refactor tail invokation into logtail.sh

src/apps.js

@@ -164,7 +164,7 @@ const appstore = require('./appstore.js'),
     domains = require('./domains.js'),
     eventlog = require('./eventlog.js'),
     fs = require('fs'),
-    LogStream = require('./log-stream.js'),
+    logs = require('./logs.js'),
     mail = require('./mail.js'),
     manifestFormat = require('cloudron-manifestformat'),
     mounts = require('./mounts.js'),
@@ -179,7 +179,6 @@ const appstore = require('./appstore.js'),
     services = require('./services.js'),
     settings = require('./settings.js'),
     shell = require('./shell.js'),
-    spawn = require('child_process').spawn,
     storage = require('./storage.js'),
     superagent = require('superagent'),
     system = require('./system.js'),
@@ -2025,19 +2024,10 @@ async function getLogs(app, options) {
 
     const appId = app.id;
 
-    const lines = options.lines === -1 ? '+1' : options.lines,
-        format = options.format || 'json',
-        follow = options.follow;
-
-    assert.strictEqual(typeof format, 'string');
-
-    const args = [ '--lines=' + lines ];
-    if (follow) args.push('--follow', '--retry', '--quiet'); // same as -F. to make it work if file doesn't exist, --quiet to not output file headers, which are no logs
-
     const logPaths = await getLogPaths(app);
-    const cp = spawn('/usr/bin/tail', args.concat(logPaths));
+    const cp = logs.tail(logPaths, { lines: options.lines, follow: options.follow });
 
-    const logStream = new LogStream({ format, source: appId });
+    const logStream = new logs.LogStream({ format: options.format || 'json', source: appId });
     logStream.close = cp.kill.bind(cp, 'SIGKILL'); // hook for caller. closing stream kills the child process
 
     cp.stdout.pipe(logStream);