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child_process: truncate output when maxBuffer is exceeded

Preserves truncated output for `child_process.exec()` when `maxBuffer`
is exceeded.

This is particularly useful for commands which have indistinguishable
error codes for what output they produce.

PR-URL: #24951
Reviewed-By: Ruben Bridgewater <ruben@bridgewater.de>
Reviewed-By: Anna Henningsen <anna@addaleax.net>
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Fishrock123 committed Dec 11, 2018
1 parent 5f86682 commit e47f972d6851b3196b3b2ba611929f25a5fcadb6
Showing with 45 additions and 16 deletions.
  1. +12 −8 doc/api/child_process.md
  2. +14 −2 lib/child_process.js
  3. +19 −6 test/parallel/test-child-process-exec-maxBuffer.js
@@ -147,8 +147,9 @@ changes:
`'/bin/sh'` on UNIX, `process.env.ComSpec` on Windows.
* `timeout` {number} **Default:** `0`
* `maxBuffer` {number} Largest amount of data in bytes allowed on stdout or
stderr. If exceeded, the child process is terminated. See caveat at
[`maxBuffer` and Unicode][]. **Default:** `200 * 1024`.
stderr. If exceeded, the child process is terminated and any output is
truncated. See caveat at [`maxBuffer` and Unicode][].
**Default:** `200 * 1024`.
* `killSignal` {string|integer} **Default:** `'SIGTERM'`
* `uid` {number} Sets the user identity of the process (see setuid(2)).
* `gid` {number} Sets the group identity of the process (see setgid(2)).
@@ -245,8 +246,9 @@ changes:
* `encoding` {string} **Default:** `'utf8'`
* `timeout` {number} **Default:** `0`
* `maxBuffer` {number} Largest amount of data in bytes allowed on stdout or
stderr. If exceeded, the child process is terminated. See caveat at
[`maxBuffer` and Unicode][]. **Default:** `200 * 1024`.
stderr. If exceeded, the child process is terminated and any output is
truncated. See caveat at [`maxBuffer` and Unicode][].
**Default:** `200 * 1024`.
* `killSignal` {string|integer} **Default:** `'SIGTERM'`
* `uid` {number} Sets the user identity of the process (see setuid(2)).
* `gid` {number} Sets the group identity of the process (see setgid(2)).
@@ -779,8 +781,9 @@ changes:
* `killSignal` {string|integer} The signal value to be used when the spawned
process will be killed. **Default:** `'SIGTERM'`.
* `maxBuffer` {number} Largest amount of data in bytes allowed on stdout or
stderr. If exceeded, the child process is terminated. See caveat at
[`maxBuffer` and Unicode][]. **Default:** `200 * 1024`.
stderr. If exceeded, the child process is terminated and any output is
truncated. See caveat at [`maxBuffer` and Unicode][].
**Default:** `200 * 1024`.
* `encoding` {string} The encoding used for all stdio inputs and outputs.
**Default:** `'buffer'`.
* `windowsHide` {boolean} Hide the subprocess console window that would
@@ -842,8 +845,9 @@ changes:
* `killSignal` {string|integer} The signal value to be used when the spawned
process will be killed. **Default:** `'SIGTERM'`.
* `maxBuffer` {number} Largest amount of data in bytes allowed on stdout or
stderr. If exceeded, the child process is terminated. See caveat at
[`maxBuffer` and Unicode][]. **Default:** `200 * 1024`.
stderr. If exceeded, the child process is terminated and any output is
truncated. See caveat at [`maxBuffer` and Unicode][].
**Default:** `200 * 1024`.
* `encoding` {string} The encoding used for all stdio inputs and outputs.
**Default:** `'buffer'`.
* `shell` {boolean|string} If `true`, runs `command` inside of a shell. Uses
@@ -343,9 +343,15 @@ exports.execFile = function execFile(file /* , args, options, callback */) {

child.stdout.on('data', function onChildStdout(chunk) {
var encoding = child.stdout._readableState.encoding;
stdoutLen += encoding ? Buffer.byteLength(chunk, encoding) : chunk.length;
const length = encoding ?
Buffer.byteLength(chunk, encoding) :
chunk.length;
stdoutLen += length;

if (stdoutLen > options.maxBuffer) {
const truncatedLen = options.maxBuffer - (stdoutLen - length);
_stdout.push(chunk.slice(0, truncatedLen));

ex = new ERR_CHILD_PROCESS_STDIO_MAXBUFFER('stdout');
kill();
} else {
@@ -360,9 +366,15 @@ exports.execFile = function execFile(file /* , args, options, callback */) {

child.stderr.on('data', function onChildStderr(chunk) {
var encoding = child.stderr._readableState.encoding;
stderrLen += encoding ? Buffer.byteLength(chunk, encoding) : chunk.length;
const length = encoding ?
Buffer.byteLength(chunk, encoding) :
chunk.length;
stderrLen += length;

if (stderrLen > options.maxBuffer) {
const truncatedLen = options.maxBuffer - (stderrLen - length);
_stderr.push(chunk.slice(0, truncatedLen));

ex = new ERR_CHILD_PROCESS_STDIO_MAXBUFFER('stderr');
kill();
} else {
@@ -22,13 +22,13 @@ function runChecks(err, stdio, streamName, expected) {
}

{
const cmd = 'echo "hello world"';
const cmd = 'echo hello world';

cp.exec(
cmd,
{ maxBuffer: 5 },
common.mustCall((err, stdout, stderr) => {
runChecks(err, { stdout, stderr }, 'stdout', '');
runChecks(err, { stdout, stderr }, 'stdout', 'hello');
})
);
}
@@ -42,7 +42,7 @@ const unicode = '中文测试'; // length = 4, byte length = 12
cmd,
{ maxBuffer: 10 },
common.mustCall((err, stdout, stderr) => {
runChecks(err, { stdout, stderr }, 'stdout', '');
runChecks(err, { stdout, stderr }, 'stdout', '中文测试\n');
})
);
}
@@ -54,7 +54,7 @@ const unicode = '中文测试'; // length = 4, byte length = 12
cmd,
{ maxBuffer: 3 },
common.mustCall((err, stdout, stderr) => {
runChecks(err, { stdout, stderr }, 'stderr', '');
runChecks(err, { stdout, stderr }, 'stderr', '中文测');
})
);
}
@@ -66,7 +66,7 @@ const unicode = '中文测试'; // length = 4, byte length = 12
cmd,
{ encoding: null, maxBuffer: 10 },
common.mustCall((err, stdout, stderr) => {
runChecks(err, { stdout, stderr }, 'stdout', '');
runChecks(err, { stdout, stderr }, 'stdout', '中文测试\n');
})
);

@@ -80,9 +80,22 @@ const unicode = '中文测试'; // length = 4, byte length = 12
cmd,
{ encoding: null, maxBuffer: 3 },
common.mustCall((err, stdout, stderr) => {
runChecks(err, { stdout, stderr }, 'stderr', '');
runChecks(err, { stdout, stderr }, 'stderr', '中文测');
})
);

child.stderr.setEncoding('utf-8');
}

{
const cmd = `"${process.execPath}" -e "console.error('${unicode}');"`;

cp.exec(
cmd,
{ encoding: null, maxBuffer: 5 },
common.mustCall((err, stdout, stderr) => {
const buf = Buffer.from(unicode).slice(0, 5);
runChecks(err, { stdout, stderr }, 'stderr', buf);
})
);
}

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