# Tangle-Accelerator Development
###### tags: `tangle-accelerator`

<img src="https://i.imgur.com/9bjZKpJ.jpg" >

## HTTP Server
* build with C++ boost/beast library
* ==TODO==: 測試多個 request 同時進來

## JSON parser
解析 request，並以 JSON 格式 response，使用 cJSON 實做

下列 function 需要 serialization:
* generate_address
* get_tips
* send_transfer

## Function Overview
core function 皆會使用到 `entangled/cclient`，參考到 [IOTA cclient 使用指南](/643NQmXjT9uhq5Do14v8PQ)

### Core
* [x] ta_generate_address - **may need updated**(下方 issue)
* [x] ta_get_tips - **may need updated**
* [x] cclient_get_txn_to_approve - **may need updated**
* [x] cclient_get_tips - **may need updated**
* [ ] ta_send_transfer - **on-going**
* [ ] ta_find_transaction_by_tag - **on-going**
* [ ] ta_get_txn_msg

### Should be deprecated
* insert_to_trytes: cclient 已有其他方式
* ta_attach_debug_message_to_tangle: 交給 test case 處理

### TangleID
* TODO

### send_transfer
#### dcurl
為了使用 dcurl 進行 PoW 加速，我們需要
實做 attachToTangle 流程

### `send_transfer` Flow
* [x] Generate new address
* [x] Make transaction
* [x] Set address
* [x] Set tag
* [x] Set message
* [x] Set value
* [ ] Make bundle
* [x] Add transaction
* [ ] Finalize
* [x] calculate bundle hash
* [ ] Fill bundle hash through txs
* pyota will fill in bundle hash in `finalize`
* [x] getTransactionToApprove
* [x] get transaction trytes
* `transaction_sesrialize_to_flex_trits`
* [x] Fill in trunk, branch in each transaction
* [x] Fill in timestamp in each transaction
* [ ] PoW
* [ ] fill in nonce

## IOTA transaction tryte offset

| offset|start|len|
|:--|:--|:--|
|SIGNATURE_MESSAGE_FRAGMENT_OFFSET|0|6561|
|ADDRESS_TRINARY_OFFSET|6561|243|
|VALUE_TRINARY_OFFSET|6804|81|
|OBSOLETE_TAG_TRINARY_OFFSET|6885|81|
|TIMESTAMP_TRINARY_OFFSET|6966|27|
|CURRENT_INDEX_TRINARY_OFFSET|6993|27|
|LAST_INDEX_TRINARY_OFFSET|7020|27|
|BUNDLE_TRINARY_OFFSET|7047|243|
|TRUNK_TRANSACTION_TRINARY_OFFSET|7290 (2430 tryte)|243|
|BRANCH_TRANSACTION_TRINARY_OFFSET|7533 (2511 tryte)|243|
|TAG_TRINARY_OFFSET|7776|81|
|ATTACHMENT_TIMESTAMP_<br>TRINARY_OFFSET|7857 (2619 tryte)|27|
|ATTACHMENT_TIMESTAMP_<br>LOWER_BOUND_TRINARY_OFFSET|7884|27|
|ATTACHMENT_TIMESTAMP_<br>UPPER_BOUND_TRINARY_OFFSET|7911 (2637 tryte)|27|
|NONCE_TRINARY_OFFSET|7938 (2646 tryte)|81|

## Transaction raw trytes
transaction_sesrialize_to_flex_trits

  def as_tryte_string(self):
    # type: () -> TransactionTrytes
    """ 
    Returns a TryteString representation of the transaction.
    """
    return TransactionTrytes(
       self.signature_message_fragment
     + self.address.address
     + self.value_as_trytes
     + self.legacy_tag
     + self.timestamp_as_trytes
     + self.current_index_as_trytes
     + self.last_index_as_trytes
     + self.bundle_hash
     + self.trunk_transaction_hash                                                                                                                           
     + self.branch_transaction_hash
     + self.tag
     + self.attachment_timestamp_as_trytes
     + self.attachment_timestamp_lower_bound_as_trytes
     + self.attachment_timestamp_upper_bound_as_trytes
     + self.nonce
    )   

## common/model: Transfer
**Transfer**

typedef struct _transfer {
  transfer_type_e type;
  const flex_trit_t *address;
  const flex_trit_t *tag;
  int64_t value;
  uint64_t timestamp;
  void *meta;  // extend informations depended on transfer type.
} transfer_t;

3 types of transfer, each one has its own meta data structure:

**DATA**

typedef struct _transfer_data {
  const flex_trit_t *data;
  size_t len;
} transfer_data_t;

**VALUE_OUT**

typedef struct _transfer_value_out {
  const flex_trit_t *seed;
  uint8_t security;
  uint64_t seed_index;
} transfer_value_out_t;

**VALUE_IN**

typedef struct _transfer_value_in {
  // can have up to 2187 trytes as data
  size_t len;
  const flex_trit_t *data;
} transfer_value_in_t;

**Transfer Iterator**
transfer_iterator_new
* In this function, bundle_hash is calculated

transfer_iterator_next
* generate transaction from transfer array

**unkown nouns**
* `remainder` in prepare_transfers

## Send_transfer
1. prepare_transfer
2. get bundle trits
3. send_trytes

## Prepare_transfer
1. transfer_iterator_new
* cacluate bundle hash
2. transfer_interator_next
* generate a transaction_t object
* fill in `bundle`, `address`, `tag`, `obsolete_tag`, `timestamp`, `current_index`, `last_index`
* fill in metadata
* DATA: `message`
* VALUE_OUT: `value`, `signature`
* if index == 0, gen signature
* VALUE_IN: `value`, `signature`
4. bundle_add_transaction
5. bundle_finalize
* Since bundle hash is calculated in `transfer_iterator_new`, why do we still need `bundle_finalize`?
* [source code link](https://github.com/iotaledger/entangled/pull/629/files#diff-1b378ec08c554eb687dd17c1a1671f68R517)

## Send_trytes
1. get_transactions_to_approve
2. attach_to_tangle
3. sotre_and_broadcast

**cache server 不能獨立於 tangle-accelerator 的原因**
* 安全考量，使用者也需要信任 Caching server，但 TA 是安全的 (Root Of Trust)
* 如果 tx invalid, caching server 也不知道，TA 還能直接向 full node 查證