jobqueue: handle escaped null bytes in postgres

Postgres doesn't accept `\u0000` in the jsonb datatype. Switch to the
json datatype which is larger and slower, but accepts escaped null
bytes.

As we don't actually query or index the result jsonb directly, the
impact of this should be minimal.

See: https://www.postgresql.org/docs/current/datatype-json.html

internal/jobqueue/jobqueuetest/jobqueuetest.go

@@ -25,6 +25,7 @@ import (
 type MakeJobQueue func() (q jobqueue.JobQueue, stop func(), err error)
 
 type testResult struct {
+	Logs json.RawMessage `json:"logs,omitempty"`
 }
 
 func TestDbURL() string {
@@ -50,6 +51,7 @@ func TestJobQueue(t *testing.T, makeJobQueue MakeJobQueue) {
 	t.Run("cancel", wrap(testCancel))
 	t.Run("requeue", wrap(testRequeue))
 	t.Run("requeue-limit", wrap(testRequeueLimit))
+	t.Run("escaped-null-bytes", wrap(testEscapedNullBytes))
 	t.Run("job-types", wrap(testJobTypes))
 	t.Run("dependencies", wrap(testDependencies))
 	t.Run("multiple-workers", wrap(testMultipleWorkers))
@@ -110,7 +112,8 @@ func testErrors(t *testing.T, q jobqueue.JobQueue) {
 	require.NoError(t, err)
 	require.Equal(t, id, idFromT)
 
-	requeued, err := q.RequeueOrFinishJob(id, 0, nil)
+	require.NoError(t, err)
+	requeued, err := q.RequeueOrFinishJob(id, 0, &testResult{})
 	require.NoError(t, err)
 	require.False(t, requeued)
 
@@ -504,6 +507,18 @@ func testRequeueLimit(t *testing.T, q jobqueue.JobQueue) {
 	require.NotNil(t, result)
 }
 
+func testEscapedNullBytes(t *testing.T, q jobqueue.JobQueue) {
+	pushTestJob(t, q, "octopus", nil, nil, "")
+	id, tok, _, _, _, err := q.Dequeue(context.Background(), uuid.Nil, []string{"octopus"}, []string{""})
+	require.NoError(t, err)
+	require.NotEmpty(t, tok)
+
+	// Ensure postgres accepts escaped null bytes
+	requeued, err := q.RequeueOrFinishJob(id, 0, &testResult{Logs: []byte("{\"blegh\\u0000\": \"\\u0000\"}")})
+	require.NoError(t, err)
+	require.False(t, requeued)
+}
+
 func testHeartbeats(t *testing.T, q jobqueue.JobQueue) {
 	id := pushTestJob(t, q, "octopus", nil, nil, "")
 	// No heartbeats for queued job

pkg/jobqueue/dbjobqueue/schemas/009_jobs_alter_result_type.sql

@@ -0,0 +1,53 @@
+---- tern: disable-tx ----
+-- disable migration transaction, to allow for batched updates
+
+-- jsonb does not support unicode escaped null bytes, and we don't
+-- control much of the output generated by osbuild.
+ALTER TABLE jobs ADD COLUMN IF NOT EXISTS new_result json;
+
+-- backfill outside of the transaction to avoid locking the table
+DO $$
+DECLARE
+  remaining_rows INTEGER := 1;
+BEGIN
+  WHILE remaining_rows > 0 LOOP
+    -- CTE on jobs
+    WITH cte_jobs AS (
+       SELECT ctid
+         FROM jobs
+         WHERE result IS NOT NULL AND new_result IS NULL
+         FOR UPDATE
+         LIMIT 500
+    )
+    -- self-join on ctid
+    UPDATE jobs set new_result = result::json
+    FROM cte_jobs
+    WHERE jobs.ctid = cte_jobs.ctid;
+
+    SELECT COUNT(ctid)
+    FROM jobs
+    WHERE result IS NOT NULL AND new_result IS NULL
+    INTO remaining_rows;
+    RAISE NOTICE 'REMAINING ROWS: %', remaining_rows;
+  END LOOP;
+END $$;
+
+-- switching over the columns needs to happen in a transaction
+BEGIN;
+
+DROP VIEW ready_jobs;
+ALTER TABLE jobs DROP COLUMN result;
+ALTER TABLE jobs RENAME COLUMN new_result TO result;
+
+CREATE VIEW ready_jobs AS
+SELECT *
+FROM jobs
+WHERE started_at IS NULL
+  AND canceled = FALSE
+  AND id NOT IN (
+    SELECT job_id
+    FROM job_dependencies JOIN jobs ON dependency_id = id
+    WHERE finished_at IS NULL
+)
+ORDER BY queued_at ASC;
+COMMIT;