dump: support gzipped and atomic output

The main goal is to support gzipped output for future internal
calls (e.g. from notmuch-new) to notmuch_database_dump.

The additional dependency is not very heavy since xapian already pulls
in zlib.

We want the dump to be "atomic", in the sense that after running the
dump file is either present and complete, or not present.  This avoids
certain classes of mishaps involving overwriting a good backup with a
bad or partial one.

7 files changed, 142 insertions, 28 deletions

diff --git a/INSTALL b/INSTALL
index 690b0efd..b543c508 100644
--- a/INSTALL
+++ b/INSTALL
@@ -20,8 +20,8 @@ configure stage.
 
 Dependencies
 ------------
-Notmuch depends on three libraries: Xapian, GMime 2.4 or 2.6, and
-Talloc which are each described below:
+Notmuch depends on four libraries: Xapian, GMime 2.4 or 2.6,
+Talloc, and zlib which are each described below:
 
 	Xapian
 	------
@@ -60,6 +60,18 @@ Talloc which are each described below:
 
 	Talloc is available from http://talloc.samba.org/
 
+	zlib
+	----
+
+	zlib is an extremely popular compression library. It is used
+	by Xapian, so if you installed that you will already have
+	zlib. You may need to install the zlib headers separately.
+
+	Notmuch needs the transparent write feature of zlib introduced
+	in version 1.2.5.2 (Dec. 2011).
+
+	zlib is available from http://zlib.net
+
 Building Documentation
 ----------------------
 
@@ -79,11 +91,11 @@ dependencies with a simple simple command line. For example:
 
   For Debian and similar:
 
-        sudo apt-get install libxapian-dev libgmime-2.6-dev libtalloc-dev python-sphinx
+        sudo apt-get install libxapian-dev libgmime-2.6-dev libtalloc-dev zlib1g-dev python-sphinx
 
   For Fedora and similar:
 
-	sudo yum install xapian-core-devel gmime-devel libtalloc-devel python-sphinx
+	sudo yum install xapian-core-devel gmime-devel libtalloc-devel zlib-devel python-sphinx
 
 On other systems, a similar command can be used, but the details of
 the package names may be different.
diff --git a/Makefile.local b/Makefile.local
index 1856350e..877a9790 100644
--- a/Makefile.local
+++ b/Makefile.local
@@ -46,7 +46,7 @@ PV_FILE=bindings/python/notmuch/version.py
 # Smash together user's values with our extra values
 FINAL_CFLAGS = -DNOTMUCH_VERSION=$(VERSION) $(CPPFLAGS) $(CFLAGS) $(WARN_CFLAGS) $(extra_cflags) $(CONFIGURE_CFLAGS)
 FINAL_CXXFLAGS = $(CPPFLAGS) $(CXXFLAGS) $(WARN_CXXFLAGS) $(extra_cflags) $(extra_cxxflags) $(CONFIGURE_CXXFLAGS)
-FINAL_NOTMUCH_LDFLAGS = $(LDFLAGS) -Lutil -lutil -Llib -lnotmuch $(AS_NEEDED_LDFLAGS) $(GMIME_LDFLAGS) $(TALLOC_LDFLAGS)
+FINAL_NOTMUCH_LDFLAGS = $(LDFLAGS) -Lutil -lutil -Llib -lnotmuch $(AS_NEEDED_LDFLAGS) $(GMIME_LDFLAGS) $(TALLOC_LDFLAGS) $(ZLIB_LDFLAGS)
 FINAL_NOTMUCH_LINKER = CC
 ifneq ($(LINKER_RESOLVES_LIBRARY_DEPENDENCIES),1)
 FINAL_NOTMUCH_LDFLAGS += $(CONFIGURE_LDFLAGS)
diff --git a/configure b/configure
index 09f4650c..b8a3ce76 100755
--- a/configure
+++ b/configure
@@ -340,6 +340,18 @@ else
     errors=$((errors + 1))
 fi
 
+printf "Checking for zlib (>= 1.2.5.2)... "
+have_zlib=0
+if pkg-config --atleast-version=1.2.5.2 zlib; then
+    printf "Yes.\n"
+    have_zlib=1
+    zlib_cflags=$(pkg-config --cflags zlib)
+    zlib_ldflags=$(pkg-config --libs zlib)
+else
+    printf "No.\n"
+    errors=$((errors + 1))
+fi
+
 printf "Checking for talloc development files... "
 if pkg-config --exists talloc; then
     printf "Yes.\n"
@@ -496,6 +508,11 @@ EOF
 	echo "	Xapian library (including development files such as headers)"
 	echo "	http://xapian.org/"
     fi
+    if [ $have_zlib -eq 0 ]; then
+	echo "	zlib library (>= version 1.2.5.2, including development files such as headers)"
+	echo "	http://zlib.net/"
+	echo
+    fi
     if [ $have_gmime -eq 0 ]; then
 	echo "	Either GMime 2.4 library" $GMIME_24_VERSION_CTR "or GMime 2.6 library" $GMIME_26_VERSION_CTR
 	echo "	(including development files such as headers)"
@@ -519,11 +536,11 @@ case a simple command will install everything you need. For example:
 
 On Debian and similar systems:
 
-	sudo apt-get install libxapian-dev libgmime-2.6-dev libtalloc-dev
+	sudo apt-get install libxapian-dev libgmime-2.6-dev libtalloc-dev zlib1g-dev
 
 Or on Fedora and similar systems:
 
-	sudo yum install xapian-core-devel gmime-devel libtalloc-devel
+	sudo yum install xapian-core-devel gmime-devel libtalloc-devel zlib-devel
 
 On other systems, similar commands can be used, but the details of the
 package names may be different.
@@ -860,6 +877,10 @@ XAPIAN_LDFLAGS = ${xapian_ldflags}
 GMIME_CFLAGS = ${gmime_cflags}
 GMIME_LDFLAGS = ${gmime_ldflags}
 
+# Flags needed to compile and link against zlib
+ZLIB_CFLAGS = ${zlib_cflags}
+ZLIB_LDFLAGS = ${zlib_ldflags}
+
 # Flags needed to compile and link against talloc
 TALLOC_CFLAGS = ${talloc_cflags}
 TALLOC_LDFLAGS = ${talloc_ldflags}
@@ -898,6 +919,7 @@ CONFIGURE_CFLAGS = -DHAVE_GETLINE=\$(HAVE_GETLINE) \$(GMIME_CFLAGS)      \\
 		   -DUTIL_BYTE_ORDER=\$(UTIL_BYTE_ORDER)
 
 CONFIGURE_CXXFLAGS = -DHAVE_GETLINE=\$(HAVE_GETLINE) \$(GMIME_CFLAGS)    \\
+		     \$(ZLIB_CFLAGS)					 \\
 		     \$(TALLOC_CFLAGS) -DHAVE_VALGRIND=\$(HAVE_VALGRIND) \\
 		     \$(VALGRIND_CFLAGS) \$(XAPIAN_CXXFLAGS)             \\
 		     -DHAVE_STRCASESTR=\$(HAVE_STRCASESTR)               \\
@@ -908,5 +930,5 @@ CONFIGURE_CXXFLAGS = -DHAVE_GETLINE=\$(HAVE_GETLINE) \$(GMIME_CFLAGS)    \\
 		     -DHAVE_XAPIAN_COMPACT=\$(HAVE_XAPIAN_COMPACT)       \\
 		     -DUTIL_BYTE_ORDER=\$(UTIL_BYTE_ORDER)
 
-CONFIGURE_LDFLAGS =  \$(GMIME_LDFLAGS) \$(TALLOC_LDFLAGS) \$(XAPIAN_LDFLAGS)
+CONFIGURE_LDFLAGS =  \$(GMIME_LDFLAGS) \$(TALLOC_LDFLAGS) \$(ZLIB_LDFLAGS) \$(XAPIAN_LDFLAGS)
 EOF
diff --git a/doc/man1/notmuch-dump.rst b/doc/man1/notmuch-dump.rst
index 17d1da5c..d94cb4f8 100644
--- a/doc/man1/notmuch-dump.rst
+++ b/doc/man1/notmuch-dump.rst
@@ -19,6 +19,9 @@ recreated from the messages themselves. The output of notmuch dump is
 therefore the only critical thing to backup (and much more friendly to
 incremental backup than the native database files.)
 
+``--gzip``
+    Compress the output in a format compatible with **gzip(1)**.
+
 ``--format=(sup|batch-tag)``
     Notmuch restore supports two plain text dump formats, both with one
     message-id per line, followed by a list of tags.
diff --git a/notmuch-client.h b/notmuch-client.h
index d1106482..e1efbe0c 100644
--- a/notmuch-client.h
+++ b/notmuch-client.h
@@ -450,7 +450,9 @@ typedef enum dump_formats {
 int
 notmuch_database_dump (notmuch_database_t *notmuch,
 		       const char *output_file_name,
-		       const char *query_str, dump_format_t output_format);
+		       const char *query_str,
+		       dump_format_t output_format,
+		       notmuch_bool_t gzip_output);
 
 #include "command-line-arguments.h"
 #endif
diff --git a/notmuch-dump.c b/notmuch-dump.c
index 21702d79..2849eaba 100644
--- a/notmuch-dump.c
+++ b/notmuch-dump.c
@@ -21,9 +21,11 @@
 #include "notmuch-client.h"
 #include "hex-escape.h"
 #include "string-util.h"
+#include <zlib.h>
+
 
 static int
-database_dump_file (notmuch_database_t *notmuch, FILE *output,
+database_dump_file (notmuch_database_t *notmuch, gzFile output,
 		    const char *query_str, int output_format)
 {
     notmuch_query_t *query;
@@ -69,7 +71,7 @@ database_dump_file (notmuch_database_t *notmuch, FILE *output,
 	}
 
 	if (output_format == DUMP_FORMAT_SUP) {
-	    fprintf (output, "%s (", message_id);
+	    gzprintf (output, "%s (", message_id);
 	}
 
 	for (tags = notmuch_message_get_tags (message);
@@ -78,12 +80,12 @@ database_dump_file (notmuch_database_t *notmuch, FILE *output,
 	    const char *tag_str = notmuch_tags_get (tags);
 
 	    if (! first)
-		fputs (" ", output);
+		gzputs (output, " ");
 
 	    first = 0;
 
 	    if (output_format == DUMP_FORMAT_SUP) {
-		fputs (tag_str, output);
+		gzputs (output, tag_str);
 	    } else {
 		if (hex_encode (notmuch, tag_str,
 				&buffer, &buffer_size) != HEX_SUCCESS) {
@@ -91,12 +93,12 @@ database_dump_file (notmuch_database_t *notmuch, FILE *output,
 			     tag_str);
 		    return EXIT_FAILURE;
 		}
-		fprintf (output, "+%s", buffer);
+		gzprintf (output, "+%s", buffer);
 	    }
 	}
 
 	if (output_format == DUMP_FORMAT_SUP) {
-	    fputs (")\n", output);
+	    gzputs (output, ")\n");
 	} else {
 	    if (make_boolean_term (notmuch, "id", message_id,
 				   &buffer, &buffer_size)) {
@@ -104,7 +106,7 @@ database_dump_file (notmuch_database_t *notmuch, FILE *output,
 			     message_id, strerror (errno));
 		    return EXIT_FAILURE;
 	    }
-	    fprintf (output, " -- %s\n", buffer);
+	    gzprintf (output, " -- %s\n", buffer);
 	}
 
 	notmuch_message_destroy (message);
@@ -121,24 +123,83 @@ database_dump_file (notmuch_database_t *notmuch, FILE *output,
 int
 notmuch_database_dump (notmuch_database_t *notmuch,
 		       const char *output_file_name,
-		       const char *query_str, dump_format_t output_format)
+		       const char *query_str,
+		       dump_format_t output_format,
+		       notmuch_bool_t gzip_output)
 {
-    FILE *output = stdout;
-    int ret;
+    gzFile output = NULL;
+    const char *mode = gzip_output ? "w9" : "wT";
+    const char *name_for_error = output_file_name ? output_file_name : "stdout";
+
+    char *tempname = NULL;
+    int outfd = -1;
+
+    int ret = -1;
 
     if (output_file_name) {
-	output = fopen (output_file_name, "w");
-	if (output == NULL) {
-	    fprintf (stderr, "Error opening %s for writing: %s\n",
-		     output_file_name, strerror (errno));
-	    return EXIT_FAILURE;
-	}
+	tempname = talloc_asprintf (notmuch, "%s.XXXXXX", output_file_name);
+	outfd = mkstemp (tempname);
+    } else {
+	outfd = dup (STDOUT_FILENO);
+    }
+
+    if (outfd < 0) {
+	fprintf (stderr, "Bad output file %s\n", name_for_error);
+	goto DONE;
+    }
+
+    output = gzdopen (outfd, mode);
+
+    if (output == NULL) {
+	fprintf (stderr, "Error opening %s for (gzip) writing: %s\n",
+		 name_for_error, strerror (errno));
+	if (close (outfd))
+	    fprintf (stderr, "Error closing %s during shutdown: %s\n",
+		 name_for_error, strerror (errno));
+	goto DONE;
     }
 
     ret = database_dump_file (notmuch, output, query_str, output_format);
+    if (ret) goto DONE;
+
+    ret = gzflush (output, Z_FINISH);
+    if (ret) {
+	fprintf (stderr, "Error flushing output: %s\n", gzerror (output, NULL));
+	goto DONE;
+    }
+
+    if (output_file_name) {
+	ret = fdatasync (outfd);
+	if (ret) {
+	    fprintf (stderr, "Error syncing %s to disk: %s\n",
+		     name_for_error, strerror (errno));
+	    goto DONE;
+	}
+    }
+
+    if (gzclose_w (output) != Z_OK) {
+	fprintf (stderr, "Error closing %s: %s\n", name_for_error,
+		 gzerror (output, NULL));
+	ret = EXIT_FAILURE;
+	output = NULL;
+	goto DONE;
+    }
+
+    if (output_file_name) {
+	ret = rename (tempname, output_file_name);
+	if (ret) {
+	    fprintf (stderr, "Error renaming %s to %s: %s\n",
+		     tempname, output_file_name, strerror (errno));
+	    goto DONE;
+	}
+
+    }
+ DONE:
+    if (ret != EXIT_SUCCESS && output)
+	(void) gzclose_w (output);
 
-    if (output != stdout)
-	fclose (output);
+    if (ret != EXIT_SUCCESS && output_file_name)
+	(void) unlink (tempname);
 
     return ret;
 }
@@ -158,6 +219,7 @@ notmuch_dump_command (notmuch_config_t *config, int argc, char *argv[])
     int opt_index;
 
     int output_format = DUMP_FORMAT_BATCH_TAG;
+    notmuch_bool_t gzip_output = 0;
 
     notmuch_opt_desc_t options[] = {
 	{ NOTMUCH_OPT_KEYWORD, &output_format, "format", 'f',
@@ -165,6 +227,7 @@ notmuch_dump_command (notmuch_config_t *config, int argc, char *argv[])
 				  { "batch-tag", DUMP_FORMAT_BATCH_TAG },
 				  { 0, 0 } } },
 	{ NOTMUCH_OPT_STRING, &output_file_name, "output", 'o', 0  },
+	{ NOTMUCH_OPT_BOOLEAN, &gzip_output, "gzip", 'z', 0 },
 	{ 0, 0, 0, 0, 0 }
     };
 
@@ -181,7 +244,7 @@ notmuch_dump_command (notmuch_config_t *config, int argc, char *argv[])
     }
 
     ret = notmuch_database_dump (notmuch, output_file_name, query_str,
-				 output_format);
+				 output_format, gzip_output);
 
     notmuch_database_destroy (notmuch);
 
diff --git a/test/T240-dump-restore.sh b/test/T240-dump-restore.sh
index 0004438d..d79aca86 100755
--- a/test/T240-dump-restore.sh
+++ b/test/T240-dump-restore.sh
@@ -68,6 +68,18 @@ test_begin_subtest "dump --output=outfile --"
 notmuch dump --output=dump-1-arg-dash.actual --
 test_expect_equal_file dump.expected dump-1-arg-dash.actual
 
+# gzipped output
+
+test_begin_subtest "dump --gzip"
+notmuch dump --gzip > dump-gzip.gz
+gunzip dump-gzip.gz
+test_expect_equal_file dump.expected dump-gzip
+
+test_begin_subtest "dump --gzip --output=outfile"
+notmuch dump --gzip --output=dump-gzip-outfile.gz
+gunzip dump-gzip-outfile.gz
+test_expect_equal_file dump.expected dump-gzip-outfile
+
 # Note, we assume all messages from cworth have a message-id
 # containing cworth.org