From 0624fdd696422e718ce31f590c213e6f994f0641 Mon Sep 17 00:00:00 2001
From: Jonathan Dieter <jdieter@gmail.com>
Date: Sat, 18 Feb 2023 20:54:28 +0000
Subject: [PATCH] Add ZCK_NO_WRITE option to disable writing to a file

There are situations where we need to recreate the zchunk header for an
uncompressed file without actually writing out the zchunk file.  This
commit allows setting an `ioption`, `ZCK_NO_WRITE`, that will go through
the full process of creating the zchunk file without actually writing it
to disk, leaving you with a complete zchunk header in the end.

Signed-off-by: Jonathan Dieter <jdieter@gmail.com>
---
 include/zck.h.in      |  2 ++
 src/lib/comp/comp.c   | 10 +++++-----
 src/lib/header.c      |  2 +-
 src/lib/io.c          |  3 +++
 src/lib/zck.c         | 17 +++++++++++++++++
 src/lib/zck_private.h |  1 +
 6 files changed, 29 insertions(+), 6 deletions(-)

diff --git a/include/zck.h.in b/include/zck.h.in
index 93f4706..d641b20 100644
--- a/include/zck.h.in
+++ b/include/zck.h.in
@@ -28,6 +28,8 @@ typedef enum zck_ioption {
     ZCK_VAL_HEADER_HASH_TYPE,   /* Set what the header hash type *should* be */
     ZCK_VAL_HEADER_LENGTH,      /* Set what the header length *should* be */
     ZCK_UNCOMP_HEADER,          /* Header should contain uncompressed size, too */
+    ZCK_NO_WRITE,               /* Do not write to file when creating zck file -
+                                   Used to calculate header from existing umcompressed data */
     ZCK_COMP_TYPE = 100,        /* Set compression type using zck_comp */
     ZCK_MANUAL_CHUNK,           /* Disable auto-chunking */
     ZCK_CHUNK_MIN,              /* Minimum chunk size when manual chunking */
diff --git a/src/lib/comp/comp.c b/src/lib/comp/comp.c
index 4786e41..13cb491 100644
--- a/src/lib/comp/comp.c
+++ b/src/lib/comp/comp.c
@@ -154,7 +154,7 @@ static ssize_t comp_write(zckCtx *zck, const char *src, const size_t src_size) {
         return -1;
     zck->comp.dc_data_size += src_size;
 
-    if(dst_size > 0 && !write_data(zck, zck->temp_fd, dst, dst_size)) {
+    if(zck->no_write == 0 && dst_size > 0 && !write_data(zck, zck->temp_fd, dst, dst_size)) {
         free(dst);
         return -1;
     }
@@ -217,7 +217,7 @@ bool comp_init(zckCtx *zck) {
         }
     }
 
-    if(zck->temp_fd) {
+    if(zck->temp_fd || zck->no_write) {
         if(zck->comp.dict) {
             char *dst = NULL;
             size_t dst_size = 0;
@@ -226,7 +226,7 @@ bool comp_init(zckCtx *zck) {
                                   zck->comp.dict_size, &dst, &dst_size, 0) < 0)
                 return false;
             zck->comp.dc_data_size = zck->comp.dict_size;
-            if(!write_data(zck, zck->temp_fd, dst, dst_size)) {
+            if(zck->no_write == 0 && !write_data(zck, zck->temp_fd, dst, dst_size)) {
                 free(dst);
                 return false;
             }
@@ -242,7 +242,7 @@ bool comp_init(zckCtx *zck) {
             if(!zck->comp.end_cchunk(zck, comp, &dst, &dst_size, 0))
                 return false;
             zck->comp.dc_data_size = 0;
-            if(!write_data(zck, zck->temp_fd, dst, dst_size)) {
+            if(zck->no_write == 0 && !write_data(zck, zck->temp_fd, dst, dst_size)) {
                 free(dst);
                 return false;
             }
@@ -645,7 +645,7 @@ ssize_t ZCK_PUBLIC_API zck_end_chunk(zckCtx *zck) {
     if(!zck->comp.end_cchunk(zck, &(zck->comp), &dst, &dst_size, 1))
         return -1;
     zck->comp.dc_data_size = 0;
-    if(dst_size > 0 && !write_data(zck, zck->temp_fd, dst, dst_size)) {
+    if(zck->no_write == 0 && dst_size > 0 && !write_data(zck, zck->temp_fd, dst, dst_size)) {
         free(dst);
         return -1;
     }
diff --git a/src/lib/header.c b/src/lib/header.c
index 56d7f1b..565071e 100644
--- a/src/lib/header.c
+++ b/src/lib/header.c
@@ -462,7 +462,7 @@ bool write_header(zckCtx *zck) {
         "Writing header: %llu bytes",
         (long long unsigned) zck->lead_size
     );
-    if(!write_data(zck, zck->fd, zck->header, zck->header_size))
+    if(zck->no_write == 0 && !write_data(zck, zck->fd, zck->header, zck->header_size))
         return false;
     return true;
 }
diff --git a/src/lib/io.c b/src/lib/io.c
index 67586c1..2c6d88c 100644
--- a/src/lib/io.c
+++ b/src/lib/io.c
@@ -114,6 +114,9 @@ ssize_t tell_data(zckCtx *zck) {
 int chunks_from_temp(zckCtx *zck) {
     int read_count;
 
+    if(zck->no_write == 1)
+        return true;
+
     if(lseek(zck->temp_fd, 0, SEEK_SET) == -1)
         return false;
 
diff --git a/src/lib/zck.c b/src/lib/zck.c
index 61f92d8..8593281 100644
--- a/src/lib/zck.c
+++ b/src/lib/zck.c
@@ -349,6 +349,23 @@ bool ZCK_PUBLIC_API zck_set_ioption(zckCtx *zck, zck_ioption option, ssize_t val
             if(!set_chunk_hash_type(zck, ZCK_HASH_SHA256))
                 return false;
         }
+    } else if(option == ZCK_NO_WRITE) {
+        if(value == 0) {
+            if(zck->no_write == 1) {
+                set_error(zck, "Unable to enable write after it's been disabled");
+                return false;
+            }
+            zck->no_write = 0;
+        } else if(value == 1) {
+            zck->no_write = 1;
+            if(zck->temp_fd) {
+                close(zck->temp_fd);
+                zck->temp_fd = 0;
+            }
+        } else {
+            set_error(zck, "Unknown value %lli for ZCK_NO_WRITE", (long long) value);
+            return false;
+        }
 
     /* Hash options */
     } else if(option < 100) {
diff --git a/src/lib/zck_private.h b/src/lib/zck_private.h
index e91cf90..49a187e 100644
--- a/src/lib/zck_private.h
+++ b/src/lib/zck_private.h
@@ -271,6 +271,7 @@ struct zckCtx {
     int has_streams;
     int has_optional_elems;
     int has_uncompressed_source;
+    int no_write;
 
     char *read_buf;
     size_t read_buf_size;
-- 
2.30.2