Allocate memory for message blobs on the heap

Messages can be very large, so we don't really want to allocate them on the
stack. Switch to using the heap for them, and try to clean up some of the
string handling while we're at it.

1 files changed, 83 insertions, 50 deletions

diff --git a/javascript/olm_post.js b/javascript/olm_post.js
index 8951c11..9820354 100644
--- a/javascript/olm_post.js
+++ b/javascript/olm_post.js
@@ -4,9 +4,11 @@ var free = Module['_free'];
 var Pointer_stringify = Module['Pointer_stringify'];
 var OLM_ERROR = Module['_olm_error']();
 
-/* The 'length' argument to Pointer_stringify doesn't work if the input includes
- * characters >= 128; we therefore need to add a NULL character to all of our
- * strings. This acts as a symbolic constant to help show what we're doing.
+/* The 'length' argument to Pointer_stringify doesn't work if the input
+ * includes characters >= 128, which makes Pointer_stringify unreliable. We
+ * could use it on strings which are known to be ascii, but that seems
+ * dangerous. Instead we add a NULL character to all of our strings and just
+ * use UTF8ToString.
  */
 var NULL_BYTE_PADDING_LENGTH = 1;
 
@@ -297,59 +299,90 @@ Session.prototype['matches_inbound_from'] = restore_stack(function(
 Session.prototype['encrypt'] = restore_stack(function(
     plaintext
 ) {
-    var random_length = session_method(
-        Module['_olm_encrypt_random_length']
-    )(this.ptr);
-    var message_type = session_method(
-        Module['_olm_encrypt_message_type']
-    )(this.ptr);
-    var plaintext_array = array_from_string(plaintext);
-    var message_length = session_method(
-        Module['_olm_encrypt_message_length']
-    )(this.ptr, plaintext_array.length);
-    var random = random_stack(random_length);
-    var plaintext_buffer = stack(plaintext_array);
-    var message_buffer = stack(message_length + NULL_BYTE_PADDING_LENGTH);
-    session_method(Module['_olm_encrypt'])(
-        this.ptr,
-        plaintext_buffer, plaintext_array.length,
-        random, random_length,
-        message_buffer, message_length
-    );
-    return {
-        "type": message_type,
-        "body": Pointer_stringify(message_buffer)
-    };
+    var plaintext_buffer, message_buffer;
+    try {
+        var random_length = session_method(
+            Module['_olm_encrypt_random_length']
+        )(this.ptr);
+        var message_type = session_method(
+            Module['_olm_encrypt_message_type']
+        )(this.ptr);
+
+        var plaintext_length = Module['lengthBytesUTF8'](plaintext);
+        var message_length = session_method(
+            Module['_olm_encrypt_message_length']
+        )(this.ptr, plaintext_length);
+
+        var random = random_stack(random_length);
+
+        // need to allow space for the terminator (which stringToUTF8 always
+        // writes), hence + 1.
+        plaintext_buffer = malloc(plaintext_length + 1);
+        Module['stringToUTF8'](plaintext, plaintext_buffer, plaintext_length + 1);
+
+        message_buffer = malloc(message_length + NULL_BYTE_PADDING_LENGTH);
+
+        session_method(Module['_olm_encrypt'])(
+            this.ptr,
+            plaintext_buffer, plaintext_length,
+            random, random_length,
+            message_buffer, message_length
+        );
+        return {
+            "type": message_type,
+            "body": Module['UTF8ToString'](message_buffer),
+        };
+    } finally {
+        if (plaintext_buffer !== undefined) {
+            free(plaintext_buffer);
+        }
+        if (message_buffer !== undefined) {
+            free(message_buffer);
+        }
+    }
 });
 
 Session.prototype['decrypt'] = restore_stack(function(
     message_type, message
 ) {
-    var message_array = array_from_string(message);
-    var message_buffer = stack(message_array);
-    var max_plaintext_length = session_method(
-        Module['_olm_decrypt_max_plaintext_length']
-    )(this.ptr, message_type, message_buffer, message_array.length);
-    // caculating the length destroys the input buffer.
-    // So we copy the array to a new buffer
-    var message_buffer = stack(message_array);
-    var plaintext_buffer = stack(
-        max_plaintext_length + NULL_BYTE_PADDING_LENGTH
-    );
-    var plaintext_length = session_method(Module["_olm_decrypt"])(
-        this.ptr, message_type,
-        message_buffer, message.length,
-        plaintext_buffer, max_plaintext_length
-    );
-
-    // Pointer_stringify requires a null-terminated argument (the optional
-    // 'len' argument doesn't work for UTF-8 data).
-    Module['setValue'](
-        plaintext_buffer+plaintext_length,
-        0, "i8"
-    );
+    var message_buffer, plaintext_buffer;
+
+    try {
+        message_buffer = malloc(message.length);
+        Module['writeAsciiToMemory'](message, message_buffer, true);
+
+        var max_plaintext_length = session_method(
+            Module['_olm_decrypt_max_plaintext_length']
+        )(this.ptr, message_type, message_buffer, message.length);
+
+        // caculating the length destroys the input buffer, so we need to re-copy it.
+        Module['writeAsciiToMemory'](message, message_buffer, true);
+
+        plaintext_buffer = malloc(max_plaintext_length + NULL_BYTE_PADDING_LENGTH);
+
+        var plaintext_length = session_method(Module["_olm_decrypt"])(
+            this.ptr, message_type,
+            message_buffer, message.length,
+            plaintext_buffer, max_plaintext_length
+        );
+
+        // UTF8ToString requires a null-terminated argument, so add the
+        // null terminator.
+        Module['setValue'](
+            plaintext_buffer+plaintext_length,
+            0, "i8"
+        );
+
+        return UTF8ToString(plaintext_buffer);
+    } finally {
+        if (message_buffer !== undefined) {
+            free(message_buffer);
+        }
+        if (plaintext_buffer !== undefined) {
+            free(plaintext_buffer);
+        }
+    }
 
-    return Pointer_stringify(plaintext_buffer);
 });
 
 function Utility() {