Is there any proper documentation with examples for librpm 6.x?

[3millionminds]

Hello,

I'm trying to use librpm mixed into a Go program to get a list of all the packages installed on the system.

The documentation at https://rpm-software-management.github.io/rpm/api/index.html
only provides minimal explanations as to what the functions do,
but no explanation as to what how to use them - as in, there is no explanation that I have found that tell you to connect to the DB, instantiate a cursor, etc.

I ran across this documentation but it's from the year 2000 and very much out of date:
http://ftp.rpm.org/max-rpm/index.html

Is there any documentation with examples, or at least an outline of the process of actually querying the rpmDB with this library, anywhere?

I just need to dump all the installed RPMs with their names and versions.

Cheers.

[pmatilai]

No, we don't have a tutorial.

We have a bunch of Python examples that might help you navigate the C API though: https://github.com/rpm-software-management/rpm/tree/master/python/examples

For C examples, you'll need to go read other people's code.

[3millionminds]

Not ideal, but thanks.

Here's a full example for anyone else looking for a pure C implementation.
May not be 100% correct since C isn't my thing exactly but it works just like rpm -qa would.

#include <rpm/rpmts.h>
#include <rpm/rpmdb.h>
// #include <rpm/header.h>
#include <rpm/rpmcli.h>
#include <stdio.h>
#include <fcntl.h>

int main(void)
{
    
    rpmReadConfigFiles(NULL, NULL);
    rpmts ts = rpmtsCreate();
    if (!ts) {
        fprintf(stderr, "Failed to create rpmts\n");
        return 1;
    }

    /* Open DB in read-only mode */
    if (rpmtsOpenDB(ts, O_RDONLY) != 0) {
        fprintf(stderr, "Failed to open RPM database\n");
        rpmtsFree(ts);
        return 1;
    }

    /* NULL keyp == sequential iteration over all installed packages */
    rpmdbMatchIterator mi = rpmtsInitIterator(ts, RPMDBI_PACKAGES, NULL, 0);
    if (!mi) {
        fprintf(stderr, "Failed to create match iterator\n");
        rpmtsFree(ts);
        return 1;
    }

    Header h;
    while ((h = rpmdbNextIterator(mi)) != NULL) {
        const char *name = headerGetString(h, RPMTAG_NAME);
        const char *epoch = headerGetString(h, RPMTAG_EPOCH);
        const char *version = headerGetString(h, RPMTAG_VERSION);
        const char *release = headerGetString(h, RPMTAG_RELEASE);

        if (name && version && release)
            printf("%s-%s-%s-%s\n", name, epoch, version, release);
    }

    /* Cleanup */
    rpmdbFreeIterator(mi);
    rpmtsFree(ts);

    return 0;
}

[pmatilai]

Note that if you just want formatted strings from a header, that's easier with headerFormat():

char *nevr = headerFormat(h, "%{name}-%{epoch}-%{version}-%{release}", NULL);
printf("%s\n", nevr);
free(nevr);

Or for the traditional n-[e:]vr formatted string, just

char *nevr = headerFormat(h, "%{nevr}", NULL);

...or if you prefer a variant that will catch errors at compile-time, the N(E)VR(A) variants are also available as tag extensions, eg RPMTAG_NEVR, RPMTAG_NVR, RPMTAG_NVRA, and so on:

char *nevr = headerGetAsString(h, RPMTAG_NEVR);

[3millionminds]

Thanks for the tip!

Ideally I'll put it all in a struct and convert it to JSON, since that's the final form I am aiming for.

I'll play around with more tomorrow.

Cheers

[pmatilai]

If JSON is the format you're after then rpm >= 4.20 can do that for you: rpm -qa --json

From the API, that'd be calling headerFormat(h, "[%{*:json}]", NULL); on the headers that you want (all in this case I suppose). The caveat is that this outputs all the tags, which might be more than you want. You can use the :json formatter on any tag individually too to get the value, eg %{name:json}, but then you'll need to format the rest of the JSON by yourself.

[3millionminds]

That is extremely useful, thanks @pmatilai !