repl: break on sigint/ctrl+c

Adds the ability to stop execution of the current REPL command
when receiving SIGINT. This applies only to the default eval
function.
Fixes: #6612
PR-URL: #6635
Reviewed-By: Ben Noordhuis <info@bnoordhuis.nl>

Author: addaleax

doc/api/repl.md

@@ -390,6 +390,9 @@ added: v0.1.91
  equivalent to prefacing every repl statement with `'use strict'`.
 *`repl.REPL_MODE_MAGIC` - attempt to evaluates expressions in default
  mode. If expressions fail to parse, re-try in strict mode.
+*`breakEvalOnSigint` - Stop evaluating the current piece of code when
+`SIGINT` is received, i.e. `Ctrl+C` is pressed. This cannot be used together
+ with a custom `eval` function. Defaults to `false`.
 
 The `repl.start()` method creates and starts a `repl.REPLServer` instance.
 

lib/internal/repl.js

@@ -22,7 +22,8 @@ function createRepl(env, opts, cb) {
 opts=opts||{
 ignoreUndefined: false,
 terminal: process.stdout.isTTY,
-useGlobal: true
+useGlobal: true,
+breakEvalOnSigint: true
 };
 
 if(parseInt(env.NODE_NO_READLINE)){

lib/repl.js

@@ -24,6 +24,7 @@
 constinternalModule=require('internal/module');
 constinternalUtil=require('internal/util');
 constutil=require('util');
+constutilBinding=process.binding('util');
 constinherits=util.inherits;
 constStream=require('stream');
 constvm=require('vm');
@@ -178,7 +179,7 @@ function REPLServer(prompt,
 replMode);
 }
 
-varoptions,input,output,dom;
+varoptions,input,output,dom,breakEvalOnSigint;
 if(prompt!==null&&typeofprompt==='object'){
 // an options object was given
 options=prompt;
@@ -191,10 +192,17 @@ function REPLServer(prompt,
 prompt=options.prompt;
 dom=options.domain;
 replMode=options.replMode;
+breakEvalOnSigint=options.breakEvalOnSigint;
 }else{
 options={};
 }
 
+if(breakEvalOnSigint&&eval_){
+// Allowing this would not reflect user expectations.
+// breakEvalOnSigint affects only the behaviour of the default eval().
+thrownewError('Cannot specify both breakEvalOnSigint and eval for REPL');
+}
+
 varself=this;
 
 self._domain=dom||domain.create();
@@ -204,6 +212,7 @@ function REPLServer(prompt,
 self.replMode=replMode||exports.REPL_MODE_SLOPPY;
 self.underscoreAssigned=false;
 self.last=undefined;
+self.breakEvalOnSigint=!!breakEvalOnSigint;
 
 self._inTemplateLiteral=false;
 
@@ -267,14 +276,46 @@ function REPLServer(prompt,
 regExMatcher.test(savedRegExMatches.join(sep));
 
 if(!err){
+// Unset raw mode during evaluation so that Ctrl+C raises a signal.
+letpreviouslyInRawMode;
+if(self.breakEvalOnSigint){
+// Start the SIGINT watchdog before entering raw mode so that a very
+// quick Ctrl+C doesn’t lead to aborting the process completely.
+utilBinding.startSigintWatchdog();
+previouslyInRawMode=self._setRawMode(false);
+}
+
 try{
-if(self.useGlobal){
-result=script.runInThisContext({displayErrors: false});
-}else{
-result=script.runInContext(context,{displayErrors: false});
+try{
+constscriptOptions={
+displayErrors: false,
+breakOnSigint: self.breakEvalOnSigint
+};
+
+if(self.useGlobal){
+result=script.runInThisContext(scriptOptions);
+}else{
+result=script.runInContext(context,scriptOptions);
+}
+}finally{
+if(self.breakEvalOnSigint){
+// Reset terminal mode to its previous value.
+self._setRawMode(previouslyInRawMode);
+
+// Returns true if there were pending SIGINTs *after* the script
+// has terminated without being interrupted itself.
+if(utilBinding.stopSigintWatchdog()){
+self.emit('SIGINT');
+}
+}
 }
 }catch(e){
 err=e;
+if(err.message==='Script execution interrupted.'){
+// The stack trace for this case is not very useful anyway.
+Object.defineProperty(err,'stack',{value: ''});
+}
+
 if(err&&process.domain){
 debug('not recoverable, send to domain');
 process.domain.emit('error',err);

test/parallel/test-repl-sigint-nested-eval.js

@@ -0,0 +1,50 @@
+'use strict';
+constcommon=require('../common');
+constassert=require('assert');
+
+constspawn=require('child_process').spawn;
+
+if(process.platform==='win32'){
+// No way to send CTRL_C_EVENT to processes from JS right now.
+common.skip('platform not supported');
+return;
+}
+
+process.env.REPL_TEST_PPID=process.pid;
+constchild=spawn(process.execPath,['-i'],{
+stdio: [null,null,2]
+});
+
+letstdout='';
+child.stdout.setEncoding('utf8');
+child.stdout.pipe(process.stdout);
+child.stdout.on('data',function(c){
+stdout+=c;
+});
+
+child.stdin.write=((original)=>{
+return(chunk)=>{
+process.stderr.write(chunk);
+returnoriginal.call(child.stdin,chunk);
+};
+})(child.stdin.write);
+
+child.stdout.once('data',common.mustCall(()=>{
+process.on('SIGUSR2',common.mustCall(()=>{
+process.kill(child.pid,'SIGINT');
+child.stdout.once('data',common.mustCall(()=>{
+// Make sure REPL still works.
+child.stdin.end('"foobar"\n');
+}));
+}));
+
+child.stdin.write('process.kill(+process.env.REPL_TEST_PPID, "SIGUSR2");'+
+'vm.runInThisContext("while(true){}", '+
+'{ breakOnSigint: true });\n');
+}));
+
+child.on('close',function(code){
+assert.strictEqual(code,0);
+assert.notStrictEqual(stdout.indexOf('Script execution interrupted.'),-1);
+assert.notStrictEqual(stdout.indexOf('foobar'),-1);
+});

test/parallel/test-repl-sigint.js

@@ -0,0 +1,50 @@
+'use strict';
+constcommon=require('../common');
+constassert=require('assert');
+
+constspawn=require('child_process').spawn;
+
+if(process.platform==='win32'){
+// No way to send CTRL_C_EVENT to processes from JS right now.
+common.skip('platform not supported');
+return;
+}
+
+process.env.REPL_TEST_PPID=process.pid;
+constchild=spawn(process.execPath,['-i'],{
+stdio: [null,null,2]
+});
+
+letstdout='';
+child.stdout.setEncoding('utf8');
+child.stdout.pipe(process.stdout);
+child.stdout.on('data',function(c){
+stdout+=c;
+});
+
+child.stdin.write=((original)=>{
+return(chunk)=>{
+process.stderr.write(chunk);
+returnoriginal.call(child.stdin,chunk);
+};
+})(child.stdin.write);
+
+child.stdout.once('data',common.mustCall(()=>{
+process.on('SIGUSR2',common.mustCall(()=>{
+process.kill(child.pid,'SIGINT');
+child.stdout.once('data',common.mustCall(()=>{
+// Make sure state from before the interruption is still available.
+child.stdin.end('a*2*3*7\n');
+}));
+}));
+
+child.stdin.write('a = 1001;'+
+'process.kill(+process.env.REPL_TEST_PPID, "SIGUSR2");'+
+'while(true){}\n');
+}));
+
+child.on('close',function(code){
+assert.strictEqual(code,0);
+assert.notStrictEqual(stdout.indexOf('Script execution interrupted.\n'),-1);
+assert.notStrictEqual(stdout.indexOf('42042\n'),-1);
+});