path:
      if i > r.path.high: return false
      case p.orKind
      of PathPatternElementKind.wildcard: discard
      of PathPatternElementKind.label:
        if p.label != r.path[i]: return false
      of PathPatternElementKind.rest:
        return i == b.path.high
          # return false if ... isn't the last element

proc strongerThan(a, b: HttpBinding): bool =
  ## Check if `a` is a stronger `HttpBinding` than `b`.
  result =
    (a.host.orKind != b.host.orKind and
      a.host.orKind == HostPatternKind.host) or
    (a.method.orKind != b.method.orKind and
      a.method.orKind == MethodPatternKind.specific)
  if not result:
    if a.path.len > b.path.len: return true
    for i in a.path.low..b.path.high:
      if a.path[i].orKind != b.path[i].orKind and
          a.path[i].orKind == PathPatternElementKind.label:
        return true

proc match(driver: Driver; req: HttpRequest): Option[HttpBinding] =
  for b in driver.bindings:
    if b.match req:
      if result.isNone or b.strongerThan(result.get):
        result = some b
    else:
      echo b, " does not match ", req

method message(e: Exchange; turn: var Turn; a: AssertionRef) =
  # Send responses back into a connection.
  var res: HttpResponse
  if e.mode != HttpResponseKind.done and res.fromPreserves a.value:
    case res.orKind
    of HttpResponseKind.status:
      if e.mode == res.orKind:
        e.stream.writeLine(SupportedVersion, " ", res.status.code, " ", res.status.message)
        e.stream.writeLine("date: ", now().format(IMF))
          # add Date header automatically - RFC 9110 Section 6.6.1.
        e.mode = HttpResponseKind.header
    of HttpResponseKind.header:
      if e.mode == res.orKind:
        e.stream.writeLine(res.header.name, ": ", res.header.value)
    of HttpResponseKind.chunk:
      if e.mode == HttpResponseKind.header:
        e.mode = res.orKind
        e.stream.writeLine()
        e.ses.conn.send(move e.stream.data, endOfMessage = false)
      e.ses.conn.send(res.chunk.chunk)
    of HttpResponseKind.done:
      if e.mode == HttpResponseKind.header:
        e.stream.writeLine()
        e.ses.conn.send(move e.stream.data, endOfMessage = false)
      e.mode = res.orKind
      e.ses.conn.send(res.done.chunk)
      stop(turn)
        # stop the facet scoped to the exchange
        # so that the response capability is withdrawn

proc service(turn: var Turn; exch: Exchange) =
  ## Service an HTTP message exchange.
  var binding = exch.ses.driver.match exch.req
  if binding.isNone:
    echo "no binding for ", exch.req
    stop(turn)
  else:
    echo "driver matched binding ", binding.get
    var handler = binding.get.handler.unembed Cap
    if handler.isNone:
      stop(turn)
    else:
      publish(turn, handler.get, HttpContext(
          req: exch.req,
          res: embed newCap(turn, exch),
        ))

proc service(ses: Session) =
  ## Service a connection to an HTTP client.
  ses.facet.onStop do (turn: var Turn):
    close ses.conn
  ses.conn.onClosed do ():
    stop ses.facet
  ses.conn.onReceivedPartial do (data: seq[byte]; ctx: MessageContext; eom: bool):
    ses.facet.run do (turn: var Turn):
      var (n, req) = parseRequest(ses.conn, cast[string](data))
      if n > 0:
        req.port = BiggestInt ses.port
        inFacet(turn) do (turn: var Turn):
          preventInertCheck(turn)
          # start a new facet for this message exchange
          turn.service Exchange(
              facet: turn.facet,
              ses: ses,
              req: req,
              stream: newStringStream(),
              mode: HttpResponseKind.status
            )
      # ses.conn.receive()
  ses.conn.receive()

proc newListener(port: Port): Listener =
  var lp = newLocalEndpoint()
  lp.with port
  listen newPreconnection(local=[lp])

proc httpListen(turn: var Turn; driver: Driver; port: Port) =
  let facet = turn.facet
  var listener = newListener(port)
    # TODO: let listener
  listener.onListenError do (err: ref Exception):
    terminateFacet(facet, err)
  facet.onStop do (turn: var Turn):
    stop listener
  listener.onConnectionReceived do (conn: Connection):
    driver.facet.run do (turn: var Turn):
      # start a new turn
      linkActor(turn, "http-conn") do (turn: var Turn):
        preventInertCheck(turn)
        # facet is scoped to the lifetime of the connection
        service Session(
            facet: turn.facet,
            driver: driver,
            conn: conn,
            port: port,
          )

proc httpDriver(turn: var Turn; ds: Cap) =
  let driver = Driver(facet: turn.facet, ds: ds)

  during(turn, ds, HttpBinding?:{
        1: grab(),
      }) do (port: BiggestInt):
    publish(turn, ds, HttpListener(port: port))

  during(turn, ds, ?:HttpBinding) do (
      ho: HostPattern, po: int, me: MethodPattern, pa: PathPattern, e: Value):
    let b = HttpBinding(host: ho, port: po, `method`: me, path: pa, handler: e)
    driver.bindings.add b
  do:
    raiseAssert("need to remove binding " & $b)

  during(turn, ds, ?:HttpListener) do (port: uint16):
    bind404Handler(turn, ds, Port port)
    httpListen(turn, driver, Port port)

proc spawnHttpDriver*(turn: var Turn; ds: Cap) =
  during(turn, ds, ?:HttpDriverArguments) do (ds: Cap):
    spawnActor("http-driver", turn) do (turn: var Turn):
      httpDriver(turn, ds)

when isMainModule:
  import syndicate/relays
  runActor("main") do (turn: var Turn):
    resolveEnvironment(turn, spawnHttpDriver)