construct/ircd/http.cc

// Matrix Construct
//
// Copyright (C) Matrix Construct Developers, Authors & Contributors
// Copyright (C) 2016-2018 Jason Volk <jason@zemos.net>
//
// Permission to use, copy, modify, and/or distribute this software for any
// purpose with or without fee is hereby granted, provided that the above
// copyright notice and this permission notice is present in all copies. The
// full license for this software is available in the LICENSE file.

namespace ircd { namespace http
__attribute__((visibility("hidden")))
{
	using namespace ircd::spirit;

	struct grammar;
	struct parser extern const parser;

	extern const std::unordered_map<ircd::http::code, ircd::string_view> reason;

	[[noreturn]] void throw_error(const qi::expectation_failure<const char *> &, const bool &internal = false);
}}

BOOST_FUSION_ADAPT_STRUCT
(
    ircd::http::query,
    ( decltype(ircd::http::query::first),   first  )
    ( decltype(ircd::http::query::second),  second )
)

BOOST_FUSION_ADAPT_STRUCT
(
    ircd::http::header,
    ( decltype(ircd::http::header::first),   first  )
    ( decltype(ircd::http::header::second),  second )
)

BOOST_FUSION_ADAPT_STRUCT
(
    ircd::http::line::response,
    ( decltype(ircd::http::line::response::version),  version )
    ( decltype(ircd::http::line::response::status),   status  )
    ( decltype(ircd::http::line::response::reason),   reason  )
)

BOOST_FUSION_ADAPT_STRUCT
(
    ircd::http::line::request,
    ( decltype(ircd::http::line::request::method),    method   )
    ( decltype(ircd::http::line::request::path),      path     )
    ( decltype(ircd::http::line::request::query),     query    )
    ( decltype(ircd::http::line::request::fragment),  fragment )
    ( decltype(ircd::http::line::request::version),   version  )
)

decltype(ircd::http::reason)
ircd::http::reason
{
	{ code::CONTINUE,                            "Continue"                                        },
	{ code::SWITCHING_PROTOCOLS,                 "Switching Protocols"                             },

	{ code::OK,                                  "OK"                                              },
	{ code::CREATED,                             "Created"                                         },
	{ code::ACCEPTED,                            "Accepted"                                        },
	{ code::NON_AUTHORITATIVE_INFORMATION,       "Non-Authoritative Information"                   },
	{ code::NO_CONTENT,                          "No Content"                                      },
	{ code::PARTIAL_CONTENT,                     "Partial Content"                                 },

	{ code::MULTIPLE_CHOICES,                    "Multiple Choices"                                },
	{ code::MOVED_PERMANENTLY,                   "Moved Permanently"                               },
	{ code::FOUND,                               "Found"                                           },
	{ code::SEE_OTHER,                           "See Other"                                       },
	{ code::NOT_MODIFIED,                        "Not Modified"                                    },
	{ code::USE_PROXY,                           "Use Proxy"                                       },
	{ code::SWITCH_PROXY,                        "Switch Proxy"                                    },
	{ code::TEMPORARY_REDIRECT,                  "Temporary Redirect"                              },
	{ code::PERMANENT_REDIRECT,                  "Permanent Redirect"                              },

	{ code::BAD_REQUEST,                         "Bad Request"                                     },
	{ code::UNAUTHORIZED,                        "Unauthorized"                                    },
	{ code::FORBIDDEN,                           "Forbidden"                                       },
	{ code::NOT_FOUND,                           "Not Found"                                       },
	{ code::METHOD_NOT_ALLOWED,                  "Method Not Allowed"                              },
	{ code::NOT_ACCEPTABLE,                      "Not Acceptable"                                  },
	{ code::REQUEST_TIMEOUT,                     "Request Time-out"                                },
	{ code::CONFLICT,                            "Conflict"                                        },
	{ code::LENGTH_REQUIRED,                     "Length Required"                                 },
	{ code::PAYLOAD_TOO_LARGE,                   "Payload Too Large"                               },
	{ code::REQUEST_URI_TOO_LONG,                "Request URI Too Long"                            },
	{ code::UNSUPPORTED_MEDIA_TYPE,              "Unsupported Media Type"                          },
	{ code::RANGE_NOT_SATISFIABLE,               "Range Not Satisfiable"                           },
	{ code::EXPECTATION_FAILED,                  "Expectation Failed"                              },
	{ code::IM_A_TEAPOT,                         "Negative, I Am A Meat Popsicle"                  },
	{ code::UNPROCESSABLE_ENTITY,                "Unprocessable Entity"                            },
	{ code::PRECONDITION_REQUIRED,               "Precondition Required"                           },
	{ code::TOO_MANY_REQUESTS,                   "Too Many Requests"                               },
	{ code::REQUEST_HEADER_FIELDS_TOO_LARGE,     "Request Header Fields Too Large"                 },

	{ code::INTERNAL_SERVER_ERROR,               "Internal Server Error"                           },
	{ code::NOT_IMPLEMENTED,                     "Not Implemented"                                 },
	{ code::BAD_GATEWAY,                         "Bad Gateway"                                     },
	{ code::SERVICE_UNAVAILABLE,                 "Service Unavailable"                             },
	{ code::GATEWAY_TIMEOUT,                     "Gateway Timeout"                                 },
	{ code::HTTP_VERSION_NOT_SUPPORTED,          "HTTP Version Not Supported"                      },
	{ code::INSUFFICIENT_STORAGE,                "Insufficient Storage"                            },
	{ code::WEB_SERVER_IS_DOWN,                  "Web Server Is Down"                              },
	{ code::A_TIMEOUT_OCCURRED,                  "A Timeout Occurred"                              },
};

struct ircd::http::grammar
:qi::grammar<const char *, unused_type>
{
	using it = const char *;
	template<class R = unused_type, class... S> using rule = qi::rule<it, R, S...>;

	rule<> NUL                         { lit('\0')                                          ,"nul" };

	// insignificant whitespaces
	rule<> SP                          { lit('\x20')                                      ,"space" };
	rule<> HT                          { lit('\x09')                             ,"horizontal tab" };
	rule<> ws                          { SP | HT                                     ,"whitespace" };

	rule<> CR                          { lit('\x0D')                            ,"carriage return" };
	rule<> LF                          { lit('\x0A')                                  ,"line feed" };
	rule<> CRLF                        { CR >> LF                    ,"carriage return, line feed" };

	rule<> illegal                     { NUL | CR | LF                                  ,"illegal" };
	rule<> colon                       { lit(':')                                         ,"colon" };
	rule<> slash                       { lit('/')                               ,"forward solidus" };
	rule<> question                    { lit('?')                                 ,"question mark" };
	rule<> pound                       { lit('#')                                    ,"pound sign" };
	rule<> equal                       { lit('=')                                    ,"equal sign" };
	rule<> ampersand                   { lit('&')                                     ,"ampersand" };

	rule<string_view> token            { raw[+(char_ - (illegal | ws))]                   ,"token" };
	rule<string_view> string           { raw[+(char_ - illegal)]                         ,"string" };
	rule<string_view> line             { *ws >> -string >> CRLF                            ,"line" };

	rule<string_view> status           { raw[repeat(3)[char_("0-9")]]                    ,"status" };
	rule<short> status_code            { short_                                     ,"status code" };
	rule<string_view> reason           { string                                          ,"status" };

	rule<string_view> head_key         { raw[+(char_ - (illegal | ws | colon))]        ,"head key" };
	rule<string_view> head_val         { string                                      ,"head value" };
	rule<http::header> header          { head_key >> *ws >> colon >> *ws >> head_val     ,"header" };
	rule<unused_type> headers          { (header % (*ws >> CRLF))                       ,"headers" };

	rule<> query_terminator            { equal | question | ampersand | pound  ,"query terminator" };
	rule<> query_illegal               { illegal | ws | query_terminator          ,"query illegal" };
	rule<string_view> query_key        { raw[+(char_ - query_illegal)]                ,"query key" };
	rule<string_view> query_val        { raw[*(char_ - query_illegal)]              ,"query value" };

	rule<string_view> method           { token                                           ,"method" };
	rule<string_view> path             { raw[-slash >> *(char_ - query_illegal)]           ,"path" };
	rule<string_view> fragment         { pound >> -token                               ,"fragment" };
	rule<string_view> version          { token                                          ,"version" };

	rule<size_t> chunk_size
	{
		qi::uint_parser<size_t, 16, 1, 8>{}
		,"chunk size"
	};

	rule<string_view> chunk_extensions
	{
		';' >> raw[string]             //TODO: extensions
		,"chunk extensions"
	};

	rule<http::query> query
	{
		query_key >> -(equal >> query_val)
		,"query"
	};

	rule<string_view> query_string
	{
		question >> -raw[(query_key >> -(equal >> query_val)) % ampersand]
		,"query string"
	};

	rule<line::request> request_line
	{
		method >> +SP >> path >> -query_string >> -fragment >> +SP >> version
		,"request line"
	};

	rule<line::response> response_line
	{
		version >> +SP >> status >> -(+SP >> reason)
		,"response line"
	};

	rule<unused_type> request
	{
		request_line >> *ws >> CRLF >> -headers >> CRLF
		,"request"
	};

	rule<unused_type> response
	{
		response_line >> *ws >> CRLF >> -headers >> CRLF
		,"response"
	};

	grammar()
	:qi::grammar<const char *, unused_type>{rule<>{}}
	{}
};

struct ircd::http::parser
:grammar
{
	static size_t content_length(const string_view &val);
}
const ircd::http::parser;

/// Compose a request. This prints an HTTP head into the buffer. No real IO is
/// done here. After composing into the buffer, the user can then drive the
/// socket by sending the header and the content as specified.
///
/// If termination is false, no extra CRLF is printed to the buffer allowing
/// additional headers not specified to be appended later.
ircd::http::request::request(window_buffer &out,
                             const string_view &host,
                             const string_view &method,
                             const string_view &uri,
                             const size_t &content_length,
                             const string_view &content_type,
                             const vector_view<const header> &headers,
                             const bool &termination)
{
	writeline(out, [&method, &uri](const mutable_buffer &out) -> size_t
	{
		assert(!method.empty());
		assert(!uri.empty());
		return fmt::sprintf
		{
			out, "%s %s HTTP/1.1", method, uri
		};
	});

	if(!has(headers, "host"))
		writeline(out, [&host](const mutable_buffer &out) -> size_t
		{
			assert(!host.empty());
			return fmt::sprintf
			{
				out, "Host: %s", host
			};
		});

	if(content_length && !has(headers, "content-type"))
		writeline(out, [&content_type](const mutable_buffer &out) -> size_t
		{
			return fmt::sprintf
			{
				out, "Content-Type: %s", content_type?: "text/plain; charset=utf-8"
			};
		});

	if(!has(headers, "content-length"))
		writeline(out, [&content_length](const mutable_buffer &out) -> size_t
		{
			return fmt::sprintf
			{
				out, "Content-Length: %zu", content_length
			};
		});

	write(out, headers);

	if(termination)
		writeline(out);
}

ircd::http::request::head::head(parse::capstan &pc,
                                const headers::closure &c)
:line::request{pc}
,uri
{
	fragment? string_view { begin(path), end(fragment) }:
	query?    string_view { begin(path), end(query)    }:
	          string_view { begin(path), end(path)     }
}
,headers{[this, &pc, &c]
{
	const bool version_compatible
	{
		this->version == "HTTP/1.0" ||
		this->version == "HTTP/1.1"
	};

	if(!version_compatible)
		throw error
		{
			HTTP_VERSION_NOT_SUPPORTED, fmt::snstringf
			{
				128, "Sorry, no speak '%s'. Try HTTP/1.1 here.",
				this->version
			}
		};

	return http::headers{pc, [this, &c](const auto &h)
	{
		if(iequals(h.first, "host"_sv))
			this->host = h.second;

		else if(iequals(h.first, "expect"_sv))
			this->expect = h.second;

		else if(iequals(h.first, "te"_sv))
			this->te = h.second;

		else if(iequals(h.first, "authorization"_sv))
			this->authorization = h.second;

		else if(iequals(h.first, "connection"_sv))
			this->connection = h.second;

		else if(iequals(h.first, "content-type"_sv))
			this->content_type = h.second;

		else if(iequals(h.first, "user-agent"_sv))
			this->user_agent = h.second;

		else if(iequals(h.first, "upgrade"_sv))
			this->upgrade = h.second;

		else if(iequals(h.first, "range"_sv))
			this->range = h.second;

		else if(iequals(h.first, "if-range"_sv))
			this->if_range = h.second;

		else if(iequals(h.first, "content-length"_sv))
			this->content_length = parser.content_length(h.second);

		if(c)
			c(h);
	}};
}()}
{
}

ircd::http::request::head::operator
string_view()
const
{
	const string_view request_line
	{
		static_cast<const line::request &>(*this)
	};

	if(request_line.empty() || headers.empty())
		return request_line;

	return string_view
	{
		request_line.begin(), headers.end()
	};
}

ircd::http::response::response(window_buffer &out,
                               const code &code,
                               const size_t &content_length,
                               const string_view &content_type,
                               const http::headers &headers_s,
                               const vector_view<const header> &headers_v,
                               const bool &termination)
{
	const auto has_header{[&headers_s, &headers_v]
	(const string_view &key) -> bool
	{
		return has(headers_v, key) || has(headers_s, key);
	}};

	writeline(out, [&code](const mutable_buffer &out) -> size_t
	{
		return fmt::sprintf
		{
			out, "HTTP/1.1 %u %s", uint(code), status(code)
		};
	});

	const bool write_server_header
	{
		code >= 200 && code < 300
		&& !has_header("server")
	};

	if(write_server_header)
		writeline(out, [&code](const mutable_buffer &out) -> size_t
		{
			size_t ret{0};
			ret += copy(out, "Server: "_sv);
			ret += copy(out + ret, ircd::info::server_agent);
			return ret;
		});

	const bool write_date_header
	{
		code < 400
		&& !has_header("date")
	};

	if(write_date_header)
		writeline(out, [](const mutable_buffer &out) -> size_t
		{
			thread_local char date_buf[96];
			return fmt::sprintf
			{
				out, "Date: %s", timef(date_buf, ircd::localtime)
			};
		});

	const bool write_content_type_header
	{
		code != NO_CONTENT
		&& content_type && content_length
		&& !has_header("content-type")
	};

	if(write_content_type_header)
		writeline(out, [&content_type](const mutable_buffer &out) -> size_t
		{
			return fmt::sprintf
			{
				out, "Content-Type: %s", content_type?: "text/plain; charset=utf-8"
			};
		});

	const bool write_content_length_header
	{
		code != NO_CONTENT
		&& content_length != size_t(-1) // chunked encoding indication
		&& !has_header("content-length")
	};

	if(write_content_length_header)
		writeline(out, [&content_length](const mutable_buffer &out) -> size_t
		{
			return fmt::sprintf
			{
				out, "Content-Length: %zu", content_length
			};
		});

	const bool write_transfer_encoding_chunked
	{
		content_length == size_t(-1)
		&& !has_header("transfer-encoding")
	};

	if(write_transfer_encoding_chunked)
		writeline(out, [&content_length](const mutable_buffer &out) -> size_t
		{
			return copy(out, "Transfer-Encoding: chunked"_sv);
		});

	if(!headers_s.empty())
		out([&headers_s](const mutable_buffer &out)
		{
			return copy(out, headers_s);
		});

	if(!headers_v.empty())
		write(out, headers_v);

	if(termination)
		writeline(out);
}

ircd::http::response::head::head(parse::capstan &pc,
                                 const headers::closure &c)
:line::response{pc}
,headers
{
	http::headers{pc, [this, &c](const auto &h)
	{
		if(iequals(h.first, "content-type"s))
			this->content_type = h.second;

		else if(iequals(h.first, "content-length"s))
			this->content_length = parser.content_length(h.second);

		else if(iequals(h.first, "content-range"s))
			this->content_range = h.second;

		else if(iequals(h.first, "accept-range"s))
			this->content_range = h.second;

		else if(iequals(h.first, "transfer-encoding"s))
			this->transfer_encoding = h.second;

		else if(iequals(h.first, "server"s))
			this->server = h.second;

		if(c)
			c(h);
	}}
}
{
}

ircd::http::response::chunk::chunk(parse::capstan &pc)
try
:line{pc}
{
	static const parser::rule<size_t> grammar
	{
		eoi | (eps > (parser.chunk_size >> -parser.chunk_extensions))
		,"chunk head"
	};

	const char *start(line::begin());
	const auto res
	{
		qi::parse(start, line::end(), grammar, this->size)
	};

	assert(res == true);
}
catch(const qi::expectation_failure<const char *> &e)
{
	throw_error(e, true);
}

//
// headers
//

bool
ircd::http::has(const vector_view<const header> &headers,
                const string_view &key)
{
	return end(headers) != std::find_if(begin(headers), end(headers), [&key]
	(const header &header)
	{
		return header == key;
	});
}

bool
ircd::http::has(const headers &headers,
                const string_view &key)
{
	return headers.has(key);
}

//
// headers::headers
//

decltype(ircd::http::headers::terminator)
ircd::http::headers::terminator
{
	"\r\n\r\n"
};

ircd::http::headers::headers(parse::capstan &pc,
                             const closure &c)
:headers
{
	pc, closure_bool{[&c](const auto &header)
	{
		if(c)
			c(header);

		return true;
	}}
}
{
}

ircd::http::headers::headers(parse::capstan &pc,
                             closure_bool c)
:string_view{[&pc, &c]
() -> string_view
{
	header h{pc};
	const char *const &started{h.first.data()}, *stopped{started};
	for(; !h.first.empty(); stopped = h.second.data() + h.second.size(), h = header{pc})
		if(c && !c(h))
			c = {};

	return { started, stopped };
}()}
{
}

bool
ircd::http::headers::has(const string_view &key)
const
{
	// has header if break early from for_each
	return !for_each([&key]
	(const header &header)
	{
		// true to continue; false to break (for_each protocol)
		return iequals(header.first, key)? false : true;
	});
}

ircd::string_view
ircd::http::headers::at(const string_view &key)
const
{
	const string_view ret
	{
		this->operator[](key)
	};

	if(unlikely(!ret))
		throw std::out_of_range{key};

	return ret;
}

ircd::string_view
ircd::http::headers::operator[](const string_view &key)
const
{
	string_view ret;
	for_each([&key, &ret](const auto &header)
	{
		if(iequals(header.first, key))
		{
			ret = header.second;
			return false;
		}
		else return true;
	});

	return ret;
}

bool
ircd::http::headers::for_each(const closure_bool &closure)
const
{
	if(empty())
		return true;

	parse::buffer pb{const_buffer{*this}};
	parse::capstan pc{pb};
	header h{pc};
	for(; !h.first.empty(); h = header{pc})
		if(!closure(h))
			return false;

	return true;
}

//
// header
//

ircd::http::header::header(const line &line)
try
{
	static const auto grammar
	{
		eps > parser.header
	};

	if(line.empty())
		return;

	const char *start(line.data());
	const char *const stop(line.data() + line.size());
	qi::parse(start, stop, grammar, *this);
}
catch(const qi::expectation_failure<const char *> &e)
{
	throw_error(e);
}

ircd::http::line::response::response(const line &line)
{
	static const auto grammar
	{
		eps > parser.response_line
	};

	const char *start(line.data());
	const char *const stop(line.data() + line.size());
	qi::parse(start, stop, grammar, *this);
}

ircd::http::line::request::request(const line &line)
try
{
	static const auto grammar
	{
		eps > parser.request_line
	};

	const char *start(line.data());
	const char *const stop(line.data() + line.size());
	qi::parse(start, stop, grammar, *this);
}
catch(const qi::expectation_failure<const char *> &e)
{
	throw_error(e);
}

ircd::http::line::request::operator
string_view()
const
{
	if(method.empty())
		return string_view{};

	assert(!version.empty());
	assert(method.begin() < version.end());
	return string_view
	{
		method.begin(), version.end()
	};
}

//
// http::line
//

decltype(ircd::http::line::terminator)
ircd::http::line::terminator
{
	"\r\n"
};

ircd::http::line::line(parse::capstan &pc)
:string_view{[&pc]
{
	static const auto grammar
	{
		parser.line
	};

	string_view ret;
	pc([&ret](const char *&start, const char *const &stop)
	{
		if(!qi::parse(start, stop, grammar, ret))
		{
			ret = {};
			return false;
		}
		else return true;
	});

	return ret;
}()}
{
}

//
// query::string
//

bool
ircd::http::query::string::has(const string_view &key)
const
{
	bool ret{false};
	for_each(key, [&ret]
	(const auto &)
	{
		ret = true;
		return false;
	});

	return ret;
}

size_t
ircd::http::query::string::count(const string_view &key)
const
{
	size_t ret{0};
	for_each(key, [&ret]
	(const auto &)
	{
		++ret;
		return true;
	});

	return ret;
}

ircd::string_view
ircd::http::query::string::at(const string_view &key,
                              const size_t &idx)
const
{
	const string_view &ret
	{
		_get(key, idx)
	};

	if(!ret)
	{
		thread_local char buf[1024];
		const string_view msg{fmt::sprintf
		{
			buf, "Failed to find value for required query string key '%s' #%zu.",
			key,
			idx
		}};

		throw std::out_of_range
		{
			msg.c_str() // fmt::sprintf() will null terminate msg
		};
	}

	return ret;
}

ircd::string_view
ircd::http::query::string::operator[](const string_view &key)
const
{
	return _get(key, 0);
}

ircd::string_view
ircd::http::query::string::_get(const string_view &key,
                                size_t idx)
const
{
	string_view ret;
	for_each(key, [&idx, &ret]
	(const auto &query)
	{
		if(!idx--)
		{
			ret = query.second;
			return false;
		}
		else return true;
	});

	return ret;
}

bool
ircd::http::query::string::for_each(const string_view &key,
                                    const closure &closure)
const
{
	return for_each([&key, &closure]
	(const auto &query)
	{
		if(query.first != key)
			return true;

		return closure(query);
	});
}

bool
ircd::http::query::string::for_each(const closure &view)
const
{
	const auto action{[&view]
	(const auto &attribute, const auto &context, auto &continue_)
	{
		continue_ = view(attribute);
	}};

	const parser::rule<unused_type> grammar
	{
		-parser.question >> (parser.query[action] % parser.ampersand)
	};

	const string_view &s(*this);
	const char *start(s.begin()), *const stop(s.end());
	return qi::parse(start, stop, grammar);
}

//
// parser util
//

size_t
ircd::http::parser::content_length(const string_view &str)
{
	static const parser::rule<long> grammar
	{
		long_
	};

	long ret;
	const char *start(str.data());
	const bool parsed(qi::parse(start, start + str.size(), grammar, ret));
	if(!parsed || ret < 0)
		throw error
		{
			BAD_REQUEST, "Invalid content-length value"
		};

	return ret;
}

//
// util
//

ircd::const_buffer
ircd::http::writechunk(const mutable_buffer &buf,
                       const uint32_t &chunk_size)
{
	window_buffer wb{buf};
	writechunk(wb, chunk_size);
	return wb.completed();
}

void
ircd::http::writechunk(window_buffer &buf,
                       const uint32_t &chunk_size)
{
	writeline(buf, [&chunk_size](const mutable_buffer &out) -> size_t
	{
		return ::snprintf(data(out), size(out), "%08x", chunk_size);
	});
}

std::string
ircd::http::strung(const vector_view<const header> &headers)
{
	return ircd::string(serialized(headers), [&]
	(window_buffer out)
	{
		write(out, headers);
		return out.consumed();
	});
}

/// Indicates the buffer size required to write these headers. This size
/// may include room for a terminating null character which may be written
/// by write(headers). Only use write(headers) to know the actually written
/// string size (without null) not this.
size_t
ircd::http::serialized(const vector_view<const header> &headers)
{
	// Because the write(header) functions use fmt::sprintf we have to
	// indicate an extra space for a null string terminator to not overlof
	const size_t initial{!headers.empty()};
	return std::accumulate(std::begin(headers), std::end(headers), initial, []
	(auto &ret, const auto &pair)
	{
		//            key                 :   SP  value                CRLF
		return ret += pair.first.size() + 1 + 1 + pair.second.size() + 2;
	});
}

void
ircd::http::write(window_buffer &out,
                  const vector_view<const header> &headers)
{
	for(const auto &header : headers)
		write(out, header);
}

void
ircd::http::write(window_buffer &out,
                  const header &header)
{
	if(header.second.empty())
		return;

	assert(!header.first.empty());
	if(unlikely(header.first.empty()))
		return;

	writeline(out, [&header](const mutable_buffer &out) -> size_t
	{
		return fmt::sprintf
		{
			out, "%s: %s", header.first, header.second
		};
	});
}

/// Close over the user's closure to append a newline.
void
ircd::http::writeline(window_buffer &write,
                      const window_buffer::closure &closure)
{
	// A new window_buffer is implicit constructed out of the mutable_buffer
	// otherwise presented to this closure as its write window.
	write([&closure](window_buffer write)
	{
		const auto newline{[](const mutable_buffer &out)
		{
			return copy(out, line::terminator);
		}};

		write(closure);
		write(newline);
		return write.consumed();
	});
}

void
ircd::http::writeline(window_buffer &write)
{
	writeline(write, [](const mutable_buffer &out)
	{
		return 0;
	});
}

/// Called to translate a grammar exception into an http::error within our
/// system. This will then usually propagate back to our client.
///
/// If we are a client to another server, set internal=true. Even though this
/// still generates an HTTP error, the code is 500 so if it propagates back to
/// a client it does not indicate to *that* client that *they* made a bad
/// request from a 400 back to them.
void
ircd::http::throw_error(const qi::expectation_failure<const char *> &e,
                        const bool &internal)
{
	const auto &code_
	{
		internal?
			code::INTERNAL_SERVER_ERROR:
			code::BAD_REQUEST
	};

	const char *const &fmtstr
	{
		internal?
			"I expected a valid HTTP %s. Server sent %zu invalid characters starting with `%s'.":
			"I require a valid HTTP %s. You sent %zu invalid characters starting with `%s'."
	};

	const auto &rule
	{
		ircd::string(e.what_)
	};

	throw error
	{
		code_, fmt::snstringf
		{
			512, fmtstr,
			between(rule, "<", ">"),
			size_t(e.last - e.first),
			string_view{e.first, e.last}
		}
	};
}

//
// error
//

ircd::http::error::error(const http::code &code,
                         std::string content,
                         const vector_view<const header> &headers)
:http::error
{
	code, std::move(content), strung(headers)
}
{
}

ircd::http::error::error(const http::code &code,
                         std::string content,
                         std::string headers)
:ircd::error
{
	generate_skip
}
,content
{
	std::move(content)
}
,headers
{
	std::move(headers)
}
,code{code}
{
	auto &buf(ircd::error::buf);
	::snprintf(buf, sizeof(buf), "%u %s", uint(code), status(code).c_str());
}

//
// status
//

ircd::http::code
ircd::http::status(const string_view &str)
{
	static const auto grammar
	{
		parser.status_code
	};

	short ret;
	const char *start(str.data());
	const bool parsed(qi::parse(start, start + str.size(), grammar, ret));
	if(!parsed || ret < 0 || ret >= 1000)
		throw ircd::error{"Invalid HTTP status code"};

	return http::code(ret);
}

ircd::string_view
ircd::http::status(const http::code &code)
try
{
	return reason.at(code);
}
catch(const std::out_of_range &e)
{
	log::warning
	{
		"No reason string for HTTP status code %u", uint(code)
	};

	return ""_sv;
}