From: Mark Wooding <mdw@distorted.org.uk>
Date: Tue, 26 Sep 2017 21:51:59 +0000 (+0100)
Subject: peerdb/tripe-newpeers.in: Enhance addr-lookup syntax; return multiple addrs.
X-Git-Tag: 1.5.0~41^2~62
X-Git-Url: https://git.distorted.org.uk/~mdw/tripe/commitdiff_plain/ef7d7afbc62c58537caabba75b36d9938eb49b94

peerdb/tripe-newpeers.in: Enhance addr-lookup syntax; return multiple addrs.

Keep track of multiple addresses for each host.  Extend the $[...]
syntax to allow substitution of all of the addresses, rather than just
the first.
---

diff --git a/peerdb/peers.in.5.in b/peerdb/peers.in.5.in
index a07240b2..be9b8006 100644
--- a/peerdb/peers.in.5.in
+++ b/peerdb/peers.in.5.in
@@ -83,14 +83,19 @@ is replaced by the value assigned to the given
 .IR key .
 .hP \*o
 An occurrence of
-.BI $[ host ]
+.BI $ flags [ host ]
 is replaced by the IP address of the named
 .IR host .
 Note that
 .I host
 may itself contain
 .BI $( key )
-substitutions.
+substitutions.  The
+.I flags
+consist of zero or more of the following characters:
+.RB ` * '
+returns all of the found addresses, separated by spaces, rather than
+just the first one.
 .PP
 There is a simple concept of
 .I inheritance
diff --git a/peerdb/tripe-newpeers.in b/peerdb/tripe-newpeers.in
index 502492d9..1f17811e 100644
--- a/peerdb/tripe-newpeers.in
+++ b/peerdb/tripe-newpeers.in
@@ -63,17 +63,20 @@ class ResolverFailure (ExpectedError):
 class ResolvingHost (object):
   """
   A host name which is being looked up by a bulk-resolver instance.
+
+  Most notably, this is where the flag-handling logic lives for the
+  $FLAGS[HOSTNAME] syntax.
   """
 
   def __init__(me, name):
     """Make a new resolving-host object for the host NAME."""
     me.name = name
-    me.addr = None
+    me.addr = []
     me.failure = None
 
-  def setaddr(me, addr):
+  def addaddr(me, addr):
     """Add the address ADDR."""
-    me.addr = addr
+    me.addr.append(addr)
 
   def failed(me, msg):
     """
@@ -81,10 +84,17 @@ class ResolvingHost (object):
     """
     me.failure = msg
 
-  def get(me):
-    """Return the resolved address."""
+  def get(me, flags):
+    """Return a list of addresses according to the FLAGS string."""
     if me.failure is not None: raise ResolverFailure(me.name, me.failure)
-    return me.addr
+    aa = me.addr
+    all = False
+    for ch in flags:
+      if ch == '*': all = True
+      else: raise ValueError("unknown address-resolution flag `%s'" % ch)
+    if not aa: raise ResolverFailure(me.name, 'no matching addresses found')
+    if not all: aa = [aa[0]]
+    return aa
 
 class BulkResolver (object):
   """
@@ -113,24 +123,24 @@ class BulkResolver (object):
       me._namemap[name] = host = ResolvingHost(name)
       host._resolv = M.SelResolveByName(
         name,
-        lambda cname, alias, addr: me._resolved(host, addr[0]),
-        lambda: me._resolved(host, None))
+        lambda cname, alias, addr: me._resolved(host, addr),
+        lambda: me._resolved(host, []))
       me._noutstand += 1
 
   def run(me):
     """Run the background DNS resolver until it's finished."""
     while me._noutstand: M.select()
 
-  def lookup(me, name):
+  def lookup(me, name, flags):
     """Fetch the address corresponding to the host NAME."""
-    return me._namemap[name].get()
+    return me._namemap[name].get(flags)
 
   def _resolved(me, host, addr):
-    """Callback function: remember that ADDR is the address for HOST."""
-    if addr is None:
+    """Callback function: remember that ADDRs are the addresses for HOST."""
+    if not addr:
       host.failed('(unknown failure)')
     else:
-      host.setaddr(addr)
+      for a in addr: host.addaddr(a)
     host._resolv = None
     me._noutstand -= 1
 
@@ -158,8 +168,9 @@ RX_CONT = RX.compile(r'''(?x) ^ \s+
 ## Match a $(VAR) configuration variable reference; group 1 is the VAR.
 RX_REF = RX.compile(r'(?x) \$ \( ([^)]+) \)')
 
-## Match a $[HOST] name resolution reference; group 1 is the HOST.
-RX_RESOLVE = RX.compile(r'(?x) \$ \[ ([^]]+) \]')
+## Match a $FLAGS[HOST] name resolution reference; group 1 are the flags;
+## group 2 is the HOST.
+RX_RESOLVE = RX.compile(r'(?x) \$ ([*]*) \[ ([^]]+) \]')
 
 class ConfigSyntaxError (ExpectedError):
   def __init__(me, fname, lno, msg):
@@ -237,17 +248,17 @@ class ConfigSection (object):
 
   def _expand(me, string, resolvep):
     """
-    Expands $(...) and (optionally) $[...] placeholders in STRING.
+    Expands $(...) and (optionally) $FLAGS[...] placeholders in STRING.
 
     RESOLVEP is a boolean switch: do we bother to tax the resolver or not?
     This is turned off by MyConfigParser's resolve() method while it's
     collecting hostnames to be resolved.
     """
-    string = RX_REF.sub \
-             (lambda m: me.get(m.group(1), resolvep), string)
+    string = RX_REF.sub(lambda m: me.get(m.group(1), resolvep), string)
     if resolvep:
-      string = RX_RESOLVE.sub(lambda m: me._cp._resolver.lookup(m.group(1)),
-                              string)
+      string = RX_RESOLVE.sub(
+        lambda m: ' '.join(me._cp._resolver.lookup(m.group(2), m.group(1))),
+        string)
     return string
 
   def _parents(me):
@@ -377,8 +388,9 @@ class MyConfigParser (object):
     * It recognizes `$(VAR)' references to configuration variables during
       expansion and processes them correctly.
 
-    * It recognizes `$[HOST]' name-resolver requests and handles them
-      correctly.
+    * It recognizes `$FLAGS[HOST]' name-resolver requests and handles them
+      correctly.  FLAGS may be empty, or `*' (all addresses, space-separated,
+      rather than just the first).
 
     * Its parsing behaviour is well-defined.
 
@@ -491,7 +503,7 @@ class MyConfigParser (object):
       for key in sec.items():
         value = sec.get(key, resolvep = False)
         for match in RX_RESOLVE.finditer(value):
-          me._resolver.prepare(match.group(1))
+          me._resolver.prepare(match.group(2))
     me._resolver.run()
 
 ###--------------------------------------------------------------------------