Make librrd.c work with RRDD's inotify-based discovery mechanism (#5)

(1) This commit changes behaviour of the library to accommodate RRDD's
new plugin discovery mechanism:

* The library writes a file of static size and doesn't resize it. The
  size depends on RRD_MAX_SOURCES and no

* The library immediately writes to the file after it opens it such that
  it contains a valid header, which is picked up by RRDD.

* The library removes the file it has written when a plugin is closed.
  This is picked up by RRDD.

(2) Furthermore, the commit contains these general improvements:

* Linking the shared library requires zlib.

* Check for memory leaks using valgrind as part of CI.

* integrate new upstream release of JSON lib parson

(3) The interface for clients changed: the sample() function now
receives a pointer provided by the client. This makes it easier to write
a sample function that is shared by multiple data sources. See the
rrdtest.c for an example.

Signed-off-by: Christian Lindig <[email protected]>

Author: lindig

.gitignore

@@ -6,4 +6,5 @@ ocaml/rrdreader.native
 *.o
 *.a
 *.rrd
+*.so
 

Makefile

@@ -10,7 +10,7 @@
 
 
 NAME    = rrd-client-lib
-VERSION = 1.0.0
+VERSION = 1.1.0
 
 CC	= gcc
 CFLAGS	= -std=gnu99 -g -fpic -Wall
@@ -36,18 +36,15 @@ clean:
 test: 	rrdtest rrdclient
 	./rrdtest
 	seq 1 10 | ./rrdclient rrdclient.rrd
+	test ! -f rrdclient.rrd
 
 .PHONY: test-integration
 test-integration: rrdclient
-	seq 1 10 | while read i; do \
-		echo $$i | ./rrdclient rrdclient.rrd ;\
-		rrdreader file --once rrdclient.rrd v2 ;\
-	done
-	seq 1 20 | while read i; do \
-		echo $$i | ./rrdclient rrdclient.rrd ;\
-		sleep 4 ;\
-	done &  rrdreader file rrdclient.rrd v2 \
-	|| echo "a final exception Rrd_protocol.No_update is OK"
+	seq 1 10 | while read i; do echo $$i ; sleep 4; done \
+		| ./rrdclient rrdclient.rrd &
+	rrdreader file rrdclient.rrd v2 \
+		|| echo "a final exception Rrd_protocol.No_update is OK"
+	test ! -f rrdclient.rrd
 
 .PHONY: valgrind
 valgrind: rrdtest
@@ -70,7 +67,7 @@ librrd.a: $(OBJ)
 	ranlib $@
 
 librrd.so: $(OBJ)
-	$(CC) -shared -o $@ $(OBJ)
+	$(CC) -shared -o $@ $(OBJ) $(LIB)
 
 rrdtest: rrdtest.o librrd.a
 	$(CC) $(CFLAGS) -o $@ $^ $(LIB)

README.md

@@ -111,6 +111,9 @@ for a single machine (`RRD_LOCAL_DOMAIN`) or multiple
 NULL. If it isn't, it us used to obtain a timestamp instead of using
 time(3).
 
+When a plugin is opened, the file at `path` is being created and it is
+removed when the plugin is closed.
+
 ## Data Sources
 
 A typical client has several data sources. A data source either reports
@@ -139,24 +142,24 @@ dynamically.
         int64_t         int64;
         double          float64;
     } rrd_value_t;
-    
+
     typedef struct rrd_source {
         char           *name;       /* name of the data source */
         char           *description;        /* for user interface */
         char           *owner_uuid; /* UUID of the owner or NULL */
         char           *rrd_units;  /* for user interface */
         char           *min;        /* min <= sample() <= max */
         char           *max;        /* min <= sample() <= max */
-                        rrd_value_t(*sample) (void);  /* reads value */
+                        rrd_value_t(*sample) (void *userdata);      /* reads
+                                                                     * value */
+        void           *userdata;   /* passed to sample() */
         rrd_owner_t     owner;
         int32_t         rrd_default;        /* true: rrd daemon will archive */
         rrd_scale_t     scale;      /* presentation of value */
         rrd_type_t      type;       /* type of value */
     } RRD_SOURCE;
-    
     typedef struct rrd_plugin RRD_PLUGIN;
 
-    
     <<function declarations>>=
     int rrd_add_src(RRD_PLUGIN *plugin, RRD_SOURCE *source);
     int rrd_del_src(RRD_PLUGIN *plugin, RRD_SOURCE *source);
@@ -165,14 +168,16 @@ dynamically.
 An `RRD_SOURCE` has several descriptive fields for the value it is
 reporting. It includes a function (pointer) `sample` that obtains the
 value being reported. A value can be either a 64-bit integer or a 64-bit
-floating point value -- discriminated by `type`.
+floating point value -- discriminated by `type`.  Part of an RRD_SOURCE
+is a pointer `userdata` that is passed to `sample()`. This allows to
+share a single sample function across several RRD_SOURCE values.
 
 ## Constants and Error Handling
 
 Some functions return an error code.
 
     <<constants>>=
-    #define RRD_MAX_SOURCES         128
+    #define RRD_MAX_SOURCES         16
 
     #define RRD_OK                  0
     #define RRD_TOO_MANY_SOURCES    1
@@ -191,6 +196,20 @@ is updated. When a data source is added or removed, the existing buffer
 containing binary and meta data is invalidated, recomputed and gets
 written out.
 
+The design in constrained by the following behavior of the RRD daemon
+RRDD:
+
+* RRDD maps an RRD file into memory and does not re-read it if the
+  file size changes. Therefore the library writes a static size that
+  depends on `RRD_MAX_SOURCES` and not on the actual number of data
+  sources being in use.
+
+* RRDD reads an RRD file and expects it have valid content. Hence, the
+  library can't open the file and write it contents with a delay.
+  Therefore the library writes an RRD file that indicated that initially
+  there are no data sources and re-writes the file for each data source
+  that is added. Checksums avoid other synchronisation problems.
+
 # Data Layout
 
 The data layout is not defined by this library but by the existing