Move docs from book/ to docs/ (#8469)

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docs/src/apps/README.md

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+# Programming Model
+
+An _app_ interacts with a Solana cluster by sending it _transactions_ with one or more _instructions_. The Solana _runtime_ passes those instructions to user-contributed _programs_. An instruction might, for example, tell a program to transfer _lamports_ from one _account_ to another or create an interactive contract that governs how lamports are transfered. Instructions are executed sequentially and atomically. If any instruction is invalid, any changes made within the transaction are discarded.
+
+### Accounts and Signatures
+
+Each transaction explicitly lists all account public keys referenced by the transaction's instructions. A subset of those public keys are each accompanied by a transaction signature. Those signatures signal on-chain programs that the account holder has authorized the transaction. Typically, the program uses the authorization to permit debiting the account or modifying its data.
+
+The transaction also marks some accounts as _read-only accounts_. The runtime permits read-only accounts to be read concurrently. If a program attempts to modify a read-only account, the transaction is rejected by the runtime.
+
+### 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.
+
+## Deploying Programs to a Cluster
+
+![SDK tools](../.gitbook/assets/sdk-tools.svg)
+
+As shown in the diagram above a client creates a program and compiles it to an ELF shared object containing BPF bytecode and sends it to the Solana cluster. The cluster stores the program locally and makes it available to clients via a _program ID_. The program ID is a _public key_ generated by the client and is used to reference the program in subsequent transactions.
+
+A program may be written in any programming language that can target the Berkley Packet Filter \(BPF\) safe execution environment. The Solana SDK offers the best support for C programs, which is compiled to BPF using the [LLVM compiler infrastructure](https://llvm.org).
+
+## Storing State between Transactions
+
+If the program needs to store state between transactions, it does so using _accounts_. Accounts are similar to files in operating systems such as Linux. Like a file, an account may hold arbitrary data and that data persists beyond the lifetime of a program. Also like a file, an account includes metadata that tells the runtime who is allowed to access the data and how. Unlike a file, the account includes metadata for the lifetime of the file. That lifetime is expressed in "tokens", which is a number of fractional native tokens, called _lamports_. Accounts are held in validator memory and pay "rent" to stay there. Each validator periodically scan all accounts and collects rent. Any account that drops to zero lamports is purged.
+
+If an account is marked "executable", it will only be used by a _loader_ to run programs. For example, a BPF-compiled program is marked executable and loaded by the BPF loader. No program is allowed to modify the contents of an executable account.
+
+An account also includes "owner" metadata. The owner is a program ID. The runtime grants the program write access to the account if its ID matches the owner. If an account is not owned by a program, the program is permitted to read its data and credit the account.
+
+In the same way that a Linux user uses a path to look up a file, a Solana client uses public keys to look up accounts. To create an account, the client generates a _keypair_ and registers its public key using the `CreateAccount` instruction. The account created by `CreateAccount` is called a _system account_ and is owned by a built-in program called the System program. The System program allows clients to transfer lamports and assign account ownership.
+
+The runtime only permits the owner to debit the account or modify its data. The program then defines additional rules for whether the client can modify accounts it owns. In the case of the System program, it allows users to transfer lamports by recognizing transaction signatures. If it sees the client signed the transaction using the keypair's _private key_, it knows the client authorized the token transfer.
+
+After the runtime executes each of the transaction's instructions, it uses the account metadata to verify that none of the access rules were violated. If a program violates an access rule, the runtime discards all account changes made by all instructions and marks the transaction as failed.
+
+## Smart Contracts
+
+Programs don't always require transaction signatures, as the System program does. Instead, the program may manage _smart contracts_. A smart contract is a set of constraints that once satisfied, signal to a program that a token transfer or account update is permitted. For example, one could use the Budget program to create a smart contract that authorizes a token transfer only after some date. Once evidence that the date has past, the contract progresses, and token transfer completes.
+

docs/src/apps/drones.md

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+# Drones
+
+This section defines an off-chain service called a _drone_, which acts as custodian of a user's private key. In its simplest form, it can be used to create _airdrop_ transactions, a token transfer from the drone's account to a client's account.
+
+## Signing Service
+
+A drone is a simple signing service. It listens for requests to sign _transaction data_. Once received, the drone validates the request however it sees fit. It may, for example, only accept transaction data with a `SystemInstruction::Transfer` instruction transferring only up to a certain amount of tokens. If the drone accepts the transaction, it returns an `Ok(Signature)` where `Signature` is a signature of the transaction data using the drone's private key. If it rejects the transaction data, it returns a `DroneError` describing why.
+
+## Examples
+
+### Granting access to an on-chain game
+
+Creator of on-chain game tic-tac-toe hosts a drone that responds to airdrop requests containing an `InitGame` instruction. The drone signs the transaction data in the request and returns it, thereby authorizing its account to pay the transaction fee and as well as seeding the game's account with enough tokens to play it. The user then creates a transaction for its transaction data and the drones signature and submits it to the Solana cluster. Each time the user interacts with the game, the game pays the user enough tokens to pay the next transaction fee to advance the game. At that point, the user may choose to keep the tokens instead of advancing the game. If the creator wants to defend against that case, they could require the user to return to the drone to sign each instruction.
+
+### Worldwide airdrop of a new token
+
+Creator of a new on-chain token \(ERC-20 interface\), may wish to do a worldwide airdrop to distribute its tokens to millions of users over just a few seconds. That drone cannot spend resources interacting with the Solana cluster. Instead, the drone should only verify the client is unique and human, and then return the signature. It may also want to listen to the Solana cluster for recent entry IDs to support client retries and to ensure the airdrop is targeting the desired cluster.
+
+Note: the Solana cluster will not parallelize transactions funded by the same fee-paying account. This means that the max throughput of a single fee-paying account is limited to the number of _ticks_ processed per second by the current leader. Add additional fee-paying accounts to improve throughput.
+
+## Attack vectors
+
+### Invalid recent\_blockhash
+
+The drone may prefer its airdrops only target a particular Solana cluster. To do that, it listens to the cluster for new entry IDs and ensure any requests reference a recent one.
+
+Note: to listen for new entry IDs assumes the drone is either a validator or a _light_ client. At the time of this writing, light clients have not been implemented and no proposal describes them. This document assumes one of the following approaches be taken:
+
+1. Define and implement a light client
+2. Embed a validator
+3. Query the jsonrpc API for the latest last id at a rate slightly faster than
+
+   ticks are produced.
+
+### Double spends
+
+A client may request multiple airdrops before the first has been submitted to the ledger. The client may do this maliciously or simply because it thinks the first request was dropped. The drone should not simply query the cluster to ensure the client has not already received an airdrop. Instead, it should use `recent_blockhash` to ensure the previous request is expired before signing another. Note that the Solana cluster will reject any transaction with a `recent_blockhash` beyond a certain _age_.
+
+### Denial of Service
+
+If the transaction data size is smaller than the size of the returned signature \(or descriptive error\), a single client can flood the network. Considering that a simple `Transfer` operation requires two public keys \(each 32 bytes\) and a `fee` field, and that the returned signature is 64 bytes \(and a byte to indicate `Ok`\), consideration for this attack may not be required.
+
+In the current design, the drone accepts TCP connections. This allows clients to DoS the service by simply opening lots of idle connections. Switching to UDP may be preferred. The transaction data will be smaller than a UDP packet since the transaction sent to the Solana cluster is already pinned to using UDP.
+

docs/src/apps/javascript-api.md

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+# JavaScript API
+
+See [solana-web3](https://solana-labs.github.io/solana-web3.js/).
+

docs/src/apps/tictactoe.md

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+# Example: Tic-Tac-Toe
+
+[Click here to play Tic-Tac-Toe](https://solana-example-tictactoe.herokuapp.com/) on the Solana testnet. Open the link and wait for another player to join, or open the link in a second browser tab to play against yourself. You will see that every move a player makes stores a transaction on the ledger.
+
+## Build and run Tic-Tac-Toe locally
+
+First fetch the latest release of the example code:
+
+```bash
+$ git clone https://github.com/solana-labs/example-tictactoe.git
+$ cd example-tictactoe
+$ TAG=$(git describe --tags $(git rev-list --tags
+--max-count=1))
+$ git checkout $TAG
+```
+
+Next, follow the steps in the git repository's [README](https://github.com/solana-labs/example-tictactoe/blob/master/README.md).
+
+## Getting lamports to users
+
+You may have noticed you interacted with the Solana cluster without first needing to acquire lamports to pay transaction fees. Under the hood, the web app creates a new ephemeral identity and sends a request to an off-chain service for a signed transaction authorizing a user to start a new game. The service is called a _drone_. When the app sends the signed transaction to the Solana cluster, the drone's lamports are spent to pay the transaction fee and start the game. In a real world app, the drone might request the user watch an ad or pass a CAPTCHA before signing over its lamports.
+

docs/src/apps/webwallet.md

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+# Example Client: Web Wallet
+
+## Build and run a web wallet locally
+
+First fetch the example code:
+
+```bash
+$ git clone https://github.com/solana-labs/example-webwallet.git
+$ cd example-webwallet
+$ TAG=$(git describe --tags $(git rev-list --tags
+--max-count=1))
+$ git checkout $TAG
+```
+
+Next, follow the steps in the git repository's [README](https://github.com/solana-labs/example-webwallet/blob/master/README.md).
+