[PATCH 12/12] vcs-svn: teach line_buffer about temporary files
From: Jonathan Nieder <hidden>
Date: 2016-06-15 22:50:19
Subsystem:
the rest · Maintainer:
Linus Torvalds
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 [off-list ref]
Signed-off-by: Jonathan Nieder <redacted>
---
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