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// EXIF 元数据读取（纯 MoonBit）
// 支持 JPEG EXIF：Make/Model/Orientation/DateTime
///|
/// EXIF 元数据信息
pub(all) struct ExifInfo {
make : String
model : String
orientation : Int
date_time : String
} derive(Eq, @debug.Debug)
///|
fn read_u16_be(data : Bytes, offset : Int) -> Int {
data[offset].to_int() * 256 + data[offset + 1].to_int()
}
///|
fn read_u16_le(data : Bytes, offset : Int) -> Int {
data[offset].to_int() + data[offset + 1].to_int() * 256
}
///|
fn read_u32_be(data : Bytes, offset : Int) -> Int {
data[offset].to_int() * 16777216 +
data[offset + 1].to_int() * 65536 +
data[offset + 2].to_int() * 256 +
data[offset + 3].to_int()
}
///|
fn read_u32_le(data : Bytes, offset : Int) -> Int {
data[offset].to_int() +
data[offset + 1].to_int() * 256 +
data[offset + 2].to_int() * 65536 +
data[offset + 3].to_int() * 16777216
}
///|
fn read_exif_string(
data : Bytes,
tiff_start : Int,
entry_offset : Int,
count : Int,
little : Bool,
) -> String {
let val_offset = if count <= 4 {
tiff_start + entry_offset + 8
} else {
let ptr = if little {
read_u32_le(data, tiff_start + entry_offset + 8)
} else {
read_u32_be(data, tiff_start + entry_offset + 8)
}
tiff_start + ptr
}
// 读取 ASCII 字符串（去除尾部 \0）
let chars : Array[Byte] = []
for i in 0..<count {
let b = data[val_offset + i]
if b == b'\x00' {
break
}
chars.push(b)
}
@encoding/utf8.decode(Bytes::from_array(chars)[:]) catch {
_ => ""
}
}
///|
/// 从 JPEG 字节流读取 EXIF 元数据。
/// 返回 None 如果不含 EXIF 数据。
pub fn read_exif_from_bytes(data : Bytes) -> ExifInfo? {
let len = data.length()
if len < 4 || data[0].to_int() != 0xFF || data[1].to_int() != 0xD8 {
return None
}
// 查找 APP1 marker (0xFF 0xE1)
let mut pos = 2
let mut exif_start = -1
let mut exif_len = 0
while pos < len - 1 {
if data[pos].to_int() == 0xFF && data[pos + 1].to_int() == 0xE1 {
exif_len = read_u16_be(data, pos + 2) - 2
exif_start = pos + 4
break
}
if data[pos].to_int() == 0xFF {
let marker = data[pos + 1].to_int()
if marker == 0xDA || marker == 0xD9 {
break
}
let seg_len = read_u16_be(data, pos + 2)
pos += 2 + seg_len
} else {
pos += 1
}
}
if exif_start < 0 || exif_start + exif_len > len {
return None
}
// 检查 "Exif\0\0"
if exif_len < 6 ||
data[exif_start].to_int() != 0x45 ||
data[exif_start + 1].to_int() != 0x78 ||
data[exif_start + 2].to_int() != 0x69 ||
data[exif_start + 3].to_int() != 0x66 {
return None
}
let tiff_start = exif_start + 6
if tiff_start + 8 > len {
return None
}
// 读取字节序
let little = if data[tiff_start].to_int() == 0x49 &&
data[tiff_start + 1].to_int() == 0x49 {
true
} else if data[tiff_start].to_int() == 0x4D &&
data[tiff_start + 1].to_int() == 0x4D {
false
} else {
return None
}
// IFD0 偏移
let ifd0_offset = if little {
read_u32_le(data, tiff_start + 4)
} else {
read_u32_be(data, tiff_start + 4)
}
let ifd0_pos = tiff_start + ifd0_offset
if ifd0_pos + 2 > len {
return None
}
let entry_count = if little {
read_u16_le(data, ifd0_pos)
} else {
read_u16_be(data, ifd0_pos)
}
// 默认值
let mut make = ""
let mut model = ""
let mut orientation = 1
let mut date_time = ""
// 解析 IFD 条目
for i in 0..<entry_count {
let entry_pos = ifd0_pos + 2 + i * 12
if entry_pos + 12 > len {
break
}
let tag = if little {
read_u16_le(data, entry_pos)
} else {
read_u16_be(data, entry_pos)
}
let count = if little {
read_u32_le(data, entry_pos + 4)
} else {
read_u32_be(data, entry_pos + 4)
}
let entry_offset = entry_pos - tiff_start
match tag {
0x010F =>
make = read_exif_string(data, tiff_start, entry_offset, count, little)
0x0110 =>
model = read_exif_string(data, tiff_start, entry_offset, count, little)
0x0112 =>
orientation = if little {
read_u16_le(data, tiff_start + entry_offset + 8)
} else {
read_u16_be(data, tiff_start + entry_offset + 8)
}
0x0132 =>
date_time = read_exif_string(
data, tiff_start, entry_offset, count, little,
)
_ => ()
}
}
Some(ExifInfo::{ make, model, orientation, date_time })
}