emscripten

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Source code:

#include <stdio.h>
#include <stdlib.h>

int main(int argc, char** argv) {
    int a,b;
    while( scanf("%d %d",&a,&b)!=EOF){
        fflush(stdin);
        printf("%d %d\n", a, b);
    }
 return 0;   
}

In input.txt:

1 2
3 4
5 6

Run with "wasmtime a.wasm < input.txt" or "wasmer a.wasm < input.txt", the output is:

1 2

Is it a bug?

Looks like probably an emscripten bug yes. Something to do with the stdin handling most likely.

You can repro this without wasmtime or wasmer:

$ emcc test.c
node ./a.out.js < input.txt 
1 2

Surprisingly it also occurs with -sNODERAWFS which normally bypasses any bugs in the emscripten FS layers.