92 lines
2.4 KiB
Go
92 lines
2.4 KiB
Go
package varinterval
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import (
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"context"
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"errors"
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"sync"
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"time"
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"github.com/chihaya/chihaya/bittorrent"
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"github.com/chihaya/chihaya/middleware"
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"github.com/chihaya/chihaya/middleware/pkg/random"
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)
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// ErrInvalidModifyResponseProbability is returned for a config with an invalid
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// ModifyResponseProbability.
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var ErrInvalidModifyResponseProbability = errors.New("invalid modify_response_probability")
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// ErrInvalidMaxIncreaseDelta is returned for a config with an invalid
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// MaxIncreaseDelta.
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var ErrInvalidMaxIncreaseDelta = errors.New("invalid max_increase_delta")
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// Config represents the configuration for the varinterval middleware.
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type Config struct {
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// ModifyResponseProbability is the probability by which a response will
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// be modified.
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ModifyResponseProbability float32 `yaml:"modify_response_probability"`
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// MaxIncreaseDelta is the amount of seconds that will be added at most.
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MaxIncreaseDelta int `yaml:"max_increase_delta"`
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// ModifyMinInterval specifies whether min_interval should be increased
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// as well.
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ModifyMinInterval bool `yaml:"modify_min_interval"`
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}
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func checkConfig(cfg Config) error {
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if cfg.ModifyResponseProbability <= 0 || cfg.ModifyResponseProbability > 1 {
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return ErrInvalidModifyResponseProbability
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}
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if cfg.MaxIncreaseDelta <= 0 {
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return ErrInvalidMaxIncreaseDelta
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}
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return nil
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}
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type hook struct {
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cfg Config
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sync.Mutex
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}
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// New creates a middleware to randomly modify the announce interval from the
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// given config.
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func New(cfg Config) (middleware.Hook, error) {
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err := checkConfig(cfg)
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if err != nil {
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return nil, err
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}
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h := &hook{
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cfg: cfg,
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}
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return h, nil
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}
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func (h *hook) HandleAnnounce(ctx context.Context, req *bittorrent.AnnounceRequest, resp *bittorrent.AnnounceResponse) (context.Context, error) {
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s0, s1 := random.DeriveEntropyFromRequest(req)
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// Generate a probability p < 1.0.
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v, s0, s1 := random.Intn(s0, s1, 1<<24)
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p := float32(v) / (1 << 24)
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if h.cfg.ModifyResponseProbability == 1 || p < h.cfg.ModifyResponseProbability {
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// Generate the increase delta.
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v, _, _ = random.Intn(s0, s1, h.cfg.MaxIncreaseDelta)
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addSeconds := time.Duration(v+1) * time.Second
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resp.Interval += addSeconds
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if h.cfg.ModifyMinInterval {
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resp.MinInterval += addSeconds
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}
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return ctx, nil
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}
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return ctx, nil
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}
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func (h *hook) HandleScrape(ctx context.Context, req *bittorrent.ScrapeRequest, resp *bittorrent.ScrapeResponse) (context.Context, error) {
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// Scrapes are not altered.
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return ctx, nil
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}
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