Add Transaction Documentation (#5115)

book/src/SUMMARY.md

@@ -30,8 +30,12 @@
     - [Blocktree](blocktree.md)
   - [Gossip Service](gossip.md)
   - [The Runtime](runtime.md)
+  
+- [Anatomy of a Transaction](transaction.md)
 
 - [API Reference](api-reference.md)
+  - [Transaction](transaction-api.md)
+  - [Instruction](instruction-api.md)
   - [Blockstreamer](blockstreamer.md)
   - [JSON RPC API](jsonrpc-api.md)
   - [JavaScript API](javascript-api.md)

book/src/instruction-api.md

@@ -0,0 +1,25 @@
+# Instructions
+
+For the purposes of building a [Transaction](transaction.md), a more
+verbose instruction format is used:
+
+* **Instruction:**
+  * **program_id:** The pubkey of the on-chain program that executes the
+    instruction
+  * **accounts:** An ordered list of accounts that should be passed to
+    the program processing the instruction, including metadata detailing
+    if an account is a signer of the transaction and if it is a credit
+    only account.
+  * **data:** A byte array that is passed to the program executing the
+    instruction
+  
+A more compact form is actually included in a `Transaction`:
+
+* **CompiledInstruction:**
+  * **program_id_index:** The index of the `program_id` in the
+    `account_keys` list
+  * **accounts:** An ordered list of indices into `account_keys`
+    specifying the accounds that should be passed to the program
+    processing the instruction.
+  * **data:** A byte array that is passed to the program executing the
+    instruction

book/src/transaction-api.md

@@ -0,0 +1,48 @@
+# The Transaction
+
+### Components of a `Transaction`
+
+* **Transaction:**
+  * **message:** Defines the transaction
+    * **header:** Details the account types of and signatures required by
+      the transaction
+      *  **num_required_signatures:** The total number of signatures
+         required to make the transaction valid.
+      *  **num_credit_only_signed_accounts:** The last
+         `num_credit_only_signed_accounts` signatures refer to signing
+         credit only accounts. Credit only accounts can be used concurrently
+         by multiple parallel transactions, but their balance may only be
+         increased, and their account data is read-only.
+      *  **num_credit_only_unsigned_accounts:** The last
+         `num_credit_only_unsigned_accounts` pubkeys in `account_keys` refer
+         to non-signing credit only accounts
+    * **account_keys:** List of pubkeys used by the transaction, including
+      by the instructions and for signatures. The first
+      `num_required_signatures` pubkeys must sign the transaction.
+    * **recent_blockhash:** The ID of a recent ledger entry. Validators will
+      reject transactions with a `recent_blockhash` that is too old.
+    * **instructions:** A list of [instructions](instruction.md) that are
+      run sequentially and committed in one atomic transaction if all
+      succeed.
+  * **signatures:** A list of signatures applied to the transaction. The
+    list is always of length `num_required_signatures`, and the signature
+    at index `i` corresponds to the pubkey at index `i` in `account_keys`.
+    The list is initialized with empty signatures (i.e. zeros), and
+    populated as signatures are added.
+  
+### Transaction Signing
+
+A `Transaction` is signed by using an ed25519 keypair to sign the
+serialization of the `message`. The resulting signature is placed at the
+index of `signatures` matching the index of the keypair's pubkey in
+`account_keys`.
+
+### Transaction Serialization
+
+`Transaction`s (and their `message`s) are serialized and deserialized
+using the [bincode](https://crates.io/crates/bincode) crate with a
+non-standard vector serialization that uses only one byte for the length
+if it can be encoded in 7 bits, 2 bytes if it fits in 14 bits, or 3
+bytes if it requires 15 or 16 bits. The vector serialization is defined
+by Solana's
+[short-vec](https://github.com/solana-labs/solana/blob/master/sdk/src/short_vec.rs).

book/src/transaction.md

@@ -0,0 +1,43 @@
+# Anatomy of a Transaction
+
+Transactions encode lists of instructions that are executed
+sequentially, and only committed if all the instructions complete
+successfully. All account states are reverted upon the failure of a
+transaction. Each Transaction details the accounts used, including which
+must sign and which are credit only, a recent blockhash, the
+instructions, and any signatures.
+
+## Accounts and Signatures
+
+Each transaction explicitly lists all accounts that it needs access to.
+This includes accounts that are transferring tokens, accounts whose user
+data is being modified, and the program accounts that are being called
+by the instructions. Each account that is not an executable program can
+be marked as a requiring a signature and/or as credit only. All accounts
+marked as signers must have a valid signature in the transaction's list
+of signatures before the transaction is considered valid. Any accounts
+marked as credit only may only have their token value increased, and
+their user data is read only. Accounts are locked by the runtime,
+ensuring that they are not modified by a concurrent program while the
+transaction is running. Credit only accounts can safely be shared, so
+the runtime will allow multiple concurrent credit only locks on an
+account.
+
+## Recent Blockhash
+
+A Transaction includes a recent blockhash to prevent duplication and to
+give transactions lifetimes. Any transaction that is completely
+identical to a previous one is rejected, so adding a newer blockhash
+allows multiple transactions to repeat the exact same action.
+Transactions also have lifetimes that are defined by the blockhash, as
+any transaction whose blockhash is too old will be rejected.
+
+## Instructions
+
+Each instruction specifies a single program account (which must be
+marked executable), a subset of the transaction's accounts that should
+be passed to the program, and a data byte array instruction that is
+passed to the program. The program interprets the data array and
+operates on the accounts specified by the instructions. The program can
+return successfully, or with an error code. An error return causes the
+entire transaction to fail immediately.