[PATCH 7/8] vcs-svn: Teach line_buffer about temporary files

[Jonathan Nieder <jrnieder@gmail.com>]

It can sometimes be useful to write information temporarily to file,
to read back later.  These functions allow you to do so.

The dump file importer would use this to save a postimage from delta
application until the length is known and fast-import is ready to read
it.

Signed-off-by: Jonathan Nieder <jrnieder@gmail.com>
---
 vcs-svn/line_buffer.c   |   24 ++++++++++++++++++++++++
 vcs-svn/line_buffer.h   |    7 ++++++-
 vcs-svn/line_buffer.txt |   22 ++++++++++++++++++++++
 3 files changed, 52 insertions(+), 1 deletions(-)

diff --git a/vcs-svn/line_buffer.c b/vcs-svn/line_buffer.c
index c54031b..f583623 100644
--- a/vcs-svn/line_buffer.c
+++ b/vcs-svn/line_buffer.c
@@ -42,6 +42,30 @@ int buffer_at_eof(struct line_buffer *buf)
 	return 0;
 }
 
+int buffer_tmpfile_init(struct line_buffer *buf)
+{
+	buf->infile = tmpfile();
+	if (!buf->infile)
+		return error("cannot open temporary file: %s", strerror(errno));
+	return 0;
+}
+
+FILE *buffer_tmpfile_rewind(struct line_buffer *buf)
+{
+	rewind(buf->infile);
+	return buf->infile;
+}
+
+long buffer_tmpfile_prepare_to_read(struct line_buffer *buf)
+{
+	long pos = ftell(buf->infile);
+	if (pos < 0)
+		return error("ftell error: %s", strerror(errno));
+	if (fseek(buf->infile, 0, SEEK_SET))
+		return error("seek error: %s", strerror(errno));
+	return pos;
+}
+
 int buffer_read_char(struct line_buffer *buf)
 {
 	return fgetc(buf->infile);
diff --git a/vcs-svn/line_buffer.h b/vcs-svn/line_buffer.h
index 2375ee1..1db7434 100644
--- a/vcs-svn/line_buffer.h
+++ b/vcs-svn/line_buffer.h
@@ -16,12 +16,17 @@ int buffer_init(struct line_buffer *buf, const char *filename);
 int buffer_deinit(struct line_buffer *buf);
 int buffer_ferror(struct line_buffer *buf);
 int buffer_at_eof(struct line_buffer *buf);
+void buffer_reset(struct line_buffer *buf);
+
+int buffer_tmpfile_init(struct line_buffer *buf);
+FILE *buffer_tmpfile_rewind(struct line_buffer *buf);	/* prepare to write. */
+long buffer_tmpfile_prepare_to_read(struct line_buffer *buf);
+
 char *buffer_read_line(struct line_buffer *buf);
 char *buffer_read_string(struct line_buffer *buf, uint32_t len);
 int buffer_read_char(struct line_buffer *buf);
 void buffer_read_binary(struct strbuf *sb, uint32_t len, struct line_buffer *f);
 void buffer_copy_bytes(struct line_buffer *buf, off_t len);
 off_t buffer_skip_bytes(struct line_buffer *buf, off_t len);
-void buffer_reset(struct line_buffer *buf);
 
 #endif
diff --git a/vcs-svn/line_buffer.txt b/vcs-svn/line_buffer.txt
index d06db24..344efc3 100644
--- a/vcs-svn/line_buffer.txt
+++ b/vcs-svn/line_buffer.txt
@@ -24,6 +24,28 @@ The calling program:
 When finished, the caller can use `buffer_reset` to deallocate
 resources.
 
+Using temporary files
+---------------------
+
+Sometimes a file is just a convenient place to stash data for
+later.  A program
+
+ - initializes a `struct line_buffer` to LINE_BUFFER_INIT
+ - allocates a temporary file with `buffer_tmpfile_init`
+ - acquires an output handle by calling `buffer_tmpfile_rewind`
+ - uses standard I/O functions like `fprintf` and `fwrite` to fill
+   the temporary file
+ - declares writing is over with `buffer_tmpfile_prepare_to_read`
+ - can re-read what was written with `buffer_read_line`,
+   `buffer_read_string`, and so on
+ - can reuse the temporary file by calling `buffer_tmpfile_rewind`
+   again
+ - cleans up the temporary file with `buffer_deinit`, perhaps to
+   reuse the line_buffer for some other file.
+
+When finished, the program should use `buffer_reset` to deallocate
+resources.
+
 Functions
 ---------
 
-- 
1.7.2.3