Data URLs (data: scheme parsing and loading) #76

Phase 8 — Resource Loading + Character Encoding + Real Page Loading#

Implement data URL parsing and loading per RFC 2397.

Requirements#

• Parse data:[<mediatype>][;base64],<data> URLs
• Extract MIME type (default text/plain;charset=US-ASCII if omitted)
• Handle base64-encoded data: decode base64 payload
• Handle percent-encoded data: decode percent-encoded payload
• Integrate with ResourceLoader: data URLs should be handled locally without network fetch
• Support data URLs in <img src="data:..."> and <link href="data:..."> contexts

Implementation#

Add to the url crate or a shared utility:

pub struct DataUrl {
    pub mime_type: String,
    pub charset: Option<String>,
    pub data: Vec<u8>,
}

pub fn parse_data_url(url: &str) -> Result<DataUrl, DataUrlError>;

Base64 decoder (RFC 4648):

• Standard alphabet (A-Z, a-z, 0-9, +, /)
• Padding with '='
• Ignore whitespace in encoded data

Acceptance Criteria#

• Parse data URLs with and without base64 encoding
• Correct MIME type extraction with defaults
• Base64 decoder handles standard alphabet and padding
• Percent-decoding works for non-base64 data URLs
• Integration with ResourceLoader returns decoded data
• No external dependencies, no unsafe
• Unit tests: various data URL formats, edge cases (empty data, missing MIME type)

Dependencies#

Depends on: Resource loader