Set poolInfo expired to false when the expression is NULL.

In case that the volume is freshly created and is being written to
currently, `lastwritten` is `NULL`, which propagates through the expiry
calculation formula, resulting in a boolean field being `NULL`.
This causes an error to be raised, which results in a log line:

Jun 30 23:29:24 backup1 bareos_exporter[21509]: time="2021-06-30T23:29:24Z" level=error msg="sql: Scan error on column index 4, name \"expired\": sql/driver: couldn't convert <nil> (<nil>) into type bool" method=PoolInfo

When an error occurs while fetching pool info, statistics about pools
are not exported to prometheus at all, which may result in missing data.

Fixes #9

dataaccess.go

@@ -30,15 +30,15 @@ var queries map[string]*sqlQueries = map[string]*sqlQueries{
 		LastJob:               "SELECT JobStatus,JobBytes,JobFiles,JobErrors,StartTime,COALESCE(EndTime, NOW()) FROM Job WHERE Name = ? AND ClientId = ? AND FileSetId = ? ORDER BY StartTime DESC LIMIT 1",
 		LastSuccessfulJob:     "SELECT JobStatus,JobBytes,JobFiles,JobErrors,StartTime,COALESCE(EndTime, NOW()) FROM Job WHERE Name = ? AND ClientId = ? AND FileSetId = ? AND JobStatus IN('T', 'W') ORDER BY StartTime DESC LIMIT 1",
 		LastSuccessfulFullJob: "SELECT JobStatus,JobBytes,JobFiles,JobErrors,StartTime,COALESCE(EndTime, NOW()) FROM Job WHERE Name = ? AND ClientId = ? AND FileSetId = ? AND JobStatus IN('T', 'W') AND Level = 'F' ORDER BY StartTime DESC LIMIT 1",
-		PoolInfo:              "SELECT p.name, sum(m.volbytes) AS bytes, count(*) AS volumes, (not exists(select * from JobMedia jm where jm.mediaid = m.mediaid)) AS prunable, TIMESTAMPADD(SECOND, m.volretention, m.lastwritten) < NOW() AS expired FROM Media m LEFT JOIN Pool p ON m.poolid = p.poolid GROUP BY p.name, prunable, expired",
+		PoolInfo:              "SELECT p.name, sum(m.volbytes) AS bytes, count(*) AS volumes, (not exists(select * from JobMedia jm where jm.mediaid = m.mediaid)) AS prunable, COALESCE(TIMESTAMPADD(SECOND, m.volretention, m.lastwritten) < NOW(), false) AS expired FROM Media m LEFT JOIN Pool p ON m.poolid = p.poolid GROUP BY p.name, prunable, expired",
 		JobStates:             "SELECT JobStatus FROM Status",
 	},
 	"postgres": &sqlQueries{
 		JobList:               "SELECT j.Name, j.Type, j.ClientId, j.FileSetId, COALESCE(c.Name, ''), COALESCE(f.FileSet, ''), COUNT(*), SUM(j.JobBytes), SUM(j.JobFiles) FROM job j LEFT JOIN client c ON c.ClientId = j.ClientId LEFT JOIN fileset f ON f.FileSetId = j.FileSetId  GROUP BY j.Name, j.Type, j.ClientId, j.FileSetId, c.Name, f.FileSet HAVING MAX(j.SchedTime) >= $1",
 		LastJob:               "SELECT JobStatus,JobBytes,JobFiles,JobErrors,StartTime::timestamptz,COALESCE(EndTime::timestamptz, NOW()) FROM job WHERE Name = $1 AND ClientId = $2 AND FileSetId = $3 ORDER BY StartTime DESC LIMIT 1",
 		LastSuccessfulJob:     "SELECT JobStatus,JobBytes,JobFiles,JobErrors,StartTime::timestamptz,COALESCE(EndTime::timestamptz, NOW()) FROM job WHERE Name = $1 AND ClientId = $2 AND FileSetId = $3 AND JobStatus IN('T', 'W') ORDER BY StartTime DESC LIMIT 1",
 		LastSuccessfulFullJob: "SELECT JobStatus,JobBytes,JobFiles,JobErrors,StartTime::timestamptz,COALESCE(EndTime::timestamptz, NOW()) FROM job WHERE Name = $1 AND ClientId = $2 AND FileSetId = $3 AND JobStatus IN('T', 'W') AND Level = 'F' ORDER BY StartTime DESC LIMIT 1",
-		PoolInfo:              "SELECT p.name, sum(m.volbytes) AS bytes, count(m) AS volumes, (not exists(select * from jobmedia jm where jm.mediaid = m.mediaid)) AS prunable, (m.lastwritten + (m.volretention * interval '1s')) < NOW() as expired FROM media m LEFT JOIN pool p ON m.poolid = p.poolid GROUP BY p.name, prunable, expired",
+		PoolInfo:              "SELECT p.name, sum(m.volbytes) AS bytes, count(m) AS volumes, (not exists(select * from jobmedia jm where jm.mediaid = m.mediaid)) AS prunable, COALESCE((m.lastwritten + (m.volretention * interval '1s')) < NOW(), false) as expired FROM media m LEFT JOIN pool p ON m.poolid = p.poolid GROUP BY p.name, prunable, expired",
 		JobStates:             "SELECT JobStatus FROM status",
 	},
 }

development/mysql/03-issue-9.sql

@@ -0,0 +1,5 @@
+-- Reproduction of https://github.com/vierbergenlars/bareos_exporter/issues/9
+
+INSERT INTO Media (volumename, mediatype, firstwritten, lastwritten, labeldate, volstatus, poolid)
+    VALUES
+        ('Pool1-0100', 'NULL', NOW() - interval 1 day + interval 30 second, NULL, NOW() - interval 1 day, 'Full', (SELECT poolid from Pool WHERE name = 'Pool1'));

development/postgres/03-issue-9.sql

@@ -0,0 +1,5 @@
+-- Reproduction of https://github.com/vierbergenlars/bareos_exporter/issues/9
+
+INSERT INTO public.media (volumename, mediatype, firstwritten, lastwritten, labeldate, volstatus, poolid)
+    VALUES
+        ('Pool1-0100', 'NULL', NOW() - interval '1 day' + interval '30s', NULL, NOW() - interval '1 day', 'Full', (SELECT poolid from pool WHERE name = 'Pool1'));