add image flow

app/images.py

@@ -0,0 +1,73 @@
+from dataclasses import dataclass
+from io import BytesIO
+
+from fastapi import HTTPException, UploadFile
+from PIL import Image, UnidentifiedImageError
+
+
+MAX_IMAGE_SIDE = 1600
+JPEG_QUALITY = 80
+JPEG_MIME_TYPE = "image/jpeg"
+
+
+@dataclass(slots=True)
+class ProcessedImage:
+    blob: bytes
+    mime_type: str
+    width: int
+    height: int
+
+
+def process_upload(file: UploadFile | None) -> ProcessedImage | None:
+    if file is None or not file.filename:
+        return None
+
+    try:
+        raw_bytes = file.file.read()
+        if not raw_bytes:
+            raise HTTPException(status_code=400, detail="上传的图片内容为空")
+
+        with Image.open(BytesIO(raw_bytes)) as source_image:
+            processed_image = _prepare_image(source_image)
+    except UnidentifiedImageError as exc:
+        raise HTTPException(status_code=400, detail="上传的文件不是合法图片") from exc
+    except HTTPException:
+        raise
+    except Exception as exc:
+        raise HTTPException(status_code=400, detail="图片处理失败，请尝试更换图片") from exc
+    finally:
+        file.file.close()
+
+    return processed_image
+
+
+def _prepare_image(source_image: Image.Image) -> ProcessedImage:
+    prepared = _strip_metadata_and_convert(source_image)
+    prepared.thumbnail((MAX_IMAGE_SIDE, MAX_IMAGE_SIDE))
+
+    output = BytesIO()
+    prepared.save(output, format="JPEG", quality=JPEG_QUALITY, optimize=True)
+    blob = output.getvalue()
+
+    return ProcessedImage(
+        blob=blob,
+        mime_type=JPEG_MIME_TYPE,
+        width=prepared.width,
+        height=prepared.height,
+    )
+
+
+def _strip_metadata_and_convert(source_image: Image.Image) -> Image.Image:
+    if source_image.mode in ("RGBA", "LA"):
+        background = Image.new("RGB", source_image.size, (255, 255, 255))
+        alpha = source_image.getchannel("A")
+        background.paste(source_image.convert("RGBA"), mask=alpha)
+        return background
+
+    if source_image.mode == "P":
+        return source_image.convert("RGB")
+
+    if source_image.mode != "RGB":
+        return source_image.convert("RGB")
+
+    return source_image.copy()