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rit hash-object

Compute the SHA-1 hash of a file and optionally store it.

Synopsis​

rit hash-object [-w] <file>

Description​

This is a "plumbing" command that computes the Git object hash for a file. With -w, it also stores the object in the database.

Options​

OptionDescription
-w, --writeActually store the object in .rit/objects/

How Hashing Works​

Git doesn't just hash the raw file content. It prepends a header:

blob <size>\0<content>

For example, a file containing "Hello, World!" (13 bytes) becomes:

blob 13\0Hello, World!

This entire string is then:

  1. SHA-1 hashed → 40-character hex string
  2. Zlib compressed
  3. Stored at .rit/objects/ab/cdef... (first 2 chars / rest)

Examples​

# Just compute hash (don't store)
$ echo "Hello, World!" > hello.txt
$ rit hash-object hello.txt
8ab686eafeb1f44702738c8b0f24f2567c36da6d

# Store in object database
$ rit hash-object -w hello.txt
8ab686eafeb1f44702738c8b0f24f2567c36da6d

# Verify it was stored
$ ls .rit/objects/8a/
b686eafeb1f44702738c8b0f24f2567c36da6d

# Read it back
$ rit cat-file -p 8ab686eafeb1f44702738c8b0f24f2567c36da6d
Hello, World!

Verify Against Real Git​

You can verify your implementation matches Git:

# Using Git
$ echo "Hello, World!" | git hash-object --stdin
8ab686eafeb1f44702738c8b0f24f2567c36da6d

# Using Rit (should match!)
$ echo "Hello, World!" > test.txt
$ rit hash-object test.txt
8ab686eafeb1f44702738c8b0f24f2567c36da6d

Implementation Details​

pub fn hash_content(object_type: &str, content: &[u8]) -> String {
    // Create header
    let header = format!("{} {}\0", object_type, content.len());

    // Hash header + content
    let mut hasher = Sha1::new();
    hasher.update(header.as_bytes());
    hasher.update(content);

    hex::encode(hasher.finalize())
}

pub fn store_object(repo: &Repository, object_type: &str, content: &[u8]) -> Result<String> {
    let hash = hash_content(object_type, content);

    // Create directory
    let dir = repo.objects_dir().join(&hash[..2]);
    fs::create_dir_all(&dir)?;

    // Compress and write
    let object_path = dir.join(&hash[2..]);
    if !object_path.exists() {
        let header = format!("{} {}\0", object_type, content.len());
        let mut encoder = ZlibEncoder::new(Vec::new(), Compression::default());
        encoder.write_all(header.as_bytes())?;
        encoder.write_all(content)?;
        fs::write(&object_path, encoder.finish()?)?;
    }

    Ok(hash)
}

See Also​