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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(uint32_t tag);
__attribute__((import_module("env"), import_name("yomo_context_tag")))
extern uint32_t get_tag();
__attribute__((import_module("env"), import_name("yomo_context_data_size")))
extern size_t get_input_size();
__attribute__((import_module("env"), import_name("yomo_context_data")))
extern size_t load_input(char *pointer, size_t length);
__attribute__((import_module("env"), import_name("yomo_write")))
extern int32_t dump_output(uint32_t tag, const char *pointer, size_t length);
void yomo_init() {
void yomo_handler() {
    // load input tag & data
    uint32_t tag = get_tag();
    size_t length = get_input_size();
    char *input = malloc(length);
    load_input(input, length);
    printf("wasm c sfn received %zu bytes with tag[%#x]\n", length, tag);
    // process app data
    char *output = malloc(length);
    for (size_t i = 0; i < length; i++) {
        output[i] = toupper(input[i]);
    // dump output data
    dump_output(0x34, output, length);

Compile to WASI (opens in a new tab)

# download wasi-sdk from,
# and specify wasi-sdk version and path
$ export WASI_VERSION_FULL=20.0
$ export WASI_SDK_PATH=~/Downloads/wasi-sdk-$WASI_VERSION_FULL
$ $WASI_SDK_PATH/bin/clang --target=wasm32-wasi \
    --sysroot=$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