refactor: start() should throw if filename doesn't exist

BREAKING CHANGE: Error handling for `start` is changing.

Since `start` is an `async` function, one would expect to
be able to try/catch it. The original version ran any
failures through the `quit` method, but it's designed to
fail gracefully and work asynchronously by using `'error'`
events. This causes weird flow issues if  `start` is throwing·
because the filename does not exist. This change allows
`start` to simply throw.

Semver: major
Ref: LOG-8030

Author: darinspivey

README.md

@@ -66,9 +66,12 @@ const tail = new TailFile('/path/to/your/logfile.txt', {encoding: 'utf8'})
   .on('data', (chunk) => {
     console.log(`Recieved a utf8 character chunk: ${chunk}`)
   })
-  .on('error', (err) => {
+  .on('tail_error', (err) => {
     console.error('TailFile had an error!', err)
   })
+  .on('error', (err) => {
+    console.error('A TailFile stream error was likely encountered', err)
+  })
   .start()
   .catch((err) => {
     console.error('Cannot start.  Does the file exist?', err)
@@ -86,12 +89,14 @@ const TailFile = require('@logdna/tail-file')
 const LineSplitter = require('your-line-splitter') // There are many of these in the wild
 
 const tail = new TailFile('/path/to/your/logfile.txt')
-  .on('error', (err) => {
+  .on('tail_error', (err) => {
     console.error('TailFile had an error!', err)
+    throw err
   })
   .start()
   .catch((err) => {
     console.error('Cannot start.  Does the file exist?', err)
+    throw err
   })
 
 // Data won't start flowing until piping
@@ -111,23 +116,33 @@ recommended since it will edge out `readline` slightly in performance.
 
 ```js
 const readline = require('readline')
-const tail = new TailFile('./somelog.txt')
-  .on('error', (err) => {
-    console.error('TailFile had an error!', err)
-  })
-  .start()
-  .catch((err) => {
-    console.error('Cannot start.  Does the file exist?', err)
-})
+const TailFile = require('@logdna/tail-file')
 
-const linesplitter = readline.createInterface({
-  input: tail
-})
+async function startTail() {
+  const tail = new TailFile('./somelog.txt')
+    .on('tail_error', (err) => {
+      console.error('TailFile had an error!', err)
+    })
+
+  try {
+    await tail.start()
+    const linesplitter = readline.createInterface({
+      input: tail
+    })
+
+    linesplitter.on('line', (line) => {
+      console.log(line)
+    })
+  } catch (err) {
+    console.error('Cannot start.  Does the file exist?', err)
+  }
+}
 
-linesplitter.on('line', (line) => {
-  console.log(line)
+startTail().catch((err) => {
+  process.nextTick(() => {
+    throw err
+  })
 })
-
 ```
 
 ## Events
@@ -242,8 +257,7 @@ Useful settings such as `encoding: 'utf8'` can be used this way.
 ### `tail.start()`
 
 * Returns: [`<Promise>`][] - Resolves after the file is polled successfully
-* Emits: [`<Error>`][] and [other `Readable` events](#event-any-readable-event)
-* Rejects: If `filename` is not found, the promise is rejected
+* Rejects: If `filename` is not found
 
 Calling `start()` begins the polling of `filename` to watch for added/changed bytes.
 `start()` may be called before or after data is set up to be consumed with a

lib/tail-file.js

@@ -107,12 +107,8 @@ class TailFile extends Readable {
   }
 
   async start() {
-    try {
-      await this._openFile()
-      await this._pollFileForChanges()
-    } catch (err) {
-      return this.quit(err)
-    }
+    await this._openFile()
+    await this._pollFileForChanges()
     return
   }
 

test/tail-file.js

@@ -324,23 +324,14 @@ test('Success: startPos can be provided to start tailing at a given place', (t)
   })
 })
 
-test('Error: filename provided does not exist (poll error)', (t) => {
-  t.plan(3)
-
-  const tail = new TailFile('THISFILEDOSNOTEXIST', {maxPollFailures: 1})
-    .on('error', (err) => {
-      t.type(err, Error, 'error was emitted')
-      t.match(err, {
-        name: 'Error'
-      , code: 'ENOENT'
-      , path: 'THISFILEDOSNOTEXIST'
-      , message: /no such file or directory/
-      })
-    })
-
-  t.test('Start', async (tt) => {
-    await tail.start()
-  })
+test('Error: filename provided does not exist (throws on start)', async (t) => {
+  const tail = new TailFile('THISFILEDOSNOTEXIST')
+  await t.rejects(tail.start(), {
+    name: 'Error'
+  , code: 'ENOENT'
+  , path: 'THISFILEDOSNOTEXIST'
+  , message: /no such file or directory/
+  }, 'Expected error is thrown')
 })
 
 test('Error: poll error will retry a certain number of times', (t) => {