gistfile.patch

commit 5a7c615eea11ba4c540210c0a29c843da5def060
Author: isaacs <i@izs.me>
Date:   Tue Oct 27 11:07:00 2020 -0700

    Do not return 0-length buffer if stdio is inherited

diff --git a/README.md b/README.md
index 3b604f2..b569948 100644
--- a/README.md
+++ b/README.md
@@ -45,13 +45,18 @@ Result or error will be decorated with the properties in the `extra`
 object.  You can use this to attach some helpful info about _why_ the
 command is being run, if it makes sense for your use case.
 
+If `stdio` is set to anything other than `'inherit'`, then the result/error
+will be decorated with `stdout` and `stderr` values.  If `stdioString` is
+set to `true`, these will be strings.  Otherwise they will be Buffer
+objects.
+
 Returned promise is decorated with the `stdin` stream if the process is set
 to pipe from `stdin`.  Writing to this stream writes to the `stdin` of the
 spawned process.
 
 #### Options
 
-- `stdioString` Boolean, default `false`.  Return stdio/stderr output as
+- `stdioString` Boolean, default `false`.  Return stdout/stderr output as
   strings rather than buffers.
 - `cwd` String, default `process.cwd()`.  Current working directory for
   running the script.  Also the argument to `infer-owner` to determine
diff --git a/index.js b/index.js
index 809da93..cc73d1d 100644
--- a/index.js
+++ b/index.js
@@ -2,6 +2,11 @@ const {spawn} = require('child_process')
 
 const inferOwner = require('infer-owner')
 
+const isPipe = (stdio = 'pipe', fd) =>
+  stdio === 'pipe' || stdio === null ? true
+  : Array.isArray(stdio) ? isPipe(stdio[fd], fd)
+  : false
+
 // 'extra' object is for decorating the error a bit more
 const promiseSpawn = (cmd, args, opts, extra = {}) => {
   const cwd = opts.cwd || process.cwd()
@@ -20,13 +25,14 @@ const promiseSpawn = (cmd, args, opts, extra = {}) => {
   }, extra))
 }
 
-const stdioResult = (stdout, stderr, {stdioString}) =>
+const stdioResult = (stdout, stderr, {stdioString, stdio}) =>
   stdioString ? {
-    stdout: Buffer.concat(stdout).toString(),
-    stderr: Buffer.concat(stderr).toString(),
-  } : {
-    stdout: Buffer.concat(stdout),
-    stderr: Buffer.concat(stderr),
+    stdout: isPipe(stdio, 1) ? Buffer.concat(stdout).toString() : null,
+    stderr: isPipe(stdio, 2) ? Buffer.concat(stderr).toString() : null,
+  }
+  : {
+    stdout: isPipe(stdio, 1) ? Buffer.concat(stdout) : null,
+    stderr: isPipe(stdio, 2) ? Buffer.concat(stderr) : null,
   }
 
 const promiseSpawnUid = (cmd, args, opts, extra) => {
diff --git a/test/promise-spawn.js b/test/promise-spawn.js
index a34f565..5a79fe2 100644
--- a/test/promise-spawn.js
+++ b/test/promise-spawn.js
@@ -4,15 +4,20 @@ const Minipass = require('minipass')
 const EE = require('events')
 const fs = require('fs')
 
+const isPipe = (stdio = 'pipe', fd) =>
+  stdio === 'pipe' || stdio === null ? true
+  : Array.isArray(stdio) ? isPipe(stdio[fd], fd)
+  : false
+
 class MockProc extends EE {
   constructor (cmd, args, opts) {
     super()
     this.cmd = cmd
     this.args = args
     this.opts = opts
-    this.stdout = opts.stdio === 'inherit' ? null : new Minipass()
-    this.stderr = opts.stdio === 'inherit' ? null : new Minipass()
-    this.stdin = opts.stdio === 'inherit' ? null : new Minipass()
+    this.stdin = isPipe(opts.stdio, 0) ? new Minipass() : null
+    this.stdout = isPipe(opts.stdio, 1) ? new Minipass() : null
+    this.stderr = isPipe(opts.stdio, 2) ? new Minipass() : null
     this.code = null
     this.signal = null
     process.nextTick(() => this.run())
@@ -111,8 +116,24 @@ t.test('pass', t => t.resolveMatch(promiseSpawn('pass', [], {stdioString: true},
 t.test('pass, share stdio', t => t.resolveMatch(promiseSpawn('pass', [], { stdio: 'inherit'}, {a: 1}), {
   code: 0,
   signal: null,
-  stdout: Buffer.alloc(0),
-  stderr: Buffer.alloc(0),
+  stdout: null,
+  stderr: null,
+  a: 1,
+}))
+
+t.test('pass, share stdout', t => t.resolveMatch(promiseSpawn('pass', [], { stdioString: true, stdio: ['pipe', 'inherit', 'pipe']}, {a: 1}), {
+  code: 0,
+  signal: null,
+  stdout: null,
+  stderr: '',
+  a: 1,
+}))
+
+t.test('pass, share stderr', t => t.resolveMatch(promiseSpawn('pass', [], { stdioString: true, stdio: ['pipe', 'pipe', 'inherit']}, {a: 1}), {
+  code: 0,
+  signal: null,
+  stdout: 'OK :)',
+  stderr: null,
   a: 1,
 }))
 
@@ -129,8 +150,8 @@ t.test('fail, shared stdio', t => t.rejects(promiseSpawn('fail', [], { stdio: 'i
   message: 'command failed',
   code: 1,
   signal: null,
-  stdout: Buffer.alloc(0),
-  stderr: Buffer.alloc(0),
+  stdout: null,
+  stderr: null,
   a: 1,
 }))