Add bufferLines option to ChildProcess.exec

It ensures that stdout and stderr callbacks are triggered with whole lines

spec/stdlib/child-process-spec.coffee

@@ -1,7 +1,13 @@
 ChildProcess = require 'child-process'
 
-fdescribe 'Child Processes', ->
+describe 'Child Processes', ->
   describe ".exec(command, options)", ->
+    [stderrHandler, stdoutHandler] = []
+
+    beforeEach ->
+      stderrHandler = jasmine.createSpy "stderrHandler"
+      stdoutHandler = jasmine.createSpy "stdoutHandler"
+
     it "returns a promise that resolves to stdout and stderr", ->
       waitsForPromise ->
         cmd = "echo 'good' && echo 'bad' >&2"
@@ -9,23 +15,8 @@ fdescribe 'Child Processes', ->
           expect(stdout).toBe 'good\n'
           expect(stderr).toBe 'bad\n'
 
-    describe "when `options` contains a stdout function", ->
-      it "calls the stdout function when new data is received", ->
-        stderrHandler = jasmine.createSpy "stderrHandler"
-
-        cmd = "echo '1111' >&2 && sleep .1 && echo '2222' >&2"
-        ChildProcess.exec(cmd, stderr: stderrHandler)
-
-        waitsFor ->
-          stderrHandler.callCount > 1
-
-        runs ->
-          expect(stderrHandler.argsForCall[0][0]).toBe "1111\n"
-          expect(stderrHandler.argsForCall[1][0]).toBe "2222\n"
-
-      it "calls the stderr function when new data is received", ->
-        stdoutHandler = jasmine.createSpy "stdoutHandler"
-
+    describe "when `options` contains stdout/stderror callbacks", ->
+      it "calls the stdout callback when new data is received on stdout", ->
         cmd = "echo 'first' && sleep .1 && echo 'second' && sleep .1 && echo 'third'"
         ChildProcess.exec(cmd, stdout: stdoutHandler)
 
@@ -37,11 +28,66 @@ fdescribe 'Child Processes', ->
           expect(stdoutHandler.argsForCall[1][0]).toBe "second\n"
           expect(stdoutHandler.argsForCall[2][0]).toBe "third\n"
 
+      it "calls the stderr callback when new data is received on stderr", ->
+        cmd = "echo '1111' >&2 && sleep .1 && echo '2222' >&2"
+        ChildProcess.exec(cmd, stderr: stderrHandler)
+
+        waitsFor ->
+          stderrHandler.callCount > 1
+
+        runs ->
+          expect(stderrHandler.argsForCall[0][0]).toBe "1111\n"
+          expect(stderrHandler.argsForCall[1][0]).toBe "2222\n"
+
+      describe "when the `bufferLines` option is true ", ->
+        [simulateStdout, simulateStderr] = []
+
+        beforeEach ->
+          spyOn($native, 'exec')
+          ChildProcess.exec("print_the_things", bufferLines: true, stdout: stdoutHandler, stderr: stderrHandler)
+          { stdout, stderr } = $native.exec.argsForCall[0][1]
+          simulateStdout = stdout
+          simulateStderr = stderr
+
+        it "only triggers stdout callbacks with complete lines", ->
+          simulateStdout """
+            I am a full line
+            I am part of """
+
+          expect(stdoutHandler).toHaveBeenCalledWith("I am a full line\n")
+          stdoutHandler.reset()
+
+          simulateStdout """
+            a line
+            I am another full line\n
+          """
+
+          expect(stdoutHandler).toHaveBeenCalledWith """
+            I am part of a line
+            I am another full line\n
+          """
+
+        it "only triggers stderr callbacks with complete lines", ->
+          simulateStderr """
+            I am a full line
+            I am part of """
+
+          expect(stderrHandler).toHaveBeenCalledWith("I am a full line\n")
+          stdoutHandler.reset()
+
+          simulateStderr """
+            a line
+            I am another full line\n
+          """
+
+          expect(stderrHandler).toHaveBeenCalledWith """
+            I am part of a line
+            I am another full line\n
+          """
+
     describe "when the command fails", ->
       it "executes the callback with error set to the exit status", ->
         waitsForPromise ->
           cmd = "exit 2"
           ChildProcess.exec(cmd).fail (error) ->
             expect(error.exitStatus).toBe 2
-
-

src/stdlib/child-process.coffee

@@ -8,6 +8,11 @@ module.exports =
 class ChildProccess
   @exec: (command, options={}) ->
     deferred = $.Deferred()
+
+    if options.bufferLines
+      options.stdout = @bufferLines(options.stdout) if options.stdout
+      options.stderr = @bufferLines(options.stderr) if options.stderr
+
     $native.exec command, options, (exitStatus, stdout, stdin) ->
       if error != 0
         error = new Error("Exec failed (#{exitStatus}) command '#{command}'")
@@ -18,3 +23,11 @@ class ChildProccess
 
     deferred
 
+  @bufferLines: (callback) ->
+    buffered = ""
+    (data) ->
+      buffered += data
+      lastNewlineIndex = buffered.lastIndexOf('\n')
+      if lastNewlineIndex >= 0
+        callback(buffered.substring(0, lastNewlineIndex + 1))
+        buffered = buffered.substring(lastNewlineIndex + 1)