builder: fix invalid compressed offset in image.blob toc entry

The `blob_ctx.compressed_offset` has been set to the end of compressed
blob in tar2rafs blob dump, we shouldn't use it as the initial
compressed_offset, this will generate an invalid toc entry.

Signed-off-by: Yan Song <imeoer@linux.alibaba.com>

src/bin/nydus-image/core/blob.rs

@@ -110,7 +110,7 @@ impl Blob {
                         toc::TOC_ENTRY_BLOB_RAW,
                         compress::Algorithm::None,
                         blob_digest,
-                        blob_ctx.compressed_offset,
+                        blob_ctx.compressed_offset(),
                         blob_ctx.compressed_blob_size,
                         blob_ctx.uncompressed_blob_size,
                     )?;

src/bin/nydus-image/core/blob_compact.rs

@@ -158,23 +158,23 @@ impl ChunkSet {
             // file offset field is useless
             new_chunk.set_index(new_blob_ctx.chunk_count);
             new_chunk.set_blob_index(new_blob_idx);
-            new_chunk.set_compressed_offset(new_blob_ctx.compressed_offset);
-            new_chunk.set_uncompressed_offset(new_blob_ctx.uncompressed_offset);
+            new_chunk.set_compressed_offset(new_blob_ctx.current_compressed_offset);
+            new_chunk.set_uncompressed_offset(new_blob_ctx.current_uncompressed_offset);
             new_blob_ctx.add_chunk_meta_info(&new_chunk, None)?;
             // insert change ops
             chunks_change.push((chunk.clone(), new_chunk));
 
             new_blob_ctx.blob_hash.update(&buf);
             new_blob_ctx.chunk_count += 1;
-            new_blob_ctx.compressed_offset += chunk.compressed_size() as u64;
+            new_blob_ctx.current_compressed_offset += chunk.compressed_size() as u64;
             new_blob_ctx.compressed_blob_size += chunk.compressed_size() as u64;
 
             let aligned_size = if aligned_chunk {
                 try_round_up_4k(chunk.uncompressed_size()).unwrap()
             } else {
                 chunk.uncompressed_size() as u64
             };
-            new_blob_ctx.uncompressed_offset += aligned_size;
+            new_blob_ctx.current_uncompressed_offset += aligned_size;
             new_blob_ctx.uncompressed_blob_size += aligned_size;
         }
         new_blob_ctx.blob_id = format!("{:x}", new_blob_ctx.blob_hash.clone().finalize());

src/bin/nydus-image/core/context.rs

@@ -377,8 +377,8 @@ pub struct BlobContext {
     pub uncompressed_blob_size: u64,
 
     /// Current blob offset cursor for writing to disk file.
-    pub compressed_offset: u64,
-    pub uncompressed_offset: u64,
+    pub current_compressed_offset: u64,
+    pub current_uncompressed_offset: u64,
 
     /// The number of counts in a blob by the index of blob table.
     pub chunk_count: u32,
@@ -429,8 +429,8 @@ impl BlobContext {
             compressed_blob_size: 0,
             uncompressed_blob_size: 0,
 
-            compressed_offset: blob_offset,
-            uncompressed_offset: 0,
+            current_compressed_offset: blob_offset,
+            current_uncompressed_offset: 0,
 
             chunk_count: 0,
             chunk_size: RAFS_DEFAULT_CHUNK_SIZE as u32,
@@ -690,6 +690,12 @@ impl BlobContext {
         self.blob_hash.update(header.as_bytes());
         Ok(header)
     }
+
+    /// Get offset of compressed blob, since compressed_offset is
+    /// always >= compressed_blob_size, we can safely subtract here.
+    pub fn compressed_offset(&self) -> u64 {
+        self.current_compressed_offset - self.compressed_blob_size
+    }
 }
 
 /// BlobManager stores all blob related information during build.

src/bin/nydus-image/core/node.rs

@@ -581,9 +581,9 @@ impl Node {
         } else {
             uncompressed_size
         };
-        let pre_uncompressed_offset = blob_ctx.uncompressed_offset;
+        let pre_uncompressed_offset = blob_ctx.current_uncompressed_offset;
         blob_ctx.uncompressed_blob_size = pre_uncompressed_offset + aligned_chunk_size as u64;
-        blob_ctx.uncompressed_offset += aligned_chunk_size as u64;
+        blob_ctx.current_uncompressed_offset += aligned_chunk_size as u64;
         chunk.set_uncompressed_offset(pre_uncompressed_offset);
         chunk.set_uncompressed_size(uncompressed_size);
 
@@ -595,12 +595,12 @@ impl Node {
             let (compressed, is_compressed) = compress::compress(chunk_data, ctx.compressor)
                 .with_context(|| format!("failed to compress node file {:?}", self.path))?;
             let compressed_size = compressed.len() as u32;
-            let pre_compressed_offset = blob_ctx.compressed_offset;
+            let pre_compressed_offset = blob_ctx.current_compressed_offset;
             blob_writer
                 .write_all(&compressed)
                 .context("failed to write blob")?;
             blob_ctx.blob_hash.update(&compressed);
-            blob_ctx.compressed_offset += compressed_size as u64;
+            blob_ctx.current_compressed_offset += compressed_size as u64;
             blob_ctx.compressed_blob_size += compressed_size as u64;
 
             chunk.set_compressed_offset(pre_compressed_offset);