Support compressing during cpio backup

native/src/base/include/stream.hpp

@@ -78,6 +78,21 @@ private:
     void resize(size_t new_sz, bool zero = false);
 };
 
+class rust_vec_channel : public channel {
+public:
+    rust_vec_channel(rust::Vec<uint8_t> &data) : _data(data) {}
+
+    ssize_t read(void *buf, size_t len) override;
+    bool write(const void *buf, size_t len) override;
+    off_t seek(off_t off, int whence) override;
+
+private:
+    rust::Vec<uint8_t> &_data;
+    size_t _pos = 0;
+
+    void ensure_size(size_t sz);
+};
+
 class file_channel : public channel {
 public:
     bool write(const void *buf, size_t len) final;

native/src/base/lib.rs

@@ -44,6 +44,7 @@ pub mod ffi {
         fn set_log_level_state_cxx(level: LogLevelCxx, enabled: bool);
         fn exit_on_error(b: bool);
         fn cmdline_logging();
+        fn resize_vec(vec: &mut Vec<u8>, size: usize);
     }
 
     #[namespace = "rust"]
@@ -63,3 +64,7 @@ fn set_log_level_state_cxx(level: ffi::LogLevelCxx, enabled: bool) {
         set_log_level_state(level, enabled)
     }
 }
+
+fn resize_vec(vec: &mut Vec<u8>, size: usize) {
+    vec.resize(size, 0);
+}

native/src/base/stream.cpp

@@ -180,6 +180,47 @@ void byte_channel::resize(size_t new_sz, bool zero) {
     }
 }
 
+ssize_t rust_vec_channel::read(void *buf, size_t len) {
+    len = std::min<size_t>(len, _data.size() - _pos);
+    memcpy(buf, _data.data() + _pos, len);
+    _pos += len;
+    return len;
+}
+
+bool rust_vec_channel::write(const void *buf, size_t len) {
+    ensure_size(_pos + len);
+    memcpy(_data.data() + _pos, buf, len);
+    _pos += len;
+    return true;
+}
+
+off_t rust_vec_channel::seek(off_t off, int whence) {
+    off_t np;
+    switch (whence) {
+        case SEEK_CUR:
+            np = _pos + off;
+            break;
+        case SEEK_END:
+            np = _data.size() + off;
+            break;
+        case SEEK_SET:
+            np = off;
+            break;
+        default:
+            return -1;
+    }
+    ensure_size(np);
+    _pos = np;
+    return np;
+}
+
+void rust_vec_channel::ensure_size(size_t sz) {
+    size_t old_sz = _data.size();
+    if (sz > old_sz) {
+        resize_vec(_data, sz);
+    }
+}
+
 ssize_t fd_channel::read(void *buf, size_t len) {
     return ::read(fd, buf, len);
 }