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Blob

A Blob object in Git represents the raw content of a file. It is the simplest object type in Git, storing the uncompressed content of a file prefixed by a header.

Structure of a Blob Object​

The header of a Blob object consists of:

  1. Object Type: Always blob.
  2. Size: The size of the file content in bytes.
  3. Null Byte Separator: A null byte (\x00) separating the header from the content.

Content​

The main body contains the raw, uncompressed file content. The structure can be represented as:

blob <size>\x00<content>\x00

Notes on Size Calculation​

  • The header title (blob) and the final null byte do not count towards the total size.
  • The first null byte (\x00) is included in the size calculation.

Example​

Given a file with the content:

Run, Forrest, run!

The Blob object would appear as:

blob 19\x00Run, Forrest, run!\x00

Compression​

Like all objects in Git, the Blob content is compressed using the zlib algorithm before being stored. This compression reduces the storage size and ensures efficient data management.

Key Characteristics of Blob Objects​

  1. Raw Content Storage: Unlike Tree or Commit objects, Blob objects do not include metadata such as filenames or directories.
  2. Uniqueness via SHA-1: Each Blob is identified by a SHA-1 hash generated from its content and header. This ensures content integrity and prevents duplication.
  3. Independence from Filesystem: Blobs store only the content of files, allowing Git to track changes to file content without being affected by file renames or moves.

Decoding a Blob Object​

To interpret a Blob object:

  1. Extract the Header:
    • Identify the object type (blob).
    • Determine the size of the content.
  2. Parse the Content:
    • Read the file content following the header.
  3. Handle Compression:
    • Decompress the content if reading directly from a Git repository.

By adhering to this structure, Git ensures efficient storage and accurate tracking of file contents across versions.