Save XML files into a memory buffer rather than directly into a file

This introduces a "struct membuffer" abstraction that you can write
things into, and makes the XML saving code write to the memory buffer
rather than a file.

The UDDF export already really wanted this: it used to write to a file,
only to then read that file back into memory, delete the file, and then
*rewrite* the file after doing the magic xslt transform.

But the longer-term reason for this is that I want to try to write other
formats, and I want to try to share most helpers.  And those other
formats will need this memory buffer model.

Signed-off-by: Linus Torvalds <torvalds@linux-foundation.org>
Signed-off-by: Dirk Hohndel <dirk@hohndel.org>

6 files changed, 393 insertions, 230 deletions

diff --git a/device.h b/device.h
index 57735a64b..ad5dee6f1 100644
--- a/device.h
+++ b/device.h
@@ -8,7 +8,7 @@ extern "C" {
 
 extern struct divecomputer *fake_dc(struct divecomputer* dc);
 extern void create_device_node(const char *model, uint32_t deviceid, const char *serial, const char *firmware, const char *nickname);
-extern void call_for_each_dc(FILE *f, void (*callback)(FILE *, const char *, uint32_t,
+extern void call_for_each_dc(void *f, void (*callback)(void *, const char *, uint32_t,
 						       const char *, const char *, const char *));
 
 #ifdef __cplusplus
diff --git a/membuffer.c b/membuffer.c
new file mode 100644
index 000000000..30ba05fdb
--- /dev/null
+++ b/membuffer.c
@@ -0,0 +1,160 @@
+#include <stdarg.h>
+#include <stdlib.h>
+#include <string.h>
+#include <stdio.h>
+
+#include "dive.h"
+#include "membuffer.h"
+
+void free_buffer(struct membuffer *b)
+{
+	free(b->buffer);
+	b->buffer = NULL;
+	b->used = 0;
+	b->size = 0;
+}
+
+void flush_buffer(struct membuffer *b, FILE *f)
+{
+	if (b->used) {
+		fwrite(b->buffer, 1, b->used, f);
+		free_buffer(b);
+	}
+}
+
+/*
+ * Running out of memory isn't really an issue these days.
+ * So rather than do insane error handling and making the
+ * interface very complex, we'll just die. It won't happen
+ * unless you're running on a potato.
+ */
+static void oom(void)
+{
+	fprintf(stderr, "Out of memory\n");
+	exit(1);
+}
+
+static void make_room(struct membuffer *b, unsigned int size)
+{
+	unsigned int needed = b->used + size;
+	if (needed > b->size) {
+		char *n;
+		/* round it up to not reallocate all the time.. */
+		needed = needed * 9 / 8 + 1024;
+		n = realloc(b->buffer, needed);
+		if (!n)
+			oom();
+		b->buffer = n;
+		b->size = needed;
+	}
+}
+
+void put_bytes(struct membuffer *b, const char *str, int len)
+{
+	make_room(b, len);
+	memcpy(b->buffer + b->used, str, len);
+	b->used += len;
+}
+
+void put_string(struct membuffer *b, const char *str)
+{
+	put_bytes(b, str, strlen(str));
+}
+
+void put_vformat(struct membuffer *b, const char *fmt, va_list args)
+{
+	/* Handle the common case on the stack */
+	char buffer[128], *p;
+	int len;
+
+	len = vsnprintf(buffer, sizeof(buffer), fmt, args);
+	if (len <= sizeof(buffer)) {
+		put_bytes(b, buffer, len);
+		return;
+	}
+
+	p = malloc(len);
+	len = vsnprintf(p, len, fmt, args);
+	put_bytes(b, p, len);
+	free(p);
+}
+
+void put_format(struct membuffer *b, const char *fmt, ...)
+{
+	va_list args;
+
+	va_start(args, fmt);
+	put_vformat(b, fmt, args);
+	va_end(args);
+}
+
+void put_milli(struct membuffer *b, const char *pre, int value, const char *post)
+{
+	int i;
+	char buf[4];
+	const char *sign = "";
+	unsigned v;
+
+	v = value;
+	if (value < 0) {
+		sign = "-";
+		v = -value;
+	}
+	for (i = 2; i >= 0; i--) {
+		buf[i] = (v % 10) + '0';
+		v /= 10;
+	}
+	buf[3] = 0;
+	if (buf[2] == '0') {
+		buf[2] = 0;
+		if (buf[1] == '0')
+			buf[1] = 0;
+	}
+
+	put_format(b, "%s%s%u.%s%s", pre, sign, v, buf, post);
+}
+
+int put_temperature(struct membuffer *b, temperature_t temp, const char *pre, const char *post)
+{
+	if (!temp.mkelvin)
+		return 0;
+
+	put_milli(b, pre, temp.mkelvin - ZERO_C_IN_MKELVIN, post);
+	return 1;
+}
+
+int put_depth(struct membuffer *b, depth_t depth, const char *pre, const char *post)
+{
+	if (!depth.mm)
+		return 0;
+
+	put_milli(b, pre, depth.mm, post);
+	return 1;
+}
+
+int put_duration(struct membuffer *b, duration_t duration, const char *pre, const char *post)
+{
+	if (!duration.seconds)
+		return 0;
+
+	put_format(b, "%s%u:%02u%s", pre, FRACTION(duration.seconds, 60), post);
+	return 1;
+}
+
+int put_pressure(struct membuffer *b, pressure_t pressure, const char *pre, const char *post)
+{
+	if (!pressure.mbar)
+		return 0;
+
+	put_milli(b, pre, pressure.mbar, post);
+	return 1;
+}
+
+int put_salinity(struct membuffer *b, int salinity, const char *pre, const char *post)
+{
+	if (!salinity)
+		return 0;
+
+	put_format(b, "%s%d%s", pre, salinity / 10, post);
+	return 1;
+}
diff --git a/membuffer.h b/membuffer.h
new file mode 100644
index 000000000..bef9e76bc
--- /dev/null
+++ b/membuffer.h
@@ -0,0 +1,52 @@
+#ifndef MEMBUFFER_H
+#define MEMBUFFER_H
+
+struct membuffer {
+	unsigned int size, used;
+	char *buffer;
+};
+
+#ifdef __GNUC__
+#define __printf(x,y) __attribute__ ((__format__ (__printf__, x, y)))
+#else
+#define __printf(x,y)
+#endif
+
+extern void free_buffer(struct membuffer *);
+extern void flush_buffer(struct membuffer *, FILE *);
+extern void put_bytes(struct membuffer *, const char *, int);
+extern void put_string(struct membuffer *, const char *);
+extern __printf(2,0) void put_vformat(struct membuffer *, const char *, va_list);
+extern __printf(2,3) void put_format(struct membuffer *, const char *fmt, ...);
+
+/* Output one of our "milli" values with type and pre/post data */
+extern void put_milli(struct membuffer *, const char *, int, const char *);
+
+/*
+ * Helper functions for showing particular types. If the type
+ * is empty, nothing is done, and the function returns false.
+ * Otherwise, it returns true.
+ *
+ * The two "const char *" at the end are pre/post data.
+ *
+ * The reason for the pre/post data is so that you can easily
+ * prepend and append a string without having to test whether the
+ * type is empty. So
+ *
+ *     put_temperature(b, temp, "Temp=", " C\n");
+ *
+ * writes nothing to the buffer if there is no temperature data,
+ * but otherwise would a string that looks something like
+ *
+ *     "Temp=28.1 C\n"
+ *
+ * to the memory buffer (typically the post/pre will be some XML
+ * pattern and unit string or whatever).
+ */
+extern int put_temperature(struct membuffer *, temperature_t, const char *, const char *);
+extern int put_depth(struct membuffer *, depth_t, const char *, const char *);
+extern int put_duration(struct membuffer *, duration_t, const char *, const char *);
+extern int put_pressure(struct membuffer *, pressure_t, const char *, const char *);
+extern int put_salinity(struct membuffer *, int, const char *, const char *);
+
+#endif
diff --git a/qt-gui.cpp b/qt-gui.cpp
index 57b82b940..314e41906 100644
--- a/qt-gui.cpp
+++ b/qt-gui.cpp
@@ -452,7 +452,7 @@ bool compareDC(const DiveComputerNode &a, const DiveComputerNode &b)
 	return a.deviceId < b.deviceId;
 }
 
-void call_for_each_dc(FILE *f, void (*callback)(FILE *, const char *, uint32_t,
+void call_for_each_dc(void *f, void (*callback)(void *, const char *, uint32_t,
 						const char *, const char *, const char *))
 {
 	QList<DiveComputerNode> values = dcList.dcMap.values();
diff --git a/save-xml.c b/save-xml.c
index 704227c49..374632624 100644
--- a/save-xml.c
+++ b/save-xml.c
@@ -8,62 +8,8 @@
 
 #include "dive.h"
 #include "device.h"
+#include "membuffer.h"
 
-static void show_milli(FILE *f, const char *pre, int value, const char *unit, const char *post)
-{
-	int i;
-	char buf[4];
-	unsigned v;
-
-	fputs(pre, f);
-	v = value;
-	if (value < 0) {
-		putc('-', f);
-		v = -value;
-	}
-	for (i = 2; i >= 0; i--) {
-		buf[i] = (v % 10) + '0';
-		v /= 10;
-	}
-	buf[3] = 0;
-	if (buf[2] == '0') {
-		buf[2] = 0;
-		if (buf[1] == '0')
-			buf[1] = 0;
-	}
-
-	fprintf(f, "%u.%s%s%s", v, buf, unit, post);
-}
-
-static void show_temperature(FILE *f, temperature_t temp, const char *pre, const char *post)
-{
-	if (temp.mkelvin)
-		show_milli(f, pre, temp.mkelvin - ZERO_C_IN_MKELVIN, " C", post);
-}
-
-static void show_depth(FILE *f, depth_t depth, const char *pre, const char *post)
-{
-	if (depth.mm)
-		show_milli(f, pre, depth.mm, " m", post);
-}
-
-static void show_duration(FILE *f, duration_t duration, const char *pre, const char *post)
-{
-	if (duration.seconds)
-		fprintf(f, "%s%u:%02u min%s", pre, FRACTION(duration.seconds, 60), post);
-}
-
-static void show_pressure(FILE *f, pressure_t pressure, const char *pre, const char *post)
-{
-	if (pressure.mbar)
-		show_milli(f, pre, pressure.mbar, " bar", post);
-}
-
-static void show_salinity(FILE *f, int salinity, const char *pre, const char *post)
-{
-	if (salinity)
-		fprintf(f, "%s%d g/l%s", pre, salinity / 10, post);
-}
 /*
  * We're outputting utf8 in xml.
  * We need to quote the characters <, >, &.
@@ -74,7 +20,7 @@ static void show_salinity(FILE *f, int salinity, const char *pre, const char *po
  *
  * If we do this for attributes, we need to quote the quotes we use too.
  */
-static void quote(FILE *f, const char *text, int is_attribute)
+static void quote(struct membuffer *b, const char *text, int is_attribute)
 {
 	const char *p = text;
 
@@ -112,15 +58,15 @@ static void quote(FILE *f, const char *text, int is_attribute)
 			escape = "&quot;";
 			break;
 		}
-		fwrite(text, (p - text - 1), 1, f);
+		put_bytes(b, text, (p - text - 1));
 		if (!escape)
 			break;
-		fputs(escape, f);
+		put_string(b, escape);
 		text = p;
 	}
 }
 
-static void show_utf8(FILE *f, const char *text, const char *pre, const char *post, int is_attribute)
+static void show_utf8(struct membuffer *b, const char *text, const char *pre, const char *post, int is_attribute)
 {
 	int len;
 
@@ -134,65 +80,65 @@ static void show_utf8(FILE *f, const char *text, const char *pre, const char *po
 	while (len && isspace(text[len-1]))
 		len--;
 	/* FIXME! Quoting! */
-	fputs(pre, f);
-	quote(f, text, is_attribute);
-	fputs(post, f);
+	put_string(b, pre);
+	quote(b, text, is_attribute);
+	put_string(b, post);
 }
 
-static void save_depths(FILE *f, struct divecomputer *dc)
+static void save_depths(struct membuffer *b, struct divecomputer *dc)
 {
 	/* What's the point of this dive entry again? */
 	if (!dc->maxdepth.mm && !dc->meandepth.mm)
 		return;
 
-	fputs("  <depth", f);
-	show_depth(f, dc->maxdepth, " max='", "'");
-	show_depth(f, dc->meandepth, " mean='", "'");
-	fputs(" />\n", f);
+	put_string(b, "  <depth");
+	put_depth(b, dc->maxdepth, " max='", " m'");
+	put_depth(b, dc->meandepth, " mean='", " m'");
+	put_string(b, " />\n");
 }
 
-static void save_dive_temperature(FILE *f, struct dive *dive)
+static void save_dive_temperature(struct membuffer *b, struct dive *dive)
 {
 	if (!dive->airtemp.mkelvin && !dive->watertemp.mkelvin)
 		return;
 	if (dive->airtemp.mkelvin == dc_airtemp(&dive->dc) && dive->watertemp.mkelvin == dc_watertemp(&dive->dc))
 		return;
 
-	fputs("  <divetemperature", f);
-	if (dive->airtemp.mkelvin && dive->airtemp.mkelvin != dc_airtemp(&dive->dc))
-		show_temperature(f, dive->airtemp, " air='", "'");
-	if (dive->watertemp.mkelvin && dive->watertemp.mkelvin != dc_watertemp(&dive->dc))
-		show_temperature(f, dive->watertemp, " water='", "'");
-	fputs("/>\n", f);
+	put_string(b, "  <divetemperature");
+	if (dive->airtemp.mkelvin != dc_airtemp(&dive->dc))
+		put_temperature(b, dive->airtemp, " air='", " C'");
+	if (dive->watertemp.mkelvin != dc_watertemp(&dive->dc))
+		put_temperature(b, dive->watertemp, " water='", " C'");
+	put_string(b, "/>\n");
 }
 
-static void save_temperatures(FILE *f, struct divecomputer *dc)
+static void save_temperatures(struct membuffer *b, struct divecomputer *dc)
 {
 	if (!dc->airtemp.mkelvin && !dc->watertemp.mkelvin)
 		return;
-	fputs("  <temperature", f);
-	show_temperature(f, dc->airtemp, " air='", "'");
-	show_temperature(f, dc->watertemp, " water='", "'");
-	fputs(" />\n", f);
+	put_string(b, "  <temperature");
+	put_temperature(b, dc->airtemp, " air='", " C'");
+	put_temperature(b, dc->watertemp, " water='", " C'");
+	put_string(b, " />\n");
 }
 
-static void save_airpressure(FILE *f, struct divecomputer *dc)
+static void save_airpressure(struct membuffer *b, struct divecomputer *dc)
 {
 	if (!dc->surface_pressure.mbar)
 		return;
-	fputs("  <surface", f);
-	show_pressure(f, dc->surface_pressure, " pressure='", "'");
-	fputs(" />\n", f);
+	put_string(b, "  <surface");
+	put_pressure(b, dc->surface_pressure, " pressure='", " bar'");
+	put_string(b, " />\n");
 }
 
-static void save_salinity(FILE *f, struct divecomputer *dc)
+static void save_salinity(struct membuffer *b, struct divecomputer *dc)
 {
 	/* only save if we have a value that isn't the default of sea water */
 	if (!dc->salinity || dc->salinity == SEAWATER_SALINITY)
 		return;
-	fputs("  <water", f);
-	show_salinity(f, dc->salinity, " salinity='", "'");
-	fputs(" />\n", f);
+	put_string(b, "  <water");
+	put_salinity(b, dc->salinity, " salinity='", " g/l'");
+	put_string(b, " />\n");
 }
 
 /*
@@ -225,7 +171,7 @@ static int format_location(char *buffer, degrees_t latitude, degrees_t longitude
 	return len;
 }
 
-static void show_location(FILE *f, struct dive *dive)
+static void show_location(struct membuffer *b, struct dive *dive)
 {
 	char buffer[80];
 	const char *prefix = "  <location>";
@@ -244,23 +190,23 @@ static void show_location(FILE *f, struct dive *dive)
 		len += format_location(buffer+len, latitude, longitude);
 		if (!dive->location) {
 			memcpy(buffer+len, "/>\n", 4);
-			fputs(buffer, f);
+			put_string(b, buffer);
 			return;
 		}
 		buffer[len++] = '>';
 		buffer[len] = 0;
 		prefix = buffer;
 	}
-	show_utf8(f, dive->location, prefix,"</location>\n", 0);
+	show_utf8(b, dive->location, prefix,"</location>\n", 0);
 }
 
-static void save_overview(FILE *f, struct dive *dive)
+static void save_overview(struct membuffer *b, struct dive *dive)
 {
-	show_location(f, dive);
-	show_utf8(f, dive->divemaster, "  <divemaster>","</divemaster>\n", 0);
-	show_utf8(f, dive->buddy, "  <buddy>","</buddy>\n", 0);
-	show_utf8(f, dive->notes, "  <notes>","</notes>\n", 0);
-	show_utf8(f, dive->suit, "  <suit>","</suit>\n", 0);
+	show_location(b, dive);
+	show_utf8(b, dive->divemaster, "  <divemaster>","</divemaster>\n", 0);
+	show_utf8(b, dive->buddy, "  <buddy>","</buddy>\n", 0);
+	show_utf8(b, dive->notes, "  <notes>","</notes>\n", 0);
+	show_utf8(b, dive->suit, "  <suit>","</suit>\n", 0);
 }
 
 static int nr_cylinders(struct dive *dive)
@@ -275,7 +221,7 @@ static int nr_cylinders(struct dive *dive)
 	return nr;
 }
 
-static void save_cylinder_info(FILE *f, struct dive *dive)
+static void save_cylinder_info(struct membuffer *b, struct dive *dive)
 {
 	int i, nr;
 
@@ -288,19 +234,19 @@ static void save_cylinder_info(FILE *f, struct dive *dive)
 		int o2 = cylinder->gasmix.o2.permille;
 		int he = cylinder->gasmix.he.permille;
 
-		fprintf(f, "  <cylinder");
+		put_format(b, "  <cylinder");
 		if (volume)
-			show_milli(f, " size='", volume, " l", "'");
-		show_pressure(f, cylinder->type.workingpressure, " workpressure='", "'");
-		show_utf8(f, description, " description='", "'", 1);
+			put_milli(b, " size='", volume, " l'");
+		put_pressure(b, cylinder->type.workingpressure, " workpressure='", " bar'");
+		show_utf8(b, description, " description='", "'", 1);
 		if (o2) {
-			fprintf(f, " o2='%u.%u%%'", FRACTION(o2, 10));
+			put_format(b, " o2='%u.%u%%'", FRACTION(o2, 10));
 			if (he)
-				fprintf(f, " he='%u.%u%%'", FRACTION(he, 10));
+				put_format(b, " he='%u.%u%%'", FRACTION(he, 10));
 		}
-		show_pressure(f, cylinder->start, " start='", "'");
-		show_pressure(f, cylinder->end, " end='", "'");
-		fprintf(f, " />\n");
+		put_pressure(b, cylinder->start, " start='", " bar'");
+		put_pressure(b, cylinder->end, " end='", " bar'");
+		put_format(b, " />\n");
 	}
 }
 
@@ -316,7 +262,7 @@ static int nr_weightsystems(struct dive *dive)
 	return nr;
 }
 
-static void save_weightsystem_info(FILE *f, struct dive *dive)
+static void save_weightsystem_info(struct membuffer *b, struct dive *dive)
 {
 	int i, nr;
 
@@ -327,199 +273,207 @@ static void save_weightsystem_info(FILE *f, struct dive *dive)
 		int grams = ws->weight.grams;
 		const char *description = ws->description;
 
-		fprintf(f, "  <weightsystem");
-		show_milli(f, " weight='", grams, " kg", "'");
-		show_utf8(f, description, " description='", "'", 1);
-		fprintf(f, " />\n");
+		put_format(b, "  <weightsystem");
+		put_milli(b, " weight='", grams, " kg'");
+		show_utf8(b, description, " description='", "'", 1);
+		put_format(b, " />\n");
 	}
 }
 
-static void show_index(FILE *f, int value, const char *pre, const char *post)
+static void show_index(struct membuffer *b, int value, const char *pre, const char *post)
 {
 	if (value)
-		fprintf(f, " %s%d%s", pre, value, post);
+		put_format(b, " %s%d%s", pre, value, post);
 }
 
-static void save_sample(FILE *f, struct sample *sample, struct sample *old)
+static void save_sample(struct membuffer *b, struct sample *sample, struct sample *old)
 {
-	fprintf(f, "  <sample time='%u:%02u min'", FRACTION(sample->time.seconds,60));
-	show_milli(f, " depth='", sample->depth.mm, " m", "'");
-	show_temperature(f, sample->temperature, " temp='", "'");
-	show_pressure(f, sample->cylinderpressure, " pressure='", "'");
+	put_format(b, "  <sample time='%u:%02u min'", FRACTION(sample->time.seconds,60));
+	put_milli(b, " depth='", sample->depth.mm, " m'");
+	put_temperature(b, sample->temperature, " temp='", " C'");
+	put_pressure(b, sample->cylinderpressure, " pressure='", " bar'");
 
 	/*
 	 * We only show sensor information for samples with pressure, and only if it
 	 * changed from the previous sensor we showed.
 	 */
 	if (sample->cylinderpressure.mbar && sample->sensor != old->sensor) {
-		fprintf(f, " sensor='%d'", sample->sensor);
+		put_format(b, " sensor='%d'", sample->sensor);
 		old->sensor = sample->sensor;
 	}
 
 	/* the deco/ndl values are stored whenever they change */
 	if (sample->ndl.seconds != old->ndl.seconds) {
-		fprintf(f, " ndl='%u:%02u min'", FRACTION(sample->ndl.seconds, 60));
+		put_format(b, " ndl='%u:%02u min'", FRACTION(sample->ndl.seconds, 60));
 		old->ndl = sample->ndl;
 	}
 	if (sample->in_deco != old->in_deco) {
-		fprintf(f, " in_deco='%d'", sample->in_deco ? 1 : 0);
+		put_format(b, " in_deco='%d'", sample->in_deco ? 1 : 0);
 		old->in_deco = sample->in_deco;
 	}
 	if (sample->stoptime.seconds != old->stoptime.seconds) {
-		fprintf(f, " stoptime='%u:%02u min'", FRACTION(sample->stoptime.seconds, 60));
+		put_format(b, " stoptime='%u:%02u min'", FRACTION(sample->stoptime.seconds, 60));
 		old->stoptime = sample->stoptime;
 	}
 
 	if (sample->stopdepth.mm != old->stopdepth.mm) {
-		show_milli(f, " stopdepth='", sample->stopdepth.mm, " m", "'");
+		put_milli(b, " stopdepth='", sample->stopdepth.mm, " m'");
 		old->stopdepth = sample->stopdepth;
 	}
 
 	if (sample->cns != old->cns) {
-		fprintf(f, " cns='%u%%'", sample->cns);
+		put_format(b, " cns='%u%%'", sample->cns);
 		old->cns = sample->cns;
 	}
 
 	if (sample->po2 != old->po2) {
-		show_milli(f, " po2='", sample->po2, " bar", "'");
+		put_milli(b, " po2='", sample->po2, " bar'");
 		old->po2 = sample->po2;
 	}
-	fprintf(f, " />\n");
+	put_format(b, " />\n");
 }
 
-static void save_one_event(FILE *f, struct event *ev)
+static void save_one_event(struct membuffer *b, struct event *ev)
 {
-	fprintf(f, "  <event time='%d:%02d min'", FRACTION(ev->time.seconds,60));
-	show_index(f, ev->type, "type='", "'");
-	show_index(f, ev->flags, "flags='", "'");
-	show_index(f, ev->value, "value='", "'");
-	show_utf8(f, ev->name, " name='", "'", 1);
-	fprintf(f, " />\n");
+	put_format(b, "  <event time='%d:%02d min'", FRACTION(ev->time.seconds,60));
+	show_index(b, ev->type, "type='", "'");
+	show_index(b, ev->flags, "flags='", "'");
+	show_index(b, ev->value, "value='", "'");
+	show_utf8(b, ev->name, " name='", "'", 1);
+	put_format(b, " />\n");
 }
 
 
-static void save_events(FILE *f, struct event *ev)
+static void save_events(struct membuffer *b, struct event *ev)
 {
 	while (ev) {
-		save_one_event(f, ev);
+		save_one_event(b, ev);
 		ev = ev->next;
 	}
 }
 
-static void save_tags(FILE *f, struct tag_entry *tag_list)
+static void save_tags(struct membuffer *b, struct tag_entry *tag_list)
 {
 	int more = 0;
 	struct tag_entry *tmp = tag_list->next;
 
 	/* Only write tag attribute if the list contains at least one item  */
 	if (tmp != NULL) {
-		fprintf(f, " tags='");
+		put_format(b, " tags='");
 
 		while (tmp != NULL) {
 			if (more)
-				fprintf(f, ", ");
+				put_format(b, ", ");
 			/* If the tag has been translated, write the source to the xml file */
 			if (tmp->tag->source != NULL)
-				quote(f, tmp->tag->source, 0);
+				quote(b, tmp->tag->source, 0);
 			else
-				quote(f, tmp->tag->name, 0);
+				quote(b, tmp->tag->name, 0);
 			tmp = tmp->next;
 			more = 1;
 		}
-		fprintf(f, "'");
+		put_format(b, "'");
 	}
 }
 
-static void show_date(FILE *f, timestamp_t when)
+static void show_date(struct membuffer *b, timestamp_t when)
 {
 	struct tm tm;
 
 	utc_mkdate(when, &tm);
 
-	fprintf(f, " date='%04u-%02u-%02u'",
+	put_format(b, " date='%04u-%02u-%02u'",
 		tm.tm_year+1900, tm.tm_mon+1, tm.tm_mday);
-	fprintf(f, " time='%02u:%02u:%02u'",
+	put_format(b, " time='%02u:%02u:%02u'",
 		tm.tm_hour, tm.tm_min, tm.tm_sec);
 }
 
-static void save_samples(FILE *f, int nr, struct sample *s)
+static void save_samples(struct membuffer *b, int nr, struct sample *s)
 {
 	struct sample dummy = { };
 
 	while (--nr >= 0) {
-		save_sample(f, s, &dummy);
+		save_sample(b, s, &dummy);
 		s++;
 	}
 }
 
-static void save_dc(FILE *f, struct dive *dive, struct divecomputer *dc)
+static void save_dc(struct membuffer *b, struct dive *dive, struct divecomputer *dc)
 {
-	fprintf(f, "  <divecomputer");
-	show_utf8(f, dc->model, " model='", "'", 1);
+	put_format(b, "  <divecomputer");
+	show_utf8(b, dc->model, " model='", "'", 1);
 	if (dc->deviceid)
-		fprintf(f, " deviceid='%08x'", dc->deviceid);
+		put_format(b, " deviceid='%08x'", dc->deviceid);
 	if (dc->diveid)
-		fprintf(f, " diveid='%08x'", dc->diveid);
+		put_format(b, " diveid='%08x'", dc->diveid);
 	if (dc->when && dc->when != dive->when)
-		show_date(f, dc->when);
+		show_date(b, dc->when);
 	if (dc->duration.seconds && dc->duration.seconds != dive->dc.duration.seconds)
-		show_duration(f, dc->duration, " duration='", "'");
-	fprintf(f, ">\n");
-	save_depths(f, dc);
-	save_temperatures(f, dc);
-	save_airpressure(f, dc);
-	save_salinity(f, dc);
-	show_duration(f, dc->surfacetime, "  <surfacetime>", "</surfacetime>\n");
-
-	save_events(f, dc->events);
-	save_samples(f, dc->samples, dc->sample);
-
-	fprintf(f, "  </divecomputer>\n");
+		put_duration(b, dc->duration, " duration='", " min'");
+	put_format(b, ">\n");
+	save_depths(b, dc);
+	save_temperatures(b, dc);
+	save_airpressure(b, dc);
+	save_salinity(b, dc);
+	put_duration(b, dc->surfacetime, "  <surfacetime>", " min</surfacetime>\n");
+
+	save_events(b, dc->events);
+	save_samples(b, dc->samples, dc->sample);
+
+	put_format(b, "  </divecomputer>\n");
 }
 
-void save_dive(FILE *f, struct dive *dive)
+void save_one_dive(struct membuffer *b, struct dive *dive)
 {
 	struct divecomputer *dc;
 
-	fputs("<dive", f);
+	put_string(b, "<dive");
 	if (dive->number)
-		fprintf(f, " number='%d'", dive->number);
+		put_format(b, " number='%d'", dive->number);
 	if (dive->tripflag == NO_TRIP)
-		fprintf(f, " tripflag='NOTRIP'");
+		put_format(b, " tripflag='NOTRIP'");
 	if (dive->rating)
-		fprintf(f, " rating='%d'", dive->rating);
+		put_format(b, " rating='%d'", dive->rating);
 	if (dive->visibility)
-		fprintf(f, " visibility='%d'", dive->visibility);
+		put_format(b, " visibility='%d'", dive->visibility);
 	if (dive->tag_list != NULL)
-		save_tags(f, dive->tag_list);
+		save_tags(b, dive->tag_list);
 
-	show_date(f, dive->when);
-	fprintf(f, " duration='%u:%02u min'>\n",
+	show_date(b, dive->when);
+	put_format(b, " duration='%u:%02u min'>\n",
 		FRACTION(dive->dc.duration.seconds, 60));
-	save_overview(f, dive);
-	save_cylinder_info(f, dive);
-	save_weightsystem_info(f, dive);
-	save_dive_temperature(f, dive);
+	save_overview(b, dive);
+	save_cylinder_info(b, dive);
+	save_weightsystem_info(b, dive);
+	save_dive_temperature(b, dive);
 	/* Save the dive computer data */
 	dc = &dive->dc;
 	do {
-		save_dc(f, dive, dc);
+		save_dc(b, dive, dc);
 		dc = dc->next;
 	} while (dc);
 
-	fprintf(f, "</dive>\n");
+	put_format(b, "</dive>\n");
+}
+
+void save_dive(FILE *f, struct dive *dive)
+{
+	struct membuffer buf = {0};
+
+	save_one_dive(&buf, dive);
+	flush_buffer(&buf, f);
 }
 
-static void save_trip(FILE *f, dive_trip_t *trip)
+static void save_trip(struct membuffer *b, dive_trip_t *trip)
 {
 	int i;
 	struct dive *dive;
 
-	fprintf(f, "<trip");
-	show_date(f, trip->when);
-	show_utf8(f, trip->location, " location=\'","\'", 1);
-	fprintf(f, ">\n");
-	show_utf8(f, trip->notes, "<notes>","</notes>\n", 0);
+	put_format(b, "<trip");
+	show_date(b, trip->when);
+	show_utf8(b, trip->location, " location=\'","\'", 1);
+	put_format(b, ">\n");
+	show_utf8(b, trip->notes, "<notes>","</notes>\n", 0);
 
 	/*
 	 * Incredibly cheesy: we want to save the dives sorted, and they
@@ -529,15 +483,17 @@ static void save_trip(FILE *f, dive_trip_t *trip)
 	 */
 	for_each_dive(i, dive) {
 		if (dive->divetrip == trip)
-			save_dive(f, dive);
+			save_one_dive(b, dive);
 	}
 
-	fprintf(f, "</trip>\n");
+	put_format(b, "</trip>\n");
 }
 
-static void save_one_device(FILE *f, const char * model, uint32_t deviceid,
+static void save_one_device(void *_f, const char * model, uint32_t deviceid,
 			    const char *nickname, const char *serial_nr, const char *firmware)
 {
+	struct membuffer *b = _f;
+
 	/* Nicknames that are empty or the same as the device model are not interesting */
 	if (nickname) {
 		if (!*nickname || !strcmp(model, nickname))
@@ -556,13 +512,13 @@ static void save_one_device(FILE *f, const char * model, uint32_t deviceid,
 	if (!serial_nr && !nickname && !firmware)
 		return;
 
-	fprintf(f, "<divecomputerid");
-	show_utf8(f, model, " model='", "'", 1);
-	fprintf(f, " deviceid='%08x'", deviceid);
-	show_utf8(f, serial_nr, " serial='", "'", 1);
-	show_utf8(f, firmware, " firmware='", "'", 1);
-	show_utf8(f, nickname, " nickname='", "'", 1);
-	fprintf(f, "/>\n");
+	put_format(b, "<divecomputerid");
+	show_utf8(b, model, " model='", "'", 1);
+	put_format(b, " deviceid='%08x'", deviceid);
+	show_utf8(b, serial_nr, " serial='", "'", 1);
+	show_utf8(b, firmware, " firmware='", "'", 1);
+	show_utf8(b, nickname, " nickname='", "'", 1);
+	put_format(b, "/>\n");
 }
 
 #define VERSION 2
@@ -572,24 +528,19 @@ void save_dives(const char *filename)
 	save_dives_logic(filename, false);
 }
 
-void save_dives_logic(const char *filename, const bool select_only)
+void save_dives_buffer(struct membuffer *b, const bool select_only)
 {
 	int i;
 	struct dive *dive;
 	dive_trip_t *trip;
 
-	FILE *f = subsurface_fopen(filename, "w");
-
-	if (!f)
-		return;
-
-	fprintf(f, "<divelog program='subsurface' version='%d'>\n<settings>\n", VERSION);
+	put_format(b, "<divelog program='subsurface' version='%d'>\n<settings>\n", VERSION);
 
 	/* save the dive computer nicknames, if any */
-	call_for_each_dc(f, save_one_device);
+	call_for_each_dc(b, save_one_device);
 	if (autogroup)
-		fprintf(f, "<autogroup state='1' />\n");
-	fprintf(f, "</settings>\n<dives>\n");
+		put_format(b, "<autogroup state='1' />\n");
+	put_format(b, "</settings>\n<dives>\n");
 
 	for (trip = dive_trip_list; trip != NULL; trip = trip->next)
 		trip->index = 0;
@@ -601,14 +552,14 @@ void save_dives_logic(const char *filename, const bool select_only)
 
 			if(!dive->selected)
 				continue;
-			save_dive(f, dive);
+			save_one_dive(b, dive);
 
 		} else {
 			trip = dive->divetrip;
 
 			/* Bare dive without a trip? */
 			if (!trip) {
-				save_dive(f, dive);
+				save_one_dive(b, dive);
 				continue;
 			}
 
@@ -618,18 +569,30 @@ void save_dives_logic(const char *filename, const bool select_only)
 
 			/* We haven't seen this trip before - save it and all dives */
 			trip->index = 1;
-			save_trip(f, trip);
+			save_trip(b, trip);
 		}
 	}
-	fprintf(f, "</dives>\n</divelog>\n");
-	fclose(f);
+	put_format(b, "</dives>\n</divelog>\n");
+}
+
+void save_dives_logic(const char *filename, const bool select_only)
+{
+	struct membuffer buf = {0};
+	FILE *f;
+
+	save_dives_buffer(&buf, select_only);
+	f = subsurface_fopen(filename, "w");
+	if (f) {
+		flush_buffer(&buf, f);
+		fclose(f);
+	}
+	free_buffer(&buf);
 }
 
 void export_dives_uddf(const char *filename, const bool selected)
 {
 	FILE *f;
-	size_t streamsize;
-	char *membuf;
+	struct membuffer buf = {0};
 	xmlDoc *doc;
 	xsltStylesheetPtr xslt = NULL;
 	xmlDoc *transformed;
@@ -638,32 +601,19 @@ void export_dives_uddf(const char *filename, const bool selected)
 		return;
 
 	/* Save XML to file and convert it into a memory buffer */
-	save_dives_logic(filename, selected);
-	f = subsurface_fopen(filename, "r");
-	fseek(f, 0, SEEK_END);
-	streamsize = ftell(f);
-	rewind(f);
-
-	membuf = malloc(streamsize + 1);
-	if (!membuf || !fread(membuf, streamsize, 1, f)) {
-		fprintf(stderr, "Failed to read memory buffer\n");
-		return;
-	}
-	membuf[streamsize] = 0;
-	fclose(f);
-	unlink(filename);
+	save_dives_buffer(&buf, selected);
 
 	/*
 	 * Parse the memory buffer into XML document and
 	 * transform it to UDDF format, finally dumping
 	 * the XML into a character buffer.
 	 */
-	doc = xmlReadMemory(membuf, strlen(membuf), "divelog", NULL, 0);
+	doc = xmlReadMemory(buf.buffer, buf.used, "divelog", NULL, 0);
+	free_buffer(&buf);
 	if (!doc) {
 		fprintf(stderr, "Failed to read XML memory\n");
 		return;
 	}
-	free((void *)membuf);
 
 	/* Convert to UDDF format */
 	xslt = get_stylesheet("uddf-export.xslt");
diff --git a/subsurface.pro b/subsurface.pro
index 68982b6a8..671b7698b 100644
--- a/subsurface.pro
+++ b/subsurface.pro
@@ -83,6 +83,7 @@ SOURCES =  \
 	gettextfromc.cpp \
 	libdivecomputer.c \
 	main.cpp \
+	membuffer.c \
 	parse-xml.c \
 	planner.c \
 	profile.c \