[pbs-devel] [PATCH proxmox 2/2] proxmox: add sparse_copy(_async) to tools::io

[Dominik Csapak <d.csapak@proxmox.com>]

this is able to seek the target instead of writing zeroes, which
generates sparse files where supported

it does not guarantee that all zero bytes are skipped, only when the
buffer after a read solely consists of zeroes

Signed-off-by: Dominik Csapak <d.csapak@proxmox.com>
---
 proxmox/src/tools/io/mod.rs | 62 +++++++++++++++++++++++++++++++++++++
 1 file changed, 62 insertions(+)

diff --git a/proxmox/src/tools/io/mod.rs b/proxmox/src/tools/io/mod.rs
index 2e92ebb..53f767c 100644
--- a/proxmox/src/tools/io/mod.rs
+++ b/proxmox/src/tools/io/mod.rs
@@ -3,8 +3,70 @@
 //! The [`ReadExt`] trait provides additional operations for handling byte buffers for types
 //! implementing [`Read`](std::io::Read).
 
+use std::io::{self, Read, Write, Seek, SeekFrom, ErrorKind};
+
 mod read;
 pub use read::*;
 
 mod write;
 pub use write::*;
+
+/// copy similar to io::copy, but seeks the target when encountering
+/// zero bytes instead of writing them
+pub fn sparse_copy<R: Read + ?Sized, W: Write + Seek + ?Sized>(
+    reader: &mut R,
+    writer: &mut W,
+) -> Result<u64, io::Error> {
+    let mut buf = crate::tools::byte_buffer::ByteBuffer::new();
+    let mut written = 0;
+    loop {
+        let len = match buf.read_from(reader) {
+            Ok(0) => return Ok(written),
+            Ok(len) => len,
+            Err(ref e) if e.kind() == ErrorKind::Interrupted => continue,
+            Err(e) => return Err(e),
+        };
+
+        if crate::tools::zero::buffer_is_zero(&buf[..]) {
+            writer.seek(SeekFrom::Current(len as i64))?;
+        } else {
+            writer.write_all(&buf[..])?;
+        }
+        buf.clear();
+        written += len as u64;
+    }
+}
+
+#[cfg(feature = "tokio")]
+use tokio::io::{AsyncReadExt, AsyncWriteExt, AsyncSeekExt};
+
+#[cfg(feature = "tokio")]
+/// copy similar to tokio::io::copy, but seeks the target when encountering
+/// zero bytes instead of writing them
+pub async fn sparse_copy_async<R, W>(
+    reader: &mut R,
+    writer: &mut W,
+) -> Result<u64, io::Error>
+where
+    R: AsyncReadExt + Unpin,
+    W: AsyncWriteExt + AsyncSeekExt + Unpin,
+{
+    let mut buf = crate::tools::byte_buffer::ByteBuffer::new();
+    let mut written = 0;
+    loop {
+        let len = match buf.read_from_async(reader).await {
+            Ok(0) => return Ok(written),
+            Ok(len) => len,
+            Err(ref e) if e.kind() == ErrorKind::Interrupted => continue,
+            Err(e) => return Err(e),
+        };
+
+        if crate::tools::zero::buffer_is_zero(&buf[..]) {
+            writer.seek(SeekFrom::Current(len as i64)).await?;
+        } else {
+            writer.write_all(&buf[..]).await?;
+        }
+        buf.clear();
+        written += len as u64;
+    }
+}
-- 
2.20.1