```
     NEC Laboratories Europe GmbH

     PROPRIETARY INFORMATION

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 shall be maintained in confidence and treated as confidential
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 testing purposes, unless otherwise explicitly stated in a written
 agreement with NEC Laboratories Europe GmbH.

 Any unauthorized publication, transfer to third parties or
 duplication of the object or source code - either totally or in
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          Copyright (c) 2021 NEC Laboratories Europe GmbH
          All Rights Reserved.

 Authors: Konstantin Munichev <konstantin.munichev@neclab.eu>


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 ```

# DLT module guide

## General information
The DLT module is used to provide access to the underlying Fabric deployment. It allows clients
to add, retrieve, modify and delete blockchain-backed data, essentially working as a key-value
database. External clients should use REST API to communicate with this service, its detailed
description available below.

## Code structure
The whole DLT module consists of several packages:
- fabric package
- http package
- proto package
- client example

### Fabric package
The most important class in this package is `FabricConnector`. First, it establishes connection
with the underlying Fabric network using Java Gateway SDK. After that, it could be used as a
CRUD interface.
Other files contain auxiliary code for `FabricConnector` which allows it to register/enroll
users and to obtain smart contract instances.

### HTTP package
Contains server side HTTP handler. It accepts requests from the outside and performs the
requested operation. For the detailed description see API description section.

### Proto package
The proto package contains `Config.proto` file which contains messages for REST API. The most
important ones are `DltConfig` (it defines the whole DLT configuration) and `DltRecord` which
represents data to store in the blockchain.

### Client example
This code is not necessary to the service, but it could be used to test the service. It contains
a sample REST client which connects the service and perform all the CRUD operations. 

## REST API description
| Method | URL | Input | Response code | Output |
| --- | ----------- | --- | --- | --- |
| POST | /dlt/configure | Configuration object | 201 or 400 | Status value | 
| GET | /dlt/configure | - | 200 or 404 | Configuration object |
| POST | /dlt/record | Record object | 200, 201, 400 or 404 | Status value |
| GET | /dlt/record | Record id | 200 or 404 | Record object |

Record and configuration object are defined in `proto` package.