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//! JPEG metadata writer.
//!
//! Rewrites JPEG files with updated/added/removed metadata segments.
//! Mirrors ExifTool's WriteJPEG in Writer.pl.
use crate::error::{Error, Result};
/// JPEG segment to write.
#[derive(Debug, Clone)]
pub struct JpegSegment {
pub marker: u8,
pub data: Vec<u8>,
}
/// Rewrite a JPEG file, replacing/adding/removing metadata segments.
///
/// `source` is the original JPEG data.
/// `new_exif` is the new EXIF data (including "Exif\0\0" header), or None to keep existing.
/// `new_xmp` is the new XMP data (including namespace header), or None to keep existing.
/// `new_iptc` is the new IPTC/Photoshop data, or None to keep existing.
/// `new_comment` is the new JPEG comment, or None to keep existing.
/// `remove_exif` / `remove_xmp` / `remove_iptc` / `remove_comment`: if true, remove that segment.
pub fn write_jpeg(
source: &[u8],
new_exif: Option<&[u8]>,
new_xmp: Option<&[u8]>,
new_iptc: Option<&[u8]>,
new_comment: Option<&str>,
remove_exif: bool,
remove_xmp: bool,
remove_iptc: bool,
remove_comment: bool,
) -> Result<Vec<u8>> {
if source.len() < 2 || source[0] != 0xFF || source[1] != 0xD8 {
return Err(Error::InvalidData("not a JPEG file".into()));
}
let mut output = Vec::with_capacity(source.len());
output.extend_from_slice(&[0xFF, 0xD8]); // SOI
let mut pos = 2;
let mut wrote_exif = false;
let mut wrote_xmp = false;
let mut wrote_iptc = false;
let mut wrote_comment = false;
let mut past_first_segment = false;
// Write new segments before the first existing segment
// (ExifTool writes EXIF first, then XMP, then IPTC)
while pos + 4 <= source.len() {
// Find next marker
if source[pos] != 0xFF {
pos += 1;
continue;
}
let marker = source[pos + 1];
pos += 2;
// Skip padding 0xFF bytes
if marker == 0xFF || marker == 0x00 {
continue;
}
// SOS: end of metadata - write any remaining new segments then copy rest
if marker == 0xDA {
// Before SOS, inject any new segments we haven't written yet
if !wrote_exif {
if let Some(exif) = new_exif {
write_app1_exif(&mut output, exif);
}
}
if !wrote_xmp {
if let Some(xmp) = new_xmp {
write_app1_xmp(&mut output, xmp);
}
}
if !wrote_iptc {
if let Some(iptc) = new_iptc {
write_app13_iptc(&mut output, iptc);
}
}
if !wrote_comment {
if let Some(comment) = new_comment {
write_com(&mut output, comment);
}
}
// Copy SOS marker and all remaining data (image data + EOI)
output.extend_from_slice(&[0xFF, marker]);
output.extend_from_slice(&source[pos..]);
return Ok(output);
}
// Markers without payload (restart markers, etc.)
if marker == 0xD8 || (0xD0..=0xD7).contains(&marker) {
output.extend_from_slice(&[0xFF, marker]);
continue;
}
// Read segment length
if pos + 2 > source.len() {
break;
}
let seg_len = u16::from_be_bytes([source[pos], source[pos + 1]]) as usize;
if seg_len < 2 || pos + seg_len > source.len() {
break;
}
let seg_data = &source[pos + 2..pos + seg_len];
// On first non-SOI segment, inject new segments if needed
if !past_first_segment {
past_first_segment = true;
// Write new EXIF before existing segments (unless we'll replace an existing one)
if new_exif.is_some() && !is_exif_segment(marker, seg_data) {
if let Some(exif) = new_exif {
write_app1_exif(&mut output, exif);
wrote_exif = true;
}
}
}
// Decide what to do with this segment
match marker {
// APP1 - EXIF or XMP
0xE1 => {
if is_exif_segment(marker, seg_data) {
if remove_exif {
// Skip (remove)
} else if let Some(exif) = new_exif {
if !wrote_exif {
write_app1_exif(&mut output, exif);
wrote_exif = true;
}
// Skip original EXIF segment (replaced)
} else {
// Keep original
write_segment(&mut output, marker, &source[pos..pos + seg_len]);
}
} else if is_xmp_segment(seg_data) {
if remove_xmp {
// Skip
} else if let Some(xmp) = new_xmp {
if !wrote_xmp {
write_app1_xmp(&mut output, xmp);
wrote_xmp = true;
}
} else {
write_segment(&mut output, marker, &source[pos..pos + seg_len]);
}
} else {
// Other APP1 segment - keep
write_segment(&mut output, marker, &source[pos..pos + seg_len]);
}
}
// APP13 - Photoshop/IPTC
0xED => {
if remove_iptc {
// Skip
} else if let Some(iptc) = new_iptc {
if !wrote_iptc {
write_app13_iptc(&mut output, iptc);
wrote_iptc = true;
}
} else {
write_segment(&mut output, marker, &source[pos..pos + seg_len]);
}
}
// COM - Comment
0xFE => {
if remove_comment {
// Skip
} else if let Some(comment) = new_comment {
if !wrote_comment {
write_com(&mut output, comment);
wrote_comment = true;
}
} else {
write_segment(&mut output, marker, &source[pos..pos + seg_len]);
}
}
// All other segments - copy as-is
_ => {
write_segment(&mut output, marker, &source[pos..pos + seg_len]);
}
}
pos += seg_len;
}
// If we never hit SOS (unusual but possible for metadata-only JPEG)
Ok(output)
}
fn is_exif_segment(_marker: u8, data: &[u8]) -> bool {
data.len() > 6 && data.starts_with(b"Exif\0\0")
}
fn is_xmp_segment(data: &[u8]) -> bool {
data.len() > 29 && data.starts_with(b"http://ns.adobe.com/xap/1.0/\0")
}
fn write_segment(output: &mut Vec<u8>, marker: u8, data: &[u8]) {
output.push(0xFF);
output.push(marker);
output.extend_from_slice(data);
}
fn write_app1_exif(output: &mut Vec<u8>, exif_data: &[u8]) {
// APP1 marker + length + "Exif\0\0" + TIFF data
let mut segment = Vec::new();
segment.extend_from_slice(b"Exif\0\0");
segment.extend_from_slice(exif_data);
let total_len = (segment.len() + 2) as u16; // +2 for length field itself
output.push(0xFF);
output.push(0xE1);
output.extend_from_slice(&total_len.to_be_bytes());
output.extend_from_slice(&segment);
}
fn write_app1_xmp(output: &mut Vec<u8>, xmp_data: &[u8]) {
let mut segment = Vec::new();
segment.extend_from_slice(b"http://ns.adobe.com/xap/1.0/\0");
segment.extend_from_slice(xmp_data);
// XMP can be large; split if needed (>65533 bytes)
if segment.len() + 2 > 65535 {
// Write only what fits; extended XMP not yet supported
let max = 65533;
let total_len = (max + 2) as u16;
output.push(0xFF);
output.push(0xE1);
output.extend_from_slice(&total_len.to_be_bytes());
output.extend_from_slice(&segment[..max]);
} else {
let total_len = (segment.len() + 2) as u16;
output.push(0xFF);
output.push(0xE1);
output.extend_from_slice(&total_len.to_be_bytes());
output.extend_from_slice(&segment);
}
}
fn write_app13_iptc(output: &mut Vec<u8>, iptc_data: &[u8]) {
let mut segment = Vec::new();
segment.extend_from_slice(b"Photoshop 3.0\0");
// Wrap in 8BIM resource block
segment.extend_from_slice(b"8BIM");
segment.extend_from_slice(&0x0404u16.to_be_bytes()); // IPTC resource ID
segment.push(0); // Pascal string name (length 0)
segment.push(0); // Padding
segment.extend_from_slice(&(iptc_data.len() as u32).to_be_bytes());
segment.extend_from_slice(iptc_data);
if iptc_data.len() % 2 != 0 {
segment.push(0); // Pad to even
}
let total_len = (segment.len() + 2) as u16;
output.push(0xFF);
output.push(0xED);
output.extend_from_slice(&total_len.to_be_bytes());
output.extend_from_slice(&segment);
}
fn write_com(output: &mut Vec<u8>, comment: &str) {
let data = comment.as_bytes();
let total_len = (data.len() + 2) as u16;
output.push(0xFF);
output.push(0xFE);
output.extend_from_slice(&total_len.to_be_bytes());
output.extend_from_slice(data);
}