I have a JSON nested structure like this:
{"var1":"val1","var2":{"var1a":"val1a"}}
I have generated the cbor buffer using this function from the libcbor library.
cbor_item_t *cbor = cjson_cbor_load(json, cjson_cbor_stream_decode);
unsigned char *buffer;
size_t buffer_size;
cbor_serialize_alloc(cbor, &buffer, &buffer_size);
I'd like to generate directly the cbor object without passing by the json object, using this function...
cbor_item_t* root = cbor_new_definite_map(3);
/* Add the content */
cbor_map_add(root, (struct cbor_pair) {
.key = cbor_move(cbor_build_string("Is CBOR awesome?")),
.value = cbor_move(cbor_build_bool(true))
});
But I don't know how to add the nested structure <"var2":{>.
Do you have any suggestion?
Thank you.
Related
I'd like to make a POC of using leveldb in order to store key-value table of different data types in protobuf format.
So far I was able to open the database file, and I also saw the get function with the following signature :
virtual Status Get(const ReadOptions& options, const Slice& key, std::string* value)=0
I understand that the value is actually refers to a binary string like vector and not regular alphanumeric string, so I guess it can fit for multi type primitives like string, uint, enum) but how can it support struct/class that represent protobuf layout in c++ ?
So this is my proto file that I'd like to store in the leveldb:
message agentStatus {
string ip = 1;
uint32 port = 2;
string url = 3;
google.protobuf.Timestamp last_seen = 4;
google.protobuf.Timestamp last_keepalive = 5;
bool status = 6;
}
and this is my current POC code. How can I use the get method to access any of the variables from the table above ?
#include <leveldb/db.h>
void main () {
std::string db_file_path = "/tmp/data.db";
leveldb::DB* db;
leveldb::Status status;
leveldb::Options options;
options.create_if_missing = false;
status_ = leveldb::DB::Open(options, db_file_path, &db);
if (!status_.ok()) {
throw std::logic_error("unable to open db");
}
Thanks !
You need to serialize the protobuf message into a binary string, i.e. SerilaizeToString, and use the Put method to write the binary string to LevelDB with a key.
Then you can use the Get method to retrieve the binary value with the given key, and parse the binary string to a protobuf message, i.e. ParseFromString.
Finally, you can get fields of the message.
I am trying to download a potentially huge Azure block blob, using the C++ Azure client library. It isn't working because I don't know how to initialize a concurrency::streams::streambuf object with a buffer size. My code looks like this:
// Assume blockBlob has been created correctly.
concurrency::streams::istream blobStream = blockBlob.open_read();
// I don't know how to initialize this streambuf:
concurrency::streams::streambuf<uint8_t> dlStreamBuf;
size_t nBytesReturned = 0, nBytesToRead = 65536;
do {
// This gets the exception "Invalid streambuf object":
concurrency::task<size_t> returnedTask = blobStream.read(dlStreamBuf, nBytesToRead);
nBytesReturned = returnedTask.get();
bytesSoFar += nBytesReturned;
// Process the data in dlStreamBuf here...
} while(nBytesReturned > 0);
blobStream.close();
Note that the above streambuf is not to be confused with a standard C++ streambuf.
Can anyone advise me on how to properly construct and initialize a concurrency::streams::streambuf?
Thanks.
streambuf seems to be a template class. Try this instead:
concurrency::streams::container_buffer<std::vector<uint8_t>> output_buffer;
size_t nBytesReturned = 0, nBytesToRead = 65536;
do {
// This gets the exception "Invalid streambuf object":
concurrency::task<size_t> returnedTask = stream.read(output_buffer, nBytesToRead);
nBytesReturned = returnedTask.get();
bytesSoFar += nBytesReturned;
// Process the data in dlStreamBuf here...
} while (nBytesReturned > 0);
stream.close();
Sample code is here: https://github.com/Azure/azure-storage-cpp/blob/76cb553249ede1e6f05456d936c9a36753cc1597/Microsoft.WindowsAzure.Storage/tests/blob_streams_test.cpp#L192
I haven't used the stream methods for C++, but there are two ways mentioned in the C++ documentation about downloading to files or to steams here
The download_to_stream method ex:
// Retrieve storage account from connection string.
azure::storage::cloud_storage_account storage_account = azure::storage::cloud_storage_account::parse(storage_connection_string);
// Create the blob client.
azure::storage::cloud_blob_client blob_client = storage_account.create_cloud_blob_client();
// Retrieve a reference to a previously created container.
azure::storage::cloud_blob_container container = blob_client.get_container_reference(U("my-sample-container"));
// Retrieve reference to a blob named "my-blob-1".
azure::storage::cloud_block_blob blockBlob = container.get_block_blob_reference(U("my-blob-1"));
// Save blob contents to a file.
concurrency::streams::container_buffer<std::vector<uint8_t>> buffer;
concurrency::streams::ostream output_stream(buffer);
blockBlob.download_to_stream(output_stream);
std::ofstream outfile("DownloadBlobFile.txt", std::ofstream::binary);
std::vector<unsigned char>& data = buffer.collection();
outfile.write((char *)&data[0], buffer.size());
outfile.close();
Alternative, using download_to_file:
// Retrieve storage account from connection string.
azure::storage::cloud_storage_account storage_account = azure::storage::cloud_storage_account::parse(storage_connection_string);
// Create the blob client.
azure::storage::cloud_blob_client blob_client = storage_account.create_cloud_blob_client();
// Retrieve a reference to a previously created container.
azure::storage::cloud_blob_container container = blob_client.get_container_reference(U("my-sample-container"));
// Retrieve reference to a blob named "my-blob-2".
azure::storage::cloud_block_blob text_blob = container.get_block_blob_reference(U("my-blob-2"));
// Download the contents of a blog as a text string.
utility::string_t text = text_blob.download_text();
According to "datastax.github.io/cpp-driver/topics/basics/", the blob data type of Cassandra is matched to 'const cass_byte_t*'. Suppose the database, contains a structure saved in the form of blob; how can I fetch it.
Somebody had suggested me using cass_value_get_bytes(). Can anybody give example of how to use this function to fetch the structure?
What is the problem with cass_value_get_bytes()? You simply need to perform casting of data read to your structure, something like:
const cass_byte_t* outPtr = null;
size_t outSize = 0;
if (cass_value_get_bytes(casValue, &outPtr, &outSize) == CASS_OK) {
if (outSize == sizeof(YourStruct)) {
const YourStruct* yourStruct = reinterpret_cast<const YourStruct*>(outPtr);
}
}
In my project i use libgmime for MIME types. I'm trying to create new GMimeMessage using std::string as a body.
According to docs it can be done using GMimeStream and GMimeDataWrapper for preparing data, and then creating GMimePart from this data to be set as MIME part of new message.
The code:
std::string body = "some test data";
GMimeMessage* message = g_mime_message_new(FALSE);
//set header
g_mime_object_set_header((GMimeObject *) message, name.c_str()), value.c_str();
//create stream and write data into it.
GMimeStream* stream;
g_mime_stream_construct(stream, 0, body.length());
g_mime_stream_write_string(stream, body.c_str());
GMimeDataWrapper* wrapper = g_mime_data_wrapper_new_with_stream(stream, GMIME_CONTENT_ENCODING_DEFAULT);
//create GMimePart to be set as mime part of GMimeMessage
GMimePart* mime_part = g_mime_part_new();
g_mime_part_set_content_object(mime_part, wrapper);
g_mime_message_set_mime_part(message, (GMimeObject *) mime_part);
When i try to create message in this way, i get segfault here:
g_mime_stream_write_string(stream, body.c_str());
Maybe i'm using wrong method of message creation...
What's the right way it can be done?
You have bad initialization GMimeStream *stream. Need:
GMimeStream *stream;
/* initialize GMime */
g_mime_init (0);
/* create a stream around stdout */
stream = g_mime_stream_mem_new_with_buffer(body_part.c_str(), body_part.length());
See doc: http://spruce.sourceforge.net/gmime/tutorial/x49.html
And sample: http://fossies.org/linux/gmime/examples/basic-example.c
I have my xml as char buffer (that's fetched from server, I don't want to save it -> takes extra time and is completely obsolete):
char myword[] = "...xml..."
xmlSchemaParserCtxtPtr ctxt = xmlSchemaNewParserCtxt(xsdFilePath);
xmlDocPtr doc = ?;
Now I need to get doc. I'm trying to use following function:
doc = xmlReadMemory(myword, sizeof(myword), ?URL?, NULL, 0)
But the problem is with URL, what should I put in there..? Am I using this function right? Maybe there is another way to get xmlDocPtr?
BTW: I need xmlDocPtr to perform:
ret = xmlSchemaValidateDoc(ctxt, doc);
Simply pass a NULL pointer:
doc = xmlReadMemory(myword, sizeof(myword), NULL, NULL, 0);