Project 2: simple DNS resolver

1 files changed, 29 insertions, 0 deletions

diff --git a/project2/proj2_s4498062/dns/regexes.py b/project2/proj2_s4498062/dns/regexes.py
new file mode 100644
index 0000000..48c28c9
--- /dev/null
+++ b/project2/proj2_s4498062/dns/regexes.py
@@ -0,0 +1,29 @@
+"""Regexes used in the DNS protocol"""
+
+def grpm(regex):
+    """Make a matching group"""
+    return grp(regex, matching=True)
+
+def grp(regex, matching=False):
+    """Make a group"""
+    return r'(' + (r'' if matching else r'?:') + regex + r')'
+
+def opt(regex):
+    """Make an optional group"""
+    return grp(grp(regex) + r'?')
+
+def regex_opt_r(*regexes):
+    """Make a group that matches one of the given regexes"""
+    return grp(r'|'.join(regexes))
+
+DIGIT = r'\d'
+LETTER = r'[a-zA-Z]'
+LETDIG = grp(regex_opt_r(DIGIT, LETTER))
+LETDIGHYP = grp(regex_opt_r(LETDIG, r'-'))
+LDHSTR = grp(LETDIGHYP + r'+')
+LABEL = grp(LETTER + opt(opt(LDHSTR) + LETDIG))
+SUBDOMAIN = grp(grpm(grp(LABEL + r'\.') + r'*') + grpm(LABEL))
+DOMAIN = regex_opt_r(SUBDOMAIN, r' ')
+
+IP = r'(?:(?:\d{1,3}\.){3}\d{1,3})'
+