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package relay
import (
"crypto/rand"
"encoding/hex"
"fmt"
"io"
"nymdrop/internal/nym"
)
// Two base64 layers stack between the raw file and the wire: the client
// base64-encodes the file into the plaintext before encrypting (see
// static/crypto.js, ~4/3 inflation), then nym.Client.Send base64-encodes
// the whole ciphertext again to embed it in the JSON message sent to the
// local nym-client over its control WebSocket (~4/3 again). The combined
// ~1.78x inflation is bounded above by nym-client's own hardcoded 16MB
// WebSocket message limit, not by anything in this codebase, so this
// buffer (and the nginx/http-layer cap) must stay well under 16MB / 1.78
// once the second layer is applied. 11MB here keeps the second-layer
// base64 (~14.7MB) with real margin below the 16MB nym-client ceiling,
// which works out to a safe raw file size of roughly 8MB, not 10MB.
const maxPayloadBytes = 11 * 1024 * 1024 // 11 MB wire (first base64 layer only)
// Relay receives ciphertext and forwards it through Nym. Nothing is written to disk.
type Relay struct {
nym *nym.Client
}
func New(client *nym.Client) *Relay {
return &Relay{nym: client}
}
// Forward reads ciphertext from r, sends it over Nym, then zeros the buffer.
func (r *Relay) Forward(body io.Reader) error {
buf := make([]byte, maxPayloadBytes)
n, err := io.ReadFull(body, buf)
if err != nil && err != io.ErrUnexpectedEOF {
return fmt.Errorf("read payload: %w", err)
}
payload := buf[:n]
defer zeroBytes(payload)
// Prepend a random nonce so identical submissions look different on the wire.
nonce := make([]byte, 16)
if _, err := rand.Read(nonce); err != nil {
return fmt.Errorf("nonce: %w", err)
}
packet := append([]byte(hex.EncodeToString(nonce)+":"), payload...)
defer zeroBytes(packet)
return r.nym.Send(packet)
}
func zeroBytes(b []byte) {
for i := range b {
b[i] = 0
}
}
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