Skip to content
Write StreamFunction in C

Implement StreamFunction in C


This feature is currently in alpha and subject to change.

Install CLI

$ curl -fsSL "" | sh

Write a StreamFunction in C

#include <ctype.h>
#include <stdio.h>
#include <stdlib.h>
__attribute__((import_module("env"), import_name("yomo_observe_datatag")))
extern void observe_datatag(uint32_t tag);
__attribute__((import_module("env"), import_name("yomo_load_input")))
extern void load_input(char *pointer);
__attribute__((import_module("env"), import_name("yomo_dump_output")))
extern void dump_output(uint32_t tag, const char *pointer, size_t length);
void yomo_init() {
void yomo_handler(size_t input_length) {
    printf("wasm c sfn received %zu bytes\n", input_length);
    // load input data
    char *input = malloc(input_length);
    // process app data
    size_t output_length = input_length;
    char *output = malloc(output_length);
    for (size_t i = 0; i < input_length; i++) {
        output[i] = toupper(input[i]);
    // dump output data
    dump_output(0x34, output, output_length);

Compile to WASI (opens in a new tab)

$ export WASI_VERSION_FULL=16.0
$ export WASI_SDK_PATH=~/Downloads/wasi-sdk-$WASI_VERSION_FULL
$ WASI_SDK_PATH/bin/clang --target=wasm32-unknown-wasi \
    --sysroot=$WASI_SDK_PATH/share/wasi-sysroot \
    -nostartfiles -fvisibility=hidden -O3 \
    -Wl,--no-entry,--export=yomo_init,--export=yomo_handler \
    -o sfn.wasm sfn.c

Run Streaming Serverless Function

yomo run /path/to/sfn.wasm