From 6c85d3e28f5225dc311f5fdb392a9dc8a8c799f6 Mon Sep 17 00:00:00 2001
From: =?UTF-8?q?Damir=20Jeli=C4=87?= <poljar@termina.org.uk>
Date: Tue, 11 Aug 2020 11:24:29 +0200
Subject: [PATCH] crypto: Use TryFrom to check the accepted SAS protocols.

---
 .../src/verification/sas/sas_state.rs         | 76 ++++++++++---------
 1 file changed, 41 insertions(+), 35 deletions(-)

diff --git a/matrix_sdk_crypto/src/verification/sas/sas_state.rs b/matrix_sdk_crypto/src/verification/sas/sas_state.rs
index 7ee292c5..f53155d0 100644
--- a/matrix_sdk_crypto/src/verification/sas/sas_state.rs
+++ b/matrix_sdk_crypto/src/verification/sas/sas_state.rs
@@ -13,6 +13,7 @@
 // limitations under the License.
 
 use std::{
+    convert::TryFrom,
     mem,
     sync::{Arc, Mutex},
     time::{Duration, Instant},
@@ -70,14 +71,29 @@ struct AcceptedProtocols {
     short_auth_string: Vec<ShortAuthenticationString>,
 }
 
-impl From<AcceptV1Content> for AcceptedProtocols {
-    fn from(content: AcceptV1Content) -> Self {
-        Self {
-            method: VerificationMethod::MSasV1,
-            hash: content.hash,
-            key_agreement_protocol: content.key_agreement_protocol,
-            message_auth_code: content.message_authentication_code,
-            short_auth_string: content.short_authentication_string,
+impl TryFrom<AcceptV1Content> for AcceptedProtocols {
+    type Error = CancelCode;
+
+    fn try_from(content: AcceptV1Content) -> Result<Self, Self::Error> {
+        if !KEY_AGREEMENT_PROTOCOLS.contains(&content.key_agreement_protocol)
+            || !HASHES.contains(&content.hash)
+            || !MACS.contains(&content.message_authentication_code)
+            || (!content
+                .short_authentication_string
+                .contains(&ShortAuthenticationString::Emoji)
+                && !content
+                    .short_authentication_string
+                    .contains(&ShortAuthenticationString::Decimal))
+        {
+            Err(CancelCode::UnknownMethod)
+        } else {
+            Ok(Self {
+                method: VerificationMethod::MSasV1,
+                hash: content.hash,
+                key_agreement_protocol: content.key_agreement_protocol,
+                message_auth_code: content.message_authentication_code,
+                short_auth_string: content.short_authentication_string,
+            })
         }
     }
 }
@@ -319,34 +335,24 @@ impl SasState<Created> {
             .map_err(|c| self.clone().cancel(c))?;
 
         if let AcceptMethod::MSasV1(content) = &event.content.method {
-            if !KEY_AGREEMENT_PROTOCOLS.contains(&content.key_agreement_protocol)
-                || !HASHES.contains(&content.hash)
-                || !MACS.contains(&content.message_authentication_code)
-                || (!content
-                    .short_authentication_string
-                    .contains(&ShortAuthenticationString::Emoji)
-                    && !content
-                        .short_authentication_string
-                        .contains(&ShortAuthenticationString::Decimal))
-            {
-                Err(self.cancel(CancelCode::UnknownMethod))
-            } else {
-                let json_start_content = cjson::to_string(&self.as_content())
-                    .expect("Can't deserialize start event content");
+            let accepted_protocols =
+                AcceptedProtocols::try_from(content.clone()).map_err(|c| self.clone().cancel(c))?;
 
-                Ok(SasState {
-                    inner: self.inner,
-                    ids: self.ids,
-                    verification_flow_id: self.verification_flow_id,
-                    creation_time: self.creation_time,
-                    last_event_time: self.last_event_time,
-                    state: Arc::new(Accepted {
-                        json_start_content,
-                        commitment: content.commitment.clone(),
-                        accepted_protocols: Arc::new(content.clone().into()),
-                    }),
-                })
-            }
+            let json_start_content = cjson::to_string(&self.as_content())
+                .expect("Can't deserialize start event content");
+
+            Ok(SasState {
+                inner: self.inner,
+                ids: self.ids,
+                verification_flow_id: self.verification_flow_id,
+                creation_time: self.creation_time,
+                last_event_time: self.last_event_time,
+                state: Arc::new(Accepted {
+                    json_start_content,
+                    commitment: content.commitment.clone(),
+                    accepted_protocols: Arc::new(accepted_protocols),
+                }),
+            })
         } else {
             Err(self.cancel(CancelCode::UnknownMethod))
         }