beeta/openresty/lua/thumbnail.lua

local _M = {}

local THUMB_DIR = "/tmp/thumbs"
local CACHE_TTL = 5  -- seconds before regenerating
local FFMPEG_TIMEOUT = 15  -- seconds (needs more time for animated capture)
local ANIMATION_DURATION = 3  -- seconds of video to capture
local ANIMATION_FPS = 8  -- frames per second in output

-- SECURITY FIX: Shell escape function to prevent command injection
local function shell_escape(str)
    -- Escape single quotes by ending the quoted string, adding escaped quote, and starting new quoted string
    return "'" .. string.gsub(str, "'", "'\\''") .. "'"
end

local function file_exists(path)
    local f = io.open(path, "r")
    if f then
        f:close()
        return true
    end
    return false
end

local function file_size(path)
    local f = io.open(path, "rb")
    if f then
        local size = f:seek("end")
        f:close()
        return size or 0
    end
    return 0
end

local function file_age(path)
    -- Get file modification time using stat
    local handle = io.popen("stat -c %Y " .. path .. " 2>/dev/null")
    if not handle then
        return nil
    end
    local mtime = handle:read("*a")
    handle:close()

    if not mtime or mtime == "" then
        return nil
    end

    local now = os.time()
    return now - tonumber(mtime)
end

local function generate_thumbnail(stream_key, thumb_path)
    -- Build LLHLS URL - internal docker network
    local llhls_url = "http://ovenmediaengine:8080/app/" .. stream_key .. "/llhls.m3u8"
    local log_file = THUMB_DIR .. "/" .. stream_key .. ".log"

    -- First, try to generate animated WebP
    -- Using os.execute which blocks properly until complete
    -- SECURITY FIX: Use shell_escape to prevent command injection
    local cmd = string.format(
        "timeout %d ffmpeg -y -i %s -t %d -vf 'fps=%d,scale=320:-1:flags=lanczos' -c:v libwebp -lossless 0 -compression_level 3 -q:v 70 -loop 0 -preset default -an %s > %s 2>&1",
        FFMPEG_TIMEOUT,
        shell_escape(llhls_url),
        ANIMATION_DURATION,
        ANIMATION_FPS,
        shell_escape(thumb_path),
        shell_escape(log_file)
    )

    ngx.log(ngx.INFO, "Generating thumbnail for stream: ", stream_key)

    local exit_code = os.execute(cmd)

    -- Check if file was created and has content
    if file_exists(thumb_path) and file_size(thumb_path) > 100 then
        ngx.log(ngx.INFO, "Thumbnail generated successfully: ", thumb_path)
        os.remove(log_file)
        return true
    end

    -- If animated webp failed, try static webp (single frame)
    ngx.log(ngx.WARN, "Animated webp failed (exit: ", tostring(exit_code), "), trying static")

    -- SECURITY FIX: Use shell_escape to prevent command injection
    local static_cmd = string.format(
        "timeout %d ffmpeg -y -i %s -vframes 1 -vf 'scale=320:-1:flags=lanczos' -c:v libwebp -q:v 75 %s > %s 2>&1",
        FFMPEG_TIMEOUT,
        shell_escape(llhls_url),
        shell_escape(thumb_path),
        shell_escape(log_file)
    )

    exit_code = os.execute(static_cmd)

    if file_exists(thumb_path) and file_size(thumb_path) > 100 then
        ngx.log(ngx.INFO, "Static thumbnail generated: ", thumb_path)
        os.remove(log_file)
        return true
    end

    -- Read log file for error info
    local log_content = ""
    local log_f = io.open(log_file, "r")
    if log_f then
        log_content = log_f:read("*a") or ""
        log_f:close()
    end

    ngx.log(ngx.ERR, "Thumbnail generation failed (exit: ", tostring(exit_code), "): ", log_content:sub(-500))
    return false
end

function _M.serve()
    -- Get stream key from nginx variable
    local stream_key = ngx.var.stream_key
    if not stream_key or stream_key == "" then
        ngx.status = 400
        ngx.header["Content-Type"] = "text/plain"
        ngx.say("Missing stream key")
        return ngx.exit(400)
    end

    -- Sanitize stream key (alphanumeric, dash, underscore only)
    if not stream_key:match("^[%w%-_]+$") then
        ngx.status = 400
        ngx.header["Content-Type"] = "text/plain"
        ngx.say("Invalid stream key")
        return ngx.exit(400)
    end

    local thumb_path = THUMB_DIR .. "/" .. stream_key .. ".webp"

    -- Check if cached thumbnail exists and is fresh
    local age = file_age(thumb_path)
    local needs_refresh = not age or age > CACHE_TTL

    if needs_refresh then
        -- Generate new thumbnail
        local ok = generate_thumbnail(stream_key, thumb_path)
        if not ok then
            -- If generation failed, check if we have a stale one to serve
            if not file_exists(thumb_path) or file_size(thumb_path) < 100 then
                ngx.status = 503
                ngx.header["Content-Type"] = "text/plain"
                ngx.header["Retry-After"] = "5"
                ngx.say("Thumbnail generation in progress")
                return ngx.exit(503)
            end
            -- Serve stale thumbnail
        end
    end

    -- Verify file exists and has content
    if not file_exists(thumb_path) or file_size(thumb_path) < 100 then
        ngx.status = 503
        ngx.header["Content-Type"] = "text/plain"
        ngx.header["Retry-After"] = "5"
        ngx.say("Thumbnail not ready")
        return ngx.exit(503)
    end

    -- Serve the thumbnail file
    ngx.header["Content-Type"] = "image/webp"
    ngx.header["Cache-Control"] = "public, max-age=" .. CACHE_TTL
    ngx.header["Access-Control-Allow-Origin"] = "*"

    local f = io.open(thumb_path, "rb")
    if not f then
        ngx.status = 500
        ngx.header["Content-Type"] = "text/plain"
        ngx.say("Failed to read thumbnail")
        return ngx.exit(500)
    end

    local content = f:read("*a")
    f:close()

    ngx.print(content)
end

return _M