Add an endpoint and module for reading journald logs

Change-type: minor
Closes: #1003
Signed-off-by: Cameron Diver <cameron@balena.io>

docs/API.md

@@ -1149,6 +1149,7 @@ Response:
 	]
 }
 ```
+
 ### V2 Utilities
 
 #### Cleanup volumes with no references
@@ -1179,3 +1180,37 @@ Unsuccessful response:
 }
 ```
 
+#### Journald logs
+
+Added in supervisor version v10.1.0
+
+Retrieve a stream to the journald logs on device. This is
+equivalent to running `journalctl -o export`. Options
+supported are:
+
+##### all: boolean
+Show all fields in full, equivalent to `journalctl --all`.
+
+##### follow: boolean
+Continuously stream logs as they are generated, equivalent
+to `journalctl --follow`.
+
+##### count: integer
+Show the most recent `count` events, equivalent to
+`journalctl --line=<count>`.
+
+##### unit
+Show journal logs from `unit` only, equivalent to
+`journalctl --unit=<unit>`.
+
+Fields should be provided via POST body in JSON format.
+
+From an application container (with systemd installed):
+```
+$ curl -X POST --data '{"follow":true,"all":true}' "$BALENA_SUPERVISOR_ADDRESS/v2/journal-logs?apikey=$BALENA_SUPERVISOR_API_KEY" | systemd-journal-remote - -o log.journal
+```
+
+The `log.journal` file can then be viewed with
+```
+journalctl --file log.journal -f
+```

src/device-api/v2.ts

@@ -13,8 +13,11 @@ import {
 import { doPurge, doRestart, serviceAction } from './common';
 
 import Volume from '../compose/volume';
+import { spawnJournalctl } from '../lib/journald';
+
 import log from '../lib/supervisor-console';
 import supervisorVersion = require('../lib/supervisor-version');
+import { checkInt, checkTruthy } from '../lib/validation';
 
 export function createV2Api(router: Router, applications: ApplicationManager) {
 	const { _lockingIfNecessary, deviceState } = applications;
@@ -533,4 +536,32 @@ export function createV2Api(router: Router, applications: ApplicationManager) {
 			});
 		}
 	});
+
+	router.post('/v2/journal-logs', (req, res) => {
+		try {
+			const all = checkTruthy(req.body.all) || false;
+			const follow = checkTruthy(req.body.follow) || false;
+			const count = checkInt(req.body.count, { positive: true }) || undefined;
+			const unit = req.body.unit;
+
+			const journald = spawnJournalctl({ all, follow, count, unit });
+			res.status(200);
+			journald.stdout.pipe(res);
+			res.on('close', () => {
+				journald.kill('SIGKILL');
+			});
+			journald.on('exit', () => {
+				res.end();
+			});
+		} catch (e) {
+			log.error('There was an error reading the journalctl process', e);
+			if (res.headersSent) {
+				return;
+			}
+			res.json({
+				status: 'failed',
+				message: messageFromError(e),
+			});
+		}
+	});
 }

src/lib/journald.ts

@@ -0,0 +1,41 @@
+import { ChildProcess, spawn } from 'child_process';
+
+import constants = require('./constants');
+import log from './supervisor-console';
+
+export function spawnJournalctl(opts: {
+	all: boolean;
+	follow: boolean;
+	count?: number;
+	unit?: string;
+}): ChildProcess {
+	const args = [
+		// The directory we want to run the chroot from
+		constants.rootMountPoint,
+		'journalctl',
+		'-o',
+		'export',
+	];
+	if (opts.all) {
+		args.push('-a');
+	}
+	if (opts.follow) {
+		args.push('--follow');
+	}
+	if (opts.unit != null) {
+		args.push('-u');
+		args.push(opts.unit);
+	}
+	if (opts.count != null) {
+		args.push('-n');
+		args.push(opts.count.toString());
+	}
+
+	log.debug('Spawning journald with: chroot ', args.join(' '));
+
+	const journald = spawn('chroot', args, {
+		stdio: 'pipe',
+	});
+
+	return journald;
+}