process: allow reading from stdout/stderr sockets

Allow reading from stdio streams that are conventionally
associated with process output, since this is only convention.

This involves disabling the oddness around closing stdio
streams. Its purpose is to prevent the file descriptors
0 through 2 from being closed, since doing so can lead
to information leaks when new file descriptors are being
opened; instead, not doing anything seems like a more
reasonable choice.

Fixes: nodejs#21203

doc/api/errors.md

@@ -1552,12 +1552,28 @@ A call was made and the UDP subsystem was not running.
 
 <a id="ERR_STDERR_CLOSE"></a>
 ### ERR_STDERR_CLOSE
+<!-- YAML
+changes:
+  - version: REPLACEME
+    pr-url: https://github.com/nodejs/node/pull/???
+    description: Rather than emitting an error, `process.stderr.end()` now
+                 only closes the stream side but not the underlying resource,
+                 making this error obsolete.
+-->
 
 An attempt was made to close the `process.stderr` stream. By design, Node.js
 does not allow `stdout` or `stderr` streams to be closed by user code.
 
 <a id="ERR_STDOUT_CLOSE"></a>
 ### ERR_STDOUT_CLOSE
+<!-- YAML
+changes:
+  - version: REPLACEME
+    pr-url: https://github.com/nodejs/node/pull/???
+    description: Rather than emitting an error, `process.stderr.end()` now
+                 only closes the stream side but not the underlying resource,
+                 making this error obsolete.
+-->
 
 An attempt was made to close the `process.stdout` stream. By design, Node.js
 does not allow `stdout` or `stderr` streams to be closed by user code.

doc/api/process.md

@@ -1860,9 +1860,7 @@ important ways:
 
 1. They are used internally by [`console.log()`][] and [`console.error()`][],
    respectively.
-2. They cannot be closed ([`end()`][] will throw).
-3. They will never emit the [`'finish'`][] event.
-4. Writes may be synchronous depending on what the stream is connected to
+2. Writes may be synchronous depending on what the stream is connected to
    and whether the system is Windows or POSIX:
    - Files: *synchronous* on Windows and POSIX
    - TTYs (Terminals): *asynchronous* on Windows, *synchronous* on POSIX
@@ -2087,7 +2085,6 @@ cases:
   code will be `128` + `6`, or `134`.
 
 [`'exit'`]: #process_event_exit
-[`'finish'`]: stream.html#stream_event_finish
 [`'message'`]: child_process.html#child_process_event_message
 [`'rejectionHandled'`]: #process_event_rejectionhandled
 [`'uncaughtException'`]: #process_event_uncaughtexception
@@ -2101,7 +2098,6 @@ cases:
 [`console.error()`]: console.html#console_console_error_data_args
 [`console.log()`]: console.html#console_console_log_data_args
 [`domain`]: domain.html
-[`end()`]: stream.html#stream_writable_end_chunk_encoding_callback
 [`net.Server`]: net.html#net_class_net_server
 [`net.Socket`]: net.html#net_class_net_socket
 [`NODE_OPTIONS`]: cli.html#cli_node_options_options

lib/internal/errors.js

@@ -810,8 +810,6 @@ E('ERR_SOCKET_BUFFER_SIZE',
 E('ERR_SOCKET_CANNOT_SEND', 'Unable to send data', Error);
 E('ERR_SOCKET_CLOSED', 'Socket is closed', Error);
 E('ERR_SOCKET_DGRAM_NOT_RUNNING', 'Not running', Error);
-E('ERR_STDERR_CLOSE', 'process.stderr cannot be closed', Error);
-E('ERR_STDOUT_CLOSE', 'process.stdout cannot be closed', Error);
 E('ERR_STREAM_CANNOT_PIPE', 'Cannot pipe, not readable', Error);
 E('ERR_STREAM_DESTROYED', 'Cannot call %s after a stream was destroyed', Error);
 E('ERR_STREAM_NULL_VALUES', 'May not write null values to stream', TypeError);

lib/internal/process/stdio.js

@@ -1,15 +1,15 @@
 'use strict';
 
 const {
-  ERR_STDERR_CLOSE,
-  ERR_STDOUT_CLOSE,
   ERR_UNKNOWN_STDIN_TYPE,
   ERR_UNKNOWN_STREAM_TYPE
 } = require('internal/errors').codes;
 
 exports.setupProcessStdio = setupProcessStdio;
 exports.getMainThreadStdio = getMainThreadStdio;
 
+function dummyDestroy(err, cb) { cb(err); }
+
 function getMainThreadStdio() {
   var stdin;
   var stdout;
@@ -19,11 +19,8 @@ function getMainThreadStdio() {
     if (stdout) return stdout;
     stdout = createWritableStdioStream(1);
     stdout.destroySoon = stdout.destroy;
-    stdout._destroy = function(er, cb) {
-      // Avoid errors if we already emitted
-      er = er || new ERR_STDOUT_CLOSE();
-      cb(er);
-    };
+    // Override _destroy so that the fd is never actually closed.
+    stdout._destroy = dummyDestroy;
     if (stdout.isTTY) {
       process.on('SIGWINCH', () => stdout._refreshSize());
     }
@@ -34,11 +31,8 @@ function getMainThreadStdio() {
     if (stderr) return stderr;
     stderr = createWritableStdioStream(2);
     stderr.destroySoon = stderr.destroy;
-    stderr._destroy = function(er, cb) {
-      // Avoid errors if we already emitted
-      er = er || new ERR_STDERR_CLOSE();
-      cb(er);
-    };
+    // Override _destroy so that the fd is never actually closed.
+    stdout._destroy = dummyDestroy;
     if (stderr.isTTY) {
       process.on('SIGWINCH', () => stderr._refreshSize());
     }

test/parallel/test-stdout-cannot-be-closed-child-process-pipe.js

@@ -24,9 +24,9 @@ function parent() {
   });
 
   child.on('close', function(code, signal) {
-    assert(code);
+    assert.strictEqual(code, 0);
+    assert.strictEqual(err, '');
     assert.strictEqual(out, 'foo');
-    assert(/process\.stdout cannot be closed/.test(err));
     console.log('ok');
   });
 }

test/pseudo-tty/test-stdout-read.in

@@ -0,0 +1 @@
+Hello!

test/pseudo-tty/test-stdout-read.js

@@ -0,0 +1,3 @@
+'use strict';
+const common = require('../common');
+process.stderr.on('data', common.mustCall(console.log));

test/pseudo-tty/test-stdout-read.out

@@ -0,0 +1 @@
+<Buffer 48 65 6c 6c 6f 21 0a>