Rename backup_compression.{c,h} to compression.{c,h}

Compression option handling (level, algorithm or even workers) can be
used across several parts of the system and not only base backups.
Structures, objects and routines are renamed in consequence, to remove
the concept of base backups from this part of the code making this
change straight-forward.

pg_receivewal, that has gained support for LZ4 since babbbb5, will make
use of this infrastructure for its set of compression options, bringing
more consistency with pg_basebackup.  This cleanup needs to be done
before releasing a beta of 15.  pg_dump is a potential future target, as
well, and adding more compression options to it may happen in 16~.

Author: Michael Paquier
Reviewed-by: Robert Haas, Georgios Kokolatos
Discussion: https://postgr.es/m/YlPQGNAAa04raObK@paquier.xyz

1 files changed, 294 insertions, 0 deletions

diff --git a/src/common/compression.c b/src/common/compression.c
new file mode 100644
index 00000000000..632fae61442
--- /dev/null
+++ b/src/common/compression.c
@@ -0,0 +1,294 @@
+/*-------------------------------------------------------------------------
+ *
+ * compression.c
+ *
+ * Shared code for compression methods and specifications.
+ *
+ * A compression specification specifies the parameters that should be used
+ * when performing compression with a specific algorithm. The simplest
+ * possible compression specification is an integer, which sets the
+ * compression level.
+ *
+ * Otherwise, a compression specification is a comma-separated list of items,
+ * each having the form keyword or keyword=value.
+ *
+ * Currently, the only supported keywords are "level" and "workers".
+ *
+ * Portions Copyright (c) 1996-2022, PostgreSQL Global Development Group
+ *
+ * IDENTIFICATION
+ *		  src/common/compression.c
+ *-------------------------------------------------------------------------
+ */
+
+#ifndef FRONTEND
+#include "postgres.h"
+#else
+#include "postgres_fe.h"
+#endif
+
+#include "common/compression.h"
+
+static int	expect_integer_value(char *keyword, char *value,
+								 pg_compress_specification *result);
+
+/*
+ * Look up a compression algorithm by name. Returns true and sets *algorithm
+ * if the name is recognized. Otherwise returns false.
+ */
+bool
+parse_compress_algorithm(char *name, pg_compress_algorithm *algorithm)
+{
+	if (strcmp(name, "none") == 0)
+		*algorithm = PG_COMPRESSION_NONE;
+	else if (strcmp(name, "gzip") == 0)
+		*algorithm = PG_COMPRESSION_GZIP;
+	else if (strcmp(name, "lz4") == 0)
+		*algorithm = PG_COMPRESSION_LZ4;
+	else if (strcmp(name, "zstd") == 0)
+		*algorithm = PG_COMPRESSION_ZSTD;
+	else
+		return false;
+	return true;
+}
+
+/*
+ * Get the human-readable name corresponding to a particular compression
+ * algorithm.
+ */
+const char *
+get_compress_algorithm_name(pg_compress_algorithm algorithm)
+{
+	switch (algorithm)
+	{
+		case PG_COMPRESSION_NONE:
+			return "none";
+		case PG_COMPRESSION_GZIP:
+			return "gzip";
+		case PG_COMPRESSION_LZ4:
+			return "lz4";
+		case PG_COMPRESSION_ZSTD:
+			return "zstd";
+			/* no default, to provoke compiler warnings if values are added */
+	}
+	Assert(false);
+	return "???";	/* placate compiler */
+}
+
+/*
+ * Parse a compression specification for a specified algorithm.
+ *
+ * See the file header comments for a brief description of what a compression
+ * specification is expected to look like.
+ *
+ * On return, all fields of the result object will be initialized.
+ * In particular, result->parse_error will be NULL if no errors occurred
+ * during parsing, and will otherwise contain an appropriate error message.
+ * The caller may free this error message string using pfree, if desired.
+ * Note, however, even if there's no parse error, the string might not make
+ * sense: e.g. for gzip, level=12 is not sensible, but it does parse OK.
+ *
+ * Use validate_compress_specification() to find out whether a compression
+ * specification is semantically sensible.
+ */
+void
+parse_compress_specification(pg_compress_algorithm algorithm, char *specification,
+					   pg_compress_specification *result)
+{
+	int			bare_level;
+	char	   *bare_level_endp;
+
+	/* Initial setup of result object. */
+	result->algorithm = algorithm;
+	result->options = 0;
+	result->level = -1;
+	result->parse_error = NULL;
+
+	/* If there is no specification, we're done already. */
+	if (specification == NULL)
+		return;
+
+	/* As a special case, the specification can be a bare integer. */
+	bare_level = strtol(specification, &bare_level_endp, 10);
+	if (specification != bare_level_endp && *bare_level_endp == '\0')
+	{
+		result->level = bare_level;
+		result->options |= PG_COMPRESSION_OPTION_LEVEL;
+		return;
+	}
+
+	/* Look for comma-separated keyword or keyword=value entries. */
+	while (1)
+	{
+		char	   *kwstart;
+		char	   *kwend;
+		char	   *vstart;
+		char	   *vend;
+		int			kwlen;
+		int			vlen;
+		bool		has_value;
+		char	   *keyword;
+		char	   *value;
+
+		/* Figure start, end, and length of next keyword and any value. */
+		kwstart = kwend = specification;
+		while (*kwend != '\0' && *kwend != ',' && *kwend != '=')
+			++kwend;
+		kwlen = kwend - kwstart;
+		if (*kwend != '=')
+		{
+			vstart = vend = NULL;
+			vlen = 0;
+			has_value = false;
+		}
+		else
+		{
+			vstart = vend = kwend + 1;
+			while (*vend != '\0' && *vend != ',')
+				++vend;
+			vlen = vend - vstart;
+			has_value = true;
+		}
+
+		/* Reject empty keyword. */
+		if (kwlen == 0)
+		{
+			result->parse_error =
+				pstrdup(_("found empty string where a compression option was expected"));
+			break;
+		}
+
+		/* Extract keyword and value as separate C strings. */
+		keyword = palloc(kwlen + 1);
+		memcpy(keyword, kwstart, kwlen);
+		keyword[kwlen] = '\0';
+		if (!has_value)
+			value = NULL;
+		else
+		{
+			value = palloc(vlen + 1);
+			memcpy(value, vstart, vlen);
+			value[vlen] = '\0';
+		}
+
+		/* Handle whatever keyword we found. */
+		if (strcmp(keyword, "level") == 0)
+		{
+			result->level = expect_integer_value(keyword, value, result);
+			result->options |= PG_COMPRESSION_OPTION_LEVEL;
+		}
+		else if (strcmp(keyword, "workers") == 0)
+		{
+			result->workers = expect_integer_value(keyword, value, result);
+			result->options |= PG_COMPRESSION_OPTION_WORKERS;
+		}
+		else
+			result->parse_error =
+				psprintf(_("unknown compression option \"%s\""), keyword);
+
+		/* Release memory, just to be tidy. */
+		pfree(keyword);
+		if (value != NULL)
+			pfree(value);
+
+		/*
+		 * If we got an error or have reached the end of the string, stop.
+		 *
+		 * If there is no value, then the end of the keyword might have been
+		 * the end of the string. If there is a value, then the end of the
+		 * keyword cannot have been the end of the string, but the end of the
+		 * value might have been.
+		 */
+		if (result->parse_error != NULL ||
+			(vend == NULL ? *kwend == '\0' : *vend == '\0'))
+			break;
+
+		/* Advance to next entry and loop around. */
+		specification = vend == NULL ? kwend + 1 : vend + 1;
+	}
+}
+
+/*
+ * Parse 'value' as an integer and return the result.
+ *
+ * If parsing fails, set result->parse_error to an appropriate message
+ * and return -1.
+ */
+static int
+expect_integer_value(char *keyword, char *value, pg_compress_specification *result)
+{
+	int			ivalue;
+	char	   *ivalue_endp;
+
+	if (value == NULL)
+	{
+		result->parse_error =
+			psprintf(_("compression option \"%s\" requires a value"),
+					 keyword);
+		return -1;
+	}
+
+	ivalue = strtol(value, &ivalue_endp, 10);
+	if (ivalue_endp == value || *ivalue_endp != '\0')
+	{
+		result->parse_error =
+			psprintf(_("value for compression option \"%s\" must be an integer"),
+					 keyword);
+		return -1;
+	}
+	return ivalue;
+}
+
+/*
+ * Returns NULL if the compression specification string was syntactically
+ * valid and semantically sensible.  Otherwise, returns an error message.
+ *
+ * Does not test whether this build of PostgreSQL supports the requested
+ * compression method.
+ */
+char *
+validate_compress_specification(pg_compress_specification *spec)
+{
+	/* If it didn't even parse OK, it's definitely no good. */
+	if (spec->parse_error != NULL)
+		return spec->parse_error;
+
+	/*
+	 * If a compression level was specified, check that the algorithm expects
+	 * a compression level and that the level is within the legal range for
+	 * the algorithm.
+	 */
+	if ((spec->options & PG_COMPRESSION_OPTION_LEVEL) != 0)
+	{
+		int			min_level = 1;
+		int			max_level;
+
+		if (spec->algorithm == PG_COMPRESSION_GZIP)
+			max_level = 9;
+		else if (spec->algorithm == PG_COMPRESSION_LZ4)
+			max_level = 12;
+		else if (spec->algorithm == PG_COMPRESSION_ZSTD)
+			max_level = 22;
+		else
+			return psprintf(_("compression algorithm \"%s\" does not accept a compression level"),
+							get_compress_algorithm_name(spec->algorithm));
+
+		if (spec->level < min_level || spec->level > max_level)
+			return psprintf(_("compression algorithm \"%s\" expects a compression level between %d and %d"),
+							get_compress_algorithm_name(spec->algorithm),
+							min_level, max_level);
+	}
+
+	/*
+	 * Of the compression algorithms that we currently support, only zstd
+	 * allows parallel workers.
+	 */
+	if ((spec->options & PG_COMPRESSION_OPTION_WORKERS) != 0 &&
+		(spec->algorithm != PG_COMPRESSION_ZSTD))
+	{
+		return psprintf(_("compression algorithm \"%s\" does not accept a worker count"),
+						get_compress_algorithm_name(spec->algorithm));
+	}
+
+	return NULL;
+}