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AMQP and C++ types

An AMQP message body can hold binary data using any encoding you like. AMQP also defines its own encoding and types. The AMQP encoding is often used in message bodies because it is supported by AMQP libraries on many languages and platforms. You also need to use the AMQP types to set and examine message properties.

# Scalar types

Each type is identified by a proton::type_id.

C++ type | AMQP type_id | Description
--- | --- | ---
bool | proton::BOOLEAN | Boolean true or false
uint8_t | proton::UBYTE | 8-bit unsigned byte
int8_t | proton::BYTE | 8-bit signed byte
uint16_t | proton::USHORT | 16-bit unsigned integer
int16_t | proton::SHORT | 16-bit signed integer
uint32_t | proton::UINT | 32-bit unsigned integer
int32_t | proton::INT | 32-bit signed integer
uint64_t | proton::ULONG | 64-bit unsigned integer
int64_t | proton::LONG | 64-bit signed integer
wchar_t | proton::CHAR | 32-bit unicode code point
float | proton::FLOAT | 32-bit binary floating point
double | proton::DOUBLE | 64-bit binary floating point
proton::timestamp | proton::TIMESTAMP | 64-bit signed milliseconds since 00:00:00 (UTC), 1 January 1970.
proton::decimal32 | proton::DECIMAL32 | 32-bit decimal floating point
proton::decimal64 | proton::DECIMAL64 | 64-bit decimal floating point
proton::decimal128 | proton::DECIMAL128 | 128-bit decimal floating point
proton::uuid | proton::UUID | 128-bit universally-unique identifier
std::string | proton::STRING | UTF-8 encoded Unicode string
proton::symbol | proton::SYMBOL | 7-bit ASCII encoded string
proton::binary | proton::BINARY | Variable-length binary data

# Holder types

proton::message::body() and other message-related data can contain different types of data at runtime. There are two "holder" types provided to hold runtime typed data:

- proton::scalar can hold a scalar value of any type.
- proton::value can hold any AMQP value, scalar or compound.

You can set the value in a holder by assignment, and use the proton::get() and proton::coerce() templates to extract data in a type-safe way. Holders also provide functions to query the type of value they contain.

# Compound types

C++ type | AMQP type_id | Description
--- | --- | ---
See below | proton::ARRAY | Sequence of values of the same type
See below | proton::LIST | Sequence of values of mixed types
See below | proton::MAP | Map of key-value pairs

A proton::value containing a proton::ARRAY can convert to and from C++ sequences of the corresponding C++ type: std::vector, std::deque, std::list, and std::forward_list.

proton::LIST converts to and from sequences of proton::value or proton::scalar, which can hold mixed types of data.

proton::MAP converts to and from std::map, std::unordered_map, and sequences of std::pair.

For example, you can decode a message body with any AMQP map as follows.

    proton::message m = ...;
    std::map<proton::value, proton::value> map;
    proton::get(m.body(), map);

You can encode a message body with a map of string keys and uint64_t values like this:

    std::unordered_map<std::string, uint64_t> map;
    map["foo"] = 123;
    m.body() = map;

# Include files

proton/types.hpp includes all available type definitions and conversions. Alternatively, you can selectively include the .hpp files you want.