@36node/telegram

telegram

Install

yarn add telegram

Usage

const telegram = require("telegram");

telegram();

API

new Telegram()

Constructs a Telegram object. Returned object represents a parser which parses nothing.

decompress(buffer)

Parse a Buffer object buffer with this parser and return an object as result.

[u]int{8, 16, 32}{le, be}(name[, options])

Parse bytes as an integer and store it in a variable named name. name should consist only of alphanumeric characters and start with an alphabet.

Number of bits can be chosen from 8, 16 and 32. Byte-ordering can be either l for little endian or b for big endian. With no prefix, it parses as a signed number, with u prefixed as an unsigned number.

var parser = new Telegram()
  // Signed 32-bit integer (little endian)
  .int32le("a")
  // Unsigned 8-bit integer
  .uint8("b")
  // Signed 16-bit integer (big endian)
  .int16be("c");

bit[1-64](name, options)

Parse bytes as a bit field and store it in variable name. There are 64 methods from bit1 to bit64 each corresponding to 1-bit-length to 64-bits-length bit field.

{float, double}{le, be}(name[, options])

Parse bytes as an floating-point value and store it in a variable named name.

var parser = new Telegram()
  // 32-bit floating value (big endian)
  .floatbe("a")
  // 64-bit floating value (little endian)
  .doublele("b");

string(name, options)

Parse bytes as a string. options is an object which can have the following keys:

• encoding - (Optional, defaults to utf8) Specify which encoding to use. "utf8", "ascii", "hex" and else are valid. See Buffer.toString for more info.
• length - (Optional) Length of the string. Can be a number, string or a function. Use number for statically sized arrays.
• zeroTerminated - (Optional, defaults to false) If true, then this parser reads until it reaches zero.
• greedy - (Optional, defaults to false) If true, then this parser reads until it reaches the end of the buffer. Will consume zero-bytes.
• stripNull - (Optional, must be used with length) If true, then strip null characters from end of the string.

array(name, options)

Parse bytes as an array. options is an object which can have the following keys:

• type - (Required) Type of the array element. Can be a string or an user defined Parser object. If it's a string, you have to choose from [u]int{8, 16, 32}{le, be} | string.
• length - Length of the array. Can be a number, string or a function. Use number for statically sized arrays.

var parser = new Telegram()
  // Statically sized array
  .array("data", {
    type: "int32",
    length: 8,
  })

  // Dynamically sized array (references another variable)
  .uint8("dataLength")
  .array("data2", {
    type: "int32",
    length: "dataLength",
  })

  // Dynamically sized array (with some calculation)
  .array("data3", {
    type: "int32",
    length: function() {
      return this.dataLength - 1;
    }, // other fields are available through this
  });

nest([name,] options)

Execute an inner parser and store its result to key name. If name is null or omitted, the result of the inner parser is directly embedded into the current object. options is an object which can have the following keys:

• type - (Required) A Parser object.

skip(length[, options])

Skip parsing for length bytes. If options has key named type and the value of type is "bit", skip parsing for length bits.

endianess(endianess)

Define what endianess to use in this parser. endianess can be either "little" or "big". The default endianess of Parser is set to big-endian.

var parser = new Telegram()
  .endianess("little")
  // You can specify endianess explicitly
  .uint16be("a")
  .uint32le("a")
  // Or you can omit endianess (in this case, little-endian is used)
  .uint16("b")
  .int32("c");

Common options

These are common options that can be specified in all parsers.

• formatter - Function that transforms the parsed value into a more desired form.

  var parser = new Telegram().array("ipv4", {
    type: uint8,
    length: "4",
    formatter: function(arr) {
      return arr.join(".");
    },
  });

• assert - Do assertion on the parsed result (useful for checking magic numbers and so on). If assert is a string or number, the actual parsed result will be compared with it with === (strict equality check), and an exception is thrown if they mismatch. On the other hand, if assert is a function, that function is executed with one argument (parsed result) and if it returns false, an exception is thrown.

  // simple maginc number validation
  var ClassFile = Telegram.start()
    .endianess("big")
    .uint32("magic", { assert: 0xcafebabe });

Examples

See examples for more complex examples.

Contributing

1. Fork it!
2. Create your feature branch: git checkout -b my-new-feature
3. Commit your changes: git commit -am 'Add some feature'
4. Push to the branch: git push origin my-new-feature
5. Submit a pull request :D

Author

telegram © zzswang, Released under the MIT License.

Authored and maintained by zzswang with help from contributors (list).

github.com/zzswang · GitHub @zzswang