HTTP Filesystem Protocol Specification

Overview

The HTTP Filesystem Protocol provides a RESTful interface for performing POSIX-like filesystem operations over HTTP. It enables hierarchical file and directory manipulation using standard HTTP methods with filesystem-specific metadata encoded in HTTP headers.

Protocol Design

Core Principles

• RESTful Interface: HTTP methods map directly to filesystem operations
• Metadata in Headers: File attributes encoded as HTTP headers
• Path-based URLs: Filesystem paths map directly to URL paths
• Directory Listings: Directory contents encoded as plain text
• Atomic Operations: Individual operations are atomic

URL Structure

Filesystem paths map directly to HTTP URLs:

• Base URL: https://example.com/fs
• File path: /path/to/file.txt → https://example.com/fs/path/to/file.txt
• Directory path: /path/to/dir → https://example.com/fs/path/to/dir

Note: Directory paths MAY end with / as a convenience to automatically set Content-Type: application/x-directory.

HTTP Methods

GET - Read File/Directory

Retrieves file content or directory listing.

Request:

GET /path/to/file.txt HTTP/1.1

Response (File):

HTTP/1.1 200 OK
Content-Type: application/octet-stream
Content-Length: 1024
Content-Mode: 33188
Content-Modified: 1641024000
Content-Ownership: 1000:1000

[file content]

Response (Directory):

HTTP/1.1 200 OK
Content-Type: application/x-directory
Content-Length: 45
Content-Mode: 16877
Content-Modified: 1641024000
Content-Ownership: 1000:1000

file.txt 33188
subdir 16877

HEAD - Get Metadata Only

Retrieves file/directory metadata without content.

Request:

HEAD /path/to/file.txt HTTP/1.1

Response:

HTTP/1.1 200 OK
Content-Type: application/octet-stream
Content-Length: 1024
Content-Mode: 33188
Content-Modified: 1641024000
Content-Ownership: 1000:1000

PUT - Create/Replace File/Directory

Creates or completely replaces a file or directory.

Request (File):

PUT /path/to/file.txt HTTP/1.1
Content-Type: application/octet-stream
Content-Length: 12
Content-Mode: 33188
Content-Modified: 1641024000
Content-Ownership: 1000:1000

Hello World!

Request (Directory):

PUT /path/to/dir HTTP/1.1
Content-Type: application/x-directory
Content-Length: 0
Content-Mode: 16877
Content-Modified: 1641024000
Content-Ownership: 1000:1000

Alternative (using trailing slash convenience):

PUT /path/to/dir/ HTTP/1.1
Content-Length: 0
Content-Mode: 16877
Content-Modified: 1641024000
Content-Ownership: 1000:1000

Response:

HTTP/1.1 200 OK

OK

PATCH - Update Metadata Only

Updates file/directory metadata without changing content.

Request:

PATCH /path/to/file.txt HTTP/1.1
Content-Mode: 33261

Response:

HTTP/1.1 200 OK

OK

DELETE - Remove File/Directory

Removes a file or directory.

Request:

DELETE /path/to/file.txt HTTP/1.1

Response:

HTTP/1.1 200 OK

OK

Filesystem Metadata Headers

Content-Mode

• Purpose: Unix file mode (permissions + type)
• Format: Decimal string representation of Unix mode
• Required: No (defaults applied)
• Examples:
  • 33188 - Regular file with 0644 permissions
  • 16877 - Directory with 0755 permissions
  • 33261 - Executable file with 0755 permissions

Content-Modified

• Purpose: Last modification timestamp
• Format: Unix timestamp (seconds since epoch) as decimal string
• Required: No (current time used if omitted)
• Example: 1641024000

Content-Ownership

• Purpose: File owner and group
• Format: uid:gid format
• Required: No (defaults to 0:0)
• Example: 1000:1000

Content-Type

• Purpose: MIME type indicator
• Values:
  • application/x-directory - Directory
  • application/octet-stream - Binary file (default)
  • Other standard MIME types as appropriate
• Required: No (auto-detected from path and content)

Content-Length

• Purpose: Size of content in bytes
• Format: Decimal string
• Required: Yes for PUT requests
• Behavior: Standard HTTP header

Directory Listing Format

Directory contents are encoded as plain text with the format:

filename mode
dirname mode

Characteristics:

• One entry per line
• Space-separated name and mode
• Lexicographically sorted
• Unix mode in decimal format
• Terminated with newline

Example:

.hidden 33188
README.md 33188
bin 16877
src 16877

File vs Directory Detection

1. Primary: Content-Type header (application/x-directory)
2. Secondary: Mode value (directory flag in Unix mode)
3. Convenience: Path ending with / automatically sets directory content-type

Error Responses

HTTP Status Codes

• 200 OK - Operation successful
• 404 Not Found - File/directory does not exist
• 405 Method Not Allowed - HTTP method not supported
• 412 Precondition Failed - Conditional request failed

Error Bodies

Error responses include plain text descriptions:

HTTP/1.1 404 Not Found

Object Not Found

HTTP/1.1 405 Method Not Allowed
Allow: GET, HEAD, PUT, PATCH, DELETE

Method Not Allowed

Operation Semantics

File Operations

Reading Files:

• GET retrieves content with metadata in headers
• HEAD retrieves only metadata
• Returns 404 if file doesn't exist

Writing Files:

• PUT creates/replaces entire file
• All metadata must be provided to preserve existing values
• Content-Length header required

Modifying Files:

• PATCH updates metadata only, content unchanged
• Only provided headers are updated
• Existing metadata preserved if not specified

Directory Operations

Reading Directories:

• GET returns directory listing as plain text
• Content-Type is application/x-directory
• Entries sorted lexicographically

Creating Directories:

• PUT with Content-Type: application/x-directory header
• Empty or minimal content body
• Alternatively, PUT with path ending in / automatically sets directory content-type

Directory Maintenance:

• Server automatically maintains parent directory listings
• Adding/removing files updates parent directory
• PATCH with Content-Mode updates entry in parent listing

Protocol Extensions

Conditional Requests

Standard HTTP conditional headers supported:

• If-Match / If-None-Match
• If-Modified-Since / If-Unmodified-Since

Range Requests

Standard HTTP range requests supported for partial file reads:

• Range: bytes=0-1023

Security Considerations

Authentication & Authorization

• Protocol is transport-agnostic regarding authentication
• Implementations should use standard HTTP authentication
• Access control is implementation-specific

Path Security

• Implementations should validate paths to prevent directory traversal
• Relative path components (., ..) require careful handling
• Path injection attacks should be prevented

Implementation Guidelines

Server Requirements

• MUST support GET, HEAD, PUT, PATCH, DELETE methods
• MUST detect directories via Content-Type: application/x-directory
• SHOULD treat paths ending with / as convenience for setting directory content-type
• MUST maintain directory listings automatically
• SHOULD support conditional requests
• SHOULD validate metadata format

Client Requirements

• MUST set Content-Type: application/x-directory for directory operations
• MAY use trailing / on directory paths as convenience
• MUST send required headers on PUT operations
• MUST parse directory listing format correctly
• SHOULD handle standard HTTP error responses
• SHOULD support conditional requests

Interoperability

• Metadata header names are case-insensitive (per HTTP)
• Directory listing format is strict (space-separated, sorted)
• Unix mode values are decimal integers
• Timestamps are Unix epoch seconds

Example Workflows

Creating a File

PUT /documents/readme.txt HTTP/1.1
Content-Type: text/plain
Content-Length: 13
Content-Mode: 33188
Content-Ownership: 1000:1000

Hello, World!

Reading a Directory

GET /documents HTTP/1.1

# Response:
readme.txt 33188
scripts 16877

Changing File Permissions

PATCH /documents/script.sh HTTP/1.1
Content-Mode: 33261

Checking File Existence

HEAD /documents/config.json HTTP/1.1

# 200 = exists, 404 = doesn't exist

Future Considerations

Planned Extensions

• Extended attributes (xattrs) support
• Symbolic link operations
• File locking mechanisms
• Bulk operations
• Directory watching/notifications

Limitations

• No atomic multi-file operations
• No recursive directory operations
• Access time not currently supported
• No built-in versioning or conflict resolution