shell: add option for maxLines

src/shell.js

@@ -22,6 +22,19 @@ function shell(tag) {
 
 const SUDO = '/usr/bin/sudo';
 
+function lineCount(buffer) {
+    assert(Buffer.isBuffer(buffer));
+
+    const NEW_LINE = Buffer.from('\n');
+    let index = buffer.indexOf(NEW_LINE);
+    let count = 0;
+    while (index >= 0) {
+        index = buffer.indexOf(NEW_LINE, index+1);
+        ++count;
+    }
+    return count;
+}
+
 function spawn(tag, file, args, options) {
     assert.strictEqual(typeof tag, 'string');
     assert.strictEqual(typeof file, 'string');
@@ -30,12 +43,23 @@ function spawn(tag, file, args, options) {
 
     debug(`${tag}: ${file} ${args.join(' ').replace(/\n/g, '\\n')}`);
 
+    const maxLines = options.maxLines || Number.MAX_SAFE_INTEGER;
+
     return new Promise((resolve, reject) => {
         const cp = child_process.spawn(file, args, options);
         const stdoutBuffers = [], stderrBuffers = [];
+        let stdoutLineCount = 0, stderrLineCount = 0;
 
-        cp.stdout.on('data', (data) => stdoutBuffers.push(data));
-        cp.stderr.on('data', (data) => stderrBuffers.push(data));
+        cp.stdout.on('data', (data) => {
+            stdoutBuffers.push(data);
+            stdoutLineCount += lineCount(data);
+            if (stdoutLineCount >= maxLines) return cp.kill('SIGKILL');
+        });
+        cp.stderr.on('data', (data) => {
+            stderrBuffers.push(data);
+            stderrLineCount += lineCount(data);
+            if (stderrLineCount >= maxLines) return cp.kill('SIGKILL');
+        });
 
         cp.on('close', function (code, signal) { // always called. after 'exit' or 'error'
             const stdoutBuffer = Buffer.concat(stdoutBuffers);
@@ -47,7 +71,9 @@ function spawn(tag, file, args, options) {
 
             const e = new BoxError(BoxError.SHELL_ERROR, `${file} exited with code ${code} signal ${signal}`);
             e.stdout = stdout; // when promisified, this is the way to get stdout
+            e.stdoutLineCount = stdoutLineCount;
             e.stderr = stderr; // when promisified, this is the way to get stderr
+            e.stderrLineCount = stderrLineCount;
             e.code = code;
             e.signal = signal;