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paths edits for technical review

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mDuo13
2015-10-15 17:15:03 -07:00
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@@ -11,28 +11,17 @@ A path is made of steps that connect the sender to the receiver of the payment.
* Rippling through another account in the same currency
* Exchanging currency at an order book
In the case of a currency exchange step, the path step specifies which currency to change to, but does not record the state of the orders in the order book. Since the order of transactions is not finalized until a ledger is validated, it is impossible to determine for certain which offers a transaction will execute, until after the transaction has been validated. Consequently, you cannot know in advance which offers a transaction will take: only which order books the transaction will use.
In the case of a currency exchange step, the path step specifies which currency to change to, but does not record the state of the orders in the order book. Since the order of transactions is not finalized until a ledger is validated, it is impossible to determine for certain which offers a transaction will execute, until after the transaction has been validated. Consequently, you cannot know in advance which offers a transaction will take: only which order books the transaction will use. (You can make an educated guess, since each transaction takes the best available offers at the time it executes in the final ledger.)
Each intermediate account gains and loses equal value: either a balance ripples from a trust line to another trust line in the same currency, or they exchange currencies according to a previously-placed order.
Each intermediate account gains and loses approximately equal value: either a balance ripples from a trust line to another trust line in the same currency, or they exchange currencies according to a previously-placed order. In some cases, the amounts gained and lost may not be exact, due either to [transfer fees](https://ripple.com/knowledge_center/transfer-fees/) or rounding.
[![Diagram of three example paths](img/paths.png)](img/paths.png)
### Auto-Bridging ###
In addition to any order books that are explicitly included in a path, any currency exchange between two non-XRP currencies could potentially use XRP as an intermediary currency in a synthetic order book. This is because of auto-bridging, which serves to improve liquidity across all currency pairs by using XRP as a vehicle currency.
## Default Paths ##
In addition to any paths that are specified in the transaction, a transaction can also execute along the _default path_. The default path of a transaction depends on the nature of the payment, but basically, the default path is the simplest possible way to connect the sender and receiver using the information provided.
The default path could be any of the following:
* The trust line that connects the source account and destination account
* The trust lines to the `issuer` of the source amount and/or destination amount
* The order book that connects the source amount to the destination amount
You can use the [`tfNoDirectRipple` flag](transactions.html#payment-flags) to disable the default path. In this case, the transaction can only execute using the paths explicitly included in the transaction. Traders can use this option to take arbitrage opportunities.
# Technical Details #
@@ -49,9 +38,28 @@ By convention, the sender and the receiver are implied, rather than included exp
* The first step of a path is always implied to be the sender of the transaction, as defined by the transaction's `Account` field.
* If the transaction includes a `SendMax` field with an `issuer` that is not the sender of the transaction, that issuer is implied to be the second step of the path.
* If `issuer` of the `SendMax` _is_ the sending account, then the path starts at the sending account, and may use any of that account's trust lines in the given currency. See [special values for SendMax and Amount](transactions.html#special-issuer-values-for-sendmax-and-amount) for details.
* If the `Amount` field of the transaction includes an `issuer` that is not the same as the `Destination` of the transaction, that issuer is implied to be the second-to-last step of the path.
* Finally, last step of a path is always implied to be the receiver of a transaction, as defined by the transaction's `Destination` field.
See [Payment Transaction Type](transactions.html#payment) for more information on the fields of a Payment.
## Default Paths ##
In addition to any paths that are specified in the transaction, a transaction can also execute along the _default path_. The default path is the simplest possible way to connect the [implied steps](#implied-steps) of the transaction.
The default path could be any of the following:
* If the transaction is uses one currency (regardless of issuer), then the default path connects the accounts of the implied steps directly. This path will only work if there is a trust line connecting those accounts.
* If `SendMax` is omitted, or the `issuer` of the `SendMax` is the sender, the default path needs a trust line from the sending `Account` to the `issuer` of the destination `Amount` in order to work.
* If the `SendMax` and `Amount` have different `issuer` values, and neither are the sender or receiver, the default path is probably not useful because it would need to ripple through a trust line between the two issuers. Ripple, Inc. typically discourages issuers from trusting one another directly.
* For cross-currency transactions, the default path automatically appends the order book between the source currency (as specified in the `SendMax` field) and the destination currency (as specified in the `Amount` field).
[![Diagram of default paths](img/default-paths.png)](img/default-paths.png)
You can use the [`tfNoDirectRipple` flag](transactions.html#payment-flags) to disable the default path. In this case, the transaction can only execute using the paths explicitly included in the transaction. Traders can use this option to take arbitrage opportunities.
## Path Specifications ##
@@ -59,11 +67,11 @@ A path set is an array. Each member of the path set is another array that repres
| Field | Value | Description |
|-------|-------|-------------|
| type | Integer | The number `48` indicates a change of currency through an order book. The number `1` indicates rippling through another account. |
| type_hex | String | A hexadecimal representation of the `type` field. |
| account | String - Address | (Optional) The address of the account to ripple through. |
| currency | String - currency code | (Optional) The currency code of the currency to convert to |
| issuer | String - Address | (Optional) The issuer of the currency to convert to |
| type | Integer | **DEPRECATED**: An indicator of which other fields are present. The value `1` indicates rippling to another account. The values `16` indicates a currency change to XRP through an order book. The value `48` indicates a currency change, with a new issuer, through an order book. |
| type_hex | String | **DEPRECATED**: A hexadecimal representation of the `type` field. |
The `type` field, used for the binary serialization of a path set, is actually constructed through bitwise operations on a single integer. The bits are defined as follows: