Router: client IP address replacement.

This commit introduces the replacement of the client address based on the value
of a specified HTTP header.  This is intended for use when Unit is placed
behind a reverse proxy like nginx or a CDN.

You must specify the source addresses of the trusted proxies.  This can be
accomplished with any valid IP pattern supported by Unit's match block:

["10.0.0.1", "10.4.0.0/16", "!192.168.1.1"]

The feature is configured per listener.

The client address replacement functionality only operates when there is a
source IP match and the specified header is present.  Typically this would be
an 'X-Forwarded-For' header.

{
    "listeners": {
        "127.0.0.1:8080": {
            "client_ip": {
                "header": "X-Forwarded-For",
                "source": [
                    "10.0.0.0/8"
                ]
            },
            "pass": "applications/my_app"
        },
    }
}

If a request occurs and Unit receives a header like below:

"X-Forwarded-For: 84.123.23.23"

By default, Unit trusts the last rightmost IP in the header, so REMOTE_ADDR
will be set to 84.123.23.23 if the connection originated from 10.0.0.0/8.

If Unit runs behind consecutive reverse proxies and receives a header similar
to the following:

"X-Forwarded-For: 84.123.23.23, 10.0.0.254"

You will need to enable "recursive" checking, which walks the header from
last address to first and chooses the first non-trusted address it finds.

{
    "listeners": {
        "127.0.0.1:8080": {
            "client_ip": {
                "header": "X-Forwarded-For",
                "source": [
                    "10.0.0.0/8"
                ]
                "recursive": true,
            },
            "pass": "applications/my_app"
        },
    }
}

If a connection from 10.0.0.0/8 occurs, the chain is walked.  Here, 10.0.0.254
is also a trusted address so the client address will be replaced with
84.123.23.23.

If all IP addresses in the header are trusted, the client address is set to
the first address in the header:

If 10.0.0.0/8 is trusted and "X-Forwarded-For: 10.0.0.3, 10.0.0.2, 10.0.0.1",
the client address will be replaced with 10.0.0.3.

1 files changed, 150 insertions, 0 deletions

diff --git a/src/nxt_http_request.c b/src/nxt_http_request.c
index 16563a98..b71b25d9 100644
--- a/src/nxt_http_request.c
+++ b/src/nxt_http_request.c
@@ -10,6 +10,10 @@
 
 static nxt_int_t nxt_http_validate_host(nxt_str_t *host, nxt_mp_t *mp);
 static void nxt_http_request_start(nxt_task_t *task, void *obj, void *data);
+static nxt_int_t nxt_http_request_client_ip(nxt_task_t *task,
+    nxt_http_request_t *r);
+static nxt_sockaddr_t *nxt_http_request_client_ip_sockaddr(
+    nxt_http_request_t *r, u_char *start, size_t len);
 static void nxt_http_request_ready(nxt_task_t *task, void *obj, void *data);
 static void nxt_http_request_proto_info(nxt_task_t *task,
     nxt_http_request_t *r);
@@ -272,16 +276,162 @@ static const nxt_http_request_state_t  nxt_http_request_init_state
 static void
 nxt_http_request_start(nxt_task_t *task, void *obj, void *data)
 {
+    nxt_int_t           ret;
     nxt_http_request_t  *r;
 
     r = obj;
 
     r->state = &nxt_http_request_body_state;
 
+    ret = nxt_http_request_client_ip(task, r);
+    if (nxt_slow_path(ret != NXT_OK)) {
+        nxt_http_request_error(task, r, NXT_HTTP_INTERNAL_SERVER_ERROR);
+    }
+
     nxt_http_request_read_body(task, r);
 }
 
 
+static nxt_int_t
+nxt_http_request_client_ip(nxt_task_t *task, nxt_http_request_t *r)
+{
+    u_char                *start, *p;
+    nxt_int_t             ret, i, len;
+    nxt_str_t             *header;
+    nxt_array_t           *fields_arr;  /* of nxt_http_field_t * */
+    nxt_sockaddr_t        *sa, *prev_sa;
+    nxt_http_field_t      *f, **fields;
+    nxt_http_client_ip_t  *client_ip;
+
+    client_ip = r->conf->socket_conf->client_ip;
+
+    if (client_ip == NULL) {
+        return NXT_OK;
+    }
+
+    ret = nxt_http_route_addr_rule(r, client_ip->source, r->remote);
+    if (ret <= 0) {
+        return NXT_OK;
+    }
+
+    header = client_ip->header;
+
+    fields_arr = nxt_array_create(r->mem_pool, 2, sizeof(nxt_http_field_t *));
+    if (nxt_slow_path(fields_arr == NULL)) {
+        return NXT_ERROR;
+    }
+
+    nxt_list_each(f, r->fields) {
+        if (f->hash == client_ip->header_hash
+            && f->name_length == client_ip->header->length
+            && f->value_length > 0
+            && nxt_memcasecmp(f->name, header->start, header->length) == 0)
+        {
+            fields = nxt_array_add(fields_arr);
+            if (nxt_slow_path(fields == NULL)) {
+                return NXT_ERROR;
+            }
+
+            *fields = f;
+        }
+    } nxt_list_loop;
+
+    prev_sa = r->remote;
+    fields = (nxt_http_field_t **) fields_arr->elts;
+
+    i = fields_arr->nelts;
+
+    while (i-- > 0) {
+        f = fields[i];
+        start = f->value;
+        len = f->value_length;
+
+        do {
+            for (p = start + len - 1; p > start; p--, len--) {
+                if (*p != ' ' && *p != ',') {
+                    break;
+                }
+            }
+
+            for (/* void */; p > start; p--) {
+                if (*p == ' ' || *p == ',') {
+                    p++;
+                    break;
+                }
+            }
+
+            sa = nxt_http_request_client_ip_sockaddr(r, p, len - (p - start));
+            if (nxt_slow_path(sa == NULL)) {
+                if (prev_sa != NULL) {
+                    r->remote = prev_sa;
+                }
+
+                return NXT_OK;
+            }
+
+            if (!client_ip->recursive) {
+                r->remote = sa;
+
+                return NXT_OK;
+            }
+
+            ret = nxt_http_route_addr_rule(r, client_ip->source, sa);
+            if (ret <= 0 || (i == 0 && p == start)) {
+                r->remote = sa;
+
+                return NXT_OK;
+            }
+
+            prev_sa = sa;
+            len = p - 1 - start;
+
+        } while (len > 0);
+    }
+
+    return NXT_OK;
+}
+
+
+static nxt_sockaddr_t *
+nxt_http_request_client_ip_sockaddr(nxt_http_request_t *r, u_char *start,
+    size_t len)
+{
+    nxt_str_t       addr;
+    nxt_sockaddr_t  *sa;
+
+    addr.start = start;
+    addr.length = len;
+
+    sa = nxt_sockaddr_parse_optport(r->mem_pool, &addr);
+    if (nxt_slow_path(sa == NULL)) {
+        return NULL;
+    }
+
+    switch (sa->u.sockaddr.sa_family) {
+        case AF_INET:
+            if (sa->u.sockaddr_in.sin_addr.s_addr == INADDR_ANY) {
+                return NULL;
+            }
+
+            break;
+
+#if (NXT_INET6)
+        case AF_INET6:
+            if (IN6_IS_ADDR_UNSPECIFIED(&sa->u.sockaddr_in6.sin6_addr)) {
+                return NULL;
+            }
+
+            break;
+#endif /* NXT_INET6 */
+
+        default:
+            return NULL;
+    }
+
+    return sa;
+}
+
+
 static const nxt_http_request_state_t  nxt_http_request_body_state
     nxt_aligned(64) =
 {