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/*
* Copyright 2019 gRPC authors.
*
* Licensed under the Apache License, Version 2.0 (the "License");
* you may not use this file except in compliance with the License.
* You may obtain a copy of the License at
*
* http://www.apache.org/licenses/LICENSE-2.0
*
* Unless required by applicable law or agreed to in writing, software
* distributed under the License is distributed on an "AS IS" BASIS,
* WITHOUT WARRANTIES OR CONDITIONS OF ANY KIND, either express or implied.
* See the License for the specific language governing permissions and
* limitations under the License.
*
*/
enum ReadState {
NO_DATA,
READING_SIZE,
READING_MESSAGE,
}
export class StreamDecoder {
private readState: ReadState = ReadState.NO_DATA;
private readCompressFlag: Buffer = Buffer.alloc(1);
private readPartialSize: Buffer = Buffer.alloc(4);
private readSizeRemaining = 4;
private readMessageSize = 0;
private readPartialMessage: Buffer[] = [];
private readMessageRemaining = 0;
constructor(private maxReadMessageLength: number) {}
write(data: Buffer): Buffer[] {
let readHead = 0;
let toRead: number;
const result: Buffer[] = [];
while (readHead < data.length) {
switch (this.readState) {
case ReadState.NO_DATA:
this.readCompressFlag = data.slice(readHead, readHead + 1);
readHead += 1;
this.readState = ReadState.READING_SIZE;
this.readPartialSize.fill(0);
this.readSizeRemaining = 4;
this.readMessageSize = 0;
this.readMessageRemaining = 0;
this.readPartialMessage = [];
break;
case ReadState.READING_SIZE:
toRead = Math.min(data.length - readHead, this.readSizeRemaining);
data.copy(
this.readPartialSize,
4 - this.readSizeRemaining,
readHead,
readHead + toRead
);
this.readSizeRemaining -= toRead;
readHead += toRead;
// readSizeRemaining >=0 here
if (this.readSizeRemaining === 0) {
this.readMessageSize = this.readPartialSize.readUInt32BE(0);
if (this.maxReadMessageLength !== -1 && this.readMessageSize > this.maxReadMessageLength) {
throw new Error(`Received message larger than max (${this.readMessageSize} vs ${this.maxReadMessageLength})`);
}
this.readMessageRemaining = this.readMessageSize;
if (this.readMessageRemaining > 0) {
this.readState = ReadState.READING_MESSAGE;
} else {
const message = Buffer.concat(
[this.readCompressFlag, this.readPartialSize],
5
);
this.readState = ReadState.NO_DATA;
result.push(message);
}
}
break;
case ReadState.READING_MESSAGE:
toRead = Math.min(data.length - readHead, this.readMessageRemaining);
this.readPartialMessage.push(data.slice(readHead, readHead + toRead));
this.readMessageRemaining -= toRead;
readHead += toRead;
// readMessageRemaining >=0 here
if (this.readMessageRemaining === 0) {
// At this point, we have read a full message
const framedMessageBuffers = [
this.readCompressFlag,
this.readPartialSize,
].concat(this.readPartialMessage);
const framedMessage = Buffer.concat(
framedMessageBuffers,
this.readMessageSize + 5
);
this.readState = ReadState.NO_DATA;
result.push(framedMessage);
}
break;
default:
throw new Error('Unexpected read state');
}
}
return result;
}
}
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