Merge branch 'readme' into 'master'

Readme

See merge request !7

Readme.md

+# linker
+The linker is a [kafka sink](https://docs.confluent.io/current/connect/kafka-connect-elasticsearch/index.html) for the [neo4j](https://neo4j.com/) graph database. It consumes messages from the `linker` topic and writes them to the database.
+
+## Neo4jStreamWriter
+The Neo4jStreamWriter consumes a stream of kafka messages and writes the content of the message to the database. It is very simple and can handle backpressure.
+
+## Docker
+To build the image use the following command. The container is based on the [histub/ node-kafka-docker-base](https://source.dodis.ch/histhub/node-kafka-docker-base).
+```bash
+docker build -t source.dodis.ch:4577/histhub/linker .
+# Upload to the registry
+docker push source.dodis.ch:4577/histhub/linker
+```
+## CD
+We have a build pipeline in gitlab. So manual building of the image is no longer necessary. 
+
+## Deploy to k8
+This streaming app is part of the [deploy geolinker helm chart](https://source.dodis.ch/histhub/deploy-geolinker/wikis/deployment-manual#linker).

src/neo4j-linker.ts

-import {v1 as neo4j} from 'neo4j-driver';
-import * as jsesc from 'jsesc';
-export class Linker {
-  private nconf;
-  private logger;
-  private driver;
-  private uriBuilder;
-
-  constructor(nconf, logger, uriBuilder) {
-    this.nconf = nconf;
-    this.logger = logger;
-    this.uriBuilder = uriBuilder;
-    this.driver = neo4j.driver(
-      nconf.get('neo4j:config:uri'),
-      neo4j.auth.basic(
-        nconf.get('neo4j:config:user'),
-        nconf.get('neo4j:config:password'),
-      ),
-    );
-  }
-
-  /**
-   * Create a new node in the db if they do not exists
-   * @param node
-   * @returns {Result}
-   */
-  public newNode(node) {
-    // todo: from topic!
-    const provider = 'geonames';
-    const uri = this.uriBuilder.geoname(node.id);
-    return this.driver.session().run(`MERGE (n:Place { uri: '${uri}'})
-        ON CREATE SET n.id: '${node.id}', n.provider: ${provider}
-        ON MATCH SET n.id: '${node.id}', n.provider: ${provider}`);
-  }
-
-  /**
-   * Write connection int the db. Create nodes if they do not exists
-   * @param connection
-   */
-  public connect(connection) {
-    return new Promise( (resolve, reject) => {
-      let query = `MERGE (o:Place {uri:'${connection.from}'}) `;
-      connection.to.forEach((current, i) => {
-        query += ` MERGE (t${i}:Place {uri:'${current}'}) `;
-        query += ` MERGE (o)-[:${connection.relation.type} {author:'${connection.relation.author}'}]->(t${i}) `;
-      });
-      // get a new session
-      this.logger.info('Try to get a session');
-      this.logger.info(query);
-      const session = this.driver.session();
-      this.logger.info('Try to build network');
-      session.run(query).then(() => {
-        session.close();
-        resolve();
-      }).catch((err) => {
-        setTimeout(() => {
-          session.close();
-          reject(`Error while saving a connection to neo4j ${JSON.stringify(err)}`);
-        }, 1000);
-      });
-    });
-  }
-
-  /**
-   * There is no build in function to escape
-   * https://github.com/neo4j/neo4j-javascript-driver/issues/398
-   * @param string
-   */
-  public escape(data: string) {
-    return jsesc(data);
-  }
-}