Implemented everything upload

src/utils/caff_previewer.py

@@ -0,0 +1,56 @@
+import tempfile
+import os
+import os.path
+import shutil
+import requests
+from flask import current_app
+from .md5stuffs import calculate_md5_sum_for_file, write_file_from_stream_to_file_like_while_calculating_md5
+from .exceptions import FileIntegrityError
+import magic
+
+EXPECTED_PREVIEW_MIMETYPE = 'image/png'
+
+# The response is validated for
+# - integrity (2-way)
+# - mime type (both header and file identifying)
+# - size (handled by md5sum saver, generator thingy)
+
+def create_caff_preview(src_file: str) -> str:  # hopefully returns a file path
+
+    # Send file for previewing
+    uploaded_caff_md5sum = calculate_md5_sum_for_file(src_file)
+
+    with open(src_file, 'rb') as f:
+        r = requests.post(current_app.config['CAFF_PREVIEWER_ENDPOINT'], data=f, stream=True)
+
+    r.raise_for_status()
+
+    # Verify the results while saving the file
+    if r.headers.get("Content-type") != EXPECTED_PREVIEW_MIMETYPE:
+        raise ValueError(f"Converter output (reported by header) is not {EXPECTED_PREVIEW_MIMETYPE}")
+
+    if r.headers.get("X-request-checksum") != uploaded_caff_md5sum:
+        # This really is the most pointless check in the world
+        # But it was fun to implement
+        raise FileIntegrityError("File sent for previewing and received by previewer differ")
+
+    converted_png_fd, converted_png_path = tempfile.mkstemp(
+        prefix=os.path.basename(src_file).split('.')[0],
+        suffix='.png'
+    )
+
+    with open(converted_png_fd, "wb") as f:
+        converted_png_md5sum = write_file_from_stream_to_file_like_while_calculating_md5(r.raw, f)
+
+    if r.headers.get("X-response-checksum") != converted_png_md5sum:
+        # This does not have much point either
+        raise FileIntegrityError("File sent by previewer and received by the app differ")
+
+    with magic.Magic(flags=magic.MAGIC_MIME_TYPE) as m:
+        calculated_mimetype = m.id_filename(converted_png_path)
+
+    if calculated_mimetype != EXPECTED_PREVIEW_MIMETYPE:
+        raise ValueError(f"Converter output (calculated from file) is not {EXPECTED_PREVIEW_MIMETYPE}")
+
+    del r
+    return converted_png_path