Pr277

History.md

@@ -1,3 +1,7 @@
+# v3.5.1
+
+* [ADDED] `maxRows` option to limit the number of rows parsed. [#275](https://github.com/C2FO/fast-csv/issues/275) [#277](https://github.com/C2FO/fast-csv/pull/277) - [@cbrittingham](https://github.com/cbrittingham)
+
 # v3.5.0
 
 * Upgraded dependencies

benchmark/.eslintrc.js

@@ -1,6 +1,8 @@
 module.exports = {
+    parserOptions: {
+        project: null,
+    },
     rules: {
         "no-console": 0,
-        "@typescript-eslint/no-var-requires": 0
     },
 };

benchmark/index.js

@@ -2,7 +2,6 @@ const path = require('path');
 const fs = require('fs');
 const fastCsv = require('..');
 
-
 function camelize(str) {
     return str.replace(/_(.)/g, (a, b) => b.toUpperCase());
 }
@@ -11,7 +10,7 @@ const promisfyStream = (stream, expectedRows) => {
     let count = 0;
     return new Promise((res, rej) => {
         stream
-            .on('data', (row) => {
+            .on('data', row => {
                 count += 1;
             })
             .on('end', () => {
@@ -25,13 +24,14 @@ const promisfyStream = (stream, expectedRows) => {
     });
 };
 
-const benchmarkFastCsv = type => (num) => {
+const benchmarkFastCsv = type => num => {
     const file = path.resolve(__dirname, `./assets/${num}.${type}.csv`);
-    const stream = fs.createReadStream(file)
-        .pipe(fastCsv.parse({ headers: true }))
-        .transform((data) => {
+    const stream = fs
+        .createReadStream(file)
+        .pipe(fastCsv.parse({ headers: true, maxRows: 10 }))
+        .transform(data => {
             const ret = {};
-            [ 'first_name', 'last_name', 'email_address' ].forEach((prop) => {
+            ['first_name', 'last_name', 'email_address'].forEach(prop => {
                 ret[camelize(prop)] = data[prop];
             });
             ret.address = data.address;
@@ -47,15 +47,15 @@ async function benchmarkRun(title, num, m) {
     for (let i = 0; i < howMany; i += 1) {
         // eslint-disable-next-line no-await-in-loop
         await m(num);
-        console.log('%s: RUN(%d lines) 1 %dms', title, num, (new Date() - runStart));
+        console.log('%s: RUN(%d lines) 1 %dms', title, num, new Date() - runStart);
         runStart = new Date();
     }
     console.log('%s: 3xAVG for %d lines %dms', title, num, (new Date() - start) / howMany);
 }
 
 function runBenchmarks(num, type) {
     console.log(`\nRUNNING ${num}.${type}.csv benchmarks`, num);
-    return benchmarkRun('fast-csv', num, benchmarkFastCsv(type))
+    return benchmarkRun('fast-csv', num, benchmarkFastCsv(type));
 }
 
 function benchmarks(type) {
@@ -67,7 +67,7 @@ function benchmarks(type) {
 benchmarks('nonquoted')
     .then(() => benchmarks('quoted'))
     .then(() => process.exit())
-    .catch((e) => {
+    .catch(e => {
         console.error(e.stack);
         return process.exit(1);
     });

docs/parsing.md

@@ -17,6 +17,7 @@
     * [Ignoring Empty Rows](#csv-parse-ignoring-empty-rows)
     * [Transforming Rows](#csv-parse-transforming)
     * [Validating Rows](#csv-parse-validation)
+    * [Max Rows](#max-rows)
 
 <a name="parsing-options"></a>
 ## Options
@@ -45,6 +46,7 @@
 * `rtrim: {boolean} = false`: Set to `true` to right trim all fields.
 * `ltrim: {boolean} = false`: Set to `true` to left trim all fields.
 * `encoding: {string} = 'utf8'`: Passed to [StringDecoder](https://nodejs.org/api/string_decoder.html#string_decoder_new_stringdecoder_encoding) when decoding incoming buffers. Change if incoming content is not 'utf8' encoded.
+- `maxRows: {number}`: If number is `> 0` the specified number of rows will be parsed.(e.g. `100` would return the first 100 rows of data).
 
 <a name="parsing-events"></a>
 ## Events
@@ -585,3 +587,44 @@ Valid [row={"firstName":"timmy","lastName":"yukon"}]
 Parsed 2 rows
 ```
 
+<a name="max-rows"></a>
+[`examples/parsing/max_rows.example.example.js`](../examples/parsing/max_rows.example.js)
+
+In the following example there are 10 rows, but only 5 will be parsed because of the `maxRows` option.
+
+```javascript
+const rows = [
+    'header1,header2\n',
+    'col1,col1\n',
+    'col2,col2\n',
+    'col3,col3\n',
+    'col4,col4\n',
+    'col5,col5\n',
+    'col6,col6\n',
+    'col7,col7\n',
+    'col8,col8\n',
+    'col9,col9\n',
+    'col10,col10',
+];
+
+const stream = csv
+    .parse({ headers: true, maxRows: 5 })
+    .on('error', error => console.error(error))
+    .on('data', row => console.log(row))
+    .on('end', rowCount => console.log(`Parsed ${rowCount} rows`));
+
+rows.forEach(row => stream.write(row));
+stream.end();
+```
+
+Expected output
+
+```
+{ header1: 'col1', header2: 'col1' }
+{ header1: 'col2', header2: 'col2' }
+{ header1: 'col3', header2: 'col3' }
+{ header1: 'col4', header2: 'col4' }
+{ header1: 'col5', header2: 'col5' }
+Parsed 5 rows
+```
+

examples/parsing/max_rows.example.js

@@ -0,0 +1,24 @@
+const csv = require('../../');
+
+const rows = [
+    'header1,header2\n',
+    'col1,col1\n',
+    'col2,col2\n',
+    'col3,col3\n',
+    'col4,col4\n',
+    'col5,col5\n',
+    'col6,col6\n',
+    'col7,col7\n',
+    'col8,col8\n',
+    'col9,col9\n',
+    'col10,col10',
+];
+
+const stream = csv
+    .parse({ headers: true, maxRows: 5 })
+    .on('error', error => console.error(error))
+    .on('data', row => console.log(row))
+    .on('end', rowCount => console.log(`Parsed ${rowCount} rows`));
+
+rows.forEach(row => stream.write(row));
+stream.end();

src/parser/CsvParserStream.ts

@@ -31,6 +31,10 @@ export default class CsvParserStream extends Transform {
         this.rowTransformerValidator = new RowTransformerValidator();
     }
 
+    private get hasHitRowLimit(): boolean {
+        return this.parserOptions.limitRows && this.rowCount >= this.parserOptions.maxRows;
+    }
+
     public transform(transformFunction: RowTransformFunction): CsvParserStream {
         this.rowTransformerValidator.rowTransform = transformFunction;
         return this;
@@ -54,23 +58,31 @@ export default class CsvParserStream extends Transform {
     }
 
     public _transform(data: Buffer, encoding: string, done: TransformCallback): void {
+        // if we have hit our maxRows parsing limit then skip parsing
+        if (this.hasHitRowLimit) {
+            return done();
+        }
         try {
             const { lines } = this;
             const newLine = lines + this.decoder.write(data);
             const rows = this.parse(newLine, true);
-            this.processRows(rows, done);
+            return this.processRows(rows, done);
         } catch (e) {
-            done(e);
+            return done(e);
         }
     }
 
     public _flush(done: TransformCallback): void {
+        // if we have hit our maxRows parsing limit then skip parsing
+        if (this.hasHitRowLimit) {
+            return done();
+        }
         try {
             const newLine = this.lines + this.decoder.end();
             const rows = this.parse(newLine, false);
-            this.processRows(rows, done);
+            return this.processRows(rows, done);
         } catch (e) {
-            done(e);
+            return done(e);
         }
     }
 
@@ -86,7 +98,9 @@ export default class CsvParserStream extends Transform {
     private processRows(rows: string[][], cb: TransformCallback): void {
         const rowsLength = rows.length;
         const iterate = (i: number): void => {
-            if (i >= rowsLength) {
+            // if we have emitted all rows or we have hit the maxRows limit option
+            // then end
+            if (i >= rowsLength || this.hasHitRowLimit) {
                 return cb();
             }
             const row = rows[i];

src/parser/ParserOptions.ts

@@ -16,6 +16,7 @@ export interface ParserOptionsArgs {
     ltrim?: boolean;
     rtrim?: boolean;
     encoding?: string;
+    maxRows?: number;
 }
 
 export class ParserOptions {
@@ -57,6 +58,10 @@ export class ParserOptions {
 
     public readonly encoding: string = 'utf8';
 
+    public readonly limitRows: boolean = false;
+
+    public readonly maxRows: number = 0;
+
     public constructor(opts?: ParserOptionsArgs) {
         Object.assign(this, opts || {});
         if (this.delimiter.length > 1) {
@@ -66,5 +71,9 @@ export class ParserOptions {
         this.escapeChar = this.escape ?? this.quote;
         this.supportsComments = !isNil(this.comment);
         this.NEXT_TOKEN_REGEXP = new RegExp(`([^\\s]|\\r\\n|\\n|\\r|${this.escapedDelimiter})`);
+
+        if (this.maxRows > 0) {
+            this.limitRows = true;
+        }
     }
 }

test/parser/CsvParsingStream.test.ts

@@ -267,6 +267,24 @@ describe('CsvParserStream', () => {
         });
     });
 
+    describe('maxRows', () => {
+        it('should parse up to the specified number of maxRows', () => {
+            const maxRows = 3;
+            parseContentAndCollect(assets.withHeaders, { headers: true, maxRows }).then(({ count, rows }) => {
+                assert.deepStrictEqual(rows, assets.withHeaders.parsed.slice(0, maxRows));
+                assert.strictEqual(count, maxRows);
+            });
+        });
+
+        it('should parse all rows if maxRows === 0', () => {
+            const maxRows = 0;
+            parseContentAndCollect(assets.withHeaders, { headers: true, maxRows }).then(({ count, rows }) => {
+                assert.deepStrictEqual(rows, assets.withHeaders.parsed);
+                assert.strictEqual(count, rows.length);
+            });
+        });
+    });
+
     it('should emit an error for malformed rows', next => {
         assets.write(assets.malformed);
         const stream = csv.parseFile(assets.malformed.path, { headers: true });

test/parser/ParserOptions.test.ts

@@ -163,4 +163,24 @@ describe('ParserOptions', () => {
             assert.strictEqual(createOptions({ renameHeaders: false }).renameHeaders, false);
         });
     });
+
+    describe('#maxRows', () => {
+        it('should default maxRows 0 and limitRows to false', () => {
+            const opts = createOptions();
+            assert.strictEqual(opts.maxRows, 0);
+            assert.strictEqual(opts.limitRows, false);
+        });
+
+        it('should set maxRows to the provided option and limitRows to true if maxRows > 0', () => {
+            const opts = createOptions({ maxRows: 1 });
+            assert.strictEqual(opts.maxRows, 1);
+            assert.strictEqual(opts.limitRows, true);
+        });
+
+        it('should set maxRows to the provided option and limitRows to true if maxRows === 0', () => {
+            const opts = createOptions({ maxRows: 0 });
+            assert.strictEqual(opts.maxRows, 0);
+            assert.strictEqual(opts.limitRows, false);
+        });
+    });
 });