Implement cat-file subcommand

.github/workflows/ci.yml

@@ -24,6 +24,7 @@ concurrency:
 env:
   CARGO_TERM_COLOR: always
   RUST_VERSION_STABLE: stable
+  RUST_VERSION_NIGHTLY: nightly
 
 jobs:
   test:
@@ -51,7 +52,7 @@ jobs:
       - name: Install Rust toolchain
         uses: actions-rs/toolchain@v1
         with:
-          toolchain: ${{ env.RUST_VERSION_STABLE }}
+          toolchain: ${{ env.RUST_VERSION_NIGHTLY }}
           profile: minimal
           components: rustfmt, clippy
           override: true

.rustfmt.toml

@@ -0,0 +1,18 @@
+# Stable
+match_block_trailing_comma = true
+newline_style = "Unix"
+use_field_init_shorthand = true
+use_try_shorthand = true
+
+# Nightly
+imports_granularity = "Module"
+combine_control_expr = false
+condense_wildcard_suffixes = true
+format_code_in_doc_comments = true
+format_macro_matchers = true
+hex_literal_case = "Lower"
+normalize_comments = true
+normalize_doc_attributes = true
+overflow_delimited_expr = true
+reorder_impl_items = true
+group_imports = "StdExternalCrate"

README.md

@@ -5,18 +5,25 @@ This is a simple attempt at re-creating some of the functionality of the `git` c
 ## Features
 
 - `hash-object` - Compute the hash of an object and optionally write it to the object database.
-  - `-w` flag to write the object to the object database.
-  - `-t` flag to specify the type of the object (supported: `blob`).
-  - `<file>` argument to specify the file to hash.
+    - `-w` flag to write the object to the object database.
+    - `-t` flag to specify the type of the object (supported: `blob`).
+    - `<file>` argument to specify the file to hash.
 - `init` - Create an empty Git repository.
-  - `--bare` flag to create a bare repository.
-  - `-b` or `--initial-branch` flag to specify the initial branch.
-  - `-q` or `--quiet` flag to suppress the output.
-  - `<directory>` argument to specify the directory to initialize.
+    - `--bare` flag to create a bare repository.
+    - `-b` or `--initial-branch` flag to specify the initial branch.
+    - `-q` or `--quiet` flag to suppress the output.
+    - `<directory>` argument to specify the directory to initialize.
+- `cat-file` - Provide content or type and size information for repository objects.
+    - `-t` flag to show the type of the object.
+    - `-s` flag to show the size of the object.
+    - `-p` flag to show the content of the object (pretty-print)
+    - `--allow-unknown-type` flag to allow unknown object types (to be used with `-t` or `-s`).
+    - `<object>` argument to specify the object to show.
 
 ## Testing
 
-Due to the nature of the project, tests must be run sequentially. To run the tests, use the following command:
+Due to the nature of the project, tests must be run sequentially. To run the tests, use the
+following command:
 
 ```sh
 cargo test -- --test-threads=1

object_structure.md

@@ -0,0 +1,104 @@
+# Object Structure
+
+This document describes the structure of Git objects.
+
+## General Object Structure
+
+> [Reference](https://git-scm.com/book/en/v2/Git-Internals-Git-Objects) (Object Storage)
+
+All objects are stored in the `.git/objects` directory (or `$GIT_DIR/$GIT_OBJECT_DIRECTORY`) and
+have the following structure:
+
+```plaintext
+{type} {size}\0{content}
+```
+
+- `{type}` is the type of the object (blob, tree, commit, tag).
+- `{size}` is the size of the content in bytes.
+- `{content}` is the actual content of the object.
+
+## Blob
+
+> [Reference](https://git-scm.com/book/en/v2/Git-Internals-Git-Objects) (Object Storage)
+
+A blob object is a file. Its content is just the file data.
+
+## Tree
+
+> [Reference](https://stackoverflow.com/a/37105125/19244184)
+
+A tree object represents a directory. It contains a list of entries (no separator), each of which
+can be either a blob or a tree object.
+
+The format of each entry is as follows:
+
+```plaintext
+{mode} {filename}\0{hash}
+```
+
+- `{mode}` is the file mode (e.g., `100644` for a file, `040000` for a directory).
+- `{filename}` is the name of the file or directory.
+- `{hash}` is the SHA-1 hash of the object represented in binary form.
+
+## Commit
+
+> [Reference](https://stackoverflow.com/a/37438460/19244184)
+
+A commit object represents a commit. It contains a reference to a tree object, a list of parent
+commits, an author, a committer, and a commit message.
+
+The content of a commit object is as follows:
+
+```plaintext
+tree {tree_hash}
+{parents}
+author {author_name} <{author_email}> {author_date_seconds} {author_date_offset}
+committer {committer_name} <{committer_email}> {committer_date_seconds} {committer_date_offset}
+
+{commit_message}
+```
+
+- `{tree_hash}` is the SHA-1 hash of the tree object.
+- `{parents}` is a list of parent commit objects (if any) of the form:
+    ```plaintext
+    parent {parent_1_hash}
+    parent {parent_2_hash}
+    ...
+    ```
+- `{author_name}` is the name of the author.
+- `{author_email}` is the email address of the author.
+- `{author_date_seconds}` is the author date in seconds since the Unix epoch.
+- `{author_date_offset}` is the author date offset from UTC.
+- `{committer_name}` is the name of the committer.
+- `{committer_email}` is the email address of the committer.
+- `{committer_date_seconds}` is the committer date in seconds since the Unix epoch.
+- `{committer_date_offset}` is the committer date offset from UTC.
+- `{commit_message}` is the commit message.
+
+## Tag
+
+> [Reference](https://stackoverflow.com/a/52193441/19244184)
+
+A tag object represents a tag. It contains a reference to an object (usually a commit), a tagger,
+and
+a tag message.
+
+The content of a tag object is as follows:
+
+```plaintext
+object {object_hash}
+type {object_type}
+tag {tag_name}
+tagger {tagger_name} <{tagger_email}> {tagger_date_seconds} {tagger_date_offset}
+
+{tag_message}
+```
+
+- `{object_hash}` is the SHA-1 hash of the object being tagged.
+- `{object_type}` is the type of the object being tagged (e.g., `commit`).
+- `{tag_name}` is the name of the tag.
+- `{tagger_name}` is the name of the tagger.
+- `{tagger_email}` is the email address of the tagger.
+- `{tagger_date_seconds}` is the tagger date in seconds since the Unix epoch.
+- `{tagger_date_offset}` is the tagger date offset from UTC.
+- `{tag_message}` is the tag message.