Merge pull request #57 from matrix-org/dbkr/wasm

WebAssembly support

16 files changed, 192 insertions, 103 deletions

diff --git a/CHANGELOG.rst b/CHANGELOG.rst
index fa1eccb..9160ff1 100644
--- a/CHANGELOG.rst
+++ b/CHANGELOG.rst
@@ -1,3 +1,11 @@
+Changes in latest release
+
+BREAKING CHANGE: Olm now uses WebAssembly which means it needs
+to load the wasm file asynchronously, and therefore needs to be
+started up asynchronously. The imported module now has an init()
+method which returns a promise. The library cannot be used until
+this promise resolves. It will reject if the library fails to start.
+
 Changes in `2.3.0 <http://matrix.org/git/olm/commit/?h=2.3.0>`_
 
 This release includes the following changes since 2.2.2:
diff --git a/Makefile b/Makefile
index 4dd1f4b..8887172 100644
--- a/Makefile
+++ b/Makefile
@@ -27,9 +27,12 @@ endif
 RELEASE_TARGET := $(BUILD_DIR)/libolm.$(SO).$(VERSION)
 STATIC_RELEASE_TARGET := $(BUILD_DIR)/libolm.a
 DEBUG_TARGET := $(BUILD_DIR)/libolm_debug.$(SO).$(VERSION)
-JS_TARGET := javascript/olm.js
+JS_WASM_TARGET := javascript/olm.js
+JS_ASMJS_TARGET := javascript/olm_legacy.js
 
 JS_EXPORTED_FUNCTIONS := javascript/exported_functions.json
+JS_EXTRA_EXPORTED_RUNTIME_METHODS := ALLOC_STACK
+JS_EXTERNS := javascript/externs.js
 
 PUBLIC_HEADERS := include/olm/olm.h include/olm/outbound_group_session.h include/olm/inbound_group_session.h include/olm/pk.h
 
@@ -49,11 +52,22 @@ FUZZER_BINARIES := $(addprefix $(BUILD_DIR)/,$(basename $(FUZZER_SOURCES)))
 FUZZER_DEBUG_BINARIES := $(patsubst $(BUILD_DIR)/fuzzers/fuzz_%,$(BUILD_DIR)/fuzzers/debug_%,$(FUZZER_BINARIES))
 TEST_BINARIES := $(patsubst tests/%,$(BUILD_DIR)/tests/%,$(basename $(TEST_SOURCES)))
 JS_OBJECTS := $(addprefix $(BUILD_DIR)/javascript/,$(OBJECTS))
+
+# pre & post are the js-pre/js-post options to emcc.
+# They are injected inside the modularised code and
+# processed by the optimiser.
 JS_PRE := $(wildcard javascript/*pre.js)
 JS_POST := javascript/olm_outbound_group_session.js \
     javascript/olm_inbound_group_session.js \
     javascript/olm_pk.js \
     javascript/olm_post.js
+
+# The prefix & suffix are just added onto the start & end
+# of what comes out emcc, so are outside of the modularised
+# code and not seen by the opimiser.
+JS_PREFIX := javascript/olm_prefix.js
+JS_SUFFIX := javascript/olm_suffix.js
+
 DOCS := tracing/README.html \
     docs/megolm.html \
     docs/olm.html \
@@ -70,11 +84,23 @@ CFLAGS += -Wall -Werror -std=c99 -fPIC
 CXXFLAGS += -Wall -Werror -std=c++11 -fPIC
 LDFLAGS += -Wall -Werror
 
-EMCCFLAGS = --closure 1 --memory-init-file 0 -s NO_FILESYSTEM=1 -s INVOKE_RUN=0
+EMCCFLAGS = --closure 1 --memory-init-file 0 -s NO_FILESYSTEM=1 -s INVOKE_RUN=0 -s MODULARIZE=1
 # NO_BROWSER is kept for compatibility with emscripten 1.35.24, but is no
 # longer needed.
 EMCCFLAGS += -s NO_BROWSER=1
 
+# Olm generally doesn't need a lot of memory to encrypt / decrypt its usual
+# payloads (ie. Matrix messages), but we do need about 128K of heap to encrypt
+# a 64K event (enough to store the ciphertext and the plaintext, bearing in
+# mind that the plaintext can only be 48K because base64). We also have about
+# 36K of statics. So let's have 256K of memory.
+# (This can't be changed by the app with wasm since it's baked into the wasm).
+# (emscripten also mandates at least 16MB of memory for asm.js now, so
+# we don't use this for the legacy build.)
+EMCCFLAGS_WASM += -s TOTAL_STACK=65536 -s TOTAL_MEMORY=262144
+
+EMCCFLAGS_ASMJS += -s WASM=0
+
 EMCC.c = $(EMCC) $(CFLAGS) $(CPPFLAGS) -c
 EMCC.cc = $(EMCC) $(CXXFLAGS) $(CPPFLAGS) -c
 EMCC_LINK = $(EMCC) $(LDFLAGS) $(EMCCFLAGS)
@@ -109,7 +135,8 @@ $(FUZZER_DEBUG_BINARIES): LDFLAGS += $(DEBUG_OPTIMIZE_FLAGS)
 
 $(JS_OBJECTS): CFLAGS += $(JS_OPTIMIZE_FLAGS)
 $(JS_OBJECTS): CXXFLAGS += $(JS_OPTIMIZE_FLAGS)
-$(JS_TARGET): LDFLAGS += $(JS_OPTIMIZE_FLAGS)
+$(JS_WASM_TARGET): LDFLAGS += $(JS_OPTIMIZE_FLAGS)
+$(JS_ASMJS_TARGET): LDFLAGS += $(JS_OPTIMIZE_FLAGS)
 
 ### Fix to make mkdir work on windows and linux
 ifeq ($(shell echo "check_quotes"),"check_quotes")
@@ -150,15 +177,35 @@ static: $(STATIC_RELEASE_TARGET)
 $(STATIC_RELEASE_TARGET): $(RELEASE_OBJECTS)
 	$(AR) rcs $@ $^
 
-js: $(JS_TARGET)
+js: $(JS_WASM_TARGET) $(JS_ASMJS_TARGET)
 .PHONY: js
 
-$(JS_TARGET): $(JS_OBJECTS) $(JS_PRE) $(JS_POST) $(JS_EXPORTED_FUNCTIONS)
-	$(EMCC_LINK) \
+# Note that the output file we give to emcc determines the name of the
+# wasm file baked into the js, hence messing around outputting to olm.js
+# and then renaming it.
+$(JS_WASM_TARGET): $(JS_OBJECTS) $(JS_PRE) $(JS_POST) $(JS_EXPORTED_FUNCTIONS) $(JS_PREFIX) $(JS_SUFFIX)
+	EMCC_CLOSURE_ARGS="--externs $(JS_EXTERNS)" $(EMCC_LINK) \
+	       $(EMCCFLAGS_WASM) \
+               $(foreach f,$(JS_PRE),--pre-js $(f)) \
+               $(foreach f,$(JS_POST),--post-js $(f)) \
+               -s "EXPORTED_FUNCTIONS=@$(JS_EXPORTED_FUNCTIONS)" \
+               -s "EXTRA_EXPORTED_RUNTIME_METHODS=$(JS_EXTRA_EXPORTED_RUNTIME_METHODS)" \
+               $(JS_OBJECTS) -o $@
+	       mv $@ javascript/olmtmp.js
+	       cat $(JS_PREFIX) javascript/olmtmp.js $(JS_SUFFIX) > $@
+	       rm javascript/olmtmp.js
+
+$(JS_ASMJS_TARGET): $(JS_OBJECTS) $(JS_PRE) $(JS_POST) $(JS_EXPORTED_FUNCTIONS) $(JS_PREFIX) $(JS_SUFFIX)
+	EMCC_CLOSURE_ARGS="--externs $(JS_EXTERNS)" $(EMCC_LINK) \
+	       $(EMCCFLAGS_ASMJS) \
                $(foreach f,$(JS_PRE),--pre-js $(f)) \
                $(foreach f,$(JS_POST),--post-js $(f)) \
                -s "EXPORTED_FUNCTIONS=@$(JS_EXPORTED_FUNCTIONS)" \
+               -s "EXTRA_EXPORTED_RUNTIME_METHODS=$(JS_EXTRA_EXPORTED_RUNTIME_METHODS)" \
                $(JS_OBJECTS) -o $@
+	       mv $@ javascript/olmtmp.js
+	       cat $(JS_PREFIX) javascript/olmtmp.js $(JS_SUFFIX) > $@
+	       rm javascript/olmtmp.js
 
 build_tests: $(TEST_BINARIES)
 
diff --git a/README.rst b/README.rst
index 4f33c00..5a5413e 100644
--- a/README.rst
+++ b/README.rst
@@ -31,6 +31,9 @@ To build the javascript bindings, install emscripten from http://kripken.github.
 
     make js
 
+Note that if you run emscripten in a docker container, you need to pass through
+the EMCC_CLOSURE_ARGS environment variable.
+
 To build the android project for Android bindings, run:
 
 .. code:: bash
diff --git a/javascript/.gitignore b/javascript/.gitignore
index ec22345..3437f73 100644
--- a/javascript/.gitignore
+++ b/javascript/.gitignore
@@ -2,4 +2,5 @@
 /node_modules
 /npm-debug.log
 /olm.js
+/olm.wasm
 /reports
diff --git a/javascript/externs.js b/javascript/externs.js
new file mode 100644
index 0000000..752e937
--- /dev/null
+++ b/javascript/externs.js
@@ -0,0 +1,4 @@
+var OLM_OPTIONS;
+var olm_exports;
+var onInitSuccess;
+var onInitFail;
diff --git a/javascript/olm_inbound_group_session.js b/javascript/olm_inbound_group_session.js
index 6bc745d..7d9e401 100644
--- a/javascript/olm_inbound_group_session.js
+++ b/javascript/olm_inbound_group_session.js
@@ -1,9 +1,3 @@
-/* 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.
- */
-var NULL_BYTE_PADDING_LENGTH = 1;
-
 function InboundGroupSession() {
     var size = Module['_olm_inbound_group_session_size']();
     this.buf = malloc(size);
@@ -77,14 +71,14 @@ InboundGroupSession.prototype['decrypt'] = restore_stack(function(
 
     try {
         message_buffer = malloc(message.length);
-        Module['writeAsciiToMemory'](message, message_buffer, true);
+        writeAsciiToMemory(message, message_buffer, true);
 
         var max_plaintext_length = inbound_group_session_method(
             Module['_olm_group_decrypt_max_plaintext_length']
         )(this.ptr, message_buffer, message.length);
 
         // caculating the length destroys the input buffer, so we need to re-copy it.
-        Module['writeAsciiToMemory'](message, message_buffer, true);
+        writeAsciiToMemory(message, message_buffer, true);
 
         plaintext_buffer = malloc(max_plaintext_length + NULL_BYTE_PADDING_LENGTH);
         var message_index = stack(4);
@@ -100,14 +94,14 @@ InboundGroupSession.prototype['decrypt'] = restore_stack(function(
 
         // UTF8ToString requires a null-terminated argument, so add the
         // null terminator.
-        Module['setValue'](
+        setValue(
             plaintext_buffer+plaintext_length,
             0, "i8"
         );
 
         return {
             "plaintext": UTF8ToString(plaintext_buffer),
-            "message_index": Module['getValue'](message_index, "i32")
+            "message_index": getValue(message_index, "i32")
         }
     } finally {
         if (message_buffer !== undefined) {
diff --git a/javascript/olm_outbound_group_session.js b/javascript/olm_outbound_group_session.js
index 24ea644..e232883 100644
--- a/javascript/olm_outbound_group_session.js
+++ b/javascript/olm_outbound_group_session.js
@@ -1,10 +1,3 @@
-/* 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.
- */
-var NULL_BYTE_PADDING_LENGTH = 1;
-
-
 function OutboundGroupSession() {
     var size = Module['_olm_outbound_group_session_size']();
     this.buf = malloc(size);
@@ -66,7 +59,7 @@ OutboundGroupSession.prototype['create'] = restore_stack(function() {
 OutboundGroupSession.prototype['encrypt'] = function(plaintext) {
     var plaintext_buffer, message_buffer, plaintext_length;
     try {
-        plaintext_length = Module['lengthBytesUTF8'](plaintext);
+        plaintext_length = lengthBytesUTF8(plaintext);
 
         var message_length = outbound_group_session_method(
             Module['_olm_group_encrypt_message_length']
@@ -75,7 +68,7 @@ OutboundGroupSession.prototype['encrypt'] = function(plaintext) {
         // 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);
+        stringToUTF8(plaintext, plaintext_buffer, plaintext_length + 1);
 
         message_buffer = malloc(message_length + NULL_BYTE_PADDING_LENGTH);
         outbound_group_session_method(Module['_olm_group_encrypt'])(
@@ -86,12 +79,12 @@ OutboundGroupSession.prototype['encrypt'] = function(plaintext) {
 
         // UTF8ToString requires a null-terminated argument, so add the
         // null terminator.
-        Module['setValue'](
+        setValue(
             message_buffer+message_length,
             0, "i8"
         );
 
-        return Module['UTF8ToString'](message_buffer);
+        return UTF8ToString(message_buffer);
     } finally {
         if (plaintext_buffer !== undefined) {
             // don't leave a copy of the plaintext in the heap.
diff --git a/javascript/olm_pk.js b/javascript/olm_pk.js
index 407eaf1..5a2c7dc 100644
--- a/javascript/olm_pk.js
+++ b/javascript/olm_pk.js
@@ -35,9 +35,9 @@ PkEncryption.prototype['encrypt'] = restore_stack(function(
 ) {
     var plaintext_buffer, ciphertext_buffer, plaintext_length;
     try {
-        plaintext_length = Module['lengthBytesUTF8'](plaintext)
+        plaintext_length = lengthBytesUTF8(plaintext)
         plaintext_buffer = malloc(plaintext_length + 1);
-        Module['stringToUTF8'](plaintext, plaintext_buffer, plaintext_length + 1);
+        stringToUTF8(plaintext, plaintext_buffer, plaintext_length + 1);
         var random_length = pk_encryption_method(
             Module['_olm_pk_encrypt_random_length']
         )();
@@ -50,7 +50,7 @@ PkEncryption.prototype['encrypt'] = restore_stack(function(
             Module['_olm_pk_mac_length']
         )(this.ptr);
         var mac_buffer = stack(mac_length + NULL_BYTE_PADDING_LENGTH);
-        Module['setValue'](
+        setValue(
             mac_buffer + mac_length,
             0, "i8"
         );
@@ -58,7 +58,7 @@ PkEncryption.prototype['encrypt'] = restore_stack(function(
             Module['_olm_pk_key_length']
         )();
         var ephemeral_buffer = stack(ephemeral_length + NULL_BYTE_PADDING_LENGTH);
-        Module['setValue'](
+        setValue(
             ephemeral_buffer + ephemeral_length,
             0, "i8"
         );
@@ -72,12 +72,12 @@ PkEncryption.prototype['encrypt'] = restore_stack(function(
         );
         // UTF8ToString requires a null-terminated argument, so add the
         // null terminator.
-        Module['setValue'](
+        setValue(
             ciphertext_buffer + ciphertext_length,
             0, "i8"
         );
         return {
-            "ciphertext": Module['UTF8ToString'](ciphertext_buffer),
+            "ciphertext": UTF8ToString(ciphertext_buffer),
             "mac": Pointer_stringify(mac_buffer),
             "ephemeral": Pointer_stringify(ephemeral_buffer)
         };
@@ -169,9 +169,9 @@ PkDecryption.prototype['decrypt'] = restore_stack(function (
 ) {
     var plaintext_buffer, ciphertext_buffer, plaintext_max_length;
     try {
-        ciphertext_length = Module['lengthBytesUTF8'](ciphertext)
+        var ciphertext_length = lengthBytesUTF8(ciphertext)
         ciphertext_buffer = malloc(ciphertext_length + 1);
-        Module['stringToUTF8'](ciphertext, ciphertext_buffer, ciphertext_length + 1);
+        stringToUTF8(ciphertext, ciphertext_buffer, ciphertext_length + 1);
         var ephemeralkey_array = array_from_string(ephemeral_key);
         var ephemeralkey_buffer = stack(ephemeralkey_array);
         var mac_array = array_from_string(mac);
@@ -190,11 +190,11 @@ PkDecryption.prototype['decrypt'] = restore_stack(function (
         );
         // UTF8ToString requires a null-terminated argument, so add the
         // null terminator.
-        Module['setValue'](
+        setValue(
             plaintext_buffer + plaintext_length,
             0, "i8"
         );
-        return Module['UTF8ToString'](plaintext_buffer);
+        return UTF8ToString(plaintext_buffer);
     } finally {
         if (plaintext_buffer !== undefined) {
             // don't leave a copy of the plaintext in the heap.
diff --git a/javascript/olm_post.js b/javascript/olm_post.js
index 7a1d284..21ea890 100644
--- a/javascript/olm_post.js
+++ b/javascript/olm_post.js
@@ -1,27 +1,17 @@
-var runtime = Module['Runtime'];
 var malloc = Module['_malloc'];
 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, 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;
+var OLM_ERROR;
 
 /* allocate a number of bytes of storage on the stack.
  *
  * If size_or_array is a Number, allocates that number of zero-initialised bytes.
  */
 function stack(size_or_array) {
-    return Module['allocate'](size_or_array, 'i8', Module['ALLOC_STACK']);
+    return allocate(size_or_array, 'i8', Module['ALLOC_STACK']);
 }
 
 function array_from_string(string) {
-    return Module['intArrayFromString'](string, true);
+    return intArrayFromString(string, true);
 }
 
 function random_stack(size) {
@@ -33,11 +23,11 @@ function random_stack(size) {
 
 function restore_stack(wrapped) {
     return function() {
-        var sp = runtime.stackSave();
+        var sp = stackSave();
         try {
             return wrapped.apply(this, arguments);
         } finally {
-            runtime.stackRestore(sp);
+            stackRestore(sp);
         }
     }
 }
@@ -315,7 +305,7 @@ Session.prototype['encrypt'] = restore_stack(function(
             Module['_olm_encrypt_message_type']
         )(this.ptr);
 
-        plaintext_length = Module['lengthBytesUTF8'](plaintext);
+        plaintext_length = lengthBytesUTF8(plaintext);
         var message_length = session_method(
             Module['_olm_encrypt_message_length']
         )(this.ptr, plaintext_length);
@@ -325,7 +315,7 @@ Session.prototype['encrypt'] = restore_stack(function(
         // 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);
+        stringToUTF8(plaintext, plaintext_buffer, plaintext_length + 1);
 
         message_buffer = malloc(message_length + NULL_BYTE_PADDING_LENGTH);
 
@@ -338,14 +328,14 @@ Session.prototype['encrypt'] = restore_stack(function(
 
         // UTF8ToString requires a null-terminated argument, so add the
         // null terminator.
-        Module['setValue'](
+        setValue(
             message_buffer+message_length,
             0, "i8"
         );
 
         return {
             "type": message_type,
-            "body": Module['UTF8ToString'](message_buffer),
+            "body": UTF8ToString(message_buffer),
         };
     } finally {
         if (plaintext_buffer !== undefined) {
@@ -366,14 +356,14 @@ Session.prototype['decrypt'] = restore_stack(function(
 
     try {
         message_buffer = malloc(message.length);
-        Module['writeAsciiToMemory'](message, message_buffer, true);
+        writeAsciiToMemory(message, message_buffer, true);
 
         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);
+        writeAsciiToMemory(message, message_buffer, true);
 
         plaintext_buffer = malloc(max_plaintext_length + NULL_BYTE_PADDING_LENGTH);
 
@@ -385,7 +375,7 @@ Session.prototype['decrypt'] = restore_stack(function(
 
         // UTF8ToString requires a null-terminated argument, so add the
         // null terminator.
-        Module['setValue'](
+        setValue(
             plaintext_buffer+plaintext_length,
             0, "i8"
         );
@@ -473,22 +463,3 @@ olm_exports["get_library_version"] = restore_stack(function() {
         getValue(buf+2, 'i8'),
     ];
 });
-
-})();
-
-// export the olm functions into the environment.
-//
-// make sure that we do this *after* populating olm_exports, so that we don't
-// get a half-built window.Olm if there is an exception.
-
-if (typeof module !== 'undefined' && module.exports) {
-    // node / browserify
-    module.exports = olm_exports;
-}
-
-if (typeof(window) !== 'undefined') {
-    // We've been imported directly into a browser. Define the global 'Olm' object.
-    // (we do this even if module.exports was defined, because it's useful to have
-    // Olm in the global scope for browserified and webpacked apps.)
-    window["Olm"] = olm_exports;
-}
diff --git a/javascript/olm_pre.js b/javascript/olm_pre.js
index ae7aba5..18d836d 100644
--- a/javascript/olm_pre.js
+++ b/javascript/olm_pre.js
@@ -1,10 +1,7 @@
-var olm_exports = {};
 var get_random_values;
-var process; // Shadow the process object so that emscripten won't get
-             // confused by browserify
 
 if (typeof(window) !== 'undefined') {
-    // We've in a browser (directly, via browserify, or via webpack).
+    // We're in a browser (directly, via browserify, or via webpack).
     get_random_values = function(buf) {
         window.crypto.getRandomValues(buf);
     };
@@ -12,7 +9,9 @@ if (typeof(window) !== 'undefined') {
     // We're running in node.
     var nodeCrypto = require("crypto");
     get_random_values = function(buf) {
-        var bytes = nodeCrypto.randomBytes(buf.length);
+        // [''] syntax needed here rather than '.' to prevent
+        // closure compiler from mangling the import(!)
+        var bytes = nodeCrypto['randomBytes'](buf.length);
         buf.set(bytes);
     };
     process = global["process"];
@@ -20,14 +19,30 @@ if (typeof(window) !== 'undefined') {
     throw new Error("Cannot find global to attach library to");
 }
 
-(function() {
-    /* applications should define OLM_OPTIONS in the environment to override
-     * emscripten module settings */
-    var Module = {};
-    if (typeof(OLM_OPTIONS) !== 'undefined') {
-        for (var key in OLM_OPTIONS) {
-            if (OLM_OPTIONS.hasOwnProperty(key)) {
-                Module[key] = OLM_OPTIONS[key];
-            }
+/* applications should define OLM_OPTIONS in the environment to override
+ * emscripten module settings
+ */
+if (typeof(OLM_OPTIONS) !== 'undefined') {
+    for (var olm_option_key in OLM_OPTIONS) {
+        if (OLM_OPTIONS.hasOwnProperty(olm_option_key)) {
+            Module[olm_option_key] = OLM_OPTIONS[olm_option_key];
         }
     }
+}
+
+/* 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;
+
+Module['onRuntimeInitialized'] = function() {
+    OLM_ERROR = Module['_olm_error']();
+    if (onInitSuccess) onInitSuccess();
+};
+
+Module['onAbort'] = function(err) {
+    if (onInitFail) onInitFail(err);
+};
diff --git a/javascript/olm_prefix.js b/javascript/olm_prefix.js
new file mode 100644
index 0000000..b33dfe9
--- /dev/null
+++ b/javascript/olm_prefix.js
@@ -0,0 +1,3 @@
+var olm_exports = {};
+var onInitSuccess;
+var onInitFail;
diff --git a/javascript/olm_suffix.js b/javascript/olm_suffix.js
new file mode 100644
index 0000000..3e2f664
--- /dev/null
+++ b/javascript/olm_suffix.js
@@ -0,0 +1,32 @@
+var olmInitPromise;
+
+olm_exports['init'] = function(opts) {
+    if (olmInitPromise) return olmInitPromise;
+
+    if (opts) OLM_OPTIONS = opts;
+
+    olmInitPromise = new Promise(function(resolve, reject) {
+        onInitSuccess = function() {
+            resolve();
+        };
+        onInitFail = function(err) {
+            reject(err);
+        };
+        Module();
+    });
+    return olmInitPromise;
+};
+
+if (typeof(window) !== 'undefined') {
+    // We've been imported directly into a browser. Define the global 'Olm' object.
+    // (we do this even if module.exports was defined, because it's useful to have
+    // Olm in the global scope for browserified and webpacked apps.)
+    window["Olm"] = olm_exports;
+}
+
+if (typeof module === 'object') {
+    // Emscripten sets the module exports to be its module
+    // with wrapped c functions. Clobber it with our higher
+    // level wrapper class.
+    module.exports = olm_exports;
+}
diff --git a/javascript/package.json b/javascript/package.json
index 9cae60e..efe3705 100644
--- a/javascript/package.json
+++ b/javascript/package.json
@@ -5,6 +5,7 @@
   "main": "olm.js",
   "files": [
     "olm.js",
+    "olm.wasm",
     "README.md"
   ],
   "scripts": {
diff --git a/javascript/test/megolm.spec.js b/javascript/test/megolm.spec.js
index 8f9d24a..241d4bd 100644
--- a/javascript/test/megolm.spec.js
+++ b/javascript/test/megolm.spec.js
@@ -1,5 +1,6 @@
 /*
 Copyright 2016 OpenMarket Ltd
+Copyright 2018 New Vector Ltd
 
 Licensed under the Apache License, Version 2.0 (the "License");
 you may not use this file except in compliance with the License.
@@ -21,9 +22,13 @@ var Olm = require('../olm');
 describe("megolm", function() {
     var aliceSession, bobSession;
 
-    beforeEach(function() {
-        aliceSession = new Olm.OutboundGroupSession();
-        bobSession = new Olm.InboundGroupSession();
+    beforeEach(function(done) {
+        Olm.init().then(function() {
+            aliceSession = new Olm.OutboundGroupSession();
+            bobSession = new Olm.InboundGroupSession();
+
+            done();
+        });
     });
 
     afterEach(function() {
diff --git a/javascript/test/olm.spec.js b/javascript/test/olm.spec.js
index b7cc3ae..77dd712 100644
--- a/javascript/test/olm.spec.js
+++ b/javascript/test/olm.spec.js
@@ -1,5 +1,6 @@
 /*
 Copyright 2016 OpenMarket Ltd
+Copyright 2018 New Vector Ltd
 
 Licensed under the Apache License, Version 2.0 (the "License");
 you may not use this file except in compliance with the License.
@@ -30,11 +31,18 @@ describe("olm", function() {
     var aliceAccount, bobAccount;
     var aliceSession, bobSession;
 
-    beforeEach(function() {
-        aliceAccount = new Olm.Account();
-        bobAccount = new Olm.Account();
-        aliceSession = new Olm.Session();
-        bobSession = new Olm.Session();
+    beforeEach(function(done) {
+        // This should really be in a beforeAll, but jasmine-node
+        // doesn't support that
+        debugger;
+        Olm.init().then(function() {
+            aliceAccount = new Olm.Account();
+            bobAccount = new Olm.Account();
+            aliceSession = new Olm.Session();
+            bobSession = new Olm.Session();
+
+            done();
+        });
     });
 
     afterEach(function() {
diff --git a/javascript/test/pk.spec.js b/javascript/test/pk.spec.js
index 0b27470..34f7be5 100644
--- a/javascript/test/pk.spec.js
+++ b/javascript/test/pk.spec.js
@@ -21,9 +21,13 @@ var Olm = require('../olm');
 describe("pk", function() {
     var encryption, decryption;
 
-    beforeEach(function() {
-        encryption = new Olm.PkEncryption();
-        decryption = new Olm.PkDecryption();
+    beforeEach(function(done) {
+        Olm.init().then(function() {
+            encryption = new Olm.PkEncryption();
+            decryption = new Olm.PkDecryption();
+
+            done();
+        });
     });
 
     afterEach(function () {