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

["Daniel P. Berrangé" <berrange@redhat.com>]

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.

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.

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
> 

Regards,
Daniel
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