Add attachment preview url based on ViewerJS

The viewerJS library can display PDF files easily using pdfjs. Another
attachment route redirects to the viewerjs application to display the
current attachment.

The attachment responses have been improved in that now the response
headers are added to all responses. Additional a HEAD route has been
added to support the viewerJS application.

modules/restapi/src/main/resources/docspell-openapi.yml

@@ -1168,6 +1168,32 @@ paths:
                 $ref: "#/components/schemas/ItemProposals"
 
   /sec/attachment/{id}:
+    head:
+      tags: [ Attachment ]
+      summary: Get an attachment file.
+      description: |
+        Get the binary file belonging to the attachment with the given id.
+      security:
+        - authTokenHeader: []
+      parameters:
+        - $ref: "#/components/parameters/id"
+      responses:
+        200:
+          description: Ok
+          headers:
+            Content-Type:
+              schema:
+                type: string
+            Content-Length:
+              schema:
+                type: integer
+                format: int64
+            ETag:
+              schema:
+                type: string
+            Content-Disposition:
+              schema:
+                type: string
     get:
       tags: [ Attachment ]
       summary: Get an attachment file.
@@ -1203,6 +1229,27 @@ paths:
             application/json:
               schema:
                 $ref: "#/components/schemas/AttachmentMeta"
+  /sec/attachment/{id}/view:
+    get:
+      tags: [ Attachment ]
+      summary: A preview of the attachment
+      description: |
+        This provides a preview of the attachment. It currently uses a
+        third-party javascript library (viewerjs) to display the
+        preview. This works by redirecting to the viewerjs url with
+        the attachment url as parameter. Note that the resulting url
+        that is redirected to is not stable. It may change from
+        version to version. This route, however, is meant to provide a
+        stable url for the preview.
+      security:
+        - authTokenHeader: []
+      parameters:
+        - $ref: "#/components/parameters/id"
+      responses:
+        303:
+          description: See Other
+        200:
+          description: Ok
   /sec/queue/state:
     get:
       tags: [ Job Queue ]