From eac59ec4c843df0f7461b9945ec7c1ae7273bd80 Mon Sep 17 00:00:00 2001
From: Yuchen Dai <silentdai@gmail.com>
Date: Mon, 11 Feb 2019 11:32:25 -0800
Subject: [PATCH] add instruction of compiling wasm_example filter

Including
- Set up enscripten environment
- With a valid enscripten, build out new .wasm file
---
 examples/wasm/README.md | 21 +++++++++++++++++++++
 1 file changed, 21 insertions(+)

diff --git a/examples/wasm/README.md b/examples/wasm/README.md
index 777ed0bc7892..a947c2d008b9 100644
--- a/examples/wasm/README.md
+++ b/examples/wasm/README.md
@@ -63,3 +63,24 @@ Curl output should include our headers:
 * Connection #0 to host localhost left intact
 }
 ```
+
+# Build WASM Binary
+## prerequisite
+1. [Download and install `emscripten`](https://emscripten.org/docs/getting_started/downloads.html#installation-instructions)
+2. Activate emsdk archived version 1.38.25 (Note: by 02/11/2019 the latest build is broken for envoy-wasm)
+
+```
+# in emsdk directory
+./emsdk install sdk-1.38.25-64bit
+./emsdk activate sdk-1.38.25-64bit
+source emsdk_env.sh
+# verify
+em++ -v 2>&1 |grep Emscripten  ## should output 1.38.25
+```
+3. Build wasm filter in envoy directory 
+
+```shell
+envoy/examples/wasm$ source <path/to/emsdk>/emsdk_env.sh  # Only needed if in another shell session
+envoy/examples/wasm$ touch envoy_filter_http_wasm_example.cc && make
+```
+