Program that routes stdin to other files/programs based on prefix?

Question

I am looking for a program or (probably C)-code which I will refer to as route which takes a bytestring/stream on stdin and routes it to one of n programs, based on the intial few bytes (the prefix). The prefix will not be forwarded/piped to the destination program. I would imagine it would have a commandline interface like:

echo -n 'for-p1.perform-operation-A' | route 'for-p1.' >(program1) 'for-p2.' >(program2)
echo -n 'for-p2.perform-operation-B' | route 'for-p1.' >(program1) 'for-p2.' >(program2)

in the example given above, program1 would receive 'perform-operation-A' (as if I had executed `echo 'perform-operation-A' | program1), program2 would receive 'perform-operation-B'. The prefix always precedes the (virtual) filename of the destination.

Is there any existing solution for doing this or do I have to roll my own?

EDIT: By popular request, here is my 30min attempt at a solution, but I would vastly prefer existing solutions, or at least recommendations for libraries for the steps:

/*
build:
    sudo apt install -y build-essential && g++ main.cpp

usage example:

(
    rm output* || true
    echo -n "foo-hello" | ./a.out 2>/dev/null 'foo-' >(cat | tee -a output-foo) 'bar-' >(cat | tee -a output-bar) 1>/dev/null
    echo -n "bar-world" | ./a.out 2>/dev/null 'foo-' >(cat | tee -a output-foo) 'bar-' >(cat | tee -a output-bar) 1>/dev/null
    echo
    echo -n "output-foo: " ; cat output-foo ; echo
    echo -n "output-bar: " ; cat output-bar ; echo
)
*/

#include <fcntl.h>
#include <stdio.h>
#include <map>
#include <string>
using namespace std;

typedef FILE* File;

#define hasKey(map, key) (map.find((key)) != map.end())

// I assume this is pretty inefficient, looking for a good solution
void pipeRest(File fromFile, File toFile) {
    size_t bytesRead = 0;
    
    do {
        char data;
        bytesRead = fread(&data, 1, 1, fromFile);
        if (bytesRead) fwrite(&data, 1, 1, toFile);
    } while (bytesRead > 0);
}

int main(
    int const argc,
    char const * const * const argv
) {
    if (argc <= 1) {
        fprintf(stderr, "usage:\n\n\troute prefix1 >(ouput-program-1) prefix2 >(output-program-2) ...\n\nreads from stdin, recognizes any of n prefixes and pipes the rest to the filename following the prefix\n");
        exit(1);
    }

    // Parse [prefix outputFile] pairs from commandline args
    map<string, string> prefixesToOutputFileNames; 
    map<string, File> prefixesToOutputFiles; 
    for (int i = 0; i < argc; i++) {
        fprintf(stderr, "argv[%d] = '%s'\n", i, argv[i]);

        if (i > 0 && i % 2 == 0) {
            auto const prefix = argv[i - 1];
            fprintf(stderr, "prefix = '%s'\n", prefix);
            auto const outputFileName = argv[i];
            fprintf(stderr, "outputFileName = '%s'\n", outputFileName);
            prefixesToOutputFileNames[prefix] = outputFileName;

            auto const outputFile = fopen(outputFileName, "wb");
            
            prefixesToOutputFiles[prefix] = outputFile;
        }
    }

    // Start reading bytes from stdin, collect the prefix
    freopen(0, "rb", stdin); 

    string prefix = "";
    char nextPrefixChar[2] = { 0 };
    size_t bytesRead = 0;
    
    do {
        bytesRead = fread(nextPrefixChar, 1, 1, stdin);
        prefix += nextPrefixChar;
        fprintf(stderr, "read %zd bytes = '%s', prefix = '%s'\n", bytesRead, bytesRead ? nextPrefixChar : 0, prefix.c_str());

        if (hasKey(prefixesToOutputFiles, prefix)) {
            // Prefix found -> pipe to corresponding output file

            auto const outputFileName = prefixesToOutputFileNames[prefix];
            fprintf(stderr, "prefix '%s' was recognized, will pipe rest to '%s'\n", prefix.c_str(), outputFileName.c_str());

            auto const outputFile = prefixesToOutputFiles[prefix];
            pipeRest(stdin, outputFile);
            exit(0);
        }
    } while (bytesRead > 0);
    
    fprintf(stderr, "input ends and did not recognize any prefix, rest will be piped to stdout\n");
    
    pipeRest(stdin, stdout);

    return 0;
}

Answer 1

In bash shell, you would write just:

tee >(sed -n 's/^for\.p1\.//p' | program1) | sed -n 's/^for\.p2\.//p' | program2

The following program:

filter() {
    keyword=$1
    shift
    # https://stackoverflow.com/questions/407523/escape-a-string-for-a-sed-replace-pattern
    keyword=$(printf '%s\n' "$keyword" | sed -e 's/[]\/$*.^[]/\\&/g');
    LC_ALL=C sed -n "s/^$keyword//p" | "$@"
}
hexfilter() {
    keyword=$1
    shift
    keyword=$(printf '%s\n' "$keyword" | sed -e 's/../[\\x&]/g');
    LC_ALL=C sed -n "s/^$keyword//p" | "$@"
}
program1() { :; }
program2() { :; }

echo -e '\x00\xca\xfe\x2a world!' |
{ tee >(filter 'for.p1.' program1 >&3) >(hexfilter '00cafe2a' sed 's/^/Hello/' >&3) | filter 'for.p2.' program2 >&3; } 3>&1 |
cat

filters prefix 0x00 0xca 0xfe 0x2a and outputs Hello world!.