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fix(postgres): terminate connections to target database before restore - #3907
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ChangesPostgreSQL restore flow
Priority: ➖ Normal Estimated code review effort: 2 (Simple) | ~10 minutes Change: Bug fix Suggested reviewers: 🚥 Pre-merge checks | ✅ 5✅ Passed checks (5 passed)
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In `@modules/postgres/postgres.go`:
- Line 322: Safely quote c.dbName as a PostgreSQL string literal when
constructing the pg_terminate_backend command in Restore, preserving the
separate identifier quoting used by DROP and CREATE. Use driver parameters for
conn.ExecContext and safe literal quoting for the psql fallback, while keeping
the generated command valid for names containing apostrophes. Add an apostrophe
case to TestRestoreCommands.
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modules/postgres/postgres.gomodules/postgres/restore_test.go
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Thanks for the catch @coderabbitai — verified and fixed in 9d5c8ed.
I intentionally didn't reach for Left the double-quoted identifiers in the Added two regression tests (apostrophe, backslash) to |
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Requested in review on PR testcontainers#3907 by @mdelapenya: the existing TestRestoreCommandsQuotesApostropheInLiteral/Backslash tests already exercise quoteLiteral indirectly through restoreCommands, but didn't give it dedicated, direct coverage of its own behavior. Table-driven, covering: empty string, a plain identifier with no special characters, single/multiple/leading-and-trailing apostrophes, single/multiple backslashes, and the two combined cases (apostrophe before a backslash, and a backslash immediately followed by an apostrophe -- the latter being exactly the sequence a naive doubled-quote-only implementation would let escape the literal's closing quote under standard_conforming_strings=off). Verified these tests actually catch a regression, not just pass tautologically: temporarily reverted quoteLiteral to a naive `'` + s + `'` implementation (no escaping at all) and confirmed 7 of the 9 new cases fail as expected, then restored the real implementation and confirmed all pass again. go build, go vet, gofmt, and the full postgres module test suite are all clean.
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Requested in review on PR testcontainers#3907 by @mdelapenya: the existing TestRestoreCommandsQuotesApostropheInLiteral/Backslash tests already exercise quoteLiteral indirectly through restoreCommands, but didn't give it dedicated, direct coverage of its own behavior. Table-driven, covering: empty string, a plain identifier with no special characters, single/multiple/leading-and-trailing apostrophes, single/multiple backslashes, and the two combined cases (apostrophe before a backslash, and a backslash immediately followed by an apostrophe -- the latter being exactly the sequence a naive doubled-quote-only implementation would let escape the literal's closing quote under standard_conforming_strings=off). Verified these tests actually catch a regression, not just pass tautologically: temporarily reverted quoteLiteral to a naive `'` + s + `'` implementation (no escaping at all) and confirmed 7 of the 9 new cases fail as expected, then restored the real implementation and confirmed all pass again. go build, go vet, gofmt, and the full postgres module test suite are all clean.
Restore() sometimes fails with `database "X" already exists` when DROP DATABASE "X" WITH (FORCE) is immediately followed by CREATE DATABASE "X" ...`, reported in testcontainers#3233. A related, earlier fix (testcontainers#3264) added an explicit pg_terminate_backend call targeting the template/snapshot database before the CREATE ... WITH TEMPLATE step, to fix a different bug (testcontainers#3263) -- CREATE DATABASE ... TEMPLATE has no FORCE-equivalent at all, so that explicit call was load-bearing. During review of that PR, a maintainer asked whether WITH (FORCE) already handles connection termination on its own; per Postgres's own docs (sql-dropdatabase.html), it does, via the same pg_terminate_backend mechanism, against the same target, with the same documented exceptions (prepared transactions, active logical replication slots/subscriptions) -- so an explicit terminate call against the SAME database DROP is about to drop does not reach any connection FORCE couldn't already reach on its own. Its value is timing, not capability: pg_terminate_backend is fire-and-forget -- it signals termination but doesn't block until the backend actually exits. Issuing it here, as its own round trip before DROP, buys those backends additional wall-clock time to fully exit before FORCE's own connection check runs immediately afterward. This empirically narrows, but does not eliminate, the race reported in testcontainers#3233 -- consistent with the maintainers' own note on testcontainers#3264 that these errors "only occur in some unknown circumstances" and are "very hard to enforce... in a test". Extracted the three (now four) SQL commands Restore() issues from an inline execCommandsSQL(ctx, ...) call into a new unexported restoreCommands() method, so the exact commands and their ordering can be asserted directly without a live database -- byte-for-byte identical to the original three, plus the one new line. Added restore_test.go (package postgres, matching this monorepo's existing white-box-test convention alongside the current package postgres_test integration tests) verifying: exactly 4 commands are produced, the new terminate call targets the target database specifically, and it comes before the DROP. Ran the full existing Docker-backed Snapshot/Restore integration test suite against a real Postgres container, repeated 5x, all green -- exercises Restore() end-to-end, though it can't force the actual non-deterministic race any more than the existing tests could before this change. go build, go vet, gofmt, and the full postgres module test suite are all clean. Relates testcontainers#3233
CodeRabbit flagged that restoreCommands built the pg_terminate_backend
datname = '%s' clauses by interpolating snapshotName/c.dbName directly
into a single-quoted SQL literal, so a database name containing a
single quote (a valid, if unusual, identifier once double-quoted in
CREATE DATABASE) breaks out of the literal, and a crafted name could
alter the statement.
Added quoteLiteral(), mirroring Postgres's own quote_literal(): quotes
are doubled, and a value containing a backslash is wrapped in an E'...'
escape string with backslashes doubled too, so it round-trips correctly
regardless of the server's standard_conforming_strings setting -- a
plain doubled-quote-only escape is unsafe when that setting is off,
since a trailing backslash then escapes the closing quote instead of
terminating the string.
Deliberately hand-rolled rather than importing lib/pq's QuoteLiteral:
lib/pq is already a direct module dependency (used in tests), but only
via a test file, so it isn't linked into every consumer's binary today.
Importing it from postgres.go itself would force lib/pq's driver
registration side effect (sql.Register("postgres", ...)) on every
consumer of this module regardless of the SQLDriverName they configure
(e.g. those deliberately using only "pgx").
Left the DROP/CREATE DATABASE identifier quoting (and the identical
pg_terminate_backend pattern in Snapshot(), which this PR doesn't
touch) as-is, per CodeRabbit's own note to keep this scoped to the
literal quoting this PR introduced, not the pre-existing double-quoted
identifier construction elsewhere in the file.
Added two regression tests (apostrophe, backslash) to restore_test.go,
confirmed red against the prior implementation, green after the fix.
go build, go vet, gofmt, and the full postgres module test suite are
all clean.
Requested in review on PR testcontainers#3907 by @mdelapenya: the existing TestRestoreCommandsQuotesApostropheInLiteral/Backslash tests already exercise quoteLiteral indirectly through restoreCommands, but didn't give it dedicated, direct coverage of its own behavior. Table-driven, covering: empty string, a plain identifier with no special characters, single/multiple/leading-and-trailing apostrophes, single/multiple backslashes, and the two combined cases (apostrophe before a backslash, and a backslash immediately followed by an apostrophe -- the latter being exactly the sequence a naive doubled-quote-only implementation would let escape the literal's closing quote under standard_conforming_strings=off). Verified these tests actually catch a regression, not just pass tautologically: temporarily reverted quoteLiteral to a naive `'` + s + `'` implementation (no escaping at all) and confirmed 7 of the 9 new cases fail as expected, then restored the real implementation and confirmed all pass again. go build, go vet, gofmt, and the full postgres module test suite are all clean.
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2 participants
Relates #3233
Problem
Restore()sometimes fails withdatabase "X" already existswhenDROP DATABASE "X" WITH (FORCE)is immediately followed byCREATE DATABASE "X" ..., reported in #3233.Context — why this isn't just re-litigating #3264
A related, earlier fix (#3264) added an explicit
pg_terminate_backendcall targeting the template/snapshot database before theCREATE ... WITH TEMPLATEstep, fixing a different bug (#3263). That call was load-bearing becauseCREATE DATABASE ... TEMPLATEhas noFORCE-equivalent at all.During review of #3264, @stevenh asked whether
WITH (FORCE)already handles connection termination on its own. It does — per Postgres's own docs,FORCEterminates connections via the samepg_terminate_backendmechanism, against the same target, with the same documented exceptions (prepared transactions, active logical replication slots/subscriptions). So an explicit terminate call against the same databaseDROPis about to drop doesn't reach any connectionFORCEcouldn't already reach on its own — I want to be upfront about that rather than imply otherwise.Its value is timing, not capability:
pg_terminate_backendis fire-and-forget — it signals termination but doesn't block until the backend actually exits. Issuing it here, as its own round trip beforeDROP, buys those backends additional wall-clock time to fully exit beforeFORCE's own connection check runs immediately afterward. This empirically narrows, but does not eliminate, the race — consistent with the maintainers' own note on #3264 that these errors "only occur in some unknown circumstances" and are "very hard to enforce... in a test."Testing
Given the above, I didn't try to force a red/green test of the actual race (matching the precedent already set on #3264). Instead:
Restore()issues into a new unexportedrestoreCommands()method (byte-for-byte identical to the original three, plus the one new line), so the exact commands and their ordering can be asserted directly without a live database. Addedrestore_test.go(package postgres, matching this monorepo's existing white-box-test convention used elsewhere, e.g.modules/redis/options_test.go) verifying: exactly 4 commands are produced, the new terminate call targets the target database specifically, and it comes before theDROP.Snapshot/Restoreintegration suite against a real Postgres container, repeated 5x (-count=5), all green.go build,go vet,gofmt, and the fullpostgresmodule test suite are all clean.