server/worker_task: add TaskListInfoIterator

this is an iterator that reads/parses/updates the task list as
necessary and returns the tasks in descending order (newest first)

it does this by using our logrotate iterator and using a vecdeque

we can use this to iterate over all tasks, even if they are in the
archive and even if the archive is logrotated but only read
as much as we need

Signed-off-by: Dominik Csapak <d.csapak@proxmox.com>

src/server/worker_task.rs

@@ -1,4 +1,4 @@
-use std::collections::HashMap;
+use std::collections::{HashMap, VecDeque};
 use std::fs::File;
 use std::io::{Read, Write, BufRead, BufReader};
 use std::panic::UnwindSafe;
@@ -19,6 +19,7 @@ use proxmox::tools::fs::{create_path, open_file_locked, replace_file, CreateOpti
 
 use super::UPID;
 
+use crate::tools::logrotate::{LogRotate, LogRotateFiles};
 use crate::tools::FileLogger;
 use crate::api2::types::Userid;
 
@@ -493,6 +494,101 @@ where
     read_task_file(file)
 }
 
+enum TaskFile {
+    Active,
+    Index,
+    Archive,
+    End,
+}
+
+pub struct TaskListInfoIterator {
+    list: VecDeque<TaskListInfo>,
+    file: TaskFile,
+    archive: Option<LogRotateFiles>,
+    lock: Option<File>,
+}
+
+impl TaskListInfoIterator {
+    pub fn new(active_only: bool) -> Result<Self, Error> {
+        let (read_lock, active_list) = {
+            let lock = lock_task_list_files(false)?;
+            let active_list = read_task_file_from_path(PROXMOX_BACKUP_ACTIVE_TASK_FN)?;
+
+            let needs_update = active_list
+                .iter()
+                .any(|info| info.state.is_none() && !worker_is_active_local(&info.upid));
+
+            if needs_update {
+                drop(lock);
+                update_active_workers(None)?;
+                let lock = lock_task_list_files(false)?;
+                let active_list = read_task_file_from_path(PROXMOX_BACKUP_ACTIVE_TASK_FN)?;
+                (lock, active_list)
+            } else {
+                (lock, active_list)
+            }
+        };
+
+        let archive = if active_only {
+            None
+        } else {
+            let logrotate = LogRotate::new(PROXMOX_BACKUP_ARCHIVE_TASK_FN, true).ok_or_else(|| format_err!("could not get archive file names"))?;
+            Some(logrotate.files())
+        };
+
+        let file = if active_only { TaskFile::End } else { TaskFile::Active };
+        let lock = if active_only { None } else { Some(read_lock) };
+
+        Ok(Self {
+            list: active_list.into(),
+            file,
+            archive,
+            lock,
+        })
+    }
+}
+
+impl Iterator for TaskListInfoIterator {
+    type Item = Result<TaskListInfo, Error>;
+
+    fn next(&mut self) -> Option<Self::Item> {
+        loop {
+            if let Some(element) = self.list.pop_back() {
+                return Some(Ok(element));
+            } else {
+                match self.file {
+                    TaskFile::Active => {
+                        let index = match read_task_file_from_path(PROXMOX_BACKUP_INDEX_TASK_FN) {
+                            Ok(index) => index,
+                            Err(err) => return Some(Err(err)),
+                        };
+                        self.list.append(&mut index.into());
+                        self.file = TaskFile::Index;
+                    },
+                    TaskFile::Index | TaskFile::Archive => {
+                        if let Some(mut archive) = self.archive.take() {
+                            if let Some(file) = archive.next() {
+                                let list = match read_task_file(file) {
+                                    Ok(list) => list,
+                                    Err(err) => return Some(Err(err)),
+                                };
+                                self.list.append(&mut list.into());
+                                self.archive = Some(archive);
+                                self.file = TaskFile::Archive;
+                                continue;
+                            }
+                        }
+                        self.file = TaskFile::End;
+                        self.lock.take();
+                        return None;
+                    }
+                    TaskFile::End => return None,
+                }
+            }
+        }
+    }
+}
+
 /// Launch long running worker tasks.
 ///
 /// A worker task can either be a whole thread, or a simply tokio