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Merge pull request #766 from bigchaindb/expand-tx-validation-explanation

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Expanded/updated the docs explaining transaction validation
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Troy McConaghy 2016-11-01 18:20:39 +01:00 committed by GitHub
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docs/root/source/transaction-concepts.md
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@ -12,11 +12,18 @@ A creation transaction also establishes the conditions that must be met to trans
A _transfer transaction_ can transfer an asset by fulfilling the current conditions on the asset. It can also specify new transfer conditions.
Today, every transaction contains one fulfillment-condition pair. The fulfillment in a transfer transaction must correspond to a condition in a previous transaction.
Today, every transaction contains one fulfillment-condition pair. The fulfillment in a transfer transaction must fulfill a condition in a previous transaction.
When a node is asked to check the validity of a transaction, it must do several things, including:
When a node is asked to check if a transaction is valid, it checks several things. Some things it checks are:
* double-spending checks (for transfer transactions),
* hash validation (i.e. is the calculated transaction hash equal to its id?), and
* validation of all fulfillments, including validation of cryptographic signatures if they’re among the conditions.
* Are all the fulfillments valid? (Do they correctly satisfy the conditions they claim to satisfy?)
* If it's a creation transaction, is the asset valid?
* If it's a transfer transaction:
* Is it trying to fulfill a condition in a nonexistent transaction?
* Is it trying to fulfill a condition that's not in a valid transaction? (It's okay if the condition is in a transaction in an invalid block; those transactions are ignored. Transactions in the backlog or undecided blocks are not ignored.)
* Is it trying to fulfill a condition that has already been fulfilled, or that some other pending transaction (in the backlog or an undecided block) also aims to fulfill?
* Is the asset ID in the transaction the same as the asset ID in all transactions whose conditions are being fulfilled?
If you're curious about the details of transaction validation, the code is in the `validate` method of the `Transaction` class, in `bigchaindb/models.py` (at the time of writing).
Note: The check to see if the transaction ID is equal to the hash of the transaction body is actually done whenever the transaction is converted from a Python dict to a Transaction object, which must be done before the `validate` method can be called (since it's called on a Transaction object).