Implemented epics read/write

internal/datasource/epics/ca_wrapper.h

@@ -13,7 +13,7 @@
  * goCAConnectionCallback is called when a channel connects or disconnects.
  */
 extern void goCAMonitorCallback(uintptr_t handle, int dbrType, long count,
-                                const void *dbr, int severity,
+                                void *dbr, int severity,
                                 double epicsTimeSecs);
 extern void goCAConnectionCallback(uintptr_t handle, int connected);
 
@@ -78,7 +78,7 @@ static void caMonitorCallbackShim(struct event_handler_args args) {
     }
 
     goCAMonitorCallback((uintptr_t)args.usr, (int)args.type, (long)args.count,
-                        args.dbr, severity, timeSecs);
+                        (void *)args.dbr, severity, timeSecs);
 }
 
 /*
@@ -115,4 +115,29 @@ static int caAddMonitor(chid ch, short dbrType, uintptr_t userHandle,
                         (void *)userHandle, pEvid);
 }
 
+/* Wrappers for ca_get / ca_put, which are macros in cadef.h that expand to
+ * ca_array_get / ca_array_put with count=1.  CGo cannot call macros directly,
+ * so we provide thin static-inline shims here. */
+
+static int caGet(chtype type, chid chan, void *pValue) {
+    return ca_array_get(type, 1u, chan, pValue);
+}
+
+static int caPut(chtype type, chid chan, const void *pValue) {
+    return ca_array_put(type, 1u, chan, pValue);
+}
+
+/* Retrieve the current thread's CA context as an opaque pointer.
+ * Store the result and pass it to caAttachContext() from other threads. */
+static void *caCurrentContext(void) {
+    return (void *)ca_current_context();
+}
+
+/* Attach an existing CA context to the calling thread.  Must be called at the
+ * start of every goroutine (OS thread) that makes CA calls, if that thread did
+ * not call ca_context_create() itself.  Returns ECA_NORMAL on success. */
+static int caAttachContext(void *ctx) {
+    return ca_attach_context((struct ca_client_context *)ctx);
+}
+
 #endif /* CA_WRAPPER_H */