frostfs-sdk-go/README.md

# frostfs-sdk-go
Go implementation of FrostFS SDK. It contains high-level version-independent wrappers
for structures from [frostfs-api-go](https://git.frostfs.info/TrueCloudLab/frostfs-api-go) as well as
helper functions for simplifying node/dApp implementations.

## Repository structure

### accounting
Contains fixed-point `Decimal` type for performing balance calculations.

### eacl
Contains Extended ACL types for fine-grained access control.
There is also a reference implementation of checking algorithm which is used in FrostFS node.

### checksum
Contains `Checksum` type encapsulating checksum as well as it's kind.
Currently Sha256 and [Tillich-Zemor hashsum](https://git.frostfs.info/TrueCloudLab/tzhash) are in use.

### owner
`owner.ID` type represents single account interacting with FrostFS. In v2 version of protocol
it is just raw bytes behing [base58-encoded address](https://docs.neo.org/docs/en-us/basic/concept/wallets.html#address)
in Neo blockchain. Note that for historical reasons it contains
version prefix and checksum in addition to script-hash.

### token
Contains Bearer token type with several FrostFS-specific methods.

### ns
In FrostFS there are 2 types of name resolution: DNS and NNS. NNS stands for Neo Name Service
is just a [contract](https://git.frostfs.info/TrueCloudLab/frostfs-contract) deployed on a Neo blockchain.
Basically, NNS is just a DNS-on-chain which can be used for resolving container nice-names as well
as any other name in dApps. See our [CoreDNS plugin](https://github.com/nspcc-dev/coredns/tree/master/plugin/nns)
for the example of how NNS can be integrated in DNS.

### session
To help lightweight clients interact with FrostFS without sacrificing trust, FrostFS has a concept
of session token. It is signed by client and allows any node with which a session is established
to perform certain actions on behalf of the user.

### client
Contains client for working with FrostFS.
```go
var prmInit client.PrmInit
prmInit.SetDefaultPrivateKey(key) // private key for request signing
prmInit.ResolveFrostFSFailures() // enable erroneous status parsing

var c client.Client
c.Init(prmInit)

var prmDial client.PrmDial
prmDial.SetServerURI("grpcs://localhost:40005") // endpoint address

err := c.Dial(prmDial)
if err != nil {
    return
}
    
ctx, cancel := context.WithTimeout(context.Background(), 5 * time.Second)
defer cancel()

var prm client.PrmBalanceGet
prm.SetAccount(acc)

res, err := c.BalanceGet(ctx, prm)
if err != nil {
    return
}

fmt.Printf("Balance for %s: %v\n", acc, res.Amount())
```

#### Response status
In FrostFS every operation can fail on multiple levels, so a single `error` doesn't suffice,
e.g. consider a case when object was put on 4 out of 5 replicas. Thus, all request execution
details are contained in `Status` returned from every RPC call. dApp can inspect them
if needed and perform any desired action. In the case above we may want to report
these details to the user as well as retry an operation, possibly with different parameters.
Status wire-format is extendable and each node can report any set of details it wants.
The set of reserved status codes can be found in
[FrostFS API](https://git.frostfs.info/TrueCloudLab/frostfs-api/src/branch/master/status/types.proto). There is also
a `client.PrmInit.ResolveFrostFSFailures()` to seamlessly convert erroneous statuses into Go error type.

### policy
Contains helpers allowing conversion of placing policy from/to JSON representation
and SQL-like human-readable language.
```go
p, _ := policy.Parse(`
    REP 2
    SELECT 6 FROM F
    FILTER StorageType EQ SSD AS F`)

// Convert parsed policy back to human-readable text and print.
println(strings.Join(policy.Encode(p), "\n"))
```

### netmap
Contains CRUSH-like implementation of container node selection algorithm. Relevant details
are described in this paper http://ceur-ws.org/Vol-2344/short10.pdf . Note that it can be
outdated in some details.

`netmap/json_tests` subfolder contains language-agnostic tests for selection algorithm. 

```go
import (
    "git.frostfs.info/TrueCloudLab/frostfs-sdk-go/netmap"
    "git.frostfs.info/TrueCloudLab/frostfs-sdk-go/object"
)

func placementNodes(addr *object.Address, p *netmap.PlacementPolicy, frostfsNodes []netmap.NodeInfo) {
    // Convert list of nodes in FrostFS API format to the intermediate representation.
    nodes := netmap.NodesFromInfo(nodes)

    // Create new netmap (errors are skipped for the sake of clarity). 
    nm, _ := NewNetmap(nodes)

    // Calculate nodes of container.
    cn, _ := nm.GetContainerNodes(p, addr.ContainerID().ToV2().GetValue())

    // Return list of nodes for each replica to place object on in the order of priority.
    return nm.GetPlacementVectors(cn, addr.ObjectID().ToV2().GetValue())
}
```

### pool
Simple pool for managing connections to FrostFS nodes.

### acl, checksum, version, signature
Contain simple API wrappers.

### logger
Wrapper over `zap.Logger` which is used across FrostFS codebase.

### util
Utilities for working with signature-related code.