settings: Add support for customizing the top-left logo.

This adds a new realm_logo field, which is a horizontal-format logo to
be displayed in the top-left corner of the webapp, and any other
places where we might want a wide-format branding of the organization.

Tweaked significantly by tabbott to rebase, fix styling, etc.

Fixing the styling of this feature's loading indicator caused me to
notice the loading indicator for the realm_icon feature was also ugly,
so I fixed that too.

Fixes #7995.

zerver/lib/upload.py

@@ -116,6 +116,19 @@ def resize_avatar(image_data: bytes, size: int=DEFAULT_AVATAR_SIZE) -> bytes:
     im.save(out, format='png')
     return out.getvalue()
 
+def resize_logo(image_data: bytes) -> bytes:
+    try:
+        im = Image.open(io.BytesIO(image_data))
+        im = exif_rotate(im)
+        im.thumbnail((8*DEFAULT_AVATAR_SIZE, DEFAULT_AVATAR_SIZE), Image.ANTIALIAS)
+    except IOError:
+        raise BadImageError("Could not decode image; did you upload an image file?")
+    out = io.BytesIO()
+    if im.mode == 'CMYK':
+        im = im.convert('RGB')
+    im.save(out, format='png')
+    return out.getvalue()
+
 
 def resize_gif(im: GifImageFile, size: int=DEFAULT_EMOJI_SIZE) -> bytes:
     frames = []
@@ -187,6 +200,12 @@ class ZulipUploadBackend:
     def get_realm_icon_url(self, realm_id: int, version: int) -> str:
         raise NotImplementedError()
 
+    def upload_realm_logo_image(self, logo_file: File, user_profile: UserProfile) -> None:
+        raise NotImplementedError()
+
+    def get_realm_logo_url(self, realm_id: int, version: int) -> str:
+        raise NotImplementedError()
+
     def upload_emoji_image(self, emoji_file: File, emoji_file_name: str, user_profile: UserProfile) -> None:
         raise NotImplementedError()
 
@@ -423,6 +442,36 @@ class S3UploadBackend(ZulipUploadBackend):
         # ?x=x allows templates to append additional parameters with &s
         return "https://%s.s3.amazonaws.com/%s/realm/icon.png?version=%s" % (bucket, realm_id, version)
 
+    def upload_realm_logo_image(self, logo_file: File, user_profile: UserProfile) -> None:
+        content_type = guess_type(logo_file.name)[0]
+        bucket_name = settings.S3_AVATAR_BUCKET
+        s3_file_name = os.path.join(str(user_profile.realm.id), 'realm', 'logo')
+
+        image_data = logo_file.read()
+        upload_image_to_s3(
+            bucket_name,
+            s3_file_name + ".original",
+            content_type,
+            user_profile,
+            image_data,
+        )
+
+        resized_data = resize_logo(image_data)
+        upload_image_to_s3(
+            bucket_name,
+            s3_file_name + ".png",
+            'image/png',
+            user_profile,
+            resized_data,
+        )
+        # See avatar_url in avatar.py for URL.  (That code also handles the case
+        # that users use gravatar.)
+
+    def get_realm_logo_url(self, realm_id: int, version: int) -> str:
+        bucket = settings.S3_AVATAR_BUCKET
+        # ?x=x allows templates to append additional parameters with &s
+        return "https://%s.s3.amazonaws.com/%s/realm/logo.png?version=%s" % (bucket, realm_id, version)
+
     def ensure_medium_avatar_image(self, user_profile: UserProfile) -> None:
         file_path = user_avatar_path(user_profile)
         s3_file_name = file_path
@@ -576,6 +625,22 @@ class LocalUploadBackend(ZulipUploadBackend):
         # ?x=x allows templates to append additional parameters with &s
         return "/user_avatars/%s/realm/icon.png?version=%s" % (realm_id, version)
 
+    def upload_realm_logo_image(self, logo_file: File, user_profile: UserProfile) -> None:
+        upload_path = os.path.join('avatars', str(user_profile.realm.id), 'realm')
+
+        image_data = logo_file.read()
+        write_local_file(
+            upload_path,
+            'logo.original',
+            image_data)
+
+        resized_data = resize_logo(image_data)
+        write_local_file(upload_path, 'logo.png', resized_data)
+
+    def get_realm_logo_url(self, realm_id: int, version: int) -> str:
+        # ?x=x allows templates to append additional parameters with &s
+        return "/user_avatars/%s/realm/logo.png?version=%s" % (realm_id, version)
+
     def ensure_medium_avatar_image(self, user_profile: UserProfile) -> None:
         file_path = user_avatar_path(user_profile)
 
@@ -633,6 +698,9 @@ def copy_avatar(source_profile: UserProfile, target_profile: UserProfile) -> Non
 def upload_icon_image(user_file: File, user_profile: UserProfile) -> None:
     upload_backend.upload_realm_icon_image(user_file, user_profile)
 
+def upload_logo_image(user_file: File, user_profile: UserProfile) -> None:
+    upload_backend.upload_realm_logo_image(user_file, user_profile)
+
 def upload_emoji_image(emoji_file: File, emoji_file_name: str, user_profile: UserProfile) -> None:
     upload_backend.upload_emoji_image(emoji_file, emoji_file_name, user_profile)