Transforms

Transforms mutate a RequestSpec during batch derivation, adding variation to generated requests. They are applied in sequence by the Generator.

Transform Signature

type Transform func(spec *RequestSpec, index int, r *rand.Rand)

Each transform receives:

• spec — the cloned spec to mutate (safe to modify in place)
• index — the zero-based index in the batch
• r — a seeded *rand.Rand for deterministic randomness

Built-in Transforms (16)

Name	Function	Mutates	Description
server_ip	RandomServerIP	ServerIP	Random IPv4 address
user_agent	RandomUserAgent	Headers["User-Agent"]	Random UA from pool of 20+ real-world agents
path	RandomPath	URL path	Random suffix segment from pool
query_noise	RandomQueryNoise	Query params	Add 1-3 random noise params
status	RandomStatus	ResponseStatus	Random HTTP status (200, 201, 301, 302, 400, 401, 403, 404, 500, 502, 503)
timings	RandomTimings	Timings	Random realistic timing values
index	IndexSuffix	URL	Append /_idx=<i> query param
port	RandomPort	URL port	Replace port with random from pool
host	RandomHost	URL host	Random subdomain prefix
resp_cookie	RandomResponseCookie	ResponseCookies	Random response cookie
header	RandomHeader	Headers	Random request header
body_noise	RandomBodyNoise	PostText	Inject noise into JSON body
seq_status	SequentialStatus	ResponseStatus	Sequential status codes (200 to 500 and loop)
priority	RandomPriority	Priority	Random Chrome priority value
resource_type	RandomResourceType	ResourceType	Random Chrome resource type
connection	RandomConnection	Connection	Random connection ID

Default Transforms

When no --transform is specified, the CLI uses mock.DefaultTransforms:

var DefaultTransforms = []Transform{
    RandomServerIP,
    RandomUserAgent,
    RandomPath,
    RandomQueryNoise,
    RandomStatus,
    RandomTimings,
    IndexSuffix,
}

Transform Pipeline

Transforms are applied in the order they are specified:

flowchart LR
    Base["Base spec"] --> T1["server_ip"]
    T1 --> T2["user_agent"]
    T2 --> T3["path"]
    T3 --> T4["query_noise"]
    T4 --> T5["status"]
    T5 --> T6["timings"]
    T6 --> T7["index"]
    T7 --> Out["Derived spec"]

    style Base fill:#e1f5ff
    style Out fill:#e8f5e9

Custom Transforms

Implement the Transform function signature and pass it to GenerateSpecs:

package main

import (
    "fmt"
    "math/rand"
    "github.com/cyberspacesec/request-mock-skills/pkg/mock"
)

func MyTransform(spec *mock.RequestSpec, i int, r *rand.Rand) {
    spec.Headers["X-Custom"] = fmt.Sprintf("val-%d", r.Intn(1000))
}

func main() {
    base := mock.GetJSON("https://api.example.com/users")
    g := mock.NewGenerator(42)
    specs := g.GenerateSpecs(base, 100, MyTransform, mock.RandomServerIP)
    h, _ := mock.Generate(specs)
    // ...
}

Disabling Transforms

Pass --transform none to disable all transforms and produce exact copies of the base spec:

request-mock generate -X GET -u https://api.example.com/users -n 10 --transform none

Next

• CLI: transforms — listing transforms in CLI
• SDK Guide — using transforms in Go code
• Templates — combine with templates