chore(tvix/store): move castore.proto

This moves the castore.proto file into the //tvix/store/protos directory. Per-
component protos might make more sense, than a "tvix-wide" proto directory.

Change-Id: Ie728210174b041e9285a0e2ac605d715d0f0cbda
Reviewed-on: https://cl.tvl.fyi/c/depot/+/7285
Reviewed-by: tazjin <tazjin@tvl.su>
Tested-by: BuildkiteCI

tvix/store/protos/LICENSE

@@ -0,0 +1,21 @@
+Copyright © The Tvix Authors
+
+Permission is hereby granted, free of charge, to any person obtaining
+a copy of this software and associated documentation files (the
+“Software”), to deal in the Software without restriction, including
+without limitation the rights to use, copy, modify, merge, publish,
+distribute, sublicense, and/or sell copies of the Software, and to
+permit persons to whom the Software is furnished to do so, subject to
+the following conditions:
+
+The above copyright notice and this permission notice shall be
+included in all copies or substantial portions of the Software.
+
+THE SOFTWARE IS PROVIDED “AS IS”, WITHOUT WARRANTY OF ANY KIND,
+EXPRESS OR IMPLIED, INCLUDING BUT NOT LIMITED TO THE WARRANTIES OF
+MERCHANTABILITY, FITNESS FOR A PARTICULAR PURPOSE AND NONINFRINGEMENT.
+IN NO EVENT SHALL THE AUTHORS OR COPYRIGHT HOLDERS BE LIABLE FOR ANY
+CLAIM, DAMAGES OR OTHER LIABILITY, WHETHER IN AN ACTION OF CONTRACT,
+TORT OR OTHERWISE, ARISING FROM, OUT OF OR IN CONNECTION WITH THE
+SOFTWARE OR THE USE OR OTHER DEALINGS IN THE SOFTWARE.
+

tvix/store/protos/castore.proto

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+// SPDX-FileCopyrightText: edef <edef@unfathomable.blue>
+// SPDX-License-Identifier: OSL-3.0 OR MIT OR Apache-2.0
+
+syntax = "proto3";
+
+package tvix.store.v1;
+
+// A Directory can contain Directory, File or Symlink nodes.
+// Each of these nodes have a name attribute, which is the basename in that directory
+// and node type specific attributes.
+// The name attribute:
+//  - may not contain slashes or null bytes
+//  - needs to be unique across all three lists
+// Elements in each list need to be lexicographically ordered by the name
+// attribute.
+message Directory {
+    repeated DirectoryNode directories = 1;
+    repeated FileNode files = 2;
+    repeated SymlinkNode symlinks = 3;
+}
+
+// A DirectoryNode represents a directory in a Directory.
+message DirectoryNode {
+    // The (base)name of the directory
+    string name = 1;
+    // The blake3 hash of a Directory message, serialized in protobuf canonical form.
+    bytes digest = 2;
+    // Number of child elements in the Directory referred to by `digest`.
+    // Calculated by summing up the numbers of `directories`, `files` and
+    // `symlinks`, and for each directory, its size field. Used for inode
+    // number calculation.
+    // This field is precisely as verifiable as any other Merkle tree edge.
+    // Resolve `digest`, and you can compute it incrementally. Resolve the
+    // entire tree, and you can fully compute it from scratch.
+    // A credulous implementation won't reject an excessive size, but this is
+    // harmless: you'll have some ordinals without nodes. Undersizing is
+    // obvious and easy to reject: you won't have an ordinal for some nodes.
+    uint32 size = 3;
+}
+
+// A FileNode represents a regular or executable file in a Directory.
+message FileNode {
+    // The (base)name of the file
+    string name = 1;
+    // The blake3 digest of the file contents
+    bytes digest = 2;
+    // The file content size
+    uint32 size = 3;
+    // Whether the file is executable
+    bool executable = 4;
+}
+
+// A SymlinkNode represents a symbolic link in a Directory.
+message SymlinkNode {
+    // The (base)name of the symlink
+    string name = 1;
+    // The target of the symlink.
+    string target = 2;
+}