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>

1 files changed, 52 insertions, 0 deletions

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