From fb9491b05469861d351fd79ceaafcad5d20ff970 Mon Sep 17 00:00:00 2001
From: Travis Ralston <travisr@matrix.org>
Date: Tue, 7 Dec 2021 15:48:05 -0700
Subject: [PATCH] Extensible Events - Files

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+# MSC0000: Extensible Events - Files
+
+[MSC1767](https://github.com/matrix-org/matrix-doc/pull/1767) describes Extensible Events in detail,
+though deliberately does not include schemas for non-text messaging types. This MSC covers just file
+uploads, which is further used as a base for images, videos, etc.
+
+*Rationale*: Splitting the MSCs down into individual parts makes it easier to implement and review in
+stages without blocking other pieces of the overall idea. For example, an issue with the way images
+are represented should not block the overall schema from going through.
+
+## Proposal
+
+Using [MSC1767](https://github.com/matrix-org/matrix-doc/pull/1767)'s system, a new `m.file` primary
+event type is introduced to describe generic file uploads (PDFs, documents, etc).
+
+An example is:
+
+```json5
+{
+  "type": "m.file",
+  "content": {
+    "m.text": "Upload: foo.pdf (12 KB)", // or other m.message-like event
+    "m.file": {
+      "url": "mxc://example.org/abcd1234",
+      "name": "foo.pdf",
+      "mimetype": "application/pdf",
+      "size": 12345
+    }
+  }
+}
+```
+
+This incorporates the intended schema for the [`m.file`](https://spec.matrix.org/v1.1/client-server-api/#mfile)
+`msgtype` (minus the spurious thumbnail schema).
+
+Note that a file event requires a text fallback of `m.text`, `m.html`, or other `m.message`-compatible
+event.
+
+An encrypted file would appear as such:
+
+```json5
+{
+  "type": "m.file",
+  "content": {
+    "m.text": "Upload: foo.pdf (12 KB)", // or other m.message-like event
+    "m.file": {
+      "url": "mxc://example.org/abcd1234",
+      "name": "foo.pdf",
+      "mimetype": "application/pdf",
+      "size": 12345,
+
+      // These are all from EncryptedFile: https://spec.matrix.org/v1.1/client-server-api/#sending-encrypted-attachments
+      "key": {
+        "kty": "oct",
+        "key_ops": ["encrypt", "decrypt"],
+        "alg": "A256CTR",
+        "k": "aWF6-32KGYaC3A_FEUCk1Bt0JA37zP0wrStgmdCaW-0",
+        "ext": true
+      },
+      "iv": "w+sE15fzSc0AAAAAAAAAAA",
+      "hashes": {
+        "sha256": "fdSLu/YkRx3Wyh3KQabP3rd6+SFiKg5lsJZQHtkSAYA"
+      },
+      "v": "v2"
+    }
+  }
+}
+```
+
+The presence of a `key` JWT denotes the file is encrypted.
+
+## Potential issues
+
+The schema duplicates some of the information into the text fallback, though this is unavoidable.
+
+## Alternatives
+
+No significant alternatives known.
+
+## Security considerations
+
+The same considerations which currently apply to files and extensible events also apply here.
+
+## Transition
+
+The same transition introduced by extensible events is also applied here:
+
+```json5
+{
+  "type": "m.room.message",
+  "content": {
+    "msgtype": "m.file",
+    "body": "foo.pdf",
+    "info": {
+      "size": 774,
+      "mimetype": "application/pdf"
+    },
+    "file": {
+      "url": "mxc://example.org/f91dce7b060ed4c8f094cd3ecb498aa621bbe242",
+      "key": {
+        "kty": "oct",
+        "key_ops": ["encrypt", "decrypt"],
+        "alg": "A256CTR",
+        "k": "TLlG_OpX807zzQuuwv4QZGJ21_u7weemFGYJFszMn9A",
+        "ext": true
+      },
+      "iv": "S22dq3NAX8wAAAAAAAAAAA",
+      "hashes": {
+        "sha256": "aWOHudBnDkJ9IwaR1Nd8XKoI7DOrqDTwt6xDPfVGN6Q"
+      },
+      "v": "v2"
+    },
+
+    // Extensible Events
+    "m.text": "foo.pdf",
+    "m.file": {
+      "url": "mxc://example.org/f91dce7b060ed4c8f094cd3ecb498aa621bbe242",
+      "name": "foo.pdf",
+      "mimetype": "application/pdf",
+      "size": 774,
+      "key": {
+        "kty": "oct",
+        "key_ops": ["encrypt", "decrypt"],
+        "alg": "A256CTR",
+        "k": "TLlG_OpX807zzQuuwv4QZGJ21_u7weemFGYJFszMn9A",
+        "ext": true
+      },
+      "iv": "S22dq3NAX8wAAAAAAAAAAA",
+      "hashes": {
+        "sha256": "aWOHudBnDkJ9IwaR1Nd8XKoI7DOrqDTwt6xDPfVGN6Q"
+      },
+      "v": "v2"
+    }
+  }
+}
+```
+
+The event details are copied and quite verbose, however this is best to ensure compatibility with the
+extensible events format.
+
+## Unstable prefix
+
+While this MSC is not considered stable, implementations should use `org.matrix.msc1767.file` in place
+of `m.file` throughout this proposal. Note that this uses the namespace of the parent MSC rather than
+the namespace of this MSC - this is deliberate.
+
+Example:
+```json5
+{
+  "type": "org.matrix.msc1767.file",
+  "content": {
+    "org.matrix.msc1767.text": "Upload: foo.pdf (12 KB)", // or other org.matrix.msc1767.message-like event
+    "org.matrix.msc1767.file": {
+      "url": "mxc://example.org/abcd1234",
+      "name": "foo.pdf",
+      "mimetype": "application/pdf",
+      "size": 12345
+    }
+  }
+}
+```