[proxmox-backup.git] / src / api2 / backup / mod.rs

//! Backup protocol (HTTP2 upgrade)

use anyhow::{bail, format_err, Error};
use futures::*;
use hex::FromHex;
use hyper::header::{HeaderValue, UPGRADE};
use hyper::http::request::Parts;
use hyper::{Body, Request, Response, StatusCode};
use serde_json::{json, Value};

use proxmox_router::list_subdirs_api_method;
use proxmox_router::{
    ApiHandler, ApiMethod, ApiResponseFuture, Permission, Router, RpcEnvironment, SubdirMap,
};
use proxmox_schema::*;
use proxmox_sys::sortable;

use pbs_api_types::{
    Authid, BackupType, Operation, SnapshotVerifyState, VerifyState, BACKUP_ARCHIVE_NAME_SCHEMA,
    BACKUP_ID_SCHEMA, BACKUP_TIME_SCHEMA, BACKUP_TYPE_SCHEMA, CHUNK_DIGEST_SCHEMA,
    DATASTORE_SCHEMA, PRIV_DATASTORE_BACKUP,
};
use pbs_config::CachedUserInfo;
use pbs_datastore::backup_info::{BackupDir, BackupGroup, BackupInfo};
use pbs_datastore::index::IndexFile;
use pbs_datastore::manifest::{archive_type, ArchiveType};
use pbs_datastore::{DataStore, PROXMOX_BACKUP_PROTOCOL_ID_V1};
use pbs_tools::json::{required_array_param, required_integer_param, required_string_param};
use proxmox_rest_server::{H2Service, WorkerTask};
use proxmox_sys::fs::lock_dir_noblock_shared;

mod environment;
use environment::*;

mod upload_chunk;
use upload_chunk::*;

pub const ROUTER: Router = Router::new().upgrade(&API_METHOD_UPGRADE_BACKUP);

#[sortable]
pub const API_METHOD_UPGRADE_BACKUP: ApiMethod = ApiMethod::new(
    &ApiHandler::AsyncHttp(&upgrade_to_backup_protocol),
    &ObjectSchema::new(
        concat!("Upgraded to backup protocol ('", PROXMOX_BACKUP_PROTOCOL_ID_V1!(), "')."),
        &sorted!([
            ("store", false, &DATASTORE_SCHEMA),
            ("backup-type", false, &BACKUP_TYPE_SCHEMA),
            ("backup-id", false, &BACKUP_ID_SCHEMA),
            ("backup-time", false, &BACKUP_TIME_SCHEMA),
            ("debug", true, &BooleanSchema::new("Enable verbose debug logging.").schema()),
            ("benchmark", true, &BooleanSchema::new("Job is a benchmark (do not keep data).").schema()),
        ]),
    )
).access(
    // Note: parameter 'store' is no uri parameter, so we need to test inside function body
    Some("The user needs Datastore.Backup privilege on /datastore/{store} and needs to own the backup group."),
    &Permission::Anybody
);

fn upgrade_to_backup_protocol(
    parts: Parts,
    req_body: Body,
    param: Value,
    _info: &ApiMethod,
    rpcenv: Box<dyn RpcEnvironment>,
) -> ApiResponseFuture {
    async move {
        let debug = param["debug"].as_bool().unwrap_or(false);
        let benchmark = param["benchmark"].as_bool().unwrap_or(false);

        let auth_id: Authid = rpcenv.get_auth_id().unwrap().parse()?;

        let store = required_string_param(&param, "store")?.to_owned();

        let user_info = CachedUserInfo::new()?;
        user_info.check_privs(
            &auth_id,
            &["datastore", &store],
            PRIV_DATASTORE_BACKUP,
            false,
        )?;

        let datastore = DataStore::lookup_datastore(&store, Some(Operation::Write))?;

        let backup_type: BackupType = required_string_param(&param, "backup-type")?.parse()?;
        let backup_id = required_string_param(&param, "backup-id")?;
        let backup_time = required_integer_param(&param, "backup-time")?;

        let protocols = parts
            .headers
            .get("UPGRADE")
            .ok_or_else(|| format_err!("missing Upgrade header"))?
            .to_str()?;

        if protocols != PROXMOX_BACKUP_PROTOCOL_ID_V1!() {
            bail!("invalid protocol name");
        }

        if parts.version >= http::version::Version::HTTP_2 {
            bail!(
                "unexpected http version '{:?}' (expected version < 2)",
                parts.version
            );
        }

        let worker_id = format!("{}:{}/{}", store, backup_type, backup_id);

        let env_type = rpcenv.env_type();

        let backup_group = BackupGroup::new(backup_type, backup_id);

        let worker_type = if backup_type == BackupType::Host && backup_id == "benchmark" {
            if !benchmark {
                bail!("unable to run benchmark without --benchmark flags");
            }
            "benchmark"
        } else {
            if benchmark {
                bail!("benchmark flags is only allowed on 'host/benchmark'");
            }
            "backup"
        };

        // lock backup group to only allow one backup per group at a time
        let (owner, _group_guard) =
            datastore.create_locked_backup_group(&backup_group, &auth_id)?;

        // permission check
        let correct_owner =
            owner == auth_id || (owner.is_token() && Authid::from(owner.user().clone()) == auth_id);
        if !correct_owner && worker_type != "benchmark" {
            // only the owner is allowed to create additional snapshots
            bail!("backup owner check failed ({} != {})", auth_id, owner);
        }

        let last_backup = {
            let info = BackupInfo::last_backup(&datastore.base_path(), &backup_group, true)
                .unwrap_or(None);
            if let Some(info) = info {
                let (manifest, _) = datastore.load_manifest(&info.backup_dir)?;
                let verify = manifest.unprotected["verify_state"].clone();
                match serde_json::from_value::<SnapshotVerifyState>(verify) {
                    Ok(verify) => match verify.state {
                        VerifyState::Ok => Some(info),
                        VerifyState::Failed => None,
                    },
                    Err(_) => {
                        // no verify state found, treat as valid
                        Some(info)
                    }
                }
            } else {
                None
            }
        };

        let backup_dir = BackupDir::with_group(backup_group, backup_time)?;

        let _last_guard = if let Some(last) = &last_backup {
            if backup_dir.backup_time() <= last.backup_dir.backup_time() {
                bail!("backup timestamp is older than last backup.");
            }

            // lock last snapshot to prevent forgetting/pruning it during backup
            let full_path = datastore.snapshot_path(&last.backup_dir);
            Some(lock_dir_noblock_shared(
                &full_path,
                "snapshot",
                "base snapshot is already locked by another operation",
            )?)
        } else {
            None
        };

        let (path, is_new, snap_guard) = datastore.create_locked_backup_dir(&backup_dir)?;
        if !is_new {
            bail!("backup directory already exists.");
        }

        WorkerTask::spawn(
            worker_type,
            Some(worker_id),
            auth_id.to_string(),
            true,
            move |worker| {
                let mut env = BackupEnvironment::new(
                    env_type,
                    auth_id,
                    worker.clone(),
                    datastore,
                    backup_dir,
                );

                env.debug = debug;
                env.last_backup = last_backup;

                env.log(format!(
                    "starting new {} on datastore '{}': {:?}",
                    worker_type, store, path
                ));

                let service =
                    H2Service::new(env.clone(), worker.clone(), &BACKUP_API_ROUTER, debug);

                let abort_future = worker.abort_future();

                let env2 = env.clone();

                let mut req_fut = hyper::upgrade::on(Request::from_parts(parts, req_body))
                    .map_err(Error::from)
                    .and_then(move |conn| {
                        env2.debug("protocol upgrade done");

                        let mut http = hyper::server::conn::Http::new();
                        http.http2_only(true);
                        // increase window size: todo - find optiomal size
                        let window_size = 32 * 1024 * 1024; // max = (1 << 31) - 2
                        http.http2_initial_stream_window_size(window_size);
                        http.http2_initial_connection_window_size(window_size);
                        http.http2_max_frame_size(4 * 1024 * 1024);

                        let env3 = env2.clone();
                        http.serve_connection(conn, service).map(move |result| {
                            match result {
                                Err(err) => {
                                    // Avoid  Transport endpoint is not connected (os error 107)
                                    // fixme: find a better way to test for that error
                                    if err.to_string().starts_with("connection error")
                                        && env3.finished()
                                    {
                                        Ok(())
                                    } else {
                                        Err(Error::from(err))
                                    }
                                }
                                Ok(()) => Ok(()),
                            }
                        })
                    });
                let mut abort_future = abort_future.map(|_| Err(format_err!("task aborted")));

                async move {
                    // keep flock until task ends
                    let _group_guard = _group_guard;
                    let snap_guard = snap_guard;
                    let _last_guard = _last_guard;

                    let res = select! {
                        req = req_fut => req,
                        abrt = abort_future => abrt,
                    };
                    if benchmark {
                        env.log("benchmark finished successfully");
                        proxmox_async::runtime::block_in_place(|| env.remove_backup())?;
                        return Ok(());
                    }

                    let verify = |env: BackupEnvironment| {
                        if let Err(err) = env.verify_after_complete(snap_guard) {
                            env.log(format!(
                        "backup finished, but starting the requested verify task failed: {}",
                        err
                    ));
                        }
                    };

                    match (res, env.ensure_finished()) {
                        (Ok(_), Ok(())) => {
                            env.log("backup finished successfully");
                            verify(env);
                            Ok(())
                        }
                        (Err(err), Ok(())) => {
                            // ignore errors after finish
                            env.log(format!("backup had errors but finished: {}", err));
                            verify(env);
                            Ok(())
                        }
                        (Ok(_), Err(err)) => {
                            env.log(format!("backup ended and finish failed: {}", err));
                            env.log("removing unfinished backup");
                            proxmox_async::runtime::block_in_place(|| env.remove_backup())?;
                            Err(err)
                        }
                        (Err(err), Err(_)) => {
                            env.log(format!("backup failed: {}", err));
                            env.log("removing failed backup");
                            proxmox_async::runtime::block_in_place(|| env.remove_backup())?;
                            Err(err)
                        }
                    }
                }
            },
        )?;

        let response = Response::builder()
            .status(StatusCode::SWITCHING_PROTOCOLS)
            .header(
                UPGRADE,
                HeaderValue::from_static(PROXMOX_BACKUP_PROTOCOL_ID_V1!()),
            )
            .body(Body::empty())?;

        Ok(response)
    }
    .boxed()
}

const BACKUP_API_SUBDIRS: SubdirMap = &[
    ("blob", &Router::new().upload(&API_METHOD_UPLOAD_BLOB)),
    (
        "dynamic_chunk",
        &Router::new().upload(&API_METHOD_UPLOAD_DYNAMIC_CHUNK),
    ),
    (
        "dynamic_close",
        &Router::new().post(&API_METHOD_CLOSE_DYNAMIC_INDEX),
    ),
    (
        "dynamic_index",
        &Router::new()
            .post(&API_METHOD_CREATE_DYNAMIC_INDEX)
            .put(&API_METHOD_DYNAMIC_APPEND),
    ),
    (
        "finish",
        &Router::new().post(&ApiMethod::new(
            &ApiHandler::Sync(&finish_backup),
            &ObjectSchema::new("Mark backup as finished.", &[]),
        )),
    ),
    (
        "fixed_chunk",
        &Router::new().upload(&API_METHOD_UPLOAD_FIXED_CHUNK),
    ),
    (
        "fixed_close",
        &Router::new().post(&API_METHOD_CLOSE_FIXED_INDEX),
    ),
    (
        "fixed_index",
        &Router::new()
            .post(&API_METHOD_CREATE_FIXED_INDEX)
            .put(&API_METHOD_FIXED_APPEND),
    ),
    (
        "previous",
        &Router::new().download(&API_METHOD_DOWNLOAD_PREVIOUS),
    ),
    (
        "previous_backup_time",
        &Router::new().get(&API_METHOD_GET_PREVIOUS_BACKUP_TIME),
    ),
    (
        "speedtest",
        &Router::new().upload(&API_METHOD_UPLOAD_SPEEDTEST),
    ),
];

pub const BACKUP_API_ROUTER: Router = Router::new()
    .get(&list_subdirs_api_method!(BACKUP_API_SUBDIRS))
    .subdirs(BACKUP_API_SUBDIRS);

#[sortable]
pub const API_METHOD_CREATE_DYNAMIC_INDEX: ApiMethod = ApiMethod::new(
    &ApiHandler::Sync(&create_dynamic_index),
    &ObjectSchema::new(
        "Create dynamic chunk index file.",
        &sorted!([("archive-name", false, &BACKUP_ARCHIVE_NAME_SCHEMA),]),
    ),
);

fn create_dynamic_index(
    param: Value,
    _info: &ApiMethod,
    rpcenv: &mut dyn RpcEnvironment,
) -> Result<Value, Error> {
    let env: &BackupEnvironment = rpcenv.as_ref();

    let name = required_string_param(&param, "archive-name")?.to_owned();

    let archive_name = name.clone();
    if !archive_name.ends_with(".didx") {
        bail!("wrong archive extension: '{}'", archive_name);
    }

    let mut path = env.backup_dir.relative_path();
    path.push(archive_name);

    let index = env.datastore.create_dynamic_writer(&path)?;
    let wid = env.register_dynamic_writer(index, name)?;

    env.log(format!("created new dynamic index {} ({:?})", wid, path));

    Ok(json!(wid))
}

#[sortable]
pub const API_METHOD_CREATE_FIXED_INDEX: ApiMethod = ApiMethod::new(
    &ApiHandler::Sync(&create_fixed_index),
    &ObjectSchema::new(
        "Create fixed chunk index file.",
        &sorted!([
            ("archive-name", false, &BACKUP_ARCHIVE_NAME_SCHEMA),
            (
                "size",
                false,
                &IntegerSchema::new("File size.").minimum(1).schema()
            ),
            (
                "reuse-csum",
                true,
                &StringSchema::new(
                    "If set, compare last backup's \
                csum and reuse index for incremental backup if it matches."
                )
                .schema()
            ),
        ]),
    ),
);

fn create_fixed_index(
    param: Value,
    _info: &ApiMethod,
    rpcenv: &mut dyn RpcEnvironment,
) -> Result<Value, Error> {
    let env: &BackupEnvironment = rpcenv.as_ref();

    let name = required_string_param(&param, "archive-name")?.to_owned();
    let size = required_integer_param(&param, "size")? as usize;
    let reuse_csum = param["reuse-csum"].as_str();

    let archive_name = name.clone();
    if !archive_name.ends_with(".fidx") {
        bail!("wrong archive extension: '{}'", archive_name);
    }

    let mut path = env.backup_dir.relative_path();
    path.push(&archive_name);

    let chunk_size = 4096 * 1024; // todo: ??

    // do incremental backup if csum is set
    let mut reader = None;
    let mut incremental = false;
    if let Some(csum) = reuse_csum {
        incremental = true;
        let last_backup = match &env.last_backup {
            Some(info) => info,
            None => {
                bail!("cannot reuse index - no valid previous backup exists");
            }
        };

        let mut last_path = last_backup.backup_dir.relative_path();
        last_path.push(&archive_name);

        let index = match env.datastore.open_fixed_reader(last_path) {
            Ok(index) => index,
            Err(_) => {
                bail!("cannot reuse index - no previous backup exists for archive");
            }
        };

        let (old_csum, _) = index.compute_csum();
        let old_csum = hex::encode(&old_csum);
        if old_csum != csum {
            bail!(
                "expected csum ({}) doesn't match last backup's ({}), cannot do incremental backup",
                csum,
                old_csum
            );
        }

        reader = Some(index);
    }

    let mut writer = env.datastore.create_fixed_writer(&path, size, chunk_size)?;

    if let Some(reader) = reader {
        writer.clone_data_from(&reader)?;
    }

    let wid = env.register_fixed_writer(writer, name, size, chunk_size as u32, incremental)?;

    env.log(format!("created new fixed index {} ({:?})", wid, path));

    Ok(json!(wid))
}

#[sortable]
pub const API_METHOD_DYNAMIC_APPEND: ApiMethod = ApiMethod::new(
    &ApiHandler::Sync(&dynamic_append),
    &ObjectSchema::new(
        "Append chunk to dynamic index writer.",
        &sorted!([
            (
                "wid",
                false,
                &IntegerSchema::new("Dynamic writer ID.")
                    .minimum(1)
                    .maximum(256)
                    .schema()
            ),
            (
                "digest-list",
                false,
                &ArraySchema::new("Chunk digest list.", &CHUNK_DIGEST_SCHEMA).schema()
            ),
            (
                "offset-list",
                false,
                &ArraySchema::new(
                    "Chunk offset list.",
                    &IntegerSchema::new("Corresponding chunk offsets.")
                        .minimum(0)
                        .schema()
                )
                .schema()
            ),
        ]),
    ),
);

fn dynamic_append(
    param: Value,
    _info: &ApiMethod,
    rpcenv: &mut dyn RpcEnvironment,
) -> Result<Value, Error> {
    let wid = required_integer_param(&param, "wid")? as usize;
    let digest_list = required_array_param(&param, "digest-list")?;
    let offset_list = required_array_param(&param, "offset-list")?;

    if offset_list.len() != digest_list.len() {
        bail!(
            "offset list has wrong length ({} != {})",
            offset_list.len(),
            digest_list.len()
        );
    }

    let env: &BackupEnvironment = rpcenv.as_ref();

    env.debug(format!("dynamic_append {} chunks", digest_list.len()));

    for (i, item) in digest_list.iter().enumerate() {
        let digest_str = item.as_str().unwrap();
        let digest = <[u8; 32]>::from_hex(digest_str)?;
        let offset = offset_list[i].as_u64().unwrap();
        let size = env
            .lookup_chunk(&digest)
            .ok_or_else(|| format_err!("no such chunk {}", digest_str))?;

        env.dynamic_writer_append_chunk(wid, offset, size, &digest)?;

        env.debug(format!(
            "successfully added chunk {} to dynamic index {} (offset {}, size {})",
            digest_str, wid, offset, size
        ));
    }

    Ok(Value::Null)
}

#[sortable]
pub const API_METHOD_FIXED_APPEND: ApiMethod = ApiMethod::new(
    &ApiHandler::Sync(&fixed_append),
    &ObjectSchema::new(
        "Append chunk to fixed index writer.",
        &sorted!([
            (
                "wid",
                false,
                &IntegerSchema::new("Fixed writer ID.")
                    .minimum(1)
                    .maximum(256)
                    .schema()
            ),
            (
                "digest-list",
                false,
                &ArraySchema::new("Chunk digest list.", &CHUNK_DIGEST_SCHEMA).schema()
            ),
            (
                "offset-list",
                false,
                &ArraySchema::new(
                    "Chunk offset list.",
                    &IntegerSchema::new("Corresponding chunk offsets.")
                        .minimum(0)
                        .schema()
                )
                .schema()
            )
        ]),
    ),
);

fn fixed_append(
    param: Value,
    _info: &ApiMethod,
    rpcenv: &mut dyn RpcEnvironment,
) -> Result<Value, Error> {
    let wid = required_integer_param(&param, "wid")? as usize;
    let digest_list = required_array_param(&param, "digest-list")?;
    let offset_list = required_array_param(&param, "offset-list")?;

    if offset_list.len() != digest_list.len() {
        bail!(
            "offset list has wrong length ({} != {})",
            offset_list.len(),
            digest_list.len()
        );
    }

    let env: &BackupEnvironment = rpcenv.as_ref();

    env.debug(format!("fixed_append {} chunks", digest_list.len()));

    for (i, item) in digest_list.iter().enumerate() {
        let digest_str = item.as_str().unwrap();
        let digest = <[u8; 32]>::from_hex(digest_str)?;
        let offset = offset_list[i].as_u64().unwrap();
        let size = env
            .lookup_chunk(&digest)
            .ok_or_else(|| format_err!("no such chunk {}", digest_str))?;

        env.fixed_writer_append_chunk(wid, offset, size, &digest)?;

        env.debug(format!(
            "successfully added chunk {} to fixed index {} (offset {}, size {})",
            digest_str, wid, offset, size
        ));
    }

    Ok(Value::Null)
}

#[sortable]
pub const API_METHOD_CLOSE_DYNAMIC_INDEX: ApiMethod = ApiMethod::new(
    &ApiHandler::Sync(&close_dynamic_index),
    &ObjectSchema::new(
        "Close dynamic index writer.",
        &sorted!([
            (
                "wid",
                false,
                &IntegerSchema::new("Dynamic writer ID.")
                    .minimum(1)
                    .maximum(256)
                    .schema()
            ),
            (
                "chunk-count",
                false,
                &IntegerSchema::new(
                    "Chunk count. This is used to verify that the server got all chunks."
                )
                .minimum(1)
                .schema()
            ),
            (
                "size",
                false,
                &IntegerSchema::new(
                    "File size. This is used to verify that the server got all data."
                )
                .minimum(1)
                .schema()
            ),
            (
                "csum",
                false,
                &StringSchema::new("Digest list checksum.").schema()
            ),
        ]),
    ),
);

fn close_dynamic_index(
    param: Value,
    _info: &ApiMethod,
    rpcenv: &mut dyn RpcEnvironment,
) -> Result<Value, Error> {
    let wid = required_integer_param(&param, "wid")? as usize;
    let chunk_count = required_integer_param(&param, "chunk-count")? as u64;
    let size = required_integer_param(&param, "size")? as u64;
    let csum_str = required_string_param(&param, "csum")?;
    let csum = <[u8; 32]>::from_hex(csum_str)?;

    let env: &BackupEnvironment = rpcenv.as_ref();

    env.dynamic_writer_close(wid, chunk_count, size, csum)?;

    env.log(format!("successfully closed dynamic index {}", wid));

    Ok(Value::Null)
}

#[sortable]
pub const API_METHOD_CLOSE_FIXED_INDEX: ApiMethod = ApiMethod::new(
    &ApiHandler::Sync(&close_fixed_index),
    &ObjectSchema::new(
        "Close fixed index writer.",
        &sorted!([
            (
                "wid",
                false,
                &IntegerSchema::new("Fixed writer ID.")
                    .minimum(1)
                    .maximum(256)
                    .schema()
            ),
            (
                "chunk-count",
                false,
                &IntegerSchema::new("Chunk count. This is used to verify that the server got all chunks. Ignored for incremental backups.")
                    .minimum(0)
                    .schema()
            ),
            (
                "size",
                false,
                &IntegerSchema::new("File size. This is used to verify that the server got all data. Ignored for incremental backups.")
                    .minimum(0)
                    .schema()
            ),
            ("csum", false, &StringSchema::new("Digest list checksum.").schema()),
        ]),
    )
);

fn close_fixed_index(
    param: Value,
    _info: &ApiMethod,
    rpcenv: &mut dyn RpcEnvironment,
) -> Result<Value, Error> {
    let wid = required_integer_param(&param, "wid")? as usize;
    let chunk_count = required_integer_param(&param, "chunk-count")? as u64;
    let size = required_integer_param(&param, "size")? as u64;
    let csum_str = required_string_param(&param, "csum")?;
    let csum = <[u8; 32]>::from_hex(csum_str)?;

    let env: &BackupEnvironment = rpcenv.as_ref();

    env.fixed_writer_close(wid, chunk_count, size, csum)?;

    env.log(format!("successfully closed fixed index {}", wid));

    Ok(Value::Null)
}

fn finish_backup(
    _param: Value,
    _info: &ApiMethod,
    rpcenv: &mut dyn RpcEnvironment,
) -> Result<Value, Error> {
    let env: &BackupEnvironment = rpcenv.as_ref();

    env.finish_backup()?;
    env.log("successfully finished backup");

    Ok(Value::Null)
}

#[sortable]
pub const API_METHOD_GET_PREVIOUS_BACKUP_TIME: ApiMethod = ApiMethod::new(
    &ApiHandler::Sync(&get_previous_backup_time),
    &ObjectSchema::new("Get previous backup time.", &[]),
);

fn get_previous_backup_time(
    _param: Value,
    _info: &ApiMethod,
    rpcenv: &mut dyn RpcEnvironment,
) -> Result<Value, Error> {
    let env: &BackupEnvironment = rpcenv.as_ref();

    let backup_time = env
        .last_backup
        .as_ref()
        .map(|info| info.backup_dir.backup_time());

    Ok(json!(backup_time))
}

#[sortable]
pub const API_METHOD_DOWNLOAD_PREVIOUS: ApiMethod = ApiMethod::new(
    &ApiHandler::AsyncHttp(&download_previous),
    &ObjectSchema::new(
        "Download archive from previous backup.",
        &sorted!([("archive-name", false, &BACKUP_ARCHIVE_NAME_SCHEMA)]),
    ),
);

fn download_previous(
    _parts: Parts,
    _req_body: Body,
    param: Value,
    _info: &ApiMethod,
    rpcenv: Box<dyn RpcEnvironment>,
) -> ApiResponseFuture {
    async move {
        let env: &BackupEnvironment = rpcenv.as_ref();

        let archive_name = required_string_param(&param, "archive-name")?.to_owned();

        let last_backup = match &env.last_backup {
            Some(info) => info,
            None => bail!("no valid previous backup"),
        };

        let mut path = env.datastore.snapshot_path(&last_backup.backup_dir);
        path.push(&archive_name);

        {
            let index: Option<Box<dyn IndexFile>> = match archive_type(&archive_name)? {
                ArchiveType::FixedIndex => {
                    let index = env.datastore.open_fixed_reader(&path)?;
                    Some(Box::new(index))
                }
                ArchiveType::DynamicIndex => {
                    let index = env.datastore.open_dynamic_reader(&path)?;
                    Some(Box::new(index))
                }
                _ => None,
            };
            if let Some(index) = index {
                env.log(format!(
                    "register chunks in '{}' from previous backup.",
                    archive_name
                ));

                for pos in 0..index.index_count() {
                    let info = index.chunk_info(pos).unwrap();
                    let size = info.range.end - info.range.start;
                    env.register_chunk(info.digest, size as u32)?;
                }
            }
        }

        env.log(format!("download '{}' from previous backup.", archive_name));
        crate::api2::helpers::create_download_response(path).await
    }
    .boxed()
}