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/* This program reads a message from stdin, detects its type and decodes it.
*/
#include <stdio.h>
#include <string.h>
#include <stdlib.h>
#include <pb_decode.h>
#include "unionproto.pb.h"
/* This function reads manually the first tag from the stream and finds the
* corresponding message type. It doesn't yet decode the actual message.
*
* Returns a pointer to the MsgType_fields array, as an identifier for the
* message type. Returns null if the tag is of unknown type or an error occurs.
*/
const pb_field_t* decode_unionmessage_type(pb_istream_t *stream)
{
pb_wire_type_t wire_type;
uint32_t tag;
bool eof;
while (pb_decode_tag(stream, &wire_type, &tag, &eof))
{
if (wire_type == PB_WT_STRING)
{
const pb_field_t *field;
for (field = UnionMessage_fields; field->tag != 0; field++)
{
if (field->tag == tag && (field->type & PB_LTYPE_SUBMESSAGE))
{
/* Found our field. */
return field->ptr;
}
}
}
/* Wasn't our field.. */
pb_skip_field(stream, wire_type);
}
return NULL;
}
bool decode_unionmessage_contents(pb_istream_t *stream, const pb_field_t fields[], void *dest_struct)
{
pb_istream_t substream;
if (!pb_make_string_substream(stream, &substream))
return false;
return pb_decode(&substream, fields, dest_struct);
}
int main()
{
/* Read the data into buffer */
uint8_t buffer[512];
size_t count = fread(buffer, 1, sizeof(buffer), stdin);
pb_istream_t stream = pb_istream_from_buffer(buffer, count);
const pb_field_t *type = decode_unionmessage_type(&stream);
bool status = false;
if (type == MsgType1_fields)
{
MsgType1 msg = {};
status = decode_unionmessage_contents(&stream, MsgType1_fields, &msg);
printf("Got MsgType1: %d\n", msg.value);
}
else if (type == MsgType2_fields)
{
MsgType2 msg = {};
status = decode_unionmessage_contents(&stream, MsgType2_fields, &msg);
printf("Got MsgType2: %s\n", msg.value ? "true" : "false");
}
else if (type == MsgType3_fields)
{
MsgType3 msg = {};
status = decode_unionmessage_contents(&stream, MsgType3_fields, &msg);
printf("Got MsgType3: %d %d\n", msg.value1, msg.value2);
}
if (!status)
{
printf("Decoding failed.\n");
return 1;
}
return 0;
}
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