小中高生とご家族・PTAのための「スマホ安全＆闇バイト（ホワイト案件）防衛ガイド」：頭ごなしの禁止から対話の3ルールへ

#![forbid(unsafe_code)]

pub const JPEG_SOI: [u8; 2] = [0xFF, 0xD8];
pub const JPEG_APP1: [u8; 2] = [0xFF, 0xE1];
pub const JPEG_SOS: [u8; 2] = [0xFF, 0xDA];
pub const EXIF_HEADER: &[u8; 6] = b"Exif";

#[derive(Debug, Clone, Copy, PartialEq, Eq)]
pub enum ExifPrivacyRisk {
    CleanNoExif,
    ContainsExifMetadata,
    ContainsGpsCoordinatesTag0x8825,
    InvalidJpegStream,
}

/// Scans a raw JPEG byte stream for APP1 (`0xFFE1`) EXIF segments and detects
/// the presence of the TIFF GPS Info IFD pointer tag (`0x8825` in Big/Little Endian).
pub fn inspect_jpeg_for_gps_leak(jpeg: &[u8]) -> ExifPrivacyRisk {
    if jpeg.len() < 4 || jpeg[0..2] != JPEG_SOI {
        return ExifPrivacyRisk::InvalidJpegStream;
    }

    let mut pos = 2;
    let mut found_exif = false;

    while pos + 4 <= jpeg.len() {
        if jpeg[pos] != 0xFF {
            break;
        }
        let marker = [jpeg[pos], jpeg[pos + 1]];
        if marker == JPEG_SOS {
            break; — Start of compressed image scan data
        }
        let seg_len = u16::from_be_bytes([jpeg[pos + 2], jpeg[pos + 3]]) as usize;
        if seg_len < 2 || pos + 2 + seg_len > jpeg.len() {
            break;
        }
        let payload = &jpeg[pos + 4..pos + 2 + seg_len];
        if marker == JPEG_APP1 && payload.starts_with(EXIF_HEADER) {
            found_exif = true;
            let tiff_data = &payload[6..];
            // Check for GPS IFD Pointer Tag 0x8825 in either Little-Endian ([0x25, 0x88]) or Big-Endian ([0x88, 0x25])
            let is_little_endian = tiff_data.starts_with(b"II");
            let gps_tag = if is_little_endian { [0x25, 0x88] } else { [0x88, 0x25] };
            if tiff_data.windows(2).any(|w| w == gps_tag) {
                return ExifPrivacyRisk::ContainsGpsCoordinatesTag0x8825;
            }
        }
        pos += 2 + seg_len;
    }

    if found_exif {
        ExifPrivacyRisk::ContainsExifMetadata
    } else {
        ExifPrivacyRisk::CleanNoExif
    }
}