[PATCH 5/8] vcs-svn: Read delta preimage from file descriptor

[Jonathan Nieder <jrnieder@gmail.com>]

Teach the svndiff routines to read the preimage for a delta from a
file descriptor without reading ahead.  This way, the delta applier
can stream its input directly from fast-import's cat-blob-fd pipe.

Signed-off-by: Jonathan Nieder <jrnieder@gmail.com>
---
 test-svn-fe.c            |   10 +++++-----
 vcs-svn/sliding_window.c |   21 +++++++++------------
 vcs-svn/sliding_window.h |    2 +-
 vcs-svn/svndiff.c        |    6 +++---
 vcs-svn/svndiff.h        |    2 +-
 5 files changed, 19 insertions(+), 22 deletions(-)

diff --git a/test-svn-fe.c b/test-svn-fe.c
index 4799e4c..4ea0cd6 100644
--- a/test-svn-fe.c
+++ b/test-svn-fe.c
@@ -22,20 +22,20 @@ int main(int argc, char *argv[])
 		return 0;
 	}
 	if (argc == 5 && !strcmp(argv[1], "-d")) {
-		struct line_buffer preimage = LINE_BUFFER_INIT;
+		int preimage_fd = -1;
 		struct line_buffer delta = LINE_BUFFER_INIT;
-		if (buffer_init(&preimage, argv[2]))
+		preimage_fd = open(argv[2], O_RDONLY);
+		if (preimage_fd < 0)
 			die_errno("cannot open preimage");
 		if (buffer_init(&delta, argv[3]))
 			die_errno("cannot open delta");
 		if (svndiff0_apply(&delta, (off_t) strtoull(argv[4], NULL, 0),
-				   &preimage, stdout))
+				   preimage_fd, stdout))
 			return 1;
-		if (buffer_deinit(&preimage))
+		if (close(preimage_fd))
 			die_errno("cannot close preimage");
 		if (buffer_deinit(&delta))
 			die_errno("cannot close delta");
-		buffer_reset(&preimage);
 		buffer_reset(&delta);
 		return 0;
 	}
diff --git a/vcs-svn/sliding_window.c b/vcs-svn/sliding_window.c
index 5c08828..6d4261a 100644
--- a/vcs-svn/sliding_window.c
+++ b/vcs-svn/sliding_window.c
@@ -5,7 +5,7 @@
 
 #include "git-compat-util.h"
 #include "sliding_window.h"
-#include "line_buffer.h"
+#include "fd_buffer.h"
 #include "strbuf.h"
 
 static void strbuf_remove_from_left(struct strbuf *sb, size_t nbytes)
@@ -30,7 +30,7 @@ static int check_overflow(off_t a, size_t b)
 int move_window(struct view *view, off_t off, size_t len)
 {
 	off_t file_offset;
-	assert(view && view->file);
+	assert(view && view->fd >= 0);
 	assert(!check_overflow(view->off, view->buf.len));
 
 	if (check_overflow(off, len))
@@ -47,21 +47,18 @@ int move_window(struct view *view, off_t off, size_t len)
 	if (off > file_offset) {
 		/* Seek ahead to skip the gap. */
 		const off_t gap = off - file_offset;
-		const off_t nread = buffer_skip_bytes(view->file, gap);
+		const off_t nread = fd_skip_bytes(view->fd, gap);
 		if (nread != gap) {
-			if (!buffer_ferror(view->file))
+			if (!nread)
 				return error("Preimage ends early");
-			return error("Cannot seek forward in input: %s",
-				     strerror(errno));
+			return error("Cannot seek forward in input");
 		}
 		file_offset += gap;
 	}
-	buffer_read_binary(&view->buf, len - view->buf.len, view->file);
-	if (view->buf.len != len) {
-		if (!buffer_ferror(view->file))
-			return error("Preimage ends early");
-		return error("Cannot read preimage: %s", strerror(errno));
-	}
+	if (fd_read_binary(&view->buf, len - view->buf.len, view->fd))
+		return error("Cannot read preimage");
+	if (view->buf.len != len)
+		return error("Preimage ends early");
 	view->off = off;
 	return 0;
 }
diff --git a/vcs-svn/sliding_window.h b/vcs-svn/sliding_window.h
index b9f0552..532dc93 100644
--- a/vcs-svn/sliding_window.h
+++ b/vcs-svn/sliding_window.h
@@ -4,7 +4,7 @@
 #include "strbuf.h"
 
 struct view {
-	struct line_buffer *file;
+	int fd;
 	off_t off;
 	struct strbuf buf;
 };
diff --git a/vcs-svn/svndiff.c b/vcs-svn/svndiff.c
index 9ee7411..ef3a921 100644
--- a/vcs-svn/svndiff.c
+++ b/vcs-svn/svndiff.c
@@ -283,10 +283,10 @@ static int apply_one_window(struct line_buffer *delta, off_t *delta_len,
 }
 
 int svndiff0_apply(struct line_buffer *delta, off_t delta_len,
-		   struct line_buffer *preimage, FILE *postimage)
+		   int preimage_fd, FILE *postimage)
 {
-	struct view preimage_view = {preimage, 0, STRBUF_INIT};
-	assert(delta && preimage && postimage);
+	struct view preimage_view = {preimage_fd, 0, STRBUF_INIT};
+	assert(delta && preimage_fd >= 0 && postimage);
 
 	if (read_magic(delta, &delta_len))
 		goto fail;
diff --git a/vcs-svn/svndiff.h b/vcs-svn/svndiff.h
index a986099..9003d6e 100644
--- a/vcs-svn/svndiff.h
+++ b/vcs-svn/svndiff.h
@@ -4,6 +4,6 @@
 #include "line_buffer.h"
 
 extern int svndiff0_apply(struct line_buffer *delta, off_t delta_len,
-			  struct line_buffer *preimage, FILE *postimage);
+				int preimage_fd, FILE *postimage);
 
 #endif
-- 
1.7.2.3