学校・PTA・子育て家庭のための
「子どもとスマホ・SNS・位置情報」安心対話ガイド

#![forbid(unsafe_code)]

#[derive(Debug, Clone, Copy, PartialEq, Eq)]
pub enum JpegSanitizeError {
    InvalidSoiHeader,
    TruncatedSegmentHeader,
    InvalidSegmentLength,
    TruncatedSegmentPayload,
}

#[derive(Debug, Clone, PartialEq, Eq)]
pub struct SanitizedJpegResult {
    pub output_bytes: Vec<u8>,
    pub stripped_segments_count: usize,
    pub stripped_bytes_total: usize,
}

pub fn strip_jpeg_metadata(input: &[u8]) -> Result<SanitizedJpegResult, JpegSanitizeError> {
    if input.len() < 4 || input[0] != 0xFF || input[1] != 0xD8 {
        return Err(JpegSanitizeError::InvalidSoiHeader);
    }

    let mut out = Vec::with_capacity(input.len());
    out.extend_from_slice(&input[0..2]); — Write SOI (0xFF 0xD8)

    let mut pos = 2usize;
    let mut stripped_segments = 0usize;
    let mut stripped_bytes = 0usize;

    while pos < input.len() {
        if input[pos] != 0xFF {
            out.extend_from_slice(&input[pos..]);
            break;
        }
        while pos < input.len() && input[pos] == 0xFF {
            pos += 1;
        }
        if pos >= input.len() {
            break;
        }

        let marker = input[pos];
        pos += 1;

        // EOI (0xD9) or SOS (0xDA): copy remainder of stream directly
        if marker == 0xD9 {
            out.extend_from_slice(&[0xFF, 0xD9]);
            break;
        }
        if marker == 0xDA {
            out.extend_from_slice(&[0xFF, 0xDA]);
            out.extend_from_slice(&input[pos..]);
            break;
        }

        if pos + 2 > input.len() {
            return Err(JpegSanitizeError::TruncatedSegmentHeader);
        }
        let seg_len = u16::from_be_bytes([input[pos], input[pos + 1]]) as usize;
        if seg_len < 2 {
            return Err(JpegSanitizeError::InvalidSegmentLength);
        }
        if pos + seg_len > input.len() {
            return Err(JpegSanitizeError::TruncatedSegmentPayload);
        }

        // Strip APP1..APP15 (0xE1..=0xEF) and COM (0xFE)
        let should_strip = (0xE1..=0xEF).contains(&marker) || marker == 0xFE;
        if should_strip {
            stripped_segments += 1;
            stripped_bytes += seg_len + 2;
        } else {
            out.extend_from_slice(&[0xFF, marker]);
            out.extend_from_slice(&input[pos..pos + seg_len]);
        }

        pos += seg_len;
    }

    Ok(SanitizedJpegResult {
        output_bytes: out,
        stripped_segments_count: stripped_segments,
        stripped_bytes_total: stripped_bytes,
    })
}

#[cfg(test)]
mod tests {
    use super::*;

    #[test]
    fn test_strips_exif_app1_segment_cleanly() {
        // SOI + APP1 (len 6: 0x00, 0x06, 'E', 'x', 'i', 'f') + EOI
        let raw = [0xFF, 0xD8, 0xFF, 0xE1, 0x00, 0x06, b'E', b'x', b'i', b'f', 0xFF, 0xD9];
        let res = strip_jpeg_metadata(&raw).unwrap();
        assert_eq!(res.stripped_segments_count, 1);
        assert_eq!(res.output_bytes, vec![0xFF, 0xD8, 0xFF, 0xD9]);
    }
}