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Matthieu Monsch edited this page Jun 6, 2018 · 172 revisions

Types and schemas

readSchema(spec)

  • spec {String} Type IDL specification.

Convenience method to generate a schema from a standalone type's IDL specification. The spec must contain a single type definition, for example:

const schema = parseTypeSchema(`record Header { long id; string name; }`);
const type = Type.forSchema(schema);
type.isValid({id: 123, name: 'abc'}); // true.

Class Type

"Abstract" base Avro type class; all implementations inherit from it. It shouldn't be instantiate directly, but rather through one of the following factory methods described below.

Type.forSchema(schema, [opts])

  • schema {Object|String} Decoded schema. This schema can be a string if it is a reference to a primitive type (e.g. 'int', ), or a reference to a type in the registry (see opts below).
  • opts {Object} Parsing options. The following keys are currently supported:
    • assertLogicalTypes {Boolean} The Avro specification mandates that we fall through to the underlying type if a logical type is invalid. When set, this option will override this behavior and throw an error when a logical type can't be applied.
    • logicalTypes {Object} Optional dictionary of LogicalType. This can be used to support serialization and deserialization of arbitrary native objects.
    • namespace {String} Optional parent namespace.
    • noAnonymousTypes {Boolean} Throw an error if a named type (enum, fixed, record, or error) is missing its name field. By default anonymous types are supported; they behave exactly like their named equivalent except that they cannot be referenced, can be resolved by any compatible type, and use the type's typeName as union branch.
    • registry {Object} Registry of predefined type names. This can for example be used to override the types used for primitives or to split a schema declaration over multiple files.
    • typeHook(schema, opts) {Function} Function called before each type declaration or reference is parsed. The relevant decoded schema is available as first argument and the parsing options as second. This function can optionally return a type which will then be used in place of the result of parsing schema. Using this option, it is possible to customize the parsing process by intercepting the creation of any type. Here are a few examples of what is possible using a custom hook:
    • wrapUnions {String|Boolean} Control whether unions should be represented using a WrappedUnionType or an UnwrappedUnionType. By default, the "natural" unwrapped alternative will be used if possible, falling back to wrapping if the former would lead to ambiguities. Possible values for this option are: 'auto' (the default); 'always' or true (always wrap unions); 'never' or false (never wrap unions, an error will be thrown if an ambiguous union is parsed in this case).

Instantiate a type for its schema.

Type.forTypes(types, [opts])

  • types {Array} Array of types to combine.
  • opts {Object} All the options of Type.forSchema are available, as well as:
    • strictDefaults {Boolean} When combining records with missing fields, the default behavior is to make such fields optional (wrapping their type inside a nullable union and setting their default to null). Activating this flag will instead combine the records into a map.

Merge multiple types into one. The resulting type will support all the input types' values.

Type.forValue(val, [opts])

  • val {Any} Value to generate the type for.
  • opts {Object} All of Type.forTypes' options are supported, along with:
    • emptyArrayType {Type} Temporary type used when an empty array is encountered. It will be discarded as soon as the array's type can be inferred. Defaults to null's type.
    • valueHook(val, opts) Function called each time a type needs to be inferred from a value. This function should either return an alternate type to use, or undefined to proceed with the default inference logic.

Infer a type from a value.

Type.isType(any, [prefix...])

  • any {...} Any object.
  • prefix {String} If specified, this function will only return true if the type's type name starts with at least one of these prefixes. For example, Type.isType(type, 'union', 'int') will return true if and only if type is either a union type or integer type.

Check whether any is an instance of Type. This is similar to any instanceof Type but will work across contexts (e.g. iframes).

Type.__reset(size)

  • size {Number} New buffer size in bytes.

This method resizes the internal buffer used to encode all types. You can call this method if you are encoding very large values and need to reclaim memory. In some cases, it can also be beneficial to call this method at startup with a sufficiently large buffer size to allow the JavaScript engine to better optimize encoding.

type.aliases

Returns a list of aliases for named types and undefined for others. Note that it is possible to modify this list to add and remove aliases after the type is created (altering which types can be resolved via type.createResolver).

type.branchName

If type doesn't have a name, return its "type name" instead of undefined. (This method then returns the type's branch name when included in a union.)

type.clone(val, [opts])

  • val {...} The object to copy.
  • opts {Object} Options:
    • coerceBuffers {Boolean} Allow coercion of JSON buffer representations into actual Buffer objects. When used with unwrapped unions, ambiguities caused by this coercion are always resolved in favor of the buffer type.
    • fieldHook(field, any, type) {Function} Function called when each record field is populated. The value returned by this function will be used instead of any. field is the current Field instance and type the parent type.
    • qualifyNames {Boolean} The branch's key in the union object should be the qualified name of its type, however some serializers incorrectly omit the namespace (which can cause collisions). Passing in this option will attempt to lookup unqualified names as well and return correctly qualified names. This option has no effect when used with unwrapped unions.
    • skipMissingFields {Boolean} Ignore any missing fields (or equal to undefined). This can be useful in combination with clone's other options to perform validation after wrapping unions or coercing buffers. Fields missing in the input will be set to undefined in the output.
    • wrapUnions {Boolean} Allow wrapping of union values into their first matching branch. This option has no effect when used with unwrapped unions.

Deep copy a value of type.

type.compare(val1, val2)

  • val1 {...} Value of type.
  • val2 {...} Value of type.

Returns 0 if both values are equal according to their sort order, -1 if the first is smaller than the second , and 1 otherwise. Comparing invalid values is undefined behavior.

type.compareBuffers(buf1, buf2)

  • buf1 {Buffer} type value bytes.
  • buf2 {Buffer} type value bytes.

Similar to compare, but doesn't require decoding values.

type.createResolver(writerType)

  • writerType {Type} Writer type.

Create a resolver that can be be passed to the type's decode and fromBuffer methods. This will enable decoding values which had been serialized using writerType, according to the Avro resolution rules. If the schemas are incompatible, this method will throw an error.

For example, assume we have the following two versions of a type:

// A schema's first version.
const v1 = avro.Type.forSchema({
  name: 'Person',
  type: 'record',
  fields: [
    {name: 'name', type: 'string'},
    {name: 'age', type: 'int'}
  ]
});

// The updated version.
const v2 = avro.Type.forSchema({
  type: 'record',
  name: 'Person',
  fields: [
    {
      name: 'name', type: [
        'string',
        {
          name: 'Name',
          type: 'record',
          fields: [
            {name: 'first', type: 'string'},
            {name: 'last', type: 'string'}
          ]
        }
      ]
    },
    {name: 'phone', type: ['null', 'string'], default: null}
  ]
});

The two types are compatible since the name field is present in both (the string can be promoted to the new union) and the new phone field has a default value.

//  We can therefore create a resolver.
const resolver = v2.createResolver(v1);

// And pass it whenever we want to decode from the old type to the new.
const buf = v1.toBuffer({name: 'Ann', age: 25});
const obj = v2.fromBuffer(buf, resolver); // === {name: {string: 'Ann'}, phone: null}

See the advanced usage page for more details on how schema evolution can be used to significantly speed up decoding.

type.decode(buf, [pos,] [resolver])

  • buf {Buffer} Buffer to read from.
  • pos {Number} Offset to start reading from.
  • resolver {Resolver} Optional resolver to decode values serialized from another schema. See createResolver for how to create one.

Returns {value: value, offset: offset} if buf contains a valid encoding of type (value being the decoded value, and offset the new offset in the buffer). Returns {value: undefined, offset: -1} when the buffer is too short.

type.doc

Return the type's documentation (doc attribute in schema and docstring in IDL spec).

type.encode(val, buf, [pos])

  • val {...} The value to encode. An error will be raised if this isn't a valid type value.
  • buf {Buffer} Buffer to write to.
  • pos {Number} Offset to start writing at.

Encode a value into an existing buffer. If enough space was available in buf, returns the new (non-negative) offset, otherwise returns -N where N is the (positive) number of bytes by which the buffer was short.

type.equals(any)

  • any {...} Any object.

Check whether two types are equal (i.e. have the same canonical schema).

type.fingerprint([algorithm])

  • algorithm {String} Algorithm used to compute the hash. Defaults to 'md5'. Only 'md5' is supported in the browser.

Return a buffer identifying type.

type.fromBuffer(buf, [resolver,] [noCheck])

  • buf {Buffer} Bytes containing a serialized value of type.
  • resolver {Resolver} To decode values serialized from another schema. See createResolver for how to create an resolver.
  • noCheck {Boolean} Do not check that the entire buffer has been read. This can be useful when using an resolver which only decodes fields at the start of the buffer, allowing decoding to bail early and yield significant performance speedups.

Deserialize a buffer into its corresponding value.

type.fromString(str)

  • str {String} String representing a JSON-serialized object.

Deserialize a JSON-encoded object of type.

type.isValid(val, [opts])

  • val {...} The value to validate.
  • opts {Object} Options:
    • errorHook(path, any, type) {Function} Function called when an invalid value is encountered. When an invalid value causes its parent values to also be invalid, the latter do not trigger a callback. path will be an array of strings identifying where the mismatch occurred. This option is especially useful when dealing with complex records, for example to:
    • noUndeclaredFields {Boolean} When set, records with attributes that don't correspond to a declared field will be considered invalid. The default is to ignore any extra attributes.

Check whether val is a valid type value.

type.name

Returns type's fully qualified name if it exists, undefined otherwise.

type.random()

Returns a random value of type.

type.schema([opts])

  • opts {Object} Options:
    • exportAttrs {Boolean} Include aliases, field defaults, order, and logical type attributes in the returned schema.
    • noDeref {Boolean} Do not dereference any type names.

Returns type's canonical schema. This can be used to compare schemas for equality.

type.toBuffer(val)

  • val {...} The value to encode. It must be a valid type value.

Returns a Buffer containing the Avro serialization of val.

type.toString([val])

  • val {...} The value to serialize. If not specified, this method will return a human-friendly description of type.

Serialize an object into a JSON-encoded string.

type.typeName

Returns type's "type name" (e.g. 'int', 'record', 'fixed').

type.wrap(val)

  • val {...} The value to wrap, this value should should be valid for type. Behavior is otherwise undefined.

Convenience method to wrap a value into a valid branch for use in a wrapped union:

const intType = avro.Type.forSchema('int');
intType.wrap(123); // {int: 123}

Class ArrayType(schema, [opts])

  • schema {Object} Decoded type attributes.
  • opts {Object} Parsing options.

type.itemsType

The type of the array's items.

Class EnumType(schema, [opts])

  • schema {Object} Decoded type attributes.
  • opts {Object} Parsing options.

type.symbols

Returns the type's symbols (an array of strings representing the enum's valid values).

Class FixedType(schema, [opts])

  • schema {Object} Decoded type attributes.
  • opts {Object} Parsing options.

type.size

The size in bytes of instances of this type.

Class LogicalType(schema, [opts])

  • schema {Object} Decoded type attributes.
  • opts {Object} Parsing options.

"Abstract class" used to implement custom types. To implement a new logical type, the steps are:

  • Call LogicalType's constructor inside your own subclass' to make sure the underlying type is property set up. Throwing an error anywhere inside your constructor will prevent the logical type from being used (the underlying type will be used instead).
  • Extend LogicalType in your own subclass (typically using util.inherits).
  • Override the following methods (prefixed with an underscore because they are internal to the class that defines them and should only be called by the internal LogicalType methods):
    • _export (optional)
    • _fromValue
    • _resolve (optional)
    • _toValue

See here for more information. A couple sample implementations are available as well:

type.underlyingType

Use this method to get the underlying Avro type. This can be useful when a logical type can support different underlying types.

type._export(schema)

  • schema {Object} The type's raw exported attributes, containing type and logicalType keys.

This method should add attributes to be exported to the schema object. These will then be included into any type.getSchema calls with exportAttrs set. A default implementation exporting nothing is provided.

type._fromValue(val)

  • val {...} A value deserialized by the underlying type.

This method should return the converted value. This method is abstract and should be implemented but not called directly.

type._resolve(type)

  • type {Type} The writer's type.

This method should return:

  • undefined if the writer's values cannot be converted.
  • Otherwise, a function which converts a value deserialized by the writer's type into a wrapped value for the current type.

This method is abstract and should be implemented but not called directly.

type._toValue(any)

  • any {...} A derived value.

This method should return a value which can be serialized by the underlying type. If any isn't a valid value for this logical type, you can either return undefined or throw an exception (slower). This method is abstract and should be implemented but not called directly.

Class LongType(schema, [opts])

  • schema {Object} Decoded type attributes.
  • opts {Object} Parsing options.

LongType.__with(methods, [noUnpack])

  • methods {Object} Method implementations dictionary keyed by method name, see below for details on each of the functions to implement.
  • noUnpack {Boolean} Do not automatically unpack bytes before passing them to the above methods' fromBuffer function and pack bytes returned by its toBuffer function.

This function provides a way to support arbitrary long representations. Doing so requires implementing the following methods (a few examples are available here):

  • compare(val1, val2)

    See Type.compare.

  • isValid(val, [opts])

    See Type.isValid.

  • fromBuffer(buf)

    • buf {Buffer} Encoded long. If noUnpack is off (the default), buf will be an 8-byte buffer containing the long's unpacked representation. Otherwise, buf will contain a variable length buffer with the long's packed representation.

    This method should return the corresponding decoded long.

  • fromJSON(any)

    • any {Number|...} Parsed value. To ensure that the fromString method works correctly on data JSON-serialized according to the Avro spec, this method should at least support numbers as input.

    This method should return the corresponding decoded long.

    It might also be useful to support other kinds of input (typically the output of the long implementation's toJSON method) to enable serializing large numbers without loss of precision (at the cost of violating the Avro spec).

  • toBuffer(val)

    • val {...} Decoded long.

    If noUnpack is off (the default), this method should return an 8-byte buffer with the long's unpacked representation. Otherwise, toBuffer should return an already packed buffer (of variable length).

  • toJSON(val)

    • val {...} Decoded long.

    This method should return the long's JSON representation.

Class MapType(schema, [opts])

  • schema {Object} Decoded type attributes.
  • opts {Object} Parsing options.

type.valuesType

The type of the map's values (keys are always strings).

Class RecordType(schema, [opts])

  • schema {Object} Decoded type attributes.
  • opts {Object} Parsing options.

type.field(name)

  • name {String} Field name.

Convenience method to retrieve a field by name. A field is an object with the following methods:

class Field

field.aliases

The list of aliases for this field.

field.defaultValue()

The field's default value if specified, undefined otherwise.

field.name

The field's name.

field.order

One of 'ascending', 'descending', or 'ignored'.

field.type

The field's type.

type.fields

Returns the array of fields contained in this record.

type.recordConstructor

The Record constructor for instances of this type. Indeed, each RecordType generates a corresponding Record constructor when its schema is parsed. This helps make decoding and encoding records more efficient. This also lets us provide helpful methods on decoded values (see below).

Class Record(...)

Calling the constructor directly can sometimes be a convenient shortcut to instantiate new records of a given type. In particular, it will correctly initialize all the missing record's fields with their default values.

The Record prototype also exposes a few convenience methods described below (available on each decoded record value).

Record.type

Convenience class method to get the record's type.

record.clone([opts])

Convenience function to clone the current record.

record.compare(val)

Convenience function to compare the current record to another.

record.isValid([opts])

Convenience function to validate the current record.

record.toBuffer()

Convenience function to serialize the current record.

record.toString()

Convenience function to serialize the current record using JSON encoding.

record.wrapped()

Convenience function to wrap the record into a valid wrapped union branch.

Class UnwrappedUnionType(schema, [opts])

  • schema {Object} Decoded type attributes.
  • opts {Object} Parsing options.

This class is the default used to represent unions. Its values are decoded without a wrapping object: null and 48 would be valid values for the schema ["null", "int"] (as opposed to null and {'int': 48} for wrapped unions).

This representation is usually more convenient and natural, however it isn't able to guarantee correctness for all unions. For example, we wouldn't be able to tell which branch the value 23 comes from in a schema ["int", "float"]. More concretely, a union can be represented using this class if it has at most a single branch inside each of the categories below:

  • 'null'
  • 'boolean'
  • 'int', 'long', 'float', 'double'
  • 'string', 'enum'
  • 'bytes', 'fixed'
  • 'array'
  • 'map', 'record'

So ['null', 'int'] and ['null', 'string', {type: 'array', items: 'string'}] are supported, but ['int', 'float'] and ['bytes', {name: 'Id', type: 'fixed', size: 2}] are not.

Finally, note that by using logical types, it is possible to work around the above requirements (by delegating the branch inference to the logical types themselves).

type.types

The possible types that this union can take.

Class WrappedUnionType(schema, [opts])

  • schema {Object} Decoded type attributes.
  • opts {Object} Parsing options.

This class is the representation using for unions for types generated with forSchema's wrapUnions option set. It uses Avro's JSON encoding and is able to correctly represent all unions: branch type information is never lost since it is included in the decoded value.

type.types

The possible types that this union can take.

Additionally, each value decoded from a wrapped union exposes its corresponding type via its constructor. This is also typically faster than calling Object.keys() on the value when the active branch is unknown.

const type = new avro.types.WrappedUnionType(['int', 'long']);
const val = type.fromBuffer(new Buffer([2, 8])); // == {long: 4}
const branchType = val.constructor.type // == <LongType>

Files and streams

The following convenience functions are available for common operations on container files:

createBlobDecoder(blob, [opts])

  • blob {Blob} Binary blob.
  • opts {Object} Decoding options, passed to BlockDecoder.

Returns a readable stream of decoded objects from an Avro container blob. Only available in the browser when using the full distribution.

createBlobEncoder(schema, [opts])

  • schema {Object|String|Type} Type used to serialize.
  • opts {Object} Encoding options, passed to BlockEncoder.

Returns a duplex stream of objects. Written values will end up serialized into an Avro container blob which will be output as the stream's only readable value. Only available in the browser when using the full distribution.

createFileDecoder(path, [opts])

  • path {String} Path to Avro container file.
  • opts {Object} Decoding options, passed to BlockDecoder.

Returns a readable stream of decoded objects from an Avro container file. Not available in the browser.

createFileEncoder(path, schema, [opts])

  • path {String} Destination path.
  • schema {Object|String|Type} Type used to serialize.
  • opts {Object} Encoding options, passed to BlockEncoder.

Returns a writable stream of objects. These will end up serialized into an Avro container file. Not available in the browser.

extractFileHeader(path, [opts])

  • path {String} Path to Avro container file.
  • opts {Object} Options:
    • decode {Boolean} Decode schema and codec metadata (otherwise they will be returned as bytes). Defaults to true.

Extract header from an Avro container file synchronously. If no header is present (i.e. the path doesn't point to a valid Avro container file), null is returned. Not available in the browser.

Class BlockDecoder([opts])

  • opts {Object} Decoding options. Available keys:
    • codecs {Object} Dictionary of decompression functions, keyed by codec name. A decompression function has the signature fn(compressedData, cb) where compressedData is a buffer of compressed data, and must call cb(err, uncompressedData) on completion. The default contains handlers for the 'null' and 'deflate' codecs.
    • readerSchema {String|Object|Type} An optional schema used to resolve the values encoded in the file. This schema should be compatible with the schema used to write the file.
    • noDecode {Boolean} Do not decode records before returning them.
    • parseHook(schema) {Function} Function called to generate the type from the schema contained in the file. This can be used to pass in addtional options when parsing the schema (e.g. logical type information). See below for an example.

A duplex stream which decodes bytes coming from on Avro object container file.

Sample use of the codecs option to decode a Snappy encoded file using snappy (note checksum handling):

const crc32 = require('buffer-crc32');
const snappy = require('snappy');

const blockDecoder = new avro.streams.BlockDecoder({
  codecs: {
    snappy: function (buf, cb) {
      // Avro appends checksums to compressed blocks.
      const len = buf.length;
      const checksum = buf.slice(len - 4, len);
      snappy.uncompress(buf.slice(0, len - 4), function (err, inflated) {
        if (err) {
          cb(err);
          return;
        }
        if (!checksum.equals(crc32(inflated))) {
          // We make sure that the checksum matches.
          cb(new Error('invalid checksum'));
          return;
        }
        cb(null, inflated);
      });
    }
  }
});

Note that the BlockDecoder's opts aren't used when parsing the writer's type. A parseHook should be used instead. The example below shows how to instantiate a type with the wrapUnions option set:

const decoder = new avro.streams.BlockDecoder({
  parseHook: (schema) => {
    return avro.Type.forSchema(schema, {wrapUnions: true});
  }
});

Event 'metadata'

  • type {Type} The type used to write the file.
  • codec {String} The codec's name.
  • header {Object} The file's header, containing in particular the raw schema and codec.

This event is guaranteed to be emitted before the first 'data' event.

Event 'data'

  • data {...} Decoded element or raw bytes.

BlockDecoder.getDefaultCodecs()

Get built-in decompression functions (currently null and deflate).

Class BlockEncoder(schema, [opts])

  • schema {Object|String|Type} Schema used for encoding. Argument parsing logic is the same as for parse.
  • opts {Object} Encoding options. Available keys:
    • blockSize {Number} Maximum uncompressed size of each block data. A new block will be started when this number is exceeded. If it is too small to fit a single element, it will be increased appropriately. Defaults to 64kB.
    • codec {String} Name of codec to use for encoding. See codecs option below to support arbitrary compression functions.
    • codecs {Object} Dictionary of compression functions, keyed by codec name. A compression function has the signature fn(uncompressedData, cb) where uncompressedData is a buffer of uncompressed data, and must call cb(err, compressedData) on completion. The default contains handlers for the 'null' and 'deflate' codecs.
    • metadata {Object} Dictionary of arbitrary metadata (values must be Buffers) persisted in the container file's header. Keys prefixed by avro. are reserved.
    • writeHeader {Boolean|String} Controls whether to write the header. Valid parameter values are: 'always', true (always emit the header, even if no records have been written); 'never', false (never emit the header, useful when appending to an existing container file); 'auto' (only emit the header when the first data is written). Defaults to 'auto'.
    • syncMarker {Buffer} 16 byte buffer to use as synchronization marker inside the file. If unspecified, a random value will be generated.

A duplex stream to create Avro container object files.

Sample use of the codecs option to encode a file using snappy (note checksum handling):

const crc32 = require('buffer-crc32');
const snappy = require('snappy');

const blockEncoder = new avro.streams.BlockEncoder(someType, {
  codec: 'snappy',
  codecs: {
    snappy: function (buf, cb) {
      // Avro requires appending checksums to compressed blocks.
      const checksum = crc32(buf);
      snappy.compress(buf, function (err, deflated) {
        if (err) {
          cb(err);
          return;
        }
        const block = Buffer.alloc(deflated.length + 4);
        deflated.copy(block);
        checksum.copy(block, deflated.length);
        cb(null, block);
      });
    }
  }
});

Event 'data'

  • data {Buffer} Serialized bytes.

BlockEncoder.getDefaultCodecs()

Get built-in compression functions (currently null and deflate).

Class RawDecoder(schema, [opts])

  • schema {Object|String|Type} Writer schema. Required since the input doesn't contain a header. Argument parsing logic is the same as for parse.
  • opts {Object} Decoding options. Available keys:
    • decode {Boolean} Whether to decode records before returning them. Defaults to true.

A duplex stream which can be used to decode a stream of serialized Avro objects with no headers or blocks.

Event 'data'

  • data {...} Decoded element or raw bytes.

Class RawEncoder(schema, [opts])

  • schema {Object|String|Type} Schema used for encoding. Argument parsing logic is the same as for parse.
  • opts {Object} Encoding options. Available keys:
    • batchSize {Number} To increase performance, records are serialized in batches. Use this option to control how often batches are emitted. If it is too small to fit a single record, it will be increased automatically. Defaults to 64kB.

The encoding equivalent of RawDecoder.

Event 'data'

  • data {Buffer} Serialized bytes.

IPC & RPC

Avro also defines a way of executing remote procedure calls.

assembleProtocol(path, [opts,] cb)

  • path {String} Path to Avro IDL file.
  • opts {Object} Options:
    • ackVoidMessages {Boolean} By default, using void as response type will mark the corresponding message as one-way. When this option is set, void becomes equivalent to null.
    • delimitedCollections {Boolean} The parser will be default support collections (array items and map values) even when they aren't surrounded by </> markers; this tends to lead to cleaner inline declarations. You can disable this extensions by setting this option.
    • importHook(path, kind, cb) {Function} Function called to load each file. The default will look up the files in the local file-system and load them via fs.readFile. kind is one of 'idl', 'protocol', or 'schema' depending on the kind of import requested. In the browser, no default is provided.
    • typeRefs {Object} Type references, used to expand custom type names. This option defaults to values compatible with the Java implementation.
  • cb(err, schema) {Function} Callback. If an error occurred, its path property will contain the path to the file which caused it.

Assemble IDL files into a protocol. This protocol can then be passed to Service.forProtocol to instantiate the corresponding service.

discoverProtocol(transport, [opts,] cb)

  • transport {Transport} See below.
  • opts {Object} Options:
    • scope {String} Remove server scope.
    • timeout {Number} Maximum delay to wait for a response, 0 for no limit. Defaults to 10000.
  • cb(err, protocol) {Function} Callback.

Discover a remote server's protocol. This can be useful to emit requests to another server without having a local copy of the protocol.

readProtocol(spec, [opts])

  • spec {String} Protocol IDL specification.
  • opts {Object} Options (see assembleProtocol for details).
    • ackVoidMessages {Boolean} See assembleProtocol.
    • delimitedCollections {Boolean} See assembleProtocol.
    • typeRefs {Object} See assembleProtocol.

Synchronous version of assembleProtocol. Note that it doesn't support imports.

Class Service

Service instances are generated from a protocol declaration and define an API that can be used to send remote messages (for example to another machine or another process on the same machine).

Service.forProtocol(protocol, [opts])

  • protocol {Object} A valid Avro protocol.
  • opts {Object} All of Type.forSchema's options are accepted.

Construct a service from a protocol.

service.createClient([opts])

  • opts {Object} Options:
    • buffering {Boolean} By default emitting messages before any channels become active will fail. Setting this option will instead cause messages to be buffered until a channel becomes available.
    • channelPolicy(channels) {Function} Function to load balance between active channels. Should return one of the passed in channels. The default selects a channel at random.
    • remoteProtocols {Object} Map of remote protocols, keyed by hash, to cache locally. This will save a handshake when connecting using one of these protocols.
    • server {Server} Convenience function to connect the client to an existing server using an efficient in-memory channel.
    • strictTypes {Boolean} Disable conversion of string errors to Error objects and of null to undefined.
    • timeout {Number} Default timeout in milliseconds used when emitting requests, specify 0 for no timeout (note that this may cause memory leaks in the presence of communication errors). Defaults to 10000. This timeout can be overridden on a per-request basis. Finally, this timeout only applies to RPC handling (i.e. neither middleware or buffering count towards this timeout).
    • transport {Transport} Convenience option to add a transport to the newly created client.

Generate a client corresponding to this service. This client can be used to send messages to a server for a compatible service.

service.createServer([opts])

  • opts {Object} Options:
    • noCapitalize {Boolean} By default, handler setters will be generated on the server using the convention on<CapitalizedMessageName> (e.g. message resolveUrl would correspond to onResolveUrl). Use this option to use the raw name instead.
    • remoteProtocols {Object} Map of remote protocols, keyed by hash, to cache locally. This will save a handshake with clients connecting using one of these protocols.
    • silent {Boolean} Suppress default behavior of outputting handler errors to standard error.
    • strictTypes {Boolean} Disable automatic conversion of Error objects to strings, and null to undefined. When set, handlers' returned error parameters must either be a valid union branch or undefined.
    • systemErrorFormatter(err) {Function} Function called to format system errors before sending them to the calling client. It should return a string.

Generate a server corresponding to this service. This server can be used to respond to messages from compatible protocols' clients.

service.doc

Get the service's docstring.

service.hash

Returns a buffer containing the service's protocol's hash.

service.message(name)

  • name {String} Message name.

Get a single message from this service.

class Message

message.doc

The message's documentation (doc field).

message.errorType

The message's error type (always a union, with a string as first branch).

message.name

The message's name.

message.oneWay

Whether the message expects a response.

message.requestType

The type of this message's requests (always a record).

message.responseType

The type of this message's responses.

message.schema([opts])

Return this message's schema.

service.messages

Retrieve a list of all the messages defined in the service.

service.name

Returns the service's fully qualified name.

service.protocol

Returns the service's protocol.

service.type(name)

  • name {String} A type's fully qualified name.

Convenience function to retrieve a type defined inside this service. Returns undefined if no type exists for the given name.

service.types

Returns a list of the types declared in this service.

Class Client

Event 'channel'

  • channel {ClientChannel} The newly created channel.

Event emitted each time a channel is created.

client.activeChannels()

Returns a list of this client's currently active channels (i.e. neither draining nor destroyed).

client.createChannel(transport, [opts])

  • transport {Duplex|Object|Function} The transport used to communicate with the remote listener. Multiple argument types are supported, see below.
  • opts {Object} Options.
    • endWritable {Boolean} Set this to false to prevent the transport's writable stream from being ended when the emitter is destroyed (for stateful transports) or when a request is sent (for stateless transports). Defaults to true.
    • noPing {Boolean} Do not emit a ping request when the emitter is created. For stateful transports this will assume that a connection has already been established, for stateless transports this will delay handshakes until the first message is sent.
    • objectMode {Boolean} Expect a transport in object mode. Instead of exchanging buffers, objects {id, payload} will be written and expected. This can be used to implement custom transport encodings.
    • scope {String} Scope used to multiplex messages across a shared connection. There should be at most one emitter or listener per scope on a single stateful transport. Matching emitter/listener pairs should have matching scopes. Scoping isn't supported on stateless transports.
    • serverHash {Buffer} Hash of remote protocol to use for the initial handshake. If unspecified or the corresponding hash isn't found in the client's cache, the client's protocol will be used instead.

Generate a channel for this client. This channel can then be used to communicate with a remote server of compatible protocol.

There are two major types of transports:

  • Stateful: a pair of binary streams {readable, writable}. As a convenience passing a single duplex stream is also supported and equivalent to passing {readable: duplex, writable: duplex}.

  • Stateless: stream factory fn(cb) which should return a writable stream and call its callback argument with an eventual error and readable stream (if available).

client.destroyChannels([opts])

  • opts {Object} Options:
    • noWait {Boolean} Don't wait for pending requests to drain before destroying the channels.

Destroy all the client's currently active channels.

client.emitMessage(name, req, [opts,] [cb])

  • name {String} Name of the message to emit.
  • req {Object} Request value, must correspond to the message's declared request type.
  • opts {Object} Options. These options will be available as second argument to the chosen channel's 'outgoingCall' event.
    • timeout {Number} Request specific timeout.
  • cb(err, res) {Function} Function called with the remote call's response (and eventual error) when available. If not specified and an error occurs, the error will be emitted on the client instead.

Send a message. This is always done asynchronously.

client.remoteProtocols()

Returns the client's cached protocols.

client.service

The client's service.

client.use(middleware...)

  • middleware(wreq, wres, next) {Function} Middleware handler.

Install a middleware function.

Class WrappedRequest

headers

Map of bytes.

request

The decoded request.

Class WrappedResponse

error

Decoded error. If error is anything but undefined, the response field will be ignored and the error will be sent instead.

headers

Map of bytes.

response

Decoded response.

Class CallContext

channel

The channel used to emit or receive this message (either a ClientChannel or ServerChannel).

locals

An object useful to store call-local information to pass between middlewares and handlers.

message

The message being processed.

Class Server

Event 'channel'

  • channel {ServerChannel} The newly created channel.

Event emitted each time a channel is created.

server.activeChannels()

Returns a copy of the server's active channels.

server.createChannel(transport, [opts])

  • transport {Duplex|Object|Function} Similar to client.createChannel's corresponding argument, except that readable and writable roles are reversed for stateless transports.
  • opts {Object} Options.
    • defaultHandler(wreq, wres, prev) {Function} Function called when no handler has been installed for a given message. The default sends back a "not implemented" error response.
    • endWritable {Boolean} Set this to false to prevent the transport's writable stream from being ended when the emitter is destroyed (for stateful transports) or when a response is sent (for stateless transports). Defaults to true.
    • objectMode {Boolean} Expect a transport in object mode. Instead of exchanging buffers, objects {id, payload} will be written and expected. This can be used to implement custom transport encodings.
    • scope {String} Scope used to multiplex messages accross a shared connection. There should be at most one channel per scope on a single stateful transport. Matching channel pairs (client and server) should have matching scopes. Scoping isn't supported on stateless transports.

Generate a channel for this server. This channel can be used to respond to messages emitted from compatible clients.

server.onMessage(name, handler)

  • name {String} Message name to add the handler for. An error will be thrown if this name isn't defined in the protocol. At most one handler can exist for a given name (any previously defined handler will be overwritten).
  • handler(req, cb) {Function} Handler, called each time a message with matching name is received. The callback argument cb(err, res) should be called to send the response back to the emitter.

Add a handler for a given message.

server.remoteProtocols()

Returns the server's cached protocols.

server.service

Returns the server's service.

server.use(middleware...)

  • middleware(wreq, wres, next) {Function} Middleware handler.

Install a middleware function.

Class ClientChannel

Instance of this class are EventEmitters, with the following events:

Event 'eot'

End of transmission event, emitted after the client is destroyed and there are no more pending requests.

Event 'handshake'

  • hreq {Object} Handshake request.
  • hres {Object} Handshake response.

Emitted when the server's handshake response is received. Additionally, the following guarantees are made w.r.t. the timing of this event:

  • Destroying the channel inside a (synchronous) handler for this event will interrupt any ongoing handshake. If the handshake response's match was NONE, it will prevent a connection from taking place in the case of stateful channels and cancel the retry of the request in the case of stateless channels.
  • For stateful channels which do not reuse connections (i.e. created without setting noPing to true), this event will be emitted before any 'outgoingCall' events.

Event 'outgoingCall'

  • ctx {CallContext} The call's context.
  • opts {Object} The options used when emitting the message.

Emitted when a message was just emitted using this channel.

channel.destroy([noWait])

  • noWait {Boolean} Cancel any pending requests. By default pending requests will still be honored.

Disable the channel.

channel.client

The channel's client.

channel.destroyed

Whether the channel was destroyed.

channel.draining

Whether the channel is still accepting new requests.

channel.pending

The number of pending calls on this channel (i.e. the number of messages emitted on this channel which haven't yet had a response).

channel.ping([timeout,] [cb])

  • timeout {Number} The ping request's timeout.
  • cb(err) {Function} Function called when the request's response is received. If not specified and an error occurs, the channel will be destroyed.

channel.timeout

The channel's default timeout.

Class ServerChannel

Event 'eot'

End of transmission event, emitted after the channel is destroyed and there are no more responses to send.

Event 'handshake'

  • hreq {Object} Handshake request.
  • hres {Object} Handshake response.

Emitted right before the server sends a handshake response. This event is guaranteed to be emitted before any 'incomingCall' event. Additionally, destroying the channel synchronously in one of this event's handlers will prevent any responses from being sent back.

Event 'incomingCall'

  • context {CallContext} The call's context.
  • opts {Object} The options used when emitting the message.

Emitted when a message was just received on this channel.

channel.destroy([noWait])

  • noWait {Boolean} Don't wait for all pending responses to have been sent.

Disable this channel and release underlying streams. In general you shouldn't need to call this: channels are best destroyed from the client side.

channel.destroyed

Check whether the channel was destroyed.

channel.draining

Whether the channel is still accepting requests.

channel.pending

The number of pending calls (i.e. the number of messages received which haven't yet had their response sent).

channel.server

Get the channel's server.

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