[pbs-devel] [PATCH pbs-client v4] fix #3699: client: prefer xdg cache directory for tmp files

[Maximiliano Sandoval <m.sandoval@proxmox.com>]

Adds a helper to create temporal files in XDG_CACHE_HOME. If we cannot
create a file there, we fallback to /tmp as before.

Note that the temporary files stored by the client might grow
arbitrarily in size, making XDG_RUNTIME_DIR a less desirable option.
Citing the Arch wiki [1]:

> Should not store large files as it may be mounted as a tmpfs.

[1] https://wiki.archlinux.org/title/XDG_Base_Directory

Signed-off-by: Maximiliano Sandoval <m.sandoval@proxmox.com>
---
Differences from v3:
 - Link create_tmp_file in docs
 - Improve commit message

Differences from v2:
 - Files are created at XDG_CACHE_HOME directly
 - If opening fails, we try opening at /tmp
 - We check if the directory exists as part of the error handling of open()
 
 pbs-client/src/backup_reader.rs      | 31 ++++++++--------------------
 pbs-client/src/backup_writer.rs      | 13 ++----------
 pbs-client/src/tools/mod.rs          | 26 +++++++++++++++++++++++
 proxmox-backup-client/src/catalog.rs | 19 +++--------------
 4 files changed, 40 insertions(+), 49 deletions(-)

diff --git a/pbs-client/src/backup_reader.rs b/pbs-client/src/backup_reader.rs
index 36d8ebcf..4706abc7 100644
--- a/pbs-client/src/backup_reader.rs
+++ b/pbs-client/src/backup_reader.rs
@@ -1,7 +1,6 @@
 use anyhow::{format_err, Error};
 use std::fs::File;
 use std::io::{Seek, SeekFrom, Write};
-use std::os::unix::fs::OpenOptionsExt;
 use std::sync::Arc;
 
 use futures::future::AbortHandle;
@@ -141,18 +140,14 @@ impl BackupReader {
 
     /// Download a .blob file
     ///
-    /// This creates a temporary file in /tmp (using O_TMPFILE). The data is verified using
-    /// the provided manifest.
+    /// This creates a temporary file (See [`crate::tools::create_tmp_file`] for
+    /// details). The data is verified using the provided manifest.
     pub async fn download_blob(
         &self,
         manifest: &BackupManifest,
         name: &str,
     ) -> Result<DataBlobReader<'_, File>, Error> {
-        let mut tmpfile = std::fs::OpenOptions::new()
-            .write(true)
-            .read(true)
-            .custom_flags(libc::O_TMPFILE)
-            .open("/tmp")?;
+        let mut tmpfile = crate::tools::create_tmp_file()?;
 
         self.download(name, &mut tmpfile).await?;
 
@@ -167,18 +162,14 @@ impl BackupReader {
 
     /// Download dynamic index file
     ///
-    /// This creates a temporary file in /tmp (using O_TMPFILE). The index is verified using
-    /// the provided manifest.
+    /// This creates a temporary file (See [`crate::tools::create_tmp_file`] for
+    /// details). The index is verified using the provided manifest.
     pub async fn download_dynamic_index(
         &self,
         manifest: &BackupManifest,
         name: &str,
     ) -> Result<DynamicIndexReader, Error> {
-        let mut tmpfile = std::fs::OpenOptions::new()
-            .write(true)
-            .read(true)
-            .custom_flags(libc::O_TMPFILE)
-            .open("/tmp")?;
+        let mut tmpfile = crate::tools::create_tmp_file()?;
 
         self.download(name, &mut tmpfile).await?;
 
@@ -194,18 +185,14 @@ impl BackupReader {
 
     /// Download fixed index file
     ///
-    /// This creates a temporary file in /tmp (using O_TMPFILE). The index is verified using
-    /// the provided manifest.
+    /// This creates a temporary file (See [`crate::tools::create_tmp_file`] for
+    /// details). The index is verified using the provided manifest.
     pub async fn download_fixed_index(
         &self,
         manifest: &BackupManifest,
         name: &str,
     ) -> Result<FixedIndexReader, Error> {
-        let mut tmpfile = std::fs::OpenOptions::new()
-            .write(true)
-            .read(true)
-            .custom_flags(libc::O_TMPFILE)
-            .open("/tmp")?;
+        let mut tmpfile = crate::tools::create_tmp_file()?;
 
         self.download(name, &mut tmpfile).await?;
 
diff --git a/pbs-client/src/backup_writer.rs b/pbs-client/src/backup_writer.rs
index 8a03d8ea..f184c750 100644
--- a/pbs-client/src/backup_writer.rs
+++ b/pbs-client/src/backup_writer.rs
@@ -1,6 +1,5 @@
 use std::collections::HashSet;
 use std::future::Future;
-use std::os::unix::fs::OpenOptionsExt;
 use std::sync::atomic::{AtomicU64, AtomicUsize, Ordering};
 use std::sync::{Arc, Mutex};
 
@@ -523,11 +522,7 @@ impl BackupWriter {
         manifest: &BackupManifest,
         known_chunks: Arc<Mutex<HashSet<[u8; 32]>>>,
     ) -> Result<FixedIndexReader, Error> {
-        let mut tmpfile = std::fs::OpenOptions::new()
-            .write(true)
-            .read(true)
-            .custom_flags(libc::O_TMPFILE)
-            .open("/tmp")?;
+        let mut tmpfile = crate::tools::create_tmp_file()?;
 
         let param = json!({ "archive-name": archive_name });
         self.h2
@@ -562,11 +557,7 @@ impl BackupWriter {
         manifest: &BackupManifest,
         known_chunks: Arc<Mutex<HashSet<[u8; 32]>>>,
     ) -> Result<DynamicIndexReader, Error> {
-        let mut tmpfile = std::fs::OpenOptions::new()
-            .write(true)
-            .read(true)
-            .custom_flags(libc::O_TMPFILE)
-            .open("/tmp")?;
+        let mut tmpfile = crate::tools::create_tmp_file()?;
 
         let param = json!({ "archive-name": archive_name });
         self.h2
diff --git a/pbs-client/src/tools/mod.rs b/pbs-client/src/tools/mod.rs
index 1b0123a3..eeb24114 100644
--- a/pbs-client/src/tools/mod.rs
+++ b/pbs-client/src/tools/mod.rs
@@ -3,8 +3,10 @@ use std::collections::HashMap;
 use std::env::VarError::{NotPresent, NotUnicode};
 use std::fs::File;
 use std::io::{BufRead, BufReader};
+use std::os::unix::fs::OpenOptionsExt;
 use std::os::unix::io::FromRawFd;
 use std::process::Command;
+use std::sync::OnceLock;
 
 use anyhow::{bail, format_err, Context, Error};
 use serde_json::{json, Value};
@@ -526,3 +528,27 @@ pub fn place_xdg_file(
         .and_then(|base| base.place_config_file(file_name).map_err(Error::from))
         .with_context(|| format!("failed to place {} in xdg home", description))
 }
+
+/// Creates a temporary file (with O_TMPFILE) in XDG_CACHE_HOME. If we cannot
+/// create the file there it will be created in /tmp instead.
+pub fn create_tmp_file() -> std::io::Result<std::fs::File> {
+    static TMP_PATH: OnceLock<std::path::PathBuf> = OnceLock::new();
+    let tmp_path = TMP_PATH.get_or_init(|| {
+        xdg::BaseDirectories::new()
+            .map(|base| base.get_cache_home())
+            .unwrap_or_else(|_| std::path::PathBuf::from("/tmp"))
+    });
+
+    let mut open_opts_binding = std::fs::OpenOptions::new();
+    let builder = open_opts_binding
+        .write(true)
+        .read(true)
+        .custom_flags(libc::O_TMPFILE);
+    builder.open(tmp_path).or_else(|err| {
+        if tmp_path != std::path::Path::new("/tmp") {
+            builder.open("/tmp")
+        } else {
+            Err(err)
+        }
+    })
+}
diff --git a/proxmox-backup-client/src/catalog.rs b/proxmox-backup-client/src/catalog.rs
index 72b22e67..f3bc4ede 100644
--- a/proxmox-backup-client/src/catalog.rs
+++ b/proxmox-backup-client/src/catalog.rs
@@ -1,5 +1,4 @@
 use std::io::{Seek, SeekFrom};
-use std::os::unix::fs::OpenOptionsExt;
 use std::sync::Arc;
 
 use anyhow::{bail, format_err, Error};
@@ -104,11 +103,7 @@ async fn dump_catalog(param: Value) -> Result<Value, Error> {
 
     let mut reader = BufferedDynamicReader::new(index, chunk_reader);
 
-    let mut catalogfile = std::fs::OpenOptions::new()
-        .write(true)
-        .read(true)
-        .custom_flags(libc::O_TMPFILE)
-        .open("/tmp")?;
+    let mut catalogfile = pbs_client::tools::create_tmp_file()?;
 
     std::io::copy(&mut reader, &mut catalogfile)
         .map_err(|err| format_err!("unable to download catalog - {}", err))?;
@@ -196,11 +191,7 @@ async fn catalog_shell(param: Value) -> Result<(), Error> {
     )
     .await?;
 
-    let mut tmpfile = std::fs::OpenOptions::new()
-        .write(true)
-        .read(true)
-        .custom_flags(libc::O_TMPFILE)
-        .open("/tmp")?;
+    let mut tmpfile = pbs_client::tools::create_tmp_file()?;
 
     let (manifest, _) = client.download_manifest().await?;
     manifest.check_fingerprint(crypt_config.as_ref().map(Arc::as_ref))?;
@@ -240,11 +231,7 @@ async fn catalog_shell(param: Value) -> Result<(), Error> {
         most_used,
     );
     let mut reader = BufferedDynamicReader::new(index, chunk_reader);
-    let mut catalogfile = std::fs::OpenOptions::new()
-        .write(true)
-        .read(true)
-        .custom_flags(libc::O_TMPFILE)
-        .open("/tmp")?;
+    let mut catalogfile = pbs_client::tools::create_tmp_file()?;
 
     std::io::copy(&mut reader, &mut catalogfile)
         .map_err(|err| format_err!("unable to download catalog - {}", err))?;
-- 
2.39.2