Add openBuffer

README.md

@@ -146,6 +146,14 @@ const params = {
 let reader = await parquet.ParquetReader.openS3(client,params);
 ```
 
+### Reading data from a buffer
+
+If the complete parquet file is in buffer it can be read directly from memory without incurring any additional I/O.
+
+``` js
+const file = fs.readFileSync('fruits.parquet');
+let reader = await parquet.ParquetReader.openBuffer(file);
+```
 
 Encodings
 ---------

lib/reader.js

@@ -94,6 +94,11 @@ class ParquetReader {
     return this.openEnvelopeReader(envelopeReader);
   }
 
+  static async openBuffer(buffer) {
+    let envelopeReader = await ParquetEnvelopeReader.openBuffer(Buffer);
+    return this.openEnvelopeReader(envelopeReader);
+  }
+
   /**
    * Open the parquet file from S3 using the supplied aws client and params
    * The params have to include `Bucket` and `Key` to the file requested
@@ -224,6 +229,12 @@ class ParquetEnvelopeReader {
     return new ParquetEnvelopeReader(readFn, closeFn, fileStat.size);
   }
 
+  static async openBuffer(buffer) {
+    let readFn = (offset, length) => buffer.slice(offset,offset+length);
+    let closeFn = () => ({});
+    return new ParquetEnvelopeReader(readFn, closeFn, buffer.length);
+  }
+
   static async openS3(client, params) {
     let fileStat = await client.headObject(params).promise();