github.com/Team-Kujira/tendermint@v0.34.24-indexer/spec/abci/client-server.md (about) 1 --- 2 order: 3 3 title: Client and Server 4 --- 5 6 # Client and Server 7 8 This section is for those looking to implement their own ABCI Server, perhaps in 9 a new programming language. 10 11 You are expected to have read [ABCI Methods and Types](./abci.md) and [ABCI 12 Applications](./apps.md). 13 14 ## Message Protocol 15 16 The message protocol consists of pairs of requests and responses defined in the 17 [protobuf file](https://github.com/tendermint/tendermint/blob/v0.34.x/proto/tendermint/abci/types.proto). 18 19 Some messages have no fields, while others may include byte-arrays, strings, integers, 20 or custom protobuf types. 21 22 For more details on protobuf, see the [documentation](https://developers.google.com/protocol-buffers/docs/overview). 23 24 For each request, a server should respond with the corresponding 25 response, where the order of requests is preserved in the order of 26 responses. 27 28 ## Server Implementations 29 30 To use ABCI in your programming language of choice, there must be a ABCI 31 server in that language. Tendermint supports three implementations of the ABCI, written in Go: 32 33 - In-process ([Golang](https://github.com/tendermint/tendermint/tree/v0.34.x/abci), [Rust](https://github.com/tendermint/rust-abci)) 34 - ABCI-socket 35 - GRPC 36 37 The latter two can be tested using the `abci-cli` by setting the `--abci` flag 38 appropriately (ie. to `socket` or `grpc`). 39 40 See examples, in various stages of maintenance, in 41 [Go](https://github.com/tendermint/tendermint/tree/v0.34.x/abci/server), 42 [JavaScript](https://github.com/tendermint/js-abci), 43 [C++](https://github.com/mdyring/cpp-tmsp), and 44 [Java](https://github.com/jTendermint/jabci). 45 46 ### In Process 47 48 The simplest implementation uses function calls within Golang. 49 This means ABCI applications written in Golang can be compiled with Tendermint Core and run as a single binary. 50 51 ### GRPC 52 53 If GRPC is available in your language, this is the easiest approach, 54 though it will have significant performance overhead. 55 56 To get started with GRPC, copy in the [protobuf 57 file](https://github.com/tendermint/tendermint/blob/v0.34.x/proto/tendermint/abci/types.proto) 58 and compile it using the GRPC plugin for your language. For instance, 59 for golang, the command is `protoc --go_out=plugins=grpc:. types.proto`. 60 See the [grpc documentation for more details](http://www.grpc.io/docs/). 61 `protoc` will autogenerate all the necessary code for ABCI client and 62 server in your language, including whatever interface your application 63 must satisfy to be used by the ABCI server for handling requests. 64 65 Note the length-prefixing used in the socket implementation (TSP) does not apply for GRPC. 66 67 ### TSP 68 69 Tendermint Socket Protocol is an asynchronous, raw socket server which provides ordered message passing over unix or tcp. 70 Messages are serialized using Protobuf3 and length-prefixed with a [signed Varint](https://developers.google.com/protocol-buffers/docs/encoding?csw=1#signed-integers) 71 72 If GRPC is not available in your language, or you require higher 73 performance, or otherwise enjoy programming, you may implement your own 74 ABCI server using the Tendermint Socket Protocol. The first step is still to auto-generate the relevant data 75 types and codec in your language using `protoc`. In addition to being proto3 encoded, messages coming over 76 the socket are length-prefixed to facilitate use as a streaming protocol. proto3 doesn't have an 77 official length-prefix standard, so we use our own. The first byte in 78 the prefix represents the length of the Big Endian encoded length. The 79 remaining bytes in the prefix are the Big Endian encoded length. 80 81 For example, if the proto3 encoded ABCI message is 0xDEADBEEF (4 82 bytes), the length-prefixed message is 0x0104DEADBEEF. If the proto3 83 encoded ABCI message is 65535 bytes long, the length-prefixed message 84 would be like 0x02FFFF.... 85 86 The benefit of using this `varint` encoding over the old version (where integers were encoded as `<len of len><big endian len>` is that 87 it is the standard way to encode integers in Protobuf. It is also generally shorter. 88 89 As noted above, this prefixing does not apply for GRPC. 90 91 An ABCI server must also be able to support multiple connections, as 92 Tendermint uses four connections. 93 94 ### Async vs Sync 95 96 The main ABCI server (ie. non-GRPC) provides ordered asynchronous messages. 97 This is useful for DeliverTx and CheckTx, since it allows Tendermint to forward 98 transactions to the app before it's finished processing previous ones. 99 100 Thus, DeliverTx and CheckTx messages are sent asynchronously, while all other 101 messages are sent synchronously. 102 103 ## Client 104 105 There are currently two use-cases for an ABCI client. One is a testing 106 tool, as in the `abci-cli`, which allows ABCI requests to be sent via 107 command line. The other is a consensus engine, such as Tendermint Core, 108 which makes requests to the application every time a new transaction is 109 received or a block is committed. 110 111 It is unlikely that you will need to implement a client. For details of 112 our client, see 113 [here](https://github.com/tendermint/tendermint/tree/v0.34.x/abci/client).