Fix callback for parsing string

Makefile

@@ -24,4 +24,7 @@ nanopb_%: $(NANOPB_DIR)/proto/%.proto
 	mv -f $@.c src
 
 run:
-	platformio run
+	platformio run
+    
+test:
+	g++ src/pb_common.c src/pb_decode.c src/pb_encode.c src/tm1638.pb.c test.cpp -o test -Isrc

platformio.ini

@@ -22,4 +22,4 @@ platform = atmelavr
 framework = arduino
 board = uno
 targets = upload
-upload_port = COM3
+upload_port = COM4

proto/tm1638.proto

@@ -85,7 +85,7 @@ message SetDisplayToNumber {
 }
 
 message SetDisplayToString {
-	required string string = 1  [(nanopb).max_size = 40];	
+	required string string = 1;	
 	required int32 dots = 2;
 	required int32 pos = 3;
 	required bool has_font = 4;

test.cpp

@@ -0,0 +1,50 @@
+#include <stdint.h>
+#include <stdio.h>
+#include <string.h>
+
+extern "C" {
+    #include "pb_decode.h"
+    #include "pb_encode.h"
+    #include "tm1638.pb.h"
+}
+
+bool callbackFont(pb_istream_t *stream, const pb_field_t *field, void **arg) {
+    uint8_t buffer[256] = {0};
+    int length = stream->bytes_left;
+    if (length > sizeof(buffer) - 1) {
+        return false;
+    }
+    if (!pb_read(stream, buffer, length)) {
+        return false;
+    }    
+    memset(*arg, 0, sizeof(buffer));
+    strncpy((char*) *arg, (char*) buffer, length);
+    return true;
+}
+
+int main() {
+    FILE *fp = fopen("test.buffer", "r");
+
+    int packet_size = fgetc(fp);
+    uint8_t in_buffer[256];
+    int bytes_read = fread((char*) in_buffer, 1, packet_size, fp);
+    if (bytes_read != packet_size) {
+        printf("length problem");
+        return 1;
+    }
+
+    pb_istream_t istream = pb_istream_from_buffer(in_buffer, bytes_read);
+    _tm1638_Command command;
+    command.setDisplayToString.string.funcs.decode = &callbackFont;
+    if (!pb_decode(&istream, tm1638_Command_fields, &command)) {
+        printf("decode problem");
+        return 1;
+    }
+
+    tm1638_SetDisplayToString setDisplayToString = command.setDisplayToString;
+    char dots = setDisplayToString.dots;
+    char pos = setDisplayToString.dots;
+    
+    printf("%s\n", setDisplayToString.string.arg);
+    return 0;
+}