SSH connection status indicators

- Add Connected bool field to vfs.Entry and RemoteMount
- Track connection status in sshState.connectedHosts
- Show status icon (connected/disconnected) in pane header when browsing remote host
- Async SSH connection test with cancel support for Add Host dialog
- Colored labels and styled help text in SSH dialogs
- Confirmation dialog when deleting manually-added SSH hosts

vendor/github.com/pkg/sftp/allocator.go

@@ -0,0 +1,96 @@
+package sftp
+
+import (
+	"sync"
+)
+
+type allocator struct {
+	sync.Mutex
+	available [][]byte
+	// map key is the request order
+	used map[uint32][][]byte
+}
+
+func newAllocator() *allocator {
+	return &allocator{
+		// micro optimization: initialize available pages with an initial capacity
+		available: make([][]byte, 0, SftpServerWorkerCount*2),
+		used:      make(map[uint32][][]byte),
+	}
+}
+
+// GetPage returns a previously allocated and unused []byte or create a new one.
+// The slice have a fixed size = maxMsgLength, this value is suitable for both
+// receiving new packets and reading the files to serve
+func (a *allocator) GetPage(requestOrderID uint32) []byte {
+	a.Lock()
+	defer a.Unlock()
+
+	var result []byte
+
+	// get an available page and remove it from the available ones.
+	if len(a.available) > 0 {
+		truncLength := len(a.available) - 1
+		result = a.available[truncLength]
+
+		a.available[truncLength] = nil          // clear out the internal pointer
+		a.available = a.available[:truncLength] // truncate the slice
+	}
+
+	// no preallocated slice found, just allocate a new one
+	if result == nil {
+		result = make([]byte, maxMsgLength)
+	}
+
+	// put result in used pages
+	a.used[requestOrderID] = append(a.used[requestOrderID], result)
+
+	return result
+}
+
+// ReleasePages marks unused all pages in use for the given requestID
+func (a *allocator) ReleasePages(requestOrderID uint32) {
+	a.Lock()
+	defer a.Unlock()
+
+	if used := a.used[requestOrderID]; len(used) > 0 {
+		a.available = append(a.available, used...)
+	}
+	delete(a.used, requestOrderID)
+}
+
+// Free removes all the used and available pages.
+// Call this method when the allocator is not needed anymore
+func (a *allocator) Free() {
+	a.Lock()
+	defer a.Unlock()
+
+	a.available = nil
+	a.used = make(map[uint32][][]byte)
+}
+
+func (a *allocator) countUsedPages() int {
+	a.Lock()
+	defer a.Unlock()
+
+	num := 0
+	for _, p := range a.used {
+		num += len(p)
+	}
+	return num
+}
+
+func (a *allocator) countAvailablePages() int {
+	a.Lock()
+	defer a.Unlock()
+
+	return len(a.available)
+}
+
+func (a *allocator) isRequestOrderIDUsed(requestOrderID uint32) bool {
+	a.Lock()
+	defer a.Unlock()
+
+	_, ok := a.used[requestOrderID]
+	return ok
+}