Re: [PATCH v4 2/4] util/qemu-sockets.c: Split host:port parsing out of inet_parse

[Doug Evans <dje@google.com>]

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On Mon, Feb 22, 2021 at 1:39 AM Daniel P. Berrangé <berrange@redhat.com>
wrote:

> On Fri, Feb 19, 2021 at 02:17:42PM -0800, Doug Evans wrote:
> > On Fri, Feb 19, 2021 at 2:00 AM Daniel P. Berrangé <berrange@redhat.com>
> > wrote:
> >
> > > On Thu, Feb 18, 2021 at 12:15:36PM -0800, Doug Evans wrote:
> > > > The parsing is moved into new function inet_parse_host_and_port.
> > > > This is done in preparation for using the function in net/slirp.c.
> > > >
> > > > Signed-off-by: Doug Evans <dje@google.com>
> > > > ---
> > > >
> > > > Changes from v3:
> > > > - this patch is new in v4
> > > >   - provides new utility: inet_parse_host_and_port, updates
> inet_parse
> > > >     to use it
> > > >
> > > >  include/qemu/sockets.h |  3 ++
> > > >  util/qemu-sockets.c    | 94
> +++++++++++++++++++++++++++++++-----------
> > > >  2 files changed, 72 insertions(+), 25 deletions(-)
> > > >
> > > > diff --git a/include/qemu/sockets.h b/include/qemu/sockets.h
> > > > index 7d1f813576..f720378a6b 100644
> > > > --- a/include/qemu/sockets.h
> > > > +++ b/include/qemu/sockets.h
> > > > @@ -31,6 +31,9 @@ int socket_set_fast_reuse(int fd);
> > > >
> > > >  int inet_ai_family_from_address(InetSocketAddress *addr,
> > > >                                  Error **errp);
> > > > +const char* inet_parse_host_and_port(const char* str, int
> terminator,
> > > > +                                     char **addr, char **port, bool
> > > *is_v6,
> > > > +                                     Error **errp);
> > > >  int inet_parse(InetSocketAddress *addr, const char *str, Error
> **errp);
> > > >  int inet_connect(const char *str, Error **errp);
> > > >  int inet_connect_saddr(InetSocketAddress *saddr, Error **errp);
> > > > diff --git a/util/qemu-sockets.c b/util/qemu-sockets.c
> > > > index 8af0278f15..9fca7d9212 100644
> > > > --- a/util/qemu-sockets.c
> > > > +++ b/util/qemu-sockets.c
> > > > @@ -615,44 +615,88 @@ static int inet_parse_flag(const char
> *flagname,
> > > const char *optstr, bool *val,
> > > >      return 0;
> > > >  }
> > > >
> > > > -int inet_parse(InetSocketAddress *addr, const char *str, Error
> **errp)
> > > > +/*
> > > > + * Parse an inet host and port as "host:port<terminator>".
> > > > + * Terminator may be '\0'.
> > > > + * The syntax for ipv4 addresses is: address:port.
> > > > + * The syntax for ipv6 addresses is: [address]:port.
> > >
> > > It also supports
> > >
> > >    "The syntax for hostnames is hostname:port
> > >
> > > > + * On success, returns a pointer to the terminator. Space for the
> > > address and
> > > > + * port is malloced and stored in *host, *port, the caller must
> free.
> > > > + * *is_v6 indicates whether the address is ipv4 or ipv6. If ipv6
> then
> > > the
> > > > + * surrounding [] brackets are removed.
> > >
> > > When is_v6 is true, it indicates that a numeric ipv6 address was given.
> > > When false either a numberic ipv4 address or hostname was given.
> > >
> > > > + * On failure NULL is returned with the error stored in *errp.
> > > > + */
> > > > +const char* inet_parse_host_and_port(const char* str, int
> terminator,
> > > > +                                     char **hostp, char **portp,
> bool
> > > *is_v6,
> > > > +                                     Error **errp)
> > > >  {
> > > > -    const char *optstr, *h;
> > > > +    const char *terminator_ptr = strchr(str, terminator);
> > > > +    g_autofree char *buf = NULL;
> > > >      char host[65];
> > > >      char port[33];
> > > > -    int to;
> > > > -    int pos;
> > > > -    char *begin;
> > > >
> > > > -    memset(addr, 0, sizeof(*addr));
> > > > +    if (terminator_ptr == NULL) {
> > > > +        /* If the terminator isn't found then use the entire
> string. */
> > > > +        terminator_ptr = str + strlen(str);
> > > > +    }
> > > > +    buf = g_strndup(str, terminator_ptr - str);
> > > >
> > > > -    /* parse address */
> > > > -    if (str[0] == ':') {
> > > > -        /* no host given */
> > > > -        host[0] = '\0';
> > > > -        if (sscanf(str, ":%32[^,]%n", port, &pos) != 1) {
> > > > -            error_setg(errp, "error parsing port in address '%s'",
> str);
> > > > -            return -1;
> > > > -        }
> > >
> > >
> > > > -    } else if (str[0] == '[') {
> > > > +    if (buf[0] == '[') {
> > > >          /* IPv6 addr */
> > > > -        if (sscanf(str, "[%64[^]]]:%32[^,]%n", host, port, &pos) !=
> 2) {
> > > > -            error_setg(errp, "error parsing IPv6 address '%s'",
> str);
> > > > -            return -1;
> > > > +        if (buf[1] == ']') {
> > > > +            /* sscanf %[ doesn't recognize empty contents. */
> > > > +            host[0] = '\0';
> > > > +            if (sscanf(buf, "[]:%32s", port) != 1) {
> > > > +                error_setg(errp, "error parsing IPv6 host:port
> '%s'",
> > > buf);
> > > > +                return NULL;
> > > > +            }
> > >
> > > This is introducing new functionality to the parser. Current callers
> > > let empty string ":port" be used for both ipv4 and ipv6, based
> > > on whether the flags ",ipv4[=on|off],ipv6[=on|off]" later follow.
> > >
> >
> >
> > We're creating a new utility subroutine: Let's decide what the API is for
> > it.
> > The fact that inet_parse is passed additional parameters to specify ipv4
> vs
> > ipv6 is not something this new subroutine should care about.
> >
> > I presume you want an explicit way to represent an empty ipv6 hostname
> > > to avoid changing semantics for existing slirp CLI args, where the
> > > existing ":port" exclusively means ipv4. IIC, this is also why you
> > > needed to introduce the "is_v6" flag, because any non-empty address
> > > can be reliably parsed without needing this flag.
> > >
> >
> >
> > Actually, no. The "is_v6" flag is needed because otherwise the caller has
> > no means (other than maybe subsequent grepping for "." vs ":") for
> knowing
> > whether str contained "address" or "[address]".
> >
> > Plus, for my needs I don't need to support "[hostname]". If someone later
> > wants that supported that can be designed then.
> > Thus supporting "[hostname]" is not something I'm considering in this
> > patchset.
> >
> >
> >
> > >
> > > This is reasonable, but any such functional change should be in a
> > > separate commit from refactoring.
> > >
> > > IOW, remove this and the is_v6 flag, and add them in a separate
> > > patch to explain to the need for new functionality in the parsing.
> > >
> > > Given that existing callers don't need to support "[]", we should
> > > not let that be parsed, unless the caller passing a "is_v6" pointer
> > > which is not NULL.
> > >
> > > > +        } else {
> > > > +            if (sscanf(buf, "[%64[^]]]:%32s", host, port) != 2) {
> > > > +                error_setg(errp, "error parsing IPv6 host:port
> '%s'",
> > > buf);
> > > > +                return NULL;
> > > > +            }
> > > >          }
> > > >      } else {
> > > > -        /* hostname or IPv4 addr */
> > > > -        if (sscanf(str, "%64[^:]:%32[^,]%n", host, port, &pos) !=
> 2) {
> > > > -            error_setg(errp, "error parsing address '%s'", str);
> > > > -            return -1;
> > > > +        if (buf[0] == ':') {
> > > > +            /* no host given */
> > > > +            host[0] = '\0';
> > > > +            if (sscanf(buf, ":%32s", port) != 1) {
> > > > +                error_setg(errp, "error parsing host:port '%s'",
> buf);
> > > > +                return NULL;
> > > > +            }
> > >
> > > It would be preferreable if the parsing code was not re-ordered when
> > > extracting it. It doesn't look like a functional change, but I'm unsure
> > > why you moved it ?
> > >
> > > > +        } else {
> > > > +            /* hostname or IPv4 addr */
> > > > +            if (sscanf(buf, "%64[^:]:%32s", host, port) != 2) {
> > > > +                error_setg(errp, "error parsing host:port '%s'",
> buf);
> > > > +                return NULL;
> > > > +            }
> > > >          }
> > > >      }
> > > >
> > > > -    addr->host = g_strdup(host);
> > > > -    addr->port = g_strdup(port);
> > > > +    *hostp = g_strdup(host);
> > > > +    *portp = g_strdup(port);
> > > > +    *is_v6 = buf[0] == '[';
> > > > +
> > > > +    return terminator_ptr;
> > > > +}
> > > > +
> > > > +int inet_parse(InetSocketAddress *addr, const char *str, Error
> **errp)
> > > > +{
> > > > +    const char *optstr, *h;
> > > > +    bool is_v6;
> > > > +    int to;
> > > > +    int pos;
> > > > +    char *begin;
> > > > +
> > > > +    memset(addr, 0, sizeof(*addr));
> > > > +
> > > > +    optstr = inet_parse_host_and_port(str, ',', &addr->host,
> > > &addr->port,
> > > > +                                      &is_v6, errp);
> > >
> > > Just pass NULL since we don't need is_v6
> > >
> > > > +    if (optstr == NULL) {
> > > > +        return -1;
> > > > +    }
> > > >
> > > >      /* parse options */
> > > > -    optstr = str + pos;
> > > >      h = strstr(optstr, ",to=");
> > > >      if (h) {
> > > >          h += 4;
> > > > --
> > > > 2.30.0.617.g56c4b15f3c-goog
> > > >
> >
> >
> >
> > I can certainly defer [] handling to a later patch series.
> > Splitting the patch into one with the is_v6 flag and one without is a lot
> > of work for little gain (zero IMO): When looking at
> > inet_parse_host_and_port() as its own utility subroutine, not providing
> the
> > caller with the means to distinguish whether str was "address:port" or
> > "[address]:port" is a poor API.
>
> In general callers shouldn't care about which format was parsed. The use
> of [] is just a mechanism to reliably separate the port from the address.
> Once you have the address part getaddrinfo() will reliably parse the
> address into a sockaddr struct on its own. The is_v6 flag is only needed
> for the legacy compat needs in slirp, even that is only if we want to
> have strict equivalence with historical behaviour, as opposed to changing
> empty string to mean to listen on both IPv4+6 concurrently..
>


I guess I'll wait for Samuel to review the net/slirp changes. No point in
continually sending revisions until then.

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