FieldStorage

The FieldStorage class parses multipart/form-data content from HTTP requests, extracting individual fields and file uploads into Field objects.

FieldStorage Class

Constructor

def __init__(self, content_type: str, callbacks: bytes):

Parameters: - content_type: Content-Type header containing the boundary parameter - callbacks: Raw multipart/form-data content as bytes

Properties

boundary (Property with Setter)

Extracts and stores the boundary string from the Content-Type header.

Getter: Returns the boundary string used to separate form fields.

Setter: Parses the Content-Type header to extract the boundary parameter. - Raises TypeError if no boundary is detected in the content type

callbacks (Property with Setter)

Stores the raw multipart form data content.

Getter: Returns the raw form data as bytes.

Setter: Validates and stores the multipart form data. - Raises TypeError if value is not bytes or is empty - Raises ValueError if content doesn't match the expected boundary format

Methods

fields() -> list[Field]

Parses the multipart data and returns a list of Field objects.

Returns: List of Field objects representing form fields and file uploads

Processing Logic: 1. Splits content by boundary delimiters 2. Parses each section for headers and content 3. Extracts field name, filename, and content type using regex 4. Creates Field objects with appropriate data 5. Handles both text fields and file uploads

Magic Methods

__len__()

Returns the number of fields in the form data.

field_count = len(fieldstorage_instance)

__repr__()

Returns a string representation showing the number of files/fields.

print(fieldstorage_instance)  # FileStorage(files=3)

Usage Example

from pyweber.models.field_storage import FieldStorage

# Example multipart form data
content_type = "multipart/form-data; boundary=----WebKitFormBoundary7MA4YWxkTrZu0gW"
form_data = b'''------WebKitFormBoundary7MA4YWxkTrZu0gW
Content-Disposition: form-data; name="username"

john_doe
------WebKitFormBoundary7MA4YWxkTrZu0gW
Content-Disposition: form-data; name="avatar"; filename="profile.jpg"
Content-Type: image/jpeg

JPEG binary data here...
------WebKitFormBoundary7MA4YWxkTrZu0gW--
'''

# Create FieldStorage instance
fs = FieldStorage(content_type, form_data)

# Get all fields
fields = fs.fields()

# Access individual fields
for field in fields:
    if field.filename:
        print(f"File: {field.name} = {field.filename} ({field.content_type})")
    else:
        print(f"Field: {field.name} = {field.value.decode()}")

# Get field count
print(f"Total fields: {len(fs)}")

Field Processing

Text Fields

For regular form fields: - Extracts name from Content-Disposition header - Sets filename to None - Sets content_type to None - Stores text content as decoded string in value

File Fields

For file uploads: - Extracts name from Content-Disposition header - Extracts filename from Content-Disposition header - Extracts content_type from Content-Type header - Stores binary file content in value

Error Handling

Boundary Validation

• TypeError: Raised when no boundary parameter is found in content type
• ValueError: Raised when form data doesn't match expected boundary format

Content Validation

• TypeError: Raised when callbacks is not bytes or is empty

Integration

The FieldStorage class is used by: - Request class for parsing multipart form data - File class for creating file objects from parsed fields - Web frameworks for handling file uploads and form submissions

Common Use Cases

1. File Upload Processing: Parsing uploaded files from HTML forms
2. Form Data Extraction: Converting multipart data to structured fields
3. Content Validation: Ensuring proper multipart format
4. Mixed Content Handling: Processing forms with both text and file fields