It can sometimes be useful to write information temporarily to file,
to read back later. These functions allow a program to use the
line_buffer facilities when doing so.
It works like this:
1. find a unique filename with buffer_tmpfile_init.
2. rewind with buffer_tmpfile_rewind. This returns a stdio
handle for writing.
3. when finished writing, declare so with
buffer_tmpfile_prepare_to_read. The return value indicates
how many bytes were written.
4. read whatever portion of the file is needed.
5. if finished, remove the temporary file with buffer_deinit.
otherwise, go back to step 2,
The svn support would use this to buffer the postimage from delta
application until the length is known and fast-import can receive
the resulting blob.
Based-on-patch-by: David Barr <david.barr@xxxxxxxxxxxx>
Signed-off-by: Jonathan Nieder <jrnieder@xxxxxxxxx>
---
David, this is another piece of infrastructure from early svn-fe3
history. I've cleaned up the API a little bit but the idea is the
same. Thank you.
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 e29a81a..aedf105 100644
--- a/vcs-svn/line_buffer.c
+++ b/vcs-svn/line_buffer.c
@@ -25,6 +25,14 @@ int buffer_fdinit(struct line_buffer *buf, int fd)
return 0;
}
+int buffer_tmpfile_init(struct line_buffer *buf)
+{
+ buf->infile = tmpfile();
+ if (!buf->infile)
+ return -1;
+ return 0;
+}
+
int buffer_deinit(struct line_buffer *buf)
{
int err;
@@ -35,6 +43,22 @@ int buffer_deinit(struct line_buffer *buf)
return err;
}
+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 630d83c..96ce966 100644
--- a/vcs-svn/line_buffer.h
+++ b/vcs-svn/line_buffer.h
@@ -15,12 +15,17 @@ struct line_buffer {
int buffer_init(struct line_buffer *buf, const char *filename);
int buffer_fdinit(struct line_buffer *buf, int fd);
int buffer_deinit(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 line_buffer *buf, struct strbuf *sb, uint32_t len);
void buffer_copy_bytes(struct line_buffer *buf, uint32_t len);
void buffer_skip_bytes(struct line_buffer *buf, uint32_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 4e8fb71..e89cc41 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
+---------------------
+
+Temporary files provide a place to store data that should not outlive
+the calling program. A program
+
+ - initializes a `struct line_buffer` to LINE_BUFFER_INIT
+ - requests 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
+ - removes the temporary file with `buffer_deinit`, perhaps to
+ reuse the line_buffer for some other file.
+
+When finished, the calling program can use `buffer_reset` to deallocate
+resources.
+
Functions
---------
--
1.7.4.rc0.580.g89dc.dirty
--
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