Add API for downloading media file metadata

Will eventually add API to do this in batch form for all media files in
the project, then we can (e.g.) download metadata immediately and
download file contents on-demand, or download and cache all file
contents prior to going offline.

Author: rmunn

backend/FwLite/LcmCrdt/MediaServer/IMediaServerClient.cs

@@ -8,6 +8,9 @@ public interface IMediaServerClient
     [Get("/api/media/{fileId}")]
     Task<HttpResponseMessage> DownloadFile(Guid fileId);
 
+    [Get("/api/media/metadata/{fileId}")]
+    Task<HttpResponseMessage> GetFileMetadata(Guid fileId);
+
     [Post("/api/media")]
     [Multipart]
     Task<MediaUploadFileResponse> UploadFile(MultipartItem file,

backend/FwLite/LcmCrdt/MediaServer/LcmMediaService.cs

@@ -7,6 +7,7 @@
 using LcmCrdt.RemoteSync;
 using Microsoft.Extensions.Logging;
 using MiniLcm.Media;
+using System.Net.Http.Json;
 
 namespace LcmCrdt.MediaServer;
 
@@ -69,6 +70,29 @@ public async Task<ReadFileResponse> GetFileStream(Guid fileId)
         return new(File.OpenRead(localResource.LocalPath), Path.GetFileName(localResource.LocalPath));
     }
 
+    public async Task<LcmFileMetadata> GetFileMetadata(Guid fileId)
+    {
+        var mediaClient = await MediaServerClient();
+        var response = await mediaClient.GetFileMetadata(fileId);
+        if (!response.IsSuccessStatusCode)
+        {
+            throw new Exception($"Failed to retrieve metadata for file {fileId}: {response.StatusCode} {response.ReasonPhrase}");
+        }
+        var metadata = await response.Content.ReadFromJsonAsync<LcmFileMetadata>();
+        if (metadata is null)
+        {
+            // Try to get content into error message, but if buffering not enabled for this request, give up
+            var content = "";
+            try
+            {
+                content = await response.Content.ReadAsStringAsync();
+            }
+            catch { } // Oh well, we tried
+            throw new Exception($"Failed to retrieve metadata for file {fileId}: response was in incorrect format. {content}");
+        }
+        return metadata;
+    }
+
     private async Task<(Stream? stream, string? filename)> RequestMediaFile(Guid fileId)
     {
         var mediaClient = await MediaServerClient();