Handle parser errors without crashing

README.md

@@ -315,7 +315,7 @@ Fires when the process has been terminated, with an error or not.
 
 #### event: `pythonError`
 
-Fires when the process terminates with a non-zero exit code.
+Fires when the process terminates with a non-zero exit code or an output parser throws before normal completion. Parser exceptions are also passed to `.end()` and reject `PythonShell.run()`.
 
 #### event: `error`
 

index.ts

@@ -169,6 +169,7 @@ export class PythonShell extends EventEmitter {
 
     let self = this;
     let errorData = '';
+    let parserError: Error;
     EventEmitter.call(this);
 
     options = <Options>extend({}, PythonShell.defaultOptions, options);
@@ -205,7 +206,15 @@ export class PythonShell extends EventEmitter {
       // note that setting the encoding turns the chunk into a string
       stdoutSplitter.setEncoding(options.encoding || 'utf8');
       this.stdout.pipe(stdoutSplitter).on('data', (chunk: string) => {
-        this.emit('message', self.parser(chunk));
+        if (parserError) return;
+        let parsedChunk: any;
+        try {
+          parsedChunk = self.parser(chunk);
+        } catch (err) {
+          parserError = err instanceof Error ? err : new Error(String(err));
+          return;
+        }
+        this.emit('message', parsedChunk);
       });
     }
 
@@ -215,7 +224,15 @@ export class PythonShell extends EventEmitter {
       // note that setting the encoding turns the chunk into a string
       stderrSplitter.setEncoding(options.encoding || 'utf8');
       this.stderr.pipe(stderrSplitter).on('data', (chunk: string) => {
-        this.emit('stderr', self.stderrParser(chunk));
+        if (parserError) return;
+        let parsedChunk: any;
+        try {
+          parsedChunk = self.stderrParser(chunk);
+        } catch (err) {
+          parserError = err instanceof Error ? err : new Error(String(err));
+          return;
+        }
+        this.emit('stderr', parsedChunk);
       });
     }
 
@@ -266,6 +283,12 @@ export class PythonShell extends EventEmitter {
             'process exited with code ' + self.exitCode,
           );
         }
+      } else if (parserError) {
+        err = new PythonShellError(parserError.message);
+        err.stack = parserError.stack;
+      }
+
+      if (err) {
         err = <PythonShellError>extend(err, {
           executable: pythonPath,
           options: pythonOptions.length ? pythonOptions : null,

test/test-python-shell.ts

@@ -1,5 +1,5 @@
 import * as should from 'should';
-import { PythonShell } from '..';
+import { NewlineTransformer, PythonShell } from '..';
 import { sep, join } from 'path';
 import { EOL as newline } from 'os';
 import { chdir, cwd } from 'process';
@@ -415,6 +415,51 @@ describe('PythonShell', function () {
         })
         .end(done);
     });
+    it('should report JSON parser errors through the end callback', function (done) {
+      let pyshell = new PythonShell('echo_text.py', {
+        mode: 'json',
+        formatter: 'text',
+      });
+      pyshell.send('not-json').end(function (err) {
+        should.exist(err);
+        err.should.be.an.Error;
+        err.message.should.match(/JSON|Unexpected token/);
+        done();
+      });
+    });
+    it('should not treat message listener exceptions as parser errors', function (done) {
+      let splitter = new NewlineTransformer();
+      let pyshell = new PythonShell('exit-code.py', { mode: 'text' }, splitter);
+      let listenerError = new Error('message listener failed');
+      let thrownError: Error;
+
+      pyshell.on('message', function () {
+        throw listenerError;
+      });
+
+      try {
+        splitter.emit('data', 'hello');
+      } catch (err) {
+        thrownError = err;
+      }
+
+      should.exist(thrownError);
+      thrownError.should.be.exactly(listenerError);
+      pyshell.end(function (err) {
+        should.not.exist(err);
+        done();
+      });
+    });
+    it('should prefer process errors over parser errors on non-zero exit', function (done) {
+      PythonShell.run('echo_hi_then_error.py', { mode: 'json' }).then(
+        () => done('expected the process to reject'),
+        (err) => {
+          err.message.should.be.exactly('Exception: fibble-fah');
+          err.stack.should.containEql('----- Python Traceback -----');
+          done();
+        },
+      );
+    });
     it('should properly buffer partial messages', function (done) {
       // echo_text_with_newline_control echoes text with $'s replaced with newlines
       let pyshell = new PythonShell('echo_text_with_newline_control.py', {
@@ -494,6 +539,46 @@ describe('PythonShell', function () {
         .send('world')
         .end(done);
     });
+    it('should report stderr parser errors through the end callback', function (done) {
+      let pyshell = new PythonShell('stderrLogging.py', {
+        stderrParser: function () {
+          throw new Error('stderr parser failed');
+        },
+      });
+      pyshell.end(function (err) {
+        should.exist(err);
+        err.message.should.be.exactly('stderr parser failed');
+        done();
+      });
+    });
+    it('should not treat stderr listener exceptions as parser errors', function (done) {
+      let splitter = new NewlineTransformer();
+      let pyshell = new PythonShell(
+        'exit-code.py',
+        { mode: 'text' },
+        null,
+        splitter,
+      );
+      let listenerError = new Error('stderr listener failed');
+      let thrownError: Error;
+
+      pyshell.on('stderr', function () {
+        throw listenerError;
+      });
+
+      try {
+        splitter.emit('data', 'hello');
+      } catch (err) {
+        thrownError = err;
+      }
+
+      should.exist(thrownError);
+      thrownError.should.be.exactly(listenerError);
+      pyshell.end(function (err) {
+        should.not.exist(err);
+        done();
+      });
+    });
     it('should not be invoked when mode is "binary"', function (done) {
       let pyshell = new PythonShell('stderrLogging.py', {
         stderrParser: 'binary',