add docker build

Dockerfile

@@ -0,0 +1,13 @@
+FROM ubuntu:19.04
+
+RUN apt-get update \
+ && apt-get install -y ca-certificates \
+                       curl \
+                       git \
+                       make
+
+RUN curl -L https://github.com/CraneStation/wasi-sdk/releases/download/wasi-sdk-4/wasi-sdk-4.0-linux-amd64.tar.gz | tar xz --strip-components=1 -C /
+
+VOLUME /code
+WORKDIR /code
+CMD make

Makefile

@@ -1,9 +1,10 @@
 TARGET = hello_world
-CC = clang
-SYSROOT = --sysroot=/tmp/wasi-sdk/
-TARGET_TRIPLE = --target=wasm32-unknown-wasi
-CFLAGS = -nostartfiles -fvisibility=hidden -Wl,--no-entry,--demangle,--allow-undefined
-EXPORT_FUNCS = -Wl,--export=allocate,--export=deallocate,--export=invoke
+CC = /opt/wasi-sdk/bin/clang
+SYSROOT = /opt/wasi-sdk/share/sysroot
+TARGET_TRIPLE = wasm32-unknown-wasi
+CFLAGS = -nostartfiles -fvisibility=hidden
+LDFLAGS = -Wl,--no-entry,--demangle,--allow-undefined
+EXPORT_FUNCS = --export=allocate,--export=deallocate,--export=invoke
 SDK = sdk/allocator.c sdk/logger.c
 
 .PHONY: default all clean
@@ -12,7 +13,7 @@ default: $(TARGET)
 all: default
 
 $(TARGET): main.c $(SDK)
-	$(CC) $(SYSROOT) $(TARGET_TRIPLE) $(CFLAGS) $(EXPORT_FUNCS) $^ -o $@.wasm
+	$(CC) --sysroot=$(SYSROOT) --target=$(TARGET_TRIPLE) $(CFLAGS) $(LDFLAGS) -Wl,$(EXPORT_FUNCS) $^ -o $@.wasm
 
 .PRECIOUS: $(TARGET)
 

README.md

@@ -1,9 +1,12 @@
-# C template
+# How to build
 
-Template backend project for Rust
-
-## How to compile
+This app could be built either with docker 
 
 ```bash
-~$ make
-```
+docker-compose up
+```
+
+or by Makefile with [wasi-sdk](https://github.com/CraneStation/wasi-sdk) installed
+```bash
+make
+```

docker-compose.yml

@@ -0,0 +1,7 @@
+version: '3'
+services:
+  hello_world:
+    build:
+      context: .
+    volumes:
+     - .:/code

main.c

@@ -1,6 +1,25 @@
 #include "sdk/allocator.h"
 #include "sdk/logger.h"
+#include <string.h>
+
+const char *const greeting = "Hello world! From ";
+const int RESPONSE_SIZE_BYTES = 4;
 
 char *invoke(const char *str, int length) {
+    const size_t greeting_length = strlen(greeting);
+    // TODO: add check for overflow
+    const size_t response_length = length + RESPONSE_SIZE_BYTES + greeting_length;
 
+    char *response = (char *)allocate(response_length);
+
+    wasm_log(str, length);
+
+    for(int i = 0; i < RESPONSE_SIZE_BYTES; ++i) {
+        response[i] = (response_length >> 8*i) & 0xFF;
+    }
+
+    memcpy(response + RESPONSE_SIZE_BYTES, greeting, greeting_length);
+    memcpy(response + RESPONSE_SIZE_BYTES + greeting_length, str, length);
+
+    return response;
 }

sdk/allocator.h

@@ -3,10 +3,25 @@
 
 #include <stddef.h> // for size_t
 
-// used by Wasm VM for byte array passing (should be exported from module)
+/**
+ * Allocates a memory region of given size.
+ *
+ * Used by Wasm VM for byte array passing. Should be exported from module.
+ *
+ * @param size a size of needed memory region.
+ * @return a pointer to allocated memory region.
+ */
 void *allocate(size_t size);
 
-// used by Wasm VM for freeing previous memory allocated by allocate function
+/**
+ * Frees a memory region.
+ *
+ * Used by Wasm VM for freeing previous memory allocated by `allocate` function.
+ * Should be exported from module.
+ *
+ * @param ptr the pointer to the previously allocated memory region.
+ * @param size the size of the previously allocated memory region.
+ */
 void deallocate(void *ptr, size_t size);
 
 #endif //FLUENCE_C_SDK_ALLOCATOR_H

sdk/logger.h

@@ -1,7 +1,11 @@
 #ifndef FLUENCE_C_SDK_LOGGER_H
 #define FLUENCE_C_SDK_LOGGER_H
 
-// writes provided string to Wasm VM logger
+/**
+ * Writes provided string to Wasm VM logger.
+ *
+ * @param log_message a message that should be logged.
+ */
 void wasm_log(const char *str, int len);
 
 #endif //FLUENCE_C_SDK_LOGGER_H