diff --git a/.gitignore b/.gitignore
index 479c5590..e38531b4 100644
--- a/.gitignore
+++ b/.gitignore
@@ -1,5 +1,7 @@
 *.sublime-project
 *.sublime-workspace
 node_modules
+fetchlogs
+sessionexports
 bundle.js
 target
diff --git a/src/main.js b/src/main.js
index 6d6ed505..9e973bb9 100644
--- a/src/main.js
+++ b/src/main.js
@@ -1,4 +1,6 @@
 import HomeServerApi from "./matrix/hs-api.js";
+// import {RecordRequester, ReplayRequester} from "./matrix/net/replay.js";
+import fetchRequest from "./matrix/net/fetch.js";
 import StorageFactory from "./matrix/storage/idb/create.js";
 import SessionsStore from "./matrix/sessions-store/localstorage/SessionsStore.js";
 import BrawlViewModel from "./domain/BrawlViewModel.js";
@@ -6,9 +8,21 @@ import BrawlView from "./ui/web/BrawlView.js";
 
 export default async function main(container) {
     try {
+        // to replay:
+        // const fetchLog = await (await fetch("/fetchlogs/constrainterror.json")).json();
+        // const replay = new ReplayRequester(fetchLog, {delay: false});
+        // const request = replay.request;
+
+        // to record:
+        // const recorder = new RecordRequester(fetchRequest);
+        // const request = recorder.request;
+        // window.getBrawlFetchLog = () => recorder.log();
+
+        // normal network:
+        const request = fetchRequest;
         const vm = new BrawlViewModel({
             storageFactory: new StorageFactory(),
-            createHsApi: (homeServer, accessToken = null) => new HomeServerApi(homeServer, accessToken),
+            createHsApi: (homeServer, accessToken = null) => new HomeServerApi({homeServer, accessToken, request}),
             sessionStore: new SessionsStore("brawl_sessions_v1"),
             clock: Date //just for `now` fn
         });
diff --git a/src/matrix/hs-api.js b/src/matrix/hs-api.js
index 2c9b5548..d4f9e1f7 100644
--- a/src/matrix/hs-api.js
+++ b/src/matrix/hs-api.js
@@ -1,30 +1,25 @@
 import {
     HomeServerError,
-    RequestAbortError,
-    NetworkError
 } from "./error.js";
 
 class RequestWrapper {
-    constructor(promise, controller) {
-        if (!controller) {
-            const abortPromise = new Promise((_, reject) => {
-                this._controller = {
-                    abort() {
-                        const err = new Error("fetch request aborted");
-                        err.name = "AbortError";
-                        reject(err);
-                    }
-                };
-            });
-            this._promise = Promise.race([promise, abortPromise]);
-        } else {
-            this._promise = promise;
-            this._controller = controller;
-        }
+    constructor(method, url, requestResult) {
+        this._requestResult = requestResult;
+        this._promise = this._requestResult.response().then(response => {
+            // ok?
+            if (response.status >= 200 && response.status < 300) {
+                return response.body;
+            } else {
+                switch (response.status) {
+                    default:
+                        throw new HomeServerError(method, url, response.body);
+                }
+            }
+        });
     }
 
     abort() {
-        this._controller.abort();
+        return this._requestResult.abort();
     }
 
     response() {
@@ -32,13 +27,13 @@ class RequestWrapper {
     }
 }
 
-// todo: everywhere here, encode params in the url that could have slashes ... mainly event ids?
 export default class HomeServerApi {
-    constructor(homeserver, accessToken) {
+    constructor({homeServer, accessToken, request}) {
         // store these both in a closure somehow so it's harder to get at in case of XSS?
         // one could change the homeserver as well so the token gets sent there, so both must be protected from read/write
-        this._homeserver = homeserver;
+        this._homeserver = homeServer;
         this._accessToken = accessToken;
+        this._requestFn = request;
     }
 
     _url(csPath) {
@@ -66,42 +61,12 @@ export default class HomeServerApi {
             headers.append("Content-Type", "application/json");
             bodyString = JSON.stringify(body);
         }
-        const controller = typeof AbortController === "function" ? new AbortController() : null;
-        // TODO: set authenticated headers with second arguments, cache them
-        let promise = fetch(url, {
+        const requestResult = this._requestFn(url, {
             method,
             headers,
             body: bodyString,
-            signal: controller && controller.signal,
-            mode: "cors",
-            credentials: "omit",
-            referrer: "no-referrer",
-            cache: "no-cache",
         });
-        promise = promise.then(async (response) => {
-            if (response.ok) {
-                return await response.json();
-            } else {
-                switch (response.status) {
-                    default:
-                        throw new HomeServerError(method, url, await response.json())
-                }
-            }
-        }, err => {
-            if (err.name === "AbortError") {
-                throw new RequestAbortError();
-            } else if (err instanceof TypeError) {
-                // Network errors are reported as TypeErrors, see
-                // https://developer.mozilla.org/en-US/docs/Web/API/Fetch_API/Using_Fetch#Checking_that_the_fetch_was_successful
-                // this can either mean user is offline, server is offline, or a CORS error (server misconfiguration).
-                // 
-                // One could check navigator.onLine to rule out the first
-                // but the 2 later ones are indistinguishable from javascript.
-                throw new NetworkError(`${method} ${url}: ${err.message}`);
-            }
-            throw err;
-        });
-        return new RequestWrapper(promise, controller);
+        return new RequestWrapper(method, url, requestResult);
     }
 
     _post(csPath, queryParams, body) {
diff --git a/src/matrix/net/fetch.js b/src/matrix/net/fetch.js
new file mode 100644
index 00000000..48a13969
--- /dev/null
+++ b/src/matrix/net/fetch.js
@@ -0,0 +1,66 @@
+import {
+    RequestAbortError,
+    NetworkError
+} from "../error.js";
+
+class RequestResult {
+    constructor(promise, controller) {
+        if (!controller) {
+            const abortPromise = new Promise((_, reject) => {
+                this._controller = {
+                    abort() {
+                        const err = new Error("fetch request aborted");
+                        err.name = "AbortError";
+                        reject(err);
+                    }
+                };
+            });
+            this._promise = Promise.race([promise, abortPromise]);
+        } else {
+            this._promise = promise;
+            this._controller = controller;
+        }
+    }
+
+    abort() {
+        this._controller.abort();
+    }
+
+    response() {
+        return this._promise;
+    }
+}
+
+export default function fetchRequest(url, options) {
+    const controller = typeof AbortController === "function" ? new AbortController() : null;
+    if (controller) {
+        options = Object.assign(options, {
+            signal: controller.signal
+        });
+    }
+    options = Object.assign(options, {
+        mode: "cors",
+        credentials: "omit",
+        referrer: "no-referrer",
+        cache: "no-cache",
+    });
+    const promise = fetch(url, options).then(async response => {
+        const {status} = response;
+        const body = await response.json();
+        return {status, body};
+    }, err => {
+        if (err.name === "AbortError") {
+            throw new RequestAbortError();
+        } else if (err instanceof TypeError) {
+            // Network errors are reported as TypeErrors, see
+            // https://developer.mozilla.org/en-US/docs/Web/API/Fetch_API/Using_Fetch#Checking_that_the_fetch_was_successful
+            // this can either mean user is offline, server is offline, or a CORS error (server misconfiguration).
+            // 
+            // One could check navigator.onLine to rule out the first
+            // but the 2 later ones are indistinguishable from javascript.
+            throw new NetworkError(`${options.method} ${url}: ${err.message}`);
+        }
+        throw err;
+    });
+    return new RequestResult(promise, controller);
+}
diff --git a/src/matrix/net/replay.js b/src/matrix/net/replay.js
new file mode 100644
index 00000000..b6ddcb74
--- /dev/null
+++ b/src/matrix/net/replay.js
@@ -0,0 +1,108 @@
+import {
+    RequestAbortError,
+    NetworkError
+} from "../error.js";
+
+class RequestLogItem {
+    constructor(url, options) {
+        this.url = url;
+        this.options = options;
+        this.error = null;
+        this.body = null;
+        this.status = status;
+        this.start = performance.now();
+        this.end = 0;
+    }
+
+    async handleResponse(response) {
+        this.end = performance.now();
+        this.status = response.status;
+        this.body = response.body;
+    }
+
+    handleError(err) {
+        this.end = performance.now();
+        this.error = {
+            aborted: err instanceof RequestAbortError,
+            network: err instanceof NetworkError,
+            message: err.message,
+        };
+    }
+}
+
+export class RecordRequester {
+    constructor(request) {
+        this._origRequest = request;
+        this._requestLog = [];
+        this.request = this.request.bind(this);
+    }
+
+    request(url, options) {
+        const requestItem = new RequestLogItem(url, options);
+        this._requestLog.push(requestItem);
+        try {
+            const requestResult = this._origRequest(url, options);
+            requestResult.response().then(response => {
+                requestItem.handleResponse(response);
+            });
+            return requestResult;
+        } catch (err) {
+            requestItem.handleError(err);
+            throw err;
+        }
+    }
+
+    log() {
+        return this._requestLog;
+    }
+}
+
+export class ReplayRequester {
+    constructor(log, options) {
+        this._log = log.slice();
+        this._options = options;
+        this.request = this.request.bind(this);
+    }
+
+    request(url, options) {
+        const idx = this._log.findIndex(item => {
+            return item.url === url && options.method === item.options.method;
+        });
+        if (idx === -1) {
+            return new ReplayRequestResult({status: 404}, options);
+        } else {
+            const [item] = this._log.splice(idx, 1);
+            return new ReplayRequestResult(item, options);
+        }
+    }
+}
+
+class ReplayRequestResult {
+    constructor(item, options) {
+        this._item = item;
+        this._options = options;
+        this._aborted = false;
+    }
+
+    abort() {
+        this._aborted = true;
+    }
+
+    async response() {
+        if (this._options.delay) {
+            const delay = this._item.end - this._item.start;
+            await new Promise(resolve => setTimeout(resolve, delay));
+        }
+        if (this._item.error || this._aborted) {
+            const error = this._item.error;
+            if (error.aborted || this._aborted) {
+                throw new RequestAbortError(error.message);
+            } else if (error.network) {
+                throw new NetworkError(error.message);
+            } else {
+                throw new Error(error.message);
+            }
+        }
+        return this._item;
+    }
+}