From eccca89dd54604cd185d56fd780b3e60db3c0fc1 Mon Sep 17 00:00:00 2001
From: Juanjo Diaz <juanjo.diazmo@gmail.com>
Date: Tue, 10 Apr 2018 05:28:29 +0300
Subject: [PATCH] fix: Support empty array with opts.fields (#281)

---
 lib/JSON2CSVParser.js              |  2 +-
 lib/JSON2CSVTransform.js           | 23 +++++++++++++++++------
 test/JSON2CSVParser.js             | 12 ++++++++++++
 test/JSON2CSVTransform.js          | 18 ++++++++++++++++++
 test/fixtures/json/emptyArray.json |  1 +
 5 files changed, 49 insertions(+), 7 deletions(-)
 create mode 100644 test/fixtures/json/emptyArray.json

diff --git a/lib/JSON2CSVParser.js b/lib/JSON2CSVParser.js
index e4e25062..4d7c29fa 100644
--- a/lib/JSON2CSVParser.js
+++ b/lib/JSON2CSVParser.js
@@ -40,7 +40,7 @@ class JSON2CSVParser extends JSON2CSVBase {
   preprocessData(data) {
     const processedData = Array.isArray(data) ? data : [data];
 
-    if (!this.opts.fields && processedData.length === 0 || typeof processedData[0] !== 'object') {
+    if (!this.opts.fields && (processedData.length === 0 || typeof processedData[0] !== 'object')) {
       throw new Error('Data should not be empty or the "fields" option should be included');
     }
 
diff --git a/lib/JSON2CSVTransform.js b/lib/JSON2CSVTransform.js
index e53808c8..bbc527cc 100644
--- a/lib/JSON2CSVTransform.js
+++ b/lib/JSON2CSVTransform.js
@@ -27,6 +27,10 @@ class JSON2CSVTransform extends Transform {
       this.push('\ufeff');
     }
 
+    if (this.opts.fields) {
+      this.pushHeader();
+    }
+
   }
 
   /**
@@ -120,6 +124,18 @@ class JSON2CSVTransform extends Transform {
     done();
   }
 
+  /**
+   * Generate the csv header and pushes it downstream.
+   */
+  pushHeader() {
+    if (this.opts.header) {
+      const header = this.getHeader(this.opts);
+      this.emit('header', header);
+      this.push(header);
+      this._hasWritten = true;
+    }
+  }
+
   /**
    * Transforms an incoming json data to csv and pushes it downstream.
    *
@@ -130,12 +146,7 @@ class JSON2CSVTransform extends Transform {
     
     if (!this._hasWritten) {
       this.opts.fields = this.opts.fields || Object.keys(processedData[0]);
-      if (this.opts.header) {
-        const header = this.getHeader(this.opts);
-        this.emit('header', header);
-        this.push(header);
-        this._hasWritten = true;
-      }
+      this.pushHeader();
     }
 
     processedData.forEach(row => {
diff --git a/test/JSON2CSVParser.js b/test/JSON2CSVParser.js
index 8cd7c87c..28f9fcb6 100644
--- a/test/JSON2CSVParser.js
+++ b/test/JSON2CSVParser.js
@@ -37,6 +37,18 @@ module.exports = (testRunner, jsonFixtures, csvFixtures) => {
     t.end();
   });
 
+  testRunner.add('should handle empty array', (t) => {
+    const opts = {
+      fields: ['carModel', 'price', 'color']
+    };
+
+    const parser = new Json2csvParser(opts);
+    const csv = parser.parse(jsonFixtures.emptyArray);
+
+    t.equal(csv, csvFixtures.emptyObject);
+    t.end();
+  });
+
   testRunner.add('should hanlde array with nulls', (t) => {
     const input = [null];
     const opts = {
diff --git a/test/JSON2CSVTransform.js b/test/JSON2CSVTransform.js
index d8822e42..238a9b93 100644
--- a/test/JSON2CSVTransform.js
+++ b/test/JSON2CSVTransform.js
@@ -97,6 +97,24 @@ module.exports = (testRunner, jsonFixtures, csvFixtures) => {
       .on('error', err => t.notOk(true, err.message));
   });
 
+  testRunner.add('should handle empty array', (t) => {
+    const opts = {
+      fields: ['carModel', 'price', 'color']
+    };
+
+    const transform = new Json2csvTransform(opts);
+    const processor = jsonFixtures.emptyArray().pipe(transform);
+
+    let csv = '';
+    processor
+      .on('data', chunk => (csv += chunk.toString()))
+      .on('end', () => {
+        t.equal(csv, csvFixtures.emptyObject);
+        t.end();
+      })
+      .on('error', err => t.notOk(true, err.message));
+  });
+
   testRunner.add('should hanlde array with nulls', (t) => {
     const input = new Readable();
     input._read = () => {};
diff --git a/test/fixtures/json/emptyArray.json b/test/fixtures/json/emptyArray.json
new file mode 100644
index 00000000..0637a088
--- /dev/null
+++ b/test/fixtures/json/emptyArray.json
@@ -0,0 +1 @@
+[]
\ No newline at end of file