Documentation
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Overview ¶
Package usbpd decodes USB Power Delivery (USB-PD) messages — the protocol spoken over the USB-C CC line to negotiate power (and to tunnel alternate modes and vendor-defined messages). USB-PD is an emerging hardware-attack surface: a malicious charger or a PD-capable cable can advertise bogus power capabilities, drive a sink to request out-of-spec voltage, or carry vendor-defined messages that trigger device-specific behaviour — so a captured PD exchange (from a CC-line analyzer) is real recon. A USB-PD message identifies the **negotiation step** — a Source/Sink Capabilities advertisement (and the offered voltages/currents), a Request, an Accept/Reject/PS_RDY, a role swap, a Vendor-Defined Message — which is the headline for charger / cable analysis. It joins the project's USB analysis stack (internal/usbdesc, internal/hidreport, internal/usbhid).
Wrap-vs-native judgement ¶
Native. A USB-PD message is a 16-bit little-endian header (message type, roles, spec revision, message id, data-object count) optionally followed by 32-bit little-endian Data Objects. A bit-field read + a per-message-type walk; stdlib only, no new go.mod dep.
Verifiable / no confidently-wrong output ¶
The header bit layout, the control- and data-message type tables, and the Fixed / Variable / Battery Power Data Object layouts follow the USB Power Delivery specification — deterministic and byte-checkable against spec- built PDOs (e.g. 5 V @ 3 A). The control-vs-data message-type dispatch is driven by the header's data-object count (no ambiguity). Only the standardised, well-defined fields are decoded: the header, and — for Source/Sink Capabilities — the Fixed (voltage/current + role flags), Variable and Battery PDOs; an Augmented PDO (PPS / AVS) is surfaced by type with its 32-bit value raw, and the Request RDO, BIST, Vendor-Defined and other data messages' objects are surfaced as raw hex (their layouts are position-dependent and would be confidently-wrong without the prior Capabilities context). The input is the raw on-wire bytes (little-endian).
Index ¶
Constants ¶
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Variables ¶
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Functions ¶
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Types ¶
type DataObject ¶
type DataObject struct {
Raw string `json:"raw"`
Kind string `json:"kind,omitempty"` // PDO type / "RDO" / "VDO" / etc.
VoltageV string `json:"voltage_v,omitempty"`
MaxCurrentA string `json:"max_current_a,omitempty"`
Flags string `json:"flags,omitempty"`
}
DataObject is one 32-bit USB-PD data object.
type Result ¶
type Result struct {
HeaderHex string `json:"header_hex"`
MessageClass string `json:"message_class"` // "control" | "data"
MessageType int `json:"message_type"`
MessageName string `json:"message_name"`
SpecRevision string `json:"spec_revision"`
PortPowerRole string `json:"port_power_role"`
PortDataRole string `json:"port_data_role"`
MessageID int `json:"message_id"`
NumDataObjects int `json:"num_data_objects"`
Extended bool `json:"extended,omitempty"`
DataObjects []DataObject `json:"data_objects,omitempty"`
Notes []string `json:"notes,omitempty"`
}
Result is the decoded view of a USB-PD message.
Source Files