lua continue

Lua中没有内置的continue关键字，但是可以通过一些技巧来实现continue的功能。常见的方法有三种：
1. 在循环中再定义一个循环，并且这个循环只执行一次。
2. 利用for循环的break关键字实现。
3. 利用goto语句实现。

其中第一种方法需要在循环中再定义一个循环，并且这个循环只执行一次，通过在内层循环中使用break来实现continue的功能。第二种方法是在循环中使用while循环，通过在while循环中使用break来实现continue的功能。第三种方法是利用goto语句，在循环中使用goto continue来跳过本次循环，并且可以正常使用break功能。

需要注意的是，虽然这些方法可以实现continue的功能，但是在实际编程中应该尽量避免使用这些技巧，因为它们会使代码变得难以理解和维护。

相关问题

lua http 源码

以下是 Lua 5.1 版本的 http 模块源码，可以用来实现 HTTP 客户端请求：

-----------------------------------------------------------------------------
-- LuaSocket module for HTTP/1.1 client support
-- Diego Nehab, et al.
-- 04/11/2007
-----------------------------------------------------------------------------
local base = _G
local string = require("string")
local math = require("math")
local socket = require("socket")
local url = require("socket.url")
module("socket.http")

-- the default user agent string
USERAGENT = "LuaSocket 2.0.2"

-- timeout values
TIMEOUT = 60
TIMEOUT_CONNECT = socket._TIMEOUT

-- code 204 is no content, but the server sent a response header
-- code 304 is not modified, so there's no need to resend the content
-- code 205 is a reset content request, we must accept the new content
-- code 206 is a partial content response, we must adjust our range
-- code 301 is a redirect, we must look for the location header
-- code 302 is a redirect, but some buggy servers send content along
-- code 303 is a redirect, but with a get method
-- code 307 is a redirect, but we must keep the method
-- code 401 is a authentication request, we must resend with proper creds
-- code 407 is a proxy authentication request, same as 401
NOCONTENT_CODES = "204 304 205 206"
REDIRECT_CODES = "301 302 303 307"
AUTHREQUIRED_CODES = "401 407"
DEFAULT_REDIRECT_TIMES = 5
-- the default port for each protocol
PORT = { http = 80, https = 443, }

-- get a connection object
local function get_connection(u, redir)
    local proxy = base._PROXY or socket._PROXY
    local conn = {
        try = socket.tcp(),
        proxy = proxy and url.parse(proxy),
        ssl = u.scheme == "https",
        live = true,
        redirected = false,
        redirectcount = 0,
        redirectstring = "",
        host = u.host,
        port = u.port or PORT[u.scheme],
        method = "GET",
        url = u,
        sink = nil,
        headers = { 
            ["user-agent"] = USERAGENT, 
            ["host"] = u.host,
        },
        source = socket.source("close-when-done", conn.try)
    }
    if conn.proxy then
        conn.host = conn.proxy.host
        conn.port = conn.proxy.port
        conn.headers["host"] = u.authority
    end
    if redir then
        conn.redirected = true
        conn.redirectcount = redir.redirectcount + 1
        conn.redirectstring = redir.redirectstring.."\n"..u.request
    end
    return conn
end

-- close a connection
local function close_connection(c)
    if c.try then c.try:close() end
    c.try = nil
    c.live = nil
end

-- receive a line from a connection or a sink
local function receive(fd, pat, t)
    local st, chunk
    local buffer = {}
    local receive_chunk = fd.receive or fd.read or fd
    t = t or TIMEOUT
    repeat
        st, chunk = receive_chunk(fd, pat)
        if st then
            buffer[#buffer + 1] = chunk
        else
            return nil, chunk
        end
    until string.find(buffer[#buffer] or "", pat, nil, true) or st == nil
    return table.concat(buffer)
end

-- send data through a connection or a source
local function send(fd, data)
    if not fd.send then
        if type(fd) ~= "function" then
            error("invalid send source")
        end
        fd(data)
    else
        fd:send(data)
    end
end

-- convert headers to a string
local function headers_to_string(headers)
    local buffer = {}
    for field, value in pairs(headers) do
        buffer[#buffer + 1] = string.format("%s: %s", field, value)
    end
    buffer[#buffer + 1] = ""
    return table.concat(buffer, "\r\n")
end

-- convert headers from a string to a table
local function headers_from_string(header_string)
    local headers = {}
    local pos = 1
    local eol = string.find(header_string, "\n", pos, true)
    while eol do
        local line = string.sub(header_string, pos, eol - 1)
        line = string.gsub(line, "[\r\n]+$", "")
        pos = eol + 1
        eol = string.find(header_string, "\n", pos, true)
        if line ~= "" then
            local field, value = string.match(line, "^(.-):%s*(.*)$")
            if field then
                field = string.lower(field)
                if headers[field] then
                    headers[field] = headers[field]..", "..value
                else
                    headers[field] = value
                end
            end
        else
            break
        end
    end
    return headers
end

-- perform a generic HTTP request
local function request(req)
    local u = url.parse(req.url)
    local c = get_connection(u, req.redirection)
    if not c.try then return nil, "unable to connect to "..u.host end
    c.try:settimeout(TIMEOUT_CONNECT, "t")
    local res = { }
    local pat = "^(.-)\r?\n"
    -- send request line
    local reqline = string.format("%s %s HTTP/1.1", req.method, u.path or "/")
    if u.query then reqline = reqline.."?"..u.query end
    send(c.try, string.format("%s\r\n", reqline))
    -- add headers
    if req.source then
        c.headers["transfer-encoding"] = "chunked"
        c.headers["connection"] = "close"
        c.headers["expect"] = "100-continue"
    end
    for i, header in ipairs(req.headers) do
        local name, value = string.match(header, "^(.-):%s*(.*)$")
        if name then
            c.headers[string.lower(name)] = value
        end
    end
    if not c.headers["host"] then
        c.headers["host"] = u.authority
    end
    send(c.try, headers_to_string(c.headers))
    send(c.try, "\r\n")
    -- send request body
    if req.source then
        local source = req.source
        while true do
            local chunk = source()
            if not chunk then
                send(c.try, "0\r\n\r\n")
                break
            end
            send(c.try, string.format("%x\r\n", string.len(chunk)))
            send(c.try, chunk)
            send(c.try, "\r\n")
        end
    end
    c.try:settimeout(TIMEOUT, "t")
    -- receive response
    local status
    local headers = {}
    local body
    status = receive(c.try, pat)
    if status then
        local ver, code, message = string.match(status, "^(%S+)%s+(%S+)%s+(.-)\r?$")
        if ver and code and message then
            status = {
                major = tonumber(string.match(ver, "HTTP/(%d)%.%d")),
                minor = tonumber(string.match(ver, "HTTP/%d%.(%d)")),
                code = tonumber(code),
                message = message
            }
            -- receive headers
            local header_string, err = receive(c.try, "\r?\n\r?\n")
            if header_string then
                headers = headers_from_string(header_string)
                -- handle 100 Continue responses
                if status.code == 100 then
                    status, headers, body = request(req)
                -- handle 300 redirects
                elseif string.find(REDIRECT_CODES, code, 1, true) then
                    local location = headers.location
                    if location then
                        location = url.absolute(u, location)
                        if req.redirection then
                            if req.redirection.redirectcount >= DEFAULT_REDIRECT_TIMES then
                                return nil, "too many redirections"
                            end
                            if req.redirection.redirectstring:find(location.request, 1, true) then
                                return nil, "infinite redirection loop"
                            end
                        else
                            req.redirection = {
                                redirectcount = 0,
                                redirectstring = req.url.request,
                            }
                        end
                        req.url = location
                        close_connection(c)
                        return request(req)
                    end
                -- handle 401 and 407 authentication requests
                elseif string.find(AUTHREQUIRED_CODES, code, 1, true) then
                    if req.auth and c.headers.authorization then
                        return nil, "invalid authentication credentials"
                    end
                    local auth = headers["www-authenticate"] 
                        or headers["proxy-authenticate"]
                    if auth then
                        local realm = string.match(auth, "realm=\"([^\"]*)\"")
                        if not realm then
                            realm = string.match(auth, "realm=([^,]*)")
                        end
                        if realm then
                            local user, password = req.auth(realm)
                            if user then
                                c.headers.authorization = 
                                    socket.try(socket.url.build({ 
                                        scheme = "basic", 
                                        user = user, 
                                        password = password 
                                    }))
                                close_connection(c)
                                return request(req)
                            end
                        end
                    end
                end
                -- get response body
                local length = tonumber(headers["content-length"])
                if headers["transfer-encoding"] == "chunked" then
                    local decoder = socket.protect(function(chunk)
                        local size = tonumber(chunk, 16)
                        if size == 0 then return "" end
                        return receive(c.try, string.format("^([^\r\n]*)\r?\n(.*)\r?\n.{0,%d}$", size - 1), TIMEOUT)
                    end)
                    body = socket.sink("into-string")
                    while true do
                        local chunk, err = decoder()
                        if err or chunk == "" then break end
                        body(chunk)
                    end
                elseif length then
                    body = receive(c.try, string.format("^%(.{%d})$", length), TIMEOUT)
                elseif headers.connection == "close" then
                    body = receive(c.try, nil, TIMEOUT)
                end
            end
        else
            status = nil
        end
        if not status then
            close_connection(c)
            return nil, "invalid server response"
        end
        res.status = status
        res.headers = headers
        res.body = body
        res.request = req
        return res
    else
        close_connection(c)
        return nil, "unable to receive status line"
    end
end

-- HTTP/1.1 methods
function request_uri(u, req)
    req = req or {}
    req.method = req.method or "GET"
    req.headers = req.headers or {}
    req.url = url.absolute(u, req.url)
    return request(req)
end

function request_string(u, s)
    local req = {
        method = "GET",
        headers = {},
        url = u,
        source = socket.source("string", s),
    }
    req.headers["content-length"] = string.len(s)
    return request(req)
end

function request_file(u, f)
    local req = {
        method = "PUT",
        headers = {},
        url = u,
        source = socket.source("file", f),
    }
    req.headers["content-length"] = socket.filesize(f)
    return request(req)
end

-- HTTP/1.0.0 methods
function get(u, headers)
    return request_uri(u, { method = "GET", headers = headers or {} })
end

function post(u, body, headers)
    return request_uri(u, { 
        method = "POST", 
        headers = headers or {},
        source = socket.source("string", body),
    })
end

function put(u, body, headers)
    return request_uri(u, { 
        method = "PUT", 
        headers = headers or {},
        source = socket.source("string", body),
    })
end

function delete(u, headers)
    return request_uri(u, { method = "DELETE", headers = headers or {} })
end

function options(u, headers)
    return request_uri(u, { method = "OPTIONS", headers = headers or {} })
end

function trace(u, headers)
    return request_uri(u, { method = "TRACE", headers = headers or {} })
end

-- exports
_headers_to_string = headers_to_string
_headers_from_string = headers_from_string

该模块提供了一系列 HTTP 请求方法，可以根据需要进行调用。其中，`request_uri` 方法可以实现对 URL 的请求，`get`、`post`、`put`、`delete`、`options`、`trace` 方法则分别对应了 HTTP 协议中的常见请求方法。

lua写A星算法

以下是一个简单的 Lua 实现 A* 算法的示例代码：

-- 定义节点结构体
local Node = {
    x = 0, -- 节点的 x 坐标
    y = 0, -- 节点的 y 坐标
    g = 0, -- 从起点到当前节点的实际代价
    h = 0, -- 从当前节点到目标节点的估计代价
    f = 0, -- f = g + h
    parent = nil, -- 父节点
}

-- 计算曼哈顿距离
local function manhattanDistance(node, target)
    return math.abs(node.x - target.x) + math.abs(node.y - target.y)
end

-- A* 算法
local function aStar(start, target, map)
    -- 初始化 open 和 close 列表
    local open = {}
    local close = {}

    -- 将起点加入 open 列表
    table.insert(open, start)

    while #open > 0 do
        -- 选取 f 值最小的节点
        local current = open[1]
        for i = 2, #open do
            if open[i].f < current.f then
                current = open[i]
            end
        end

        -- 如果当前节点为目标节点，则返回路径
        if current.x == target.x and current.y == target.y then
            local path = {}
            while current.parent ~= nil do
                table.insert(path, 1, current)
                current = current.parent
            end
            table.insert(path, 1, start)
            return path
        end

        -- 将当前节点从 open 列表中移除，并加入 close 列表
        for i = #open, 1, -1 do
            if open[i].x == current.x and open[i].y == current.y then
                table.remove(open, i)
                break
            end
        end
        table.insert(close, current)

        -- 遍历当前节点的邻居节点
        local neighbors = {}
        if map[current.x - 1] and map[current.x - 1][current.y] then
            table.insert(neighbors, map[current.x - 1][current.y])
        end
        if map[current.x + 1] and map[current.x + 1][current.y] then
            table.insert(neighbors, map[current.x + 1][current.y])
        end
        if map[current.x][current.y - 1] then
            table.insert(neighbors, map[current.x][current.y - 1])
        end
        if map[current.x][current.y + 1] then
            table.insert(neighbors, map[current.x][current.y + 1])
        end

        for _, neighbor in ipairs(neighbors) do
            -- 如果邻居节点已经在 close 列表中，则忽略
            local isInClose = false
            for i = 1, #close do
                if close[i].x == neighbor.x and close[i].y == neighbor.y then
                    isInClose = true
                    break
                end
            end
            if isInClose then
                goto continue
            end

            -- 如果邻居节点不可通行，则忽略
            if not neighbor.walkable then
                goto continue
            end

            -- 计算邻居节点的实际代价
            local g = current.g + 1

            -- 如果邻居节点不在 open 列表中，则添加到 open 列表
            local isInOpen = false
            for i = 1, #open do
                if open[i].x == neighbor.x and open[i].y == neighbor.y then
                    isInOpen = true
                    break
                end
            end
            if not isInOpen then
                neighbor.parent = current
                neighbor.g = g
                neighbor.h = manhattanDistance(neighbor, target)
                neighbor.f = g + neighbor.h
                table.insert(open, neighbor)
            else
                -- 如果邻居节点已经在 open 列表中，则更新 f 值和父节点
                if g < neighbor.g then
                    neighbor.parent = current
                    neighbor.g = g
                    neighbor.f = g + neighbor.h
                end
            end

            ::continue::
        end
    end

    -- 没有找到路径，返回空表
    return {}
end

在使用该算法时，需要先定义地图和起点、目标点的位置。地图可以用一个二维数组来表示，每个元素表示一个节点，包含节点的 x、y 坐标和是否可通行等信息。下面是一个简单的示例：

local map = {
    { {x=1, y=1, walkable=true}, {x=1, y=2, walkable=true}, {x=1, y=3, walkable=true} },
    { {x=2, y=1, walkable=true}, {x=2, y=2, walkable=false}, {x=2, y=3, walkable=true} },
    { {x=3, y=1, walkable=true}, {x=3, y=2, walkable=true}, {x=3, y=3, walkable=true} },
}

local start = map[1][1]
local target = map[3][3]

local path = aStar(start, target, map)

该示例中，起点为地图左上角节点，目标点为地图右下角节点。节点的 `walkable` 属性表示是否可通行，其中 `false` 表示不可通行。算法返回的结果是一个包含路径节点的数组，按顺序表示从起点到目标点的路径。