Light State Machine

This is a simple generic state machine. It comes with an example URI parser implementation that uses the state machine to parse URI's.

The state machine supports CanEnter, CanExit, OnEnter, OnExit event handlers. There is also a special FailState that can follow any state. The first state is always StartState and the final states are either EndState or FailState.

Use light state machine in your project

1. Take cpp and h files from light_state_machine subdirectory
2. Create your own Context class. See StateMachineClient/context.h for an example.
3. Create your own StateID class enum. See StateMachineClient/state_id.h for an example.
4. Build the state graph. For an example see uri_parser/graph_builder.cpp. The graph is stlplus::digraph class.

URI parser

uri-parser reads the uri string from stdin.

Command example:

echo "foo://john:swordfish@info.example.com:8080/documents/receipt?name=fred&size=10#origin" | ./bin/debug/uri-parser

Output:

scheme=foo
user=john
password=swordfish
host=info.example.com
port=8080
query=name=fred&size=10
path=/documents
path=/receipt
fragment=origin

URI parser implementation details

The parsing process includes several steps.

1. Tokenizer
2. State machine walks through URI components

Each state represents one or more tokens. A state tests the next token in CanEnter handler and the method returns true if the state can process the token. If there are no states that the state machine can enter, it transitions to FailState.

Below are the state transitions for the example in "Example output" above:

Scheme => Colon => Slash => Slash => Authority => Host => Colon => BadPort => User => Colon => Password => AtExpected => Host => Colon => Port => Slash => Path => Slash => Question => Query => Sharp => Fragment => End

You can enable the state trace in src/Makefile Uncomment # CXXFLAGS += -DTRACE_STATE_MACHINE

BadPort state was hit because it was not clear if what was after Colon was a port or a password. This state exists to handle this scenario and move to User assuming that the bad port (non-numeric) is a password. A simmilar AtUnexpected state exists for parsing Host and hitting At.

You can see the graph of states in graph_builder.cpp. I is for declaring a new state node and L is for linking two nodes. docs/states.jpg shows the complete state transition map.

System requirements

Linux
Mingw
C++11 g++ or clang

Compile

Build:

make

Release:

make RELEASE=on

Verbose:

make VERBOSE=on

Clean:

make clean

Tests:

make tests

Acknowledgments

1. stlplus
2. gtest
3. plog

License

Creative Commons BSD License