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diff --git a/src/jaegertracing/thrift/doc/specs/thrift-binary-protocol.md b/src/jaegertracing/thrift/doc/specs/thrift-binary-protocol.md new file mode 100644 index 000000000..a85268517 --- /dev/null +++ b/src/jaegertracing/thrift/doc/specs/thrift-binary-protocol.md @@ -0,0 +1,254 @@ +Thrift Binary protocol encoding +=============================== + +<!-- +-------------------------------------------------------------------- + +Licensed to the Apache Software Foundation (ASF) under one +or more contributor license agreements. See the NOTICE file +distributed with this work for additional information +regarding copyright ownership. The ASF licenses this file +to you 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. + +-------------------------------------------------------------------- +--> + +This documents describes the wire encoding for RPC using the older Thrift *binary protocol*. + +The information here is _mostly_ based on the Java implementation in the Apache thrift library (version 0.9.1 and +0.9.3). Other implementation however, should behave the same. + +For background on Thrift see the [Thrift whitepaper (pdf)](https://thrift.apache.org/static/files/thrift-20070401.pdf). + +# Contents + +* Binary protocol + * Base types + * Message + * Struct + * List and Set + * Map +* BNF notation used in this document + +# Binary protocol + +## Base types + +### Integer encoding + +In the _binary protocol_ integers are encoded with the most significant byte first (big endian byte order, aka network +order). An `int8` needs 1 byte, an `int16` 2, an `int32` 4 and an `int64` needs 8 bytes. + +The CPP version has the option to use the binary protocol with little endian order. Little endian gives a small but +noticeable performance boost because contemporary CPUs use little endian when storing integers to RAM. + +### Enum encoding + +The generated code encodes `Enum`s by taking the ordinal value and then encoding that as an int32. + +### Binary encoding + +Binary is sent as follows: + +``` +Binary protocol, binary data, 4+ bytes: ++--------+--------+--------+--------+--------+...+--------+ +| byte length | bytes | ++--------+--------+--------+--------+--------+...+--------+ +``` + +Where: + +* `byte length` is the length of the byte array, a signed 32 bit integer encoded in network (big endian) order (must be >= 0). +* `bytes` are the bytes of the byte array. + +### String encoding + +*String*s are first encoded to UTF-8, and then send as binary. + +### Double encoding + +Values of type `double` are first converted to an int64 according to the IEEE 754 floating-point "double format" bit +layout. Most run-times provide a library to make this conversion. Both the binary protocol as the compact protocol then +encode the int64 in 8 bytes in big endian order. + +### Boolean encoding + +Values of `bool` type are first converted to an int8. True is converted to `1`, false to `0`. + +## Message + +A `Message` can be encoded in two different ways: + +``` +Binary protocol Message, strict encoding, 12+ bytes: ++--------+--------+--------+--------+--------+--------+--------+--------+--------+...+--------+--------+--------+--------+--------+ +|1vvvvvvv|vvvvvvvv|unused |00000mmm| name length | name | seq id | ++--------+--------+--------+--------+--------+--------+--------+--------+--------+...+--------+--------+--------+--------+--------+ +``` + +Where: + +* `vvvvvvvvvvvvvvv` is the version, an unsigned 15 bit number fixed to `1` (in binary: `000 0000 0000 0001`). + The leading bit is `1`. +* `unused` is an ignored byte. +* `mmm` is the message type, an unsigned 3 bit integer. The 5 leading bits must be `0` as some clients (checked for + java in 0.9.1) take the whole byte. +* `name length` is the byte length of the name field, a signed 32 bit integer encoded in network (big endian) order (must be >= 0). +* `name` is the method name, a UTF-8 encoded string. +* `seq id` is the sequence id, a signed 32 bit integer encoded in network (big endian) order. + +The second, older encoding (aka non-strict) is: + +``` +Binary protocol Message, old encoding, 9+ bytes: ++--------+--------+--------+--------+--------+...+--------+--------+--------+--------+--------+--------+ +| name length | name |00000mmm| seq id | ++--------+--------+--------+--------+--------+...+--------+--------+--------+--------+--------+--------+ +``` + +Where `name length`, `name`, `mmm`, `seq id` are as above. + +Because `name length` must be positive (therefore the first bit is always `0`), the first bit allows the receiver to see +whether the strict format or the old format is used. Therefore a server and client using the different variants of the +binary protocol can transparently talk with each other. However, when strict mode is enforced, the old format is +rejected. + +Message types are encoded with the following values: + +* _Call_: 1 +* _Reply_: 2 +* _Exception_: 3 +* _Oneway_: 4 + +## Struct + +A *Struct* is a sequence of zero or more fields, followed by a stop field. Each field starts with a field header and +is followed by the encoded field value. The encoding can be summarized by the following BNF: + +``` +struct ::= ( field-header field-value )* stop-field +field-header ::= field-type field-id +``` + +Because each field header contains the field-id (as defined by the Thrift IDL file), the fields can be encoded in any +order. Thrift's type system is not extensible; you can only encode the primitive types and structs. Therefore is also +possible to handle unknown fields while decoding; these are simply ignored. While decoding the field type can be used to +determine how to decode the field value. + +Note that the field name is not encoded so field renames in the IDL do not affect forward and backward compatibility. + +The default Java implementation (Apache Thrift 0.9.1) has undefined behavior when it tries to decode a field that has +another field-type then what is expected. Theoretically this could be detected at the cost of some additional checking. +Other implementation may perform this check and then either ignore the field, or return a protocol exception. + +A *Union* is encoded exactly the same as a struct with the additional restriction that at most 1 field may be encoded. + +An *Exception* is encoded exactly the same as a struct. + +### Struct encoding + +In the binary protocol field headers and the stop field are encoded as follows: + +``` +Binary protocol field header and field value: ++--------+--------+--------+--------+...+--------+ +|tttttttt| field id | field value | ++--------+--------+--------+--------+...+--------+ + +Binary protocol stop field: ++--------+ +|00000000| ++--------+ +``` + +Where: + +* `tttttttt` the field-type, a signed 8 bit integer. +* `field id` the field-id, a signed 16 bit integer in big endian order. +* `field-value` the encoded field value. + +The following field-types are used: + +* `BOOL`, encoded as `2` +* `BYTE`, encoded as `3` +* `DOUBLE`, encoded as `4` +* `I16`, encoded as `6` +* `I32`, encoded as `8` +* `I64`, encoded as `10` +* `STRING`, used for binary and string fields, encoded as `11` +* `STRUCT`, used for structs and union fields, encoded as `12` +* `MAP`, encoded as `13` +* `SET`, encoded as `14` +* `LIST`, encoded as `15` + +## List and Set + +List and sets are encoded the same: a header indicating the size and the element-type of the elements, followed by the +encoded elements. + +``` +Binary protocol list (5+ bytes) and elements: ++--------+--------+--------+--------+--------+--------+...+--------+ +|tttttttt| size | elements | ++--------+--------+--------+--------+--------+--------+...+--------+ +``` + +Where: + +* `tttttttt` is the element-type, encoded as an int8 +* `size` is the size, encoded as an int32, positive values only +* `elements` the element values + +The element-type values are the same as field-types. The full list is included in the struct section above. + +The maximum list/set size is configurable. By default there is no limit (meaning the limit is the maximum int32 value: +2147483647). + +## Map + +Maps are encoded with a header indicating the size, the element-type of the keys and the element-type of the elements, +followed by the encoded elements. The encoding follows this BNF: + +``` +map ::= key-element-type value-element-type size ( key value )* +``` + +``` +Binary protocol map (6+ bytes) and key value pairs: ++--------+--------+--------+--------+--------+--------+--------+...+--------+ +|kkkkkkkk|vvvvvvvv| size | key value pairs | ++--------+--------+--------+--------+--------+--------+--------+...+--------+ +``` + +Where: + +* `kkkkkkkk` is the key element-type, encoded as an int8 +* `vvvvvvvv` is the value element-type, encoded as an int8 +* `size` is the size of the map, encoded as an int32, positive values only +* `key value pairs` are the encoded keys and values + +The element-type values are the same as field-types. The full list is included in the struct section above. + +The maximum map size is configurable. By default there is no limit (meaning the limit is the maximum int32 value: +2147483647). + +# BNF notation used in this document + +The following BNF notation is used: + +* a plus `+` appended to an item represents repetition; the item is repeated 1 or more times +* a star `*` appended to an item represents optional repetition; the item is repeated 0 or more times +* a pipe `|` between items represents choice, the first matching item is selected +* parenthesis `(` and `)` are used for grouping multiple items |