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addr: Refactor find_my_address() to simplify it

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Instead of a complex if/else block, use a table of functions that have the
same interface and each of them attempt to find the address one after the
other.

Pointed out by nickm's during review.

Signed-off-by: David Goulet <dgoulet@torproject.org>
This commit is contained in:
David Goulet 2020-06-24 10:35:27 -04:00
parent 25a451bac7
commit 59f5c3d263
1 changed files with 99 additions and 78 deletions
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177
src/app/config/resolve_addr.c
View File

@ -22,19 +22,6 @@
/** Maximum "Address" statement allowed in our configuration. */
#define MAX_CONFIG_ADDRESS 2
/** Errors use when finding our IP address. Some are transient and some are
* persistent, just attach semantic to the values. They are all negative so
* one can do a catch all. */
#define ERR_FAIL_RESOLVE -1 /* Hostname resolution failed. */
#define ERR_GET_HOSTNAME -2 /* Unable to get local hostname. */
#define ERR_NO_OPT_ADDRESS -3 /* No Address in config. */
#define ERR_TOO_MANY_ADDRESS -4 /* Too many Address for one family. */
#define ERR_GET_INTERFACE -5 /* Unable to query network interface. */
#define ERR_UNUSABLE_ADDRESS -6 /* Unusable address. It is internal. */
#define ERR_DEFAULT_DIRAUTH -7 /* Using default authorities. */
#define ERR_ADDRESS_IS_INTERNAL -8 /* IP is internal. */
/** Ease our life. Arrays containing state per address family. These are to
* add semantic to the code so we know what is accessed. */
#define IDX_NULL 0 /* Index to zeroed address object. */
@ -42,6 +29,18 @@
#define IDX_IPV6 2 /* Index to AF_INET6. */
#define IDX_SIZE 3 /* How many indexes do we have. */
/** Function in our address function table return one of these code. */
typedef enum {
/* The address has been found. */
FN_RET_OK = 0,
/* The failure requirements were not met and thus it is recommended that the
* caller stops the search. */
FN_RET_BAIL = 1,
/* The address was not found or failure is transient so the caller should go
* to the next method. */
FN_RET_NEXT = 2,
} fn_address_ret_t;
/** Last resolved addresses. */
static tor_addr_t last_resolved_addrs[IDX_SIZE];
@ -80,6 +79,11 @@ resolved_addr_reset_last(int family)
tor_addr_make_null(&last_resolved_addrs[af_to_idx(family)], family);
}
/** Errors returned by address_can_be_used() in order for the caller to know
* why the address is denied or not. */
#define ERR_DEFAULT_DIRAUTH -1 /* Using default authorities. */
#define ERR_ADDRESS_IS_INTERNAL -2 /* IP is internal. */
/** @brief Return true iff the given IP address can be used as a valid
* external resolved address.
*
@ -151,11 +155,12 @@ address_can_be_used(const tor_addr_t *addr, const or_options_t *options,
* @return Return 0 on success that is an address has been found or resolved
* successfully. Return error code ERR_* found at the top of the file.
*/
static int
static fn_address_ret_t
get_address_from_config(const or_options_t *options, int warn_severity,
int family, const char **method_out,
char **hostname_out, tor_addr_t *addr_out)
{
int ret;
bool explicit_ip = false;
int num_valid_addr = 0;
@ -172,7 +177,8 @@ get_address_from_config(const or_options_t *options, int warn_severity,
if (!options->Address) {
log_info(LD_CONFIG, "No Address option found in configuration.");
return ERR_NO_OPT_ADDRESS;
/* No Address statement, inform caller to try next method. */
return FN_RET_NEXT;
}
for (const config_line_t *cfg = options->Address; cfg != NULL;
@ -199,11 +205,10 @@ get_address_from_config(const or_options_t *options, int warn_severity,
num_valid_addr++;
continue;
} else {
/* If we have hostname we are unable to resolve, it is an persistent
* error and thus we stop right away. */
/* Hostname that can't be resolved, this is a fatal error. */
log_fn(warn_severity, LD_CONFIG,
"Could not resolve local Address '%s'. Failing.", cfg->value);
return ERR_FAIL_RESOLVE;
return FN_RET_BAIL;
}
}
@ -211,18 +216,32 @@ get_address_from_config(const or_options_t *options, int warn_severity,
log_fn(warn_severity, LD_CONFIG,
"No Address option found for family %s in configuration.",
fmt_af_family(family));
return ERR_NO_OPT_ADDRESS;
/* No Address statement for family, inform caller to try next method. */
return FN_RET_NEXT;
}
if (num_valid_addr >= MAX_CONFIG_ADDRESS) {
/* Too many Address for same family. This is a fatal error. */
log_fn(warn_severity, LD_CONFIG,
"Found %d Address statement of address family %s. "
"Only one is allowed.", num_valid_addr, fmt_af_family(family));
return ERR_TOO_MANY_ADDRESS;
return FN_RET_BAIL;
}
/* Great, we found an address. */
return address_can_be_used(addr_out, options, warn_severity, explicit_ip);
ret = address_can_be_used(addr_out, options, warn_severity, explicit_ip);
if (ret != 0) {
/* One of the requirement of this interface is if an internal Address is
* used, custom authorities must be defined else it is a fatal error.
* Furthermore, if the Address was resolved to an internal interface, we
* stop immediately. */
return FN_RET_BAIL;
}
/* Address can be used. We are done. */
log_fn(warn_severity, LD_CONFIG, "Address found in configuration: %s",
fmt_addr(addr_out));
return FN_RET_OK;
}
/** @brief Get IP address from the local hostname by calling gethostbyname()
@ -240,7 +259,7 @@ get_address_from_config(const or_options_t *options, int warn_severity,
* @return Return 0 on success that is an address has been found and resolved
* successfully. Return error code ERR_* found at the top of the file.
*/
static int
static fn_address_ret_t
get_address_from_hostname(const or_options_t *options, int warn_severity,
int family, const char **method_out,
char **hostname_out, tor_addr_t *addr_out)
@ -259,24 +278,33 @@ get_address_from_hostname(const or_options_t *options, int warn_severity,
if (tor_gethostname(hostname, sizeof(hostname)) < 0) {
log_fn(warn_severity, LD_NET, "Error obtaining local hostname");
return ERR_GET_HOSTNAME;
/* Unable to obtain the local hostname is a fatal error. */
return FN_RET_BAIL;
}
if (tor_addr_lookup(hostname, family, addr_out)) {
log_fn(warn_severity, LD_NET,
"Could not resolve local hostname '%s'. Failing.", hostname);
return ERR_FAIL_RESOLVE;
/* Unable to resolve, inform caller to try next method. */
return FN_RET_NEXT;
}
ret = address_can_be_used(addr_out, options, warn_severity, false);
if (ret < 0) {
return ret;
if (ret == ERR_DEFAULT_DIRAUTH) {
/* Non custom authorities, inform caller to try next method. */
return FN_RET_NEXT;
} else if (ret == ERR_ADDRESS_IS_INTERNAL) {
/* Internal address is a fatal error. */
return FN_RET_BAIL;
}
/* addr_out contains the address of the local hostname. */
*method_out = "GETHOSTNAME";
*hostname_out = tor_strdup(hostname);
return 0;
/* Found it! */
log_fn(warn_severity, LD_CONFIG, "Address found from local hostname: %s",
fmt_addr(addr_out));
return FN_RET_OK;
}
/** @brief Get IP address from a network interface.
@ -286,40 +314,49 @@ get_address_from_hostname(const or_options_t *options, int warn_severity,
* @param family IP address family. Only AF_INET and AF_INET6 are supported.
* @param method_out OUT: Always "INTERFACE" on success which is detailed in
* the control-spec.txt as actions for "STATUS_SERVER".
* @param hostname_out OUT: String containing the local hostname. For this
* function, it is always set to NULL.
* @param addr_out OUT: Tor address found attached to the interface.
*
* @return Return 0 on success that is an address has been found. Return
* error code ERR_* found at the top of the file.
*/
static int
static fn_address_ret_t
get_address_from_interface(const or_options_t *options, int warn_severity,
int family, const char **method_out,
tor_addr_t *addr_out)
char **hostname_out, tor_addr_t *addr_out)
{
int ret;
tor_assert(method_out);
tor_assert(hostname_out);
tor_assert(addr_out);
/* Set them to NULL for safety reasons. */
*method_out = NULL;
*hostname_out = NULL;
log_debug(LD_CONFIG, "Attempting to get address from network interface");
if (get_interface_address6(warn_severity, family, addr_out) < 0) {
log_fn(warn_severity, LD_CONFIG,
"Could not get local interface IP address.");
return ERR_GET_INTERFACE;
/* Unable to get IP from interface. Inform caller to try next method. */
return FN_RET_NEXT;
}
ret = address_can_be_used(addr_out, options, warn_severity, false);
if (ret < 0) {
return ret;
/* Unable to use address. Inform caller to try next method. */
return FN_RET_NEXT;
}
*method_out = "INTERFACE";
return 0;
/* Found it! */
log_fn(warn_severity, LD_CONFIG, "Address found from interface: %s",
fmt_addr(addr_out));
return FN_RET_OK;
}
/** @brief Update the last resolved address cache using the given address.
@ -393,6 +430,21 @@ update_resolved_cache(const tor_addr_t *addr, const char *method_used,
*done_one_resolve = true;
}
/** Address discovery function table. The order matters as in the first one is
* executed first and so on. */
static fn_address_ret_t
(*fn_address_table[])(
const or_options_t *options, int warn_severity, int family,
const char **method_out, char **hostname_out, tor_addr_t *addr_out) =
{
/* These functions are in order for our find address algorithm. */
get_address_from_config,
get_address_from_hostname,
get_address_from_interface,
};
/** Length of address table as in how many functions. */
static const size_t fn_address_table_len = ARRAY_LENGTH(fn_address_table);
/** @brief Attempt to find our IP address that can be used as our external
* reachable address.
*
@ -465,8 +517,7 @@ find_my_address(const or_options_t *options, int family, int warn_severity,
tor_addr_t *addr_out, const char **method_out,
char **hostname_out)
{
int ret;
const char *method_used;
const char *method_used = NULL;
char *hostname_used = NULL;
tor_addr_t my_addr;
@ -481,51 +532,24 @@ find_my_address(const or_options_t *options, int family, int warn_severity,
* Step 1: Discover address by attempting 3 different methods consecutively.
*/
/* Attempt #1: Get address from configuration. */
ret = get_address_from_config(options, warn_severity, family, &method_used,
&hostname_used, &my_addr);
if (ret == 0) {
log_fn(warn_severity, LD_CONFIG, "Address found in configuration: %s",
fmt_addr(&my_addr));
} else {
/* Unable to resolve an Address statement is a failure. Also, using
* default dirauth error means that the configured address is internal
* which is only accepted if custom authorities are used. */
if (ret == ERR_FAIL_RESOLVE || ret == ERR_DEFAULT_DIRAUTH) {
/* Go over the function table. They are in order. */
for (size_t idx = 0; idx < fn_address_table_len; idx++) {
fn_address_ret_t ret = fn_address_table[idx](options, warn_severity,
family, &method_used,
&hostname_used, &my_addr);
if (ret == FN_RET_BAIL) {
return false;
} else if (ret == FN_RET_OK) {
goto found;
}
/* Attempt #2: Get local hostname and resolve it. */
ret = get_address_from_hostname(options, warn_severity, family,
&method_used, &hostname_used, &my_addr);
if (ret == 0) {
log_fn(warn_severity, LD_CONFIG, "Address found from local hostname: "
"%s", fmt_addr(&my_addr));
} else if (ret < 0) {
/* Unable to get the hostname results in a failure. If the address is
* internal, we stop right away. */
if (ret == ERR_GET_HOSTNAME || ret == ERR_ADDRESS_IS_INTERNAL) {
return false;
}
/* Attempt #3: Get address from interface. */
ret = get_address_from_interface(options, warn_severity, family,
&method_used, &my_addr);
if (ret == 0) {
log_fn(warn_severity, LD_CONFIG, "Address found from interface: %s",
fmt_addr(&my_addr));
} else {
/* We've exhausted our attempts. Failure. */
log_fn(warn_severity, LD_CONFIG, "Unable to find our IP address.");
return false;
}
}
tor_assert(ret == FN_RET_NEXT);
}
tor_assert(method_used);
/* From here, my_addr is a valid IP address of "family" and can be used as
* our external IP address. */
/* We've exhausted our attempts. Failure. */
log_fn(warn_severity, LD_CONFIG, "Unable to find our IP address.");
return false;
found:
/*
* Step 2: Update last resolved address cache and inform the control port.
*/
@ -535,10 +559,7 @@ find_my_address(const or_options_t *options, int family, int warn_severity,
*method_out = method_used;
}
if (hostname_out) {
*hostname_out = NULL;
if (hostname_used) {
*hostname_out = hostname_used;
}
*hostname_out = hostname_used;
} else {
tor_free(hostname_used);
}