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package webhook
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import (
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"bytes"
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"context"
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"crypto/hmac"
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"crypto/sha256"
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"encoding/hex"
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"encoding/json"
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"fmt"
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"net"
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"net/http"
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"syscall"
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"time"
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// Attempts is how many times a delivery is tried. Chapter 23.4.
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const Attempts = 3
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// Client refuses a denied address, whatever a name resolved to or a redirect asks for.
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func Client() *http.Client {
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// Checked in the dialer, after resolving and before connecting, closing the window between.
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dialer := &net.Dialer{
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Timeout: 10 * time.Second,
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Control: func(network, address string, c syscall.RawConn) error {
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return AllowedAddr(address)
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},
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return &http.Client{
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Timeout: 30 * time.Second,
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CheckRedirect: func(req *http.Request, via []*http.Request) error {
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// Re-check every redirect, because a pass that then hops to 169.254.169.254 is the attack.
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if len(via) >= 5 {
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return fmt.Errorf("too many redirects")
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return Allowed(req.Context(), req.URL.String())
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},
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Transport: &http.Transport{
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DialContext: func(ctx context.Context, network, addr string) (net.Conn, error) {
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if err := AllowedAddr(addr); err != nil {
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return nil, err
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return dialer.DialContext(ctx, network, addr)
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},
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},
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// Sign is HMAC-SHA256, with the config naming a secret whose value lives on the server.
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func Sign(secret string, body []byte) string {
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mac := hmac.New(sha256.New, []byte(secret))
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mac.Write(body)
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return "sha256=" + hex.EncodeToString(mac.Sum(nil))
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// Deliver posts one event, retrying with backoff up to attempts times.
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func Deliver(ctx context.Context, url, secret string, payload any, attempts int) error {
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body, err := json.Marshal(payload)
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if err != nil {
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return err
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if err := Allowed(ctx, url); err != nil {
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return err
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client := Client()
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var last error
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for attempt := range max(attempts, 1) {
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if attempt > 0 {
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select {
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case <-ctx.Done():
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return ctx.Err()
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case <-time.After(time.Duration(1<<attempt) * time.Second):
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req, err := http.NewRequestWithContext(ctx, http.MethodPost, url, bytes.NewReader(body))
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if err != nil {
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return err
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req.Header.Set("Content-Type", "application/json")
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req.Header.Set("User-Agent", "barerepo")
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if secret != "" {
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req.Header.Set("Barerepo-Signature", Sign(secret, body))
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resp, err := client.Do(req)
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if err != nil {
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last = err
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continue
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resp.Body.Close()
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if resp.StatusCode < 300 {
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return nil
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last = fmt.Errorf("%s", resp.Status)
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return last