construct/ircd/resource.cc

// Matrix Construct
//
// Copyright (C) Matrix Construct Developers, Authors & Contributors
// Copyright (C) 2016-2019 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.

///////////////////////////////////////////////////////////////////////////////
//
// resource/resource.h
//

decltype(ircd::resource::log)
ircd::resource::log
{
	"resource", 'r'
};

decltype(ircd::resource::resources)
ircd::resource::resources
{};

ircd::resource &
ircd::resource::find(const string_view &path_)
{
	const string_view path
	{
		rstrip(path_, '/')
	};

	auto it
	{
		resources.lower_bound(path)
	};

	if(it == end(resources)) try
	{
		--it;
		if(it == begin(resources) || !startswith(path, it->first))
			return *resources.at("/");
	}
	catch(const std::out_of_range &e)
	{
		throw http::error
		{
			http::code::NOT_FOUND
		};
	}

	auto rpath{it->first};
	//assert(!endswith(rpath, '/'));

	// Exact file or directory match
	if(path == rpath)
		return *it->second;

	// Directories handle all paths under them.
	while(!startswith(path, rpath))
	{
		// Walk the iterator back to find if there is a directory prefixing this path.
		if(it == begin(resources))
			throw http::error
			{
				http::code::NOT_FOUND
			};

		--it;
		rpath = it->first;
		if(~it->second->opts->flags & it->second->DIRECTORY)
			continue;

		// If the closest directory still doesn't match hand this off to the
		// webroot which can then service or 404 this itself.
		if(!startswith(path, rpath))
			return *resources.at("/");
	}

	// Check if the resource is a directory; if not, it can only
	// handle exact path matches.
	if(~it->second->opts->flags & it->second->DIRECTORY && path != rpath)
		throw http::error
		{
			http::code::NOT_FOUND
		};

	if(it->second->opts->flags & it->second->DIRECTORY)
	{
		const auto rem(lstrip(path, rpath));
		if(!empty(rem) && !startswith(rem, '/'))
			throw http::error
			{
				http::code::NOT_FOUND
			};
	}

	return *it->second;
}

//
// resource::resource
//

ircd::resource::resource(const string_view &path)
:resource
{
	path, {}
}
{
}

ircd::resource::resource(const string_view &path,
                         struct opts opts)
:path
{
	rstrip(path, '/')
}
,opts
{
	std::make_unique<const struct opts>(std::move(opts))
}
,resources_it{[this]
{
	const auto iit
	{
		resources.emplace(this->path, this)
	};

	if(!iit.second)
		throw error
		{
			"resource \"%s\" already registered", this->path
		};

	return unique_const_iterator<decltype(resources)>
	{
		resources, iit.first
	};
}()}
{
	log::debug
	{
		log, "Registered resource \"%s\"",
		path.empty()?
			string_view{"/"}:
			this->path
	};
}

ircd::resource::~resource()
noexcept
{
	log::debug
	{
		log, "Unregistered resource \"%s\"",
		path.empty()?
			string_view{"/"}:
			path
	};
}

ircd::resource::method &
ircd::resource::operator[](const string_view &name)
const try
{
	return *methods.at(name);
}
catch(const std::out_of_range &e)
{
	thread_local char buf[512];
	const http::header headers[]
	{
		{ "Allow", allow_methods_list(buf) }
	};

	throw http::error
	{
		http::METHOD_NOT_ALLOWED, {}, headers
	};
}

ircd::string_view
ircd::resource::allow_methods_list(const mutable_buffer &buf)
const
{
	size_t len(0);
	if(likely(size(buf)))
		buf[len] = '\0';

	auto it(begin(methods));
	if(it != end(methods))
	{
		len = strlcat(buf, it->first);
		for(++it; it != end(methods); ++it)
		{
			len = strlcat(buf, " ");
			len = strlcat(buf, it->first);
		}
	}

	return { data(buf), len };
}

///////////////////////////////////////////////////////////////////////////////
//
// resource/method.h
//

namespace ircd
{
	extern conf::item<seconds> cache_warmup_time;
	static void cache_warm_origin(const string_view &origin);
}

decltype(ircd::resource::method::idle_dock)
ircd::resource::method::idle_dock;

//
// method::method
//

ircd::resource::method::method(struct resource &resource,
                               const string_view &name,
                               handler function)
:method
{
	resource, name, std::move(function), {}
}
{
}

ircd::resource::method::method(struct resource &resource,
                               const string_view &name,
                               handler function,
                               struct opts opts)
:resource
{
	&resource
}
,name
{
	name
}
,function
{
	std::move(function)
}
,opts
{
	std::make_unique<const struct opts>(std::move(opts))
}
,stats
{
	std::make_unique<struct stats>()
}
,methods_it{[this, &name]
{
	const auto iit
	{
		this->resource->methods.emplace(this->name, this)
	};

	if(!iit.second)
		throw error
		{
			"resource \"%s\" already registered", name
		};

	return unique_const_iterator<decltype(resource::methods)>
	{
		this->resource->methods,
		iit.first
	};
}()}
{
}

ircd::resource::method::~method()
noexcept
{
	assert(resource);
	if(stats && stats->pending)
		log::dwarning
		{
			"Resource '%s' method '%s' still waiting for %zu pending requests",
			resource->path,
			name,
			stats->pending
		};

	idle_dock.wait([this]
	{
		return !stats || stats->pending == 0;
	});
}

void
ircd::resource::method::operator()(client &client,
                                   const http::request::head &head,
                                   const string_view &content_partial)
try
{
	const unwind on_idle{[this]
	{
		if(stats->pending == 0)
			idle_dock.notify_all();
	}};

	++stats->requests;
	const scope_count pending
	{
		stats->pending
	};

	// Bail out if the method limited the amount of content and it was exceeded.
	if(head.content_length > opts->payload_max)
		throw http::error
		{
			http::PAYLOAD_TOO_LARGE
		};

	// Check if the resource method wants a specific MIME type. If no option
	// is given by the resource then any Content-Type by the client will pass.
	if(opts->mime.first)
	{
		const auto &ct(split(head.content_type, ';'));
		const auto &supplied(split(ct.first, '/'));
		const auto &charset(ct.second);
		const auto &required(opts->mime);
		if(required.first != supplied.first
		||(required.second && required.second != supplied.second))
			throw http::error
			{
				http::UNSUPPORTED_MEDIA_TYPE
			};
	}

	// This timer will keep the request from hanging forever for whatever
	// reason. The resource method may want to do its own timing and can
	// disable this in its options structure.
	const net::scope_timeout timeout
	{
		*client.sock, opts->timeout, [this, &client]
		(const bool &timed_out)
		{
			if(timed_out)
				this->handle_timeout(client);
		}
	};

	// Content that hasn't yet arrived is remaining
	const size_t content_remain
	{
		head.content_length - client.content_consumed
	};

	// View of the content that will be passed to the resource handler. Starts
	// with the content received so far which is actually in the head's buffer.
	// One of three things can happen now:
	//
	// - There is no more content so we pass this as-is right to the resource.
	// - There is more content, so we allocate a content buffer, copy what we
	// have to it, read the rest off the socket, and then reassign this view.
	// - There is more content, but the resource wants to read it off the
	// socket on its own terms, so we pass this as-is.
	string_view content
	{
		content_partial
	};

	if(content_remain && ~opts->flags & CONTENT_DISCRETION)
	{
		// Copy any partial content to the final contiguous allocated buffer;
		client.content_buffer = unique_buffer<mutable_buffer>{head.content_length};
		memcpy(data(client.content_buffer), data(content_partial), size(content_partial));

		// Setup a window inside the buffer for the remaining socket read.
		const mutable_buffer content_remain_buffer
		{
			data(client.content_buffer) + size(content_partial), content_remain
		};

		// Read the remaining content off the socket.
		client.content_consumed += read_all(*client.sock, content_remain_buffer);
		assert(client.content_consumed == head.content_length);
		content = string_view
		{
			data(client.content_buffer), head.content_length
		};
	}

	// We take the extra step here to clear the assignment to client.request
	// when this request stack has finished for two reasons:
	// - It allows other ctxs to peep at the client::list to see what this
	//   client/ctx/request is currently working on with some more safety.
	// - It prevents an easy source for stale refs wrt the longpoll thing.
	const scope_restore client_request
	{
		client.request, resource::request
		{
			head, content
		}
	};

	const auto pathparm
	{
		lstrip(head.path, resource->path)
	};

	client.request.parv =
	{
		client.request.param, tokens(pathparm, '/', client.request.param)
	};

	// Client access token verified here. On success, user_id owning the token
	// is copied into the client.request structure. On failure, the method is
	// checked to see if it requires authentication and if so, this throws.
	authenticate(client, client.request);

	// Server X-Matrix header verified here. Similar to client auth, origin
	// which has been authed is referenced in the client.request. If the method
	// requires, and auth fails or not provided, this function throws.
	// Otherwise it returns a string_view of the origin name in
	// client.request.origin, or an empty string_view if an origin was not
	// apropos for this request (i.e a client request rather than federation).
	if(verify_origin(client, client.request))
	{
		assert(client.request.origin);

		// If we have an error cached from previously not being able to
		// contact this origin we can clear that now that they're alive.
		server::errclear(client.request.origin);

		// The origin was verified so we can invoke the cache warming now.
		cache_warm_origin(client.request.origin);
	}

	// Finally handle the request.
	call_handler(client, client.request);
	++stats->completions;
}
catch(const http::error &e)
{
	if(unlikely(e.code == http::INTERNAL_SERVER_ERROR))
		++stats->internal_errors;

	throw;
}
catch(const std::system_error &)
{
	throw;
}
catch(const ctx::interrupted &)
{
	throw;
}
catch(...)
{
	++stats->internal_errors;
	throw;
}

void
ircd::resource::method::call_handler(client &client,
                                     resource::request &request)
try
{
	function(client, request);
}
catch(const json::print_error &e)
{
	throw m::error
	{
		http::INTERNAL_SERVER_ERROR, "M_NOT_JSON", "Generator Protection: %s", e.what()
	};
}
catch(const json::not_found &e)
{
	throw m::error
	{
		http::BAD_REQUEST, "M_BAD_JSON", "Required JSON field: %s", e.what()
	};
}
catch(const json::error &e)
{
	throw m::error
	{
		http::BAD_REQUEST, "M_NOT_JSON", "%s", e.what()
	};
}
catch(const ctx::timeout &e)
{
	throw m::error
	{
		http::BAD_GATEWAY, "M_REQUEST_TIMEOUT", "%s", e.what()
	};
}
catch(const mods::unavailable &e)
{
	throw m::UNAVAILABLE
	{
		"%s", e.what()
	};
}
catch(const std::bad_function_call &e)
{
	throw m::UNAVAILABLE
	{
		"%s", e.what()
	};
}
catch(const std::out_of_range &e)
{
	throw m::NOT_FOUND
	{
		"%s", e.what()
	};
}

void
ircd::resource::method::handle_timeout(client &client)
const
{
	log::derror
	{
		log, "%s Timed out in %s `%s'",
		client.loghead(),
		name,
		resource->path
	};

	stats->timeouts++;

	// The interrupt is effective when the socket has already been
	// closed and/or the client is still stuck in a request for
	// some reason.
	if(client.reqctx)
		ctx::interrupt(*client.reqctx);

	//TODO: If we know that no response has been sent yet
	//TODO: we can respond with http::REQUEST_TIMEOUT instead.
	client.close(net::dc::RST, net::close_ignore);
}

/// Authenticate a client based on access_token either in the query string or
/// in the Authentication bearer header. If a token is found the user_id owning
/// the token is copied into the request. If it is not found or it is invalid
/// then the method being requested is checked to see if it is required. If so
/// the appropriate exception is thrown.
ircd::string_view
ircd::resource::method::authenticate(client &client,
                                     resource::request &request)
const
{
	request.access_token =
	{
		request.query["access_token"]
	};

	if(empty(request.access_token))
	{
		const auto authorization
		{
			split(request.head.authorization, ' ')
		};

		if(iequals(authorization.first, "bearer"_sv))
			request.access_token = authorization.second;
	}

	const bool requires_auth
	{
		opts->flags & REQUIRES_AUTH
	};

	if(!request.access_token && requires_auth)
		throw m::error
		{
			http::UNAUTHORIZED, "M_MISSING_TOKEN",
			"Credentials for this method are required but missing."
		};

	if(!request.access_token)
		return {};

	static const m::event::fetch::opts fopts
	{
		m::event::keys::include
		{
			"sender"
		}
	};

	const m::room::state tokens{m::user::tokens, &fopts};
	tokens.get(std::nothrow, "ircd.access_token", request.access_token, [&request]
	(const m::event &event)
	{
		// The user sent this access token to the tokens room
		request.user_id = m::user::id
		{
			at<"sender"_>(event)
		};
	});

	if(!request.user_id && requires_auth)
		throw m::error
		{
			http::UNAUTHORIZED, "M_UNKNOWN_TOKEN",
			"Credentials for this method are required but invalid."
		};

	return request.user_id;
}

decltype(ircd::resource::method::x_matrix_verify_origin)
ircd::resource::method::x_matrix_verify_origin
{
	{ "name",     "ircd.resource.x_matrix.verify_origin" },
	{ "default",  true                                   },
};

decltype(ircd::resource::method::x_matrix_verify_origin)
ircd::resource::method::x_matrix_verify_destination
{
	{ "name",     "ircd.resource.x_matrix.verify_destination" },
	{ "default",  true                                        },
};

ircd::string_view
ircd::resource::method::verify_origin(client &client,
                                      request &request)
const try
{
	const bool required
	{
		opts->flags & VERIFY_ORIGIN
	};

	const auto authorization
	{
		split(request.head.authorization, ' ')
	};

	const bool supplied
	{
		iequals(authorization.first, "X-Matrix"_sv)
	};

	if(!required && !supplied)
		return {};

	if(required && !supplied)
		throw m::error
		{
			http::UNAUTHORIZED, "M_MISSING_AUTHORIZATION",
			"Required X-Matrix Authorization was not supplied"
		};

	if(x_matrix_verify_destination && !m::my_host(request.head.host))
		throw m::error
		{
			http::UNAUTHORIZED, "M_NOT_MY_HOST",
			"The X-Matrix Authorization destination host is not recognized here."
		};

	const m::request::x_matrix x_matrix
	{
		request.head.authorization
	};

	const m::request object
	{
		x_matrix.origin, request.head.host, name, request.head.uri, request.content
	};

	if(x_matrix_verify_origin && !object.verify(x_matrix.key, x_matrix.sig))
		throw m::error
		{
			http::FORBIDDEN, "M_INVALID_SIGNATURE",
			"The X-Matrix Authorization is invalid."
		};

	request.node_id = {m::node::id::origin, x_matrix.origin};
	request.origin = x_matrix.origin;
	return request.origin;
}
catch(const m::error &)
{
	throw;
}
catch(const std::exception &e)
{
	log::derror
	{
		resource::log, "X-Matrix Authorization from %s: %s",
		string(remote(client)),
		e.what()
	};

	throw m::error
	{
		http::UNAUTHORIZED, "M_UNKNOWN_ERROR",
		"An error has prevented authorization: %s",
		e.what()
	};
}

decltype(ircd::cache_warmup_time)
ircd::cache_warmup_time
{
	{ "name",     "ircd.cache_warmup_time" },
	{ "default",  3600L                    },
};

/// We can smoothly warmup some memory caches after daemon startup as the
/// requests trickle in from remote servers. This function is invoked after
/// a remote contacts and reveals its identity with the X-Matrix verification.
///
/// This process helps us avoid cold caches for the first requests coming from
/// our server. Such requests are often parallel requests, for ex. to hundreds
/// of servers in a Matrix room at the same time.
///
/// This function does nothing after the cache warmup period has ended.
void
ircd::cache_warm_origin(const string_view &origin)
try
{
	if(ircd::uptime() > seconds(cache_warmup_time))
		return;

	// Make a query through SRV and A records.
	//net::dns::resolve(origin, net::dns::prefetch_ipport);
}
catch(const std::exception &e)
{
	log::derror
	{
		resource::log, "Cache warming for '%s' :%s",
		origin,
		e.what()
	};
}

///////////////////////////////////////////////////////////////////////////////
//
// resource/response.h
//

//
// resource::response::chunked
//

ircd::resource::response::chunked::chunked(client &client,
                                           const http::code &code,
                                           const size_t &buffer_size)
:chunked
{
	client, code, "application/json; charset=utf-8"_sv, string_view{}, buffer_size
}
{
}

ircd::resource::response::chunked::chunked(client &client,
                                           const http::code &code,
                                           const vector_view<const http::header> &headers,
                                           const size_t &buffer_size)
:chunked
{
	client, code, "application/json; charset=utf-8"_sv, headers, buffer_size
}
{
}

ircd::resource::response::chunked::chunked(client &client,
                                           const http::code &code,
                                           const string_view &content_type,
                                           const vector_view<const http::header> &headers,
                                           const size_t &buffer_size)
:chunked
{
	client,
	code,
	content_type,
	[&headers]
	{
		// Note that the headers which are composed into this buffer are
		// copied again before the response goes out from resource::response.
		// There must not be any context switch between now and that copy so
		// we can return a string_view of this TLS buffer.

		thread_local char buffer[4_KiB];
		window_buffer sb{buffer};
		http::write(sb, headers);
		return string_view{sb.completed()};
	}(),
	buffer_size
}
{
}

decltype(ircd::resource::response::chunked::default_buffer_size)
ircd::resource::response::chunked::default_buffer_size
{
	{ "name",    "ircd.resource.response.chunked.buffer_size" },
	{ "default", long(96_KiB)                                 },
};

ircd::resource::response::chunked::chunked(client &client,
                                           const http::code &code,
                                           const string_view &content_type,
                                           const string_view &headers,
                                           const size_t &buffer_size)
:response
{
	client, code, content_type, size_t(-1), headers
}
,c
{
	&client
}
,buf
{
	buffer_size
}
{
	assert(!empty(content_type));
}

ircd::resource::response::chunked::~chunked()
noexcept try
{
	if(!c)
		return;

	if(!std::uncaught_exceptions())
		finish();
	else
		c->close(net::dc::RST, net::close_ignore);
}
catch(...)
{
	return;
}

std::function<ircd::const_buffer (const ircd::const_buffer &)>
ircd::resource::response::chunked::flusher()
{
	return std::bind(&chunked::flush, this, ph::_1);
}

bool
ircd::resource::response::chunked::finish()
{
	if(!c)
		return false;

	write(const_buffer{}, false);
	c = nullptr;
	return true;
}

ircd::const_buffer
ircd::resource::response::chunked::flush(const const_buffer &buf)
{
	const const_buffer wrote
	{
		data(buf), write(buf)
	};

	return wrote;
}

size_t
ircd::resource::response::chunked::write(const const_buffer &chunk,
                                         const bool &ignore_empty)
try
{
	size_t ret{0};

	if(!c)
		return ret;

	if(ignore_empty && empty(chunk))
		return ret;

	//TODO: bring iov from net::socket -> net::write_() -> client::write_()
	char headbuf[32];
	ret += c->write_all(http::writechunk(headbuf, size(chunk)));
	ret += size(chunk)? c->write_all(chunk) : 0UL;
	ret += c->write_all("\r\n"_sv);
	return ret;
}
catch(...)
{
	this->c = nullptr;
	throw;
}

//
// resource::response
//

// A buffer of this size will be passed to the socket and sent
// out and must be on stack.
decltype(ircd::resource::response::HEAD_BUF_SZ)
ircd::resource::response::HEAD_BUF_SZ
{
	4_KiB
};

ircd::resource::response::response(client &client,
                                   const http::code &code)
:response{client, json::object{json::empty_object}, code}
{
}

ircd::resource::response::response(client &client,
                                   const http::code &code,
                                   const json::iov &members)
:response{client, members, code}
{
}

ircd::resource::response::response(client &client,
                                   const json::members &members,
                                   const http::code &code)
:response{client, code, members}
{
}

ircd::resource::response::response(client &client,
                                   const json::value &value,
                                   const http::code &code)
:response{client, code, value}
{
}

ircd::resource::response::response(client &client,
                                   const http::code &code,
                                   const json::value &value)
try
{
	const auto size
	{
		serialized(value)
	};

	const unique_buffer<mutable_buffer> buffer
	{
		size
	};

	switch(type(value))
	{
		case json::ARRAY:
		{
			response(client, json::array{stringify(mutable_buffer{buffer}, value)}, code);
			return;
		}

		case json::OBJECT:
		{
			response(client, json::object{stringify(mutable_buffer{buffer}, value)}, code);
			return;
		}

		default: throw m::error
		{
			http::INTERNAL_SERVER_ERROR, "M_NOT_JSON", "Cannot send json::%s as response content", type(value)
		};
	}
}
catch(const json::error &e)
{
	throw m::error
	{
		http::INTERNAL_SERVER_ERROR, "M_NOT_JSON", "Generator Protection: %s", e.what()
	};
}

ircd::resource::response::response(client &client,
                                   const http::code &code,
                                   const json::members &members)
try
{
	const auto size
	{
		serialized(members)
	};

	const unique_buffer<mutable_buffer> buffer
	{
		size
	};

	const json::object object
	{
		stringify(mutable_buffer{buffer}, members)
	};

	response(client, object, code);
}
catch(const json::error &e)
{
	throw m::error
	{
		http::INTERNAL_SERVER_ERROR, "M_NOT_JSON", "Generator Protection: %s", e.what()
	};
}

ircd::resource::response::response(client &client,
                                   const json::iov &members,
                                   const http::code &code)
try
{
	const auto size
	{
		serialized(members)
	};

	const unique_buffer<mutable_buffer> buffer
	{
		size
	};

	const json::object object
	{
		stringify(mutable_buffer{buffer}, members)
	};

	response(client, object, code);
}
catch(const json::error &e)
{
	throw m::error
	{
		http::INTERNAL_SERVER_ERROR, "M_NOT_JSON", "Generator Protection: %s", e.what()
	};
}

ircd::resource::response::response(client &client,
                                   const json::object &object,
                                   const http::code &code)
{
	static const string_view content_type
	{
		"application/json; charset=utf-8"
	};

	assert(json::valid(object, std::nothrow));
	response(client, object, content_type, code);
}

ircd::resource::response::response(client &client,
                                   const json::array &array,
                                   const http::code &code)
{
	static const string_view content_type
	{
		"application/json; charset=utf-8"
	};

	assert(json::valid(array, std::nothrow));
	response(client, array, content_type, code);
}

ircd::resource::response::response(client &client,
                                   const string_view &content,
                                   const string_view &content_type,
                                   const http::code &code,
                                   const vector_view<const http::header> &headers)
{
	assert(empty(content) || !empty(content_type));

	// contents of this buffer get copied again when further passed to
	// response{}; we can get this off the stack if that remains true.
	thread_local char buffer[4_KiB];
	window_buffer sb{buffer};
	{
		const critical_assertion ca;
		http::write(sb, headers);
	}

	response
	{
		client, content, content_type, code, string_view{sb.completed()}
	};
}

ircd::resource::response::response(client &client,
                                   const string_view &content,
                                   const string_view &content_type,
                                   const http::code &code,
                                   const string_view &headers)
{
	assert(empty(content) || !empty(content_type));

	// Head gets sent
	response
	{
		client, code, content_type, size(content), headers
	};

	// All content gets sent
	const size_t written
	{
		size(content)?
			client.write_all(content):
			0
	};

	assert(written == size(content));
}

decltype(ircd::resource::response::access_control_allow_origin)
ircd::resource::response::access_control_allow_origin
{
	{ "name",      "ircd.resource.access_control.allow_origin" },
	{ "default",   "*"                                         }
};

ircd::resource::response::response(client &client,
                                   const http::code &code,
                                   const string_view &content_type,
                                   const size_t &content_length,
                                   const string_view &headers)
{
	assert(!content_length || !empty(content_type));

	const auto request_time
	{
		client.timer.at<microseconds>()
	};

	thread_local char rtime_buf[32];
	const string_view rtime
	{
		pretty(rtime_buf, request_time, true)
	};

	char head_buf[HEAD_BUF_SZ];
	window_buffer head{head_buf};
	http::response
	{
		head,
		code,
		content_length,
		content_type,
		headers,
		{
			{ "Access-Control-Allow-Origin",  string_view(access_control_allow_origin) },
			{ "X-IRCd-Request-Timer",         rtime                                    },
		},
	};

	// Maximum size is realistically ok but ideally a small
	// maximum; this exception should hit the developer in testing.
	if(unlikely(!head.remaining()))
		throw panic
		{
			"HTTP headers too large for buffer of %zu", sizeof(head_buf)
		};

	size_t wrote{0};
	std::exception_ptr eptr; try
	{
		wrote = client.write_all(head.completed());
	}
	catch(...)
	{
		eptr = std::current_exception();
	}

	#ifdef RB_DEBUG
	const log::level level
	{
		ushort(code) >= 200 && ushort(code) < 300?
			log::level::DEBUG:
		ushort(code) >= 300 && ushort(code) < 400?
			log::level::DWARNING:
		ushort(code) >= 400 && ushort(code) < 500?
			log::level::DERROR:
		ushort(code) == 500?
			log::level::ERROR:
		ushort(code) > 500?
			log::level::DERROR:
			log::level::ERROR
	};

	log::logf
	{
		log, level,
		"%s HTTP %u `%s' %s in %s; %s content-length:%s wrote:%zu %s%s",
		client.loghead(),
		uint(code),
		client.request.head.path,
		http::status(code),
		rtime,
		content_type,
		ssize_t(content_length) >= 0?
			lex_cast(content_length):
			"chunked"_sv,
		wrote,
		eptr?
			"error:"_sv:
			string_view{},
		what(eptr)
	};
	#endif

	if(eptr)
		std::rethrow_exception(eptr);

	assert(wrote == size(head.completed()));
}

///////////////////////////////////////////////////////////////////////////////
//
// resource/redirect.h
//

//
// redirect::permanent::permanent
//

ircd::resource::redirect::permanent::permanent(const string_view &old_path,
                                               const string_view &new_path,
                                               struct opts opts)
:resource
{
	old_path, std::move(opts)
}
,new_path
{
	new_path
}
,_options
{
	*this, "OPTIONS", std::bind(&permanent::handler, this, ph::_1, ph::_2)
}
,_trace
{
	*this, "TRACE", std::bind(&permanent::handler, this, ph::_1, ph::_2)
}
,_head
{
	*this, "HEAD", std::bind(&permanent::handler, this, ph::_1, ph::_2)
}
,_get
{
	*this, "GET", std::bind(&permanent::handler, this, ph::_1, ph::_2)
}
,_put
{
	*this, "PUT", std::bind(&permanent::handler, this, ph::_1, ph::_2)
}
,_post
{
	*this, "POST", std::bind(&permanent::handler, this, ph::_1, ph::_2)
}
,_patch
{
	*this, "PATCH", std::bind(&permanent::handler, this, ph::_1, ph::_2)
}
,_delete
{
	*this, "DELETE", std::bind(&permanent::handler, this, ph::_1, ph::_2)
}
{
}

ircd::resource::response
ircd::resource::redirect::permanent::handler(client &client,
                                             const request &request)
{
	thread_local char buf[response::HEAD_BUF_SZ];

	const string_view postfix
	{
		lstrip(request.head.uri, this->path)
	};

	const string_view location{fmt::sprintf
	{
		buf, "%s/%s",
		rstrip(this->new_path, '/'),
		lstrip(postfix, '/')
	}};

	return response
	{
		client, {}, {}, http::PERMANENT_REDIRECT,
		{
			http::header { "Location", location }
		}
	};
}