From 67365b92cc146cc475b19b1b4dab73a1dc8cebc0 Mon Sep 17 00:00:00 2001
From: midipix <writeonce@midipix.org>
Date: Sat, 20 Jul 2024 23:33:36 +0000
Subject: io interfaces: added tpax_io_seek() [for both mapped and unmapped
 archives].

---
 include/tpax/tpax.h   |  2 ++
 project/common.mk     |  1 +
 src/io/tpax_io_seek.c | 86 +++++++++++++++++++++++++++++++++++++++++++++++++++
 3 files changed, 89 insertions(+)
 create mode 100644 src/io/tpax_io_seek.c

diff --git a/include/tpax/tpax.h b/include/tpax/tpax.h
index bb6aae7..f5ca8b2 100644
--- a/include/tpax/tpax.h
+++ b/include/tpax/tpax.h
@@ -207,6 +207,8 @@ tpax_api int  tpax_meta_init_rustar_header  (const char * pathname, const struct
                                              const char * linkname, struct tpax_ustar_header *);
 
 /* low-level interfaces */
+tpax_api int  tpax_io_seek                  (struct tpax_driver_ctx *, off_t, int);
+
 tpax_api int  tpax_io_create_memory_snapshot(const struct tpax_driver_ctx *, int, const char *,
                                              const struct stat *, void *);
 
diff --git a/project/common.mk b/project/common.mk
index d600ff2..a547077 100644
--- a/project/common.mk
+++ b/project/common.mk
@@ -4,6 +4,7 @@ API_SRCS = \
 	src/driver/tpax_unit_ctx.c \
 	src/io/tpax_create_memory_snapshot.c \
 	src/io/tpax_create_tmpfs_snapshot.c \
+	src/io/tpax_io_seek.c \
 	src/logic/tpax_archive_enqueue.c \
 	src/logic/tpax_archive_reset.c \
 	src/logic/tpax_archive_write.c \
diff --git a/src/io/tpax_io_seek.c b/src/io/tpax_io_seek.c
new file mode 100644
index 0000000..01e0683
--- /dev/null
+++ b/src/io/tpax_io_seek.c
@@ -0,0 +1,86 @@
+/**************************************************************/
+/*  tpax: a topological pax implementation                    */
+/*  Copyright (C) 2020--2024  SysDeer Technologies, LLC       */
+/*  Released under GPLv2 and GPLv3; see COPYING.TPAX.         */
+/**************************************************************/
+
+#include <stdint.h>
+#include <unistd.h>
+#include <fcntl.h>
+#include <errno.h>
+
+#include <tpax/tpax.h>
+#include <tpax/tpax_specs.h>
+#include "tpax_driver_impl.h"
+#include "tpax_errinfo_impl.h"
+
+static int tpax_io_seek_fileio(
+	struct tpax_driver_ctx *    dctx,
+	off_t                       offset,
+	int                         whence)
+{
+	int fdin;
+
+	fdin = tpax_driver_fdin(dctx);
+
+	if ((offset = lseek(fdin,offset,whence)) < 0)
+		return TPAX_SYSTEM_ERROR(dctx);
+
+	tpax_set_driver_cpos(dctx,offset);
+
+	return 0;
+}
+
+static int tpax_io_seek_mapped(
+	struct tpax_driver_ctx *    dctx,
+	off_t                       offset,
+	int                         whence)
+{
+	struct tpax_driver_ctx_impl * ictx;
+	size_t                        aoffset;
+
+	ictx = tpax_get_driver_ictx(dctx);
+
+	if (whence == SEEK_CUR) {
+		offset += tpax_get_driver_cpos(dctx);
+
+	} else if (whence == SEEK_END) {
+		offset += ictx->mapsize;
+	}
+
+	if ((offset < 0) || ((aoffset = offset) > ictx->mapsize))
+		return TPAX_CUSTOM_ERROR(
+			dctx,
+			TPAX_ERR_FLOW_ERROR);
+
+	tpax_set_driver_cpos(dctx,offset);
+
+	return 0;
+}
+
+int tpax_io_seek(struct tpax_driver_ctx * dctx, off_t offset, int whence)
+{
+	switch (whence) {
+		case SEEK_SET:
+		case SEEK_CUR:
+		case SEEK_END:
+			break;
+
+		default:
+			return TPAX_CUSTOM_ERROR(
+				dctx,
+				TPAX_ERR_FLOW_ERROR);
+	}
+
+	if (dctx->cctx->srcflags & TPAX_SOURCE_DATA_FILEIO) {
+		return tpax_io_seek_fileio(dctx,offset,whence);
+
+	} else if (dctx->cctx->srcflags & TPAX_SOURCE_DATA_MAPPED) {
+		return tpax_io_seek_mapped(dctx,offset,whence);
+
+	}
+
+	return TPAX_CUSTOM_ERROR(
+		dctx,
+		TPAX_ERR_FLOW_ERROR);
+}
-- 
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