JSON RPC Server
Interacting with Metacces Geth requires sending requests to specific JSON-RPC API methods. Geth supports all standard JSON-RPC API endpoints. The RPC requests must be sent to the node and the response returned to the client using some transport protocol. This page outlines the available transport protocols in Metacces Geth, providing the information users require to choose a transport protocol for a specific user scenario.
Introduction
JSON-RPC is provided on multiple transports. Metacces supports JSON-RPC over HTTP, WebSocket and Unix Domain Sockets. Transports must be enabled through command-line flags.
Metacces JSON-RPC APIs use a name-space system. RPC methods are grouped into several categories depending on their purpose. All method names are composed of the namespace, an underscore, and the actual method name within the namespace. For example, the eth_call method resides in the eth namespace.
Access to RPC methods can be enabled on a per-namespace basis.
Transports
There are three transport protocols available in Metacces: IPC, HTTP and Websockets.
HTTP Server (https://oli.accesscan.io)
HTTP is a unidirectional transport protocol that connects a client and server. The client sends a request to the server, and the server returns a response back to the client. An HTTP connection is closed after the response for a given request is sent.
HTTP is supported in every browser as well as almost all programming toolchains. Due to its ubiquity it has become the most widely used transport for interacting with Geth. To start a HTTP server in Metacces RPC, include the --http flag:
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If no other commands are provided, Geth falls back to its default behaviour of accepting connections from the local loopback interface (127.0.0.1). The default listening port is 8545. The ip address and listening port can be customized using the --http.addr and --http.port flags:
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Not all of the JSON-RPC method namespaces are enabled for HTTP requests by default. Instead, they have to be whitelisted explicitly when Geth is started. Calling non-whitelisted RPC namespaces returns an RPC error with code -32602.
The default whitelist allows access to the eth, net and web3 namespaces. To enable access to other APIs like debugging (debug), they must be configured using the --http.api flag. Enabling these APIs over HTTP is not recommended because access to these methods increases the attack surface.
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Since the HTTP server is reachable from any local application, additional protection is built into the server to prevent misuse of the API from web pages. To enable access to the API from a web page (for example to use the online IDE, Remix), the server needs to be configured to accept Cross-Origin requests. This is achieved using the --http.corsdomain flag.
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The --http.corsdomain command also accepts wildcards that enable access to the RPC from any origin:
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WebSocket Server (wss://ws.accesscan.io)
Websocket is a bidirectional transport protocol. A Websocket connection is maintained by client and server until it is explicitly terminated by one. Most modern browsers support Websocket which means it has good tooling.
Because Websocket is bidirectional, servers can push events to clients. That makes Websocket a good choice for use-cases involving event subscription. Another benefit of Websocket is that after the handshake procedure, the overhead of individual messages is low, making it good for sending high number of requests.
Configuration of the WebSocket endpoint in Metacces Geth follows the same pattern as the HTTP transport. WebSocket access can be enabled using the --ws flag. If no additional information is provided, Geth falls back to its default behaviour which is to establish the Websocket on port 8546. The --ws.addr, --ws.port and --ws.api flags can be used to customize settings for the WebSocket server. For example, to start Geth with a Websocket connection for RPC using the custom port 32000 and whitelisting the eth, net and web3 namespaces:
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Cross-Origin request protection also applies to the WebSocket server. The --ws.origins flag can be used to allow access to the server from web pages:
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As with --http.corsdomain, using the wildcard --ws.origins '*' allows access from any origin.
IPC Server
IPC is normally available for use in local environments where the node and the console exist on the same machine. Metacces Geth creates a pipe in the computers local file system (at ipcpath) that configures a connection between node and console. The geth.ipc file can also be used by other processes on the same machine to interact with Geth.
On UNIX-based systems (Linux, OSX) the IPC is a UNIX domain socket. On Windows IPC is provided using named pipes. The IPC server is enabled by default and has access to all JSON-RPC namespaces.
The listening socket is placed into the data directory by default. On Linux and macOS, the default location of the geth socket is
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On Windows, IPC is provided via named pipes. The default location of the Metacces geth pipe is:
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The location of the socket can be customized using the --ipcpath flag. IPC can be disabled using the --ipcdisable flag.
Choosing a transport protocol
The following table summarizes the relative strengths and weaknesses of each transport protocol so that users can make informed decisions about which to use.
As a general rule IPC is most secure because it is limited to interactions on the local machine and cannot be exposed to external traffic. It can also be used to subscribe to events. HTTP is a familiar and idempotent transport that closes connections between requests and can therefore have lower overall overheads if the number of requests is fairly low. Websockets provides a continuous open channel that can enable event subscriptions and streaming and handle large volumes of requests with smaller per-message overheads.
Summary
RPC requests to a Metacces node can be made using three different transport protocols. The protocols are enabled at startup using their respective flags. The right choice of transport protocol depends on the specific use case.
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