feat(iroh): use reflink if possible (#1581)

reflink-copy is a clone of the abandoned reflink crate. Last time there
were some failures on android, so let's see if it works now...

## Description

<!-- A summary of what this pull request achieves and a rough list of
changes. -->

## Notes & open questions

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## Change checklist

- [ ] Self-review.
- [ ] Documentation updates if relevant.
- [ ] Tests if relevant.

iroh/Cargo.toml

@@ -67,13 +67,14 @@ colored = { version = "2.0.4", optional = true }
 
 # Examples
 ed25519-dalek = { version = "2.0.0", features = ["serde", "rand_core"], optional = true }
+reflink-copy = { version = "0.1.8", optional = true }
 
 [features]
 default = ["cli", "metrics"]
 cli = ["clap", "config", "console", "dirs-next", "indicatif", "multibase", "quic-rpc/quinn-transport", "tokio/rt-multi-thread", "tracing-subscriber", "flat-db", "mem-db", "iroh-collection", "shell-words", "shellexpand", "rustyline", "colored", "toml", "human-time", "comfy-table"]
 metrics = ["iroh-metrics"]
 mem-db = []
-flat-db = []
+flat-db = ["reflink-copy"]
 iroh-collection = []
 test = []
 example-sync = ["cli"]

iroh/src/baomap/flat.rs

@@ -883,7 +883,11 @@ impl Store {
                 let temp_path = self.temp_path();
                 // copy the data, since it is not stable
                 progress.try_send(ImportProgress::CopyProgress { id, offset: 0 })?;
-                std::fs::copy(&path, &temp_path)?;
+                if reflink_copy::reflink_or_copy(&path, &temp_path)?.is_none() {
+                    tracing::debug!("reflinked {} to {}", path.display(), temp_path.display());
+                } else {
+                    tracing::debug!("copied {} to {}", path.display(), temp_path.display());
+                }
                 ImportFile::TempFile(temp_path)
             }
         };
@@ -1165,7 +1169,11 @@ impl Store {
             tracing::debug!("copying {} to {}", source.display(), target.display());
             progress(0)?;
             // todo: progress
-            std::fs::copy(&source, &target)?;
+            if reflink_copy::reflink_or_copy(&source, &target)?.is_none() {
+                tracing::debug!("reflinked {} to {}", source.display(), target.display());
+            } else {
+                tracing::debug!("copied {} to {}", source.display(), target.display());
+            }
             progress(size)?;
             let mut state = self.0.state.write().unwrap();
             let Some(entry) = state.complete.get_mut(&hash) else {