Add tests for low-level PGLZ [de]compression routines

The goal of this module is to provide an entry point for the coverage of
the low-level compression and decompression PGLZ routines.  The new test
is moved to a new parallel group, with all the existing
compression-related tests added to it.

This includes tests for the cases detected by fuzzing that emulate
corrupted compressed data, as fixed by 2b5ba2a0a1:
- Set control bit with read of a match tag, where no data follows.
- Set control bit with read of a match tag, where 1 byte follows.
- Set control bit with match tag where length nibble is 3 bytes
(extended case).

While on it, some tests are added for compress/decompress roundtrips,
and for check_complete=false/true.  Like 2b5ba2a0a1, backpatch to all
the stable branches.

Discussion: https://postgr.es/m/adw647wuGjh1oU6p@paquier.xyz
Backpatch-through: 14

src/test/regress/expected/compression_pglz.out

@@ -0,0 +1,65 @@
+--
+-- Tests for PGLZ compression
+--
+-- directory paths and dlsuffix are passed to us in environment variables
+\getenv libdir PG_LIBDIR
+\getenv dlsuffix PG_DLSUFFIX
+\set regresslib :libdir '/regress' :dlsuffix
+CREATE FUNCTION test_pglz_compress(bytea)
+  RETURNS bytea
+  AS :'regresslib' LANGUAGE C STRICT;
+CREATE FUNCTION test_pglz_decompress(bytea, int4, bool)
+  RETURNS bytea
+  AS :'regresslib' LANGUAGE C STRICT;
+-- Round-trip with pglz: compress then decompress.
+SELECT test_pglz_decompress(test_pglz_compress(
+    decode(repeat('abcd', 100), 'escape')), 400, false) =
+    decode(repeat('abcd', 100), 'escape') AS roundtrip_ok;
+ roundtrip_ok 
+--------------
+ t
+(1 row)
+
+SELECT test_pglz_decompress(test_pglz_compress(
+    decode(repeat('abcd', 100), 'escape')), 400, true) =
+    decode(repeat('abcd', 100), 'escape') AS roundtrip_ok;
+ roundtrip_ok 
+--------------
+ t
+(1 row)
+
+-- Decompression with rawsize too large, fails to fill the destination
+-- buffer.
+SELECT test_pglz_decompress(test_pglz_compress(
+    decode(repeat('abcd', 100), 'escape')), 500, true);
+ERROR:  pglz_decompress failed
+-- Decompression with rawsize too small, fails with source not fully
+-- consumed.
+SELECT test_pglz_decompress(test_pglz_compress(
+    decode(repeat('abcd', 100), 'escape')), 100, true);
+ERROR:  pglz_decompress failed
+-- Corrupted compressed data.  Set control bit with read of a match tag,
+-- no data follows.
+SELECT length(test_pglz_decompress('\x01'::bytea, 1024, false)) AS ctrl_only_len;
+ ctrl_only_len 
+---------------
+             0
+(1 row)
+
+SELECT test_pglz_decompress('\x01'::bytea, 1024, true);
+ERROR:  pglz_decompress failed
+-- Corrupted compressed data.  Set control bit with read of a match tag,
+-- 1 byte follows.
+SELECT test_pglz_decompress('\x01ff'::bytea, 1024, false);
+ERROR:  pglz_decompress failed
+SELECT test_pglz_decompress('\x01ff'::bytea, 1024, true);
+ERROR:  pglz_decompress failed
+-- Corrupted compressed data.  Set control bit with match tag where length
+-- nibble is 3 bytes (extended length), no data follows.
+SELECT test_pglz_decompress('\x010f01'::bytea, 1024, false);
+ERROR:  pglz_decompress failed
+SELECT test_pglz_decompress('\x010f01'::bytea, 1024, true);
+ERROR:  pglz_decompress failed
+-- Clean up
+DROP FUNCTION test_pglz_compress;
+DROP FUNCTION test_pglz_decompress;

src/test/regress/parallel_schedule

@@ -123,7 +123,12 @@ test: plancache limit plpgsql copy2 temp domain rangefuncs prepare conversion tr
 # The stats test resets stats, so nothing else needing stats access can be in
 # this group.
 # ----------
-test: partition_merge partition_split partition_join partition_prune reloptions hash_part indexing partition_aggregate partition_info tuplesort explain compression compression_lz4 memoize stats predicate numa eager_aggregate graph_table_rls planner_est
+test: partition_merge partition_split partition_join partition_prune reloptions hash_part indexing partition_aggregate partition_info tuplesort explain memoize stats predicate numa eager_aggregate graph_table_rls planner_est
+
+# ----------
+# Another group of parallel tests (compression)
+# ----------
+test: compression compression_lz4 compression_pglz
 
 # event_trigger depends on create_am and cannot run concurrently with
 # any test that runs DDL

src/test/regress/regress.c

@@ -27,6 +27,7 @@
 #include "catalog/pg_type.h"
 #include "commands/sequence.h"
 #include "commands/trigger.h"
+#include "common/pg_lzcompress.h"
 #include "executor/executor.h"
 #include "executor/functions.h"
 #include "executor/spi.h"
@@ -1422,3 +1423,68 @@ test_instr_time(PG_FUNCTION_ARGS)
 
 	PG_RETURN_BOOL(true);
 }
+
+/*
+ * test_pglz_compress
+ *
+ * Compress the input using pglz_compress().  Only the "always" strategy is
+ * currently supported.
+ *
+ * Returns the compressed data, or NULL if compression fails.
+ */
+PG_FUNCTION_INFO_V1(test_pglz_compress);
+Datum
+test_pglz_compress(PG_FUNCTION_ARGS)
+{
+	bytea	   *input = PG_GETARG_BYTEA_PP(0);
+	char	   *source = VARDATA_ANY(input);
+	int32		slen = VARSIZE_ANY_EXHDR(input);
+	int32		maxout = PGLZ_MAX_OUTPUT(slen);
+	bytea	   *result;
+	int32		clen;
+
+	result = (bytea *) palloc(maxout + VARHDRSZ);
+	clen = pglz_compress(source, slen, VARDATA(result),
+						 PGLZ_strategy_always);
+	if (clen < 0)
+		PG_RETURN_NULL();
+
+	SET_VARSIZE(result, clen + VARHDRSZ);
+	PG_RETURN_BYTEA_P(result);
+}
+
+/*
+ * test_pglz_decompress
+ *
+ * Decompress the input using pglz_decompress().
+ *
+ * The second argument is the expected uncompressed data size.  The third
+ * argument is here for the check_complete flag.
+ *
+ * Returns the decompressed data, or raises an error if decompression fails.
+ */
+PG_FUNCTION_INFO_V1(test_pglz_decompress);
+Datum
+test_pglz_decompress(PG_FUNCTION_ARGS)
+{
+	bytea	   *input = PG_GETARG_BYTEA_PP(0);
+	int32		rawsize = PG_GETARG_INT32(1);
+	bool		check_complete = PG_GETARG_BOOL(2);
+	char	   *source = VARDATA_ANY(input);
+	int32		slen = VARSIZE_ANY_EXHDR(input);
+	bytea	   *result;
+	int32		dlen;
+
+	if (rawsize < 0)
+		elog(ERROR, "rawsize must not be negative");
+
+	result = (bytea *) palloc(rawsize + VARHDRSZ);
+
+	dlen = pglz_decompress(source, slen, VARDATA(result),
+						   rawsize, check_complete);
+	if (dlen < 0)
+		elog(ERROR, "pglz_decompress failed");
+
+	SET_VARSIZE(result, dlen + VARHDRSZ);
+	PG_RETURN_BYTEA_P(result);
+}

src/test/regress/sql/compression_pglz.sql

@@ -0,0 +1,53 @@
+--
+-- Tests for PGLZ compression
+--
+
+-- directory paths and dlsuffix are passed to us in environment variables
+\getenv libdir PG_LIBDIR
+\getenv dlsuffix PG_DLSUFFIX
+
+\set regresslib :libdir '/regress' :dlsuffix
+
+CREATE FUNCTION test_pglz_compress(bytea)
+  RETURNS bytea
+  AS :'regresslib' LANGUAGE C STRICT;
+CREATE FUNCTION test_pglz_decompress(bytea, int4, bool)
+  RETURNS bytea
+  AS :'regresslib' LANGUAGE C STRICT;
+
+-- Round-trip with pglz: compress then decompress.
+SELECT test_pglz_decompress(test_pglz_compress(
+    decode(repeat('abcd', 100), 'escape')), 400, false) =
+    decode(repeat('abcd', 100), 'escape') AS roundtrip_ok;
+SELECT test_pglz_decompress(test_pglz_compress(
+    decode(repeat('abcd', 100), 'escape')), 400, true) =
+    decode(repeat('abcd', 100), 'escape') AS roundtrip_ok;
+
+-- Decompression with rawsize too large, fails to fill the destination
+-- buffer.
+SELECT test_pglz_decompress(test_pglz_compress(
+    decode(repeat('abcd', 100), 'escape')), 500, true);
+
+-- Decompression with rawsize too small, fails with source not fully
+-- consumed.
+SELECT test_pglz_decompress(test_pglz_compress(
+    decode(repeat('abcd', 100), 'escape')), 100, true);
+
+-- Corrupted compressed data.  Set control bit with read of a match tag,
+-- no data follows.
+SELECT length(test_pglz_decompress('\x01'::bytea, 1024, false)) AS ctrl_only_len;
+SELECT test_pglz_decompress('\x01'::bytea, 1024, true);
+
+-- Corrupted compressed data.  Set control bit with read of a match tag,
+-- 1 byte follows.
+SELECT test_pglz_decompress('\x01ff'::bytea, 1024, false);
+SELECT test_pglz_decompress('\x01ff'::bytea, 1024, true);
+
+-- Corrupted compressed data.  Set control bit with match tag where length
+-- nibble is 3 bytes (extended length), no data follows.
+SELECT test_pglz_decompress('\x010f01'::bytea, 1024, false);
+SELECT test_pglz_decompress('\x010f01'::bytea, 1024, true);
+
+-- Clean up
+DROP FUNCTION test_pglz_compress;
+DROP FUNCTION test_pglz_decompress;