# Git LFS

Git Large File Storage (LFS) replaces large files in your repository with small pointer files. The actual file content is stored on a separate LFS server. Pitmaster can parse and create LFS pointers and communicate with LFS servers via the batch API. It does not read `.gitattributes` or run the LFS clean and smudge filters: `add()` stores files as they are, and `checkout()` writes pointer files. Fetching the real content is up to your code, as shown below.

## LFS Pointer Files

When a file is tracked by LFS, git stores a pointer file instead of the actual content:

```
version https://git-lfs.github.com/spec/v1
oid sha256:4d7a214614ab2935c943f9e0ff69d22eadbb8f32b1258daaa5e2ca24d17e2393
size 12345
```

The pointer contains:
- `version`: the LFS spec version URL
- `oid`: SHA-256 hash of the actual file content (prefixed with `sha256:`)
- `size`: the actual file size in bytes

### Parsing pointers

```php
use Pitmaster\Lfs\LfsPointer;

$content = file_get_contents('.git-lfs-tracked-file');
$pointer = LfsPointer::parse($content);

if ($pointer !== null) {
    echo "OID: {$pointer->oid}\n";
    echo "Size: {$pointer->size}\n";
    echo "Version: {$pointer->version}\n";
}
```

`parse()` returns `null` when the `version`, `oid sha256:`, or `size` line is missing. It does not validate the values (a non-hex OID or non-numeric size is accepted).

### Detecting pointers

```php
if (LfsPointer::isPointer($blobContent)) {
    // This blob is an LFS pointer, not actual file content
    $pointer = LfsPointer::parse($blobContent);
}
```

`isPointer()` checks for the presence of the version URL, `oid sha256:`, and `size` fields without full parsing.

### Creating pointers

```php
// From known OID and size
$pointer = new LfsPointer(
    oid: '4d7a214614ab2935c943f9e0ff69d22eadbb8f32b1258daaa5e2ca24d17e2393',
    size: 12345,
);

// From file content (computes SHA-256 hash)
$pointer = LfsPointer::forContent($actualFileContent);

echo $pointer->oid;   // SHA-256 hash
echo $pointer->size;  // Content length
```

### Serializing pointers

```php
$content = $pointer->serialize();
// "version https://git-lfs.github.com/spec/v1\noid sha256:4d7a21...\nsize 12345\n"
```

## LFS Client

The `LfsClient` communicates with LFS servers using the batch API (POST to `<url>/objects/batch`).

### Creating a client

```php
use Pitmaster\Lfs\LfsClient;

// From a git remote URL (appends /info/lfs)
$client = LfsClient::fromRemoteUrl('https://github.com/user/repo.git');
// LFS URL: https://github.com/user/repo.git/info/lfs

// Direct URL
$client = new LfsClient('https://lfs.example.com/repo', timeout: 60);
```

The `fromRemoteUrl()` method follows the standard convention: append `/info/lfs` to the git URL (adding `.git` if not present). Only HTTP(S) remote URLs give a usable LFS URL; SCP-style SSH remotes (`git@host:repo.git`) do not.

`LfsClient` uses PHP's HTTP stream wrapper (`allow_url_fopen` must be enabled). It sends no credentials and ignores the `header` map returned with each action, so it works only with LFS servers and storage URLs that need no authentication. It is not tied to a repository handle, so it makes network requests even when you work with a repository opened with `Pitmaster::processFreeOptions()`.

### Downloading files

```php
// Single file download
$content = $client->download($pointer->oid, $pointer->size);
file_put_contents('large-file.bin', $content);
```

Under the hood, `download()`:
1. Sends a batch request for the `download` operation
2. Receives a download URL from the server
3. Fetches the file content from that URL

The downloaded bytes are not checked against the OID or size.

### Batch download

```php
$results = $client->batchDownload([
    ['oid' => 'abc123...', 'size' => 12345],
    ['oid' => 'def456...', 'size' => 67890],
]);

foreach ($results as $result) {
    if ($result['error'] !== null) {
        echo "Error: {$result['error']}\n";
        continue;
    }

    if ($result['href'] !== null) {
        // Download from $result['href']
    }
}
```

### Uploading files

```php
$client->upload($pointer->oid, $pointer->size, $fileContent);
```

Upload sends a batch request for the `upload` operation. If the server already has the object, it returns no upload URL and the operation is a no-op. The result of the upload request itself is not checked, so a failed upload is not reported, and the `verify` action is not called.

### Batch upload

```php
$results = $client->batchUpload([
    ['oid' => 'abc123...', 'size' => 12345],
]);

foreach ($results as $result) {
    if ($result['href'] !== null) {
        // Server needs this object, upload to $result['href']
    }
    // No href means server already has it
}
```

## Batch API protocol

The LFS batch API uses JSON over HTTP:

### Request

```
POST <lfs-url>/objects/batch
Content-Type: application/vnd.git-lfs+json
Accept: application/vnd.git-lfs+json

{
    "operation": "download",
    "transfers": ["basic"],
    "objects": [
        {"oid": "abc123...", "size": 12345}
    ]
}
```

### Response

```json
{
    "objects": [
        {
            "oid": "abc123...",
            "size": 12345,
            "actions": {
                "download": {
                    "href": "https://storage.example.com/abc123...",
                    "header": {
                        "Authorization": "Bearer token"
                    }
                }
            }
        }
    ]
}
```

## Integrating LFS with repository operations

When reading a repository that uses LFS, blob content may be LFS pointers rather than actual file data. To get the real content:

```php
$blob = $repo->readObject($hash);

if (LfsPointer::isPointer($blob->content)) {
    $pointer = LfsPointer::parse($blob->content);
    $remoteUrl = $repo->config()->get('remote.origin.url');
    $client = LfsClient::fromRemoteUrl($remoteUrl);
    $realContent = $client->download($pointer->oid, $pointer->size);
} else {
    $realContent = $blob->content;
}
```

## Error handling

A failed or invalid batch request, and a failed download request, throw `ProtocolException`. `download()` also throws when the server returns no download URL for the object, without the server's error message. `batchDownload()` and `batchUpload()` do not throw for per-object errors; they return them in the `error` field.

```php
use Pitmaster\Exceptions\ProtocolException;

try {
    $content = $client->download($oid, $size);
} catch (ProtocolException $e) {
    // Server unreachable, invalid response, no download URL
    echo "LFS error: {$e->getMessage()}\n";
}
```

## LFS pointer properties

The `LfsPointer` class is readonly:

```php
$pointer->oid;      // string: SHA-256 hash (hex)
$pointer->size;     // int: file size in bytes
$pointer->version;  // string: spec version URL
```