feat: add a json allocation helper

Makefile

@@ -11,6 +11,8 @@ test:
 	extism call example/tiny_countvowels.wasm count_vowels --wasi --input "this is a test" --set-config '{"thing": "1234"}'
 	extism call example/tiny_http.wasm        http_get     --wasi --log-level info --allow-host "jsonplaceholder.typicode.com"
 	extism call example/tiny_reactor.wasm read_file --input "example/reactor/test.txt" --allow-path ./example/reactor --wasi --log-level info
+	extism call example/tiny_countvowels.wasm count_vowels_roundtrip_json_mem --wasi 
 
 	extism call example/std_countvowels.wasm _start     --wasi --input "this is a test" --set-config '{"thing": "1234"}'
-	extism call example/std_http.wasm        _start     --wasi --log-level info --allow-host "jsonplaceholder.typicode.com"
+	extism call example/std_http.wasm        _start     --wasi --log-level info --allow-host "jsonplaceholder.typicode.com"
+

example/countvowels/std_main.go

@@ -17,6 +17,7 @@ func main() {
 	countVowels()
 	countVowelsTyped()
 	countVowelsJSONOutput()
+	countVowelsJSONRoundtripMem()
 }
 
 // CountVowelsInput represents the JSON input provided by the host.
@@ -54,6 +55,32 @@ func countVowelsJSONOutput() int32 {
 	return 0
 }
 
+//export count_vowels_roundtrip_json_mem
+func countVowelsJSONRoundtripMem() int32 {
+	a := CountVowelsOuptut{Count: 42, Total: 2.1e7, Vowels: "aAeEiIoOuUyY"}
+	mem, err := pdk.AllocateJSON(&a)
+	if err != nil {
+		pdk.SetError(err)
+		return -1
+	}
+
+	// find the data in mem and ensure it's the same once decoded
+	var b CountVowelsOuptut
+	err = pdk.JSONFrom(mem.Offset(), &b)
+	if err != nil {
+		pdk.SetError(err)
+		return -1
+	}
+
+	if a.Count != b.Count || a.Total != b.Total || a.Vowels != b.Vowels {
+		pdk.SetErrorString("roundtrip JSON failed")
+		return -1
+	}
+
+	pdk.OutputString("JSON roundtrip: a === b")
+	return 0
+}
+
 func countVowels() int32 {
 	input := pdk.Input()
 

example/countvowels/tiny_main.go

@@ -44,6 +44,32 @@ func countVowelsJSONOutput() int32 {
 	return 0
 }
 
+//export count_vowels_roundtrip_json_mem
+func countVowelsJSONRoundtripMem() int32 {
+	a := CountVowelsOuptut{Count: 42, Total: 2.1e7, Vowels: "aAeEiIoOuUyY"}
+	mem, err := pdk.AllocateJSON(&a)
+	if err != nil {
+		pdk.SetError(err)
+		return -1
+	}
+
+	// find the data in mem and ensure it's the same once decoded
+	var b CountVowelsOuptut
+	err = pdk.JSONFrom(mem.Offset(), &b)
+	if err != nil {
+		pdk.SetError(err)
+		return -1
+	}
+
+	if a.Count != b.Count || a.Total != b.Total || a.Vowels != b.Vowels {
+		pdk.SetErrorString("roundtrip JSON failed")
+		return -1
+	}
+
+	pdk.OutputString("JSON roundtrip: a === b")
+	return 0
+}
+
 //export count_vowels
 func countVowels() int32 {
 	input := pdk.Input()

extism_pdk.go

@@ -134,6 +134,16 @@ func AllocateString(data string) Memory {
 	return AllocateBytes([]byte(data))
 }
 
+// AllocateJSON allocates and saves the type `any` into Memory on the host.
+func AllocateJSON(v any) (Memory, error) {
+	b, err := json.Marshal(v)
+	if err != nil {
+		return Memory{}, err
+	}
+
+	return AllocateBytes(b), nil
+}
+
 // InputString returns the input data from the host as a UTF-8 string.
 func InputString() string {
 	return string(Input())