examples: out_multiinstance: add helper functions to manage context

Signed-off-by: Warren Fernandes <[email protected]>

Author: Jason Keene

examples/out_multiinstance/Dockerfile

@@ -7,18 +7,16 @@ ENV GOOS=linux\
 
 COPY / /root/
 
-RUN go get github.com/fluent/fluent-bit-go/...
-
 RUN go build \
     -buildmode=c-shared \
     -o /out_multiinstance.so \
-    out.go
+    github.com/fluent/fluent-bit-go/examples/out_multiinstance
 
 FROM fluent/fluent-bit:1.1
 
 COPY --from=gobuilder /out_multiinstance.so /fluent-bit/bin/
-COPY --from=gobuilder /root/fluent-bit.conf /fluent-bit/etc/
-COPY --from=gobuilder /root/plugins.conf /fluent-bit/etc/
+COPY --from=gobuilder /root/examples/out_multiinstance/fluent-bit.conf /fluent-bit/etc/
+COPY --from=gobuilder /root/examples/out_multiinstance/plugins.conf /fluent-bit/etc/
 
 EXPOSE 2020
 

examples/out_multiinstance/README.md

@@ -43,7 +43,7 @@ func FLBPluginInit(ctx unsafe.Pointer) int {
 	id := output.FLBPluginConfigKey(plugin, "id")
 	log.Printf("[multiinstance] id = %q", id)
 	// Set the context to point to any Go variable
-	output.FLBPluginSetContext(plugin, unsafe.Pointer(&id))
+	output.FLBPluginSetContext(plugin, id)
 	return output.FLB_OK
 }
 ```
@@ -63,10 +63,10 @@ data, the proper bytes length and the associated tag.
 ```go
 //export FLBPluginFlushCtx
 func FLBPluginFlushCtx(ctx, data unsafe.Pointer, length C.int, tag *C.char) int {
-
-    id := *(*string)(ctx)
-    log.Printf("[multiinstance] Flush called for id: %s", *id)
-    return output.FLB_OK
+	// Type assert context back into the original type for the Go variable
+	id := output.FLBPluginGetContext(ctx).(string)
+	log.Printf("[multiinstance] Flush called for id: %s", id)
+	return output.FLB_OK
 }
 ```
 
@@ -94,8 +94,7 @@ func FLBPluginExit() int {
 Build the docker image locally to see how it works.
 
 ```bash
-$ cd $GOPATH/src/github.com/fluent/fluent-bit-go/examples/out_multiinstance
-$ docker build . -t fluent-bit-multiinstance
+$ docker build . -t fluent-bit-multiinstance -f examples/out_multiinstance/Dockerfile
 $ docker run -it --rm fluent-bit-multiinstance
 ```
 

examples/out_multiinstance/out.go

@@ -1,4 +1,3 @@
-// +build example
 package main
 
 import (
@@ -20,7 +19,8 @@ func FLBPluginInit(plugin unsafe.Pointer) int {
 	id := output.FLBPluginConfigKey(plugin, "id")
 	log.Printf("[multiinstance] id = %q", id)
 	// Set the context to point to any Go variable
-	output.FLBPluginSetContext(plugin, unsafe.Pointer(&id))
+	output.FLBPluginSetContext(plugin, id)
+
 	return output.FLB_OK
 }
 
@@ -32,8 +32,8 @@ func FLBPluginFlush(data unsafe.Pointer, length C.int, tag *C.char) int {
 
 //export FLBPluginFlushCtx
 func FLBPluginFlushCtx(ctx, data unsafe.Pointer, length C.int, tag *C.char) int {
-	// Cast context back into the original type for the Go variable
-	id := *(*string)(ctx)
+	// Type assert context back into the original type for the Go variable
+	id := output.FLBPluginGetContext(ctx).(string)
 	log.Printf("[multiinstance] Flush called for id: %s", id)
 
 	dec := output.NewDecoder(data, int(length))

output/output.go

@@ -67,7 +67,15 @@ func FLBPluginConfigKey(plugin unsafe.Pointer, key string) string {
 	return C.GoString(C.output_get_property(_key, plugin))
 }
 
-func FLBPluginSetContext(plugin, ctx unsafe.Pointer) {
+var contexts []interface{}
+
+func FLBPluginSetContext(plugin unsafe.Pointer, ctx interface{}) {
+	i := len(contexts)
+	contexts = append(contexts, ctx)
 	p := (*FLBOutPlugin)(plugin)
-	p.context.remote_context = ctx
+	p.context.remote_context = unsafe.Pointer(uintptr(i))
+}
+
+func FLBPluginGetContext(i unsafe.Pointer) interface{} {
+	return contexts[int(uintptr(i))]
 }