# NIP-17 Gift Wrap Send Failure — Investigation

## Status: Resolved — Fixed in code (2026-04-11)

## Date Discovered: 2026-04-11

## Symptom

Every outbound NIP-17 DM send from the Anvil agent fails with:
```
NIP-17 send aborted: gift_wrap creation failed for 1ec454734dcbf6fe...
auto DM fallback to NIP-04 for 1ec454734dcbf6fe... after NIP-17 send failure
```

The agent successfully falls back to NIP-04 (kind 4), so DMs are still delivered. However, NIP-17 outbound is completely broken.

**Inbound NIP-17 works fine** — the agent successfully receives and decrypts kind 1059 gift wraps from the admin.

## Affected Code Path

### Send path (broken):
1. `nostr_handler_send_dm_auto_with_role()` in `src/nostr_handler.c:3193` — routes to NIP-17 when `dm_protocol` is `nip17` or `both`
2. `nostr_handler_send_dm_nip17_with_role()` in `src/nostr_handler.c:4050` — creates chat event, calls `nostr_nip17_send_dm()`
3. `nostr_nip17_send_dm()` in `nostr_core_lib/nostr_core/nip017.c:260` — iterates recipients, creates seal + gift wrap
4. `nostr_nip59_create_seal()` in `nostr_core_lib/nostr_core/nip059.c:150` — **encrypts rumor JSON with NIP-44**
5. `nostr_nip59_create_gift_wrap()` in `nostr_core_lib/nostr_core/nip059.c:226` — wraps seal with random key

### Receive path (working):
1. `on_event()` receives kind 1059
2. `nostr_nip17_receive_dm()` in `nostr_core_lib/nostr_core/nip017.c:326` — unwraps gift, unseals rumor
3. Successfully extracts kind 14 content

## Probable Root Cause: Fixed Buffer Overflow in Seal Encryption

In `nostr_core_lib/nostr_core/nip059.c:163-165`:

```c
char encrypted_content[4096]; // Should be large enough for most events
int encrypt_result = nostr_nip44_encrypt(sender_private_key, recipient_public_key,
                                        rumor_json, encrypted_content, sizeof(encrypted_content));
```

The seal creation uses a **fixed 4096-byte stack buffer** for the NIP-44 encrypted output. The rumor JSON includes the full DM message content. When the agent sends long responses (the FIPS mesh conversation had multi-KB markdown tables), the rumor JSON easily exceeds 4096 bytes after NIP-44 encryption overhead (base64 encoding roughly 4/3x expansion + padding + nonce).

**Evidence:**
- The agent's DM responses in the log were 2-5KB of markdown content
- After JSON serialization of the kind 14 rumor (adding pubkey, tags, created_at, kind fields), the total is larger
- NIP-44 encryption adds: 32-byte nonce + padding + base64 encoding → roughly 1.5-2x expansion
- A 3KB message → ~4.5KB rumor JSON → ~6-9KB encrypted → overflows 4096 buffer
- `nostr_nip44_encrypt()` returns error, `nostr_nip59_create_seal()` returns NULL
- `nostr_nip17_send_dm()` skips the recipient, returns 0 wraps
- `nostr_handler_send_dm_nip17_with_role()` logs "gift_wrap creation failed"

**Why receive works:** The receive path uses `nostr_nip44_decrypt()` which likely allocates dynamically or has a larger buffer.

## Secondary Suspect: NIP-44 Encryption Implementation

The NIP-44 encrypt function itself may have issues with large payloads. Need to check:
- `nostr_nip44_encrypt()` in `nostr_core_lib/nostr_core/nip044.c`
- Whether it handles the output buffer size parameter correctly
- Whether it returns an error code that distinguishes "buffer too small" from other failures

## Anvil Config Context

The Anvil agent's genesis config (`/home/user/anvil/genesis.jsonc`) has:
```json
"dm_protocol": "nip04"
```

But the encrypted user-settings on Nostr (kind 30078) may have overridden this to `"both"` at runtime, which is why NIP-17 send is being attempted.

## Recommended Fix

### Option A: Dynamic allocation (preferred)
Replace the fixed 4096-byte buffer in `nostr_nip59_create_seal()` with dynamic allocation:
```c
size_t rumor_len = strlen(rumor_json);
size_t encrypted_buf_size = rumor_len * 2 + 256; // generous overhead for NIP-44
char* encrypted_content = malloc(encrypted_buf_size);
```

### Option B: Larger fixed buffer (quick fix)
Increase the buffer to 64KB or 128KB:
```c
char encrypted_content[131072]; // 128KB should handle any reasonable DM
```
Note: This is a stack allocation, so very large buffers could cause stack overflow.

### Also check `nostr_nip59_create_gift_wrap()`
The gift wrap function at `nip059.c:226` may have a similar fixed-buffer issue for encrypting the seal JSON.

## Log Evidence

From `/home/user/anvil/debug.log` (2026-04-11):

```
[2026-04-11 09:45:14] [WARN ] NIP-17 send aborted: gift_wrap creation failed for 1ec454734dcbf6fe...
[2026-04-11 09:45:14] [WARN ] auto DM fallback to NIP-04 for 1ec454734dcbf6fe... after NIP-17 send failure
[2026-04-11 09:50:16] [WARN ] NIP-17 send aborted: gift_wrap creation failed for 1ec454734dcbf6fe...
[2026-04-11 09:50:16] [WARN ] auto DM fallback to NIP-04 for 1ec454734dcbf6fe... after NIP-17 send failure
[2026-04-11 09:53:42] [WARN ] NIP-17 send aborted: gift_wrap creation failed for 1ec454734dcbf6fe...
[2026-04-11 09:53:42] [WARN ] auto DM fallback to NIP-04 for 1ec454734dcbf6fe... after NIP-17 send failure
```

This pattern is 100% consistent — every outbound NIP-17 attempt fails, every time.

## Related Files

- `nostr_core_lib/nostr_core/nip059.c` — Gift wrap / seal creation (probable bug location)
- `nostr_core_lib/nostr_core/nip044.c` — NIP-44 encryption (check buffer handling)
- `nostr_core_lib/nostr_core/nip017.c` — NIP-17 DM send/receive orchestration
- `src/nostr_handler.c:4050` — Agent-level NIP-17 send function
- `plans/nip17_messaging.md` — Original NIP-17 implementation plan

## Related Existing Plan

The `plans/nip17_messaging.md` document covers the original NIP-17 implementation. This investigation is specifically about the send-side gift wrap failure that emerged in production.

## Resolution Summary

Implemented in `nostr_core_lib/nostr_core/nip059.c`:

- Replaced fixed encryption buffers in `nostr_nip59_create_seal()` and `nostr_nip59_create_gift_wrap()` with dynamically sized heap buffers calculated from NIP-44 padding/base64 overhead.
- Replaced fixed decrypt buffers in `nostr_nip59_unwrap_gift()` and `nostr_nip59_unseal_rumor()` with dynamic buffers sized from ciphertext length.
- Added missing cleanup path in `nostr_nip59_create_seal()` for failure after encryption allocation.

Expected outcome: outbound NIP-17 gift wrap creation no longer fails for multi-KB DM payloads due to fixed buffer limits.
