refactor(media-proxy): split into modules and harden streaming (#2437)

fluxer_media_proxy/src/asset_size.rs

@@ -0,0 +1,62 @@
+// SPDX-License-Identifier: AGPL-3.0-or-later
+
+pub use crate::constants::{clamp_size, parse_image_size};
+
+#[cfg(test)]
+mod tests {
+    use super::*;
+    use crate::constants::{AssetKind, DEFAULT_IMAGE_SIZE, IMAGE_SIZES};
+
+    #[test]
+    fn unparsable_sizes_fall_back_to_the_default() {
+        assert_eq!(DEFAULT_IMAGE_SIZE, parse_image_size(None));
+        assert_eq!(DEFAULT_IMAGE_SIZE, parse_image_size(Some("")));
+        assert_eq!(DEFAULT_IMAGE_SIZE, parse_image_size(Some("-1")));
+        assert_eq!(DEFAULT_IMAGE_SIZE, parse_image_size(Some("99999999999")));
+        assert_eq!(DEFAULT_IMAGE_SIZE, parse_image_size(Some("not-a-number")));
+    }
+
+    #[test]
+    fn parsable_sizes_snap_up_to_the_next_rung() {
+        assert_eq!(16, parse_image_size(Some("0")));
+        assert_eq!(640, parse_image_size(Some("640")));
+        assert_eq!(1024, parse_image_size(Some("641")));
+        assert_eq!(1024, parse_image_size(Some("777")));
+        assert_eq!(1024, parse_image_size(Some("1000")));
+        assert_eq!(16384, parse_image_size(Some("99999")));
+        for size in IMAGE_SIZES {
+            assert_eq!(*size, parse_image_size(Some(&size.to_string())));
+        }
+        assert_eq!(16384, parse_image_size(Some("16384")));
+    }
+
+    #[test]
+    fn an_off_ladder_size_never_serves_fewer_pixels_than_requested() {
+        for requested in 1..=4096u32 {
+            let served = parse_image_size(Some(&requested.to_string()));
+            assert!(
+                served >= requested,
+                "size={requested} served {served}, a silent downscale"
+            );
+        }
+    }
+
+    #[test]
+    fn snapping_is_idempotent() {
+        for raw in [0u32, 1, 17, 641, 777, 1000, 4097, 99999] {
+            let once = parse_image_size(Some(&raw.to_string()));
+            let twice = parse_image_size(Some(&once.to_string()));
+            assert_eq!(once, twice, "size={raw} did not settle");
+        }
+    }
+
+    #[test]
+    fn clamping_respects_kind_bounds_and_leaves_attachments_alone() {
+        assert_eq!(128, clamp_size(1, AssetKind::Avatar));
+        assert_eq!(1024, clamp_size(4096, AssetKind::Avatar));
+        assert_eq!(480, clamp_size(16, AssetKind::Banner));
+        assert_eq!(512, clamp_size(4096, AssetKind::Emoji));
+        assert_eq!(4096, clamp_size(4096, AssetKind::Attachment));
+        assert_eq!(1, clamp_size(0, AssetKind::Attachment));
+    }
+}