Refactor the pg_dump zlib code from pg_backup_custom.c to a separate file,

to make it easier to reuse that code. There is no user-visible changes.

This is in preparation for the patch to add a new archive format, a directory,
to perform a custom-like dump but with each table being dumped to a separate
file (that in turn is a prerequisite for parallel pg_dump). This also makes it
easier to add new compression methods in the future, and makes the
pg_backup_custom.c code easier to read, when the compression-related code is
factored out.

Joachim Wieland, with heavy editorialization by me.

src/bin/pg_dump/Makefile

@@ -20,7 +20,7 @@ override CPPFLAGS := -I$(libpq_srcdir) $(CPPFLAGS)
 
 OBJS=	pg_backup_archiver.o pg_backup_db.o pg_backup_custom.o \
 	pg_backup_files.o pg_backup_null.o pg_backup_tar.o \
-	dumputils.o $(WIN32RES)
+	dumputils.o compress_io.o $(WIN32RES)
 
 KEYWRDOBJS = keywords.o kwlookup.o
 

src/bin/pg_dump/compress_io.h

+/*-------------------------------------------------------------------------
+ *
+ * compress_io.h
+ *   Interface to compress_io.c routines
+ *
+ * Portions Copyright (c) 1996-2010, PostgreSQL Global Development Group
+ * Portions Copyright (c) 1994, Regents of the University of California
+ *
+ * IDENTIFICATION
+ *     src/bin/pg_dump/compress_io.h
+ *
+ *-------------------------------------------------------------------------
+ */
+
+#ifndef __COMPRESS_IO__
+#define __COMPRESS_IO__
+
+#include "postgres_fe.h"
+#include "pg_backup_archiver.h"
+
+/* Initial buffer sizes used in zlib compression. */
+#define ZLIB_OUT_SIZE	4096
+#define ZLIB_IN_SIZE	4096
+
+struct _CompressorState;
+
+typedef enum
+{
+	COMPR_ALG_NONE,
+	COMPR_ALG_LIBZ
+} CompressionAlgorithm;
+
+/* Prototype for callback function to WriteDataToArchive() */
+typedef size_t (*WriteFunc)(ArchiveHandle *AH, const char *buf, size_t len);
+
+/*
+ * Prototype for callback function to ReadDataFromArchive()
+ *
+ * ReadDataFromArchive will call the read function repeatedly, until it
+ * returns 0 to signal EOF. ReadDataFromArchive passes a buffer to read the
+ * data into in *buf, of length *buflen. If that's not big enough for the
+ * callback function, it can free() it and malloc() a new one, returning the
+ * new buffer and its size in *buf and *buflen.
+ *
+ * Returns the number of bytes read into *buf, or 0 on EOF.
+ */
+typedef size_t (*ReadFunc)(ArchiveHandle *AH, char **buf, size_t *buflen);
+
+typedef struct _CompressorState
+{
+	CompressionAlgorithm comprAlg;
+	WriteFunc			writeF;
+
+#ifdef HAVE_LIBZ
+	z_streamp			zp;
+	char			   *zlibOut;
+	size_t				zlibOutSize;
+#endif
+} CompressorState;
+
+extern CompressorState *AllocateCompressor(int compression, WriteFunc writeF);
+extern void ReadDataFromArchive(ArchiveHandle *AH, int compression,
+								ReadFunc readF);
+extern size_t WriteDataToArchive(ArchiveHandle *AH, CompressorState *cs,
+								 const void *data, size_t dLen);
+extern void EndCompressor(ArchiveHandle *AH, CompressorState *cs);
+
+#endif

src/bin/pg_dump/pg_backup_archiver.h

@@ -49,6 +49,7 @@
 #define GZCLOSE(fh) fclose(fh)
 #define GZWRITE(p, s, n, fh) (fwrite(p, s, n, fh) * (s))
 #define GZREAD(p, s, n, fh) fread(p, s, n, fh)
+/* this is just the redefinition of a libz constant */
 #define Z_DEFAULT_COMPRESSION (-1)
 
 typedef struct _z_stream
@@ -266,7 +267,11 @@ typedef struct _archiveHandle
 	DumpId		maxDumpId;		/* largest DumpId among all TOC entries */
 
 	struct _tocEntry *currToc;	/* Used when dumping data */
-	int			compression;	/* Compression requested on open */
+	int			compression;	/* Compression requested on open
+								 * Possible values for compression:
+								 *  -1   Z_DEFAULT_COMPRESSION
+								 *   0	COMPRESSION_NONE
+								 *  1-9	levels for gzip compression */
 	ArchiveMode mode;			/* File mode - r or w */
 	void	   *formatData;		/* Header data specific to file format */