imageinfo 0.7.27

Rust library to get image size and format without loading/decoding.
Documentation 
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use crate::{ImageFormat, ImageInfo, ImageInfoError, ImageInfoResult, ImageSize, ReadInterface};
use std::cmp::min;
use std::io::{BufRead, Seek};

// https://www.fileformat.info/format/png/corion.htm
pub fn try_png<R>(ri: &mut ReadInterface<R>, length: usize) -> ImageInfoResult<ImageInfo>
where
    R: BufRead + Seek,
{
    if length < 24 {
        return Err(ImageInfoError::UnrecognizedFormat);
    }
    let buffer = ri.read(0, min(length, 40))?;
    if !buffer.cmp(0, 4, b"\x89PNG") {
        return Err(ImageInfoError::UnrecognizedFormat);
    }

    if buffer.cmp(12, 4, b"IHDR") {
        return Ok(ImageInfo {
            format: ImageFormat::PNG,
            ext: "png",
            full_ext: "png",
            mimetype: "image/png",
            size: ImageSize {
                width: buffer.read_u32_be(16) as i64,
                height: buffer.read_u32_be(20) as i64,
            },
            entry_sizes: vec![],
        });
    } else if buffer.cmp(12, 4, b"CgBI") && buffer.len() >= 40 && buffer.cmp(28, 4, b"IHDR") {
        return Ok(ImageInfo {
            format: ImageFormat::PNG,
            ext: "png",
            full_ext: "png",
            mimetype: "image/png",
            size: ImageSize {
                width: buffer.read_u32_be(32) as i64,
                height: buffer.read_u32_be(36) as i64,
            },
            entry_sizes: vec![],
        });
    }

    Err(ImageInfoError::UnrecognizedFormat)
}