/**
 * Copyright (c) 2009, 2010 Eric Wong (all bugs are Eric's fault)
 * Copyright (c) 2005 Zed A. Shaw
 * You can redistribute it and/or modify it under the same terms as Ruby.
 */
#include "ruby.h"
#include "ext_help.h"
#include <assert.h>
#include <stdlib.h>
#include <string.h>
#include <sys/types.h>
#include "c_util.h"

static VALUE eParserError;
static ID id_sq, id_sq_set;

/** Defines common length and error messages for input length validation. */
#define DEF_MAX_LENGTH(N, length) \
  static const size_t MAX_##N##_LENGTH = length; \
  static const char MAX_##N##_LENGTH_ERR[] = \
    "HTTP element " # N  " is longer than the " # length " allowed length."

/**
 * Validates the max length of given input and throws an ParserError
 * exception if over.
 */
#define VALIDATE_MAX_LENGTH(len, N) do { \
  if (len > MAX_##N##_LENGTH) \
    rb_raise(eParserError, MAX_##N##_LENGTH_ERR); \
} while (0)

/* Defines the maximum allowed lengths for various input elements.*/
DEF_MAX_LENGTH(FIELD_NAME, 256);
DEF_MAX_LENGTH(FIELD_VALUE, 80 * 1024);
DEF_MAX_LENGTH(HEADER, (1024 * (80 + 32)));
DEF_MAX_LENGTH(REASON, 256);

#define UH_FL_CHUNKED  0x1
#define UH_FL_HASBODY  0x2
#define UH_FL_INBODY   0x4
#define UH_FL_HASTRAILER   0x8
#define UH_FL_INTRAILER 0x10
#define UH_FL_INCHUNK  0x20
#define UH_FL_KEEPALIVE 0x40
#define UH_FL_HASHEADER 0x80

struct http_parser {
  int cs; /* Ragel internal state */
  unsigned int flags;
  size_t mark;
  size_t offset;
  union { /* these 2 fields don't nest */
    size_t field;
    size_t query;
  } start;
  union {
    size_t field_len; /* only used during header processing */
    size_t dest_offset; /* only used during body processing */
  } s;
  VALUE cont; /* Qfalse: unset, Qnil: ignored header, T_STRING: append */
  VALUE status; /* String or Qnil */
  union {
    off_t content;
    off_t chunk;
  } len;
};

#define REMAINING (unsigned long)(pe - p)
#define LEN(AT, FPC) (FPC - buffer - hp->AT)
#define MARK(M,FPC) (hp->M = (FPC) - buffer)
#define PTR_TO(F) (buffer + hp->F)
#define STR_NEW(M,FPC) rb_str_new(PTR_TO(M), LEN(M, FPC))

#define HP_FL_TEST(hp,fl) ((hp)->flags & (UH_FL_##fl))
#define HP_FL_SET(hp,fl) ((hp)->flags |= (UH_FL_##fl))
#define HP_FL_UNSET(hp,fl) ((hp)->flags &= ~(UH_FL_##fl))
#define HP_FL_ALL(hp,fl) (HP_FL_TEST(hp, fl) == (UH_FL_##fl))

static void finalize_header(struct http_parser *hp)
{
  if ((HP_FL_TEST(hp, HASTRAILER) && ! HP_FL_TEST(hp, CHUNKED)))
    rb_raise(eParserError, "trailer but not chunked");
}

/*
 * handles values of the "Connection:" header, keepalive is implied
 * for HTTP/1.1 but needs to be explicitly enabled with HTTP/1.0
 * Additionally, we require GET/HEAD requests to support keepalive.
 */
static void hp_keepalive_connection(struct http_parser *hp, VALUE val)
{
  /* REQUEST_METHOD is always set before any headers */
  if (STR_CSTR_CASE_EQ(val, "keep-alive")) {
    /* basically have HTTP/1.0 masquerade as HTTP/1.1+ */
    HP_FL_SET(hp, KEEPALIVE);
  } else if (STR_CSTR_CASE_EQ(val, "close")) {
    /*
     * it doesn't matter what HTTP version or request method we have,
     * if a server says "Connection: close", we disable keepalive
     */
    HP_FL_UNSET(hp, KEEPALIVE);
  } else {
    /*
     * server could've sent anything, ignore it for now.  Maybe
     * "HP_FL_UNSET(hp, KEEPALIVE);" just in case?
     * Raising an exception might be too mean...
     */
  }
}

static void
http_version(struct http_parser *hp, VALUE hdr, const char *ptr, size_t len)
{
  if (CONST_MEM_EQ("HTTP/1.1", ptr, len)) {
    /* HTTP/1.1 implies keepalive unless "Connection: close" is set */
    HP_FL_SET(hp, KEEPALIVE);
  }
}

static void
status_phrase(struct http_parser *hp, VALUE hdr, const char *ptr, size_t len)
{
  long nr;

  hp->status = rb_str_new(ptr, len);

  /* RSTRING_PTR is null terminated, ptr is not */
  nr = strtol(RSTRING_PTR(hp->status), NULL, 10);

  if (nr < 100 || nr > 999)
    rb_raise(eParserError, "invalid status: %s", RSTRING_PTR(hp->status));

  if ( !((nr >= 100 && nr <= 199) || nr == 204 || nr == 304) )
    HP_FL_SET(hp, HASBODY);
}

static inline void invalid_if_trailer(struct http_parser *hp)
{
  if (HP_FL_TEST(hp, INTRAILER))
    rb_raise(eParserError, "invalid Trailer");
}

static void write_cont_value(struct http_parser *hp,
                             char *buffer, const char *p)
{
  char *vptr;

  if (hp->cont == Qfalse)
    rb_raise(eParserError, "invalid continuation line");

  if (NIL_P(hp->cont))
    return; /* we're ignoring this header (probably Status:) */

  assert(TYPE(hp->cont) == T_STRING && "continuation line is not a string");
  assert(hp->mark > 0 && "impossible continuation line offset");

  if (LEN(mark, p) == 0)
    return;

  if (RSTRING_LEN(hp->cont) > 0)
    --hp->mark;

  vptr = PTR_TO(mark);

  if (RSTRING_LEN(hp->cont) > 0) {
    assert((' ' == *vptr || '\t' == *vptr) && "invalid leading white space");
    *vptr = ' ';
  }
  rb_str_buf_cat(hp->cont, vptr, LEN(mark, p));
}

static void write_value(VALUE hdr, struct http_parser *hp,
                        const char *buffer, const char *p)
{
  VALUE f, v;
  VALUE hclass;
  const char *fptr = PTR_TO(start.field);
  long flen = hp->s.field_len;
  const char *vptr;
  long vlen;

  HP_FL_SET(hp, HASHEADER);

  /* Rack does not like Status headers, so we never send them */
  if (CSTR_CASE_EQ(fptr, flen, "status")) {
    hp->cont = Qnil;
    return;
  }

  vptr = PTR_TO(mark);
  vlen = LEN(mark, p);
  VALIDATE_MAX_LENGTH(vlen, FIELD_VALUE);
  VALIDATE_MAX_LENGTH(flen, FIELD_NAME);
  f = rb_str_new(fptr, flen);
  v = rb_str_new(vptr, vlen);

  /* needs more tests for error-checking here */
  /*
   * TODO:
   * some of these tests might be too strict for real-world HTTP servers,
   * report real-world examples as we find them:
   */
  if (STR_CSTR_CASE_EQ(f, "connection")) {
    hp_keepalive_connection(hp, v);
  } else if (STR_CSTR_CASE_EQ(f, "content-length")) {
    if (! HP_FL_TEST(hp, HASBODY))
      rb_raise(eParserError, "Content-Length with no body expected");
    if (HP_FL_TEST(hp, CHUNKED))
      rb_raise(eParserError,
               "Content-Length when chunked Transfer-Encoding is set");
    hp->len.content = parse_length(vptr, vlen);

    if (hp->len.content < 0)
      rb_raise(eParserError, "invalid Content-Length");

    invalid_if_trailer(hp);
  } else if (STR_CSTR_CASE_EQ(f, "transfer-encoding")) {
    if (STR_CSTR_CASE_EQ(v, "chunked")) {
      if (! HP_FL_TEST(hp, HASBODY))
        rb_raise(eParserError,
                 "chunked Transfer-Encoding with no body expected");
      if (hp->len.content >= 0)
        rb_raise(eParserError,
                 "chunked Transfer-Encoding when Content-Length is set");

      hp->len.chunk = 0;
      HP_FL_SET(hp, CHUNKED);
    }
    invalid_if_trailer(hp);
  } else if (STR_CSTR_CASE_EQ(f, "trailer")) {
    if (! HP_FL_TEST(hp, HASBODY))
      rb_raise(eParserError, "trailer with no body");
    HP_FL_SET(hp, HASTRAILER);
    invalid_if_trailer(hp);
  }

  hclass = CLASS_OF(hdr);
  if (hclass == rb_cArray) {
    rb_ary_push(hdr, rb_ary_new3(2, f, v));
    hp->cont = v;
  } else {
    /* hash-ish, try rb_hash_* first and fall back to slow rb_funcall */
    VALUE e;

    /* try to read the existing value */
    if (hclass == rb_cHash)
      e = rb_hash_aref(hdr, f);
    else
      e = rb_funcall(hdr, id_sq, 1, f);

    if (NIL_P(e)) {
      /* new value, freeze it since it speeds up MRI slightly */
      OBJ_FREEZE(f);

      if (hclass == rb_cHash)
        rb_hash_aset(hdr, f, v);
      else
        rb_funcall(hdr, id_sq_set, 2, f, v);

      hp->cont = v;
    } else {
      /*
       * existing value, append to it, Rack 1.x uses newlines to represent
       * repeated cookies:
       *    { 'Set-Cookie' => "a=b\nc=d" }
       * becomes:
       *    "Set-Cookie: a=b\r\nSet-Cookie: c=d\r\n"
       */
      rb_str_buf_cat(e, "\n", 1);
      hp->cont = rb_str_buf_append(e, v);
    }
  }
}

/** Machine **/

%%{
  machine http_parser;

  action mark {MARK(mark, fpc); }

  action start_field { MARK(start.field, fpc); }
  action write_field { hp->s.field_len = LEN(start.field, fpc); }
  action start_value { MARK(mark, fpc); }
  action write_value { write_value(hdr, hp, buffer, fpc); }
  action write_cont_value { write_cont_value(hp, buffer, fpc); }
  action http_version { http_version(hp, hdr, PTR_TO(mark), LEN(mark, fpc)); }
  action status_phrase { status_phrase(hp, hdr, PTR_TO(mark), LEN(mark, fpc)); }

  action add_to_chunk_size {
    hp->len.chunk = step_incr(hp->len.chunk, fc, 16);
    if (hp->len.chunk < 0)
      rb_raise(eParserError, "invalid chunk size");
  }
  action header_done {
    finalize_header(hp);
    cs = http_parser_first_final;

    if (HP_FL_TEST(hp, CHUNKED))
      cs = http_parser_en_ChunkedBody;

    /*
     * go back to Ruby so we can call the Rack application, we'll reenter
     * the parser iff the body needs to be processed.
     */
    goto post_exec;
  }

  action end_trailers {
    cs = http_parser_first_final;
    goto post_exec;
  }

  action end_chunked_body {
    HP_FL_SET(hp, INTRAILER);
    cs = http_parser_en_Trailers;
    ++p;
    assert(p <= pe && "buffer overflow after chunked body");
    goto post_exec;
  }

  action skip_chunk_data {
  skip_chunk_data_hack: {
    size_t nr = MIN((size_t)hp->len.chunk, REMAINING);
    memcpy(RSTRING_PTR(hdr) + hp->s.dest_offset, fpc, nr);
    hp->s.dest_offset += nr;
    hp->len.chunk -= nr;
    p += nr;
    assert(hp->len.chunk >= 0 && "negative chunk length");
    if ((size_t)hp->len.chunk > REMAINING) {
      HP_FL_SET(hp, INCHUNK);
      goto post_exec;
    } else {
      fhold;
      fgoto chunk_end;
    }
  }}

  include kcar_http_common "kcar_http_common.rl";
}%%

/** Data **/
%% write data;

static void http_parser_init(struct http_parser *hp)
{
  int cs = 0;
  memset(hp, 0, sizeof(struct http_parser));
  hp->cont = Qfalse; /* zero on MRI, should be optimized away by above */
  hp->status = Qnil;
  hp->len.content = -1;
  %% write init;
  hp->cs = cs;
}

/** exec **/
static void http_parser_execute(struct http_parser *hp,
  VALUE hdr, char *buffer, size_t len)
{
  const char *p, *pe;
  int cs = hp->cs;
  size_t off = hp->offset;

  if (cs == http_parser_first_final)
    return;

  assert(off <= len && "offset past end of buffer");

  p = buffer+off;
  pe = buffer+len;

  assert((void *)(pe - p) == (void *)(len - off) &&
         "pointers aren't same distance");

  if (HP_FL_TEST(hp, INCHUNK)) {
    HP_FL_UNSET(hp, INCHUNK);
    goto skip_chunk_data_hack;
  }
  %% write exec;
post_exec: /* "_out:" also goes here */
  if (hp->cs != http_parser_error)
    hp->cs = cs;
  hp->offset = p - buffer;

  assert(p <= pe && "buffer overflow after parsing execute");
  assert(hp->offset <= len && "offset longer than length");
}

static struct http_parser *data_get(VALUE self)
{
  struct http_parser *hp;

  Data_Get_Struct(self, struct http_parser, hp);
  assert(hp && "failed to extract http_parser struct");
  return hp;
}

static void mark(void *ptr)
{
  struct http_parser *hp = ptr;

  rb_gc_mark(hp->cont);
  rb_gc_mark(hp->status);
}

static VALUE alloc(VALUE klass)
{
  struct http_parser *hp;
  return Data_Make_Struct(klass, struct http_parser, mark, -1, hp);
}

/**
 * call-seq:
 *    Kcar::Parser.new => parser
 *
 * Creates a new parser.
 *
 * Document-method: reset
 *
 * call-seq:
 *    parser.reset => parser
 *
 * Resets the parser so it can be reused by another client
 */
static VALUE initialize(VALUE self)
{
  http_parser_init(data_get(self));

  return self;
}

static void advance_str(VALUE str, off_t nr)
{
  long len = RSTRING_LEN(str);

  if (len == 0)
    return;

  rb_str_modify(str);

  assert(nr <= len && "trying to advance past end of buffer");
  len -= nr;
  if (len > 0) /* unlikely, len is usually 0 */
    memmove(RSTRING_PTR(str), RSTRING_PTR(str) + nr, len);
  rb_str_set_len(str, len);
}

/**
 * call-seq:
 *   parser.body_bytes_left => nil or Integer
 *
 * Returns the number of bytes left to run through Parser#filter_body.
 * This will initially be the value of the "Content-Length" HTTP header
 * after header parsing is complete and will decrease in value as
 * Parser#filter_body is called for each chunk.  This should return
 * zero for responses with no body.
 *
 * This will return nil on "Transfer-Encoding: chunked" responses as
 * well as HTTP/1.0 responses where Content-Length is not set
 */
static VALUE body_bytes_left(VALUE self)
{
  struct http_parser *hp = data_get(self);

  if (HP_FL_TEST(hp, CHUNKED))
    return Qnil;
  if (hp->len.content >= 0)
    return OFFT2NUM(hp->len.content);

  return Qnil;
}

/**
 * Document-method: chunked
 * call-seq:
 *    parser.chunked? => true or false
 *
 * This is used to detect if a response uses chunked Transfer-Encoding or not.
 */
static VALUE chunked(VALUE self)
{
  struct http_parser *hp = data_get(self);

  return HP_FL_TEST(hp, CHUNKED) ? Qtrue : Qfalse;
}

/**
 * Document-method: headers
 * call-seq:
 *    parser.headers(hdr, data) => hdr or nil
 *
 * Takes a Hash and a String of data, parses the String of data filling
 * in the Hash returning the Hash if parsing is finished, nil otherwise
 * When returning the hdr Hash, it may modify data to point to where
 * body processing should begin.
 *
 * Raises ParserError if there are parsing errors.
 */
static VALUE headers(VALUE self, VALUE hdr, VALUE data)
{
  struct http_parser *hp = data_get(self);

  rb_str_update(data);

  http_parser_execute(hp, hdr, RSTRING_PTR(data), RSTRING_LEN(data));
  VALIDATE_MAX_LENGTH(hp->offset, HEADER);

  if (hp->cs == http_parser_first_final ||
      hp->cs == http_parser_en_ChunkedBody) {
    advance_str(data, hp->offset + 1);
    hp->offset = 0;
    if (HP_FL_TEST(hp, INTRAILER))
      return hdr;
    else
      return rb_ary_new3(2, hp->status, hdr);
  }

  if (hp->cs == http_parser_error)
    rb_raise(eParserError, "Invalid HTTP format, parsing fails.");

  return Qnil;
}

static int chunked_eof(struct http_parser *hp)
{
  return ((hp->cs == http_parser_first_final) || HP_FL_TEST(hp, INTRAILER));
}

/**
 * call-seq:
 *    parser.body_eof? => true or false
 *
 * Detects if we're done filtering the body or not.  This can be used
 * to detect when to stop calling Parser#filter_body.
 */
static VALUE body_eof(VALUE self)
{
  struct http_parser *hp = data_get(self);

  if (!HP_FL_TEST(hp, HASHEADER) && HP_FL_ALL(hp, KEEPALIVE))
    return Qtrue;

  if (HP_FL_TEST(hp, CHUNKED))
    return chunked_eof(hp) ? Qtrue : Qfalse;

  if (! HP_FL_TEST(hp, HASBODY))
    return Qtrue;

  return hp->len.content == 0 ? Qtrue : Qfalse;
}

/**
 * call-seq:
 *    parser.keepalive? => true or false
 *
 * This should be used to detect if a request can really handle
 * keepalives and pipelining.  Currently, the rules are:
 *
 * 1. MUST be HTTP/1.1 +or+ HTTP/1.0 with "Connection: keep-alive"
 * 2. MUST NOT have "Connection: close" set
 * 3. If there is a response body, either a) Content-Length is set
 *    or b) chunked encoding is used
 */
static VALUE keepalive(VALUE self)
{
  struct http_parser *hp = data_get(self);

  if (HP_FL_ALL(hp, KEEPALIVE)) {
    if (HP_FL_TEST(hp, HASHEADER) && HP_FL_TEST(hp, HASBODY) ) {
      if (HP_FL_TEST(hp, CHUNKED) || (hp->len.content >= 0))
        return Qtrue;

      /* unknown Content-Length and not chunked, we must assume close */
      return Qfalse;
    } else {
      /* 100 Continue, 304 Not Modified, etc... */
      return Qtrue;
    }
  }
  return Qfalse;
}

/**
 * call-seq:
 *    parser.filter_body(buf, data) => nil/data
 *
 * Takes a String of +data+, will modify data if dechunking is done.
 * Returns +nil+ if there is more data left to process.  Returns
 * +data+ if body processing is complete. When returning +data+,
 * it may modify +data+ so the start of the string points to where
 * the body ended so that trailer processing can begin.
 *
 * Raises ParserError if there are dechunking errors.
 * Basically this is a glorified memcpy(3) that copies +data+
 * into +buf+ while filtering it through the dechunker.
 */
static VALUE filter_body(VALUE self, VALUE buf, VALUE data)
{
  struct http_parser *hp = data_get(self);
  char *dptr;
  long dlen;

  rb_str_update(data);
  dptr = RSTRING_PTR(data);
  dlen = RSTRING_LEN(data);

  StringValue(buf);
  rb_str_resize(buf, dlen); /* we can never copy more than dlen bytes */
  OBJ_TAINT(buf); /* keep weirdo $SAFE users happy */

  if (!HP_FL_TEST(hp, CHUNKED))
    rb_raise(rb_eRuntimeError, "filter_body is only for chunked bodies");

  if (!chunked_eof(hp)) {
    hp->s.dest_offset = 0;
    http_parser_execute(hp, buf, dptr, dlen);
    if (hp->cs == http_parser_error)
      rb_raise(eParserError, "Invalid HTTP format, parsing fails.");

    assert(hp->s.dest_offset <= hp->offset &&
           "destination buffer overflow");
    advance_str(data, hp->offset);
    rb_str_set_len(buf, hp->s.dest_offset);

    if (RSTRING_LEN(buf) == 0 && chunked_eof(hp)) {
      assert(hp->len.chunk == 0 && "chunk at EOF but more to parse");
    } else {
      data = Qnil;
    }
  }
  hp->offset = 0; /* for trailer parsing */
  return data;
}

void Init_kcar_ext(void)
{
  VALUE mKcar = rb_define_module("Kcar");
  VALUE cParser = rb_define_class_under(mKcar, "Parser", rb_cObject);

  eParserError = rb_define_class_under(mKcar, "ParserError", rb_eIOError);

  rb_define_alloc_func(cParser, alloc);
  rb_define_method(cParser, "initialize", initialize, 0);
  rb_define_method(cParser, "reset", initialize, 0);
  rb_define_method(cParser, "headers", headers, 2);
  rb_define_method(cParser, "trailers", headers, 2);
  rb_define_method(cParser, "filter_body", filter_body, 2);
  rb_define_method(cParser, "body_bytes_left", body_bytes_left, 0);
  rb_define_method(cParser, "body_eof?", body_eof, 0);
  rb_define_method(cParser, "keepalive?", keepalive, 0);
  rb_define_method(cParser, "chunked?", chunked, 0);

  /*
   * The maximum size a single chunk when using chunked transfer encoding.
   * This is only a theoretical maximum used to detect errors in clients,
   * it is highly unlikely to encounter clients that send more than
   * several kilobytes at once.
   */
  rb_define_const(cParser, "CHUNK_MAX", OFFT2NUM(UH_OFF_T_MAX));

  /*
   * The maximum size of the body as specified by Content-Length.
   * This is only a theoretical maximum, the actual limit is subject
   * to the limits of the file system used for +Dir.tmpdir+.
   */
  rb_define_const(cParser, "LENGTH_MAX", OFFT2NUM(UH_OFF_T_MAX));
  id_sq = rb_intern("[]");
  id_sq_set = rb_intern("[]=");
}