json lines reader, writer

packages/api/src/shell/jsonLinesWriter.js

@@ -0,0 +1,30 @@
+const fs = require('fs');
+const stream = require('stream');
+
+class StringifyStream extends stream.Transform {
+  constructor({ header }) {
+    super({ objectMode: true });
+    this.header = header;
+    this.wasHeader = false;
+  }
+  _transform(chunk, encoding, done) {
+    if (!this.wasHeader) {
+      if (this.header) this.push(JSON.stringify(chunk) + '\n');
+      this.wasHeader = true;
+    } else {
+      this.push(JSON.stringify(chunk) + '\n');
+    }
+    done();
+  }
+}
+
+async function jsonLinesWriter({ fileName, encoding = 'utf-8', header = true }) {
+  console.log(`Writing file ${fileName}`);
+  const stringify = new StringifyStream({ header });
+  const fileStream = fs.createWriteStream(fileName, encoding);
+  stringify.pipe(fileStream);
+  stringify['finisher'] = fileStream;
+  return stringify;
+}
+
+module.exports = jsonLinesWriter;