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Check-ins Using Download Hex

Artifact e8df1aa2d99e6ca40885db7042a27f34c153e0077a34a864b9097961d81af83a:

//! `zit tarball` / `zit zip` (#95) — export a check-in's effective file set as
//! an archive instead of a working tree.
//!
//! No new history logic lives here. `Repository.files` already walks a
//! check-in's effective set through sub-manifests and delta baselines, in
//! canonical filename order; `Repository.blob` already reconstructs a blob
//! through its delta chain and verifies it against its F-card id. This verb is
//! that same walk with a writer that appends to an archive, which is why it is
//! small: the format and the selection policy live in `archive.zig`, and what
//! is left here is the repository handle, the output file, and the diagnostics.
//!
//! The one property worth stating at this layer: **a member whose content the
//! store does not hold is a refusal, never an omission.** A sparse store
//! deliberately elides out-of-cone blobs, and an archive quietly missing those
//! files would be the failure mode that looks exactly like success — right
//! member count, plausible size, missing source. So the whole member set is
//! checked for presence BEFORE a single byte is written, and the refusal names
//! the files rather than reporting a count.

const std = @import("std");
const zit = @import("zit");
const cli = @import("zit").cli;
const archive = @import("zit").archive;
const artifact = @import("zit").artifact;
const Repository = @import("zit").Repository;

const main = @import("../main.zig");
const openRepo = main.openRepo;
const not_a_repo_msg = main.not_a_repo_msg;

/// Which archive format a run writes. The enumeration and selection are shared
/// whole; only the writer differs.
pub const Kind = enum {
    tarball,
    zip,

    fn verb(self: Kind) []const u8 {
        return switch (self) {
            .tarball => "tarball",
            .zip => "zip",
        };
    }

    fn help(self: Kind) []const u8 {
        return switch (self) {
            .tarball => main.tarball_help,
            .zip => main.tarball_help, // the zip writer lands with its own help
        };
    }
};

/// How many members one archive may carry. The same bound the managed set
/// already imposes on a checkout, restated here so the collection loop below
/// is finite by inspection rather than by trusting the manifest it walked.
const max_members: usize = zit.managed.max_entries;

/// Largest single member. A blob is reconstructed whole into memory to be
/// written, exactly as `zit cat` does, so this is `cat`'s bound and not a new
/// policy — an archive is not a streaming decompressor.
const max_member_bytes: u64 = 1 << 32;

/// A selected member: its repository path, its mode, and its blob id. Paths
/// and hashes borrow the `FileList`, which outlives this slice.
const Member = struct {
    path: []const u8,
    mode: artifact.FileMode,
    hash: []const u8,
};

pub fn runTarball(
    gpa: std.mem.Allocator,
    io: std.Io,
    arena: std.mem.Allocator,
    verb_args: []const []const u8,
    streams: cli.Streams,
    amb: cli.Ambient,
) cli.Exit {
    return run(.tarball, gpa, io, arena, verb_args, streams, amb);
}

fn run(
    kind: Kind,
    gpa: std.mem.Allocator,
    io: std.Io,
    arena: std.mem.Allocator,
    verb_args: []const []const u8,
    streams: cli.Streams,
    amb: cli.Ambient,
) cli.Exit {
    const verb = kind.verb();
    const parsed = switch (cli.parseArchiveArgs(verb_args)) {
        .ok => |p| p,
        .unknown_option => |t| return cli.usageError(streams, verb, .unknown_option, t),
        .extra_argument => |t| return cli.usageError(streams, verb, .extra_argument, t),
        .empty_value => |t| return cli.usageError(streams, verb, .empty_value, t),
        .repeated_option => |t| return cli.usageError(streams, verb, .repeated_option, t),
    };
    if (parsed.help) {
        streams.out.writeAll(kind.help()) catch {};
        return .ok;
    }
    const version = parsed.version orelse
        return cli.usageError(streams, verb, .no_checkin, "");
    // OUTPUTFILE is required unless there is nothing to write.
    if (parsed.output == null and !parsed.list)
        return cli.usageError(streams, verb, .no_file, "");
    if (parsed.name) |n| {
        if (n.len > archive.max_top_dir_len or std.mem.indexOfScalar(u8, n, '/') != null) {
            streams.err.print(
                "zit {s}: --name must be a single directory name of at most {d} bytes\n",
                .{ verb, archive.max_top_dir_len },
            ) catch {};
            return .usage;
        }
    }

    var repo: Repository = undefined;
    var root_dir: std.Io.Dir = undefined;
    const rc = openRepo(gpa, io, arena, streams, verb, amb.repo_override, parsed.no_cache, false, &repo, &root_dir);
    if (rc != .ok) return rc;
    defer root_dir.close(io);
    defer repo.deinit(gpa);

    const rid = repo.resolve(version, .checkin) catch |e| switch (e) {
        error.NotFound => return fail(streams, verb, "check-in '{s}' not found", .{version}),
        error.Ambiguous => return fail(streams, verb, "name '{s}' is ambiguous", .{version}),
        error.OutOfMemory => return oom(streams, verb),
    };

    var list = (repo.files(gpa, rid) catch |e| return filesFail(streams, verb, e)) orelse
        return fail(streams, verb, "check-in content is missing", .{});
    defer list.deinit(gpa);

    // Collect the selected members first, so nothing is written before the
    // whole set is known to be admissible AND present.
    var members: std.ArrayListUnmanaged(Member) = .empty;
    defer members.deinit(gpa);
    var it = list.iterator();
    while (it.next()) |f| {
        std.debug.assert(f.hash != null); // the walk suppresses delete markers
        archive.admit(f.filename) catch |e| return admitFail(streams, verb, f.filename, e);
        if (!archive.selected(f.filename, parsed.include, parsed.exclude)) continue;
        if (members.items.len >= max_members)
            return fail(streams, verb, "check-in carries more than {d} files", .{max_members});
        members.append(gpa, .{
            .path = f.filename,
            .mode = artifact.fileModeOf(f.perm),
            .hash = f.hash.?,
        }) catch return oom(streams, verb);
    }

    // Presence, before any output. A sparse store interns an elided blob's
    // name while holding no bytes, so this is a real question even when the
    // manifest looks complete — and answering it costs a lookup per member,
    // not an inflate.
    var missing: usize = 0;
    for (members.items) |m| {
        const held = repo.blobPresent(gpa, m.hash) catch |e| return openFail(streams, verb, e);
        if (held) continue;
        if (missing == 0) {
            streams.err.print(
                "zit {s}: this store does not hold every file in the check-in; refusing to write a partial archive\n",
                .{verb},
            ) catch {};
        }
        missing += 1;
        // Name them rather than counting them: "3 files missing" sends the
        // operator to guess which, and the remedy differs per path.
        if (missing <= 20) streams.err.print("zit {s}:   {s}\n", .{ verb, m.path }) catch {};
    }
    if (missing > 20) {
        streams.err.print("zit {s}:   ... and {d} more\n", .{ verb, missing - 20 }) catch {};
    }
    if (missing != 0) {
        streams.err.print(
            "zit {s}: widen the cone with 'zit cone add PATH' (which fetches), or archive from a dense store\n",
            .{verb},
        ) catch {};
        return .failure;
    }

    // The top-level directory: the operator's, or derived.
    var name_buf: [archive.max_top_dir_len]u8 = undefined;
    const checkin_hash = repo.hashOf(rid);
    const top = parsed.name orelse archive.defaultTopDir(
        parsed.output orelse "",
        checkin_hash[0..@min(checkin_hash.len, 16)],
        &name_buf,
    );

    if (parsed.list) {
        for (members.items) |m| streams.out.print("{s}/{s}\n", .{ top, m.path }) catch {};
        return .ok;
    }

    // Members carry the CHECK-IN's own time, never the clock: it is what makes
    // two runs on two machines agree, and `SOURCE_DATE_EPOCH` already pins it
    // at the moment the D card was written.
    const mtime_ms = repo.state().mtimeOf(rid) orelse 0;
    const mtime: u64 = mtime_ms / 1000;

    return writeArchive(kind, gpa, io, &repo, streams, verb, parsed.output.?, top, members.items, mtime);
}

/// Whether an output path means "write nothing" — fossil's convention, and the
/// half of `--list` that lets a preview run against a real command line.
fn writesNothing(path: []const u8) bool {
    return path.len == 0 or std.mem.eql(u8, path, "/dev/null");
}

fn writeArchive(
    kind: Kind,
    gpa: std.mem.Allocator,
    io: std.Io,
    repo: *Repository,
    streams: cli.Streams,
    verb: []const u8,
    output: []const u8,
    top: []const u8,
    members: []const Member,
    mtime: u64,
) cli.Exit {
    std.debug.assert(kind == .tarball); // zip lands in its own change
    if (writesNothing(output)) return .ok;

    var out_file = std.Io.Dir.cwd().createFile(io, output, .{ .truncate = true }) catch {
        streams.err.print("zit {s}: cannot create '{s}'\n", .{ verb, output }) catch {};
        return .failure;
    };
    defer out_file.close(io);

    var file_buf: [64 * 1024]u8 = undefined;
    var file_writer = out_file.writerStreaming(io, &file_buf);

    // gzip through the shared deflate: its container header is a fixed
    // constant with a zeroed mtime and no host byte, so the compressed wrapper
    // cannot leak a build environment into an otherwise reproducible archive.
    var window: [std.compress.flate.max_window_len]u8 = undefined;
    var gz = std.compress.flate.Compress.init(
        &file_writer.interface,
        &window,
        .gzip,
        .default,
    ) catch return writeFail(streams, verb, output);
    const w = &gz.writer;

    for (members) |m| {
        const bytes = (repo.blob(gpa, m.hash) catch |e| return openFail(streams, verb, e)) orelse {
            // Presence was checked above, so reaching here means the store
            // changed under us mid-run. Fail rather than emit a short member.
            streams.err.print("zit {s}: content for '{s}' disappeared mid-archive\n", .{ verb, m.path }) catch {};
            return .failure;
        };
        defer gpa.free(bytes);
        if (bytes.len > max_member_bytes)
            return fail(streams, verb, "'{s}' is larger than one archive member may be", .{m.path});

        // A symlink's blob content IS its target path, so it becomes the link
        // field of a symlink header and contributes no member content — a
        // writer that missed this would emit a small text file where a link
        // belonged, and the archive would look perfectly correct until use.
        const is_link = m.mode == .symlink;
        const size: u64 = if (is_link) 0 else bytes.len;
        const link_target: ?[]const u8 = if (is_link) bytes else null;
        if (is_link and bytes.len > archive.ustar_name_len) {
            return fail(streams, verb, "'{s}' links to a target too long for tar", .{m.path});
        }

        var path_buf: [zit.managed.max_path_len + archive.max_top_dir_len + 1]u8 = undefined;
        const joined = std.fmt.bufPrint(&path_buf, "{s}/{s}", .{ top, m.path }) catch
            return fail(streams, verb, "'{s}' is too long to archive under '{s}'", .{ m.path, top });

        archive.beginTarMember(w, joined, size, m.mode, mtime, link_target) catch
            return writeFail(streams, verb, output);
        if (!is_link) {
            w.writeAll(bytes) catch return writeFail(streams, verb, output);
            archive.endTarMember(w, size) catch return writeFail(streams, verb, output);
        }
    }
    archive.writeTarEnd(w) catch return writeFail(streams, verb, output);
    gz.finish() catch return writeFail(streams, verb, output);
    file_writer.interface.flush() catch return writeFail(streams, verb, output);
    return .ok;
}

fn fail(s: cli.Streams, verb: []const u8, comptime fmt: []const u8, args: anytype) cli.Exit {
    s.err.print("zit {s}: ", .{verb}) catch {};
    s.err.print(fmt ++ "\n", args) catch {};
    return .failure;
}

fn oom(s: cli.Streams, verb: []const u8) cli.Exit {
    s.err.print("zit {s}: out of memory\n", .{verb}) catch {};
    return .failure;
}

fn writeFail(s: cli.Streams, verb: []const u8, output: []const u8) cli.Exit {
    s.err.print("zit {s}: cannot write '{s}'\n", .{ verb, output }) catch {};
    return .failure;
}

fn admitFail(s: cli.Streams, verb: []const u8, path: []const u8, e: archive.Error) cli.Exit {
    switch (e) {
        error.ReservedPath => s.err.print(
            "zit {s}: the check-in names a reserved control path '{s}'; refusing to archive it\n",
            .{ verb, path },
        ) catch {},
        error.PathTooLong => s.err.print("zit {s}: path '{s}' is too long\n", .{ verb, path }) catch {},
    }
    return .failure;
}

fn filesFail(s: cli.Streams, verb: []const u8, e: Repository.FilesError) cli.Exit {
    switch (e) {
        error.OutOfMemory => return oom(s, verb),
        error.NotARepo => s.err.writeAll(not_a_repo_msg) catch {},
        error.CannotRead => s.err.print("zit {s}: cannot read repository: input/output error\n", .{verb}) catch {},
        error.Corrupt => s.err.print("zit {s}: cannot read repository: repository is corrupt\n", .{verb}) catch {},
        error.NotManifest => s.err.print("zit {s}: not a check-in\n", .{verb}) catch {},
        error.BaselineUnresolvable => s.err.print("zit {s}: cannot resolve the baseline of a delta check-in\n", .{verb}) catch {},
        error.BaselineIsDelta => s.err.print("zit {s}: the baseline of a delta check-in is itself a delta\n", .{verb}) catch {},
    }
    return .failure;
}

fn openFail(s: cli.Streams, verb: []const u8, e: Repository.OpenError) cli.Exit {
    switch (e) {
        error.OutOfMemory => return oom(s, verb),
        error.NotARepo => s.err.writeAll(not_a_repo_msg) catch {},
        error.CannotRead => s.err.print("zit {s}: cannot read repository: input/output error\n", .{verb}) catch {},
        error.Corrupt => s.err.print("zit {s}: cannot read repository: repository is corrupt\n", .{verb}) catch {},
    }
    return .failure;
}