Merge PR #2447: Cleanup docs/light

docs/lite/getting_started.md

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+# Getting Started
+
+To start a REST server, we need to specify the following parameters:
+
+| Parameter   | Type      | Default                 | Required | Description                                          |
+| ----------- | --------- | ----------------------- | -------- | ---------------------------------------------------- |
+| chain-id    | string    | null                    | true     | chain id of the full node to connect                 |
+| node        | URL       | "tcp://localhost:46657" | true     | address of the full node to connect                  |
+| laddr       | URL       | "tcp://localhost:1317"  | true     | address to run the rest server on                    |
+| trust-node  | bool      | "false"                 | true     | Whether this LCD is connected to a trusted full node |
+| trust-store | DIRECTORY | "$HOME/.lcd"            | false    | directory for save checkpoints and validator sets    |
+
+For example::
+
+```bash
+gaiacli rest-server --chain-id=test \
+    --laddr=tcp://localhost:1317 \
+    --node tcp://localhost:26657 \
+    --trust-node=false
+```
+
+The server listens on HTTPS by default. You can set the SSL certificate to be used by the server with these additional flags:
+
+```bash
+gaiacli rest-server --chain-id=test \
+    --laddr=tcp://localhost:1317 \
+    --node tcp://localhost:26657 \
+    --trust-node=false \
+    --certfile=mycert.pem --keyfile=mykey.key
+```
+
+If no certificate/keyfile pair is supplied, a self-signed certificate will be generated and its fingerprint printed out.
+Append `--insecure` to the command line if you want to disable the secure layer and listen on an insecure HTTP port.
+
+For more information about the Gaia-Lite RPC, see the [swagger documentation](https://cosmos.network/rpc/)

docs/lite/readme.md

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+# Overview
+
+**See the Cosmos SDK lite Client RPC documentation [here](https://cosmos.network/rpc/)**
+
+## Introduction
+
+A lite client allows clients, such as mobile phones, to receive proofs of the state of the
+blockchain from any full node. lite clients do not have to trust any full node, since they are able
+to verify any proof they receive and hence full nodes cannot lie about the state of the network.
+
+A lite client can provide the same security as a full node with the minimal requirements on
+bandwidth, computing and storage resource. As well, it can also provide modular functionality
+according to users' configuration. These fantastic features allow developers to build fully secure,
+efficient and usable mobile apps, websites or any other applications without deploying or
+maintaining any full blockchain nodes.
+
+### What is a lite Client
+
+The LCD is split into two separate components. The first component is generic for any Tendermint
+based application. It handles the security and connectivity aspects of following the header chain
+and verify proofs from full nodes against locally trusted validator set. Furthermore it exposes
+exactly the same API as any Tendermint Core node. The second component is specific for the Cosmos
+Hub (Gaiad). It works as a query endpoint and exposes the application specific functionality, which
+can be arbitrary. All queries against the application state have to go through the query endpoint.
+The advantage of the query endpoint is that it can verify the proofs that the application returns.
+
+### High-Level Architecture
+
+An application developer that would like to build a third party integration can ship his application
+with the LCD for the Cosmos Hub (or any other zone) and only needs to initialise it. Afterwards his
+application can interact with the zone as if it was running against a full node.
+
+![high-level](pics/high-level.png)
+
+An application developer that wants to build an third party application for the Cosmos Hub (or any
+other zone) should build it against it's canonical API. That API is a combination of multiple parts.
+All zones have to expose ICS0 (TendermintAPI). Beyond that any zone is free to choose any
+combination of module APIs, depending on which modules the state machine uses. The Cosmos Hub will
+initially support ICS0 (TendermintAPI), ICS1 (KeyAPI), ICS20 (TokenAPI), ICS21 (StakingAPI) and
+ICS22 (GovernanceAPI).
+
+All applications are expected to only run against the LCD. The LCD is the only piece of software
+that offers stability guarantees around the zone API.
+
+### Comparision
+
+A full node of ABCI is different from its lite client in the following ways:
+
+|| Full Node | LCD | Description|
+|-| ------------- | ----- | -------------- |
+| Execute and verify transactions|Yes|No|Full node will execute and verify all transactions while LCD won't|
+| Verify and save blocks|Yes|No|Full node will verify and save all blocks while LCD won't|
+| Participate consensus| Yes|No|Only when the full node is a validtor, it will participate consensus. LCD nodes never participate consensus|
+| Bandwidth cost|Huge|Little|Full node will receive all blocks. if the bandwidth is limited, it will fall behind the main network. What's more, if it happens to be a validator,it will slow down the consensus process. LCD requires little bandwidth. Only when serving local request, it will cost bandwidth|
+| Computing resource|Huge|Little|Full node will execute all transactions and verify all blocks which require much computing resource|
+| Storage resource|Huge|Little|Full node will save all blocks and ABCI states. LCD just saves validator sets and some checkpoints|
+| Power consume|Huge|Little|Full nodes have to be deployed on machines which have high performance and will be running all the time. So power consume will be huge. LCD can be deployed on the same machines as users' applications, or on independent machines but with poor performance. Besides, LCD can be shutdown anytime when necessary. So LCD only consume very little power, even mobile devices can meet the power requirement|
+| Provide APIs|All cosmos APIs|Modular APIs|Full node supports all cosmos APIs. LCD provides modular APIs according to users' configuration|
+| Secuity level| High|High|Full node will verify all transactions and blocks by itself. LCD can't do this, but it can query any data from other full nodes and verify the data independently. So both full node and LCD don't need to trust any third nodes, they all can achieve high security|
+
+According to the above table, LCD can meet all users' functionality and security requirements, but
+only requires little resource on bandwidth, computing, storage and power.
+
+## Achieving Security
+
+### Trusted Validator Set
+
+The base design philosophy of the LCD follows two rules:
+
+1. **Doesn't trust any blockchain nodes, including validator nodes and other full nodes**
+2. **Only trusts the whole validator set**
+
+The original trusted validator set should be prepositioned into its trust store, usually this
+validator set comes from genesis file. During runtime, if LCD detects a different validator set,
+it will verify it and save new validated validator set to the trust store.
+
+![validator-set-change](pics/validatorSetChange.png)
+
+### Trust Propagation
+
+From the above section, we come to know how to get trusted validator set and how lcd keeps track of
+validator set evolution. Validator set is the foundation of trust, and the trust can propagate to
+other blockchain data, such as block and transaction. The propagate architecture is shown as
+follows:
+
+![change-process](pics/trustPropagate.png)
+
+In general, by trusted validator set, LCD can verify each block commit which contains all pre-commit
+data and block header data. Then the block hash, data hash and appHash are trusted. Based on this
+and merkle proof, all transactions data and ABCI states can be verified too.

docs/lite/specification.md

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+# Specifications
+
+This specification describes how to implement the LCD. LCD supports modular APIs. Currently, only
+ICS0 (TendermintAPI), ICS1 (Key API) and ICS20 (Token API) are supported. Later, if necessary, more
+APIs can be included.
+
+## Build and Verify Proof of ABCI States
+
+As we all know,  storage of cosmos-sdk based application contains multi-substores. Each substore is
+implemented by a IAVL store. These substores are organized by simple Merkle tree. To build the tree,
+we need to extract name, height and store root hash from these substores to build a set of simple
+Merkle leaf nodes, then calculate hash from leaf nodes to root. The root hash of the simple Merkle
+tree is the AppHash which will be included in block header.
+
+![Simple Merkle Tree](pics/simpleMerkleTree.png)
+
+As we have discussed in [LCD trust-propagation](https://github.com/irisnet/cosmos-sdk/tree/bianjie/lcd_spec/docs/spec/lcd#trust-propagation),
+the AppHash can be verified by checking voting power against a trusted validator set. Here we just
+need to build proof from ABCI state to AppHash. The proof contains two parts:
+
+* IAVL proof
+* Substore to AppHash proof
+
+### IAVL Proof
+
+The proof has two types: existance proof and absence proof. If the query key exists in the IAVL
+store, then it returns key-value and its existance proof. On the other hand, if the key doesn't
+exist, then it only returns absence proof which can demostrate the key definitely doesn't exist.
+
+### IAVL Existance Proof
+
+```go
+type CommitID struct {
+    Version int64
+    Hash    []byte
+}
+
+type storeCore struct {
+    CommitID CommitID
+}
+
+type MultiStoreCommitID struct {
+    Name string
+    Core storeCore
+}
+
+type proofInnerNode struct {
+    Height  int8
+    Size    int64
+    Version int64
+    Left    []byte
+    Right   []byte
+}
+
+type KeyExistsProof struct {
+    MultiStoreCommitInfo []MultiStoreCommitID //All substore commitIDs
+    StoreName string //Current substore name
+    Height  int64 //The commit height of current substore
+    RootHash cmn.HexBytes //The root hash of this IAVL tree
+    Version  int64 //The version of the key-value in this IAVL tree
+    InnerNodes []proofInnerNode //The path from to root node to key-value leaf node
+}
+```
+
+The data structure of exist proof is shown as above. The process to build and verify existance proof
+is shown as follows:
+
+![Exist Proof](pics/existProof.png)
+
+Steps to build proof:
+
+* Access the IAVL tree from the root node.
+* Record the visited nodes in InnerNodes,
+* Once the target leaf node is found, assign leaf node version to proof version
+* Assign the current IAVL tree height to proof height
+* Assign the current IAVL tree rootHash to proof rootHash
+* Assign the current substore name to proof StoreName
+* Read multistore commitInfo from db by height and assign it to proof StoreCommitInfo
+
+Steps to verify proof:
+
+* Build leaf node with key, value and proof version.
+* Calculate leaf node hash
+* Assign the hash to the first innerNode's rightHash, then calculate first innerNode hash
+* Propagate the hash calculation process. If prior innerNode is the left child of next innerNode, then assign the prior innerNode hash to the left hash of next innerNode. Otherwise, assign the prior innerNode hash to the right hash of next innerNode.
+* The hash of last innerNode should be equal to the rootHash of this proof. Otherwise, the proof is invalid.
+
+### IAVL Absence Proof
+
+As we all know, all IAVL leaf nodes are sorted by the key of each leaf nodes. So we can calculate
+the postition of the target key in the whole key set of this IAVL tree. As shown below, we can find
+out the left key and the right key. If we can demonstrate that both left key and right key
+definitely exist, and they are adjacent nodes. Thus the target key definitely doesn't exist.
+
+![Absence Proof1](pics/absence1.png)
+
+If the target key is larger than the right most leaf node or less than the left most key, then the
+target key definitely doesn't exist.
+
+![Absence Proof2](pics/absence2.png)![Absence Proof3](pics/absence3.png)
+
+```go
+type proofLeafNode struct {
+    KeyBytes   cmn.HexBytes
+    ValueBytes cmn.HexBytes
+    Version    int64
+}
+
+type pathWithNode struct {
+    InnerNodes []proofInnerNode
+    Node proofLeafNode
+}
+
+type KeyAbsentProof struct {
+    MultiStoreCommitInfo []MultiStoreCommitID
+    StoreName string
+    Height  int64
+    RootHash cmn.HexBytes
+    Left  *pathWithNode // Proof the left key exist
+    Right *pathWithNode  //Proof the right key exist
+}
+```
+
+The above is the data structure of absence proof. Steps to build proof:
+
+* Access the IAVL tree from the root node.
+* Get the deserved index(Marked as INDEX) of the key in whole key set.
+* If the returned index equals to 0, the right index should be 0 and left node doesn't exist
+* If the returned index equals to the size of the whole key set, the left node index should be INDEX-1 and the right node doesn't exist.
+* Otherwise, the right node index should be INDEX and the left node index should be INDEX-1
+* Assign the current IAVL tree height to proof height
+* Assign the current IAVL tree rootHash to proof rootHash
+* Assign the current substore name to proof StoreName
+* Read multistore commitInfo from db by height and assign it to proof StoreCommitInfo
+
+Steps to verify proof:
+
+* If only right node exist, verify its exist proof and verify if it is the left most node
+* If only left node exist, verify its exist proof and verify if it is the right most node.
+* If both right node and left node exist, verify if they are adjacent.
+
+### Substores to AppHash Proof
+
+After verify the IAVL proof, then we can start to verify substore proof against AppHash. Firstly,
+iterate MultiStoreCommitInfo and find the substore commitID by proof StoreName. Verify if yhe Hash
+in commitID equals to proof RootHash. If not, the proof is invalid. Then sort the substore
+commitInfo array by the hash of substore name. Finally, build the simple Merkle tree with all
+substore commitInfo array and verify if the Merkle root hash equal to appHash.
+
+![substore proof](pics/substoreProof.png)
+
+```go
+func SimpleHashFromTwoHashes(left []byte, right []byte) []byte {
+    var hasher = ripemd160.New()
+
+    err := encodeByteSlice(hasher, left)
+    if err != nil {
+        panic(err)
+    }
+
+    err = encodeByteSlice(hasher, right)
+    if err != nil {
+        panic(err)
+    }
+
+    return hasher.Sum(nil)
+}
+
+func SimpleHashFromHashes(hashes [][]byte) []byte {
+    // Recursive impl.
+    switch len(hashes) {
+        case 0:
+            return nil
+        case 1:
+            return hashes[0]
+        default:
+            left := SimpleHashFromHashes(hashes[:(len(hashes)+1)/2])
+            right := SimpleHashFromHashes(hashes[(len(hashes)+1)/2:])
+            return SimpleHashFromTwoHashes(left, right)
+    }
+}
+```
+
+## Verify block header against validator set
+
+Above sections refer appHash frequently. But where does the trusted appHash come from? Actually,
+appHash exist in block header, so next we need to verify blocks header at specific height against
+LCD trusted validator set. The validation flow is shown as follows:
+
+![commit verification](pics/commitValidation.png)
+
+When the trusted validator set doesn't match the block header, we need to try to update our
+validator set to the height of this block. LCD have a rule that each validator set change should not
+affact more than 1/3 voting power. Compare with the trusted validator set, if the voting power of
+target validator set changes more than 1/3. We have to verify if there are hidden validator set
+change before the target validator set. Only when all validator set changes obey this rule, can our
+validator set update be accomplished.
+
+For instance:
+
+![Update validator set to height](pics/updateValidatorToHeight.png)
+
+* Update to 10000, tooMuchChangeErr
+* Update to 5050,  tooMuchChangeErr
+* Update to 2575, Success
+* Update to 5050, Success
+* Update to 10000,tooMuchChangeErr
+* Update to 7525, Success
+* Update to 10000, Success