Struct Scans 

pub struct Scans {
    pub metadata_end: Option<usize>,
    pub frame_render_start: Option<usize>,
    pub first_scan_end: Option<usize>,
    pub good_scan_end: Option<usize>,
    pub file_size: usize,
}

Key positions in a progressive image file

cloudflare_soos::Scans::from_file(&input_file)?.cf_priority_change_headers()?;

Fields

metadata_end: Option<usize>

Byte position where metadata ends. This many bytes are preceeding start of pixel data. It’s usually <200 bytes, unless the image has color profiles or other bloat.

frame_render_start: Option<usize>

All metadata + minimum amount of data to make browsers render anything (in case they don’t reserve space based on metadata)

first_scan_end: Option<usize>

Byte position where the first (lowest-quality) progressive scan ends. This many bytes are needed to display anything on screen. It’s usually 12-15% of the file size.

good_scan_end: Option<usize>

Byte position where most of ok-quality pixel data ends. This many bytes are needed to display a good-enough image. It’s usually about 50% of the file size.

file_size: usize

Size of the whole image file, in bytes. The size is only used for heuristics, so the value may be approximate, but it must be greater than all other positions set in this struct.

Implementations

impl Scans

pub fn from_file(input_file: &[u8]) -> Result<Self>

Analyze an image file to find byte ranges of its metadata and progressive scans

Examples found in repository

examples/rfc9218-priority.rs (line 16)

fn main() {
    let mut args = env::args().skip(1);
    let input_path = args.next().unwrap_or_else(|| usage());
    let input_file = fs::read(input_path).expect("The specified input file could not be opened");

    let scans = soos::Scans::from_file(&input_file).expect("Scan failed");

    println!("{scans:#?}");
    println!("priority: {}", scans.rfc9218_priority_change_headers().unwrap());
}

examples/cf-priority.rs (line 16)

fn main() {
    let mut args = env::args().skip(1);
    let input_path = args.next().unwrap_or_else(|| usage());
    let input_file = fs::read(input_path).expect("The specified input file could not be opened");

    let scans = soos::Scans::from_file(&input_file).expect("Scan failed");

    println!("{scans:#?}");
    let (pri, pri_change) = scans.cf_priority_change_headers().unwrap();
    println!("cf-priority: {pri}");
    println!("cf-priority-change: {pri_change}");
}

examples/chop.rs (line 18)

fn main() {
    let mut args = env::args_os().skip(1);
    let input_path = PathBuf::from(args.next().unwrap_or_else(|| usage()));
    let input_file = fs::read(&input_path).expect("The specified input file could not be opened");

    let scans = soos::Scans::from_file(&input_file).expect("Scan failed");

    println!("{scans:#?}");

    write_up_to(&input_path, &input_file, "0-meta", scans.metadata_end);
    write_up_to(
        &input_path,
        &input_file,
        "1-render",
        scans.frame_render_start,
    );
    write_up_to(
        &input_path,
        &input_file,
        "2-first_scan",
        scans.first_scan_end,
    );
    write_up_to(&input_path, &input_file, "3-good_scan", scans.good_scan_end);
}

pub fn cf_priority_change_headers(&self) -> Result<(String, String)>

Assumes the HTTP2 priorities are:

• 50 = critical js/css, fonts + image metadata
• 30 = regular js/css, followed by other images + JPEG DC
• 20 = low-priority image bodies
• 10 = idle

Returns cf-priority and cf-priority-change header values, respectively.

Examples found in repository

examples/cf-priority.rs (line 19)

fn main() {
    let mut args = env::args().skip(1);
    let input_path = args.next().unwrap_or_else(|| usage());
    let input_file = fs::read(input_path).expect("The specified input file could not be opened");

    let scans = soos::Scans::from_file(&input_file).expect("Scan failed");

    println!("{scans:#?}");
    let (pri, pri_change) = scans.cf_priority_change_headers().unwrap();
    println!("cf-priority: {pri}");
    println!("cf-priority-change: {pri_change}");
}

pub fn rfc9218_priority_change_headers(&self) -> Result<String>

https://www.rfc-editor.org/rfc/rfc9218.html

Examples found in repository

examples/rfc9218-priority.rs (line 19)

fn main() {
    let mut args = env::args().skip(1);
    let input_path = args.next().unwrap_or_else(|| usage());
    let input_file = fs::read(input_path).expect("The specified input file could not be opened");

    let scans = soos::Scans::from_file(&input_file).expect("Scan failed");

    println!("{scans:#?}");
    println!("priority: {}", scans.rfc9218_priority_change_headers().unwrap());
}

Trait Implementations

impl Clone for Scans

fn clone(&self) -> Scans

Returns a duplicate of the value.

fn clone_from(&mut self, source: &Self)

Performs copy-assignment from source.

impl Debug for Scans

fn fmt(&self, f: &mut Formatter<'_>) -> Result

Formats the value using the given formatter.

impl Default for Scans

fn default() -> Scans

Returns the “default value” for a type.

impl PartialEq for Scans

fn eq(&self, other: &Scans) -> bool

Tests for self and other values to be equal, and is used by ==.

fn ne(&self, other: &Rhs) -> bool

Tests for !=. The default implementation is almost always sufficient, and should not be overridden without very good reason.

impl StructuralPartialEq for Scans