Cargo.lock

@@ -2035,6 +2035,7 @@ name = "lanspread-peer"
 version = "0.1.0"
 dependencies = [
  "bytes",
+ "crc32fast",
  "eyre",
  "futures",
  "gethostname",
@@ -2059,13 +2060,16 @@ dependencies = [
 name = "lanspread-peer-cli"
 version = "0.1.0"
 dependencies = [
+ "bytes",
  "eyre",
  "lanspread-compat",
  "lanspread-db",
  "lanspread-peer",
+ "lanspread-proto",
  "serde",
  "serde_json",
  "tokio",
+ "tokio-util",
 ]
 
 [[package]]

Cargo.toml

@@ -14,6 +14,7 @@ members = [
 [workspace.dependencies]
 base64 = "0.22"
 bytes = { version = "1", features = ["serde"] }
+crc32fast = "1"
 eyre = "0.6"
 futures = "0.3"
 gethostname = "1"

NEXT_STEPS.md

@@ -0,0 +1,64 @@
+# Streamed Install Next Steps
+
+I’d treat the prototype as proof of the hard part: “can we stream
+archive-derived install bytes into `local/` without making the receiver a
+source?” Yes. Next I’d harden the pieces that decide whether this is
+product-ready.
+
+1. **Move from CLI-only to real app integration**
+
+   Add a GUI command/control path for “stream install / low disk mode”,
+   probably behind an explicit option. The Tauri crate currently opts out with
+   `stream_install_provider: None`, so the GUI cannot use it yet.
+
+2. **Replace per-file `unrar p` with a final archive provider**
+
+   The prototype provider is intentionally simple: `unrar lt`, then `unrar p`
+   per file. Good for non-solid archives, bad for solid archives. Final shape
+   should be a one-pass provider with real entry boundaries, likely via libunrar
+   or a purpose-built wrapper.
+
+3. **Handle solid archives deliberately**
+
+   Add archive inspection that decides:
+
+   - non-solid: per-file streaming is fine
+   - solid: one sequential archive pass only
+
+   This is the big architectural fork we discussed, and the prototype’s
+   provider is the thing to swap.
+
+4. **Decide the integrity model**
+
+   Current prototype verifies streamed bytes against RAR CRC32 from the
+   sender’s archive headers. That catches corruption and provider bugs. It does
+   not protect against a malicious peer lying. If you care about that, the next
+   step is catalog-side trusted hashes for archive or extracted files.
+
+5. **Upgrade retry/resume semantics**
+
+   Right now, failed stream means failed operation and rollback. Next useful
+   step:
+
+   - retry whole stream from another trusted peer
+   - later, maybe keep completed files and restart only the interrupted file
+   - avoid byte-offset resume until there’s a strong reason
+
+6. **Expand scenario coverage**
+
+   I’d add cases for:
+
+   - sender disconnect mid-stream
+   - receiver cancel mid-stream
+   - corrupted/truncated stream fails and leaves no `local/`
+   - already-installed game rejects streamed install
+   - multi-archive `.eti` roots stream in sorted order
+
+7. **Clean product semantics**
+
+   Decide how the UI labels this state. It is installed but not downloaded, so
+   “Local only” is technically correct, but users may need a clear affordance
+   like “Installed, not shareable”.
+
+My recommended next slice: make the provider abstraction final-ish, then
+implement a real one-pass provider. Everything else builds cleanly on that.

PEER_CLI_SCENARIOS.md

@@ -46,6 +46,8 @@ for deterministic local runs; mDNS/macvlan remains an environment smoke path.
 | S36 | Latest singleton beats stale majority | Five peers advertise one game; one peer has `20260501`, four peers have `20250101`. | `list-games` reports `eti_game_version=20260501`; all descriptors and chunks come from the singleton latest peer; stale peers contribute zero bytes. |
 | S37 | Single-source download throughput | A source peer advertises a temporary catalog game with one sparse `2 GiB` `.eti`; an empty client downloads it with `install=false`. | The client emits `download-finished` with throughput measurements (`bytes`, `duration_ms`, `mib_per_s`, `mbit_per_s`), and the downloaded archive size matches the source. |
 | S38 | First-play launch-setting stamping | `fixture-persona/css` ships a real RAR `.eti` whose tree buries a CRLF `SmartSteamEmu.ini` with a stub `PersonaName` line under `engine/bin/win64/steam_settings/`, plus a stub `account_name.txt` and `language.txt` under `profiles/local/`. A peer installs `css` (with `--unrar`), then sends `play css` with a username and language, then `play css` again. | After install the marker `games/css/launch_settings_applied` is absent and the stub files are intact under `local/`. The first `play` returns `already_applied=false` with `account_name_written`, `language_written`, and `persona_name_written` all true; the deep `SmartSteamEmu.ini` `PersonaName` value becomes the username with its `\r\n` ending and sibling lines preserved, `account_name.txt` becomes the username, `language.txt` becomes the passed language, and the marker now exists. A second `play` returns `already_applied=true`, rewrites nothing, and leaves the files untouched even if their values were reset externally. |
+| S39 | Streamed install without keeping archive payload | Empty client connects to `fixture-bravo`, then sends `stream-install cnctw`. The source has real RAR `.eti` payload entries under `bin/` and `data/`; the receiver uses the container-bundled `unrar` stream provider. | Client emits `got-game-files`, `download-begin`, streamed `download-chunk-finished`, `download-finished`, `install-begin`, and `install-finished`. Local `cnctw` is `downloaded=false`, `installed=true`, `availability=LocalOnly`; root `version.ini` and `.eti` are absent; `local/bin/cnctw-payload.bin` and `local/data/cnctw-assets.dat` match `unrar p` output by SHA-256. |
+| S40 | Streamed install receiver is not a peer source | After S39, a third peer connects only to the streamed-install receiver. | The third peer may see the receiver's local-only summary in peer snapshots, but `list-games` remote aggregation does not expose `cnctw` as downloadable, `peer_count` remains zero/absent, and attempting `download cnctw` fails with no local files created. |
 
 ## Version-Skew Contract
 
@@ -105,13 +107,37 @@ Use S38 to pin down how launcher settings are stamped into an installed game:
   line keeps its existing line ending (`\n` or `\r\n`).
 - The marker records only that we *tried*: it is written unconditionally after
   the first play, so a game with none of these files is still marked done.
-- S38 needs a real archive expanded with `--unrar`, so it runs against the host
+- S38 needs a real archive expanded with `--unrar`; the Docker matrix image now
-  `lanspread-peer-cli` binary rather than the Docker matrix image (which omits
+  carries the Linux sidecar for streamed-install coverage, while the peer
-  `unrar`). The peer crate's `launch_settings` unit tests cover the rewrite,
+  crate's `launch_settings` unit tests cover the rewrite, line-ending, and
-  line-ending, and marker logic deterministically.
+  marker logic deterministically.
 
 ## Run Log
 
+### 2026-06-07 - Streamed Install Prototype (S39-S40)
+
+- Code under test added `stream-install` to `lanspread-peer-cli`, a peer
+  `StreamInstallGame` command, streamed install frames over QUIC, and an
+  injected `unrar lt`/`unrar p` provider for archive-derived bytes.
+- Gates before Docker: `just fmt` and
+  `RUSTC_WRAPPER= CARGO_BUILD_RUSTC_WRAPPER= just test` passed for the
+  workspace.
+- Runner:
+  `python3 crates/lanspread-peer-cli/scripts/run_extended_scenarios.py S39 S40 --build-image`
+  passed against the rebuilt `lanspread-peer-cli:dev` image.
+- S39 streamed a catalog-version-adjusted `cnctw` fixture from a real RAR
+  `.eti` into the receiver's `local/` only. The receiver had
+  `downloaded=false`, `installed=true`, `availability=LocalOnly`, no root
+  `version.ini`, no root `.eti`, and payload SHA-256 hashes
+  `82f4da22dc042166def2a5ee2eca19fc9e52785f99838e86c32167cb342e2588`
+  (`bin/cnctw-payload.bin`) and
+  `abf833a06c74ea9f17d505c2684186491898ce906405e0f098f0deac19476b06`
+  (`data/cnctw-assets.dat`) matching `unrar p`.
+- S40 connected an observer only to that streamed-install receiver. The
+  observer saw the receiver's `cnctw` summary as local-only, remote aggregation
+  hid it as a downloadable source, and `download cnctw` failed with
+  `no peers have game cnctw`.
+
 ### 2026-05-28 - First-Play Launch-Setting Stamping (S38)
 
 - Code under test moved the `account_name.txt`/`language.txt` overwrite out of

crates/lanspread-peer-cli/Cargo.toml

@@ -14,11 +14,14 @@ path = "src/main.rs"
 lanspread-compat = { path = "../lanspread-compat" }
 lanspread-db = { path = "../lanspread-db" }
 lanspread-peer = { path = "../lanspread-peer" }
+lanspread-proto = { path = "../lanspread-proto" }
 
+bytes = { workspace = true }
 eyre = { workspace = true }
 serde = { workspace = true }
 serde_json = { workspace = true }
 tokio = { workspace = true }
+tokio-util = { workspace = true }
 
 [lints.clippy]
 needless_pass_by_value = "allow"

crates/lanspread-peer-cli/Dockerfile

@@ -4,14 +4,16 @@ WORKDIR /work
 COPY . .
 RUN cargo build --release -p lanspread-peer-cli
 
-FROM debian:bookworm-slim
+FROM debian:trixie-slim
 
 RUN apt-get update \
-    && apt-get install -y --no-install-recommends ca-certificates \
+    && apt-get install -y --no-install-recommends ca-certificates libstdc++6 \
     && rm -rf /var/lib/apt/lists/*
 
 COPY --from=build /work/target/release/lanspread-peer-cli /usr/local/bin/lanspread-peer-cli
 COPY crates/lanspread-tauri-deno-ts/src-tauri/game.db /app/game.db
+COPY crates/lanspread-tauri-deno-ts/src-tauri/binaries/unrar-x86_64-unknown-linux-gnu /usr/local/bin/unrar
+RUN chmod +x /usr/local/bin/unrar
 
 ENTRYPOINT ["lanspread-peer-cli"]
 CMD ["--games-dir", "/games", "--state-dir", "/state", "--catalog-db", "/app/game.db"]

crates/lanspread-peer-cli/scripts/run_extended_scenarios.py

@@ -1,5 +1,5 @@
 #!/usr/bin/env python3
-"""Run the peer-cli scenarios S1-S36 through Docker."""
+"""Run the peer-cli scenarios S1-S40 through Docker."""
 
 from __future__ import annotations
 
@@ -8,6 +8,7 @@ import hashlib
 import json
 import os
 import queue
+import shlex
 import shutil
 import subprocess
 import sys
@@ -325,6 +326,8 @@ class Runner:
             ("S35", self.s35_unknown_game_filtered),
             ("S36", self.s36_latest_singleton),
             ("S37", self.s37_single_source_download_throughput),
+            ("S39", self.s39_streamed_install_local_only),
+            ("S40", self.s40_streamed_receiver_not_source),
         ]
 
         for scenario_id, scenario in scenarios:
@@ -1060,6 +1063,114 @@ class Runner:
             f"{throughput['chunks']} chunks"
         )
 
+    def stream_install_cnctw(self, prefix: str) -> tuple[Peer, Peer]:
+        source_dir = self.fixture_root / f"{prefix}-bravo"
+        copy_game("cnctw", source_dir, version="20160128")
+        source = self.peer(f"{prefix}-bravo", games_dir=source_dir)
+        client = self.peer(f"{prefix}-client")
+        connect_many(client, [source])
+        wait_remote_game(client, "cnctw", peer_count=1)
+        waiter = LineWaiter(len(client.output))
+        client.send({"cmd": "stream-install", "game_id": "cnctw"})
+        client.wait_for(
+            event_is("got-game-files", "cnctw"),
+            timeout=20,
+            description="got cnctw files",
+            waiter=waiter,
+        )
+        client.wait_for(
+            event_is("download-begin", "cnctw"),
+            timeout=20,
+            description="stream begin cnctw",
+            waiter=waiter,
+        )
+        client.wait_for(
+            event_is("download-finished", "cnctw"),
+            timeout=60,
+            description="stream finish cnctw",
+            waiter=waiter,
+        )
+        client.wait_for(
+            event_is("install-finished", "cnctw"),
+            timeout=30,
+            description="stream install cnctw",
+            waiter=waiter,
+        )
+        return source, client
+
+    def s39_streamed_install_local_only(self) -> str:
+        source, client = self.stream_install_cnctw("s39")
+        game = wait_local_game(client, "cnctw", downloaded=False, installed=True)
+        assert_game_state(
+            game,
+            downloaded=False,
+            installed=True,
+            availability="LocalOnly",
+        )
+
+        game_root = client.host_games_dir / "cnctw"
+        assert_not_exists(game_root / "version.ini")
+        assert_not_exists(game_root / "cnctw.eti")
+
+        expected = {
+            "bin/cnctw-payload.bin": unrar_entry_sha256(
+                source, "cnctw", "bin/cnctw-payload.bin"
+            ),
+            "data/cnctw-assets.dat": unrar_entry_sha256(
+                source, "cnctw", "data/cnctw-assets.dat"
+            ),
+        }
+        actual = {
+            rel: sha256_file(game_root / "local" / rel)
+            for rel in expected
+        }
+        if actual != expected:
+            raise ScenarioError(f"streamed local payload hashes mismatched: {actual} != {expected}")
+
+        streamed_bytes = sum(
+            int(item.get("data", {}).get("length", 0))
+            for item in client.output
+            if item.get("type") == "event"
+            and item.get("event") == "download-chunk-finished"
+            and item.get("data", {}).get("game_id") == "cnctw"
+        )
+        expected_bytes = 3 * 1024 * 1024
+        if streamed_bytes != expected_bytes:
+            raise ScenarioError(
+                f"streamed byte count mismatch: {streamed_bytes} != {expected_bytes}"
+            )
+
+        return (
+            "cnctw streamed into local/ only; root archive and version.ini absent; "
+            f"payload hashes={actual}"
+        )
+
+    def s40_streamed_receiver_not_source(self) -> str:
+        _source, receiver = self.stream_install_cnctw("s40")
+        observer = self.peer("s40-observer")
+        connect_many(observer, [receiver])
+        receiver_snapshot = wait_peer_has_game(observer, receiver.peer_id, "cnctw")
+        summary = next(
+            game
+            for game in receiver_snapshot.get("games", [])
+            if game.get("id") == "cnctw"
+        )
+        if summary.get("availability") != "LocalOnly" or summary.get("downloaded"):
+            raise ScenarioError(f"receiver did not advertise cnctw as local-only: {summary}")
+
+        wait_remote_absent(observer, "cnctw", timeout=5)
+        err = observer.send(
+            {"cmd": "download", "game_id": "cnctw", "install": False},
+            expect_error=True,
+        )
+        if "no peers have game cnctw" not in err["error"]:
+            raise ScenarioError(f"unexpected local-only download error: {err}")
+        assert_not_exists(observer.host_games_dir / "cnctw")
+        return (
+            "observer saw receiver's local-only cnctw snapshot, but remote aggregation hid it "
+            f"and download errored '{err['error']}'"
+        )
+
 
 def run(command: list[str], description: str) -> subprocess.CompletedProcess[str]:
     result = subprocess.run(
@@ -1177,6 +1288,25 @@ def create_large_sparse_game(root: Path, *, size: int) -> None:
         handle.truncate(size)
 
 
+def sha256_file(path: Path) -> str:
+    hasher = hashlib.sha256()
+    with path.open("rb") as handle:
+        for chunk in iter(lambda: handle.read(1024 * 1024), b""):
+            hasher.update(chunk)
+    return hasher.hexdigest()
+
+
+def unrar_entry_sha256(peer: Peer, game_id: str, relative_path: str) -> str:
+    command = (
+        f"unrar p -inul /games/{shlex.quote(game_id)}/{shlex.quote(game_id)}.eti "
+        f"{shlex.quote(relative_path)} | sha256sum"
+    )
+    output = peer.docker_exec("sh", "-c", command).stdout.strip()
+    if not output:
+        raise ScenarioError(f"empty sha256 output for {game_id}:{relative_path}")
+    return output.split()[0]
+
+
 def format_bytes(size: int) -> str:
     return f"{size / 1024 / 1024 / 1024:.2f} GiB"
 

crates/lanspread-peer-cli/src/lib.rs

@@ -5,15 +5,21 @@
 use std::{
     net::SocketAddr,
     path::{Path, PathBuf},
+    process::Stdio,
     time::Duration,
 };
 
+use bytes::Bytes;
 use eyre::{Context, OptionExt};
-use lanspread_peer::{UnpackFuture, Unpacker};
+use lanspread_peer::{StreamInstallFuture, StreamInstallProvider, UnpackFuture, Unpacker};
+use lanspread_proto::StreamInstallFrame;
 use serde::Serialize;
 use serde_json::{Value, json};
+use tokio::{io::AsyncReadExt, sync::mpsc};
+use tokio_util::sync::CancellationToken;
 
 pub const DEFAULT_FIXTURE_VERSION: &str = "20250101";
+const STREAM_CHUNK_SIZE: usize = 256 * 1024;
 
 #[derive(Debug, Clone, PartialEq, Eq)]
 pub struct CommandEnvelope {
@@ -33,6 +39,9 @@ pub enum CliCommand {
         game_id: String,
         install_after_download: bool,
     },
+    StreamInstall {
+        game_id: String,
+    },
     Install {
         game_id: String,
     },
@@ -63,6 +72,7 @@ impl CliCommand {
             Self::ListGames => "list-games",
             Self::SetGameDir { .. } => "set-game-dir",
             Self::Download { .. } => "download",
+            Self::StreamInstall { .. } => "stream-install",
             Self::Install { .. } => "install",
             Self::Uninstall { .. } => "uninstall",
             Self::Play { .. } => "play",
@@ -101,6 +111,9 @@ pub fn parse_command_value(value: &Value) -> eyre::Result<CommandEnvelope> {
             game_id: game_id(object)?,
             install_after_download: install_after_download(object)?,
         },
+        "stream-install" => CliCommand::StreamInstall {
+            game_id: game_id(object)?,
+        },
         "install" => CliCommand::Install {
             game_id: game_id(object)?,
         },
@@ -254,6 +267,270 @@ impl Unpacker for ExternalUnrarUnpacker {
     }
 }
 
+pub struct ExternalUnrarStreamProvider {
+    program: PathBuf,
+}
+
+impl ExternalUnrarStreamProvider {
+    #[must_use]
+    pub fn new(program: PathBuf) -> Self {
+        Self { program }
+    }
+}
+
+impl StreamInstallProvider for ExternalUnrarStreamProvider {
+    fn stream_archive<'a>(
+        &'a self,
+        archive: &'a Path,
+        frames: mpsc::Sender<StreamInstallFrame>,
+        cancel_token: CancellationToken,
+    ) -> StreamInstallFuture<'a> {
+        Box::pin(async move {
+            let listing = unrar_listing(&self.program, archive).await?;
+            let archive_name = archive
+                .file_name()
+                .and_then(|name| name.to_str())
+                .unwrap_or("archive.eti")
+                .to_string();
+
+            send_stream_frame(
+                &frames,
+                StreamInstallFrame::ArchiveBegin {
+                    archive_name: archive_name.clone(),
+                    solid: listing.solid,
+                },
+            )
+            .await?;
+
+            for entry in listing.entries {
+                if cancel_token.is_cancelled() {
+                    eyre::bail!("streamed archive {} was cancelled", archive.display());
+                }
+
+                match entry.kind {
+                    RarEntryKind::Directory => {
+                        send_stream_frame(
+                            &frames,
+                            StreamInstallFrame::Directory {
+                                relative_path: entry.relative_path,
+                            },
+                        )
+                        .await?;
+                    }
+                    RarEntryKind::File => {
+                        send_stream_frame(
+                            &frames,
+                            StreamInstallFrame::FileBegin {
+                                relative_path: entry.relative_path.clone(),
+                                size: entry.size,
+                                crc32: entry.crc32,
+                            },
+                        )
+                        .await?;
+                        stream_unrar_file(
+                            &self.program,
+                            archive,
+                            &entry.relative_path,
+                            &frames,
+                            cancel_token.clone(),
+                        )
+                        .await?;
+                        send_stream_frame(
+                            &frames,
+                            StreamInstallFrame::FileEnd {
+                                relative_path: entry.relative_path,
+                            },
+                        )
+                        .await?;
+                    }
+                }
+            }
+
+            send_stream_frame(&frames, StreamInstallFrame::ArchiveEnd { archive_name }).await
+        })
+    }
+}
+
+#[derive(Debug, Clone, PartialEq, Eq)]
+struct RarListing {
+    solid: bool,
+    entries: Vec<RarEntry>,
+}
+
+#[derive(Debug, Clone, PartialEq, Eq)]
+struct RarEntry {
+    relative_path: String,
+    kind: RarEntryKind,
+    size: u64,
+    crc32: Option<u32>,
+}
+
+#[derive(Debug, Clone, Copy, PartialEq, Eq)]
+enum RarEntryKind {
+    File,
+    Directory,
+}
+
+#[derive(Default)]
+struct RarEntryDraft {
+    relative_path: Option<String>,
+    kind: Option<RarEntryKind>,
+    size: Option<u64>,
+    crc32: Option<u32>,
+}
+
+async fn unrar_listing(program: &Path, archive: &Path) -> eyre::Result<RarListing> {
+    let output = tokio::process::Command::new(program)
+        .arg("lt")
+        .arg("-cfg-")
+        .arg(archive)
+        .output()
+        .await?;
+    if !output.status.success() {
+        eyre::bail!(
+            "unrar lt failed for {} with status {}: {}",
+            archive.display(),
+            output.status,
+            String::from_utf8_lossy(&output.stderr)
+        );
+    }
+
+    parse_unrar_listing(&String::from_utf8_lossy(&output.stdout))
+}
+
+fn parse_unrar_listing(output: &str) -> eyre::Result<RarListing> {
+    let mut solid = false;
+    let mut entries = Vec::new();
+    let mut current = RarEntryDraft::default();
+
+    for line in output.lines() {
+        let trimmed = line.trim();
+        if let Some(details) = trimmed.strip_prefix("Details:") {
+            solid = details.to_ascii_lowercase().contains("solid");
+            continue;
+        }
+
+        if let Some(name) = trimmed.strip_prefix("Name:") {
+            push_rar_entry(&mut entries, std::mem::take(&mut current))?;
+            current.relative_path = Some(name.trim().to_string());
+            continue;
+        }
+
+        if let Some(kind) = trimmed.strip_prefix("Type:") {
+            current.kind = match kind.trim() {
+                "File" => Some(RarEntryKind::File),
+                "Directory" => Some(RarEntryKind::Directory),
+                _ => None,
+            };
+            continue;
+        }
+
+        if let Some(size) = trimmed.strip_prefix("Size:") {
+            current.size = Some(size.trim().parse()?);
+            continue;
+        }
+
+        if let Some(crc) = trimmed.strip_prefix("CRC32:") {
+            current.crc32 = Some(u32::from_str_radix(crc.trim(), 16)?);
+        }
+    }
+
+    push_rar_entry(&mut entries, current)?;
+    Ok(RarListing { solid, entries })
+}
+
+fn push_rar_entry(entries: &mut Vec<RarEntry>, draft: RarEntryDraft) -> eyre::Result<()> {
+    let Some(relative_path) = draft.relative_path else {
+        return Ok(());
+    };
+
+    let Some(kind) = draft.kind else {
+        return Ok(());
+    };
+
+    let size = match kind {
+        RarEntryKind::File => draft
+            .size
+            .ok_or_else(|| eyre::eyre!("RAR file entry {relative_path} has no Size"))?,
+        RarEntryKind::Directory => 0,
+    };
+
+    entries.push(RarEntry {
+        relative_path,
+        kind,
+        size,
+        crc32: draft.crc32,
+    });
+    Ok(())
+}
+
+async fn stream_unrar_file(
+    program: &Path,
+    archive: &Path,
+    relative_path: &str,
+    frames: &mpsc::Sender<StreamInstallFrame>,
+    cancel_token: CancellationToken,
+) -> eyre::Result<()> {
+    let mut child = tokio::process::Command::new(program)
+        .arg("p")
+        .arg("-inul")
+        .arg("-cfg-")
+        .arg(archive)
+        .arg(relative_path)
+        .stdout(Stdio::piped())
+        .stderr(Stdio::null())
+        .spawn()?;
+
+    let mut stdout = child
+        .stdout
+        .take()
+        .ok_or_eyre("unrar stdout was not captured")?;
+    let mut buffer = vec![0_u8; STREAM_CHUNK_SIZE];
+
+    loop {
+        let read = tokio::select! {
+            () = cancel_token.cancelled() => {
+                let _ = child.kill().await;
+                eyre::bail!("streaming {relative_path} from {} was cancelled", archive.display());
+            }
+            read = stdout.read(&mut buffer) => read?,
+        };
+
+        if read == 0 {
+            break;
+        }
+
+        send_stream_frame(
+            frames,
+            StreamInstallFrame::FileChunk {
+                bytes: Bytes::copy_from_slice(&buffer[..read]),
+            },
+        )
+        .await?;
+    }
+
+    let status = child.wait().await?;
+    if !status.success() {
+        eyre::bail!(
+            "unrar p failed for {}:{} with status {status}",
+            archive.display(),
+            relative_path
+        );
+    }
+
+    Ok(())
+}
+
+async fn send_stream_frame(
+    frames: &mpsc::Sender<StreamInstallFrame>,
+    frame: StreamInstallFrame,
+) -> eyre::Result<()> {
+    frames
+        .send(frame)
+        .await
+        .map_err(|_| eyre::eyre!("streamed install frame receiver closed"))
+}
+
 pub fn result_line(id: &Option<Value>, command: &str, data: Value) -> eyre::Result<String> {
     output_line(json!({
         "type": "result",
@@ -344,6 +621,57 @@ mod tests {
         assert_eq!(parsed["data"]["peer_count"], 0);
     }
 
+    #[test]
+    fn parses_stream_install_command() {
+        let parsed = parse_command_line(r#"{"cmd":"stream-install","game_id":"cnctw"}"#)
+            .expect("command should parse");
+
+        assert_eq!(
+            parsed.command,
+            CliCommand::StreamInstall {
+                game_id: "cnctw".to_string(),
+            }
+        );
+    }
+
+    #[test]
+    fn parses_unrar_technical_listing() {
+        let listing = parse_unrar_listing(
+            r#"
+Archive: game.eti
+Details: RAR 5
+
+        Name: bin/payload.bin
+        Type: File
+        Size: 123
+       CRC32: 38B488A7
+
+        Name: bin
+        Type: Directory
+"#,
+        )
+        .expect("listing should parse");
+
+        assert!(!listing.solid);
+        assert_eq!(
+            listing.entries,
+            vec![
+                RarEntry {
+                    relative_path: "bin/payload.bin".to_string(),
+                    kind: RarEntryKind::File,
+                    size: 123,
+                    crc32: Some(0x38B4_88A7),
+                },
+                RarEntry {
+                    relative_path: "bin".to_string(),
+                    kind: RarEntryKind::Directory,
+                    size: 0,
+                    crc32: None,
+                },
+            ]
+        );
+    }
+
     #[tokio::test]
     async fn fixture_unpacker_creates_install_payload() {
         let temp = TempDir::new("lanspread-peer-cli-fixture");

crates/lanspread-peer-cli/src/main.rs

@@ -17,6 +17,7 @@ use lanspread_peer::{
     ActiveOperation,
     ActiveOperationKind,
     InstallOperation,
+    NoopStreamInstallProvider,
     PeerCommand,
     PeerEvent,
     PeerGameDB,
@@ -24,6 +25,7 @@ use lanspread_peer::{
     PeerRuntimeHandle,
     PeerSnapshot,
     PeerStartOptions,
+    StreamInstallProvider,
     migrate_legacy_state,
     start_peer_with_options,
 };
@@ -31,6 +33,7 @@ use lanspread_peer_cli::{
     CliCommand,
     CommandEnvelope,
     DEFAULT_FIXTURE_VERSION,
+    ExternalUnrarStreamProvider,
     ExternalUnrarUnpacker,
     FixtureSeed,
     FixtureUnpacker,
@@ -134,10 +137,15 @@ async fn main() -> eyre::Result<()> {
     let (tx_events, rx_events) = mpsc::unbounded_channel();
     let peer_game_db = Arc::new(RwLock::new(PeerGameDB::new()));
     let catalog = Arc::new(RwLock::new(catalog));
-    let unpacker: Arc<dyn lanspread_peer::Unpacker> = match args.unrar {
+    let unrar_for_streaming = args.unrar.clone().or_else(default_unrar_program);
+    let unpacker: Arc<dyn lanspread_peer::Unpacker> = match args.unrar.clone() {
         Some(path) => Arc::new(ExternalUnrarUnpacker::new(path)),
         None => Arc::new(FixtureUnpacker),
     };
+    let stream_install_provider: Arc<dyn StreamInstallProvider> = match unrar_for_streaming {
+        Some(path) => Arc::new(ExternalUnrarStreamProvider::new(path)),
+        None => Arc::new(NoopStreamInstallProvider),
+    };
 
     let mut handle = start_peer_with_options(
         args.games_dir.clone(),
@@ -148,6 +156,7 @@ async fn main() -> eyre::Result<()> {
         PeerStartOptions {
             state_dir: Some(args.state_dir.clone()),
             active_outbound_transfers: None,
+            stream_install_provider: Some(stream_install_provider),
         },
     )?;
     let sender = handle.sender();
@@ -249,6 +258,15 @@ async fn handle_command(
             })?;
             Ok(json!({"queued": true, "game_id": game_id, "install": install_after_download}))
         }
+        CliCommand::StreamInstall { game_id } => {
+            ensure_catalog_game(shared, game_id).await?;
+            ensure_no_active_operation(shared, game_id).await?;
+            let _ = game_files_for_download(sender, shared, game_id).await?;
+            sender.send(PeerCommand::StreamInstallGame {
+                id: game_id.clone(),
+            })?;
+            Ok(json!({"queued": true, "game_id": game_id}))
+        }
         CliCommand::Install { game_id } => {
             ensure_catalog_game(shared, game_id).await?;
             ensure_no_active_operation(shared, game_id).await?;
@@ -729,6 +747,15 @@ fn default_catalog_db() -> Option<PathBuf> {
     .find(|path| path.exists())
 }
 
+fn default_unrar_program() -> Option<PathBuf> {
+    [
+        PathBuf::from("/usr/local/bin/unrar"),
+        PathBuf::from("/usr/bin/unrar"),
+    ]
+    .into_iter()
+    .find(|path| path.exists())
+}
+
 fn next_string(args: &mut impl Iterator<Item = OsString>, flag: &str) -> eyre::Result<String> {
     args.next()
         .ok_or_else(|| eyre::eyre!("{flag} requires a value"))?

crates/lanspread-peer/Cargo.toml

@@ -14,6 +14,7 @@ lanspread-utils = { path = "../lanspread-utils" }
 
 # external
 bytes = { workspace = true }
+crc32fast = { workspace = true }
 eyre = { workspace = true }
 futures = { workspace = true }
 gethostname = { workspace = true }

crates/lanspread-peer/src/context.rs

@@ -6,7 +6,14 @@ use lanspread_db::db::{GameCatalog, GameDB};
 use tokio::sync::{RwLock, mpsc::UnboundedSender};
 use tokio_util::{sync::CancellationToken, task::TaskTracker};
 
-use crate::{PeerEvent, Unpacker, events, library::LocalLibraryState, peer_db::PeerGameDB};
+use crate::{
+    PeerEvent,
+    StreamInstallProvider,
+    Unpacker,
+    events,
+    library::LocalLibraryState,
+    peer_db::PeerGameDB,
+};
 
 /// Thread-safe map of active outbound file transfers grouped by game ID.
 pub type OutboundTransfers = Arc<RwLock<HashMap<String, Vec<(u64, CancellationToken)>>>>;
@@ -38,6 +45,7 @@ pub struct Ctx {
     pub active_operations: Arc<RwLock<HashMap<String, OperationKind>>>,
     pub active_downloads: Arc<RwLock<HashMap<String, CancellationToken>>>,
     pub unpacker: Arc<dyn Unpacker>,
+    pub stream_install_provider: Arc<dyn StreamInstallProvider>,
     pub catalog: Arc<RwLock<GameCatalog>>,
     pub peer_id: Arc<String>,
     pub shutdown: CancellationToken,
@@ -57,6 +65,7 @@ pub struct PeerCtx {
     pub catalog: Arc<RwLock<GameCatalog>>,
     pub peer_id: Arc<String>,
     pub tx_notify_ui: tokio::sync::mpsc::UnboundedSender<PeerEvent>,
+    pub stream_install_provider: Arc<dyn StreamInstallProvider>,
     pub shutdown: CancellationToken,
     pub task_tracker: TaskTracker,
     pub active_outbound_transfers: OutboundTransfers,
@@ -86,6 +95,7 @@ impl Ctx {
         task_tracker: TaskTracker,
         catalog: Arc<RwLock<GameCatalog>>,
         active_outbound_transfers: OutboundTransfers,
+        stream_install_provider: Arc<dyn StreamInstallProvider>,
     ) -> Self {
         Self {
             game_dir: Arc::new(RwLock::new(game_dir)),
@@ -97,6 +107,7 @@ impl Ctx {
             active_operations: Arc::new(RwLock::new(HashMap::new())),
             active_downloads: Arc::new(RwLock::new(HashMap::new())),
             unpacker,
+            stream_install_provider,
             catalog,
             peer_id: Arc::new(peer_id),
             shutdown,
@@ -120,6 +131,7 @@ impl Ctx {
             catalog: self.catalog.clone(),
             peer_id: self.peer_id.clone(),
             tx_notify_ui,
+            stream_install_provider: self.stream_install_provider.clone(),
             shutdown: self.shutdown.clone(),
             task_tracker: self.task_tracker.clone(),
             active_outbound_transfers: self.active_outbound_transfers.clone(),

crates/lanspread-peer/src/handlers.rs

@@ -11,6 +11,7 @@ use std::{
 
 use lanspread_db::db::{GameDB, GameFileDescription};
 use tokio::sync::{RwLock, mpsc::UnboundedSender};
+use tokio_util::sync::CancellationToken;
 
 use crate::{
     InstallOperation,
@@ -33,6 +34,7 @@ use crate::{
     peer_db::PeerGameDB,
     remote_peer::ensure_peer_id_for_addr,
     services::{HandshakeCtx, perform_handshake_with_peer},
+    stream_install::receive_streamed_install,
 };
 
 // =============================================================================
@@ -450,6 +452,91 @@ pub async fn handle_install_game_command(
     spawn_install_operation(ctx, tx_notify_ui, id);
 }
 
+pub async fn handle_stream_install_game_command(
+    ctx: &Ctx,
+    tx_notify_ui: &UnboundedSender<PeerEvent>,
+    id: String,
+) {
+    if !catalog_contains(ctx, &id).await {
+        log::warn!("Ignoring streamed install command for non-catalog game {id}");
+        send_download_failed(tx_notify_ui, &id);
+        return;
+    }
+
+    let games_folder = { ctx.game_dir.read().await.clone() };
+    let game_root = games_folder.join(&id);
+    if local_dir_is_directory(&game_root).await {
+        log::warn!("Ignoring streamed install command for already-installed game {id}");
+        send_download_failed(tx_notify_ui, &id);
+        return;
+    }
+
+    let expected_version = catalog_expected_version(ctx, &id).await;
+    let mut peers = {
+        match ctx
+            .peer_game_db
+            .read()
+            .await
+            .validate_file_sizes_majority(&id, expected_version.as_deref())
+        {
+            Ok((validated_files, peer_whitelist, _)) if !validated_files.is_empty() => {
+                peer_whitelist
+            }
+            Ok(_) => {
+                log::error!("No trusted peers available for streamed install of {id}");
+                send_download_failed(tx_notify_ui, &id);
+                return;
+            }
+            Err(err) => {
+                log::error!(
+                    "File size majority validation failed for streamed install {id}: {err}"
+                );
+                send_download_failed(tx_notify_ui, &id);
+                return;
+            }
+        }
+    };
+    peers.sort();
+    let Some(peer_addr) = peers.into_iter().next() else {
+        log::error!("No peer selected for streamed install of {id}");
+        send_download_failed(tx_notify_ui, &id);
+        return;
+    };
+
+    match begin_operation(ctx, tx_notify_ui, &id, OperationKind::Downloading).await {
+        BeginOperationResult::Started => {}
+        BeginOperationResult::AlreadyActive => {
+            log::warn!("Operation for {id} already in progress; ignoring streamed install request");
+            return;
+        }
+        BeginOperationResult::DrainTimedOut => {
+            log::error!("Timed out waiting for outbound transfers before streamed install of {id}");
+            send_download_failed(tx_notify_ui, &id);
+            return;
+        }
+    }
+
+    let cancel_token = ctx.shutdown.child_token();
+    ctx.active_downloads
+        .write()
+        .await
+        .insert(id.clone(), cancel_token.clone());
+
+    let ctx_clone = ctx.clone();
+    let tx_notify_ui = tx_notify_ui.clone();
+    ctx.task_tracker.spawn(async move {
+        run_stream_install_operation(
+            ctx_clone,
+            tx_notify_ui,
+            id,
+            game_root,
+            peer_addr,
+            cancel_token,
+        )
+        .await;
+    });
+}
+
 /// Handles the `UninstallGame` command.
 pub async fn handle_uninstall_game_command(
     ctx: &Ctx,
@@ -490,6 +577,151 @@ pub async fn handle_cancel_download_command(
     cancel_token.cancel();
 }
 
+async fn run_stream_install_operation(
+    ctx: Ctx,
+    tx_notify_ui: UnboundedSender<PeerEvent>,
+    id: String,
+    game_root: PathBuf,
+    peer_addr: SocketAddr,
+    cancel_token: CancellationToken,
+) {
+    let download_guard = OperationGuard::download(
+        id.clone(),
+        ctx.active_operations.clone(),
+        ctx.active_downloads.clone(),
+        tx_notify_ui.clone(),
+    );
+
+    events::send(
+        &tx_notify_ui,
+        PeerEvent::DownloadGameFilesBegin { id: id.clone() },
+    );
+
+    let transaction = match install::begin_streamed_install(&game_root, ctx.state_dir.as_ref(), &id)
+        .await
+    {
+        Ok(transaction) => transaction,
+        Err(err) => {
+            log::error!("Failed to prepare streamed install for {id}: {err}");
+            finish_failed_stream_download(&ctx, &tx_notify_ui, &id, download_guard, false).await;
+            return;
+        }
+    };
+
+    let receive_result = receive_streamed_install(
+        peer_addr,
+        &id,
+        transaction.staging_dir(),
+        tx_notify_ui.clone(),
+        cancel_token.clone(),
+    )
+    .await;
+
+    match receive_result {
+        Ok(()) => {
+            if transition_download_to_install(&ctx, &tx_notify_ui, &id, OperationKind::Installing)
+                .await
+            {
+                clear_active_download(&ctx, &id).await;
+                send_download_finished(&tx_notify_ui, &id);
+                download_guard.disarm();
+                commit_streamed_install(&ctx, &tx_notify_ui, id, transaction).await;
+            } else {
+                if let Err(err) = transaction.rollback().await {
+                    log::error!("Failed to roll back streamed install for {id}: {err}");
+                }
+                finish_failed_stream_download(&ctx, &tx_notify_ui, &id, download_guard, false)
+                    .await;
+            }
+        }
+        Err(err) => {
+            if let Err(rollback_err) = transaction.rollback().await {
+                log::error!("Failed to roll back streamed install for {id}: {rollback_err}");
+            }
+            let download_was_cancelled = cancel_token.is_cancelled();
+            if download_was_cancelled {
+                log::info!("Streamed install download cancelled for {id}: {err}");
+            } else {
+                log::error!("Streamed install download failed for {id}: {err}");
+            }
+            finish_failed_stream_download(
+                &ctx,
+                &tx_notify_ui,
+                &id,
+                download_guard,
+                download_was_cancelled,
+            )
+            .await;
+        }
+    }
+}
+
+async fn finish_failed_stream_download(
+    ctx: &Ctx,
+    tx_notify_ui: &UnboundedSender<PeerEvent>,
+    id: &str,
+    guard: OperationGuard,
+    cancelled: bool,
+) {
+    if let Err(err) = refresh_local_game_for_ending_operation(ctx, tx_notify_ui, id).await {
+        log::error!("Failed to refresh local library after streamed install failure: {err}");
+    }
+    end_download_operation(ctx, tx_notify_ui, id).await;
+    guard.disarm();
+    send_download_failed_unless_cancelled(tx_notify_ui, id, cancelled);
+}
+
+async fn commit_streamed_install(
+    ctx: &Ctx,
+    tx_notify_ui: &UnboundedSender<PeerEvent>,
+    id: String,
+    transaction: install::StreamedInstallTransaction,
+) {
+    let operation_guard = OperationGuard::new(
+        id.clone(),
+        ctx.active_operations.clone(),
+        tx_notify_ui.clone(),
+    );
+    events::send(
+        tx_notify_ui,
+        PeerEvent::InstallGameBegin {
+            id: id.clone(),
+            operation: InstallOperation::Installing,
+        },
+    );
+
+    match transaction.commit().await {
+        Ok(()) => {
+            if let Err(err) = refresh_local_game_for_ending_operation(ctx, tx_notify_ui, &id).await
+            {
+                log::error!("Failed to refresh local library after streamed install: {err}");
+            }
+            end_operation(ctx, tx_notify_ui, &id).await;
+            operation_guard.disarm();
+            events::send(
+                tx_notify_ui,
+                PeerEvent::InstallGameFinished { id: id.clone() },
+            );
+        }
+        Err(err) => {
+            log::error!("Streamed install commit failed for {id}: {err}");
+            if let Err(refresh_err) =
+                refresh_local_game_for_ending_operation(ctx, tx_notify_ui, &id).await
+            {
+                log::error!(
+                    "Failed to refresh local library after streamed install commit failure: {refresh_err}"
+                );
+            }
+            end_operation(ctx, tx_notify_ui, &id).await;
+            operation_guard.disarm();
+            events::send(
+                tx_notify_ui,
+                PeerEvent::InstallGameFailed { id: id.clone() },
+            );
+        }
+    }
+}
+
 fn spawn_install_operation(ctx: &Ctx, tx_notify_ui: &UnboundedSender<PeerEvent>, id: String) {
     let ctx = ctx.clone();
     let tx_notify_ui = tx_notify_ui.clone();
@@ -1264,6 +1496,7 @@ mod tests {
             TaskTracker::new(),
             Arc::new(RwLock::new(GameCatalog::from_ids(["game".to_string()]))),
             Arc::new(RwLock::new(HashMap::new())),
+            Arc::new(crate::NoopStreamInstallProvider),
         )
     }
 

crates/lanspread-peer/src/install/mod.rs

@@ -4,5 +4,13 @@ mod transaction;
 pub mod unpack;
 
 pub use remove::remove_downloaded;
-pub use transaction::{install, recover_on_startup, uninstall, update};
+pub(crate) use transaction::root_eti_archives;
+pub use transaction::{
+    StreamedInstallTransaction,
+    begin_streamed_install,
+    install,
+    recover_on_startup,
+    uninstall,
+    update,
+};
 pub use unpack::{UnpackFuture, Unpacker};

crates/lanspread-peer/src/install/transaction.rs

@@ -33,6 +33,103 @@ struct InstallFsState {
     backup: FsEntryState,
 }
 
+pub struct StreamedInstallTransaction {
+    game_root: PathBuf,
+    state_dir: PathBuf,
+    id: String,
+    staging: PathBuf,
+    eti_version: Option<String>,
+}
+
+impl StreamedInstallTransaction {
+    #[must_use]
+    pub fn staging_dir(&self) -> &Path {
+        &self.staging
+    }
+
+    pub async fn commit(self) -> eyre::Result<()> {
+        let local = local_dir(&self.game_root);
+        let result = async {
+            tokio::fs::rename(&self.staging, &local)
+                .await
+                .wrap_err_with(|| format!("failed to promote streamed install for {}", self.id))?;
+            reset_launch_settings_marker(&self.state_dir, &self.id).await?;
+            write_intent(
+                &self.state_dir,
+                &self.id,
+                &InstallIntent::none(&self.id, self.eti_version.clone()),
+            )
+            .await
+        }
+        .await;
+
+        if result.is_err() {
+            if let Err(cleanup_err) = remove_dir_all_if_exists(&self.staging).await {
+                log::warn!(
+                    "Failed to clean streamed install staging {}: {cleanup_err}",
+                    self.staging.display()
+                );
+            }
+            let _ = write_intent(
+                &self.state_dir,
+                &self.id,
+                &InstallIntent::none(&self.id, self.eti_version.clone()),
+            )
+            .await;
+        }
+
+        result
+    }
+
+    pub async fn rollback(self) -> eyre::Result<()> {
+        let staging_result = remove_dir_all_if_exists(&self.staging).await;
+        let intent_result = write_intent(
+            &self.state_dir,
+            &self.id,
+            &InstallIntent::none(&self.id, self.eti_version.clone()),
+        )
+        .await;
+
+        staging_result?;
+        intent_result
+    }
+}
+
+pub async fn begin_streamed_install(
+    game_root: &Path,
+    state_dir: &Path,
+    id: &str,
+) -> eyre::Result<StreamedInstallTransaction> {
+    if path_is_dir(&local_dir(game_root)).await {
+        eyre::bail!("game {id} is already installed");
+    }
+
+    tokio::fs::create_dir_all(game_root).await?;
+    let eti_version = read_downloaded_version(game_root).await;
+    write_intent(
+        state_dir,
+        id,
+        &InstallIntent::new(id, InstallIntentState::Installing, eti_version.clone()),
+    )
+    .await?;
+
+    let staging = installing_dir(game_root);
+    if let Err(err) = prepare_owned_empty_dir(&staging).await {
+        let _ = write_intent(state_dir, id, &InstallIntent::none(id, eti_version)).await;
+        return Err(err);
+    }
+
+    let staging = tokio::fs::canonicalize(&staging).await.unwrap_or(staging);
+
+    Ok(StreamedInstallTransaction {
+        game_root: game_root.to_path_buf(),
+        state_dir: state_dir.to_path_buf(),
+        id: id.to_string(),
+        staging,
+        eti_version,
+    })
+}
+
 pub async fn install(
     game_root: &Path,
     state_dir: &Path,
@@ -258,7 +355,7 @@ async fn unpack_archives(
     Ok(())
 }
 
-async fn root_eti_archives(game_root: &Path) -> eyre::Result<Vec<PathBuf>> {
+pub(crate) async fn root_eti_archives(game_root: &Path) -> eyre::Result<Vec<PathBuf>> {
     let mut entries = tokio::fs::read_dir(game_root).await?;
     let mut archives = Vec::new();
     while let Some(entry) = entries.next_entry().await? {

crates/lanspread-peer/src/lib.rs

@@ -32,6 +32,7 @@ mod remote_peer;
 mod services;
 mod startup;
 mod state_paths;
+mod stream_install;
 #[cfg(test)]
 mod test_support;
 
@@ -82,6 +83,7 @@ pub use crate::{
     launch_settings::{LaunchSettingsOutcome, apply_launch_settings_once},
     startup::PeerRuntimeHandle,
     state_paths::{launch_settings_applied_path, setup_done_path},
+    stream_install::{NoopStreamInstallProvider, StreamInstallFuture, StreamInstallProvider},
 };
 
 // =============================================================================
@@ -243,6 +245,8 @@ pub enum PeerCommand {
         file_descriptions: Vec<GameFileDescription>,
         install_after_download: bool,
     },
+    /// Stream archive-expanded bytes directly into `local/` without keeping root archives.
+    StreamInstallGame { id: String },
     /// Install already-downloaded archives into `local/`.
     InstallGame { id: String },
     /// Remove only the `local/` install for a game.
@@ -260,11 +264,29 @@ pub enum PeerCommand {
 }
 
 /// Optional startup settings for non-GUI callers and tests.
-#[derive(Clone, Debug, Default)]
+#[derive(Clone, Default)]
 pub struct PeerStartOptions {
     /// Directory used for peer identity and other state.
     pub state_dir: Option<PathBuf>,
     pub active_outbound_transfers: Option<crate::context::OutboundTransfers>,
+    /// Provider used to stream archive entries for low-disk streamed installs.
+    pub stream_install_provider: Option<Arc<dyn StreamInstallProvider>>,
+}
+
+impl std::fmt::Debug for PeerStartOptions {
+    fn fmt(&self, f: &mut std::fmt::Formatter<'_>) -> std::fmt::Result {
+        f.debug_struct("PeerStartOptions")
+            .field("state_dir", &self.state_dir)
+            .field(
+                "active_outbound_transfers",
+                &self.active_outbound_transfers.as_ref().map(|_| "..."),
+            )
+            .field(
+                "stream_install_provider",
+                &self.stream_install_provider.as_ref().map(|_| "..."),
+            )
+            .finish()
+    }
 }
 
 // =============================================================================
@@ -314,11 +336,14 @@ pub fn start_peer_with_options(
     let PeerStartOptions {
         state_dir,
         active_outbound_transfers,
+        stream_install_provider,
     } = options;
     let state_dir = resolve_state_dir(state_dir.as_deref());
     let game_dir = game_dir.into();
     let active_outbound_transfers = active_outbound_transfers
         .unwrap_or_else(|| Arc::new(RwLock::new(std::collections::HashMap::new())));
+    let stream_install_provider =
+        stream_install_provider.unwrap_or_else(|| Arc::new(NoopStreamInstallProvider));
     log::info!(
         "Starting peer system with game directory: {}",
         game_dir.display()
@@ -338,6 +363,7 @@ pub fn start_peer_with_options(
         unpacker,
         catalog,
         active_outbound_transfers,
+        stream_install_provider,
     ))
 }
 
@@ -355,6 +381,7 @@ async fn run_peer(
     task_tracker: TaskTracker,
     catalog: Arc<RwLock<GameCatalog>>,
     active_outbound_transfers: crate::context::OutboundTransfers,
+    stream_install_provider: Arc<dyn StreamInstallProvider>,
 ) -> eyre::Result<()> {
     let ctx = Ctx::new(
         peer_game_db,
@@ -366,6 +393,7 @@ async fn run_peer(
         task_tracker,
         catalog,
         active_outbound_transfers,
+        stream_install_provider,
     );
     if let Err(err) = load_local_library(&ctx, &tx_notify_ui).await {
         log::error!("Failed to load initial local game database: {err}");
@@ -439,6 +467,9 @@ async fn handle_peer_commands(
                 )
                 .await;
             }
+            PeerCommand::StreamInstallGame { id } => {
+                handlers::handle_stream_install_game_command(ctx, tx_notify_ui, id).await;
+            }
             PeerCommand::InstallGame { id } => {
                 handle_install_game_command(ctx, tx_notify_ui, id).await;
             }

crates/lanspread-peer/src/services/handshake.rs

@@ -319,6 +319,7 @@ mod tests {
             TaskTracker::new(),
             Arc::new(RwLock::new(catalog)),
             Arc::new(RwLock::new(HashMap::new())),
+            Arc::new(crate::NoopStreamInstallProvider),
         );
         *ctx.local_peer_addr.write().await = Some(addr([127, 0, 0, 1], 4000));
 

crates/lanspread-peer/src/services/local_monitor.rs

@@ -384,6 +384,7 @@ mod tests {
             TaskTracker::new(),
             Arc::new(RwLock::new(catalog)),
             Arc::new(RwLock::new(std::collections::HashMap::new())),
+            Arc::new(crate::NoopStreamInstallProvider),
         )
     }
 

crates/lanspread-peer/src/services/stream.rs

@@ -15,6 +15,7 @@ use crate::{
     local_games::{get_game_file_descriptions, is_local_dir_name, local_download_matches_catalog},
     peer::{send_game_file_chunk, send_game_file_data},
     services::handshake::{HandshakeCtx, accept_inbound_hello, spawn_library_resync},
+    stream_install::{send_game_install_stream, send_stream_install_error},
 };
 
 type ResponseWriter = FramedWrite<SendStream, LengthDelimitedCodec>;
@@ -99,6 +100,9 @@ async fn dispatch_request(
         } => {
             handle_file_chunk_request(ctx, game_id, relative_path, offset, length, framed_tx).await
         }
+        Request::StreamInstall { game_id } => {
+            handle_stream_install_request(ctx, game_id, framed_tx).await
+        }
         Request::Goodbye { peer_id } => {
             handle_goodbye(ctx, remote_addr, peer_id).await;
             framed_tx
@@ -386,6 +390,49 @@ async fn handle_file_chunk_request(
     FramedWrite::new(tx, LengthDelimitedCodec::new())
 }
 
+async fn handle_stream_install_request(
+    ctx: &PeerCtx,
+    game_id: String,
+    framed_tx: ResponseWriter,
+) -> ResponseWriter {
+    log::info!("Received StreamInstall request for {game_id} from peer");
+
+    let (guard, cancel_token) = TransferGuard::new(
+        game_id.clone(),
+        ctx.active_outbound_transfers.clone(),
+        ctx.tx_notify_ui.clone(),
+        &ctx.shutdown,
+    )
+    .await;
+
+    let mut tx = framed_tx.into_inner();
+    let game_dir = ctx.game_dir.read().await.clone();
+    if !can_serve_game(ctx, &game_dir, &game_id).await {
+        log::info!(
+            "Declining StreamInstall for {game_id} because the game is not currently transferable"
+        );
+        tx = send_stream_install_error(tx, format!("game {game_id} is not transferable")).await;
+        drop(guard);
+        return FramedWrite::new(tx, LengthDelimitedCodec::new());
+    }
+
+    let game_root = game_dir.join(&game_id);
+    let (returned_tx, result) = send_game_install_stream(
+        ctx.stream_install_provider.clone(),
+        tx,
+        &game_root,
+        &game_id,
+        cancel_token,
+    )
+    .await;
+    if let Err(err) = result {
+        log::warn!("StreamInstall for {game_id} ended with error: {err}");
+    }
+
+    drop(guard);
+    FramedWrite::new(returned_tx, LengthDelimitedCodec::new())
+}
+
 async fn handle_goodbye(ctx: &PeerCtx, _remote_addr: Option<SocketAddr>, peer_id: String) {
     log::info!("Received Goodbye from peer {peer_id}");
     let removed = { ctx.peer_game_db.write().await.remove_peer(&peer_id) };
@@ -442,6 +489,7 @@ mod tests {
             TaskTracker::new(),
             Arc::new(RwLock::new(catalog)),
             Arc::new(RwLock::new(std::collections::HashMap::new())),
+            Arc::new(crate::NoopStreamInstallProvider),
         )
         .to_peer_ctx(tx_notify_ui)
     }

crates/lanspread-peer/src/startup.rs

@@ -23,6 +23,7 @@ use crate::{
     PeerCommand,
     PeerEvent,
     PeerRuntimeComponent,
+    StreamInstallProvider,
     Unpacker,
     context::Ctx,
     events,
@@ -87,6 +88,7 @@ pub(crate) fn spawn_peer_runtime(
     unpacker: Arc<dyn Unpacker>,
     catalog: Arc<RwLock<GameCatalog>>,
     active_outbound_transfers: crate::context::OutboundTransfers,
+    stream_install_provider: Arc<dyn StreamInstallProvider>,
 ) -> PeerRuntimeHandle {
     let shutdown = CancellationToken::new();
     let task_tracker = TaskTracker::new();
@@ -107,6 +109,7 @@ pub(crate) fn spawn_peer_runtime(
             runtime_tracker.clone(),
             catalog,
             active_outbound_transfers,
+            stream_install_provider,
         )
         .await
         {

crates/lanspread-peer/src/stream_install.rs

@@ -0,0 +1,372 @@
+use std::{
+    future::Future,
+    net::SocketAddr,
+    path::{Path, PathBuf},
+    pin::Pin,
+    sync::Arc,
+};
+
+use bytes::Bytes;
+use crc32fast::Hasher;
+use futures::{SinkExt, StreamExt};
+use lanspread_proto::{Message, Request, StreamInstallFrame};
+use s2n_quic::stream::SendStream;
+use tokio::{
+    fs::File,
+    io::AsyncWriteExt,
+    sync::{mpsc, mpsc::UnboundedSender},
+};
+use tokio_util::{
+    codec::{FramedRead, FramedWrite, LengthDelimitedCodec},
+    sync::CancellationToken,
+};
+
+use crate::{
+    PeerEvent,
+    install::root_eti_archives,
+    network::connect_to_peer,
+    path_validation::validate_game_file_path,
+};
+
+const FRAME_CHANNEL_DEPTH: usize = 16;
+
+pub type StreamInstallFuture<'a> = Pin<Box<dyn Future<Output = eyre::Result<()>> + Send + 'a>>;
+
+pub trait StreamInstallProvider: Send + Sync {
+    fn stream_archive<'a>(
+        &'a self,
+        archive: &'a Path,
+        frames: mpsc::Sender<StreamInstallFrame>,
+        cancel_token: CancellationToken,
+    ) -> StreamInstallFuture<'a>;
+}
+
+#[derive(Debug, Default)]
+pub struct NoopStreamInstallProvider;
+
+impl StreamInstallProvider for NoopStreamInstallProvider {
+    fn stream_archive<'a>(
+        &'a self,
+        archive: &'a Path,
+        _frames: mpsc::Sender<StreamInstallFrame>,
+        _cancel_token: CancellationToken,
+    ) -> StreamInstallFuture<'a> {
+        Box::pin(async move {
+            eyre::bail!(
+                "streamed install provider is not configured for {}",
+                archive.display()
+            )
+        })
+    }
+}
+
+pub(crate) async fn send_stream_install_error(
+    tx: SendStream,
+    message: impl Into<String>,
+) -> SendStream {
+    let mut framed_tx = FramedWrite::new(tx, LengthDelimitedCodec::new());
+    if let Err(err) = framed_tx
+        .send(
+            StreamInstallFrame::Error {
+                message: message.into(),
+            }
+            .encode(),
+        )
+        .await
+    {
+        log::warn!("Failed to send streamed install error frame: {err}");
+    }
+    if let Err(err) = framed_tx.close().await {
+        log::debug!("Failed to close streamed install error response: {err}");
+    }
+    framed_tx.into_inner()
+}
+
+pub(crate) async fn send_game_install_stream(
+    provider: Arc<dyn StreamInstallProvider>,
+    tx: SendStream,
+    game_root: &Path,
+    game_id: &str,
+    cancel_token: CancellationToken,
+) -> (SendStream, eyre::Result<()>) {
+    let archives = match root_eti_archives(game_root).await {
+        Ok(archives) => archives,
+        Err(err) => {
+            let message = err.to_string();
+            let tx = send_stream_install_error(tx, message.clone()).await;
+            return (tx, Err(eyre::eyre!(message)));
+        }
+    };
+    if archives.is_empty() {
+        let message = format!("no .eti archives found for {game_id}");
+        let tx = send_stream_install_error(tx, message.clone()).await;
+        return (tx, Err(eyre::eyre!(message)));
+    }
+
+    let (frame_tx, mut frame_rx) = mpsc::channel(FRAME_CHANNEL_DEPTH);
+    let producer_cancel = cancel_token.child_token();
+    let game_id_for_producer = game_id.to_string();
+    let producer = tokio::spawn({
+        let provider = provider.clone();
+        let producer_cancel = producer_cancel.clone();
+        async move {
+            for archive in archives {
+                if producer_cancel.is_cancelled() {
+                    eyre::bail!("streamed install for {game_id_for_producer} was cancelled");
+                }
+
+                if let Err(err) = provider
+                    .stream_archive(&archive, frame_tx.clone(), producer_cancel.clone())
+                    .await
+                {
+                    let message = err.to_string();
+                    let _ = frame_tx.send(StreamInstallFrame::Error { message }).await;
+                    return Err(err);
+                }
+            }
+
+            let _ = frame_tx.send(StreamInstallFrame::Complete).await;
+            Ok(())
+        }
+    });
+
+    let mut framed_tx = FramedWrite::new(tx, LengthDelimitedCodec::new());
+    let mut send_result = Ok(());
+
+    while let Some(frame) = frame_rx.recv().await {
+        if let Err(err) = framed_tx.send(frame.encode()).await {
+            producer_cancel.cancel();
+            send_result = Err(eyre::eyre!("failed to send streamed install frame: {err}"));
+            break;
+        }
+    }
+
+    let close_result = framed_tx
+        .close()
+        .await
+        .map_err(|err| eyre::eyre!("failed to close streamed install stream: {err}"));
+    let tx = framed_tx.into_inner();
+    let producer_result = match producer.await {
+        Ok(result) => result,
+        Err(err) => Err(eyre::eyre!("streamed install producer task failed: {err}")),
+    };
+    let result = send_result.and(producer_result).and(close_result);
+
+    (tx, result)
+}
+
+pub(crate) async fn receive_streamed_install(
+    peer_addr: SocketAddr,
+    game_id: &str,
+    staging_dir: &Path,
+    tx_notify_ui: UnboundedSender<PeerEvent>,
+    cancel_token: CancellationToken,
+) -> eyre::Result<()> {
+    let staging_dir = tokio::fs::canonicalize(staging_dir)
+        .await
+        .unwrap_or_else(|_| staging_dir.to_path_buf());
+    let mut conn = connect_to_peer(peer_addr).await?;
+    let stream = conn.open_bidirectional_stream().await?;
+    let (rx, tx) = stream.split();
+    let mut framed_tx = FramedWrite::new(tx, LengthDelimitedCodec::new());
+
+    framed_tx
+        .send(
+            Request::StreamInstall {
+                game_id: game_id.to_string(),
+            }
+            .encode(),
+        )
+        .await?;
+    framed_tx.close().await?;
+
+    let mut framed_rx = FramedRead::new(rx, LengthDelimitedCodec::new());
+    let mut current_file: Option<IncomingFile> = None;
+
+    loop {
+        let next = tokio::select! {
+            () = cancel_token.cancelled() => eyre::bail!("streamed install for {game_id} was cancelled"),
+            next = framed_rx.next() => next,
+        };
+
+        let Some(frame) = next else {
+            eyre::bail!("streamed install ended before Complete");
+        };
+        let frame = frame?.freeze();
+        let frame = StreamInstallFrame::decode(frame);
+
+        match frame {
+            StreamInstallFrame::ArchiveBegin {
+                archive_name,
+                solid,
+            } => {
+                log::info!(
+                    "Receiving streamed install archive {archive_name} for {game_id} (solid={solid})"
+                );
+            }
+            StreamInstallFrame::Directory { relative_path } => {
+                let path = resolve_stream_path(&staging_dir, &relative_path)?;
+                tokio::fs::create_dir_all(path).await?;
+            }
+            StreamInstallFrame::FileBegin {
+                relative_path,
+                size,
+                crc32,
+            } => {
+                if current_file.is_some() {
+                    eyre::bail!("received FileBegin for {relative_path} before previous FileEnd");
+                }
+                let path = resolve_stream_path(&staging_dir, &relative_path)?;
+                if let Some(parent) = path.parent() {
+                    tokio::fs::create_dir_all(parent).await?;
+                }
+                let file = File::create(&path).await?;
+                current_file = Some(IncomingFile::new(relative_path, path, size, crc32, file));
+            }
+            StreamInstallFrame::FileChunk { bytes } => {
+                let Some(file) = current_file.as_mut() else {
+                    eyre::bail!("received FileChunk without FileBegin");
+                };
+                file.write_chunk(game_id, peer_addr, &tx_notify_ui, bytes)
+                    .await?;
+            }
+            StreamInstallFrame::FileEnd { relative_path } => {
+                let Some(file) = current_file.take() else {
+                    eyre::bail!("received FileEnd for {relative_path} without FileBegin");
+                };
+                file.finish(&relative_path).await?;
+            }
+            StreamInstallFrame::ArchiveEnd { archive_name } => {
+                log::info!("Finished streamed install archive {archive_name} for {game_id}");
+            }
+            StreamInstallFrame::Complete => {
+                if current_file.is_some() {
+                    eyre::bail!("streamed install completed with an open file");
+                }
+                return Ok(());
+            }
+            StreamInstallFrame::Error { message } => {
+                eyre::bail!("streamed install sender failed: {message}");
+            }
+        }
+    }
+}
+
+struct IncomingFile {
+    relative_path: String,
+    path: PathBuf,
+    expected_size: u64,
+    expected_crc32: Option<u32>,
+    received: u64,
+    hasher: Hasher,
+    file: File,
+}
+
+impl IncomingFile {
+    fn new(
+        relative_path: String,
+        path: PathBuf,
+        expected_size: u64,
+        expected_crc32: Option<u32>,
+        file: File,
+    ) -> Self {
+        Self {
+            relative_path,
+            path,
+            expected_size,
+            expected_crc32,
+            received: 0,
+            hasher: Hasher::new(),
+            file,
+        }
+    }
+
+    async fn write_chunk(
+        &mut self,
+        game_id: &str,
+        peer_addr: SocketAddr,
+        tx_notify_ui: &UnboundedSender<PeerEvent>,
+        bytes: Bytes,
+    ) -> eyre::Result<()> {
+        let offset = self.received;
+        let length = u64::try_from(bytes.len())?;
+        if offset.saturating_add(length) > self.expected_size {
+            eyre::bail!(
+                "streamed file {} exceeded expected size {}",
+                self.relative_path,
+                self.expected_size
+            );
+        }
+        self.file.write_all(&bytes).await?;
+        self.hasher.update(&bytes);
+        self.received = self.received.saturating_add(length);
+
+        let _ = tx_notify_ui.send(PeerEvent::DownloadGameFileChunkFinished {
+            id: game_id.to_string(),
+            peer_addr,
+            relative_path: format!("{game_id}/local/{}", self.relative_path),
+            offset,
+            length,
+        });
+        Ok(())
+    }
+
+    async fn finish(mut self, relative_path: &str) -> eyre::Result<()> {
+        if self.relative_path != relative_path {
+            eyre::bail!(
+                "streamed file end mismatch: began {}, ended {relative_path}",
+                self.relative_path
+            );
+        }
+        self.file.flush().await?;
+
+        if self.received != self.expected_size {
+            eyre::bail!(
+                "streamed file {} size mismatch: got {}, expected {}",
+                self.relative_path,
+                self.received,
+                self.expected_size
+            );
+        }
+
+        if let Some(expected) = self.expected_crc32 {
+            let actual = self.hasher.finalize();
+            if actual != expected {
+                eyre::bail!(
+                    "streamed file {} CRC32 mismatch: got {actual:08X}, expected {expected:08X}",
+                    self.relative_path
+                );
+            }
+        }
+
+        log::debug!(
+            "Received streamed file {} -> {}",
+            self.relative_path,
+            self.path.display()
+        );
+        Ok(())
+    }
+}
+
+fn resolve_stream_path(staging_dir: &Path, relative_path: &str) -> eyre::Result<PathBuf> {
+    validate_game_file_path(staging_dir, relative_path)
+}
+
+#[cfg(test)]
+mod tests {
+    use super::*;
+    use crate::test_support::TempDir;
+
+    #[test]
+    fn stream_paths_stay_inside_staging_dir() {
+        let temp = TempDir::new("lanspread-stream-install-path");
+        let staging = temp.path().join("staging");
+        std::fs::create_dir_all(&staging).expect("staging should be created");
+        let staging = std::fs::canonicalize(staging).expect("staging should canonicalize");
+
+        assert!(resolve_stream_path(&staging, "bin/game.exe").is_ok());
+        assert!(resolve_stream_path(&staging, "../outside").is_err());
+        assert!(resolve_stream_path(&staging, "/absolute").is_err());
+        assert!(resolve_stream_path(&staging, "C:/windows").is_err());
+    }
+}

crates/lanspread-proto/src/lib.rs

@@ -4,7 +4,7 @@ use bytes::Bytes;
 use lanspread_db::db::{Game, GameFileDescription};
 use serde::{Deserialize, Serialize};
 
-pub const PROTOCOL_VERSION: u32 = 4;
+pub const PROTOCOL_VERSION: u32 = 5;
 
 pub use lanspread_db::db::Availability;
 
@@ -67,6 +67,9 @@ pub enum Request {
         offset: u64,
         length: u64,
     },
+    StreamInstall {
+        game_id: String,
+    },
     Hello(Hello),
     LibraryDelta {
         peer_id: String,
@@ -94,6 +97,35 @@ pub enum Response {
     InternalPeerError(String),
 }
 
+#[derive(Clone, Debug, Serialize, Deserialize)]
+pub enum StreamInstallFrame {
+    ArchiveBegin {
+        archive_name: String,
+        solid: bool,
+    },
+    Directory {
+        relative_path: String,
+    },
+    FileBegin {
+        relative_path: String,
+        size: u64,
+        crc32: Option<u32>,
+    },
+    FileChunk {
+        bytes: Bytes,
+    },
+    FileEnd {
+        relative_path: String,
+    },
+    ArchiveEnd {
+        archive_name: String,
+    },
+    Complete,
+    Error {
+        message: String,
+    },
+}
+
 // Add Message trait
 pub trait Message {
     fn decode(bytes: Bytes) -> Self;
@@ -145,3 +177,29 @@ impl Message for Response {
         }
     }
 }
+
+impl Message for StreamInstallFrame {
+    fn decode(bytes: Bytes) -> Self {
+        match serde_json::from_slice(&bytes) {
+            Ok(t) => t,
+            Err(e) => {
+                tracing::error!(?e, "StreamInstallFrame decoding error");
+                StreamInstallFrame::Error {
+                    message: format!("stream install frame decoding error: {e}"),
+                }
+            }
+        }
+    }
+
+    fn encode(&self) -> Bytes {
+        match serde_json::to_vec(self) {
+            Ok(s) => Bytes::from(s),
+            Err(e) => {
+                tracing::error!(?e, "StreamInstallFrame encoding error");
+                Bytes::from(format!(
+                    r#"{{"Error": {{"message": "encoding error: {e}"}}}}"#
+                ))
+            }
+        }
+    }
+}

crates/lanspread-tauri-deno-ts/src-tauri/src/lib.rs

@@ -1876,6 +1876,7 @@ async fn ensure_peer_started(app_handle: &AppHandle, games_folder: &Path) {
         PeerStartOptions {
             state_dir: Some(state_dir),
             active_outbound_transfers: Some(state.active_outbound_transfers.clone()),
+            stream_install_provider: None,
         },
     ) {
         Ok(handle) => {