make openssl digest objects thread local (#47)

CHANGELOG.md

@@ -1,3 +1,6 @@
+## 3.2.1
+  - Fixed concurrent SHA fingerprinting by making the instances thread local
+
 ## 3.2.0
   - Added support for non-keyed, regular hash functions [#18](https://github.com/logstash-plugins/logstash-filter-fingerprint/issues/18)
 

lib/logstash/filters/fingerprint.rb

@@ -100,7 +100,6 @@ class << self; alias_method :fingerprint, :fingerprint_murmur3; end
       # nothing
     else
       class << self; alias_method :fingerprint, :fingerprint_openssl; end
-      @digest = select_digest(@method)
     end
   end
 
@@ -153,19 +152,27 @@ def fingerprint_ipv4_network(ip_string)
   end
 
   def fingerprint_openssl(data)
+    # since OpenSSL::Digest instances aren't thread safe, we must ensure that
+    # each pipeline worker thread gets its own instance.
+    # Also, since a logstash pipeline may contain multiple fingerprint filters
+    # we must include the id in the thread local variable name, so that we can
+    # store multiple digest instances
+    digest_string = "digest-#{id}"
+    Thread.current[digest_string] ||= select_digest(@method)
+    digest = Thread.current[digest_string]
     # in JRuby 1.7.11 outputs as ASCII-8BIT
     if @key.nil?
       if @base64encode
-        @digest.base64digest(data.to_s).force_encoding(Encoding::UTF_8)
+        digest.base64digest(data.to_s).force_encoding(Encoding::UTF_8)
       else
-        @digest.hexdigest(data.to_s).force_encoding(Encoding::UTF_8)
+        digest.hexdigest(data.to_s).force_encoding(Encoding::UTF_8)
       end
     else
       if @base64encode
-        hash = OpenSSL::HMAC.digest(@digest, @key, data.to_s)
+        hash = OpenSSL::HMAC.digest(digest, @key, data.to_s)
         Base64.strict_encode64(hash).force_encoding(Encoding::UTF_8)
       else
-        OpenSSL::HMAC.hexdigest(@digest, @key, data.to_s).force_encoding(Encoding::UTF_8)
+        OpenSSL::HMAC.hexdigest(digest, @key, data.to_s).force_encoding(Encoding::UTF_8)
       end
     end
   end

logstash-filter-fingerprint.gemspec

@@ -1,7 +1,7 @@
 Gem::Specification.new do |s|
 
   s.name            = 'logstash-filter-fingerprint'
-  s.version         = '3.2.0'
+  s.version         = '3.2.1'
   s.licenses        = ['Apache-2.0']
   s.summary         = "Fingerprints fields by replacing values with a consistent hash"
   s.description     = "This gem is a Logstash plugin required to be installed on top of the Logstash core pipeline using $LS_HOME/bin/logstash-plugin install gemname. This gem is not a stand-alone program"