Documentation
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Overview ¶
Package mcpclient implements the MCP client (consumer side) the harness uses to talk to external MCP servers.
v0.1: stdio transport only (the only one needed for the gofastr-introspection and kiln MCP servers shipped with the v0.1 profile presets). HTTP+SSE / streamable HTTP land in v0.2.
Wire format: JSON-RPC 2.0 (newline-delimited).
Package mcpclient is part of the GoFastr harness.
See docs/harness-architecture.md for the architecture this package implements.
Index ¶
- Variables
- type Client
- func (c *Client) Call(ctx context.Context, method string, params any) (json.RawMessage, error)
- func (c *Client) CallTool(ctx context.Context, name string, args json.RawMessage) (json.RawMessage, error)
- func (c *Client) Close() error
- func (c *Client) ListTools(ctx context.Context) ([]ToolDescriptor, error)
- func (c *Client) Notify(_ context.Context, method string, params any) error
- type SHA256MismatchError
- type Source
- type ToolDescriptor
Constants ¶
This section is empty.
Variables ¶
var ErrClosed = errors.New("mcpclient: closed")
ErrClosed is returned when methods are called after Close.
Functions ¶
This section is empty.
Types ¶
type Client ¶
type Client struct {
// contains filtered or unexported fields
}
Client speaks the MCP wire protocol over stdio against a child process. Concurrency-safe.
func Spawn ¶
Spawn launches the MCP server subprocess and performs the `initialize` handshake. If `expectedSHA256` is non-empty, the binary is checked against the hash and refused on mismatch.
func (*Client) CallTool ¶
func (c *Client) CallTool(ctx context.Context, name string, args json.RawMessage) (json.RawMessage, error)
CallTool invokes a tool. Returns the structured result.
type SHA256MismatchError ¶
SHA256MismatchError is returned when the configured binary hash doesn't match the on-disk hash. Maps to the ReasonMCPServerSHA256Mismatch wire error code.
func (*SHA256MismatchError) Error ¶
func (e *SHA256MismatchError) Error() string
type Source ¶
type Source struct {
// contains filtered or unexported fields
}
Source adapts an MCP Client into a tool.ToolSource. Tools the remote server exposes are surfaced under namespace prefixes like "mcp:kiln.create_entity" so they don't collide with built-ins.
func NewSource ¶
NewSource constructs a Source.
discovery selects between:
- "eager": tools/list + schemas fetched at startup. Use for low-tool-count servers (<=20 tools).
- "lazy": tools/list only at startup; tool_schema fetched on first invocation. Default for high-tool-count servers.
Per the spec, /list already returns names + descriptions + inputSchema. The "lazy" mode in v0.1 just defers tool registration to later if no schema has been seen — but most servers return schemas in /list anyway, so the actual savings come from server implementations that elide schemas in /list.
type ToolDescriptor ¶
type ToolDescriptor struct {
Name string `json:"name"`
Description string `json:"description,omitempty"`
InputSchema json.RawMessage `json:"inputSchema,omitempty"`
}
ToolDescriptor is the tier-1 metadata for one tool.
Source Files