Protobuf URL

Google Maps web clients and APIs use a specific way to encode Protobuf messages into URLs. It is composed of a text sequence of the following elements:

• Delimiter: “!” for private API, “&” for public API
• Field number: base 10 integer
• Field type: single character, see table below
• Value: see table below

Type notation

	Type	Representation	Notes
d	double	Base 10 decimal
f	float
i	int32	Base 10 integer
j	int64
u	uint32
v	uint64
x	fixed32
y	fixed64
g	sfixed32
h	sfixed64
n	sint32
o	sint64
e	enum
b	bool
m	message	Value is the number of subsequent “!”-separated blocks contained in the message.
s	string	Plain string	“*” and “!” encoded as “*2A” and “*21”.
z	Base64 string	Base64url, no padding.
B	bytes

Server (decoding) implementation notes:

• Payload is converted on the fly to wire format, as such type character does not matter much, as long as wire type and representation matches.
• As such, embedded messages can be encoded in raw form using z and B types.

Client (encoding) implementation notes:

• A C++ implementation is compiled into Google Earth's desktop and Android clients. The class is named “JsProtoUrlSerializer”.

Testing reflection

This will return wire format representation for the “5” embedded message.

$ curl -s 'https://kh.google.com/rt/earth/ViewportMetadata?pb=!1u0!5m2!9998sabcd!12y1' | tail -c+12 | protoc --decode_raw

This will enumerate existing types and their minimal outputs.

$ for i in {A..Z} {a..z}; do x=`curl -s 'https://kh.google.com/rt/earth/ViewportMetadata?pb=!1u0!5m1!4'$i'0' | tail -c+12 | hexdump -ve '1/1 "%.2x "'`; [[ -z $x ]] || echo $i $x; done

External links

See here for generic type information:

• https://developers.google.com/protocol-buffers/docs/encoding#structure
• https://developers.google.com/protocol-buffers/docs/proto#scalar