Plugin protocol reference
How Nu runs plugins
Nu plugins must be an executable file with a filename starting with nu_plugin_. All interaction with the plugin is handled over standard input (stdin) and output (stdout). Standard error (stderr) is not redirected, and can be used by the plugin to print messages directly.
Plugins are always passed --stdio as a command line argument. Other command line arguments are reserved for options that might be added in the future, including other communication methods. Plugins that support the protocol as described in this document should reject other arguments and print an informational message to stderr.
Immediately after spawning a plugin, Nu expects the plugin to send its encoding type. Currently two encoding types are supported: json and msgpack. The desired encoding type should be sent first with the length of the string as a single byte integer and then the encoding type string. That is, with C-like escape syntax, "\x04json" or "\x07msgpack". In this document, the JSON format will be used for readability, but the MessagePack format is largely equivalent. See the Encoding section for specific intricacies of the formats.
Nu will then send messages in the desired encoding. The first message is always Hello. The plugin must send a Hello message indicating the expected Nu version that it is compatible with, and any supported protocol features. The engine will also send a Hello message with its version, and any supported protocol features. The plugin may verify that it is compatible with the Nu version provided by the engine, but the engine will end communication with a plugin if it is determined to be unsupported. The plugin must not use protocol features it supports if they are not also confirmed to be supported by the engine in its Hello message. It is not permitted to send any other messages before sending Hello.
The plugin should then receive and respond to messages until its stdin is closed.
Typical plugin interaction after the initial handshake looks like this:
- The engine sends a
Call. The call contains an ID used to identify the response. - If the
inputof the call specified a stream, the engine will send stream messages. These do not need to be consumed before the plugin sends its response. - The plugin sends a
CallResponse, with the same ID from step 1. - If the plugin specified stream data as output in the response, it should now send stream messages with the corresponding stream ID(s).
The plugin should respond to further plugin calls. The engine may send additional plugin calls before responses have been received, and it is up to the plugin to decide whether to handle each call immediately as it is received, or to process only one at a time and hold on to them for later. In any case, sending another plugin call before a response has been received should not cause an error.
The plugin may send engine calls during the execution of a call to request operations from the engine. Engine calls are only valid within the context of a call and may not be sent otherwise.
The engine may send a Goodbye message to the plugin indicating that it will no longer send any more plugin calls. Upon receiving this message, the plugin may choose not to accept any more plugin calls, and should exit after any in-progress plugin calls have finished.
Hello
After the encoding type has been decided, both the engine and plugin must send a Hello message containing relevant version and protocol support information.
| Field | Type | Usage |
|---|---|---|
| protocol | string | Must be "nu-plugin". |
| version | string | The engine's version, or the target version of Nu that the plugin supports. |
| features | array | Protocol features supported by the plugin. Unrecognized elements must be ignored. |
To be accepted, the version specified must be semver compatible with the engine's version. "0.x.y" and "x.y.z" for differing values of "x" are considered to be incompatible.
There are currently no protocol features defined, and they are only likely to be used once Nu releases versions after stabilization at "1.0.0".
Plugins may decide to refuse engine versions with more strict criteria than specified here.
Example:
{
"Hello": {
"protocol": "nu-plugin",
"version": "0.90.2",
"features": []
}
}
Input messages
These are messages sent from the engine to the plugin. Hello and Stream messages are also included.
Call
The body of this message is a 2-tuple (array): (id, call). The engine sends unique IDs for each plugin call it makes. The ID is needed to send the CallResponse.
Signature plugin call
Ask the plugin to send its command signatures. Takes no arguments. Returns Signature or Error
Example:
{
"Call": [0, "Signature"]
}
Run plugin call
Tell the plugin to run a command. The argument is the following map:
| Field | Type | Usage |
|---|---|---|
| name | string | The name of the command to run |
| call | EvaluatedCall | Information about the invocation, including arguments |
| input | PipelineDataHeader | Pipeline input to the command |
EvaluatedCall is a map:
| Field | Type | Usage |
|---|---|---|
| head | Span | The position of the beginning of the command execution. |
| positional | Value array | Positional arguments. |
| named | 2-tuple (string, Value or null) array | Named arguments, such as switches. |
Named arguments are always sent by their long name, never their short name.
Returns PipelineData or Error.
Example:
{
"Call": [
0,
{
"Run": {
"name": "inc",
"call": {
"head": {
"start": 40400,
"end": 40403
},
"positional": [
{
"String": {
"val": "0.1.2",
"span": {
"start": 40407,
"end": 40415
}
}
}
],
"named": [
[
"major",
{
"Bool": {
"val": true,
"span": {
"start": 40404,
"end": 40406
}
}
}
]
]
}
}
}
]
}
CustomValueOp plugin call
Perform an operation on a custom value received from the plugin. The argument is a 2-tuple (array): (custom_value, op).
The custom value is specified in spanned format, as a PluginCustomValue without the type field, and not as a Value - see the examples.
ToBaseValue
Returns a plain value that is representative of the custom value, or an error if this is not possible. Sending a custom value back for this operation is not allowed. The response type is PipelineData or Error. If the operation produces a stream, it will be consumed to a value.
Example:
{
"Call": [
0,
{
"CustomValueOp": [
{
"item": {
"name": "version",
"data": [0, 0, 0, 0, 1, 0, 0, 0, 2, 0, 0, 0]
},
"span": {
"start": 90,
"end": 96
}
},
"ToBaseValue"
]
}
]
}
FollowPathInt
Returns the result of following a numeric cell path (e.g. $custom_value.0) on the custom value. This is most commonly used with custom types that act like lists or tables. The argument is a spanned unsigned integer. The response type is PipelineData or Error. The result may be another custom value. If the operation produces a stream, it will be consumed to a value.
Example:
$version.0
{
"Call": [
0,
{
"CustomValueOp": [
{
"item": {
"name": "version",
"data": [0, 0, 0, 0, 1, 0, 0, 0, 2, 0, 0, 0]
},
"span": {
"start": 90,
"end": 96
}
},
{
"FollowPathInt": {
"item": 0,
"span": {
"start": 320,
"end": 321
}
}
}
]
}
]
}
FollowPathString
Returns the result of following a string cell path (e.g. $custom_value.field) on the custom value. This is most commonly used with custom types that act like lists or tables. The argument is a spanned string. The response type is PipelineData or Error. The result may be another custom value. If the operation produces a stream, it will be consumed to a value.
Example:
$version.field
{
"Call": [
0,
{
"CustomValueOp": [
{
"item": {
"name": "version",
"data": [0, 0, 0, 0, 1, 0, 0, 0, 2, 0, 0, 0]
},
"span": {
"start": 90,
"end": 96
}
},
{
"FollowPathString": {
"item": "field",
"span": {
"start": 320,
"end": 326
}
}
}
]
}
]
}
PartialCmp
Compares the custom value to another value and returns the Ordering that should be used, if any. The argument type is a Value, which may be any value - not just the same custom value type. The response type is Ordering. Error may also be returned, but at present the error is unlikely to be presented to the user - the engine will act as if you had sent {"Ordering": null}.
Example (comparing two version custom values):
{
"Call": [
0,
{
"CustomValueOp": [
{
"item": {
"name": "version",
"data": [0, 0, 0, 0, 1, 0, 0, 0, 2, 0, 0, 0]
},
"span": {
"start": 90,
"end": 96
}
},
{
"PartialCmp": {
"Custom": {
"val": {
"type": "PluginCustomValue",
"name": "version",
"data": [0, 0, 0, 0, 1, 0, 0, 0, 3, 0, 0, 0]
},
"span": {
"start": 560,
"end": 566
}
}
}
}
]
}
]
}
Operation
Returns the result of evaluating an Operator on this custom value with another value. The argument is a 2-tuple: (operator, value), where operator is a spanned Operator and value is a Value, which may be any value - not just the same custom value type. The response type is PipelineData or Error. The result may be another custom value. If the operation produces a stream, it will be consumed to a value.
Example:
$version + 7
{
"Call": [
0,
{
"CustomValueOp": [
{
"item": {
"name": "version",
"data": [0, 0, 0, 0, 1, 0, 0, 0, 2, 0, 0, 0]
},
"span": {
"start": 90,
"end": 96
}
},
{
"Operation": [
{
"item": {
"Math": "Plus"
},
"span": {
"start": 180,
"end": 181
}
},
{
"Int": {
"val": 7,
"span": {
"start": 183,
"end": 184
}
}
}
]
}
]
}
]
}
Dropped
This op is used to notify the plugin that a PluginCustomValue that had notify_on_drop set to true was dropped in the engine - i.e., all copies of it have gone out of scope. For more information on exactly under what circumstances this is sent, see the drop notification section of the plugin reference. The response type is Empty pipeline data or Error.
Example:
{
"Call": [
0,
{
"CustomValueOp": [
{
"item": {
"name": "handle",
"data": [78, 60],
"notify_on_drop": true
},
"span": {
"start": 1820,
"end": 1835
}
},
"Dropped"
]
}
]
}
EngineCallResponse
A response to an engine call made by the plugin. The argument is a 2-tuple (array): (engine_call_id, engine_call)
The engine_call_id refers to the same number that the engine call being responded to originally contained. The plugin must send unique IDs for each engine call it makes. Like CallResponse, there are multiple types of responses:
Error engine call response
A failure result. Contains a ShellError.
Example:
{
"EngineCallResponse": [
0,
{
"Error": {
"LabeledError": {
"msg": "The connection closed.",
"labels": [],
"code": null,
"url": null,
"help": null,
"inner": []
}
}
}
]
}
PipelineData engine call response
A successful result with a Nu Value or stream. The body is a PipelineDataHeader.
Example:
{
"EngineCallResponse": [
0,
{
"ListStream": {
"id": 23
}
}
]
}
Config engine call response
A successful result of a Config engine call. The body is a Config.
Example:
{
"EngineCallResponse": [
0,
{
"Config": {
"external_completer": null,
"filesize_metric": true,
"table_mode": "Rounded",
"table_move_header": false,
...
}
}
]
}
This example is abbreviated, as the Config object is large and ever-changing.
ValueMap engine call response
A successful result for engine calls that produce plain maps, such as the GetEnvVars engine call. The body is a map from strings to Values.
Example:
{
"EngineCallResponse": [
0,
{
"ValueMap": {
"FOO": {
"String": {
"val": "bar",
"span": {
"start": 2020,
"end": 2024
}
}
}
}
}
]
}
Goodbye
Indicate that no further plugin calls are expected, and that the plugin should exit as soon as it is finished processing any in-progress plugin calls.
This message is not a map, it is just a bare string, as it takes no arguments.
Example:
"Goodbye"
Output messages
These are messages sent from the plugin to the engine. Hello and Stream messages are also included.
CallResponse
Error plugin call response
An error occurred while attempting to fulfill the request. The body is a LabeledError.
It is strongly preferred to provide labeled messages whenever possible to let the user know where the problem might be in their script. If there is no more suitable span from a value that can be used, head from EvaluatedCall is a good fallback.
Example:
{
"CallResponse": [
0,
{
"Error": {
"msg": "A really bad error occurred",
"labels": [
{
"text": "I don't know, but it's over nine thousand!",
"span": {
"start": 9001,
"end": 9007
}
}
],
"code": "my_plugin::bad::really_bad",
"url": "https://example.org/my_plugin/error/bad/really_bad.html",
"help": "you can solve this by not doing the bad thing",
"inner": [
{
"msg": "The bad thing"
}
]
}
}
]
}
Signature plugin call response
A successful response to a Signature plugin call. The body is an array of signatures.
Example:
{
"CallResponse": [
0,
{
"Signature": [
{
"sig": {
"name": "len",
"usage": "calculates the length of its input",
"extra_usage": "",
"search_terms": [],
"required_positional": [],
"optional_positional": [],
"rest_positional": null,
"vectorizes_over_list": false,
"named": [
{
"long": "help",
"short": "h",
"arg": null,
"required": false,
"desc": "Display the help message for this command",
"var_id": null,
"default_value": null
}
],
"input_type": "String",
"output_type": "Int",
"input_output_types": [],
"allow_variants_without_examples": false,
"is_filter": false,
"creates_scope": false,
"allows_unknown_args": false,
"category": "Default"
},
"examples": []
}
]
}
]
}
Ordering plugin call response
A successful response to the PartialCmp custom value op. The body is either Ordering if the comparison is possible, or null if the values can't be compared.
Example:
{
"CallResponse": [
0,
{
"Ordering": "Less"
}
]
}
Example with incomparable values:
{
"CallResponse": [
0,
{
"Ordering": null
}
]
}
PipelineData plugin call response
A successful result with a Nu Value or stream. The body is a PipelineDataHeader.
Example:
{
"CallResponse": [
0,
{
"Value": {
"Int": {
"val": 42,
"span": {
"start": 12,
"end": 14
}
}
}
}
]
}
EngineCall
Plugins can make engine calls during execution of a call. The body is a map with the following keys:
| Field | Type | Usage |
|---|---|---|
| context | integer | The ID of the call that this engine call relates to. |
| id | integer | A unique ID for this engine call, in order to send the response. |
| call | EngineCall | One of the options described below. |
The context must be an ID of a call that was received that is currently in one of two states:
- The response has not been sent yet.
- The response contained stream data (i.e.
ListStreamorExternalStream), and at least one of the streams started by the response is still sending data (i.e.Endhas not been sent).
After a response has been fully sent, and streams have ended, the context from that call can no longer be used.
The engine call ID must be unique for the lifetime of the plugin, and it is suggested that this be a sequentially increasing number across all engine calls made by the plugin. It is not separated by context; the response only contains the id.
GetConfig engine call
Get the Nushell engine configuration. Returns a Config response if successful.
Example:
{
"EngineCall": {
"context": 0,
"id": 0,
"call": "GetConfig"
}
}
GetPluginConfig engine call
Get the configuration for the plugin, from its section in $env.config.plugins.NAME if present. Returns a PipelineData response if successful, which will contain either a Value or be Empty if there is no configuration for the plugin set.
If the plugin configuration was specified as a closure, the engine will evaluate that closure and return the result, which may cause an error response.
Example:
{
"EngineCall": {
"context": 3,
"id": 8,
"call": "GetPluginConfig"
}
}
GetEnvVar engine call
Get an environment variable from the caller's scope. Returns a PipelineData response if successful, which will contain either a Value or be Empty if the environment variable is not present.
Example:
{
"EngineCall": {
"context": 7,
"id": 41,
"call": {
"GetEnvVar": "PATH"
}
}
}
GetEnvVars engine call
Get all environment variables from the caller's scope. Returns a ValueMap response if successful, with all of the environment variables in the scope.
Example:
{
"EngineCall": {
"context": 9,
"id": 72,
"call": "GetEnvVars"
}
}
GetCurrentDir engine call
Get the current directory path in the caller's scope. This always returns an absolute path as a string Value pipeline data response if successful. The span contained within the value response is unlikely to be useful, and may be zero.
Example:
{
"EngineCall": {
"context": 7,
"id": 40,
"call": "GetCurrentDir"
}
}
AddEnvVar engine call
Set an environment variable in the caller's scope. The environment variable can only be propagated to the caller's scope if called before the plugin call response is sent. Either way, it is propagated to other engine calls made within the same context. The argument is a 2-tuple: (name, value). The response type is Empty pipeline data when successful.
Example:
{
"EngineCall": {
"context": 7,
"id": 42,
"call": {
"AddEnvVar": [
"FOO",
{
"String": {
"val": "bar",
"span": {
"start": 2020,
"end": 2024
}
}
}
]
}
}
}
GetHelp engine call
Get fully formatted help text for the current command. This can help with implementing top-level commands that just list their subcommands, rather than implementing any specific functionality. The response on success is Value pipeline data that always contains a string.
Example:
{
"EngineCall": {
"context": 1,
"id": 2,
"call": "GetHelp"
}
}
EvalClosure engine call
Pass a Closure and arguments to the engine to be evaluated. Returns a PipelineData response if successful with the output of the closure, which may be a stream.
| Field | Type | Usage |
|---|---|---|
| closure | spanned Closure | The closure to call, generally from a Value. |
| positional | Value array | Positional arguments for the closure. |
| input | PipelineDataHeader | Input for the closure. |
| redirect_stdout | boolean | Whether to redirect stdout if the closure ends in an external command. |
| redirect_stderr | boolean | Whether to redirect stderr if the closure ends in an external command. |
The Closure is not wrapped as a Value - i.e., it doesn't have {"Closure": ...} around it.
Example:
{
"EngineCall": {
"context": 7,
"id": 40,
"call": {
"EvalClosure": {
"closure": {
"item": {
"block_id": 72,
"captures": []
},
"span": {
"start": 780,
"end": 812
}
},
"positional": [
{
"Int": {
"val": 7,
"span": {
"start": 3080,
"end": 3081
}
}
}
],
"input": "Empty",
"redirect_stdout": true,
"redirect_stderr": false
}
}
}
}
Option
Sets options that affect how the engine treats the plugin. No response is expected for this message.
GcDisabled option
Set to true to stop the plugin from being automatically garbage collected, or false to enable it again.
Example:
{
"Option": {
"GcDisabled": true
}
}
Stream messages
Streams can be sent by both the plugin and the engine. The agent that is sending the stream is known as the producer, and the agent that receives the stream is known as the consumer.
All stream messages reference a stream ID. This identifier is an integer starting at zero and is specified by the producer in the message that described what the stream would be used for: for example, Call or CallResponse. A producer should not reuse identifiers it has used once before. The most obvious implementation is sequential, where each new stream gets an incremented number. It is not necessary for stream IDs to be totally unique across both the plugin and the engine: stream 0 from the plugin and stream 0 from the engine are different streams.
Data
This message is sent from producer to consumer. The body is a 2-tuple (array) of (id, data).
The data is either a List map for a list stream, in which case the body is the Value to be sent, or Raw for a raw stream, in which case the body is either an Ok map with a byte buffer, or an Err map with a ShellError.
Examples:
{
"Data": [
0,
{
"List": {
"String": {
"val": "Hello, world!",
"span": {
"start": 40000,
"end": 40015
}
}
}
}
]
}
{
"Data": [
0,
{
"Raw": {
"Ok": [72, 101, 108, 108, 111, 44, 32, 119, 111, 114, 108, 100, 33]
}
}
]
}
{
"Data": [
0,
{
"Raw": {
"Err": {
"IOError": {
"msg": "disconnected"
}
}
}
}
]
}
End
This message is sent from producer to consumer. The body is a single value, the id.
Must be sent at the end of a stream by the producer. The producer must not send any more Data messages after the end of the stream.
The consumer must send Drop in reply unless the stream ended because the consumer chose to drop the stream.
Example:
{
"End": 0
}
Ack
This message is sent from consumer to producer. The body is a single value, the id.
Sent by the consumer in reply to each Data message, indicating that the consumer has finished processing that message. Ack is used for flow control. If a consumer does not need to process a stream immediately, or is having trouble keeping up, it should not send Ack messages until it is ready to process more Data.
Example:
{
"Ack": 0
}
Drop
This message is sent from consumer to producer. The body is a single value, the id.
Sent by the consumer to indicate disinterest in further messages from a stream. The producer may send additional Data messages after Drop has been received, but should make an effort to stop sending messages and End the stream as soon as possible.
The consumer should not consider Data messages sent after Drop to be an error, unless End has already been received.
The producer must send End in reply unless the stream ended because the producer ended the stream.
Example:
{
"Drop": 0
}
Encoding
JSON
The JSON encoding defines messages as JSON objects. No separator or padding is required. Whitespace within the message object as well as between messages is permitted, including newlines.
The engine is more strict about the format it emits: every message ends with a newline, and unnecessary whitespace and newlines will not be emitted within a message. It is explicitly supported for a plugin to choose to parse the input from the engine by parsing each line received as a separate message, as this is most commonly supported across all languages.
Byte arrays are encoded as plain JSON arrays of numbers representing each byte. While this is inefficient, it is maximally portable.
MessagePack should be preferred where possible if performance is desired, especially if byte streams are expected to be a common input or output of the plugin.
MessagePack
MessagePack is a machine-first binary encoding format with a data model very similar to JSON. Messages are encoded as maps. There is no separator between messages, and no padding character is accepted.
Most messages are encoded in the same way as their JSON analogue. For example, the following Hello message in JSON:
{
"Hello": {
"protocol": "nu-plugin",
"version": "0.90.2",
"features": []
}
}
is encoded in the MessagePack format as:
81 // map, one element
a5 "Hello" // 5-character string
83 // map, three elements
a8 "protocol" // 8-character string
a9 "nu-plugin" // 9-character string
a7 "version" // 7-character string
a6 "0.90.2" // 6-character string
a8 "features" // 8-character string
90 // array, zero elements
(verbatim byte strings quoted for readability, non-printable bytes in hexadecimal)
Byte arrays are encoded with MessagePack's native byte arrays, which impose zero constraints on the formatting of the bytes within. In general, the MessagePack encoding is much more efficient than JSON and should be the first choice for plugins where performance is important and MessagePack is available.
Value types
The Value enum describes all structured data used in Nu.
Example:
{
"Int": {
"val": 5,
"span": {
"start": 90960,
"end": 90963
}
}
}
Bool
A boolean.
| Field | Type |
|---|---|
| val | boolean |
| span | Span |
Example:
true
{
"Bool": {
"val": true,
"span": {
"start": 4040,
"end": 4044
}
}
}
Int
A 64-bit signed integer.
| Field | Type |
|---|---|
| val | integer |
| span | Span |
Example:
-2
{
"Int": {
"val": -2,
"span": {
"start": 4040,
"end": 4042
}
}
}
Float
A 64-bit (double precision) floating point number.
| Field | Type |
|---|---|
| val | double |
| span | Span |
Example:
36.4
{
"Float": {
"val": 36.4,
"span": {
"start": 8040,
"end": 8044
}
}
}
Filesize
A quantity of bytes, internally a 64-bit signed integer representing the number of bytes. This is pretty-printed to the user with a more human scale, e.g. 32.4 MiB.
| Field | Type |
|---|---|
| val | integer |
| span | Span |
Example:
32.4MiB
{
"Filesize": {
"val": 33973248,
"span": {
"start": 7740,
"end": 7747
}
}
}
Duration
A duration of time, internally a 64-bit signed integer representing the number of nanoseconds. This is pretty-printed to the user with a more human scale, e.g. 8sec 375ms 604µs 528ns.
| Field | Type |
|---|---|
| val | integer |
| span | Span |
Example:
8375604528ns
{
"Duration": {
"val": 8375604528,
"span": {
"start": 181462,
"end": 181465
}
}
}
Date
A date/time value, including the time zone, represented in RFC 3339 format. This is printed to the user according to their locale.
| Field | Type |
|---|---|
| val | string |
| span | Span |
Example:
1996-12-19T16:39:57-08:00
{
"Date": {
"val": "1996-12-19T16:39:57-08:00",
"span": {
"start": 181525,
"end": 181528
}
}
}
Range
A range of values.
| Field | Type |
|---|---|
| val | Range |
| span | Span |
Range has two variants, IntRange and FloatRange:
IntRange
| Field | Type |
|---|---|
| start | integer |
| step | integer |
| end | Bound integer |
Examples:
0..
{
"Range": {
"val": {
"IntRange": {
"start": 0,
"step": 1,
"end": "Unbounded"
}
},
"span": {
"start": 1380,
"end": 1383
}
}
}
7..10
{
"Range": {
"val": {
"IntRange": {
"start": 7,
"step": 1,
"end": { "Included": 10 }
}
},
"span": {
"start": 1380,
"end": 1385
}
}
}
7..<10
{
"Range": {
"val": {
"IntRange": {
"start": 7,
"step": 1,
"end": { "Excluded": 10 }
}
},
"span": {
"start": 1380,
"end": 1386
}
}
}
0..64..128
{
"Range": {
"val": {
"IntRange": {
"start": 0,
"step": 64,
"end": { "Included": 128 }
}
},
"span": {
"start": 1380,
"end": 1390
}
}
}
FloatRange
Identical to IntRange but for floats instead.
| Field | Type |
|---|---|
| start | double |
| step | double |
| end | Bound double |
Example:
7.5..10.5
{
"Range": {
"val": {
"FloatRange": {
"start": 7.5,
"step": 1,
"end": { "Included": 10.5 }
}
},
"span": {
"start": 1380,
"end": 1389
}
}
}
String
A UTF-8 string.
| Field | Type |
|---|---|
| val | string |
| span | Span |
Example:
"Hello, nu!"
{
"String": {
"val": "Hello, nu!",
"span": {
"start": 8990,
"end": 9002
}
}
}
Glob
A filesystem glob, selecting multiple files or directories depending on the expansion of wildcards.
If no_expand is true, the expansion of wildcards is disabled and this just acts as a literal path.
| Field | Type |
|---|---|
| val | string |
| no_expand | boolean |
| span | Span |
Example:
"src/**/*.rs" | into glob
{
"Glob": {
"val": "src/**/*.rs",
"no_expand": false,
"span": {
"start": 9400,
"end": 9413
}
}
}
Record
An associative key-value map. If records are contained in a list, this renders as a table. The keys are always strings, but the values may be any type.
| Field | Type |
|---|---|
| val | map: string ⇒ Value |
| span | Span |
Example:
{foo: 5, bar: "hello nushell"}
{
"Record": {
"val": {
"foo": {
"Int": {
"val": 42,
"span": {
"start": 659813,
"end": 659814
}
}
},
"bar": {
"String": {
"val": "hello nushell",
"span": {
"start": 659821,
"end": 659836
}
}
}
},
"span": {
"start": 659807,
"end": 659837
}
}
}
List
A list of values of any type.
| Field | Type |
|---|---|
| vals | Value array |
| span | Span |
Example:
[1, 2, foo, bar]
{
"List": {
"vals": [
{
"Int": {
"val": 1,
"span": {
"start": 659951,
"end": 659952
}
}
},
{
"Int": {
"val": 2,
"span": {
"start": 659954,
"end": 659955
}
}
},
{
"String": {
"val": "foo",
"span": {
"start": 659957,
"end": 659960
}
}
},
{
"String": {
"val": "bar",
"span": {
"start": 659962,
"end": 659965
}
}
}
],
"span": {
"start": 659950,
"end": 659966
}
}
}
Block
A reference to a parsed block of Nushell code, without any captured variables.
| Field | Type |
|---|---|
| val | unsigned integer (block id) |
| span | Span |
Example:
{
"Block": {
"val": 44500,
"span": {
"start": 59400,
"end": 59480
}
}
}
Closure
A reference to a parsed block of Nushell code, with variables captured from scope.
| Field | Type |
|---|---|
| val | Closure |
| span | Span |
Closure is defined as:
| Field | Type |
|---|---|
| block_id | unsigned integer |
| captures | array of pairs (unsigned integer var_id, Value) |
The plugin should not try to inspect the contents of the closure. It is recommended that this is only used as an argument to the EvalClosure engine call. The exact representation of a closure is likely to change in the future to avoid serializing all of the captures.
Example:
let foo = "bar"
{ || $foo }
{
"Closure": {
"val": {
"block_id": 1965,
"captures": [
[
862,
{
"String": {
"val": "bar",
"span": {
"start": 660030,
"end": 660041
}
}
}
]
]
},
"span": {
"start": 660030,
"end": 660041
}
}
}
Nothing
The absence of a value, represented by null within Nushell.
| Field | Type |
|---|---|
| span | Span |
Example:
null
{
"Nothing": {
"span": {
"start": 64550,
"end": 64554
}
}
}
Error
An error contained within a value. Trying to operate on the value will most likely cause the error to be forwarded. When writing plugins, error values should typically be handled by returning the error from the command when encountered.
ShellErrors encountered in the plugin protocol are always LabeledErrors.
| Field | Type |
|---|---|
| val | ShellError |
| span | Span |
Example:
error make {
msg: "foo"
label: {
text: "bar"
span: {
start: 0
end: 0
}
}
}
{
"Error": {
"val": {
"LabeledError": {
"msg": "foo",
"labels": [
{
"text": "bar",
"span": {
"start": 0,
"end": 0
}
}
],
"code": null,
"url": null,
"help": null,
"inner": []
}
}
}
}
Binary
An array of raw bytes. This is sometimes returned from operations that detect data that isn't valid as UTF-8, but can also be created with into binary or binary literals.
| Field | Type |
|---|---|
| val | byte array |
| span | Span |
Note that the encoding of byte arrays in JSON and MessagePack is different - the former uses an array of numbers, but the latter uses the native byte array support.
Example:
0x[aa bb cc dd]
{
"Binary": {
"val": [170, 187, 204, 221],
"span": {
"start": 659637,
"end": 659652
}
}
}
CellPath
Represents a path into subfields of lists, records, and tables.
| Field | Type |
|---|---|
| val | CellPath |
| span | Span |
CellPath is defined as:
| Field | Type |
|---|---|
| members | PathMember |
PathMember has two variants, String or Int, and both contain the following fields:
| Field | Type |
|---|---|
| val | string / unsigned integer |
| span | Span |
| optional | boolean |
Optional path members will not cause errors if they can't be accessed - the path access will just return Nothing instead.
Example:
foo.0?.bar
# [foo {value: 0, optional: true} bar] | into cell-path
{
"CellPath": {
"val": {
"members": [
{
"String": {
"val": "foo",
"span": {
"start": 659835,
"end": 659838
},
"optional": false
}
},
{
"Int": {
"val": 0,
"span": {
"start": 659847,
"end": 659848
},
"optional": true
}
},
{
"String": {
"val": "bar",
"span": {
"start": 659866,
"end": 659869
},
"optional": false
}
}
]
},
"span": {
"start": 659873,
"end": 659887
}
}
}
Custom
Represents data types that extend the base nushell types with custom functionality. Plugins can use custom values to implement native-like data types that can be indexed by cell paths, operated on by operators, and compared in plugin-defined ways.
Custom values for plugins may only contain the following content map:
| Field | Type | Usage |
|---|---|---|
| type | string | Must be "PluginCustomValue". |
| name | string | The human-readable name of the custom value emitted by the plugin. |
| data | byte array | Plugin-defined representation of the custom value. |
| notify_on_drop | boolean | Enable drop notification. Default false if not present. |
Plugins will only be sent custom values that they have previously emitted. Custom values from other plugins or custom values used within the Nu engine itself are not permitted to be sent to or from the plugin.
notify_on_drop is an optional field that should be omitted if false, to save bytes. If this is not convenient for your implementation, "notify_on_drop": false is still valid, but it's preferred to not include it.
Example:
{
"Custom": {
"val": {
"type": "PluginCustomValue",
"name": "database",
"data": [36, 190, 127, 40, 12, 3, 46, 83],
"notify_on_drop": true
},
"span": {
"start": 320,
"end": 340
}
}
}
LazyRecord
Lazy record types are not allowed across the plugin boundary. They will be collected to Record before sending.
Embedded Nu types
Several types used within the protocol come from elsewhere in Nu's source code, especially the nu-protocol crate.
Rust enums are usually encoded in serde's default format:
"Variant" // Variant
{ "Variant": value } // Variant(value)
{ "Variant": [a, b] } // Variant(a, b)
{
"Variant": {
"one": 1,
"two": 2
}
} // Variant { one: 1, two: 2 }
Structs are encoded as maps of their fields, without the name of the struct.
Span
Describes a region of code in the engine's memory, used mostly for providing diagnostic error messages to the user with context about where a value that caused an error came from.
| Field | Type | Usage |
|---|---|---|
| start | integer | The index of the first character referenced. |
| end | integer | The index after the last character referenced. |
PipelineDataHeader
Describes either a single value, or the beginning of a stream.
| Variant | Usage |
|---|---|
Empty | No values produced; an empty stream. |
Value | A single value |
ListStream | Specify a list stream that will be sent. |
ExternalStream | Specify an external stream that will be sent. |
Empty header variant
An empty stream. Nothing will be sent. There is no identifier, and this is equivalent to a Nothing value.
The representation is the following string:
"Empty"
Value header variant
A single value. Does not start a stream, so there is no identifier. Contains a Value.
Example:
{
"Value": {
"Int": {
"val": 2,
"span": {
"start": 9090,
"end": 9093
}
}
}
}
ListStream header variant
Starts a list stream. Expect Data messages with the referenced ID.
Contains ListStreamInfo, a map:
| Field | Type | Usage |
|---|---|---|
| id | integer | The stream identifier |
Example:
{
"ListStream": {
"id": 2
}
}
ExternalStream header variant
External streams are composed of optional stdout and stderr raw streams and/or an exit_code list stream.
| Field | Type | Usage |
|---|---|---|
| span | Span | The source code reference that caused the stream. |
| stdout | RawStreamInfo or null | Standard output of the command |
| stderr | RawStreamInfo or null | Standard error of the command |
| exit_code | ListStreamInfo or null | The exit code (integer) of the command |
| trim_end_newline | boolean | True if Nu should remove the last newline from the stream |
RawStreamInfo is a map as follows:
| Field | Type | Usage |
|---|---|---|
| id | integer | The stream identifier |
| is_binary | boolean | True if the stream should be immediately treated as binary (non-text) data. |
| known_size | integer or null | If known, the size of the stream contents in bytes. |
The exit code stream is also optional, and is expected to send one integer representing a command exit code at any time, where 0 represents success and any other value is treated as a failure - but will not automatically cause an error to be generated within Nu.
Example:
{
"ExternalStream": {
"stdout": {
"id": 0,
"is_binary": true,
"known_size": 262144
},
"stderr": null,
"exit_code": {
"id": 1
}
}
}
ShellError
The only variant of ShellError permitted to cross the plugin protocol boundary is LabeledError. Any other errors will be converted to this type.
As such, anywhere ShellError is used, the plugin protocol will only contain {"LabeledError": ...} - i.e., a wrapped labeled error.
LabeledError
A flexible, generic error type, with any number of labeled spans.
| Field | Type | Usage |
|---|---|---|
| msg | string | The main error message to show at the top of the error. |
| labels | ErrorLabel array? | Spans and messages to label the error in the source code. |
| code | string? | A unique machine- and search-friendly code that can be matched against, e.g. nu::shell::missing_config_value |
| url | string? | A URL that links to additional information about the error. |
| help | string? | Additional help for the error, usually a hint about what the user might try. |
| inner | LabeledError array? | Additional errors referenced by the error, possibly the cause(s) of this error. |
Most of the fields are not required - only msg must be present. ErrorLabel (in the labels array) is as follows:
| Field | Type | Usage |
|---|---|---|
| text | string | The message for the label. |
| span | Span | The span in the source code that the label should point to. |
{
"msg": "A really bad error occurred",
"labels": [
{
"text": "I don't know, but it's over nine thousand!",
"span": {
"start": 9001,
"end": 9007
}
}
],
"code": "my_plugin::bad::really_bad",
"url": "https://example.org/my_plugin/error/bad/really_bad.html",
"help": "you can solve this by not doing the bad thing",
"inner": [
{
"msg": "The bad thing"
}
]
}
Config
This struct describes the configuration of Nushell. It is quite large and frequently changing, so please refer to the Rust documentation if there is anything you need from it.
Ordering
We serialize the Rust Ordering type as literal strings, for example:
'Less'; // left hand side is less than right hand side
'Equal'; // both values are equal
'Greater'; // left hand side is greater than right hand side
Operator
Serialized with serde's default enum representation. Examples:
{ "Math": "Append" } // ++ Math(Append)
{ "Bits": "BitOr" } // | Bits(BitOr)
{ "Comparison": "RegexMatch" } // =~ Comparison(RegexMatch)