Writing/reading protocol buffers

For sending complex JSON/JavaScript objects to C++ binaries over a wire, I am using Protocol Buffers. There is native protobuf support for Node.js these days, so I'm not using any other bindings.

// Set maximum execution time of binary to equal the
// remainder of processing time, minus a second to allow
// for parsing.
var timeLimit = context.getRemainingTimeInMillis() - 1000;

// Check if meta parameters are given in the request.
// Assign default values if they are not.
var model = new protocols.Model();

// Sort the resolutions.
function descending(a, b) {
    if (a.width > b.width) {
        return -1;
    } else if (a.width < b.width) {
        return 1;
    }
    return 0;
}

// Construct image objects.
var images = request.images.map(function(image) {
    // Perform the sort.
    image.resolutions.sort(descending);

    // Create an image protobuffer.
    var imageProto = new protocols.Model.Image();

    // Assign the original's resolution to the image.
    imageProto.setWidth(image.resolutions[0].width);
    imageProto.setHeight(image.resolutions[0].height);

    // Return the result.
    return imageProto;
});

// Construct flag enumeration references.
var flags = request.flags.map(function(flag) {
    return protocols.Model.Flag[flag];
});

// Assign request properties to protobuf.
model.setImagesList     (images                                                     );
model.setFlagsList      (flags                                                      );
model.setMinNoOfPages   (request.minNoOfPages   ? request.minNoOfPages  : 1         );
model.setMaxNoOfPages   (request.maxNoOfPages   ? request.maxNoOfPages  : 1         );
model.setMaxPerPage     (request.maxPerPage     ? request.maxPerPage    : 5         );
model.setPageWidth      (request.pageWidth      ? request.pageWidth     : 3508      );
model.setPageHeight     (request.pageHeight     ? request.pageHeight    : 2480      );
model.setTimeLimit      (request.timeLimit      ? request.timeLimit     : timeLimit );
model.setBorderWidth    (request.borderWidth    ? request.borderWidth   : 0         );
model.setMinDim         (request.minDim         ? request.minDim        : 0         );

// This is where things go wrong.
var serialized = model.serializeBinary();
fs.writeFileSync('model.pb', serialized);
var read = fs.readFileSync('model.pb'),
    model2 = protocols.Model.deserializeBinary(read);

console.log(model.toObject());
console.log(model2.toObject());

Above is the piece of code I'm stuck on. I managed to compile a protobuf message:

syntax = "proto3";

package layout;

message Model {

    enum Flag {
        FILL_PAGE = 0;
        BORDERS = 1;
    }

    message Image {
        int32 width = 1;
        int32 height = 2;
    }

    repeated Flag flags = 1;
    repeated Image images = 2;

    string avoid_layout = 3;
    int32 min_no_of_pages = 4;
    int32 max_no_of_pages = 5;
    int32 max_per_page = 6;
    int32 page_width = 7;
    int32 page_height = 8;
    int32 time_limit = 9;
    int32 border_width = 10;
    int32 min_dim = 11;
}

However, documentation on JavaScript support for protobuf is minimal (https://developers.google.com/protocol-buffers/docs/reference/javascript-generated#message) and I can't figure out how I can read my messages to a file, and then read them again. Can someone explain to me how to do this?

I imagine the solution is some variation on the last few lines of my code, but currently I'm getting this error:

AssertionError: Failure: Type not convertible to Uint8Array.

---

You are probably witnessing some obscure case of node Buffer not being recognized as Uint8Array . I found a relevant issue report. So try enforcing the type with

protocols.Model.deserializeBinary(new Uint8Array(read));

or replacing the constructor. That suggestion is particularly similar to yours - it is reading a binary file too.

链接地址: http://www.djcxy.com/p/48340.html

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