Fix mx_mech handling (haraka#26)

Fix mx_mech evaluations; currently it will only look up the first MX
record address and compare that against the list of valid IPs due to the
old async pending checks being left in place which cannot be used when
async/await is used as they will always evaluate to a truthy value.

Checklist:

- [ ] docs updated
- [X] tests updated
- [ ] Changes.md updated

lib/spf.js

@@ -38,6 +38,9 @@ class SPF {
 
     this.mech_ip4 = this.mech_ip
     this.mech_ip6 = this.mech_ip
+
+    // Used for tests only
+    this._found_mx_addrs = [];
   }
 
   const_translate(value) {
@@ -486,17 +489,15 @@ class SPF {
       }
     }
 
-    let pending = 0
     let addresses = []
     // RFC 4408 Section 10.1
     if (mxes.length > this.LIMIT) return this.SPF_PERMERROR
 
+    let cidr;
     for (const element of mxes) {
-      pending++
       const mx = element.exchange
       // Calculate which IP method to use
       let resolve_method
-      let cidr
       if (this.ip_ver === 'ipv4') {
         cidr = cidr4
         resolve_method = 'resolve4'
@@ -519,49 +520,44 @@ class SPF {
         }
       }
 
-      pending--
-      if (addrs) {
-        this.log_debug(`mech_mx: mx=${mx} addresses=${addrs.join(',')}`)
-        addresses = addrs.concat(addresses)
-      }
-      if (pending === 0) {
-        if (!addresses.length) return this.SPF_NONE
-        // All queries run; see if our IP matches
-        if (cidr) {
-          // CIDR match type
-          for (const address of addresses) {
-            const range = ipaddr.parse(address)
-            if (this.ipaddr.match(range, cidr)) {
-              this.log_debug(
-                `mech_mx: ${this.ip} => ${address}/${cidr}: MATCH!`,
-              )
-              return this.return_const(qualifier)
-            } else {
-              this.log_debug(
-                `mech_mx: ${this.ip} => ${address}/${cidr}: NO MATCH`,
-              )
-            }
-          }
-          // No matches
-          return this.SPF_NONE
+      this.log_debug(`mech_mx: mx=${mx} addresses=${addrs.join(',')}`)
+      addresses = addrs.concat(addresses)
+    }
+
+    if (!addresses.length) return this.SPF_NONE
+    this._found_mx_addrs = addresses;
+
+    // All queries run; see if our IP matches
+    if (cidr) {
+      // CIDR match type
+      for (const address of addresses) {
+        const range = ipaddr.parse(address)
+        if (this.ipaddr.match(range, cidr)) {
+          this.log_debug(
+            `mech_mx: ${this.ip} => ${address}/${cidr}: MATCH!`,
+          )
+          return this.return_const(qualifier)
         } else {
-          if (addresses.includes(this.ip)) {
-            this.log_debug(
-              `mech_mx: ${this.ip} => ${addresses.join(',')}: MATCH!`,
-            )
-            return this.return_const(qualifier)
-          } else {
-            this.log_debug(
-              `mech_mx: ${this.ip} => ${addresses.join(',')}: NO MATCH`,
-            )
-            return this.SPF_NONE
-          }
+          this.log_debug(
+            `mech_mx: ${this.ip} => ${address}/${cidr}: NO MATCH`,
+          )
         }
       }
-      // In case we didn't run any queries...
-      if (pending === 0) return this.SPF_NONE
+      // No matches
+      return this.SPF_NONE
+    } else {
+      if (addresses.includes(this.ip)) {
+        this.log_debug(
+          `mech_mx: ${this.ip} => ${addresses.join(',')}: MATCH!`,
+        )
+        return this.return_const(qualifier)
+      } else {
+        this.log_debug(
+          `mech_mx: ${this.ip} => ${addresses.join(',')}: NO MATCH`,
+        )
+        return this.SPF_NONE
+      }
     }
-    if (pending === 0) this.SPF_NONE
   }
 
   async mech_ptr(qualifier, args) {

test/spf.js

@@ -53,6 +53,15 @@ describe('SPF', function () {
     }
   })
 
+  it('resolves more than one IP in mech_mx', async function () {
+    this.timeout = 4000
+    this.SPF.domain = 'gmail.com'
+    this.SPF.ip_ver = 'ipv4'
+
+    await this.SPF.mech_mx()
+    assert.equal((this.SPF._found_mx_addrs.length > 1), true)
+  })
+
   it('check_host, gmail.com, fail', async function () {
     this.timeout = 3000
     this.SPF.count = 0