Add converter processor (#4178)

plugins/processors/converter/README.md

@@ -0,0 +1,57 @@
+# Converter Processor
+
+The converter processor is used to change the type of tag or field values.  In
+addition to changing field types it can convert fields to tags and vis versa.
+
+Values that cannot be converted are dropped.
+
+**Note:** When converting tags to fields, take care not to ensure the series is still
+uniquely identifiable.  Fields with the same series key (measurement + tags)
+will overwrite one another.
+
+### Configuration:
+```toml
+# Convert values to another metric value type
+[processors.converter]
+  ## Tags to convert
+  ##
+  ## The table key determines the target type, and the array of key-values
+  ## select the keys to convert.  The array may contain globs.
+  ##   <target-type> = [<tag-key>...]
+  [processors.converter.tags]
+    string = []
+    integer = []
+    unsigned = []
+    boolean = []
+    float = []
+
+  ## Fields to convert
+  ##
+  ## The table key determines the target type, and the array of key-values
+  ## select the keys to convert.  The array may contain globs.
+  ##   <target-type> = [<field-key>...]
+  [processors.converter.fields]
+    tag = []
+    string = []
+    integer = []
+    unsigned = []
+    boolean = []
+    float = []
+```
+
+### Examples:
+
+```toml
+[processors.converter]
+  [processors.converter.tags]
+    string = ["port"]
+
+  [processors.converter.fields]
+    integer = ["scboard_*"]
+    tag = ["ParseServerConfigGeneration"]
+```
+
+```diff
+- apache,port=80,server=debian-stretch-apache BusyWorkers=1,BytesPerReq=0,BytesPerSec=0,CPUChildrenSystem=0,CPUChildrenUser=0,CPULoad=0.00995025,CPUSystem=0.01,CPUUser=0.01,ConnsAsyncClosing=0,ConnsAsyncKeepAlive=0,ConnsAsyncWriting=0,ConnsTotal=0,IdleWorkers=49,Load1=0.01,Load15=0,Load5=0,ParentServerConfigGeneration=3,ParentServerMPMGeneration=2,ReqPerSec=0.00497512,ServerUptimeSeconds=201,TotalAccesses=1,TotalkBytes=0,Uptime=201,scboard_closing=0,scboard_dnslookup=0,scboard_finishing=0,scboard_idle_cleanup=0,scboard_keepalive=0,scboard_logging=0,scboard_open=100,scboard_reading=0,scboard_sending=1,scboard_starting=0,scboard_waiting=49 1502489900000000000
++ apache,server=debian-stretch-apache,ParentServerConfigGeneration=3 port="80",BusyWorkers=1,BytesPerReq=0,BytesPerSec=0,CPUChildrenSystem=0,CPUChildrenUser=0,CPULoad=0.00995025,CPUSystem=0.01,CPUUser=0.01,ConnsAsyncClosing=0,ConnsAsyncKeepAlive=0,ConnsAsyncWriting=0,ConnsTotal=0,IdleWorkers=49,Load1=0.01,Load15=0,Load5=0,ParentServerMPMGeneration=2,ReqPerSec=0.00497512,ServerUptimeSeconds=201,TotalAccesses=1,TotalkBytes=0,Uptime=201,scboard_closing=0i,scboard_dnslookup=0i,scboard_finishing=0i,scboard_idle_cleanup=0i,scboard_keepalive=0i,scboard_logging=0i,scboard_open=100i,scboard_reading=0i,scboard_sending=1i,scboard_starting=0i,scboard_waiting=49i 1502489900000000000
+```